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of the Museum of
Comparative Zoology

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FEB 15 2011

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^he Wilson Journal

of Ornithology

Volume 118, Number 1, March 2006

Published by the
Wilson Ornithological Society

THE WILSON ORNITHOLOGICAL SOCIETY
FOUNDED DECEMBER 3, 1888

Named after ALEXANDER WILSON, the first American Ornithologist.

President — Doris J. Watt, Dept, of Biology, Saint Mary’s College, Notre Dame, IN 46556, USA; e-mail:
dwatt@saintmarys.edu

First Vice-President — James D. Rising, Dept, of Zoology, Univ. of Toronto, Toronto, ON M5S 3G5,
Canada; e-mail: rising@zoo.utoronto.ca

Second Vice-President — E. Dale Kennedy, Biology Dept., Albion College, Albion, MI 49224, USA;
e-mail: dkennedy@albion.edu

Editor — James A. Sedgwick, U.S. Geological Survey, Fort Collins Science Center, 2150 Centre Ave.,
Bldg. C, Fort Collins, CO 80526, USA; e-mail: wjo@usgs.gov

Secretary — Sara R. Morris, Dept, of Biology, Canisius College, Buffalo, NY 14208, USA; e-mail:
morriss@canisius.edu

Treasurer — Melinda M. Clark, 52684 Highland Dr., South Bend, IN 46635, USA; e-mail: MClark@tcservices.biz

Elected Council Members — Robert C. Beason, Mary Gustafson, and Timothy O’Connell (terms expire
2006); Mary Bomberger Brown, Robert L. Curry, and James R. Hill, III (terms expire 2007); Kathy G.
Beal, Daniel Klem, Jr., and Douglas W. White (terms expire 2008).

Membership dues per calendar year are: Active, $21.00; Student, $15.00; Family, $25.00; Sustaining,
$30.00; Life memberships $500 (payable in four installments).

The Wilson Journal of Ornithology is sent to all members not in arrears for dues.

THE WILSON JOURNAL OF ORNITHOLOGY
(formerly The Wilson Bulletin )

THE WILSON JOURNAL OF ORNITHOLOGY (ISSN 1559-4491) is published quarterly in March, June,
September, and December by the Wilson Ornithological Society, 810 East 10th St., Lawrence, KS 66044-8897. The
subscription price, both in the United States and elsewhere, is $40.00 per year. Periodicals postage paid at Lawrence, KS.
POSTMASTER: Send address changes to OSNA, 5400 Bosque Blvd., Ste. 680, Waco, TX 76710.

All articles and communications for publications should be addressed to the Editor. Exchanges should be addressed
to The Josselyn Van Tyne Memorial Library, Museum of Zoology, Ann Arbor, Michigan 48109.

Subscriptions, changes of address, and claims for undelivered copies should be sent to OSNA, 5400 Bosque Blvd.,
Ste. 680, Waco, TX 76710. Phone: (254) 399-9636; e-mail: business@osnabirds.org. Back issues or single copies are
available for $12.00 each. Most back issues of the journal are available and may be ordered from OSNA. Special prices
will be quoted for quantity orders. All issues of the journal published before 2000 are accessible on a free Web site at the
Univ. of New Mexico library (http://elibrary.unm. edu/sora/). The site is fully searchable, and full-text reproductions of all
papers (including illustrations) are available as either PDF or DjVu files.

COVER: Wilson’s Snipe ( Gallinago delicata). Illustration by Scott Rashid.

FRONTISPIECE. An adult White-masked Antbird ( Pithys castaneus ) above and a juvenile below. Previously
known from only the type specimen, the species was rediscovered in 2001 in northwestern Department Loreto,
Peru (see p. 13). Original painting (watercolor and gouache) by Daniel F. Lane.

VOL. 118, NO. 1

ne Wilson Journal
of Ornithology

Published by the Wilson Ornithological Society
March 2006 PAGES 1—130

The Wilson Journal of Ornithology 118(1): 1-2, 2006

MESSAGE FROM THE EDITOR: THE NEW
WILSON JOURNAL OF ORNITHOLOGY

This issue of your journal — 118(1), March
2006 — is the debut issue of The Wilson Journal
of Ornithology. As indicated in the insert letter
that came with your December 2003 issue, the
Wilson Council, Wilson Society officers, and I
spent considerable time over the last year de-
bating— and eventually agreeing on — the need
to update the journal’s name and appearance.
We believe that the new name maintains the
tradition of honoring Alexander Wilson, more
clearly reflects the journal’s theme and content,
and is more contemporary. In addition to the
new journal name, the front and back covers
have been redesigned, the title page is new,
and we have added a new feature to The Wil-
son Journal of Ornithology.

The front cover of each issue will portray a
different illustration of one of the species
named after Alexander Wilson. Pen and ink or
halftone artwork was solicited from over two
dozen artists, and we selected those illustra-
tions that we believe demonstrate both orni-
thological and artistic merit. The Wilson’s Snipe
on the March cover is a halftone by artist Scott
Rashid. Pen and ink illustrations of the Wilson’s
Phalarope, Wilson’s Plover, and Wilson’s
Storm-Petrel will appear on the covers of the
June, September, and December issues, re-
spectively. The fifth species named after Al-

exander Wilson, Wilson’s Warbler, will appear
on the cover of each issue in a logo designed
by George Miksch Sutton, and the Wilson’s
Warblers that appeared on the cover from 1962
to 2005 — also by G. M. Sutton — will now ap-
pear on the title page of the first article in each
issue.

The back cover (Contents) has also been re-
designed, to make it more aesthetically pleas-
ing and easier to read. A new feature, “Once
Upon a Time in American Ornithology,” de-
buts, as well. This feature will put forward the
observations and reflections of naturalists from
times past — to afford retrospection and to re-
mind us all of the exhilaration that comes from
being afield and how it once was in American
ornithology. I encourage Wilson Ornithologi-
cal Society members and other readers of the
journal to submit favorite historical field ac-
counts (including a brief introductory state-
ment) for consideration of publication in a fu-
ture issue.

I realize that such cosmetic modifications
will have little long-term effect on subscrip-
tions, membership, or the ornithological sci-
ence offered in The Wilson Journal of Orni-
thology. Combined with a renewed commit-
ment and more substantive changes behind the
scenes, however, I believe that the publication

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

of this issue does mark a new beginning for
the Wilson Ornithological Society and its jour-
nal: (1) the journal has been published on time
beginning with the June 2005 issue, (2) most
authors are receiving an initial decision on
their work within 3-4 months, (3) the time
from manuscript submission to publication
now averages only about 12 months, and (4)
manuscript submissions are up >20% from
2004. I sincerely hope that you, the readers
and authors, welcome the new look and the

improvements we continue to make to The
Wilson Journal of Ornithology. I thank Wilson
Council and officers; Keith Parsons, Karen
Ridgway, and the graphics department at Allen
Press; Teri Kman; and The Wilson Journal of
Ornithology Editorial Office staff — Beth Dillon,
Alison Goffredi, and Cynthia Melcher. All were
instrumental in the execution and realization of
the new design changes and in helping to
bring The Wilson Journal of Ornithology back
on schedule. — James A. Sedgwick, Editor.

The Wilson Journal of Ornithology 1 18(1):3-12, 2006

VARIATION IN MASS OF FEMALE PROTHONOTARY WARBLERS

DURING NESTING

CHARLES R. B LEM 123 AND LEANN B. BLEM1 2

ABSTRACT. — Over an 18-year period (1987-2004), we examined variation in body mass of female Protho-
notary Warblers ( Protonotaria citrea) captured throughout their nesting cycle. As is typical for many small
passerine birds, body mass was greatest during egg laying and decreased throughout incubation and feeding of
young. Mass decreased significantly between the onset of incubation and fledging of both first and second broods.
Mass loss was gradual during incubation, noteworthy during the first 2 days of feeding nestlings, but did not
continue to decrease throughout the feeding period. Mass lost while raising the first brood was regained before
initiating the second brood. Mass of female warblers, adjusted for effects of nest attempt, year, clutch size, and
day and stage of nesting, increased slightly with age. Body mass of nesting female warblers varied significantly
with day of the nest cycle during incubation but not during egg laying or feeding of young. Mass was associated
with clutch size during incubation in both first and second broods, but was not associated significantly with
brood size when females were feeding nestlings. Frequency of food delivery to nestlings was associated nega-
tively with female body mass. Females typically made more feeding trips per day than males. Feeding rates
were correlated among pairs; that is, females with higher rates of delivery were mated to males that made a
higher number of trips. Received 18 February 2005, accepted 21 October 2005.

Mass loss is often used as an index of re-
productive costs in birds (see review in Mer-
kle and Barclay 1996), largely because it is a
consistent factor in patterns of avian life his-
tory. During the breeding season, female pas-
serine birds typically gain mass in the period
before egg laying, maintain or gradually lose
a small amount during incubation, and then
lose a significant amount of mass during
brooding (e.g., Ricklefs 1974; Freed 1981;
Moreno 1989a, 1989b). A similar pattern of
change during breeding has been documented
in several passerine birds (e.g.. Freed 1981,
Ricklefs and Hussell 1984, Hillstrom 1995,
Merila and Wiggins 1997). Researchers have
hypothesized that mass loss may be a proxi-
mate response to energetic demands (e.g.,
Nice 1937, Hussell 1972, Askenmo 1977).
Specifically, mass loss should be greatest dur-
ing periods when energy demands are great-
est, particularly near fledging when nestlings
have acquired the ability to thermoregulate,
and are relatively large. According to this hy-
pothesis, mass loss should be a function of
brood size. A second hypothesis suggests that
decreased mass reduces the energy required

1 Dept, of Biology, Virginia Commonwealth Univ.,
1000 W. Cary St., Richmond, VA 23284-2012, USA.

2 Current address: Flathead Lake Biological Station,
311 Bio Station Lane, Poison, MT 59860, USA.

3 Corresponding author; e-mail:
cblem@saturn.vcu.edu

for flight when food demands of nestlings are
greatest, thus reducing energy requirements of
females and increasing the efficiency of feed-
ing the young (e.g.. Freed 1981, Norberg
1981, Hinsley 2000). In this instance, body
mass should decrease shortly after eggs hatch
and should be independent of brood size. A
final hypothesis is that mass loss results from
degeneration of female reproductive tissues
during the nesting cycle (Ricklefs 1974, Rick-
lefs and Hussell 1984), and should not pro-
gressively occur during incubation or feeding
of young. Some studies have eliminated the
tissue degeneration hypothesis because gonad-
al atrophy is over before the period when
mass loss is greatest (Moreno 1989a, 1989b;
Merkle and Barclay 1996). It is difficult to
isolate these three hypotheses, however, and
some researchers have not found them to be
mutually exclusive (e.g., Hillstrom 1995, Mer-
ila and Wiggins 1997).

The question that usually has been ad-
dressed is: “Is mass loss evidence of energy
demand and/or does it reduce costs of flight
and enhance parental fitness?” It has been
shown that energy expenditure is related sig-
nificantly to rates of nest visitation, but not
always in a linear manner (Bryant 1988). Fur-
thermore, decreased body mass of adults rear-
ing young may enhance their fitness through
reduction of energy demand during the period
of feeding nestlings. Our study examined

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

measurements of body mass of female Pro-
thonotary Warblers ( Protonotaria citrea) ob-
tained over an 1 8-year period. With these data,
we attempted to answer three questions: (1)
How does female body mass in this species
vary over the breeding season? (2) Does body
mass vary significantly among stages of nest-
ing and among years? (3) What are the roles
of brood size, stage of reproduction, and nest
attempt in determining body mass in this spe-
cies?

METHODS

Study area and measurement of mass. — Be-
ginning in March 1987, we placed wooden
nest boxes along tidal creeks in swamp forest
on and near Presquile National Wildlife Ref-
uge (37° 20' N, 77° 15' W) near Hopewell,
Virginia (Blem and Blem 1991, 1992, 1994).
The dominant tree species were black gum
(Nyssa sylvatica), red maple ( Acer rubrum),
and ash ( Fraxinus sp.). Tidal amplitude in the
swamp during spring tides was >1 m. Nest
boxes were placed on metal poles at approx-
imately 100-m intervals along creek banks.
Box dimensions were 28LX9WX6D cm
and the entrance hole was 3.8 cm in diameter
(see Blem and Blem 1991). We determined
optimal nest-box sites during the first 2 years
of the study (Blem and Blem 1991) and boxes
were adjusted accordingly to maximize their
usage by warblers. The number of nest boxes
used in the study was gradually increased
from 141 in 1987 to 320 in 2004.

The contents of boxes were documented 6—
20 times during the breeding season each year,
depending upon the demands of other inves-
tigations of reproductive output. Females were
captured as they exited nest boxes, weighed
to the nearest 0.1 g on a portable electronic
balance, and banded with federal bands. No
warbler in these analyses was weighed twice
per stage, and usually not more than once dur-
ing the same nest attempt. Midday (10:00-
14:00 EST) masses (g) did not vary signifi-
cantly with time of day (mass = -0.04 hr +
16.3, P = 0.49, R 2 = 0.008, n = 2,124). Only
midday masses were used in the following
analyses. We recorded dates of first eggs and
clutch sizes for those nests visited often
enough that we could be certain of the timing.
Clutch size throughout the study was consid-
ered to be the number of eggs present at the

onset of incubation. We converted first egg
(nest start) dates into Julian days for analysis.
Prothonotary Warblers generally produce two
clutches each season (Petit 1989), and second
clutches typically include fewer eggs (Blem et
al. 1999). We therefore divided nests with
eggs in two groups — “first nests,” in which
first eggs were laid from 25 April through 20
May, and “second nests,” in which first eggs
were laid after 20 May (see Petit 1989). Some
of the second nests may have been replace-
ment clutches for first nests that had been dep-
redated, but we are certain that many of them
were produced by females that had success-
fully fledged young (Podlesak and Blem 2001,
2002). We used 20 May as the separation date
because it represents a major hiatus in laying
and is the date after which few first clutches
have been laid at our study site. It also was
used because of the length of time necessary
for Prothonotary Warblers to complete one
nesting cycle (approximately 27 days) after a
mean potential starting date of 24 April (Blem
and Blem 1992). We divided nesting into three
phases: laying (and egg formation), incuba-
tion, and feeding young. The first phase ended
with the first day of incubation and included
birds that were building nests as well as laying
eggs. The second phase began with the first
egg and ended with hatching (Fig. 1).

Feeding visits. — In 2002, we recorded feed-
ing visits by warblers at individual boxes dur-
ing first broods by means of battery-powered
remote video cameras with programmable,
portable videocassette recorders. We obtained
>500 hr of nest-activity records at eight nests
(four broods of three young and four broods
of five young) on days 7 through 10. Video
cameras were small and camouflaged and did
not noticeably alter behavior of the warblers.
Individual visits (see Figs. 2-3) were tran-
scribed from replays of the recordings in the
lab. We totaled all feeding visits made by both
parents from dawn-to-dark for all 4 days. We
could not accurately assess prey size from the
recordings, but we did count the number of
items — mostly caterpillars — that were dis-
tinctly larger than 2 cm (“large prey”), as
judged by the entry hole in the nest box. Fe-
male warblers were weighed 2 days before
nestlings fledged.

Analyses. — Over the 18-year period, we ob-
tained 2,124 measurements of body mass from

}dy r

and Blent • MASS OF FEMALE PROTHONOTARY WARBLERS

First broods

n= 145

i • *•.}( .i. .....

t •• • *! • ir

n = 1 ,343

n = 237

Second broods

0 -5

Egg laying

5 10

Incubation

Days

15 20 25

Feeding nestlings

(g) of female Prothonotary Warblers during nesting in eastern Virginia, 1987-2004 (day
tion). Numerous circles are hidden under duplicate values ( n = 2,124).

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

FIG. 2. Feeding visits/nest/day made by female Prothonotary Warblers during days 7-10 of feeding nestlings
versus female body mass at the end of incubation, eastern Virginia, 2002. Open circles represent broods of three
nestlings; solid circles represent broods of five nestlings. Nest visitation was a function of female body mass,
regardless of brood size.

977 different adult female warblers. For anal-
ysis, we partitioned these measurements
among nesting attempts (first and second
nests, n — 1,344 and 780, respectively) and
stages of nesting (egg formation and laying,
incubating, and feeding). The number of mea-
surements in each stage-year combination var-
ied from 24 during laying in second nests to
1,344 during incubation in first nests. Clutch
size varied from two to six eggs and ages of
females ranged from 1 to 8 years.

To examine differences in mass between
nests and among stages of nesting and brood
sizes (adjusted for day of nesting), we used
univariate ANCOVA with multiple indepen-
dent variables in PROC GLM (SAS Institute,
Inc. 2000). Brood size, nest attempt, age,
stage of nesting, and their interactions were
considered fixed (categorical) effects in vari-
ous models. Day of nesting (range = —9 to
24; 0 = day of onset of incubation) was a
continuous variable. Analysis of covariance

was done using the PROC GLM procedure
because the data set was unbalanced among
effects (Zar 1999). Type III sums of squares
were used, adjusting significance of each fac-
tor for the effects of all other variables. Single
comparisons of means were done by means of
appropriate Mests based on tests of equality
of variances (SAS Institute, Inc. 2000). Few
females were measured more than once during
the same stage of nesting in a given nest in
the same year; therefore, we did not use re-
peated measures analyses. Because some of
the associated variables were not measured
with each measurement of body mass, sample
sizes vary among analyses. All r-tests were
two-tailed. Means are presented ± SD. Statis-
tical significance was set at P < 0.05.

RESULTS

Body mass. — In the following analyses and
comparisons, we assumed that patterns found
between specific points along a regression

Blem and Blem • MASS OF FEMALE PROTHONOTARY WARBLERS

Female visits/nest/day

FIG. 3. Feeding visits/nest/day by mated pairs of Prothonotary Warblers during days 7-10 of feeding nest-
lings, eastern Virginia, 2002. Open circles represent broods of three nestlings; solid circles represent broods of
five nestlings. Males brought food less often than females, but the frequency of male visits/nest/day was a
function of that of females.

were representative of patterns deduced from
single measurements of numerous females.
This was confirmed in our observations of
multiple measurements of a few single fe-
males (CRB unpubl. data).

Body mass of female Prothonotary War-
blers varied over the breeding season in the
typical passerine pattern. That is, variation
was greatest during egg laying, mass de-
creased gradually during incubation, and then
there was a noteworthy decrease in mass im-
mediately after the eggs hatched (Fig. 1). Af-
ter the decline immediately after hatching,
adult female mass did not change over time
throughout the period of feeding nestlings.
Mean body masses did not differ between nest
attempts during egg formation and laying
(first nests: 16.9 ± 1.2, n = 143; second nests:
16.8 ± 1.9, n = 93, Fh235 = 0.20, P = 0.65),
but did differ between nests during incubation
(first nests: 16.2 ± 0.9, n = 1,225; second
nests: 15.6 ± 0.9, n = 304, FU526 = 6.7, P =
0.011) and during the feeding phase (first

nests: 15.2 ± 1.0, n = 238; second nests: 14.9
± 0.8, n = 121; F1>358 = 6.7, P = 0.012). Mass
did not vary with day of nesting in the laying
or feeding stages of either nesting attempt, but
it did decline significantly with day of incu-
bation (first nests: Ful3 42 = 18.0, P < 0.001;
second nests: F1303 = 33.5, P < 0.001).

As judged by the collective scatter of in-
dividual masses over time, females collective-
ly lost 10.1% of their body mass between the
onset of incubation and fledging of first
broods and 1 1 .3% in second broods. Much of
this loss appeared to occur during the first 2
days of feeding nestlings (5.4 and 7.7%, re-
spectively). Mass lost during first broods was
regained before the initiation of second
broods. Body mass extremes were 11.9 g for
an incubating bird and 21.0 g for a female
during the early days of egg laying.

When the data set including all variables
was considered (n = 1,814; Fig. 1), mass var-
ied significantly with nest attempt, stage of
nesting, clutch size (2-6), female age (1-8

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

TABLE 1. Analysis of covariance of body mass of female Prothonotary Warblers in eastern Virginia, 1987-
2004 (n = 1,814). All two-way and three-way interactions were statistically insignificant except for nesting
attempt X stage of nesting. Clutch sizes were 2-6 and ages were 1-8 years. Days of nesting ranged from -9
through 24.

Source

P > F

Nesting attempt

7.6

0.006

Stage of nesting

27.0

<0.001

Clutch size

10.4

<0.001

Age

6.8

<0.001

Day of nest cycle

35.7

<0.001

Year

2.6

0.015

Nesting attempt X stage of nesting

2.8

0.050

years), day of the nest cycle, and year (Table
1). There was a significant interaction between
nesting attempt (first/second nest) and stage of
nesting, but no other two-way and three-way
interactions were statistically significant.
When stages of nesting were analyzed indi-
vidually, body mass during the laying and
feeding stages did not differ among clutches/
broods of different sizes and mass did not
vary significantly with day of nesting in these
stages.

Body mass adjusted for effects of nest at-
tempt, year, clutch size, and day and stage of
nesting varied significantly with female age
(Fu 213 = 15.0, P < 0.001; Table 2). Unad-
justed masses indicated that much of this
change occurred between birds in their first
year (SY birds) and all older age classes
(ASY). Measurements of mass were obtained
from a large range of ages, including 64 mea-
surements that exceeded the published maxi-
mum age (5 years 1 1 months) for the species
(Kennard 1975).

During incubation, mass was significantly

TABLE 2. Least-squares means of body mass
among incubating female Prothonotary Warblers dur-
ing mid-incubation (days 3-8) as a function of age
(years) in eastern Virginia, 1987-2004 (/? = 1,540).
All means were adjusted for the effects of nest attempt,
clutch size, and day and stage of nesting.

Age

Mean mass (g)

16.0

275

16.3

565

16.4

420

16.4

147

16.1

associated with day of nesting and clutch size
(Table 3). Mass tended to decrease gradually
throughout incubation. Birds with larger
clutches during first nesting attempts tended
to have greater body mass; birds with small
clutches in second nests had the lowest body
mass.

Feeding visits. — Total nest visits per day
made by females during days 7-10 of feeding
nestlings was a function of female body mass,
regardless of brood size (three young; Fl3 =
13.8, P = 0.023, R2 = 0.80; five young: F13
= 15.5, P = 0.034, R2 = 0.85; Fig. 2). Males
brought food less often than females (three
young: x2 = 38.2, df = 1, P < 0.052; five

TABLE 3. Analysis of covariance of body mass
among female Prothonotary Warblers in eastern Vir-
ginia, 1987-2004 by stage of nesting ( n = 2,124 in all
analyses). Clutch and brood sizes were 2-6 and ages
were 1-6 years; days of nesting ranged from —9
through 24 (day 0 = first day of incubation).

Source

P > F

Egg formation and laying (/?

= 169)

Nesting attempt

0.9

0.34

Clutch size

2.2

0.092

Day of nesting

0.2

0.70

Age

1.7

0.13

Incubation {n = 1,647)
Nesting attempt

52.3

<0.001

Clutch size

9.3

<0.001

Day of nesting

40.4

<0.001

Age

6.3

<0.001

Feeding nestlings ( n =
Nesting attempt

308)

4.3

0.039

Brood size

1.0

0.45

Day of nesting

0.3

0.58

Age

1.3

0.26

Blem and Blem • MASS OF FEMALE PROTHONOTARY WARBLERS

TABLE 4. Mean visitation rates (no./day
total) for days 7-10 of nestling development in

± SD) of male
eastern Virginia

and female Prothonotary Warblers (percent of
l, 2002.

Female visits

Male visits

Brood size

Per nest

Per nestling

Per nest

Per nestling

3 {n = 4)
5 (n = 4)

306 ± 95 (63.8)
396 ± 148 (56.5)

102.0

79.2

171 ± 40 (36.2)
295 ± 108 (43.5)

57.0

59.0

young: x2 = 12.1, df = 1, P < 0.054; Table
4), but frequency of male visits per day was
a function of that of females (female visits =
1.0 ± 1.06 X male visits; R2 = 0.75, Fl3 =
17.7, p = 0.006; Fig. 3). Female feeding trips
per nestling decreased with brood size (x2 =
9.3, df = 1, P < 0.05; Table 4), but male trips
per nestling did not decrease (x2 = 0.034, df
= 1, P > 0.05). The percentage of total pa-
rental visits made by males declined from a
high of 44.0% on day 7 to a low of 34.8% on
day 10. Males brought significantly more
“large prey items” to the nest than did fe-
males (males: 330, females: 210; x2 = 26.7,
df = 1, p < 0.05). These prey items were
mostly Hexagenia sp. mayflies and lepidop-
teran caterpillars. There was no significant dif-
ference in the number of larger prey delivered
by males to different brood sizes (175 in
broods of three, 155 in broods of five; x2 =
1.2, df = 1, P > 0.05).

DISCUSSION

Body mass clearly is associated with stage
of breeding activity in small passerines (Freed
1981, Ricklefs and Hussell 1984, Cichon
2001), and each stage — egg formation and
laying, incubation, and feeding of nestlings
is characterized by a different pattern of mass
change (e.g., Fig. 1). Mass change of female
Prothonotary Warblers in our study was sim-
ilar to that reported in several other studies of
passerine species (e.g.. Freed 1981, Ricklefs
and Hussell 1984, Johnson et al. 1990, Hills-
trom 1995). During egg laying, body mass
varied greatly with follicle formation and re-
lease of eggs, then declined progressively
throughout incubation (Fig. 1), and dropped
sharply at hatching. Female mass then re-
mained relatively constant throughout the pe-
riod of feeding nestlings. Mass changes in
Prothonotary Warblers during egg laying and
incubation were similar to those of all small
passerines and require little explanation. Mass

loss at hatching is more complex and differs
among species. Because the significance of
this loss is uncertain, the behavior and com-
positional dynamics of females requires closer
scrutiny.

Two potential hypotheses have been pro-
posed to explain mass loss of female birds
during feeding of nestlings: (1) energy de-
mand (cost of reproduction hypothesis = re-
serve mobilization hypothesis; Cavitt and
Thompson 1997), and (2) long-term benefits
from reduction of power demands for flight
during feeding (mass adjustment hypothesis =
flight efficiency hypothesis). Forming and lay-
ing eggs, incubating, and feeding nestlings re-
quires additional collection and expenditure of
energy, whereas adjusting mass to save energy
expended in flight during the numerous trips
made while feeding young is an adaptive loss.

It has become obvious that body mass can
vary as a result of energy demand during ex-
treme years (Merila and Wiggins 1997) or
with larger broods (Nur 1984). It appears to
be axiomatic that reserves should be depleted
during times of high-energy demand and it is
well known that body mass and energy re-
serves are closely related (Blem 1990). Part
of the variation in mass within stages of the
nest cycle may result from differences in an-
nual factors, such as temperature extremes, in-
clement weather (Merila and Wiggins 1997),
or brood number (De Laet and Dhondt 1989).
Because of our large sample size, we were
able to detect annual variation within the in-
cubation period of first nests, largely by elim-
inating much of the variation associated with
several other variables. Others (e.g., Johnson
et al. 1990) have likewise found significant
annual variations in mass of breeding birds,
and extreme environmental conditions in ex-
ceptional years have important influences on
body mass (Merila and Wiggins 1997).

Not all studies, however, have shown that
energy demand is an important factor in body

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

mass. For example, larger broods are not al-
ways associated with greater mass loss of fe-
males (Pinkowski 1978, this study), even
though energy expenditure by females in-
creases with brood size (Sanz et al. 1998).
Furthermore, food-supplementation studies
have provided mixed results. Food supple-
ments did not affect female mass, brood mass,
or length of the nestling period among House
Wrens ( Troglodytes aedon\ Cavitt and
Thompson 1997) or Northern Wheatears
( Oenanthe oenanthe; Moreno 1989a). How-
ever, food-supplemented female Mountain
Bluebirds ( Sialia currucoides; Garcia et al.
1993) maintained greater body mass and
fledged larger young than females receiving
no food supplementation. Some studies have
found that female mass is a negative function
of brood size (Nur 1984, Merila and Wiggins
1997), and that energy demand during first
broods may influence the probability of hav-
ing a second brood in some species (De Laet
and Dhondt 1989). In Prothonotary Warblers,
it appears that many females totally recover
lost mass fairly quickly between nest attempts.
It has been suggested that species breeding in
different environments may respond different-
ly to stress associated with increased energy
requirements and there may not be selection
for adaptive mass loss (Cavitt and Thompson
1997).

The pattern of mass change in female Pro-
thonotary Warblers in our study does not sup-
port the cost of reproduction hypothesis, but
it does support the mass adjustment hypothe-
sis. Important supporting observations includ-
ed ( 1 ) the regular loss of mass after hatching
in both nesting attempts, (2) the lack of influ-
ence of brood size on female mass, (3) no
increasing loss in female mass as young grew
and when feeding activity levels were great-
est, (4) more feeding trips made by females
that weighed less, and (5) little evidence that
males adjusted their feeding efforts to offset
demands on females. Trivers (1972) predicted
that, within breeding pairs, females would
provide the largest proportion of nestling care
because they had a larger share of investment
of energy than males. In our study, female
Prothonotary Warblers made more feeding
trips than males (both broods). Male Protho-
notary Warblers, however, brought a greater
proportion of large prey, which may have sig-

nificantly offset female effort during later
stages in the nesting cycle even though males
made fewer trips as nestlings neared fledging.

The mass adjustment hypothesis suggests
that birds benefit from mass loss due to de-
creased wing loading (e.g.. Freed 1981, Nor-
berg 1981, Ricklefs and Hussell 1984, Cavitt
and Thompson 1997). Energy saved by mass
reduction may enable parent birds to raise
more young faster or produce fledglings with
greater mass. Observations supporting the
mass adjustment hypothesis include (1) great-
er loss of mass before the period of maximum
energy requirement (e.g., Freed 1981, Ricklefs
and Hussell 1984, Merkle and Barclay 1996,
this study), (2) loss of mass independent of
brood size (e.g., Freed 1981, this study) or
length of incubation (Sanz and Moreno 1995,
this study), and (3) no increase in body mass
among food-supplemented females feeding
nestlings (Cavitt and Thompson 1997). In our
study, mass loss of females during incubation
was correlated with clutch size, but mass of
females feeding nestlings was not affected by
brood size, nor did female mass decrease
throughout nestling development. If increased
energy demand is important, then female mass
should decline significantly as nestlings grow,
although it is possible that males may “pick
up the slack.” That is, male warblers might
feed young more frequently or with higher-
quality food in large broods than small, thus
reducing energy demands on females and al-
lowing them to maintain their mass and fit-
ness. Our observations weakly support these
ideas. Males did bring more large prey items
than females, but this did not vary with brood
size or with nestling age. Furthermore, males
made fewer visits late in the nesting cycle
than females. This pattern is nearly identical
with that documented for Willow Tits ( Poecile
montanus ; Rytkonen et al. 1996). Similar
studies have shown that nest visitation rates
may be greater in males of some species
(Grundel 1987), greater in females of others
(Pinkowski 1978, Conrad and Robertson
1993), or may not differ between the sexes
(Best 1977, Knapton 1984, Omland and Sher-
ry 1994). The significance of the age:body
mass relationship during the reproductive pe-
riod is not clear. We are aware of few studies
that have demonstrated an age effect on mass
(see De Laet and Dhondt 1989, Merila and

Blem and Blem • MASS OF FEMALE PROTHONOTARY WARBLERS

1 1

Wiggins 1997). In our study, however, female
age had a significant effect on body mass,
even after mass was adjusted for the effects
of many other variables.

Mass variation of female birds during nest-
ing obviously is a complex phenomenon.
Deeper insight into mass variations will be ob-
tained only with studies that combine mea-
sures of body composition, condition of re-
production tracts, and measures of hormone
levels with stage of nesting. While time-con-
suming, collecting large data sets over nu-
merous years is well worth the trouble, but
would be even more valuable if simultaneous
studies could be carried out at several sites
over the range of the species.

ACKNOWLEDGMENTS

We thank the officials of the Eastern Virginia Rivers
National Wildlife Refuge (NWR) Complex for per-
mission to conduct this study at Presquile NWR. The
North American Bluebird Society financially support-
ed box construction. More than 100 students, friends,
and faculty colleagues assisted in this project and we
thank them all, especially A. S. and K. C. Seidenberg
and J. R. and R. J. Reilly for their continuous help
over many years. We thank L. B. Williams, K. R. Guis-
inger, and D. S. Stevens for transcribing visits of war-
blers from long, boring tape recordings. The Virginia
Society of Ornithology and several of its chapters
helped fund our efforts. This is Rice Center for Envi-
ronmental Life Sciences Research Contribution No.
001.

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The Wilson Journal of Ornithology 1 18(1): 13— 22, 2006

THE REDISCOVERY AND NATURAL HISTORY OF THE
WHITE-MASKED ANTBIRD ( PITHYS CASTANEUS)

DANIEL F. LANE,1 6 THOMAS VALQUI H.,1 2 JOSE ALVAREZ A.,1 2 3
JESSICA ARMENTA,25 AND KAREN ECKHARDT4 5 6

ABSTRACT. — In July 2001, a Louisiana State University Museum of Natural Science expedition rediscovered
the White-masked Antbird ( Pithys castaneus ) at a site along the Rfo Morona in northwestern Departmento
Loreto, Peru. Prior to this rediscovery, the species was known only from the type specimen, taken in 1937, and
nothing was recorded concerning its natural history. The lack of additional specimens led to speculation that P.
castaneus was a hybrid. Here, we present data demonstrating that the White-masked Antbird is a valid species,
and we report the first observations of its behavior, habitat, morphology, and voice. Received 14 January 2005,
accepted 1 1 October 2005.

In 1938, Berlioz (1938) described a distinc-
tive new species of antbird in the genus Pith-
ys— until then considered monotypic — from a
single specimen collected by Ramon Olalla on
16 September 1937 at “Andoas, lower [Rio]
Pastaza, eastern Ecuador.” This new species,
the White-masked Antbird ( Pithys castaneus ),
has remained one of the most intriguing mys-
teries of Neotropical ornithology for over 60
years (see David and Gosselin 2002 for gen-
der of scientific name). Besides the collector,
no biologist had ever seen the bird alive, and
there is no information on the species’ natural
history or preferred habitat. The type locality,
“Andoas,” is particularly intriguing in that at
least three sites in the Pastaza area bear this
name (Stevens and Traylor 1983, Paynter
1993), and according to T. Mark {in lift.), we
may never really know the true location of the
type locality.

The type specimen, a male (contra Ridgely
and Tudor 1994), is housed at the Paris Mu-
seum in France. According to Berlioz (1938,
1948), it was part of a collection that included
three specimens of White-plumed Antbird (P.
albifrons peruvianas ) and therefore appeared

1 Louisiana State Univ. Museum of Natural Science,
1 19 Foster Hall, Baton Rouge, LA 70803, USA.

2 Dept, of Biological Sciences, Louisiana State
Univ., Baton Rouge, LA 70803, USA.

3 Inst, de Investigaciones de la Amazonia Peruana
(IIAP), Av. Quinones Km. 2.5, Iquitos, Peru.

4 Museo de Historia Natural de la Univ. Nacional
Mayor de San Marcos, Apartado 14-0434, Lima, Peru.

5 Current address: Dept, of Biological Sciences, P.O.
Box 413, Lapham Hall, Univ. of Wisconsin, Milwau-
kee, WI 53201, USA.

6 Corresponding author; e-mail: dlane@lsu.edu

to be a sympatric congener. It differed from
P. albifrons in its larger size, its lack of any
gray on the body, and its lack of elongated
plumes on the face or throat.

Decades passed without any additional re-
cords of P. castaneus. Subsequent authors
doubted the validity of the species, and many
suggested that it represented nothing more
than a hybrid of P. albifrons and another ant-
bird species (Sibley and Monroe 1990, Schu-
lenberg and Stotz 1991, Collar et al. 1992,
Stattersfield and Capper 2000, Ridgely and
Greenfield 2001b). Willis (1984) and person-
nel at the Philadelphia Academy of Natural
Sciences (ANSP; Collar et al. 1992, Ridgely
and Tudor 1994) searched without success for
P. castaneus along the upper Rio Pastaza in
Peru and Ecuador, respectively.

Thus, when our Louisiana State University
Museum of Natural Science (LSUMZ) orni-
thological field team visited several sites in
northwestern Departamento Loreto, Peru,
from May through July 2001 , it was with great
surprise that we found P. castaneus to be fair-
ly common at one of our field sites. The main
goal of our fieldwork was to inventory the
avifauna of two isolated patches of varillal
(white sand) forest (see Whitney and Alvarez
1998; Alvarez and Whitney 2001, 2003). One
of these forest patches was in the interfluvium
between the Morona and Santiago rivers in
northern Peru, north of the Rio Maranon, only
about 60 km west of the Rfo Pastaza, and it
was there that we found P. castaneus.

Remarkably, while reviewing specimen ma-
terial at the Museo de Historia Natural de la
Universidad Mayor San Marcos (MUSM),

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

FIG. 1 . Known localities for Pithy s castaneus in northwestern Departmento Loreto, Peru. The star represents
suspected location of “Andoas,” the type locality, on the Rio Pastaza (Berlioz 1938). The square represents the
location of the species’ rediscovery in July 2001 on the west bank of the Rio Morona (04° 17' S, 77° 14' W).
The Cordillera Campanquis lies between the ribs Morona and Santiago, immediately to the west of our field
site.

Lima, in November 2002, we discovered two
additional specimens of P. castaneus (one
adult and one juvenile). These specimens were
reportedly taken somewhere in the Cordillera
Campanquis region on the border of Depart-
mentos Amazonas and Loreto between the
Morona and Santiago rivers (see Fig. 1), in
the mid- to late 1990s by a Peruvian anthro-
pologist, Andres Treneman (I. Franke J. pers.
comm.). Unfortunately, no additional speci-
men data are available, and the collector could
not be contacted for additional information.

METHODS

Locality. — We established a campsite on the
west bank of the Rio Morona about 54 km
north-northwest of its mouth (04° 17' S, 77°
14' W; Fig. 1), Departmento Loreto. The

study site was on the south side of the mouth
of Quebrada Cashacano, a right-bank tributary
of the Rfo Morona, about 2.3 km north of the
village of Tierra Blanca. We observed and
made a general collection of birds at this site
between 2 and 21 July 2001. Our camp was
set up in a clearing of a homestead abandoned
about 30 years earlier and which, reportedly,
has been reinhabited since our visit (B. Walker
pers. comm.). A preexisting trail, used for the
harvest of palm fronds for thatched-roof con-
struction, led directly into white-sand forests
for about 2 km. Another trail, cut along the
bluff above the Morona, connected the camp
with the village of Tierra Blanca. From this
trail, at least another three trails also entered
the varillal forest. Additional trails were cut
near camp for census routes and net lanes;

Lane et al. • REDISCOVERY OF WHITE-MASKED ANTBIRD

most trails were in varillal, but three also en-
tered the adjacent varzea (seasonally inundat-
ed) forest. We also found two patches of richer
clay-soil terra firme forest north and south of
the surveyed varillal forest patch, into which
we cut two trails.

Habitat. — Most of the forest where P. cas-
taneus was observed — particularly away from
major water bodies — grew on very moist,
white-sand soils. Numerous areas of wet,
swampy conditions indicated a high water ta-
ble. The terrain was without significant relief,
but throughout the varillal forest were many
small depressions where water accumulated
(particularly after rains), presumably pits re-
sulting from tree-falls. The soil consisted of
rather coarse sand with stones of up to 5 cm
in diameter (up to 15 cm in the small creeks
that transected the forest interior). Using a nat-
ural cut at the Rio Morona riverbank for ref-
erence, the sandy soil is approximately 4 m
deep at the river’s edge. Typical of many var-
illal forests, a thick layer of dead leaves and
humus covered the forest floor (Ruokolainen
and Tuomisto 1993, 1998; Richards 1996).
The forest canopy of the varillal was relative-
ly even, with a height of about 20 to 30 m.
The relative absence of buttressed trees is typ-
ical of varillal forests (Richards 1996); how-
ever, many such trees were present in more
humid forest areas at the Morona site. As has
been noted in other varillal forests (Anderson
1981, Richards 1996), there were few lianas,
and epiphytic growth was negligible.

Data collection. — We collected specimens
using mist nets and shotguns. Permits for
specimen collection were issued by Peru’s In-
stitute Nacional de Recursos Naturales (IN-
RENA). Specimens were deposited into the
collections of LSUMZ and MUSM. Skull os-
sification, gonad information, and presence of
fat in prepared specimens were determined
following standard LSUMZ specimen prepa-
ration protocol. Natural history information
was acquired through opportunistic (not sys-
tematic) encounters with P. castaneus. Spec-
trograms of voice recordings were prepared
using Canary sound analysis software (Charif
et al. 1995).

Specimens examined. — Pithy s castaneus :
Peru: Loreto; west bank of Rio Morona, —54
km NNW of the mouth, 140 m elevation (04°
17' S, 77° 14' W) (LSUMZ 172973, 172974,

172975, 172976 [skeleton and partial skin],
172977, 172978, 172979 [skeleton and partial
skin], MUSM 23504, 23505, 23506, 23507;
DFL 1646 [skeleton, uncataloged], TVH 399
[alcohol, uncataloged]).

Pithys albifrons : Ecuador: Pastaza; Coco-
naco, 300 m elevation (LSUMZ 83237); Peru:
Amazonas; Huampami, —215 m elevation
(LSUMZ 84917), Chiriaco, -320 m elevation
(LSUMZ 78514, 88018, 88019, 88022); Lor-
eto; Libertad, S bank of Rio Napo, 80 km N
of Iquitos, 120 m elevation (LSUMZ 1 10094,
110096, 110097, 110098, 110099, 110100,
1 10102, 1 10103, 1 10104, 1 10105); 157 km by
river NNE of Iquitos, N of Rio Napo, 110 m
elevation (LSUMZ 110106, 110109, 110112,
110113).

Gymnopithys leucaspis: Peru: Loreto; west
bank of Rio Morona, —54 km NNW of the
mouth, 140 m elevation (04° 17' S, IT 14' W)
(LSUMZ 172985); Quebrada Oran, -5 km N
of Rio Amazonas, 85 km NE of Iquitos, 1 10
m elevation (LSUMZ 119884, 1 19885,
119886, 119887, 119890, 119891, 119892,
119893).

Phlegopsis erythroptera: Ecuador: Sucum-
bios; Limoncocha, 300 m elevation (00° 24'
S, 76° 37' W) (LSUMZ 70916, 70917, 70919,
83314). Peru: Loreto; W bank of Rio Morona,
—54 km NNW of the mouth, 140 m elevation
(04° 17' S, IT 14' W) (LSUMZ 173001); 1.5
km S of Libertad, S bank of Rio Napo, 80 km
N of Iquitos, 120 m elevation (LSUMZ
110213, 110215, 110217); 1 km N of Rio
Napo, 157 km by river NNE of Iquitos, 110
m elevation (LSUMZ 110219); lower Rio
Napo region, E bank of Rio Yanayacu, —90
km N of Iquitos, 120 m elevation (LSUMZ
115573).

Rhegmatorhina melanosticta: Peru: Ama-
zonas; headwaters of Rio Kagka (of Rio Ce-
nepa), —790 m elevation (04° 16' S, 78° 09'
W) (LSUMZ 88028, 88029); San Martin; -15
km by trail NE of Jirillo on trail to Balsa-
puerto, 1,350 m elevation (LSUMZ 116947);
Huanuco; —35 km NE Tingo of Marfa, Ha-
cienda Santa Elena, —1,000 m elevation
(LSUMZ); Pasco; Abra Aguachini, —30 km
SW of Puerto Bermudez, 1,020 m elevation
(LSUMZ 130274); Pasco; Puellas, km 41 on
Villa Rica-Puerto Bermudez highway, 950 m
elevation (LSUMZ 106073, 106074, 106078).

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

RESULTS

Specimen data. — We collected 13 speci-
mens of Pithys castaneus during our visit to
the Rio Morona site. We prepared nine as
study skins (from which several trunk skele-
tons were saved), three as complete skeletons
(from which two partial skin specimens were
saved), and one was preserved whole in al-
cohol. Mass and lengths of flat-wing, tail, tar-
sus, and culmen (from distal edge of the nares
to bill tip) of all specimens are presented and
compared with measurements of the P. cas-
taneus holotype and other Peruvian ant
swarm-following antbirds (Table 1).

Three of the 12 specimens in “adult” plum-
age (LSUMZ 172973, MUSM 23504, MUSM
23507) still possessed a bursa of Fabricius and
one had an incompletely ossified skull (75%
ossification), suggesting that first basic plum-
age is acquired quickly and is nearly indistin-
guishable from definitive plumage (but see be-
low). One specimen (LSUMZ 172978) was a
male still largely in juvenal plumage (skull os-
sification 50%, bursa 8X6 mm). Of the 12
specimens dissected, only 2 — both with im-
mature characters — were reported to have
subcutaneous fat deposits: “trace fat” in one
and “light fat” in the other. Six of 12 speci-
mens dissected exhibited trace or light body
molt. Seven individuals had asymmetrical
wing molt, and seven had asymmetrical tail
molt. Stomach contents were reported as “in-
sect parts” for all specimens in which the
stomachs were not empty. The guts of two
specimens were infested with nematodes.

Variation in the series. — Twelve speci-
mens— 5 males and 7 females — exhibited
similar plumage, with no sexual dichroma-
tism. All these adults appeared to match the
description of P. castaneus and the photos of
the holotype very closely. Of the specimens
in “adult” plumage, two that appeared to be
in their first year (see above) have very sparse,
light-grayish scaling on the center of the
throat (unmarked white in all other individu-
als), suggesting that it may be an age-related
character. Otherwise, plumage characters were
uniform among all the “adult” specimens.
The juvenal-plumaged bird differs in being
washed with colder brown overall, particular-
ly on the breast, vent, and center of the back.
Furthermore, the white of the juvenile’s face

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Gymnopithys leucaspis (females) 5 23.8 ± 2.3 71.9 ± 1.3 42.9 ± 2.1 25.8 ± 1.2

Phlegopsis erythroptera (males) 5 58.4 ± 5.2 91.6 ± 1.7 63.3 ± 2.4 33.5 ±1.7

Phlegopsis erythroptera (females) 5 58.2 ± 7.0 88.0 ± 1.3 59.0 ± 1.0 32.0 ± 1.4

Rhegmatorhina melanosticta (males) 4 30.0 ±1.9 81.3 ± 5.2 53.0 ± 2.0 27.6 ±1.2

Rhegmatorhina melanosticta (females) 5 33.0 ± 4.7 78.0 ± 2.8 49.8 ± 2.5 27.4 ± 0.8

Lane et al. • REDISCOVERY OF WHITE-MASKED ANTBIRD

TABLE 2. Number of individuals per species attending army ant swarms ( Eciton burchelli and Labidus
praedator ) with Pithys castaneus , Departmento Loreto, Peru, July 2001. Columns represent individual swarms.
Only swarms observed for >15 min were included.

Date (ant swarma)

4 July

6 July

8 July

10 July

11 July

12 July

14 July

17 July

(E)

(L.)

(E)

(L)

(E)

Pithys castaneus

Pithys albifrons

—

Phlegopsis erythroptera

—

Gymnopithys leucaspis

—

Hylophylax poecilinota

—

Percnostola arenarum

—

Dendrocolaptes certhia

—

Dendrocincla merula

—

Xiphorhynchus ocellatus

—

Deconychura longicauda

—

a E = Eciton burchelli , L = Labidus praedator.

was restricted to the area between the eye and
gape and a longitudinal line along the center
of the throat. This specimen’s dark head mark-
ings were more extensive than those on defin-
itive-plumaged birds, and they were a duller,
sooty, dark brown (see frontispiece).

Soft-part colors were relatively uniform
across most specimens. The irides were brown
or dark brown (all soft-part colors taken from
tag data recorded at time of preparation) in
nine specimens with adult characters, dark
gray-brown in the three specimens with first-
basic characters, and dark gray in the juvenile.
Thus, iris color evidently changes from gray
to dark brown as an individual ages. In all
specimens, the maxilla was blackish-slate
with a silvery-white tomium, the latter con-
stricted at mid-bill in some individuals. Man-
dible coloration varied more. Most adults had
a mostly silvery-white tomium with blackish-
slate color on the gonys and base of the man-
dible (except the tomium). Approximately the
distal half of the juvenile’s bill was silvery-
white, and the mouth interior was dark gray.
The tarsus color of adult individuals was
brownish-orange or ochre-orange; the juve-
nile’s tarsi were dirty yellow with a gray tinge.
The toes were dirty yellow, pale orange, or
dull saffron yellow; the claws of the juvenile
bird were gray.

Behavioral observations. — Our initial ob-
servations of P. castaneus were made by TVH
and DFL at a swarm of Eciton burchelli army
ants on 4 July 2001, when the first specimens
were collected. Based on our observations, we

were confident in labeling P. castaneus a pro-
fessional army ant-follower ( sensu Willis
1967). We never saw it foraging away from
army ant swarms and observed it attending
swarms of two army ant species: Eciton bur-
chelli and Labidus praedator. For at least 1 2—
15 min on 8 July, JAA observed a single in-
dividual of P. castaneus with a female Scale-
backed Antbird ( Hylophylax poecilinota ) fol-
lowing a swarm of L. praedator ants that oc-
cupied less than 10 m2 of the forest floor. The
bird’s behavior was similar to that of others
observed following swarms of E. burchelli.
Both the P. castaneus and the H. poecilinota
individuals left the swarm for 3-4 min, only
to return later. Also observed attending
swarms of L. praedator (although independent
of the above observation) were Allpahuayo
Antbirds ( Percnostola arenarum), a species
previously unknown as an ant-follower (Isler
et al. 2001, Zimmer and Isler 2003), and Bi-
colored Antbirds ( Gymnopithys leucaspis). On
four occasions on different days, we observed
a single individual of P. castaneus quietly
passing through the forest without foraging,
suggesting movement between ant swarms or
between an ant swarm and a nest (Willis
1981). In Table 2, we present the attendance
of regular ant-following species observed at
swarms at the Morona site.

Most often, P. castaneus was observed at
or near the broad front of a moving ant col-
umn. Individuals tended to perch <0.5 m
above ground and frequently dropped to the
forest floor to investigate leaf litter or capture

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

arthropods. Birds often were observed attend-
ing a swarm for 5 to 15 min at a time and
then leaving the swarm (at least once while
carrying a food item) for roughly equal peri-
ods of time. On at least one such occasion, a
pair of P. castaneus was observed joining a
family group of G. leucaspis moving between
what appeared to be two column heads (about
30 m apart) of a single E. burchelli ant swarm.
Willis (1981) reported similar behavior for P.
albifrons. On another occasion, a single indi-
vidual was seen moving around a standing
hollow tree in which a swarm of E. burchelli
had bivouacked the previous evening, but had
not yet started its morning activity.

Most of the professional ant-following
thamnophilids at the Morona site regularly
made exaggerated tail “pounding” or “wag-
ging” movements (terms following Zimmer
and Isler 2003) while foraging at ant swarms,
especially upon returning to a perch after
pouncing on a prey item, or when agitated by
the presence of an observer. P. castaneus was
not observed regularly using any such tail
movement. Only once or twice did we notice
an individual pound its tail, usually after a
pouncing attack on prey; the tail movement
was made once and not repeated. By contrast,
DFL noted that the G. leucaspis almost con-
stantly wagged their tails laterally, although
this contrasts with the published observations
of others (e.g., Zimmer and Isler 2003). In ad-
dition, DFL observed both P. albifrons and
the Reddish-winged Bare-eye ( Phlegopsis er-
ythroptera ) regularly pounding their tails
downward (also see Willis 1981, 1984; Zim-
mer and Isler 2003). We were unable to de-
termine whether such tail movements are in-
tended as a form of inter- or intraspecific
“body language” among swarm attendants, as
a sign of agitation, or as a form of flushing
insect prey. Nevertheless, the relative lack of
such tail-moving behavior in P. castaneus
seems noteworthy. Willis (1968) reports that
the monotypic genus Skutchia also lacks ste-
reotypic tail-moving behavior, but other ob-
servers contest this (B. M. Whitney pers.
comm.).

In our observations of ant-following birds
at the Morona site (Table 2), we noted several
occurrences of one ant-following species sup-
planting another near the leading edges of ant
swarms and took this to represent a domi-

nance hierarchy among the attendant species
(see Willis 1967, 1981). From our observa-
tions, we concluded that the dominance hier-
archy (from most to least dominant) was Phle-
gopsis erythroptera , Pithys castaneus , and G.
leucaspis. Other swarm-attending antbirds, in-
cluding Pithys albifrons, noticeably avoided
the leading edge of the swarm when any of
the other professional ant-followers were pre-
sent. Our observations of the last species
agree with those of Willis (1981), who also
termed P. albifrons a subordinate ant swarm
attendant. Since the dominance hierarchy sug-
gested above has a positive correlation to
overall body size, we suggest that size may be
the ultimate cause (or, alternatively, a proxi-
mate cause — i.e., a source of maintenance) of
the hierarchy (see Table 1).

Voice. — We recorded at least seven distinct
vocalizations from P. castaneus (Fig. 2), in-
cluding a mewed whistle that rises in frequen-
cy (Fig. 2A). This is a single note often given
quietly, although occasionally it can be quite
loud, and we suspect represents the species’
“loudsong” (such as it is). To our knowledge,
P. albifrons does not give a true loudsong
(sensu Willis 1967, Isler et al. 1998, Isler and
Whitney 2002, Zimmer and Isler 2003) as do
most other thamnophilids. However, the spe-
cies is known to produce a vocalization sim-
ilar to that described above for P. castaneus :
a rarely heard, weak, mewing whistled vocal-
ization that falls in frequency and is suspected
to serve as a song (Willis 1981, Isler and
Whitney 2002; Fig. 2B). The whistled notes
of the loudsong of P. castaneus appear to be
punctuated by occasional quiet, chiming notes
(Fig. 2C), perhaps an integral part of the loud-
song. Song intervals can be as short as 2 sec
but often are longer.

P. castaneus also produced two vocaliza-
tions when alarmed or when agitated by play-
back of what we believed was the species’
song (see below). These notes of agitation
were interspersed with sharp chattered “chit!”
calls (Fig. 2D), similar to the “chip” calls de-
scribed for P. albifrons by Willis (1981). An-
other vocalization given by agitated birds was
a louder, higher-pitched “chirr,” with the in-
dividual notes more distinct (Fig. 2E) than in
the undisturbed chirr call (see below). Occa-
sionally, the agitated chirr commenced with a
chit note (Fig. 2F). While giving these vocal-

Lane et al. • REDISCOVERY OF WHITE-MASKED ANTBIRD

FIG. 2. Sound spectrograms of antbird vocalizations. Unless otherwise noted, all recordings were made by
D. F. Lane at our Rfo Morona locality, Departmento Loreto, Peru, July 2001. (A) “Song” of Pithys castaneus.
(B) “Song” of Pithys albifrons (T. A. Parker, III, and G. F. Budney, from Isler and Whitney 2002). (C) “Chime”
of Pithys castaneus. (D) “Chit” of Pithys castaneus. (E) Agitated “Chirr” of Pithys castaneus. (F) “Chit-chirr”
of Pithys castaneus. (G) “Mew” of Pithys castaneus (J. Alvarez A.). (H) “Chirr” of Pithys castaneus. (I)
“Chirr” of Pithys albifrons. (J) “Chirr” of Gymnopithys leucaspis. (K) “Chirr” of Phlegopsis erythroptera.

izations of agitation, one male (sex confirmed
by collection), was observed perched on a
horizontal branch at the edge of a treefall gap
about 2 m above the ground. This was the
highest we ever observed the species to perch,
and was likely an agitation response to play-
back of the song. On one occasion, a distinct,
quiet, mewing “eaaah” call was given by two
individuals while close to one another; we in-
terpret this as some sort of contact call or
“softsong” within the pair (Fig. 2G).

The most common vocalization was a call
given by individuals while foraging at ant
swarms. This was a deep chirr call (terms fol-
lowing Willis 1967, Zimmer and Isler 2003;
Fig. 2H), similar to vocalizations given by
most professional ant-following thamnophil-

ids when attending ant swarms, and suspected
to be a means of maintaining individual for-
aging space at the swarm (Willis 1967; M. L.
Isler in litt.). When the chirr of P. castaneus
was heard simultaneously with those of most
of the other species of professional ant-fol-
lowers at a swarm, it sounded generally loud-
er, of lower overall frequency, and descended
less obviously (see Fig. 2H-2K). Only the
chirr call of Phlegopsis erythroptera (Fig. 2K)
reaches a frequency as low as that of Pithys
castaneus , but the former can be distinguished
easily by a higher, more metallic introductory
sound and a more sharply descending com-
ponent. The chirr call of Phlegopsis erythrop-
tera was louder than that of Pithys castaneus
on occasion, but this appeared to be influ-

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

enced by emotional state and was not always
the case.

Playback experiments using recordings of
the suspected song elicited varying reactions
from individuals: some responded immediate-
ly, giving agitated calls and posing on exposed
perches that were higher than typical perches
(see above), while others approached silently
to investigate. On two occasions, individuals
approached only after 2-3 min of playback.
Playback of chirr calls resulted in a quiet, cu-
rious approach at best.

DISCUSSION

Taxonomic status of the species. — Whereas
the generic allocation of Pithys castaneus has
been considered dubious, we believe that phe-
notypic characters such as the species’ song-
like vocalization, its bold chestnut plumage,
black hood and white face, and its saffron-
yellow legs all suggest a close relationship
with P. albifrons. Furthermore, R. T. Brum-
field and J. G. Tello (unpubl. data) have been
building a molecular phylogeny of the Tham-
nophilidae, and have found P. castaneus and
P. albifrons to be sister taxa.

Potential habitat specialization. — Based on
our observations, we suspect that P. castaneus
is restricted to varillal forests. We should
note, however, that we observed and mist-net-
ted P. castaneus individuals that had followed
ant swarms from varillal into varzea forest
immediately adjacent to our campsite, and
twice we recorded individuals on richer, hilly
terra firme forest within 300 m of typical var-
illal habitat. We never encountered Hairy-
crested Antbird ( Rhegmatorhina melanosticta )
at the Morona site and wonder whether it may
be replaced by the similarly sized P. casta-
neus (see Table 1) in the region or (more like-
ly) habitat. We can find no evidence that R.
melanosticta inhabits the region between the
rios Santiago and Pastaza, but it is quite pos-
sible that this is due to poor sampling as it is
to true absence. If R. melanosticta competi-
tively excludes P. castaneus outside the Mo-
rona-Pastaza varillal forest, this may explain
the restricted distribution of the latter species.
Furthermore, if varillal forest habitat was not
included in the searches conducted by Willis
and the ANSP expedition along the Pastaza,
their failure to encounter the species may be

explained by the possible habitat specializa-
tion of P. castaneus.

Potential distribution of Pithys castaneus. —
Landsat imagery, complemented with infor-
mation from Instituto de Investigaciones de la
Amazonia Peruana personnel and local peo-
ple, shows what we interpret to be fairly large
blocks of varillal forest embedded within a
quadrangle formed by the Rio Maranon to the
south, the Rio Morona to the east, the Rio
Mayuriaga to the north, and the Cordillera
Campanquls to the west. Besides this area, P.
castaneus populations are likely to occur in
similar forest along the Rio Pastaza in Loreto
and probably into Ecuador. At present, we
have no information about the existence of
varillal forest at the latter sites. However,
some indicator species of varillal forest have
been found along the upper Rio Pastaza in Ec-
uador (e.g.. Pompadour Cotinga, Xipholena
punicea, and Red-fan Parrot, Deroptyus accip-
itrinus\ Ridgely and Greenfield 2001a), sug-
gesting that the area probably supports varillal
forest habitat. We suspect that once such for-
ests along the upper Rio Pastaza are located
and surveyed, the mystery of the true position
of the “Andoas” collecting locality finally
will be unraveled.

Conservation. — The west bank of the Rio
Morona, including the areas of varillal forest
where our work was conducted, are part of the
recently created Zona Reservada Santiago Co-
maina, created in 1999. According to Peruvian
legislation, its new status is temporary, but
supposedly, it will be ranked as a definitive
conservation unit in the future (National Park,
National Reserve, National Sanctuary, or
Communal Reserve). However, local leaders
of the Federacion de Comunidades Indlgenas
del Rio Morona informed us that they strongly
oppose the creation of a reserve and will fight
to prevent this action.

A branch of the North-Peruvian oil pipeline
that transports oil from the upper Rio Pastaza
passes through a large portion of varillal for-
est as it crosses the Rio Mayuriaga on its way
to the Rio Maranon. At present, this has meant
the destruction of only a 50-m-wide swath of
forest along the pipeline. However, an oil spill
could have drastic consequences for this rath-
er delicate habitat, particularly with its flat ter-
rain and poor drainage. Furthermore, the pipe-
line itself could represent a potential dispersal

Lane et al. • REDISCOVERY OF WHITE-MASKED AN'I BIRD

barrier for P. castaneus. It is also worth men-
tioning that there are several plans to connect
Ecuador’s Amazonian road network to the Rio
Maranon. Anecdotal evidence suggests that
many bird species of interior forest understory
are averse to crossing large openings or other
similar breaks, such as rivers or roads (Zim-
mer and Isler 2003). Thus, gaps such as those
associated with roads and pipelines may pose
barriers to gene flow in populations of these
understory species.

Population estimate. — During our stay we
surveyed about 8 km2 of white-sand forests
and encountered between six and eight differ-
ent army ant swarms of E. burchelli and two
of L. praedator. Based on our extrapolations,
we estimate the number of P. castaneus to be
between 18 and 26 individuals in the area we
surveyed. If we consider the immediate area
(the Morona-Santiago interfluvium) covered
with varillal, then the population estimate of
P. castaneus would be —1,300-2,500 individ-
uals. Prior to our rediscovery of P. castaneus,
the species was considered to be rare, with a
very restricted global distribution, and prob-
ably threatened (Bibby 1992, Stattersfield and
Capper 2000). Considering the population es-
timates and the potential threats presented
here, we recommend changing the species’
status from Data Deficient to Vulnerable, ac-
cording to the ranking criteria presented in
Stattersfield and Capper (2000). If a road or
any other invasive construction project threat-
ens the white-sand forests between the rlos
Morona and Santiago, then the species’ status
should be upgraded to a category of higher
risk.

Since our rediscovery of P. castaneus in
July 2001, and our discovery of the two Tre-
neman specimens in MUSM, we have been
informed of two subsequent observations of
P. castaneus by colleagues who visited our
Morona site. Observers visited the site 22-24
June 2002 and 24 May 2003 (M. Levy, J.
Nilsson, M. Sokol, and B. Walker pers.
comm.). Both parties saw the species, but the
2002 observation was of multiple individuals
and the observers regarded the species as
“one of the most common birds” at the site.
During the 2003 visit, however, only one in-
dividual was observed, possibly because
swarms of army ants were not easily encoun-
tered then (an artifact of the season?).

ACKNOWLEDGMENTS

We thank J. P. O’Neill as the initiator and organizer
of the 2001 expedition. Funding for the 2001 expedi-
tion was received from the Coypu Foundation and a
donation from the late R. B. Wallace. Additional fund-
ing was provided to JAA by a Fulbright Scholarship.
Permits for fieldwork were granted by INRENA, and
we particularly appreciate the efforts of M. Prieto C.
and R. Acero V. of that institution. D. Huachaca, M.
Sanchez S., A. Urbay T., M. Pizango, M. Tenazoa, H.
Pizango, F. Salazar, and R. Sandoval all provided lo-
gistical support in the field. M. L. and P. R. Isler gra-
ciously allowed us access to their data and recording
collections, and freely provided the fine maps and
sonograms for our figures. M. Levy, J. Nilsson, M.
Sokol, and B. Walker all related information from their
visits to the Morona site. T. Mark provided us with his
Andoas manuscript, and he and J. W. Fitzpatrick pro-
vided information and photos of the holotype at the
Paris Museum. L. B. McQueen produced the illustra-
tion that allowed us to recognize Pithys castaneus
while in the field. T. S. Schulenberg provided us with
rare reprints and data collected on Peruvian antbirds.
I. Franke J. kindly allowed us access to the ornitho-
logical collection in her care at MUSM, and assisted
us in trying to find more details of the two “mystery”
Pithys castaneus specimens there. This manuscript
benefited from comments by M. L. and P. R. Isler, J.
V. Remsen, Jr., T. S. Schulenberg, B. Walker, B. M.
Whitney, K. J. Zimmer, and two anonymous reviewers.

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170.

Zimmer, K. J. and M. L. Isler. 2003. Family Tham-
nophilidae (typical antbirds). Pages 448-681 in
Handbook of birds of the world, vol. 8: broadbills
to tapaculos (J. del Hoyo, A. Elliott, and D. Chris-
tie, Eds.). Lynx Edicions, Barcelona, Spain.

The Wilson Journal of Ornithology 1 1 8( 1 ):23 — 35, 2006

NESTING ECOLOGY OF LESSER PRAIRIE-CHICKENS IN SAND
SAGEBRUSH PRAIRIE OF SOUTHWESTERN KANSAS

JAMES C. PITMAN,'-1 2 3 4-8 CHRISTIAN A. HAGEN,1-5 BRENT E. JAMISON,1-6 7
ROBERT J. ROBEL,1 THOMAS M. LOUGHIN,2 AND ROGER D. APPLEGATE57

ABSTRACT. — Despite the fact that the Lesser Prairie-Chicken ( Tympanuchus pallidicinctus) is a species of
conservation concern, little is known about its nesting ecology, particularly in sand sagebrush (. Artemisia filifolia)
habitats. To find and monitor nests, we captured and equipped 227 female Lesser Prairie-Chickens with trans-
mitters (87 yearlings, 1 17 adults, and 23 of unknown age) from 1997 to 2002 in southwestern Kansas. Apparent
nest success was similar for yearlings (31%, n = 74) and adults (27%, n = 97) but differed marginally ( P =
0.090) between first nests (29%) and renests (14%). An estimated 31% of females that were unsuccessful in
their first nesting attempt initiated a second nest. The probability that a female would initiate a second nest after
failure of the initial attempt was negatively influenced by the day of incubation on which the initial attempt
failed. Over 95% of all nests were initiated and completed between 5 May and 2 July. The primary cause of
nest failure was predation by coyotes ( Canis latrans ) and gopher snakes ( Pituophis melanoleucus ). Mean clutch
size, egg fertility, hatching success, nesting and renesting frequency, and incidence of interspecific parasitism
were all similar across years and between yearlings and adults. Distances between nest sites were used as an
index to nest-site fidelity between first nests and renests and for across-year nesting attempts. Mean distances
between first nests and renests were similar for yearlings (1,071 m) and adults (1,182 m). Mean distance between
nests constructed by the same female in subsequent years (918 m) did not differ between age classes or success
of the first year’s nest. Most females (80%) nested closer to a lek other than the lek where they were captured.
Received 24 January 2005, accepted 21 September 2005.

Range-wide, Lesser Prairie-Chickens ( Tym-
panuchus pallidicinctus ) have declined by an
estimated 97% since the 1800s (Crawford
1980, Taylor and Guthery 1980). In Kansas,
Lesser Prairie-Chickens are most abundant in
the western part of the state — south of the Ar-
kansas River in mixed and shortgrass prairie
dominated by sand sagebrush {Artemisia fili-
folia). They also occur in mixed grass prairie
north of the Arkansas River, but this habitat
is generally devoid of sand sagebrush. Lesser

1 Div. of Biology, Kansas State Univ., Manhattan,
KS 66506, USA.

2 Dept, of Statistics, Kansas State Univ., Manhattan,
KS 66506, USA.

3 Survey and Research Office, Kansas Dept, of
Wildlife and Parks, P.O. Box 1525, Emporia, KS
66801, USA.

4 Current address: Survey and Research Office, Kan-
sas Dept, of Wildlife and Parks, P.O. Box 1525, Em-
poria, KS 66801, USA.

5 Current address: Oregon Dept, of Fish and Wild-
life, 61374 Parrell Rd., Bend, OR 97702, USA.

6 Current address: Missouri Dept, of Conservation,
P.O. Box 368, Clinton, MO 64735, USA.

7 Current address: Tennessee Wildlife Resources
Agency, Ellington Agricultural Center, P.O. Box
40747, Nashville, TN 37204, USA.

8 Corresponding author; e-mail:
jimp@wp.state.ks.us

Prairie-Chickens currently occupy 31 of 39
counties believed to compose their historical
distribution in Kansas, but counts of leks and
individual birds suggest that Lesser Prairie-
Chickens have experienced significant de-
clines since 1964 (Jensen et al. 2000).

The mechanisms responsible for Lesser
Prairie-Chicken population declines have not
been identified; however, aspects of nesting
ecology could be influential (Peterson and Sil-
vy 1996, Wisdom and Mills 1997). Thus,
identifying age-specific variation in nesting
variables is important to understanding a spe-
cies’ demography or life-history strategy (Pat-
ten et al. 2005). Most research on Lesser Prai-
rie-Chicken nesting ecology has been con-
ducted in sand shinnery oak {Quercus havar-
dii ) habitats in New Mexico and Texas (Davis
et al. 1979, Haukos and Broda 1989, Riley et
al. 1992). The objectives of our study were to
provide baseline information on age-specific
variation in nesting ecology, record fidelity to
previous nest sites (within-year renests and
across-year attempts), and document nest-site
locations relative to leks of Lesser Prairie-
Chickens in sand sagebrush prairie of south-
western Kansas. We examined annual varia-
tion and the effects of age on reproductive pa-
rameters and nest-site placement.

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

METHODS

Study area. — From 1997 to 2002, we stud-
ied Lesser Prairie-Chickens inhabiting sand
sagebrush habitat south of the Arkansas River
in Finney County, Kansas (37° 52' N, 100°
59' W). We initiated field work on a 7,700-ha
area in 1997 and on a nearby 5,600-ha area in
2000; we continued work on both areas
through summer 2002. Vegetation was similar
in both areas; sand sagebrush was the most
conspicuous vegetation present and was inter-
spersed with grasses, including little bluestem
( Schizachyrium scoparium), needle-and-
thread ( Stipa comata), sand lovegrass (. Era -
grostis trichodes ), sixweeks fescue ( Vulpia
octoflora ), blue grama ( Bouteloua gracilis ),
sand dropseed ( Sporobolus cryptandrus ),
sideoats grama ( B . curtipendula), and western
wheatgrass ( Agropyron smithii). The most
common forb species were Russian thistle
( Salsola kali), western ragweed ( Ambrosia
psilostachya ), sand lily ( Leucocrinum montan-
um), and common sunflower ( Helianthus an-
nuus). Each study area was bounded almost
entirely by center-pivot irrigated cropland and
grazed seasonally by livestock. Annual pre-
cipitation averaged 50 cm (U.S. Department
of Commerce 2003) and ranged from 42 cm
(2000) to 59 cm (1997) during our study.

Locating and monitoring nests. — Using
walk-in funnel traps, we captured female
Lesser Prairie-Chickens on leks from mid-
March through mid-April (Haukos et al.
1990). Except in 1997 (when age was not de-
termined), we classified captured birds as
yearlings (—10 months of age) or adults (>21
months of age) by examining the primaries
(Copelin 1963). We equipped birds with 11-g
necklace-style transmitters (life expectancy =
6-12 months; models from AVM Instrument
Company, Colfax, California; Advanced Te-
lemetry Systems, Isanti, Minnesota; and Ho-
lohil Systems, Carp, Ontario) and released
them on-site immediately after capture. Each
day, we determined locations of transmitter-
equipped birds by triangulating bearings col-
lected from a truck-mounted, null-peak telem-
etry system. Bird locations were determined
until transmitter failure, emigration from the
primary study areas, or bird death. When birds
emigrated from our study area, we re-located
them by extensive ground searches or from

fixed-wing aircraft. We monitored females
that moved off our study area two to three
times per week throughout the nesting season.

Using a hand-held antenna, we found nests
by approaching transmitter-equipped females
when their locations had remained unchanged
>3 consecutive days. If the female was in-
cubating, she was flushed so the eggs could
be counted and the clutch examined for inter-
specific parasitism (Hagen et al. 2002). We
marked nest locations with flags (1997) or
transmitters (1998-1999) at a distance of 5 m
from the nest bowl (Jamison 2000), or we re-
corded locations with a global positioning sys-
tem (2000-2002). Nest sites were not visited
again until the female departed the site with a
brood or until the nest was depredated or
abandoned. This technique allowed us to es-
timate apparent nest success only. Because we
did not determine nest status throughout in-
cubation, we did not estimate daily survival
of eggs or nests according to the Mayfield
method (Mayfield 1975).

After the departure of each nesting female,
we classified nest fate as successful (produced
at least one chick), unsuccessful, or aban-
doned. Beginning in 2000, we opened un-
hatched eggs to determine whether embryos
had developed. If the nest was depredated, we
systematically searched the area within a 10-
m radius for tracks, scat, or eggshell frag-
ments to help determine the predator’s identity
(Sargeant et al. 1998).

Statistical analyses. — We recorded clutch
size and estimated the start of incubation for
yearling and adult nests. We defined the start
of incubation as the first day on which we
detected no changes in the female’s telemetry
locations — typically, 3-5 days before a nest
was located. We estimated the initiation date
of each nest by backdating from the start of
incubation by 1 day for each egg in the clutch
(Coats 1955). We also calculated apparent
nest success (the proportion of all known nests
producing at least one chick X 100), hatching
success, egg fertility, percentage of females
attempting a nest, percentage of females re-
nesting, and the incidence of interspecific par-
asitism— separately for yearlings and adults.
We defined hatching success as the number of
eggs hatched divided by initial clutch size
(Westemeier et al. 1998b). We defined percent
fertility as the number of eggs hatching or

Pitman et al. • NESTING ECOLOGY OF LESSER PRAIRIE-CHICKENS

containing a developed embryo divided by the
total number of eggs in the nest bowl at the
time of hatching. We estimated incubation
length as the time (days) between the start of
incubation and the date when a female left the
nest with a brood (as determined from telem-
etry locations). We estimated nesting frequen-
cy as the percentage of females that attempted
a nest. Females that did not attempt a nest and
died before 31 May were excluded from our
estimate of nesting frequency. Because we
documented some first nesting attempts after
31 May, it was uncertain whether birds dying
prior to this date would have subsequently at-
tempted a nest. Interspecific parasitism was
reported as the percentage of nests containing
eggs of both Lesser Prairie-Chickens and oth-
er bird species. Interspecific nest parasitism
was previously described for the 1 997 to 1 999
field seasons (Hagen et al. 2002); here, we
summarize all records of parasitism from
1997 to 2002. The percentage of females at-
tempting to renest was estimated as the per-
centage of females known to have incubated
and lost a first clutch and that subsequently
incubated a second. Because of some small
expected cell counts, we used a Fisher’s exact
test for all comparisons (Agresti 1996). In ad-
dition, we used two-tailed f-tests for unequal
variances (Zar 1999) to compare clutch size,
incubation date, hatch date, and incubation
length between yearlings and adults.

We used logistic regression to assess the re-
lationship between the likelihood of renesting
and (1) age class, (2) clutch size of the initial
nest attempt, and (3) day into incubation when
the initial attempt failed. We excluded data
from 1997 because we did not identify age
class of birds that year. Initially, we fit seven
a priori models to data associated with 59
failed first nest attempts recorded from 1998
to 2002. We considered all four additive mod-
els and main effect models for each of the
three independent terms. We used the mini-
mization of Akaike’s Information Criterion for
small sample sizes (AICc.) to rank the models
(Burnham and Anderson 1998). All models
where AAICc < 2 were considered to be com-
peting models (Burnham and Anderson 1998).
Because age class was not included in any of
the competing models (all AAICc > 2), we
excluded this variable and developed models
using an expanded data set ( n = 69) that in-

cluded failed first nest attempts recorded from
1997 to 2002. We used the same model pro-
cedures previously described to fit three of our
a priori models that included the main effects
(1) clutch size and (2) day of incubation on
which the initial attempt failed.

We calculated distances between first nests
and renests, nesting attempts in multiple
years, and distances from nest sites to the lek
of capture and the nearest lek. We used anal-
ysis of variance (ANOVA) to determine
whether year or age class influenced the dis-
tance between an initial nest site and the re-
nest location and the affinity of nesting fe-
males to lek sites (capture lek and nearest lek).
We also used ANOVA to determine whether
age class or success of the first-year nest af-
fected distance between nest sites in subse-
quent years. For these analyses, we excluded
all data from 1997 because we did not identify
age class that year; however, we included
pooled age-class data from 1997 in the data
tables to provide an overview of nesting pa-
rameters for the duration of our study. We in-
terpreted simple effects with two-sample t-
tests when significant interactions were found
(Zar 1999). We considered all differences sig-
nificant when P < 0.05 and marginally sig-
nificant when 0.05 < P < 0.10. We report
parameter estimates and means as ± SE (or
SD as noted).

RESULTS

Nesting ecology. — We captured 227 female
Lesser Prairie-Chickens and fitted them with
transmitters (87 yearlings, 117 adults, and 23
of unknown age). We found 209 nests (77
yearling, 103 adult, and 29 unknown-age).
The percentage of females initiating a nest
was similar ( P = 0.50) for yearlings (94%)
and adults (92%; Table 1). We determined fate
for 196 of 209 (94%) nests; apparent nest suc-
cess was 26 ± 3% (51 of 196). The remaining
nests were either abandoned (2%, n = 5) or
success could not be determined from evi-
dence remaining at the nest site (4%, n = 8).
Nest success did not differ across years (x2 —
6.95, df = 5, P = 0.22) or between age classes
for first nests (P = 0.60) or renests (P = 0.82;
Table 1). An estimated 31% of all females that
were unsuccessful in their first nesting attempt
initiated a second nest, and this percentage did
not differ (P = 0.85) between yearlings and

TABLE 1 . Lesser Prairie-Chicken nesting statistics (mean ± SE), by nesting attempt and age, compiled over a 6-year period in the sand sagebrush prairie of

THE WILSON JOURNAL OF ORNITHOLOGY

Vol. 118, No. 1, March 2006

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d Nests were parasitized by either Ring-necked Pheasants or Northern Bobwhites.

Pitman et al. • NESTING ECOLOGY OF LESSER PRAIRIE-CHICKENS

adults (Table 1). However, success of renests
(14%) was marginally less than success of ini-
tial nests (29%; X2 = 3.31, df = 1, P = 0.090).
No females were known to have initiated a
third nest in the same year. Mean hatch date
(all years combined) was 1 June for first nest-
ing attempts and 22 June for renests (Fig. 1),
with a mean incubation length of 26.7 days
(Table 1). More than 95% of all nests were
initiated and completed between 5 May and 2
July (Fig. 1).

Mean clutch size did not differ between
yearlings and adults for either first nesting or
renesting attempts (Table 1). Mean clutch size
was 7.6 ± 0.4 eggs for renests, significantly
less (f188 = 1 1.77, P < 0.001) than the mean
clutch size (12.0 ± 0.1 eggs) of first nests.
Overall hatching success was 74 ± 2% and
did not differ between yearlings and adults.
Likewise, egg fertility was similar between
the two age classes, with 94 ± 1% of all eggs
containing a developed embryo (Table 1).

Six of 209 (3%) Lesser Prairie-Chicken
nests were parasitized by other bird species.
Four of the six nests contained Lesser Prairie-
Chicken and Ring-necked Pheasant ( Phasi -
anus colchicus ) eggs, and eggs of both species
hatched in two of these nests. One nest was
parasitized by a Northern Bobwhite ( Colinus
virginianus\ 10 prairie-chicken eggs and 1
quail egg), and the remaining nest was para-
sitized by both Ring-necked Pheasant and
Northern Bobwhite (3 prairie-chicken eggs, 1
pheasant egg, and 1 quail egg). Both of these
latter nests were depredated before hatching.

Nest predators. — Most (>80%) known pre-
dation events occurred >3 days after our ini-
tial nest visit (mean = 10.2 days ± 6.9 SD).
We assigned predator species to 112 of 161
(70%) unsuccessful Lesser Prairie-Chicken
nests. Coyotes ( Canis latrans ) depredated the
majority (64%) of the nests and were the pri-
mary cause of nest predation during most
years (Table 2). Snakes were responsible for
the loss of 31% and 42% of the unsuccessful
Lesser Prairie-Chicken nests in 2001 and
2002, respectively. Most of the snake preda-
tion was probably by Gopher snakes (. Pituo -
phis melanoleucus ) because they were the
most observed snake species on our study ar-
eas. Other causes of nest loss included pre-
dation by ground squirrels ( Spermophilus
spp.) and trampling by cattle (Table 2).

Renesting probability. — The probability of
a Lesser Prairie-Chicken renesting was influ-
enced by both clutch size and the day of in-
cubation on which the initial attempt failed.
An additive model including both terms was
the highest-ranking (AAICc = 0.00; AICc =
80.90), but the model including only date of
failure also had considerable support (AAIC(
= 1.48). The model including only clutch size
was not supported (AAICc = 15.24). Females
incubating initial nests later into incubation
tended to have a lower probability of renesting
(Gdate = -0.18, 95% Cl = -0.28 to -0.08;
Fig. 2). Females laying a larger clutch in the
initial nest attempt tended to be more likely
to renest (Bclutch = 0.31); however, the magni-
tude of this effect was not clear because the
confidence interval overlapped zero (95% Cl
= —0.01 to 0.63). The odds of a female at-
tempting to renest decreased by 16.2% with
each day into incubation of the initial attempt
and increased 20.2% with each one-egg in-
crease in clutch size (Fig. 2).

Nest-site location. — Between 1997 and
2002, we found 28 renests (Table 3). Distance
between first nests and renests (1,271 m) was
not influenced by age class (Flf23 = 1.69, P =
0.21) or year (F4>23 = 1.65, P = 0.21); there
was no interaction effect (F2i23 — 1.82, P =
0.19; 1998-2002 data). Similarly, the distance
between nests initiated by the same female in
subsequent years (mean = 918 m, n = 15;
Table 3) was not influenced by age class (FU4
= 0.16, P = 0.70) or success of the first-year
nest (FU4 = 0.05, P = 0.82); there was no
interaction effect (FU4 = 0.00, P = 0.98).

The distance from a nest to the nearest lek
(mean = 691 m, n = 194; Table 4) was not
influenced by year (F4164 = 1.11, P = 0.36)
or age class (F U64 = 0.00, P = 0.99), nor was
there an interaction effect (F4164 = 1.41, P =
0.23; 1998-2002 data). Of 184 nests, 147
(80%) were located closer to a lek other than
the lek where the female was last captured.
Ten nests (5%) were located >10 km from the
lek at which the incubating female was cap-
tured (median = 20.6 km, range = 10.6-56.5
km). The female nesting 56.5 km from her lek
of capture was successful in her nesting at-
tempt. The distance from nest site to the lek
where the female was captured (mean = 3,082
m, n = 184; Table 4) was not influenced by
age class (FU58 = 0.12, P = 0.73) or year

Percentage of nests Percentage of nests

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

Weekly interval

FIG. 1. Percentage of Lesser Prairie-Chicken first nests (A) and renests (B) in southwestern Kansas that
were initiated, incubated, depredated, and hatched, by weekly intervals, 1997-2002. Mean dates for each variable
are listed at the top of each figure.

Pitman et al. • NESTING ECOLOGY OF LESSER PRAIRIE-CHICKENS

TABLE 2. Probable causes of predation of Lesser Prairie-Chicken nests in the sand sagebrush prairie of
southwestern Kansas, 1997-2002.

Depredation (%)

Predator

1997
(n = 24)

1998
(n = 12)

1999
in = 20)

2000
in = 44)

2001

in = 36)

2002
in = 26)

Total3
in = 161)

Coyote

100

Ground squirreP

Snakec

1 1

Cattle

Unknown

a Percentage of all nests destroyed by each predator.

b We did not differentiate between thirteen-lined ground squirrels and spotted ground squirrels.
c Gopher snakes appeared to be the most abundant snake species.

(F4158 = 1.25 P = 0.29), and there was no
interaction effect (F4158 = 1.33, P = 0.26;

1998-2002 data).

DISCUSSION

Although rainfall during the primary 4-
month nesting period (April through July) var-

ied substantially during the 6 years of our
study (range — 22.3-38.3 cm), we document-
ed little annual variation in Lesser Prairie-
Chicken nesting activity. Our ability to detect
annual variation, however, may have been hin-
dered by relatively small sample sizes within
years, especially in the early years of the

FIG. 2. Probability of Lesser Prairie-Chickens initiating renests after failure of the initial nest attempt in
southwestern Kansas, 1997-2002. Probabilities are plotted for various clutch sizes (8, 10, 12, 14) and the day
of incubation when the initial nest attempt failed.

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

TABLE 3. Evidence of nest-site fidelity as shown by mean distances (m) between nests for Lesser Prairie-
Chickens in southwestern Kansas, 1997-2002. Within- and across-year distances are presented by age class and
nest fate.

Within-year* Across yearsb’c

Category n Distance SE n Distance SE

Age class
Yearling

1,071

327

1,170

599

Adult

1,182

263

750

365

Nest fated

Successful

—

712

438

Unsuccessful

—

1,055

453

Totale

1.271

218

918

316

a Distance between the first nest and the renest.

bFor two females that initiated >1 nest within a year, the mean coordinates of those nests were used to calculate the distance to the nest site in
subsequent years.

c Nests for one female were located in non-consecutive years; all other nests were located in consecutive years.
d Nest fate refers to fate of first nests.
e Age of four females was undetermined.

study. Additionally, we observed little age-
specific variation — except that yearlings had
slightly smaller clutches and marginally later
hatch dates for first nest attempts than did
adults.

For all known nests, initiation began in ear-
ly May; peak hatching was 1 June for first
nests and 22 June for renests (Fig. 1). Similar
dates of nest initiation (mid-April through late
May) and hatching (late May through mid-
June) have been reported from studies
throughout the species’ range (Giesen 1998,
Patten et al. 2005). Mean incubation length
was 26.7 days (this study). Because nest at-

tentiveness of grouse increases throughout the
laying period (Giesen and Braun 1979), we
may have overestimated incubation length by
misidentifying the start of incubation. How-
ever, the time required to hatch Lesser Prairie-
Chicken eggs in an incubator (24—26 days;
Coats 1955, Sutton 1968) was only slightly
less than our estimate for eggs incubated by
wild birds.

The success of all nests averaged 26% in
our study, substantially less than estimates
from New Mexico (42%) and Oklahoma
(40%; Patten et al. 2005), but similar to the
28% reported by Giesen (1998) for 10 studies

TABLE 4. Distances (m) between Lesser Prairie-Chicken nest sites and leks in southwestern Kansas, 1997-
2002.

Nest site to lek of capture Nest site to nearest lek

Category n Median Mean ± SE n Median Mean ± SE

Year

1997

1,528

1,647

226

556

557 ± 52

1998

1,134

1,727

529

577

546 ± 71

1999

2,357

2,317

332

726

701 ± 55

2000

1,282

2,874

-t-

1,006

675

742 ± 53

2001

1,396

3,241

983

727

740 ± 54

2002

2,333

5,901

1,366

631

703 ± 65

Age

Yearling

1,893

3,580

853

633

702 ± 48

Adult

1,258

3,104

591

675

718 ± 32

Total

184a

1,427

3,082

432

194b

632

691 ± 25

a Includes 25 nests of females of unknown age.
b Includes 29 nests of females of unknown age.

Pitman et al. • NESTING ECOLOGY OF LESSER PRAIRIE-CHICKENS

conducted throughout the range of the Lesser
Prairie-Chicken. Giesen (1998) suggested that
nest success from those 10 studies was nega-
tively biased due to observer disturbance at
nest sites. Negative bias in our study was like-
ly only slight because females were flushed
from their nests only once. Westemeier et al.
(1998a) reported that flushing incubating
Greater Prairie-Chickens (T. cupido ) once did
not result in reduced nest success. Also, the
number of days between our initial nest visits
and predation events averaged >10 days. In
addition, only 2% of the nests in our study
were abandoned — a much smaller percentage
than the 25% reported by Riley et al. (1992)
for Lesser Prairie-Chickens in New Mexico.
Further, one of five nests abandoned during
our study was abandoned 9 days after the re-
searcher’s visit, indicating that it probably was
not due to human disturbance.

The percentage of females initiating a sec-
ond nest during our study (31%) was between
previous estimates for Lesser Prairie-Chickens
in New Mexico (15%) and Oklahoma (79%;
Patten et al. 2005), and it was less than the
83% reported for Greater Prairie-Chickens
(Svedarsky 1988) and the 67% estimated for
Sharp-tailed Grouse (T. phasianellus\ Roers-
ma 2001). The percentage of Greater Sage-
Grouse ( Centrocercus urophasianus ) initiat-
ing a renest was highly variable (5 to 87%)
throughout their range (Schroeder et al. 1999),
and most estimates were less than what we
observed for Lesser Prairie-Chickens. Our
models indicated that the low probability of
Lesser Prairie-Chickens renesting in south-
western Kansas was influenced by the length
of incubation before their clutches were dep-
redated (>50% of unsuccessful initial clutches
were incubated >12 days prior to predation).
Similarly, Schroeder (1997) reported that
Greater Sage-Grouse in Washington whose
initial nests failed late in incubation were less
likely to renest than those whose nests failed
earlier in incubation. Clutch size of the initial
nesting attempt was also somewhat associated
with renesting probability in our study; how-
ever, the magnitude of this effect was unclear.
The positive relationship that we observed
may have been due to increased fitness asso-
ciated with females laying larger clutches or
the possibility that we misclassified some re-
nests as initial nest attempts. We speculate that

the latter was not a common occurrence dur-
ing our study, but our methods did not allow
us to locate nests that were depredated prior
to the onset of incubation.

Few prairie grouse researchers have report-
ed nest success separately for first nest at-
tempts and subsequent renestings. Bergerud
and Gratson (1988) hypothesized that preda-
tion of grouse nests was density-dependent
and that renests would be more successful
than first nest attempts due to lower nest den-
sities. They also believed that nest success
should improve as new vegetative cover ap-
pears throughout the nesting season. Success
of first and second nesting attempts of Lesser
Prairie-Chickens in Kansas, however, does not
support Bergerud and Gratson’s (1988) hy-
potheses, as first nest attempts were margin-
ally more successful than renestings. Like-
wise, Greater Prairie-Chicken nests initiated in
Kansas prior to 30 April (presumably first at-
tempts) were more successful than nests ini-
tiated after 1 May (presumably renests; Robel
1970). Initial nesting attempts for Attwater’s
Greater Prairie-Chicken ( T c. attwateri) also
were more successful than renests in 4 of 5
years (Lutz et al. 1994). Similar nest success
for first attempts and subsequent renestings
has been reported for Greater Prairie-Chickens
in Colorado (Schroeder and Braun 1992) and
Greater Sage-Grouse in Washington (Schroe-
der 1997) and Alberta, Canada (Aldridge and
Brigham 2001). The only support for Berge-
rud and Gratson’s (1988) hypothesis comes
from studies on Sharp-tailed Grouse in Min-
nesota and North Dakota, where success was
higher for second attempts than first attempts
(Christenson 1970, Schiller 1973). In our
study, Lesser Prairie-Chicken nests initiated
after 15 May were less successful (11.9%, n
= 42) than earlier nests (31.5%, n = 143),
regardless of nesting attempt. We speculate
that nests initiated after 1 5 May were less suc-
cessful due to an increase in predator efficien-
cy later in the nesting season, corresponding
to changes in the structure and composition of
vegetation. Cattle grazing began on our study
area around 15 May, and, after that date, grass
cover and visual obstruction decreased sub-
stantially (JCP unpubl. data). Grazing coupled
with normal drought conditions during the
summer months in southwestern Kansas may
result in declining habitat quality, and, there-

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

fore, the poor success of renesting Lesser Prai-
rie-Chickens. Land management practices that
maintain taller and denser vegetation structure
later into the nesting season may promote the
overall nesting success of Lesser Prairie-
Chickens.

Clutch size in Kansas averaged 11.3 eggs
in 191 completed clutches — greater than that
reported in New Mexico (8.7) and Oklahoma
(10.8; Patten et al. 2005) or in 60 completed
clutches located in other states occupied by
Lesser Prairie-Chickens (10.4; Giesen 1998).
Our study is the first to document substantially
different mean clutch sizes for first nests (12.0
eggs) and renests (7.6 eggs). Merchant (1982)
reported mean clutch size for initial and sec-
ond nesting attempts, but his estimates were
similar for both (9.8 and 10.7 eggs, respec-
tively). In our study, the percentage of eggs
containing a developed embryo was 94% and
hatching success was 74%. Egg fertility has
not been reported previously for the Lesser
Prairie-Chicken, but hatching success of eggs
was estimated at >90% across three studies
(see Giesen 1998). The lower hatching suc-
cess observed in our study reflects partial nest
losses that occurred in 32 of 48 (67%) suc-
cessful nests.

Identifying nest predators from nest re-
mains is difficult because patterns of egg
breakage overlap among, and even within,
predator species (Lariviere 1999). Uncertain-
ties were reduced on our study area, however,
because coyotes and gopher snakes were the
only common species capable of preying on
Lesser Prairie-Chicken nests. Studies in New
Mexico and Texas revealed that Chihuahuan
Ravens ( Corvus cryptoleucus ), badgers ( Tax-
idea taxus), striped skunks ( Mephitis mephi-
tis), and ground squirrels were the primary
predators of Lesser Prairie-Chicken nests (Da-
vis et al. 1979, Haukos and Broda 1989, Riley
et al. 1992). However, few corvids, badgers,
or striped skunks were observed on our study
area, and, although ground squirrels were
abundant (estimated from casual roadside ob-
servations), they were identified as important
nest predators during only 1 year (2000).

Davis et al. (1979) documented snakes
preying on Lesser Prairie-Chicken nests in
New Mexico. We found little evidence for
snake predation of nests during the early years
of our study (Jamison 2000), but snake abun-

dance appeared to increase (estimated from
casual roadside observations), as did nest pre-
dation by snakes, in the later years (Pitman
2003). Snakes may have been responsible for
most partial-nest depredations because of the
lack of eggshell fragments at partly depredat-
ed nests. Also, three incubating Lesser Prairie-
Chickens were likely killed by snakes because
their intact carcasses were found with a thin
film of mucus covering the heads. In each
case, it appeared as if a snake had tried to
swallow the bird.

Interspecific nest parasitism has been re-
ported for Greater Prairie-Chickens and
Sharp-tailed Grouse (Leach 1994, Westemeier
et al. 1998b), but had not been reported for
Lesser Prairie-Chickens before our work in
Kansas (Hagen et al. 2002). Only 6 of 209
(3%) nests were parasitized by Ring-necked
Pheasants and/or Northern Bobwhites, and 2
of the 6 (33%) nests produced Lesser Prairie-
Chicken chicks. Hatching success of eggs in
these two nests was 72%, similar to the 74%
estimated for 46 unparasitized nests (Hagen et
al. 2002). Our study provided no evidence that
nest parasitism negatively affected nest suc-
cess or hatchability of Lesser Prairie-Chick-
ens.

Bergerud and Gratson (1988) hypothesized
that successful female grouse would nest in
the same area in the subsequent breeding sea-
son. In southwestern Kansas, female Lesser
Prairie-Chickens nested within 712 m of the
site of their previous year’s nest site (if suc-
cessful). This degree of philopatry is similar
to that reported for Greater Sage-Grouse in
Wyoming (Berry and Eng 1985) and Idaho
(Fischer et al. 1993). Greater Sage-Grouse in
Washington showed less philopatry to a pre-
vious year’s successful nest location, moving
an average of 1 ,600 m in the subsequent nest-
ing season (Schroeder and Robb 2003).

The association between lek location and
nest placement has important management im-
plications for identifying critical nesting hab-
itat. Bradbury (1981) hypothesized that fe-
male home ranges included only one lek and
that >50% of all females should locate their
nests nearer to that lek than other nearby leks.
Studies of Greater Sage-Grouse and Sharp-
tailed Grouse have provided support for this
hypothesis (Bradbury et al. 1989, Giesen
1997). In Colorado and Minnesota, however.

Pitman et al. • NESTING ECOLOGY OF LESSER PRAIRIE-CHICKENS

only 23 of 89 (26%; Schroeder 1991) and 7
of 18 (39%; Svedarsky 1988) Greater Prairie-
Chickens nested closer to their lek of capture
than to other leks, respectively. Similarly, in
Idaho Wakkinen et al. (1992) found 92% of
Greater Sage-Grouse nests within 3 km of a
lek, but only 55% were within 3 km of the
lek of capture. Our Lesser Prairie-Chicken
nesting data also do not support Bradbury’s
(1981) hypothesis: 80% of our females (147
of 184) nested closer to a lek other than that
on which they were captured. More impor-
tantly, we located >80% of all nests within 1
km of a known lek site; thus, we believe that
providing secure nesting habitat within 1 km
of a lek site is an important management strat-
egy*

Our study provides the first comprehensive
description of Lesser Prairie-Chicken nesting
ecology in terms of age-specific reproductive
effort. Our estimates of Lesser Prairie-Chick-
en nesting parameters should be viewed as ap-
proximations, however, because our method-
ology did not allow us to locate nests that
were destroyed during the laying process.
Nevertheless, our estimates provide a much
better understanding of Lesser Prairie-Chick-
en demography in sand sagebrush habitats.
The low nest success we observed (26%) is
troubling, especially if >50% nest success is
required for population stability (Westemeier
1979). Sensitivity analyses have revealed that
nest success is one of the most influential de-
mographic parameters affecting population
growth of prairie grouse (Peterson and Silvy
1996, Wisdom and Mills 1997, Hagen 2003).
Thus, habitat management designed to en-
hance nest success of Lesser Prairie-Chickens
in southwestern Kansas should be a priority.
Similar information on nesting ecology from
Lesser Prairie-Chicken populations in other
states and habitat types is needed to identify
regional and site-specific conservation needs
and to aid in the development of range-wide
population models.

ACKNOWLEDGMENTS

We thank the private landowners of southwestern
Kansas and the Sunflower Electric Power Corporation
for property access. C. C. Griffin, G. C. Salter, T. G.
Shane, T. L. Walker, Jr., and T. J. Whyte assisted with
fieldwork. This study was supported by Kansas State
University, Division of Biology; Kansas Agricultural
Experiment Station (Contribution No. 04-41 1-J); Kan-

sas Department of Wildlife and Parks; Federal Aid in
Wildlife Restoration Projects W-47-R and W-53-R;
and Westar Energy, Inc. Finally, we thank J. W. Con-
nelly, M. A. Schroeder, and three anonymous review-
ers for comments on earlier drafts of this manuscript.

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The Wilson Journal of Ornithology 118(1 ):36 — 4 1 , 2006

A COMPARATIVE BEHAVIORAL STUDY OF THREE GREATER
SAGE-GROUSE POPULATIONS

SONJA E. TAYLOR1 3 AND JESSICA R. YOUNG1 2 3

ABSTRACT. — We compared male strut behavior of the genetically distinct Lyon, Nevada/Mono, California
Greater Sage-Grouse ( Centrocercus urophasianus ) population with that of two proximal populations: Nye, Ne-
vada, and Lassen, California. We measured strut rates and nine acoustic components of the strut display in all
three populations. Male strut rates did not differ among populations. Acoustic components of the Lyon/Mono
and Lassen populations were similar, whereas the Nye population was distinct. The genetically distinct Lyon /
Mono population was more similar behaviorally to the Nye population than the genetically similar Nye and
Lassen populations were to each other. Overall, the Lyon/Mono population did not exhibit detectable differences
in male strut behavior. Reproductive isolation through sexual selection does not appear to have occurred in the
Lyon/Mono population. Received 27 September 2004, accepted 19 October 2005.

Two recent studies based on mitochondrial
gene sequence (Benedict et al. 2003, Oyler-
McCance et al. 2005) and nuclear microsat-
ellite markers (Oyler-McCance et al. 2005) re-
vealed a genetically distinct population of
Greater Sage-Grouse ( Centrocercus urophas-
ianus) on the Nevada/California border (Lyon,
Nevada/Mono, California). Those studies in-
dicated that the Lyon/Mono Greater Sage-
Grouse population is more genetically distinct
from other Greater Sage-Grouse populations
than is the newly described (Young et al.
2000) Gunnison Sage-Grouse (C. minimus)
species. Several factors, including the appar-
ent genetic and geographic isolation of Lyon/
Mono sage-grouse from other populations, the
degradation and loss of sagebrush (Artemisia
spp.) habitat, and an overall population de-
cline, have made this a population of interest
from both evolutionary and conservation per-
spectives.

Morphological (Hupp and Braun 1991) and
behavioral studies (Young et al. 1994) of Gun-
nison Sage-Grouse provided evidence that
sexual selection had driven speciation in the
isolated populations of sage-grouse in south-
western Colorado and southeastern Utah. The
use of both mitochondrial (Kahn et al. 1999)
and nuclear markers (Oyler-McCance et al.

1 Rocky Mountain Center for Conservation Genetics
and Systematics, Dept, of Biological Sciences, Univ.
of Denver, Denver, CO 80208, USA.

2 Western State College of Colorado, Dept, of Nat-
ural and Environmental Sciences, Gunnison, CO
81231, USA.

3 Corresponding author; e-mail:
sonja_taylor@comcast.net

1999) supported the morphological and be-
havioral data and led to species designation
for the Gunnison Sage-Grouse (American Or-
nithologists’ Union 2000, Young et al. 2000).
A similar approach would determine whether
the genetic distinctiveness of the Lyon/Mono
population has been manifested morphologi-
cally and/or behaviorally as it has in Gunnison
Sage-Grouse. If so, it could potentially lead to
a taxonomic reclassification.

Male mating success and mate-choice cues
(Gibson and Bradbury 1985), territoriality
(Gibson and Bradbury 1987), components of
female choice (Gibson et al. 1991), and male
strutting behavior (Young et al. 1994) have
been studied previously in the Mono sage-
grouse population. However, with the excep-
tion of Young et al. (1994), there have been
no comparative studies among populations.
Young et al. (1994) compared secondary sex-
ual characteristics from male strut displays
among three populations — one Gunnison
Sage-Grouse population (Gunnison Basin,
Colorado) and two Greater Sage-Grouse pop-
ulations (Mono, California, and Jackson, Col-
orado). The structure of the Gunnison male
strut display was strikingly different from that
of the other two populations. However, the
comparison of the similarly structured strut
display between males from Mono and Jack-
son indicated statistically significant differ-
ences in most of the acoustic measures.

In light of the genetic distinctiveness of
Lyon/Mono sage-grouse and the behavioral
results of Young et al. (1994), we undertook
a further examination of male strut display be-
havior. We compared the Lyon/Mono popu-

Taylor and Young • GREATER SAGE-GROUSE BEHAVIOR

FIG. 1. Current Greater Sage-Grouse distribution in California and Nevada, and locations of three sample
populations (modified from Schroeder et al. 2004).

lation with two proximal populations of
Greater Sage-Grouse (Fig. 1). We tested the
hypothesis that the Lyon/Mono population’s
behavior is measurably different from that of
other Greater Sage-Grouse populations and
may, in fact, be considered a separate taxon
given the genetic differences. Alternatively,
although the Lyon/Mono population appears
genetically isolated, behaviorally it may not
be significantly different from other Greater
Sage-Grouse populations, indicating that sex-
ual selection resulting in pre-mating isolating
mechanisms has not occurred.

METHODS

The three populations we studied are from
the southwestern edge of the Greater Sage-
Grouse range in Nevada and California (Fig.
1). Behavioral measurements of male strut

displays were taken at five leks. Greater Sage-
Grouse in Lyon County, Nevada, and Mono
County, California, form a connected, inter-
breeding population (Lyon/Mono). Record-
ings were completed between 9 and 17 April
2001 at three leks from the Lyon/Mono pop-
ulation: Lyon County, Nevada (Desert Creek
2 lek; 38° 42' N, 1 19° 18' W; 1,603 m), south-
ern Mono County, California (Long Valley 1
lek; 37° 42' N, 118° 48' W; 2,124 m), and
northern Mono County, California (Biedeman
lek; 38° 12' N, 119°6'W; 2,447 m). Of the
three recorded Lyon/Mono leks, the Desert
Creek and Biedeman leks are farthest apart
(123 km). Lassen County, California (Eastside
lek; 40° 18' N, 120° 0'W; 1,490 m), is ap-
proximately 250 km north and Nye County,
Nevada (Roadside lek; 38° 42' N, 1 16° 47' W;
2,121 m), is approximately 215 km east of the

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

■

Air sac pops

jL-Whistle minimum

■ /

. Whistle peak

Whistlp start ^ *

• « ■ — * ** ^1

Time (sec)

FIG. 2. Typical sonagram of a Greater Sage-Grouse male strut display. The two air sac pops, whistle start
frequency, whistle peak, and whistle minimum are labeled. See Table 1 for all acoustic components (modified
from Young et al. 1994).

Lyon/Mono population; recordings at these
sites were completed between 3 and 1 1 April
2002. The number of males sampled from
each of the five leks was as follows: Desert
Creek 2 (n = 6), Long Valley 1 ( n = 9),
Biedeman ( n — 9), Eastside ( n = 11), and
Roadside ( n = 14); therefore, the sample size
for the Lyon/Mono population was n = 24.

Males perform a ritualized strut display in
which they take a few steps forward and brush
their wings twice against their esophageal
pouch producing loud swishing noises (Fig.
2). Following these wing movements, males
compress air sacs and produce syringeal
sounds to complete a single strut display
(Hjorth 1970). Male strut displays were re-
corded and compared using the methods of
Young et al. (1994) with the following mod-
ifications. Only adult males were monitored,
and these were distinguished from juveniles in
the field by the presence of a clear white upper
breast on adults. Individual males were iden-
tified by their tail patterns (Wiley 1973). At
least 15 struts per male were recorded using
a Sony DCR TRV720 digital camcorder and
a Sennheiser MKH70-P48 microphone.
Sounds of individual struts were digitized at
22 kHz using Canary 1.2.4 sound analysis
software (Cornell Laboratory of Ornithology,
Ithaca, New York).

We measured nine acoustic components
(Table 1, Fig. 2) and calculated population
means derived from individual male averages

for each component. An estimate of repeat-
ability ([r = s2a/(s2 + s2a)]; Lessells and Boag
1987) was used to measure the proportion of
within-individual variation within populations
for each component. Repeatabilities range
from 0 (low) to 1.0 (high). High repeatabilities
indicate that the measured trait varies little
within individuals relative to the population
variation, suggesting that the trait could re-
spond to sexual selection.

To calculate strut display rate, we timed be-
tween-strut intervals using Etholog 2.2, an
ethological transcription tool (Ottoni 2000).
The display rate for each male was based on
7—40 consecutive struts in which no more than
30 sec had lapsed between struts. Females
were present on all leks during strut-rate mea-
surements, but any male included in the strut-
rate analyses had to have females within 20
m of them during recording. This criterion
lowered the sample sizes (number of males)
for population strut-rate estimation (Fig. 3).
At the Lassen and Lyon leks, measurements
were taken as one female moved throughout
the leks. The southern Mono, northern Mono,
and Nye leks all had multiple females visiting
leks over the various days that measurements
were taken.

We used analysis of variance (ANOVA) to
assess differences among populations for each
acoustic component and strut rate. We then
used the GT2-method (Hochberg 1974) to
make unplanned comparisons among popula-

Taylor and Young • GREATER SAGE-GROUSE BEHAVIOR

TABLE 1. Nine measured acoustic components of male Greater Sage-Grouse strut display in three popu-
lations from Nevada and California. Males were recorded while strutting during spring 2001 and 2002.

Lyon, Nevada/Mono, Lassen, California Nye, Nevada

California ( n = 24) (n = 11) (n = 14)

Acoustic

Measured variable

component

Mean

First pop to whistle peak
(msec)

Whistle peak to whistle

73.41

0.37

73.85

0.65

70.30

0.52

<0.001

minimum (msec)

40.21

0.28

39.81

0.32

41.69

0.61

0.012

Pop to pop (msec)
Whistle start frequency

199.89

0.73

199.64

0.97

192.24

0.88

<0.001

(Hz)

861.17

7.61

861.65

10.97

930.19

20.19

<0.001

Whistle peak (Hz)

2,619.83

21.06

2,657.32

23.09

2,873.84

42.85

<0.001

Whistle minimum (Hz)
Whistle start to peak dif-

533.58

5.89

514.48

7.56

637.26

9.63

<0.001

ference (Hz)
Whistle peak to mini-

1,771.61

20.69

1,795.22

23.94

1,944.72

35.09

<0.001

mum difference (Hz)
Whistle start to mini-

2,096.48

21.90

2,151.64

17.61

2,241.51

39.14

0.002

mum difference (Hz)

333.90

11.33

353.70

13.99

290.38

16.80

0.020

a ANOVA.

tion means with unequal sample sizes for
acoustic components. This method uses the
studentized maximum modulus distribution m
to compute a minimum significant difference
(MSD). The significance level for the
ANOVA was set at P — 0.05 and for the GT2-
method it was lowered from P = 0.05 to P =
0.017 using a Bonferroni correction (a" = a/
k; Sokal and Rohlf 1995) for multiple tests.
We used a" = 0.01 when referring to the stu-
dentized maximum modulus m critical values
table (GT2-method).

RESULTS

All nine acoustic components of the strut
display differed among populations (ANOVA,

8.5

^ 8.0
j/5
D

2, 7.5

| 7.0
w

6.5
6.0

Lyon/Mono Lassen Nye

(ii)

F 2,31 = 3.97, P = 0.029

(16)

(7)

all P < 0.05; Table 1). The acoustic compo-
nents of the males’ displays were similar be-
tween Lyon/Mono and Lassen, whereas those
of Nye males’ displays were consistently dis-
tinct from those of the other two populations.
Nye differed from both Lyon/Mono and Las-
sen for acoustic components 1 and 3-7 (GT2-
test, all P < 0.01). For component 8, Nye dif-
fered only from Lyon/Mono (GT2-test, P <
0.010). All other pairwise population compar-
isons for minimum significant differences
were not significant (GT2-test, all P > 0.01).

Repeatability estimates of the acoustic com-
ponents ranged from 0.41 to 0.84 in Lassen,
0.57 to 0.96 in Nye, and 0.35 to 0.91 in Lyon/
Mono (Table 2). The highest repeatability es-
timate for all three populations was for whistle
peak (component 5).

Strut rates (struts/min) differed (F2<31 =
3.97, P = 0.029) among populations (Fig. 3).
However, pairwise comparisons between pop-
ulations indicated that none were significant
(GT2-test, all P > 0.01). Lassen males had the
highest strutting rate (7.84 struts/min), where-
as males from Nye had the lowest strutting
rate (6.92 struts/min). Lyon/Mono males had
an intermediate strutting rate (7.21 struts/min).

FIG. 3. Means (with standard error bars) and
ANOVA result for strut rates of male Greater Sage-
Grouse from three populations: Lyon, Nevada/Mono,
California; Lassen, California; and Nye, Nevada. Sam-
ple sizes (number of males) are in parentheses.

DISCUSSION

We measured behavioral traits and second-
ary sexual characteristics that are related to
sexual selection in sage-grouse, which could

THE WILSON JOURNAL OL ORNITHOLOGY • Vol. 118, No. 1, March 2006

TABLE 2. Repeatability estimates of strut display
acoustic components within individual males from
three Greater Sage-Grouse populations in California
and Nevada. Males were recorded while strutting dur-
ing spring 2001 and 2002.

Acoustic

component

Lyon, Nevada/
Mono, California
n = 24

Lassen,
California
n = 11

Nye, Nevada
n = 14

0.51

0.78

0.65

0.35

0.44

0.62

0.64

0.74

0.65

0.57

0.67

0.79

0.91

0.84

0.96

0.57

0.68

0.79

0.53

0.80

0.88

0.74

0.49

0.87

0.41

0.57

therefore lead to divergence. Based on behav-
ioral differences in male strut displays, our
study did not support the idea that the genet-
ically distinct Lyon/Mono population should
be considered for separate taxonomic status.
The Lyon/Mono and Lassen populations were
similar to each other, while the Nye popula-
tion was the most unique across nine acoustic
components of male mating displays. How-
ever, across six components (1-4, 6, 9), the
Nye versus Lassen populations were either
more different or as different as Nye versus
Lyon/Mono populations (Table 1). Even
though the Lyon/Mono population is geneti-
cally distinct, male mating behaviors are more
similar to those of the Nye population than
those of the genetically similar Nye and Las-
sen populations are to each other (Table 1).

The repeatability estimates generally varied
widely across populations. However, three
acoustic components (3, 5, and 9) were rela-
tively comparable among the three popula-
tions. The high repeatability estimates for
components 3 (pop to pop) and 5 (whistle
peak) indicate that these traits vary little with-
in individual males relative to the variation
within populations and could potentially re-
spond to selection. Young et al. (1994) also
found high repeatability estimates for whistle
peak, which has been shown to be related to
female mate choice (Gibson and Bradbury
1985, but see Gibson et al. 1991). A low re-
peatability for component 9 (whistle start to
minimum difference) is most likely the result
of high levels of variability within individuals

rather than a lack of genetic variation or in-
accuracies in measurement (Boake 1989). Nye
had the highest repeatability estimates for sev-
en of the nine acoustic components, suggest-
ing low variation in the acoustic measure-
ments, despite samples being taken across
several days with multiple females being pres-
ent.

Although strut rates did differ among pop-
ulations, pairwise comparisons of strut rate
did not differ statistically between popula-
tions. This result agrees with the observations
of Young et al. (1994), who found that strut
rates did not differ between two Greater Sage-
Grouse populations — Mono, California, and
Jackson, Colorado. Strut rates may vary with
time of day, time of season, and proximity of
females (R. M. Gibson pers. comm.); there-
fore, variation in strut rate within and between
males may outweigh differences in strut rates
among populations except in strong cases of
population divergence.

Our results suggest that the Lyon/Mono
population does not exhibit any appreciable
behavioral differences in male mating displays
from other Greater Sage-Grouse populations.
The Lyon/Mono population is significantly
different genetically from the Lassen popula-
tion (Benedict et al. 2003, Oyler-McCance et
al. 2005), yet behaviorally, the Lyon/Mono
and Lassen populations have similar acoustic
strut components and strut rates. The impli-
cations of the slight behavioral differences ob-
served in the Nye population on female mate
choice may be determined upon further be-
havioral observations that include additional
leks, years, and populations. It is possible that
there are measurable differences in acoustic
components of the strut display between most
populations, but these differences are gener-
ally minimized by gene flow.

The Lyon/Mono population is genetically
more diverse and distinct than the Gunnison
Sage-Grouse species (Kahn et al. 1999, Oyler-
McCance et al. 1999, Benedict et al. 2003,
Oyler-McCance et al. 2005). Using mitochon-
drial DNA sequence, Benedict et al. (2003)
estimated that the Lyon/Mono population has
been isolated from other Greater Sage-Grouse
populations for tens of thousands of years.
Yet, neither local adaptation to ecological or
environmental factors, nor genetic drift, nor
sexual selection has led to detectable pheno-

Taylor and Young • GREATER SAGE-GROUSE BEHAVIOR

typic (behavioral) differences in this popula-
tion. Reproductive isolation does not appear
to have occurred through sexual selection in
the Lyon/Mono population as it has in the
Gunnison Sage-Grouse species.

ACKNOWLEDGMENTS

Funding and support for this project was provided
by the California Department of Fish and Game, Quail
Unlimited, the National Fish and Wildlife Foundation,
Western State College of Colorado, and the Bureau of
Land Management. We are grateful to D. S. Blanken-
ship, F. A. Hall, T. L. Russi, J. Fatooh, S. L. Nelson,

R. M. Gibson, W. F. Mandeville, and T. Slatauski for
logistical and field support. We appreciate M. K. Bollig
and M. D. Kascak for their assistance with graphics.
We thank C. E. Braun, J. W. Connelly, R. M. Gibson,

S. J. Oyler-McCance, K. P. Reese, and J. St. John for
helpful comments on the manuscript. Finally, we thank
S. L. Thode and R. D. Taylor for patience and support.

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The Wilson Journal of Ornithology 1 1 8( 1 ):42— 52, 2006

FIRST KNOWN SPECIMEN OF A HYBRID BUTEO: SWAINSON’S
HAWK ( BUTEO SWAINSONI) X ROUGH-LEGGED HAWK
(B. LAGOPUS) FROM LOUISIANA

WILLIAM S. CLARK1 2 3 ’ AND CHRISTOPHER C. WITT-

ABSTRACT. — We report a specimen that appears to be a hybrid between Swainson’s Hawk ( Buteo swainsoni)
and Rough-legged Hawk ( B . lagopus ), which, to our knowledge, is the first hybrid specimen for the genus.
There are few reports of hybridization between Buteo species, most of which have been observations of inter-
specific nesting pairs. The specimen described herein was collected in Louisiana and initially identified as a
Rough-legged Hawk because of its feathered tarsi and the dark bellyband and carpals. A DNA sequence from
the maternally inherited mitochondrial ND6 gene was identical to a published sequence for Swainson’s Hawk.
Nuclear DNA sequences from two introns contained only five variable sites among a panel of five potential
parental taxa, but the hybrid sequence was most consistent with parentage by Rough-legged and Swainson’s
hawks. The feathered tarsi of the hybrid strongly suggested that the father was either a Rough-legged or Fer-
ruginous hawk ( B . regalis ), the only North American raptors other than Golden Eagle ( Aquila chrysaetos ) that
have feathered tarsi. Plumage and size characters were inconsistent with those of Ferruginous Hawk, and, other
than the darkly pigmented leg feathers, were intermediate between the light morphs of Swainson’s and Rough-
legged hawks. The breeding range of Swainson’s Hawk in Alaska and northern Canada is poorly known, but it
overlaps that of the Rough-legged Hawk in at least a few locations, albeit at low densities, which may be a
factor in hybridization. The occurrence of this hybrid is evidence of the potential for interbreeding between
North American members of the genus Buteo , most of which are genetically closely related. Such hybridization
could have implications for genetic diversity, adaptation, or the evolution of reproductive barriers. In any case,
such hybrids present field and museum identification problems. Received 6 December 2004, accepted 3 October
2005.

Few documented cases of hybridization ex-
ist between any 2 of the 27 or so species in
the genus Buteo. Hybrid combinations have
been reported for Long-legged Buzzard ( B .
rufinus ) and Upland Buzzard (B. hemilasius )
in Asia (Pfander and Schmigalew 2001),
Common Buzzard (B. buteo ) and Long-legged
Buzzard in Europe (Dudas et al. 1999), and
Red-shouldered Hawk (B. lineatus) and Gray
Hawk ( Asturina nitidus ) in North America
(Lasley 1989). Additionally, an adult Swain-
son’s Hawk (B. swainsoni ) bred for more than
8 years with a presumably escaped South
American Red-backed Hawk (Red-backed
Buzzard, B. polyosoma ) in Colorado, USA,
and produced offspring in some years (Allen
1988, Wheeler 1988); a Red-tailed Hawk ( B .
jamaicensis ) that escaped from a falconer bred
with a Common Buzzard in Scotland (Murray
1970). However, to our knowledge, there are

1 2301 S. Whitehouse Cir., Harlingen, TX 78550,
USA.

2 Dept, of Biological Sciences and Museum of Nat-
ural Science, Louisiana State Univ., 119 Foster Hall,
Baton Rouge, LA 70803, USA.

3 Corresponding author; e-mail;
raptours@earthlink.net

no museum specimens of the offspring of such
unions. Thus, it was with great interest that
we found a specimen of an apparent hybrid in
the Louisiana State University Museum of
Natural Science (LSUMNS), Baton Rouge. It
is a juvenile male, has feathered tarsi and
mostly dark carpal patches, was collected near
Baton Rouge, Louisiana, and was identified as
a Rough-legged Hawk (B. lagopus ). Its plum-
age appears almost the same as that of a prob-
able hybrid between the same two species,
first seen and photographed in November
2002 by Martin Reid near Ft. Worth, Texas;
WSC observed and took photos of that bird
in January 2003.

Herein we present a description of the pu-
tative hybrid Buteo based on its morphology,
plumage, and mitochondrial and nuclear DNA
sequences. A comparison of the hybrid to a
set of potential parental Buteo taxa led to the
conclusion that it descended from the mating
of a female Swainson’s Hawk with a male
Rough-legged Hawk. Although not shown on
some published range maps, Swainson’s
Hawks breed sparsely throughout at least a
part of the Rough-legged Hawk’s breeding
range in far-northern North America.

Clark and Witt • HYBRID BUTEO SPECIMEN

METHODS

WSC noted that the specimen, LSUMZ
159785, which was stored with a handful of
juvenile light-morph Rough-legged Hawks,
differed from them and was much like a pre-
sumed hybrid he had seen and photographed
near Ft. Worth, Texas in January 2003. After
a comparison of this specimen with those of
juvenile Rough-legged and Swainson’s hawks,
he determined that it might be a hybrid. The
specimen had been collected on 4 November
1994 in East Baton Rouge Parish, Highway
30 at Burtville, Louisiana, by S. W. Cardiff
and D. L. Dittmann. A tissue sample was de-
posited in the LSUMNS Collection of Genetic
Resources (catalog No. B23743). The speci-
men was sexed internally as a male (left testis
7X11 mm) and was in juvenal plumage; the
skull was 75% ossified.

We used a DNEasy tissue kit (Qiagen, Va-
lencia, California) to extract DNA from frozen
muscle tissue of the putative hybrid specimen,
and one specimen of each of the following
taxa: Rough-legged Hawk, Swainson’s Hawk,
Red-tailed Hawk, Harlan’s Red-tailed Hawk
( B . jamaicensis harlani), and Ferruginous
Hawk. We amplified the mitochondrial ND6
gene for the hybrid specimen in 25 jjlI PCR
reactions using Amplitaq Gold (Applied Bio-
systems [ABI], Foster City, California) with
the primers tPROfwd and tGLUrev (Haring et
al. 1999). For all six specimens, we amplified
two nuclear loci, as follows: (1) intron 5 and
flanking exon regions of the cytosolic ade-
nylate kinase gene (AK1) using the primers
AK5b + and AK6c- (Shapiro and Dumbacher
2001), and (2) intron 3 and flanking exon re-
gions of the Z-chromosome-linked muscle-
specific receptor tyrosine kinase gene
(MUSK) using primers designed by F. K.
Barker: MUSK-E3F (CTTCCATGCACTAC
AATGGGAAA) and MUSK-E4R (CTCTGA
ACATTGTGGATCCTCAA). Standard PCR
reactions were run on an MJ Research PTC-
200 thermal-cycler under the following tem-
perature regime: initial denaturation at 95° C
for 8 min; 35 cycles of 92° C for 20 sec, 55°
C for 60 sec, 72° C for 60 sec; and a final
extension at 72° C for 10 min. For MUSK, the
annealing temperature was adjusted to 50° C.
Negative control reactions were used for all
extractions and PCR to insure against contam-

ination. PCR products were purified using a
Qiagen Gel Extraction Kit (Qiagen, Valencia,
California). Cycle-sequencing reactions were
carried out in both directions using the prim-
ers described above in quarter- or sixteenth-
volume reactions with a Big Dye Terminator
Cycle Sequencing Kit (ver. 2 or 3.1, ABI). Cy-
cle-sequencing products were purified using
Sephadex columns. Purified samples were
electrophoresed on an ABI 377 or 3100 au-
tomated sequencer. Sequences were assem-
bled and edited using Sequencher 4.2.2
(Gene Codes Corporation, Ann Arbor, Mich-
igan). The ND6 sequence was compared with
published sequences for various Buteo species
(Riesing et al. 2003).

We compared morphology and plumage of
the hybrid to a panel of five potential parental
taxa. We followed the “contradictory charac-
ters” approach of Rohwer (1994) to eliminate
potential pairs of parental taxa for which char-
acters of the presumed hybrid fall outside of
the range of variation. We assembled standard
measurements of body mass, wing chord (un-
flattened), exposed culmen, and hallux (Bald-
win et al. 1931) for juvenile males of potential
paternal taxa from banding data for Swain-
son’s, Rough-legged, and eastern Red-tailed
hawks ( B . j. borealis), and from museum
specimen data for western Red-tailed ( B . j.
calurus ), Harlan’s Red-tailed, and Ferruginous
hawks. We performed two stepwise discrimi-
nant function analyses with these four mor-
phological variables using SPSS ver. 11.5
(SPSS, Inc. 2002). In both stepwise analyses,
we used 0.05 probability of F for entry and
0.10 probability of F for removal of each var-
iable, set equal prior probabilities of group
membership, and used within-group covari-
ance matrices. The three Ferruginous Hawk
specimens were not included in the analysis
due to small sample size, and the single Har-
lan’s Red-tailed Hawk individual was includ-
ed in the western Red-tailed Hawk group. The
first discriminant function analysis included
Rough-legged, Swainson’s, eastern Red-tailed,
and western Red-tailed hawks as groups. All
four morphological variables were significant
and included in the final model, and three sig-
nificant discriminant functions were generat-
ed. The putative hybrid individual and the
three Ferruginous Hawks were then classified
using these discriminant functions. In the sec-

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

ond discriminant function analysis, we only
included Rough-legged and Swainson’s hawks
as groups. Only mass, wing chord, and cul-
men were significant and included in the final
model, and only one discriminant function ex-
plained 100% of the variation between the two
groups. The putative hybrid was then again
classified according to this discriminant func-
tion. To account for possible shrinkage of mu-
seum specimens relative to live birds (Winker
1993), we repeated all analyses under the as-
sumption of a 3% reduction in size due to dry-
ing. The adjustment for shrinkage had no sub-
stantive effect on the results. Finally, with re-
spect to plumage characters, we compared the
specimen with juvenile male Swainson’s and
Rough-legged hawks, including pigmentation
of the head, upperparts, breast, belly, tail, and
legs, and emargination of the seventh primary
(P7).

RESULTS

The mitochondrial DNA sequence of the
putative hybrid, totaling 558 bp, was an iden-
tical match to a published sequence from a
Swainson’s Hawk collected in New Mexico
(Table 1; GenBank accession No. AY2 13028).
The sequence was 0.76% divergent from its
nearest relative, the Galapagos Hawk (B. ga-
lapagoensis ), and 3.23-3.58% divergent from
the only sympatric congeners: Red-tailed, Fer-
ruginous, and Rough-legged hawks (Clark and
Wheeler 2001, Riesing et al. 2003; Table 1).
Mitochondrial haplotypes are shared between
mothers and their offspring because the mi-
tochondrial genome is non-recombining and
maternally inherited (Lansman et al. 1983).
The identical mtDNA sequences of the spec-
imen and a known Swainson’s Hawk strongly
suggests that the maternal parent was a Swain-
son’s Hawk.

The nuclear AK1 sequence of the putative
hybrid, totaling 542 bp, was identical to se-
quences from the Swainson’s, Rough-legged,
eastern Red-tailed, Harlan’s, and Ferruginous
hawks. The complete lack of variation at this
locus prevents the elimination of any of these
taxa as potential parents. The nuclear MUSK
sequence, totaling 599 bp, contained five var-
iable sites for the six taxa included in this
study (Table 2). Among the five variable sites
was a substitution unique to the Ferruginous
Hawk sample (T; site no. 480), and another

Louisiana State University Museum of Natural Science, Baton Rouge.

Clark and Witt • HYBRID BUTEO SPECIMEN

TABLE 2. Variable sites on the 599 bp MUSK gene sequence for the presumed Buteo hybrid and five other
buteos. The sites span part of exon 3, the entire intron 3, and part of exon 4, corresponding to positions 131 1922-
1312509 of the Gallus gallus chromosome Z genomic contig (GenBank NW 060751). Both states (i.e., A/T and
A/G) are reported for heterozygous sites, as inferred by unambiguous double peaks on chromatograms.

Variable position

113

157

452

480

Hybrid

A/T

A/G

Swainson’s Hawk

Rough-legged Hawk

A/T

A/G

Ferruginous Hawk

Eastern Red-tailed Hawk

Harlan’s Red-tailed Hawk

that was shared only by the eastern Red-tailed
and Harlan’s Red-tailed hawks (T; site no.
157). At two other sites (nos. 65 and 1 13), the
Rough-legged Hawk and the hybrid were both
heterozygous (A/T and A/G), with one exclu-
sively shared state and one state in common
with all other taxa (Table 2). The fifth variable
site (no. 452) was heterozygous in the hybrid
specimen only. Heterozygotes were inferred
when chromatograms showed strong signal
and unambiguous double peaks of nearly
equal height.

We identified the paternal parent using phe-
notypic characters. Red-tailed Hawk, includ-
ing Harlan’s Hawk, can be eliminated as the
putative father because it always has unfeath-
ered tarsi. It seems unlikely that two species
with bare tarsi would produce a hybrid with
feathered tarsi. Further, the Red-tailed Hawk’s
culmen is considerably larger than that of the
hybrid (Table 3). Finally, juvenile Red-tailed

Hawks share few plumage characters with the
hybrid (Wheeler and Clark 1995, Clark and
Wheeler 2001); we would not expect, for ex-
ample, a hybrid Red-tailed Hawk X Swain-
son’s Hawk juvenile to have the heavy, dark
bellyband (Fig. 1) or the dark carpal patches
of the hybrid.

Both Ferruginous and Rough-legged hawks
have feathered tarsi and are the most likely
paternal candidates of the hybrid specimen.
However, Ferruginous Hawks have noticeably
wider gapes (Bechard and Schmutz 1995) and
longer bills, wings, and halluces than the hy-
brid (Table 3). The measurements of the hy-
brid are far closer to those of Swainson’s
Hawk than to Ferruginous Hawk, suggesting
that the bird is not intermediate in size as
would be expected in an FI hybrid between
these two species. In contrast, the measure-
ments for body mass and wing chord are in-
termediate between juvenile male Swainson’s

TABLE 3. Comparison of measurements (mean ± SE) of the hybrid Buteo specimen with juvenile male
Rough-legged, Swainson’s, Ferruginous, eastern Red-tailed, western Red-tailed, and Harlan’s Red-tailed hawks.
Body mass and wing chord of the hybrid are intermediate between Rough-legged and Swainson’s hawks. Culmen
and hallux are closest to Swainson’s Hawk.

Body mass (g)

Wing chord (mm)

Culmen (mm)

Hallux (mm)

Hybrid

702.0

381.0

19.3

21.4

Swainson’s Hawk3

638.3 ± 16.8

378.5 ± 2.4

21.4 ± 0.3

21.7 ± 0.4

Rough-legged Hawkb

860.8 ± 12.6

398.2 ± 1.6

21.5 ± 0.1

23.9 ± 0.2

Ferruginous-Hawkc

1,091.4 ± 14.3

413.7 ± 1.8

25.0 ± 0.3

25.6 ± 0.3

Eastern Red-tailed Hawkd

825.4 ± 15.8

351.8 ± 1.9

27.2 ± 0.2

24.1 ± 0.2

Western Red-tailed Hawke

905.5 ± 30.3

374.4 ± 2.9

24.2 ± 0.3

27.7 ± 0.4

Harlan’s Red- tailed Hawkf

932.0

365.0

23.5

26.0

3 Unpublished banding data from Texas and New Jersey, sex determined by size.
b Unpublished banding data from New York, sex determined by size.

e MVZ (Museum of Vertebrate Zoology, University of California, Berkeley) specimen data from California.
d Unpublished banding data from New Jersey, sex determined by size.

e MVZ specimen data from British Columbia, California, Arizona, New Mexico, and Nevada.
f MVZ specimen data from British Columbia.

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

FIG. 1 . Specimens showing ventral view of the hybrid Buteo (center), compared with juvenile male Rough-
legged Hawk (left) and juvenile male Swainson’s Hawk (right). Characters of the hybrid are intermediate.

and Rough-legged hawks (Table 3). Finally,
the plumage characters of both light- and
dark-morph juvenile Ferruginous Hawks do
not match those of the specimen (Wheeler and
Clark 1995, Clark and Wheeler 2001); a hy-
brid Ferruginous Hawk X Swainson’s Hawk
juvenile, for example, would not be expected
to have the dark bellyband (Fig. 1) nor the
dark carpal patches of the hybrid.

Most plumage characters of the hybrid
specimen are similar to those of juvenile male
Swainson’s or Rough-legged hawks, or inter-
mediate between them (Figs. 1-2, Table 4).

The notching of P7 is also intermediate (Fig.
3). This feather has a noticeable abrupt wid-
ening or “notch” on the trailing edge for
Rough-legged Hawk (same for Ferruginous
and Red-tailed hawks) but not for Swainson’s
Hawk. The widening begins 93 mm from the
tip on a juvenile male specimen Rough-legged
Hawk (Fig. 3 A), widening about 15 mm at an
angle of 70° to the feather shaft. P7 on a ju-
venile male Swainson’s Hawk specimen be-
gan widening gradually 47 mm from the tip
and lacked a distinctive notch (Fig. 3B). The
hybrid’s P7 began widening 59 mm from the

Clark and Witt • HYBRID BUTEO SPECIMEN

FIG. 2. Specimens showing dorsal view of the hybrid Buteo (center), compared with juvenile male Rough-
legged Hawk (left), and juvenile male Swainson’s Hawk (right). Characters of the hybrid are intermediate.

tip with a notch and widened about 9 mm at
a 60° angle (Fig. 3C).

In the first discriminant function analysis,
which included Rough-legged, Swainson’s,
eastern Red-tailed, and western Red-tailed
hawks as groups, the first two discriminant
functions explained 96.2% of the variation be-
tween the groups (Fig. 4A). The first function
correlated strongly with culmen (r = 0.651)
and wing chord (r = —0.513) and explained
80.1% of the variance. The second function
correlated strongly with hallux (r = 0.814)
and body mass (r = 0.646) and explained

16.1% of the variance. Using both functions,
the hybrid was classified as a Rough-legged
Hawk with 3 1 .2% probability, as a Swainson’s
Hawk with 68.8% probability, and as an east-
ern or western Red-tailed Hawk with 0%
probability. In the second discriminant func-
tion analysis, which included only Rough-leg-
ged and Swainson’s hawks as groups, one dis-
criminant function explained 100% of the var-
iation between the groups (Fig. 4B). This
function correlated strongly with mass (r =
0.875) and wing chord (r = -0.580). Using
this function, the hybrid was classified as a

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

TABLE 4. Comparison of plumage characters of the hybrid Buteo specimen with juvenile male Rough-
legged and Swainson’s hawks. Characters of the hybrid are intermediate or like one or the other of the parent
species.

Character

Rough-legged Hawk

Swainson’s Hawk

Hybrid

Crown

Pale

Dark

Dark, pale streaks

Superciliary

None

Rufous

Buffy

Malar

Narrow

Wide

Back feathers

Brown, pale sides

Dark brown, pale
tips

Dark brown, pale tips and sides

Breast

Lightly streaked

Heavily streaked

Belly

Solidly dark

Buffy

Dark with pale edges

Legs

Feathered, lightly marked

Bare

Feathered, darkly marked

Uppertail

White base, dusky tip, no
bands

Gray-brown, dark
bands

Narrow white base, gray-brown,
dark bands

Primary, outer web

Grayish cast

Dark

Grayish cast

Primary, inner

web

Pale, no barring

Darker, barring

Pale, barring

Rough-legged Hawk with 45.4% probability
and as a Swainson’s Hawk with 54.5% prob-
ability.

DISCUSSION

Based on mtDNA, we conclude that the
mother of this putative hybrid is a Swainson’s
Hawk. The most likely paternal candidates are
raptors with feathered tarsi. Rough-legged and

Ferruginous hawks. The latter was eliminated
because of its plumage characters, much larg-
er size, and unique MUSK intron haplotype.

Independent lines of evidence converged on
the identification of the specimen as a hybrid
between Swainson’s and Rough-legged hawk.
The combination of morphological and mo-
lecular characters, as in the diagnosis of a hy-
brid manakin ( Ilicura X Chiroxiphia) by Ma-

FIG. 3. Notching of primary 7. (A) Rough-legged Hawk, (B) hybrid, and (C) Swainson’s Hawk. The pos-
terior margin of each P7 is highlighted in white. (Scale is not the same on each figure.) The shape of P7 of the
hybrid is intermediate and unlike those of any Buteo species.

Clark and Witt • HYBRID BUTEO SPECIMEN

• Eastern Red-tailed Hawk

a Western Red-tailed Hawk o Rough-legged Hawk (RLHA)

O Harlan's Hawk & Swainson's Hawk (SWHA)

Discriminant function 1

FIG. 4. Discriminant function analyses comparing
juvenile males of Buteo species. In panel (A), plots of
points along the first two significant discriminant func-
tions are from an analysis that included Rough-legged,
Swainson’s, eastern Red-tailed, and western Red-tailed
hawks as groups. These two discriminant functions ex-
plained 96.2% of the variation between the groups.
The Harlan’s Hawk was included in the western Red-
tailed Hawk group, but was plotted with a unique sym-
bol. The hybrid individual and three Ferruginous
Hawks were then classified and plotted using these dis-
criminant functions. In panel (B), points are plotted
according to a discriminant function from an analysis
that only included Rough-legged and Swainson’s
hawks as groups. One discriminant function explained
100% of the variation between the two groups. The
hybrid was classified and plotted according to this dis-
criminant function.

rini and Hackett (2002), is a powerful method
for the identification of avian hybrids. In par-
ticular, the comparison of a single mtDNA se-
quence to the growing database of published
sequences is an outstanding tool for identifi-
cation of the maternal parent. In this case, the
mtDNA sequence of the hybrid strongly sug-

gests that its maternal parent was a Swain-
son’s Hawk. The mother could have been a
species other than Swainson’s Hawk only if
the mitochondrial identity were a mere artifact
of incomplete lineage sorting. We consider
this possibility unlikely because the mitochon-
drial study of Riesing et al. (2003) demon-
strated that geographically heterogeneous
samples of five Rough-legged, two Ferrugi-
nous, nine Red-tailed, and three Swainson’s
hawks are each reciprocally monophyletic,
and the divergence levels between Swainson’s
Hawk and each of its sympatric congeners are
greater than 3%.

The paucity of variation in the two nuclear
introns illustrates the difficulty of using nu-
clear DNA to diagnose hybrids among closely
related species. Intraspecific variation and lack
of lineage sorting pose significant challenges
to the conclusive identification of hybrid in-
dividuals, and these problems are compound-
ed when potential parental taxa cannot be
thoroughly sampled at the population level.
Despite these difficulties, our sample of a sin-
gle individual for each potential parental tax-
on yielded some variation that was consistent
with the identification of Rough-legged Hawk
as the paternal species. The eastern Red-
tailed, Harlan’s Red-tailed, and Ferruginous
hawk samples each contained single substi-
tutions on the MUSK intron that were not
found in the hybrid. In contrast, only the
Swainson’s and Rough-legged hawk samples
were completely compatible with parentage of
the hybrid. Importantly, two heterozygous po-
sitions in the hybrid each contained a state
that was shared exclusively with the Rough-
legged Hawk sample.

Plumage and morphological characters of
the hybrid specimen were generally interme-
diate between those of juvenile males of the
parent species. This pattern is born out by the
discriminant function analyses and is consis-
tent with the characters of hybrids between
other species of birds (e.g.. Graves 1990, Roh-
wer 1994, Marini and Hackett 2002). How-
ever, the coloration of the tarsi feathers was
not intermediate. Juvenile male Rough-legged
Hawks have buffy tarsal feathers with sparse,
dark markings, whereas Swainson’s Hawks
have bare tarsi. The hybrid specimen has tar-
sal feathers with heavy, dark barring, clearly
not intermediate. The expectation that hybrid

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

traits fall within the range of traits expressed
by the parental taxa is based on the assump-
tion that most traits are additive and polygenic
(Falconer 1989) and is implicit in most hybrid
diagnoses. Nonetheless, hybrids can also ex-
press traits that are extreme relative to those
of the parental taxa (Rieseberg et al. 1999). It
is possible that the darkly pigmented tarsal
feathers could be one such transgressive trait,
caused by complementary gene action, over-
dominance, or epistasis. Swainson’s and
Rough-legged hawk populations are known to
possess genetic variation that results in differ-
ences in the quantity and distribution of mel-
anin-based plumage pigments (Clark and
Wheeler 2001). Rohwer (1994) reported other
examples of characters that were not inter-
mediate between those of the parental species.
The culmen, and, to a lesser degree, the hallux
of the hybrid were slightly smaller than our
Swainson’s and Rough-legged hawk measure-
ments for those characters, providing another
potential example of a non-intermediate char-
acter. However, specimen shrinkage could at
least partly account for this difference.

The Swainson’s Hawk breeds in an un-
known amount of the breeding range of the
Rough-legged Hawk in far northwestern
North America. This is the extreme northern
periphery of their distribution, and they occur
at very low densities in taiga habitat where
they are sympatric with the Rough-legged
Hawk (England et al. 1997, Bechard and
Swem 2002, Sinclair et al. 2003). This could
increase the possibility that a female Swain-
son’s Hawk could fail to find a conspecific
mate. Given the broad overlap in distribution
between Swainson’s, Red-tailed, and Ferrugi-
nous hawks, the lack of documented instances
of hybridization or interspecific pairings be-
tween any two of these three species suggests
behavioral barriers to reproduction. Such bar-
riers may not exist between Swainson’s and
Rough-legged hawks, which overlap only
marginally and may have come into sympatry
only recently. This hybrid pairing is consistent
with the model of Short (1969), who proposed
that hybridization is most likely to occur at
the edges of a species’ range.

Swainson’s Hawks are rare during Novem-
ber in the area where the hybrid individual
was found; there is only one November record
for East Baton Rouge Parish, despite intensive

coverage by birdwatchers and collectors
(LSUMNS data). Although Lowery (1974) in-
dicated that Rough-legged Hawk is a regular
winter visitor to Louisiana, and several sub-
sequent sight-based reports lacking photos
have been accepted by the Louisiana Bird Re-
cords Committee, the only physical evidence
substantiating the occurrence of a Rough-leg-
ged Hawk in Louisiana is a specimen collect-
ed on 12 March 1933 at Grand Isle (LSUMZ
4803). The present hybrid occurred at a place
(and time) unexpected for either species —
Rough-legged Hawks should occur farther
north and Swainson’s Hawks farther south.
This intermediate migratory behavior, as well
as a myriad of other ecological differences be-
tween Swainson’s and Rough-legged hawks,
suggests potential sources of reduced fitness
in hybrids. Hybridization can provide a mech-
anism for gene flow between species, partic-
ularly if hybrids are interfertile with parental
species and do not suffer reduced fitness (Ar-
nold 1992). Alternatively, hybrid unfitness can
reinforce behavioral pre-mating barriers
through natural selection (Saetre et al. 1997),
particularly in taxa such as Swainson’s and
Rough-legged hawks that may have recently
come into secondary contact.

Hybrids between raptor species are reported
infrequently, most likely because they are
rare, but also because they are difficult to di-
agnose in the field and are underrepresented
in collections. That this specimen went unrec-
ognized for 9 years after being collected un-
derscores the field and museum identification
problems posed by hybrids. Hybrids have
been reported between Red Kite ( Milvus mil-
vus) and Black Kite (A/, migrans) in Sweden
(Sylven 1977), a possible hybrid Rueppell’s
Vulture ( Gyps rueppellii ) and Cape Vulture
( G . coprotheres ) in Botswana (Borello 2001),
Brown Goshawk {Accipiter fasciatus ) and
Grey Goshawk (A. novaehollandiae ) in Aus-
tralia (Olsen 1995), Shikra (A. badius ) and Le-
vant Sparrowhawk (A. brevipes) in Israel
(Yosef et al. 2001), Pallid Harrier ( Circus ma-
crourus ) and Montagu’s Harrier (C. pygargus )
in Finland (Forsman 1995), Western Marsh
Harrier (C. aeruginosus ) and Eastern Marsh
Harrier (C. spilonotus ) in Siberia (Fefelov
2001), and Greater Spotted Eagle ( Aquila
clanga) and Lesser Spotted Eagle (A. poma-
rina) in Latvia (Bergmanis et al. 1996). We

Clark and Witt • HYBRID BUTEO SPECIMEN

were unable to locate a copy of Suchelet
(1897), who apparently reported a hybrid be-
tween Common Buzzard and Rough-legged
Hawk. Most unusual were intergeneric hy-
brids reported between Black Kite and Com-
mon Buzzard near Rome, Italy, that produced
rather strange-looking offspring (Corso and
Glidi 1998). Equally unusual was a pairing
between Gyrfalcon ( Falco rusticolus ) and Per-
egrine Falcon (F. peregrinus), in which both
members of the pair were females (Gjershaug
et al. 1998). The hybrid Turkey Vulture X
Black Vulture reported by Mcllhenny (1937)
was later determined to be a practical joke
(Jackson 1988). Most instances of hybridiza-
tion listed above were determined at the nests
by observing that the adults were different
species, although one was a hybrid captured
for banding (Yosef et al. 2001) and another
was identified using field observations and
photographs (Corso and Glidi 1998).

To our knowledge, our report is the first of
a hybrid specimen arising from two Buteo
species, and, perhaps, the first hybrid speci-
men for any raptor. It provides the first con-
clusive documentation of hybridization be-
tween two native North American members of
the genus Buteo. A pairing of a Red-shoul-
dered Hawk with a Gray Hawk (Lasley 1989)
produced a downy chick, but it did not fledge,
and there were neither photographs nor spec-
imens from this union.

ACKNOWLEDGMENTS

This study was facilitated by the Collections of
Birds and the Collection of Genetic Resources at the
LSU Museum of Natural Science, and the Collection
of Birds at the Museum of Vertebrate Zoology, Uni-
versity of California, Berkeley. We thank S. W. Cardiff
and D. L. Dittmann for finding and collecting this un-
usual specimen and P. Bloom, A. Hinde, Braddock Bay
Raptor Research, and Cape May Raptor Banding Pro-
ject for sharing measurements of juvenile male Swain-
son’s, Rough-legged, and Red-tailed hawks with us. F.
K. Barker provided previously unpublished primers for
the MUSK gene. J. V. Remsen, Jr., J. Schmutz, T.
Swem, S. M. Witt, and an anonymous reviewer made
helpful comments on previous drafts.

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The Wilson Journal of Ornithology 1 1 8( 1 ):53 — 58, 2006

NOCTURNAL HUNTING BY PEREGRINE FALCONS AT THE
EMPIRE STATE BUILDING, NEW YORK CITY

ROBERT DeCANDIDO1 34 AND DEBORAH ALLEN1 2 3 4

ABSTRACT. — We report on nocturnal hunting by Peregrine Falcons ( Falco peregrinus) at the Empire State
Building in Manhattan, New York City. From 4 August through 13 November 2004, we saw Peregrine Falcons
on 41 of 77 nights of observation. During this period, they hunted migrating birds on 25 evenings, with the first
hunting attempt occurring an average of 119 min after sunset. Peregrine Falcons made 111 hunting attempts
and captured 37 birds (33% success). Hunting success was highest in September, but was most often observed
in October. Peregrines hunted migratory birds at night more frequently in autumn than in spring. Peregrines
were significantly more likely to be present on autumn nights when >50 migrants were passing by the Empire
State Building. Although the lights associated with skyscrapers are believed to disorient migrating birds and
result in many bird-to-skyscraper collisions each year. Peregrine Falcons are able to take advantage of the
situation. Skyscrapers provide hunting perches at altitudes often flown by nocturnal migrants, and disorientation
caused by the lights sometimes results in birds circling skyscrapers and possibly becoming more vulnerable to
predation by falcons. Received 26 January 2005, accepted 11 October 2005.

Several diurnal raptor species, including
Black-shouldered Kite ( Elanus axillaris ), Bald
Eagle ( Haliaeetus leucocephalus), and Lesser
Kestrel ( Falco naumanni ), forage at night (see
Kaiser 1989, McLaughlin 1989, Negro et al.
2000). Others, such as Turkey Vulture ( Ca -
thartes aura). Osprey ( Pandion haliaetus ),
Northern Harrier ( Circus cyaneus ), and Le-
vant Sparrowhawk ( Accipiter brevipes), have
been observed flying or migrating at night
(Tabor and McAllister 1988, Russell 1991,
Yosef 2003, DeCandido et al. 2006).

Peregrine Falcons ( Falco peregrinus) are
considered nocturnal migrants in some parts
of the world (Cochran 1985, Ellis et al. 1990),
and they are known to hunt at night (Clunie
1976, Russell 1998). With increased numbers
of peregrines nesting and wintering in cities,
biologists are beginning to document noctur-
nal activity by these falcons in all seasons.
Recently, there have been reports of urban
peregrines feeding young and/or hunting at
night in North America (Cade and Bird 1990,
Wendt et al. 1991, Cade et al. 1996), England
(Crick et al. 2003), France (Marconot 2003),
Germany (Schneider and Wilden 1994, Klad-

1 Hawk Mountain Sanctuary, Acopian Center for
Conservation Learning, 410 Summer Valley Rd., Or-
wigsburg, PA 17961, USA.

2 P.O. Box 1452, Peter Stuyvesant Station, New
York, NY 10009, USA.

3 Current address: 1831 Fowler Ave., The Bronx,
NY 10462, USA.

4 Corresponding author; e-mail: rdcny@earthlink.net

ny 2001), Netherlands (van Dijk 2000, van
Geneijgen 2000), Poland (Rejt 2000, 2001,
2004a), Hong Kong (Feare et al. 1995), and
Taiwan (K. Y. Huang and L. L. Severinghaus
unpubl. data). However, direct observation
and analysis of nocturnal hunting by Peregrine
Falcons, particularly during migration, is rare
in the literature.

In New York City, New York, the number
and distribution of Peregrine Falcons has
changed considerably since such observations
were first recorded in the late 1920s. Before
the era of DDT (until 1946), from autumn
through early spring, lone female peregrines
were much more common at skyscrapers than
males (Herbert and Herbert 1965). Peregrine
Falcons rarely nested in the city, and nocturnal
activity by these falcons was not reported in
any season (Herbert and Herbert 1965). Be-
ginning in the mid-1990s, however, more pairs
of Peregrine Falcons have begun residing
year-round in Manhattan (and the metropoli-
tan area) than previously noted (B. A. Loucks
pers. comm., C. Nadareski unpubl. data.). To-
day, most, if not all, of the seven pairs of per-
egrines that nest in Manhattan remain on ter-
ritory year-round. Here, we report our obser-
vations of Peregrine Falcon activity at night
during the 2004 southbound bird migration at
one location in New York City.

METHODS

Most of our observations of Peregrine Fal-
cons and nocturnal migrants occurred during

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

the southbound migration, from 4 August to
13 November 2004; we made observations on
77 of 102 evenings during that period. In
spring 2004, we observed northbound mi-
grants on 33 evenings from 19 April through
25 May. In spring 2002, we made observa-
tions on only 2 evenings (8 May and 15 May).

We made our observations from the outside
observation deck (elevation —325 m above
ground level) of the Empire State Building
(ESB), located in midtown Manhattan in New
York City. We arrived each evening approxi-
mately 15-30 min prior to sunset. Bird mi-
gration, on average, began 30-90 min after
sunset. Any Peregrine Falcon activities de-
fined as nocturnal occurred after nautical twi-
light (1 hr after sunset). We were able to con-
duct our study until 22:45 EST each evening
(August through October) and until 23:45 in
November; the observation deck of the build-
ing was closed to all visitors after these times.
In spring 2004, we observed from just before
sunset until 22:45 each evening, and in spring
2002, we observed from 19:00 until 21:00.
During fall migration, the northwest corner of
the building provided the best vantage point
to count the greatest number of migrating
birds, and in spring, we observed migrants
from the southwest corner of the observation
deck. These locations afforded unobstructed
views to the horizon and the sky above. We
used 10X binoculars to follow peregrines
when they made long flights in pursuit of
prey. It was possible to observe migrating
birds and the activities of peregrines because
the upper floors of the building were illumi-
nated with (external) upward-directed halogen
lights, and the spire above us was illuminated
with (internal) florescent lights. We could not
identify the majority of migrants to species
because the external halogen lights washed
out most plumage details. However, this light-
ing array permitted us to count migrants up to
—30-60 m above the highest point (445 m
agl) of the ESB, and up to 30 m (perpendic-
ular) from the observation deck. We estimated
that the building’s lights allowed us to see per-
egrines chasing small birds in flight up to 60-
80 m distant.

Count protocols to assess nocturnal bird mi-
gration in 2004 followed those described in
Bildstein and Zalles (1995) for migrating rap-
tors. An individual was considered a migrant

if it passed south-to-north (or north-to- south)
across an imaginary east-west line at the site,
and continued north (or south) out of sight.
On 2 evenings during southbound migration,
when >100 birds simultaneously circled the
ESB, we estimated the maximum number of
birds circling per hour and recorded it as the
number of migrants seen for that hour. We de-
fined the peak of migration as the several-day
period in which we counted the highest num-
ber of migrants. For both northbound and
southbound migration, total counts presented
here do not include migrating waterfowl, her-
ons, or gulls.

We defined a hunting attempt as one in
which a Peregrine Falcon approached to with-
in 1 m of its intended prey. On a few occa-
sions, peregrines made repeated stoops at the
same prey, but did not capture or gain control
of it. Each of these stoops was considered a
separate hunting attempt. Several times, we
observed a peregrine strike a bird but fail to
seize it. We classified these as unsuccessful
hunting attempts.

We defined the peak period of Peregrine
Falcon activity as that during which we ob-
served falcons at the ESB during the greatest
number of consecutive nights. We used cor-
relation statistics (Microsoft Excel 2003) to
analyze data collected during this peak period.
We compared (a) the time of arrival of the first
migrant after sunset with the arrival of the first
Peregrine Falcon, and (b) the time of arrival
of the first migrant with the time of the first
peregrine hunting attempt. Means are present-
ed as ± SD.

RESULTS

During southbound migration in 2004, we
saw the first Peregrine Falcon at night on 4
August and the last one on the evening of 9
November. During this time, at least two adult
peregrines (male and female), as well as im-
mature^), used the ESB as a hunting perch.
Peregrines were seen hunting or flying at night
on 53% (41 of 77) of the evenings we spent
at the ESB (Table 1). Falcons were signifi-
cantly more likely to be present on evenings
when >50 migrants were counted in migra-
tion (x2 = 14.7, df = 1, P = 0.001; Table 1).
Of the 67 nights we observed migrating birds,
peregrines hunted migrants on 25 nights
(37%), made 111 hunting attempts, and cap-

DeCandido and Allen • NOCTURNAL HUNTING BY PEREGRINE FALCONS

TABLE 1. Summary of nocturnal hunting behavior by Peregrine
migrants present after sunset in autumn 2004 at the Empire State Build

Falcons in relation
ing. New York.

to the number of

Number classes of migrant passerines

Total

1-10

11-50

51-100

101-250

251 +

No. nights migrants counted

No. nights peregrines present

No. nights peregrines hunted

—

No. hunting attempts

—

111

No. successful hunts

—

Hunting success

—

28%

41%

53%

28%

33%

No. nights male observed hunting

—

No. nights female observed hunting

—

No. nights unknown sex observed hunting

—

tured prey 37 times (33% success). All of the
migrants we observed being captured or
chased were in the warbler-to-oriole size class.

The peak of Peregrine Falcon activity oc-
curred from 26 September through 14 October
2004. During that time, we conducted obser-
vations on 17 nights; on 16 of those nights we
observed Peregrine Falcons, and on 1 1 nights
we observed them hunting (70 total hunts, 21
prey captures, 30% success). During this pe-
riod, the first migrant birds were observed 65
± 20 min after sunset (range = 42-1 14 min);
Peregrine Falcons arrived 91 ±41 min after
sunset (range = 47-190 min), and made their
first hunting attempt 45 ± 59 min later (range
= 61-284 min), or approximately 136 min af-
ter sunset. There was no correlation between
passage of the evening’s first migrant and the
arrival of a Peregrine Falcon at the ESB (r2 =
0.10, P = 0.73) or between passage of the first
migrant and the time of a peregrine’s first
hunting attempt (r2 = 0.15, P — 0.24).

Nocturnal hunting success was greatest in
September (12 of 27, 44%) and lowest in No-

vember (1 of 8, 13%; Table 2). On 10 October
from 20:12 to 20:42, a male Peregrine Falcon
made 25 hunting attempts and captured 9
birds (36%), caching the birds on the ESB
tower after each kill. Throughout the autumn,
we observed Peregrine Falcons capture only
migratory birds, although a few Rock Pigeons
( Columba livia), and at least two bat species.
Little Brown ( Myotis lucifugus ) and Red ( Las -
iurus borealis ) bats, were present on some
evenings. We could identify only two prey
species: a Baltimore Oriole (. Icterus galbula)
captured on 23 August, and a Yellow-billed
Cuckoo ( Coccyzus americanus) taken on 9
October. On 3 and 9 November, despite high
numbers of American Woodcocks ( Scolopax
minor ) migrating past the ESB tower (36
counted each night), no peregrines were ob-
served.

In autumn 2004, most bird migration oc-
curred at eye-level and above the observation
deck. We counted 10,826 migrating birds, and
the peak of the migration occurred from 5 to
11 October when 3,871 migrants (36% of the

TABLE 2. Summary of nocturnal hunting behavior and success by Peregrine Falcons during four autumn
months in 2004 at the Empire State Building, New York.

Aug

Sep

Oct

Nov

Total

No. hunting attempts

111

No. successful hunts

Hunting success

38%

44%

30%

13%

33%

No. nights one peregrine present

No. nights ^2 peregrines present

No. nights hunting observed

No. nights male made a hunting attempt

No. nights female made a hunting attempt

No. nights unknown sex made a hunting attempt

—

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

fall flight) were counted, averaging 1 14 birds/
hr on these 7 evenings. In spring 2004, we
counted 3,359 migrants during 33 nights of
observation. The peak of the migration oc-
curred from 6 to 15 May when 1,752 migrants
(52% of the spring flight) were counted, av-
eraging 51 birds/hr on these 10 evenings.
Lone Peregrine Falcons were observed on 2
evenings: 24 April (0 migrants counted) and
22 May (79 counted), but no hunting attempts
were observed on either night. On 15 May
2002, we observed an adult female peregrine
make 10 unsuccessful hunting attempts on mi-
grants from 20:15 until 21:00.

In the breeding season of 2004, a pair of
Peregrine Falcons may have attempted to nest
on the ESB (B. A. Loucks pers. comm.). It is
possible that this pair executed many of the
hunting attempts we observed in autumn
2004. During 5 evenings between 26 Septem-
ber and 7 October, we saw an adult male and
an adult female peregrine perched near one
another, each vocalizing with the “eechup” or
“creaking” call, and the “wailing” calls (see
Ratcliffe 1980). On 3 October, we observed
three adults (a male, his mate, and a second
female) perched for <5 min within —20 m of
one another on the ESB tower until the second
female was chased away — mostly by the fe-
male of the pair. An immature peregrine was
present on 3 evenings: 9 and 14 October, and
9 November 2004, although we could not be
sure if it was the same bird on all 3 evenings.
On 5 October, a Peregrine Falcon passed high
overhead flying south on moderate northerly
winds while an adult female flew back and
forth near the ESB. It was not uncommon to
see peregrines flying high above (25-75 m)
the top of the ESB tower at night in Septem-
ber and October.

DISCUSSION

Tall, lighted, man-made structures present
opportunities for biologists to study nocturnal
hunting by Peregrine Falcons that may not be
observed readily in remote locations. Urban
skyscrapers provide hunting platforms that
permit these raptors to perch at or above the
elevation of nocturnal migrants, and the lights
used to illuminate tall buildings can disorient
migrating birds that may then circle these
structures, especially on evenings with over-
cast skies and light winds. These migrants

constitute an abundant, easily accessible re-
source for resident Peregrine Falcons, and for
peregrines migrating through the area as well.

In New York City in 2004, Peregrine Fal-
cons were more likely to be present and hunt-
ing at the ESB on autumn nights when >50
migrants were observed. The peak of pere-
grine activity at the ESB corresponded to the
peak of the southbound bird migration from
late September through mid-October. During
this time, two adult peregrines occasionally
perched near one another and used the ESB
as a hunting platform. More night migrants
were attracted to the building’s lights during
autumn rather than spring migration, and
many more circled the tower for longer time
periods from August through late October. In
spring, there are fewer nocturnal migrants,
and these mostly pass higher above New York
City on warm air currents that override heavi-
er, cooler air near the ground (see Kerlinger
and Moore 1989). Each of these factors likely
influences a peregrine’s decision to hunt mi-
grants more frequently at night during au-
tumn. On the only spring night (15 May 2002)
during which we did see several peregrine
hunting attempts, winds were —24-32 km/hr
from the northwest, and many migrants passed
at or just above the level of the observation
deck.

Peregrine Falcons hunted migrants in two
ways: pursuit and “still hunting” ( sensu Cade
1982). At the ESB, greater success occurred
when they pursued prey in level flight from
behind; however, peregrines more often em-
ployed still hunting from a west- or north-fac-
ing perch on the spire above the observation
deck. When still hunting, they launched their
attacks at a 5 to 15° angle down toward in-
coming migrants flying along a northwest-to-
southwest route past the ESB. Such direct at-
tacks were often unsuccessful, and peregrines
had to make additional short stoops to secure
the prey. If the intended prey was able to
dodge the initial attack, it would then fly
straight down toward the ground, and pere-
grines often made no further pursuits. We nev-
er observed targeted prey attempt to escape by
“ringing up,” nor did we ever observe birds
mass together in a flock when a Peregrine Fal-
con flew among them. On some nights (e.g.,
10 October), when many migrants passed the
ESB and peregrines captured several birds, we

DeCandido and Allen • NOCTURNAL HUNTING BY PERLGRINE FALCONS

also observed unsuccessful hunting attempts
that were considerably less intense than others
made on the same evening. Such behavior
may account for the low hunting success rate
on nights when >250 migrants were counted.

As camera use increases for 24-hr nest sur-
veillance, it may become possible to deter-
mine whether Peregrine Falcons frequently
hunt at night during the nesting season, and
whether this varies from year to year (see Rejt
2004b). Future studies at the ESB may also
determine whether nocturnal flights made to-
ward conspecifics are directed at neighboring
Peregrine Falcons or at night-migrating fal-
cons simply passing through the area.

ACKNOWLEDGMENTS

We thank B. A. Loucks for information and kind
words of encouragement. We also acknowledge C. A.
Nadareski’s long-term work with Peregrine Falcons in
the metropolitan area. A. Braunlich and E. J. A. Drew-
itt directed us to recent literature about nocturnal Per-
egrine Falcon activity in Europe and Asia. We thank
H. Q. P. Crick for providing information about Pere-
grine Falcons in England. K. L. Bildstein, J. B. Buch-
anan, and D. Panko each critically read the manuscript
and made many helpful suggestions regarding how to
interpret the data. We also wish to thank two anony-
mous reviewers for their comments and ideas. In New
York City, S. Critelli, C. R. Howard, M. W. Kola-
kowski, W. J. Paulson, B. J. Saunders, E. Shapiro, S.
J. Wiley, and C. A. Wood observed Peregrine Falcons
with us. We thank the staff of the Empire State Build-
ing, including L. A. Ruth and all security personnel,
for facilitating our research and making our evenings
at the building much more pleasant. We dedicate this
paper to Rev. M. A. Hegyi who encouraged the senior
author to study New York City’s fauna and flora. This
is Hawk Mountain Sanctuary’s contribution to conser-
vation science number 124.

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166. [In Polish]

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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

grines at the nest during nestling period. Vestnik
Zoologii 38:87-90.

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The Wilson Journal of Ornithology 1 1 8( 1 ):59 — 63, 2006

FIELD EXPERIMENTS ON EGGSHELL REMOVAL BY
MOUNTAIN PLOVERS

TEX A. SORDAHL1

ABSTRACT. — I conducted 18 eggshell removal trials at six Mountain Plover ( Charadrius montanus ) nests
in the Pawnee National Grassland, Weld County, Colorado, during June 1994. Eggshell fragments were placed
at various distances (10 cm to 10 m) from active nests. Attending adult plovers removed eggshells throughout
the incubation period. When eggshells were placed within 2 m of the nest, plovers usually removed them
immediately upon their return to the nest. Shells placed farther away — up to 10 m — were removed after longer
time intervals. Plovers removed shells by picking them up with their bills and running or flying away with them
before dropping them 6 to 100 m from the nest. When returning to their nests, plovers approached by ground.
Of the five hypotheses proposed in the literature to explain the function of eggshell removal behavior in birds,
only one (reducing cues predators might use for finding nests) predicts removal of shells already outside the
nest and disposal of shells far from the nest. Thus, my results support an anti-predator function for eggshell
removal in Mountain Plovers. Received 3 November 2004, accepted 1 October 2005.

Shortly after their young hatch, many birds
remove the empty eggshells and dispose of
them away from the nest (Nethersole-Thomp-
son and Nethersole-Thompson 1942, Skutch
1976). This behavior is well developed in
charadriiform birds, including shorebirds and
gulls. In their classic paper, Tinbergen et al.
(1962) suggested five possible hypotheses for
the adaptive value of eggshell removal behav-
ior: (1) eggshells might provide cues that
would attract predators to the nest; (2) later-
hatching eggs might become encapsulated, the
young in hatching eggs thus becoming trapped
inside a double shell (termed “egg-capping”
by Derrickson and Warkentin 1991); (3) sharp
edges of shells might injure chicks in the nest;
(4) organic material associated with eggshells
might promote growth of pathogenic bacteria
and mold in the nest; and (5) hatched shells
could interfere with brooding chicks in the
nest. Tinbergen’s field experiments with gull
eggs, which are cryptically colored externally
but conspicuously white inside, supported the
first hypothesis by showing that artificial nests
with eggshells nearby experienced greater pre-
dation rates than those without nearby egg-
shells (Tinbergen et al. 1962, Tinbergen
1963). Tinbergen, however, did not rule out
the remaining hypotheses. Subsequent litera-
ture has tended to support the predation (Sor-
dahl 1994, Sandercock 1996) and egg-capping
hypotheses (Derrickson and Warkentin 1991,

1 Dept, of Biology, Luther College, Decorah, I A
52101, USA; e-mail: sordahlt@luther.edu

Sandercock 1996, Verbeek 1996, Hauber
2003).

Hypotheses 3, 4, and 5 seem unlikely ex-
planations of the evolution of eggshell remov-
al behavior in shorebirds because their eggs
usually hatch synchronously and the precocial
young leave the nest within 24 hr of hatching.
Sandercock (1996) reported observations of
egg-capping in two sandpiper species, sup-
porting hypothesis 2. However, he recognized
that egg-capping alone could not account for
the form of removal behavior typically seen
in shorebirds — specifically, the disposal of
eggshells far from the nest — and concluded
that both egg-capping and predation have con-
tributed to the evolution of eggshell removal
behavior in these birds.

Here, I report the results of field trials on
eggshell removal behavior of Mountain Plo-
vers ( Charadrius montanus). Mountain Plo-
vers nest on the ground in very open habitat,
where predation is the major cause of egg and
chick losses (Graul 1975, McCaffery et al.
1984, Sordahl 1991, Miller and Knopf 1993,
Knopf 1996, Knopf and Rupert 1996). Gen-
eral aspects of eggshell removal in this species
were described by Graul (1975). My experi-
ments enabled me to provide a quantitative
description of the behavior and to evaluate its
function.

METHODS

I performed field trials on eggshell removal
by Mountain Plovers from 9 to 18 June 1994
at Pawnee National Grassland, Weld County,

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

TABLE 1. Results of 18 field trials on eggshell removal behavior at six Mountain Plover nests. Pawnee
National Grassland, Colorado, 9-18 June 1994. In each trial, one-third of a complete eggshell (of Mountain
Plover or Japanese Quail) was placed near the nest and the behavior of the adult was observed upon its return
to the nest.

Nest3

Incubation day

Shell type

Nest-shell
distance (m)

Time until
removal (min)

Removal

method

Disposal
distance (m)

Quail

0.5

0.08

Fly

Quail

0.7

—

Quail

0.6

Fly

Quail

1.0

Run-fly

Quail

0.5

0.17

Run

Quail

2.5

Run

Quail

5.0

105

—

Quail

10.0

—

Quail

1.5

—

S2C

Quail

0.2

Run

Quail

0.5

Run

Plover

2.0

Run-fly

100

Quail

3.0

Run

Quail

4.0

—

- —

Plover

0.1

Run

Plover

0.3

Fly

Quail

0.7

Run

Plover

1.5

Run

a Mountain Plovers typically exhibit uniparental care; therefore, egg removals were assumed to represent the behavior of one adult per nest.
b Missing data in the table indicate that shell removal was not observed (see text) or that the disposed shell was not found.
c Nest S2 contained four eggs; all other nests contained three.

Colorado (40° 45' N, 104° 00' W). This short-
grass prairie site has been well described else-
where (Graul 1973, 1975; McCaffery et al.
1984). Its vegetation was very short and
sparse, and it was grazed by cattle.

I studied eggshell removal at six Mountain
Plover nests. Five nests contained three-egg
clutches (normal for Mountain Plovers) and
one nest contained four eggs. The attending
adults were not marked for identification, but
since uniparental care is typical in this species
(Knopf 1996), it is likely that I tested six dif-
ferent individuals. Mountain Plovers are sex-
ually monomorphic (Hayman et al. 1986,
Knopf 1996), so I was unable to determine the
sex of the birds. Trials entailed placing ap-
proximately one-third of a complete eggshell
on the ground (interior — or white — side up) at
various distances (ranging from 10 cm to 10
m) from the nest and then observing the be-
havior of the adult when it returned to its nest.
I conducted 18 trials, 14 with Japanese Quail
{Coturnix japonica) eggshells obtained com-
mercially and 4 with Mountain Plover egg-
shells that I found opportunistically in the
field. The two species’ shells are similar in
size and appearance, both having earth-tone

background colors and dark, irregular mark-
ings. Adult plovers responded similarly to the
two kinds of shells; therefore, I pooled the
results.

Observations were made from a vehicle
about 100 m from nests with 7 X 35 binoc-
ulars. For each trial, I recorded the nest-to-
shell distance, the amount of time elapsed be-
tween the adult’s return to the nest and re-
moval of the shell, the removal method (run
or fly), the disposal distance, and the method
(run or fly) of returning to the nest after shell
disposal. At least one egg hatched in every
nest and, assuming that incubation begins
when the clutch is complete and the average
incubation period is 29 days (Knopf 1996), I
used backdating to determine days since in-
cubation began. I measured the distances of
eggshells from nests with a tape measure, and
disposal distances of shells that I was able to
relocate by pacing.

RESULTS

The number of trials conducted at each of
the six nests was 6, 3, 3, 3, 2, and 1 (Table
1). The attending adult Mountain Plover re-
moved shells at all six nests. Nine of 18 shells

Sordahl • EGGSHELL REMOVAL BY MOUNTAIN PLOVERS

FIG. 1. Relationship between the distance egg-
shells were placed from Mountain Plover nests and the
time elapsed before the adult removed the shell, 9-18
June 1994, Pawnee National Grassland, Weld County,
Colorado. Three of the 17 points overlap at 0.5 m (2
are hidden).

were removed immediately upon the adult’s
return to the nest; 2 more were removed with-
in 10 sec. Two other shells were removed 3
min and 10 min after the adults had returned.
Four of the remaining five shells were re-
moved in less than 2 hr. The final shell, placed
10 m from the nest, was not removed during
15 min of observation, at which time I de-
parted the nest site; the following morning I
found the shell 22 m from the nest. Although
it is possible that the wind or another animal
moved this shell, it seems most likely that the
adult plover moved it. Overall, shells placed
within 2 m of the nest were removed promptly
(most of them immediately), whereas shells
placed farther away were removed after longer
intervals (Fig. 1). Eggshell removal was doc-
umented on incubation days 5-9, 15, 16, 20,
23, 25, and 27 (Table 1).

I recorded eggshell removal and adult re-
turn to the nest for 13 of 18 trials (Table 1).
During the remaining five trials, which had
long eggshell removal times, my vigilance
was intermittent and I did not observe the ac-
tual removal. However, by checking for the
eggshell as soon as I noticed that the bird was
off the nest, I was able to record removal
times with only a small margin of error (ex-
cept in the case described above, where I left
the site before removal occurred). When a
Mountain Plover removed an eggshell, it pick-
ed the shell up with its bill and ran away with

it (8 of 13 observations), flew off with it (3
of 13 observations), or ran 2-3 m before fly-
ing off with it (2 of 13 observations). On 14
occasions I was able to recover shells where
they were dropped; disposal distances ranged
from 6 to 100 m from the nest (Table 1). Plo-
vers tended to dispose of shells at greater dis-
tances when they flew (mean = 70.0 m, range
— 30—100, n = 5) than when they ran (mean
= 17.0 m, range = 6-30, n = 8). On four
occasions I recorded which facet (inside or
outside) of a recovered shell was exposed; two
shells were lying with the cryptic outside fac-
ing up and two were lying with the conspic-
uous inside of the shell facing upward. After
disposing of the shells, adults always returned
to their nests by a ground approach (13 of 13
observations), which is typical of plovers
(TAS pers. obs.).

DISCUSSION

My field experiments demonstrated that
Mountain Plovers remove eggshells through-
out the incubation period. This may be true
for most birds, and the expression of the be-
havior long before hatching occurs likely has
been selected for in the context of removal of
damaged eggs (Nethersole-Thompson and
Nethersole-Thompson 1942, Montevecchi
1976, Kemal and Rothstein 1988, Sordahl
1994). Removal of dead chicks from the nest
also has been reported (Nethersole-Thompson
1951:183, Skutch 1976:284, Sordahl 1994).

Because it had already been demonstrated
that Mountain Plovers remove eggshells lo-
cated in their nests (Graul 1975, Knopf 1996;
TAS pers. obs.), I designed my experiments
to determine whether they would remove
shells placed outside the nest and, if so, how
far from the nest they would go to remove
shells. I observed adults immediately remove
shells that had been placed up to 3 m from
their nests (Table 1, Fig. 1). They also even-
tually removed shells at distances of 4, 5, and
probably 10 m, as well. Because the average
disposal distance was only 17 m for birds that
removed eggshells by running, it seems un-
likely that Mountain Plovers would remove
shells located much farther from their nests
than 10 m.

The closer a shell was placed to the nest,
the more quickly it was removed (Fig. 1). The
proximate explanation for this probably is that

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118 , No. 1, March 2006

adults were less likely to detect eggshells that
were farther from the nest. Even though
Mountain Plover nesting habitat is shortgrass
prairie, the line of sight a plover has when
making a ground approach to its nest is low
enough that even small obstructions could in-
terfere with its ability to notice a distant shell.
An ultimate explanation for this finding would
be that the risk of predation due to the pres-
ence of eggshells diminishes with distance
from the nest, as shown by Tinbergen et al.
(1962) for Black-headed Gull (. Larus ridibun-
dus ) eggs. Tinbergen et al. (1962) found that
a broken eggshell ^1 m from an artificial
clutch increased the predation rate, but an
eggshell 2 m away did not. If the radius of
increased risk is similar for Mountain Plovers,
one might expect them to be less diligent
about removing shells >2 m from the nest.
My results are consistent with this because the
birds did not immediately remove shells that
were >2-3 m away. Nevertheless, they even-
tually did remove those shells, which suggests
that such shells pose at least some risk to the
clutch.

Although eggshell removal and disposal
distances have not been investigated system-
atically in birds, these distances most likely
represent a compromise between the benefits
of removal and the costs of leaving the nest
when young are hatching. Factors that prob-
ably influence these distances are habitat (es-
pecially open habitats in the case of Mountain
Plovers), the degree of nest dispersion (widely
spaced in Mountain Plovers), and which spe-
cies of egg and chick predators inhabit the
area (mammals and snakes are thought to be
important predators of Mountain Plovers;
Knopf 1996).

Of the five hypotheses explaining the adap-
tive value of eggshell removal, the only one
that predicts removal of eggshells already out-
side the nest is the predation hypothesis. It
also is the only hypothesis that predicts dis-
posal far from the nest. Thus my results sup-
port an anti-predator function for eggshell re-
moval in Mountain Plovers. Similarly, fecal
sac removal by many nidicolous birds (which
is analogous to eggshell removal) involves
disposal of fecal sacs far from the nest (Petit
et al. 1989 and references therein), and this
behavior also seems best explained as a means
of reducing cues that could lead predators to

nests (Petit et al. 1989, Lang et al. 2002).
However, I cannot rule out the possibility that
eggshell removal serves functions other than
predation avoidance. For example, if there is
a risk that wind may blow shells back into the
nest, it may be adaptive to dispose of them
far away so they do not threaten the chicks
with encapsulation or injury. Further research
is needed to examine these alternative expla-
nations of eggshell removal behavior.

ACKNOWLEDGMENTS

I especially thank C. A. Ristau for enabling me to
study Mountain Plovers in Colorado. She and F. L.
Knopf generously shared information about nests they
had found. The manuscript benefited from comments
by D. I. Bishop, S. J. Dinsmore, M. B. Wunder, and
two anonymous referees. This research was conducted,
in part, on the Central Plains Experimental Range op-
erated by the USDA Agricultural Research Service and
made available to the Long Term Ecological Research
Program administered by Colorado State University. I
thank M. Lindquist for courtesies extended during my
stay. I was supported by a Luther College Faculty Re-
search Grant.

LITERATURE CITED

Derrickson, K. C. and I. G. Warkentin. 1991. The
role of egg-capping in the evolution of eggshell
removal. Condor 93:757-759.

Graul, W. D. 1973. Adaptive aspects of the Mountain
Plover social system. Living Bird 12:69-94.
Graul, W. D. 1975. Breeding biology of the Mountain
Plover. Wilson Bulletin 87:6-31.

Hauber, M. E. 2003. Egg-capping is a cost paid by
hosts of interspecific brood parasites. Auk 120:
860-865.

Hayman, P, J. M archant, and T. Prater. 1986.
Shorebirds: an identification guide to the waders
of the world. Houghton Mifflin, Boston, Massa-
chusetts.

Kemal, R. E. and S. I. Rothstein. 1988. Mechanisms
of avian egg recognition: adaptive responses to
eggs with broken shells. Animal Behaviour 36:
175-183.

Knopf, F. L. 1996. Mountain Plover ( Charadrius mon-
tanus). The Birds of North America, no. 211.
Knopf, F. L. and J. R. Rupert. 1996. Reproduction
and movements of Mountain Plovers breeding in
Colorado. Wilson Bulletin 108:28—35.

Lang, J. D., C. A. Straight, and P. A. Gowaty. 2002.
Observations of fecal sac disposal by Eastern
Bluebirds. Condor 104:205-207.

McCaffery, B. J., T. A. Sordahl, and P. Zahler.
1984. Behavioral ecology of the Mountain Plover
in northeastern Colorado. Wader Study Group
Bulletin 40:18-21.

Miller, B. J. and F. L. Knopf. 1993. Growth and sur-

Sordahl • EGGSHELL REMOVAL BY MOUNTAIN PLOVERS

vival of Mountain Plovers. Journal of Field Or-
nithology 64:500-506.

Montevecchi, W. A. 1976. Eggshell removal by
Laughing Gulls. Bird-Banding 47:129—135.

Nethersole-Thompson, C. and D. Nethersole-
Thompson. 1942. Egg-shell disposal by birds.
British Birds 35:162-169, 190-200, 214-223,
241-250.

Nethersole-Thompson, D. 1951. The Greenshank.
Collins, London, Great Britain.

Petit, K. E., L. J. Petit, and D. R. Petit. 1989. Fecal
sac removal: do the pattern and distance of dis-
persal affect the chance of nest predation? Condor
91:479-482.

Sandercock, B. K. 1996. Egg-capping and eggshell
removal by Western and Semipalmated sandpip-
ers. Condor 98:431-433.

Skutch, A. F. 1976. Parent birds and their young. Uni-
versity of Texas Press, Austin.

Sordahl, T. A. 1991. Antipredator behavior of Moun-
tain Plover chicks. Prairie Naturalist 23:109-1 15.

Sordahl, T. A. 1994. Eggshell removal behavior of
American Avocets and Black-necked Stilts. Jour-
nal of Field Ornithology 65:461—465.

Tinbergen, N. 1963. The shell menace. Natural His-
tory 72(7):28-35.

Tinbergen, N., G. J. Broekhuysen, F. Feekes, J. C.
W. Houghton, H. Kruuk, and E. Szulc. 1962.
Egg shell removal by the Black-headed Gull, La-
rus ridibundus L.: a behaviour component of cam-
ouflage. Behaviour 19:74-117.

Verbeek, N. A. M. 1996. Occurrence of egg-capping
in birds’ nests. Auk 113:703-705.

The Wilson Journal of Ornithology 1 1 8( 1 ):64 — 69, 2006

SEED-SIZE SELECTION IN MOURNING DOVES AND
EURASIAN COLLARED-DOVES

STEVEN E. HAYSLETTE1

ABSTRACT. — I studied seed-size selection among Mourning Doves ( Zenaida macroura ) and Eurasian Col-
lared-Doves ( Streptopelia decaocto ), two newly sympatric species for which mechanisms of seed selection are
not well understood. I measured and compared mean length, breadth, and thickness of seeds available to, and
consumed by, these species in feeding trials of penned birds. Both species selected com ( Zea mays ) seeds that
were shorter and narrower than average, but Eurasian Collared-Doves selected com that was thicker than average
and sunflower ( Helianthus annuus ) seeds that were broader and thicker than average. Mourning Doves consumed
com of average thickness, and wheat ( Triticum aestivum ) and sunflower seeds of average size with respect to
all dimensions. Corn consumption by both species seems limited by seed length and breadth, but Mourning
Dove consumption of smaller seed types (wheat and milo [Sorghum vulgare ]) appears largely unaffected by
seed size. Among larger seed types (com and sunflower), Eurasian Collared-Doves may select thicker- and/or
broader-than-average seeds to maximize foraging efficiency. Sunflower and com seeds consumed did not vary
between species with respect to any dimension, but Eurasian Collared-Doves seemed willing to select, and able
to eat, broader and thicker seeds than Mourning Doves, which may limit foraging competition between these
species. Received 7 February 2005, accepted 23 November 2005.

Seed selection by granivorous birds is a
complex phenomenon potentially affected by
a number of factors (Ramos 1996), the rela-
tive contributions of which remain poorly un-
derstood in many avian granivores. In partic-
ular, seed selection by doves and other species
that do not husk seeds before swallowing is
not well understood; most studies of seed se-
lection in birds have focused on finches and
other species that husk seeds during the course
of foraging. Generally, these studies have re-
vealed that the physical characteristics of
seeds affecting handling time, such as size,
shape, and hardness, are important determi-
nants of preference, and that nutritional com-
position of foods appears relatively unimpor-
tant (Willson 1971, Willson and Harmeson
1973, Goldstein and Baker 1984, De Nagy
Koves Hrabar and Perrin 2002), especially
without consideration of the overall econom-
ics of nutrient intake and the factors affecting
it (Greig-Smith and Wilson 1985).

One approach to understanding the effect of
seed size on selection has been to examine
size selection by one or more species for a
single seed type (Hespenheide 1966, Myton
and Ficken 1967, Willson 1972, Abbott et al.
1975, Greig-Smith and Crocker 1986, van der
Meij and Bout 2000). A number of these stud-
ies have indicated seed-size preference within

1 Dept, of Biology, Tennessee Tech Univ., Cooke-
ville, TN 38505, USA; e-mail: shayslette@tntech.edu

a species (Greig-Smith and Crocker 1986, van
der Meij and Bout 2000), and/or correspon-
dence between size selection and bill size
among multiple species (Hespenheide 1966,
Myton and Ficken 1967, Willson 1972). One
study indicated no size preferences and/or no
seed size/bill size correspondence (Abbott et
al. 1975), but this study focused on a seed-
husking species. Because doves and pigeons
have relatively long slender bills and pecking
behaviors that maximize speed of seed intake
without husking seeds (De Nagy Koves Hra-
bar and Perrin 2002), seed size may be ex-
pected to affect seed handling and preferences
differently than in most species studied pre-
viously.

The overall goal of this project was to de-
termine the effect of seed size on food selec-
tion by Mourning Doves {Zenaida macroura)
and Eurasian Collared-Doves {Streptopelia
decaocto). Eurasian Collared-Doves are recent
exotic invaders of North America, and may
compete for food or other resources with na-
tive species, such as Mourning Doves, to the
detriment of native species (Romagosa 2002).
Bill-size-related differences in seed-size selec-
tion between Eurasian Collared-Doves and
Mourning Doves may mitigate competition
between these species for food resources,
however (Poling and Hayslette 2006). Subdi-
vision of food resources among sympatric avi-
an granivores often is based on bill-size-relat-

Hayslette • SEED-SIZE SELECTION IN DOVES

ed differences in seed-size selection (Grant
1986, Faaborg 1988, Ricklefs 2001). Mourn-
ing Dove bill length averages 12.83-14.53 ±
0.97-1.01 mm (Mirarchi and Baskett 1994),
whereas collared-dove bill length averages
16.9 ± 0.71 mm for males and 16.6 ± 1.02
mm for females (Romagosa 2002). Corre-
sponding differences in seed-size selection
patterns between these species may have im-
portant implications regarding dietary overlap
and competition, and ultimately, coexistence
of the two species.

In cafeteria trials, previous work has indi-
cated that Mourning Doves and other dove
species prefer small, round seeds such as
white proso millet ( Panicum miliaceum ;
Hayslette and Mirarchi 2001, De Nagy Koves
Hrabar and Perrin 2002), and consume rela-
tively few large-seeded species such as com
{Zea mays ) and sunflower ( Helianthus an-
nuus’, LeBlanc and Otis 1998, Hayslette and
Mirarchi 2001). These results appear enig-
matic, as wild Mourning Doves are known to
exploit com and sunflower as important food
sources (Lewis 1993). De Nagy Koves Hrabar
and Perrin (2002) concluded that among Di-
amond Doves ( Geopelia cuneata ), seed size
becomes a limiting factor above a threshold
size, but below that threshold, size is of little
importance in food handling and selection. I
hypothesized that seed size has little influence
on Mourning Dove selection of small seeds,
but that preferences for, and consumption of,
larger seeds, such as com and sunflower, are
limited by seed size. Based on this hypothesis,
I predicted that Mourning Doves would pref-
erentially select smaller than average corn
seeds, and that this within-seed-type selectiv-
ity for size would decrease with progressively
smaller seed types. I also hypothesized that
Eurasian Collared-Doves are less limited than
Mourning Doves by size of com and sunflow-
er seeds because their bills are larger; thus,
they are able to exploit com and sunflower
food sources to a greater extent than Mourn-
ing Doves. Previous research has shown that
Eurasian Collared-Doves consume more com
than Mourning Doves in cafeteria trials (Pol-
ing and Hayslette 2006). Based on this, I pre-
dicted that Eurasian Collared-Doves would
show less within-seed-type selectivity for
smaller com and sunflower seeds than Mourn-

ing Doves, and would select larger corn and
sunflower seeds than Mourning Doves.

METHODS

The first phase of this research was con-
ducted at the captive Mourning Dove research
facility at Auburn University, Alabama, from
June to August 2000. I used 15 2nd-year
Mourning Doves, captured as immatures on
the university campus during the previous
breeding season; doves were initially housed
and cared for according to Mirarchi (1993).
Prior to feeding trials, doves were fed an equal
mixture (by volume) of the four foods used in
feeding trials (described below) plus proso
millet and browntop millet ( Panicum fasci-
culatum). I randomly assigned doves to five
flocks of three birds each, and each flock was
used in a 20-hr feeding trial in a 3.7 X 7.3 X
2.0-m outdoor aviary. During each trial, doves
were offered 200 seeds of each of four spe-
cies— corn, black-oil sunflower, milo ( Sor-
ghum vulgare), and wheat ( Triticum aesti-
vum). Trials were preceded by >24-hr accli-
mation periods, during which doves were fed
an equal mixture (by volume) of test seeds
only, followed by 24-hr fasting periods. Prior
to each trial, I estimated size of seeds offered
using a sample of 20 seeds drawn at random
from each 200-seed batch. I attempted to in-
sure that sizes of seeds in samples were rep-
resentative of those in feeding batches by
comparing the mass of each sample to the
mass of the batch from which it was drawn.
Because I sampled 10% of each batch (20 out
of 200 seeds), mass of a representative sample
would be 10% of the mass of the batch from
which it was drawn. Thus, a sample was
deemed representative and used if the ratio of
sample mass to batch mass was 0.100 ±
0.003. If not, the sample was returned to the
batch and redrawn. Using digital calipers, I
measured length, breadth, and thickness (cor-
responding to the longest, intermediate-most,
and shortest dimensions, respectively; Greig-
Smith and Crocker 1986) of each seed in each
sample to the nearest 0.1 mm. Seeds of each
species were then hand-scattered on a separate
wooden seed tray (41 X 41 X 4 cm) filled
with commercially available topsoil; trays
were randomly arranged in a 2 X 2 arrange-
ment on the floor of the aviary, with 1.8 m
between adjoining trays. After allowing doves

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

to forage from the trays for 20 hr, I removed
the trays and removed and counted the seeds
that remained on the trays. If >20 seeds re-
mained, I estimated size of seeds remaining in
the batch using a sample of 20 seeds as before
the trial. Analogous to pre-trial sampling,
post-trial samples were deemed acceptable
based on comparisons of sample mass and
batch mass. A sample was used if the ratio of
sample mass to batch mass was within 0.003
of the ratio of sample seed number (20) to
batch seed number. If not, the sample was re-
turned to the batch and redrawn. I compared
number of seeds consumed among seed types
using one-way analysis of variance (ANOVA)
and Tukey’s procedure. I calculated mean size
of each pre- and post-trial sample with respect
to all three size dimensions. I calculated the
average size of seeds consumed with respect
to each dimension for each seed type in each
trial based on number of seeds consumed and
pre- versus post-trial differences in average
available seed size. The formula for this cal-
culation is

Se = {(200 X Sh ) - [(200 - Ne) X Sa] }/Ne,

where Se = average size of seeds eaten, Sb =
average size of seeds prior to foraging (initial
sample), Sa = average size of seeds not con-
sumed, and Ne = number of seeds consumed.
I then used a paired Mest — with trials as rep-
licates— to compare mean size consumed with
mean size available for each size dimension
and each seed type.

The second phase of this research was con-
ducted at the captive avian research facility at
Tennessee Tech University during January-
April 2004. I used 14 Mourning Doves and
13 Eurasian Collared-Doves captured during
July— September 2003 in Coffee County, Ten-
nessee. Methods generally followed those
used previously, except as noted below. Indi-
viduals of each species were tested in a se-
quential manner in 2.4 X 1.8 X 1.8-m pens.
Corn and sunflower seeds ( n = 200) were pre-
sented to each individual in separate 5.5- and
4-hr trials, respectively; trials involving corn
were longer due to the slower consumption of
corn by both species. Trial order (i.e., seed
type) was determined randomly for each dove,
so that approximately half the individuals re-
ceived corn first, and half received sunflower
first. The two trials for each dove were inter-

ceded by 24-hr acclimation and fasting peri-
ods. Seeds were scattered in trays without top-
soil. Pre- and post-trial seed sampling and
measurements were conducted as in the pre-
vious trials, and similar analyses were con-
ducted separately for each species, with indi-
viduals serving as replicates. Additionally, I
used two-sample f-tests to compare the aver-
age length, breadth, and thickness of seeds, by
seed type, that each dove species consumed.
Trials in which doves consumed <25 seeds
were omitted from analyses because I sus-
pected that dove foraging during these trials
was too limited to allow for sufficient discrim-
ination among available seeds. I did not con-
duct statistical comparisons of corn and sun-
flower consumption because trial length dif-
fered between seed types. I conducted all
analyses using SAS/STAT (SAS Institute, Inc.
1990) and set a = 0.05. All means are pre-
sented ± SE.

RESULTS

In the first phase (2000 Alabama study),
consumption of seeds during trials varied
among seed types (F3 19 = 11.9, P < 0.001).
Doves consumed more milo, wheat, and sun-
flower (161.2 ± 24.3, 142.2 ± 20.4, and 103
± 23.4 seeds, respectively), than corn (8.4 ±
3.0 seeds). Doves ate nearly all (198 + ) of the
200 milo seeds offered in three of five trials,
and consumed almost no (<2) corn seeds in
two of five trials, so these seed types were
excluded from further analyses. One trial, in
which doves ate 198 wheat seeds, was omitted
from analysis of wheat size consumption.
Wheat and sunflower seeds consumed were
average in size with respect to all dimensions
(Table 1).

In the second phase (2004 Tennessee
study). Mourning Doves consumed 24.9 ±4.1
corn and 50.1 ± 10.3 sunflower seeds, and
Eurasian Collared-Doves consumed an aver-
age of 47.0 ± 4.9 corn and 52.5 ± 8.7 sun-
flower seeds during trials. Two collared-doves
and eight Mourning Doves ate <25 corn
seeds, and one collared-dove and four Mourn-
ing Doves ate <25 sunflower seeds; these
doves were not included in seed-size analyses.
Both Mourning Doves and Eurasian Collared-
Doves selected smaller-than-average corn
seeds with respect to length and breadth (Ta-
ble 1). Mourning Doves consumed corn seeds

Hayslette • SEED-SIZE SELECTION IN DOVES

TABLE 1. Measurements (mm) of seeds initially available to, and consumed by. Mourning Doves (MODO;
2000 and 2004) and Eurasian Collared-Doves (EUCD; 2004) in seed-size selection trials on captive birds in
Tennessee and Alabama.

Initially available Consumed

Year Food Dimension

Species

/ta

Mean

2000 Wheat Length

MODO

6.3

0.1

6.4

0.2

-0.9

Breadth

MODO

3.1

0.0

3.1

0.0

0.3

Thickness

MODO

2.6

0.0

2.5

0.0

1.3

Sunflower Length

MODO

9.8

0.1

10.3

0.5

-1.1

Breadth

MODO

5.2

0.1

5.0

0.2

2.6

Thickness

MODO

3.1

0.1

2.7

0.3

2.0

2004 Corn Length

MODO

12.7

0.1

12.3

0.1

4.3C

EUCD

12.7

0.1

12.1

0.3

2.7C

Breadth

MODO

8.4

0.1

7.9

0.2

6. lc

EUCD

8.4

0.0

7.6

0.2

5.3C

Thickness

MODO

4.5

0.1

4.6

0.3

-0.3

EUCD

1 1

4.6

0.1

5.2

0.2

-3.0C

Sunflower Length

MODO

10.4

0.1

10.5

0.3

-0.4

EUCD

10.2

0.1

10.2

0.4

0.2

Breadth

MODO

4.9

0.0

5.0

0.3

-0.1

EUCD

4.9

0.1

5.8

0.3

— 3.0C

Thickness

MODO

2.9

0.0

3.0

0.3

-0.3

EUCD

2.8

0.0

3.5

0.2

— 3.5C

a Sample size (n) equals number of three-bird flocks in

2000, individual doves in 2004.

b r-values from paired r-tests comparing sizes of seeds

initially available

and seeds consumed; df

= n - 1.

c P < 0.05.

of average thickness, but collared-doves se-

determining ease

with

which

seeds are

lected corn seeds that were thicker than av-
erage. Mean size of corn seeds consumed by
the two species did not differ with respect to
length, breadth, or thickness (—1.0 < tl5 <
2.8, all P > 0.1 1). Mourning Doves consumed
sunflower seeds that were of average size with
respect to all dimensions, and average length.

swallowed. Thickness seems important, how-
ever, in species that husk seeds before swal-
lowing. In a similar study of Eurasian Bull-
finches ( Pyrrhula pyrrhula), sunflower seeds
consumed were 4.6% thinner, 3.1% narrower,
and 2.1% shorter than average (Greig-Smith
and Crocker 1986). Willson (1972) concluded

breadth, and thickness of sunflower seeds con-

that Purple Finches ( Carpodacus purpureus )

sumed were similar (within 0.3 mm) to aver-
age sizes consumed by Mourning Doves in
the 2000 study. Eurasian Collared-Doves con-
sumed sunflower seeds of average length, but
selected seeds of larger than average breadth
and thickness. Mean size of sunflower seeds
consumed did not differ (—0.7 < t20 ^ 1.6, all
P ^ 0.12) between dove species with respect
to any dimension.

selected seeds based on thickness rather than
length. The sunflower seeds we used seemed
to be below the size threshold suggested by
De Nagy Koves Hrabar and Perrin (2002),
above which size becomes a factor affecting
dove seed handling and selection. We used
seeds of black oil sunflower, a relatively
small-seeded sunflower variety commonly
used in food plantings for Mourning Doves in

DISCUSSION

Results suggest that seed length and breadth
limit Mourning Dove consumption of corn;
seed thickness seems less important in selec-
tion. If seeds such as corn are oriented length-
wise as they are swallowed, it seems logical
that the smaller of the two cross-sectional di-
mensions (thickness) would be less important

the southeastern U.S. These seeds were small-
er than sunflower seeds used in previous stud-
ies (Hespenheide 1966, Willson 1972, Greig-
Smith and Crocker 1986, Diaz 1990). As pre-
dicted, consumption of smaller seeds, such as
milo and wheat, seemed unaffected by seed
size. Preference by Mourning Doves for milo
in this study agrees with preference patterns
documented elsewhere (Poling and Hayslette

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

2006), and suggests that seed preference in
this species may be based, at least in part, on
seed size and/or shape. Selection patterns fa-
voring small seeds have been documented in
several studies of seed-husking species (Hes-
penheide 1966; Willson 1971, 1972; Keating
et al. 1992), but De Nagy Koves Hrabar and
Perrin (2002) suggested that dove food pref-
erences are influenced more by seed shape
than size; round seeds are handled more rap-
idly than, and preferred to, elongate seeds. Be-
cause milo was both the smallest and roundest
of the seeds we tested, it is impossible to tell
which of these seed characteristics actually in-
fluenced seed selection.

As with Mourning Doves, consumption of
corn by Eurasian Collared-Doves seems lim-
ited by seed length and breadth. In contrast to
Mourning Doves, however, Eurasian Collared-
Doves were influenced by corn seed thickness,
choosing thicker-than-average seeds. If seed
thickness is relatively unimportant in deter-
mining handling and/or swallowing efficiency,
as postulated earlier for Mourning Doves, per-
haps the Eurasian Collared-Dove’s selection
of thicker seeds increases foraging efficiency
by increasing nutrient intake (benefit) per unit
handling time (cost) (Stephens and Krebs
1986). Likewise, selection of broader- and
thicker-than-average sunflower seeds may in-
crease foraging profitability of Eurasian Col-
lared-Doves. Selection for large foods, pre-
sumably to maximize foraging profitability,
has been reported in other seed-eating birds
(Myton and Ficken 1967, Ramos 1996).

Selection of larger than average corn and
sunflower seeds with respect to certain dimen-
sions by Eurasian Collared-Doves, but not by
Mourning Doves (paired Mests), suggests that
collared-doves select thicker corn seeds, and
broader and thicker sunflower seeds, than do
Mourning Doves. Although direct between-
species comparisons of average seed sizes
consumed failed to reveal any such differenc-
es, the average corn seed consumed by col-
lared-doves was 0.5 mm thicker than that eat-
en by Mourning Doves, and the average sun-
flower seed consumed by collared-doves was
0.8 mm broader and 0.5 mm thicker. Selection
for larger seeds by Eurasian Collared-Doves
than by Mourning Doves likely is related to
differences in their bill sizes (Hespenheide
1966, Myton and Ficken 1967, Willson 1972).

Previous authors have expressed concern
about how the recent Eurasian Collared-Dove
invasion of North America may affect native
species, particularly ecologically similar spe-
cies, such as the Mourning Dove, with which
Eurasian Collared-Doves may compete (Rom-
agosa and McEneaney 1999, Romagosa and
Labisky 2000, Romagosa 2002). A recent
study of food-selection patterns of these two
dove species revealed a high degree (95%) of
dietary overlap between them (Poling and
Hayslette 2006), although this was based on
relative consumption of different seed types in
a cafeteria experiment, rather than on size
preferences within seed types. If genuine, the
Eurasian Collared-Dove’s preferences for
seeds that are broader and/or thicker than
those selected by Mourning Doves may result
in differential exploitation of larger seeds,
such as corn and sunflower, and concomitant
mitigation of foraging competition between
them. Partitioning of food resources among
sympatric species based on seed size has been
documented in a number of avian granivore
communities (Grant 1986, Faaborg 1988,
Ricklefs 2001). Similarly, limited foraging
competition may mean greater potential for
coexistence of Mourning Doves and Eurasian
Collared-Doves than previously believed.

ACKNOWLEDGMENTS

I thank M. P. Cook, A. Goodman, T. D. Poling, C.
Smith, D. Smith, C. Spiller, J. Turner, and T. M. Un-
deutsch for assistance with data collection. Funding
and other support for this project was provided by the
Alabama Department of Conservation and Natural Re-
sources (Division of Wildlife and Freshwater Fisher-
ies), Auburn University School of Forestry and Wild-
life Sciences, Tennessee Tech University Department
of Biology, and Tennessee Wildlife Resources Agency.
This research was approved by, and conducted in ac-
cordance with, the Auburn University Institutional An-
imal Care and Use Committee (protocol review num-
ber 0009-R-0786), and Tennessee Tech University In-
stitutional Committee for the Care and Use of Lab An-
imals in Experimentation (protocol review number
1 [02-03]). I thank M. R. Perrin and two anonymous
referees for their comments on an earlier draft of the
manuscript.

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The Wilson Journal of Ornithology 1 18(1):70— 74, 2006

LOW NESTING SUCCESS OF LOGGERHEAD SHRIKES IN AN
AGRICULTURAL LANDSCAPE

JEFFERY W. WALK,124 ERIC L. KERSHNER,13 AND RICHARD E. WARNER1

ABSTRACT. — Southeastern Illinois is dominated by cropland, and the remaining pastures or grasslands are
marginally suitable for breeding Loggerhead Shrikes ( Lanius ludovicianus), owing, in part, to limited nest sites.
From 1998 through 2000, we recorded poor nest success (26%) among shrikes, although results of earlier studies
(1967-1972) in this region indicated that nest success was 72 to 80%. Clutch size (5.7 eggs) and fledglings/
successful nest (4.4 young/successful nest) were similar to those reported in previous studies. During our study,
generalist mammalian predators were abundant, and most nest failures (88%) were caused by predation. We
suggest that the loss of grassland habitat and agricultural intensification has resulted in reduced nest success,
and this may be true in other areas of the species’ range as well. Received 20 August 2003, accepted 23 November
2005.

The Loggerhead Shrike {Lanius ludovici-
anus) is of conservation interest throughout its
range, and has been designated a “Bird of
Conservation Concern” (U.S. Fish and Wild-
life Service 2002). The range of the species
has contracted greatly over the past half-cen-
tury (Cade and Woods 1997), and Christmas
Bird Count and Breeding Bird Survey data in-
dicate a continent-wide decrease in abun-
dance. The sharpest declines have occurred in
the core of the shrike’s range in southern and
Gulf Coast areas (Yosef 1996).

Most studies of Loggerhead Shrikes have
revealed high nest success (mean of 56%;
Yosef 1996, Esely and Bollinger 2001), sug-
gesting that problems associated with winter
habitat and survival may be causes for popu-
lation declines (Haas and Sloane 1989, Brooks
and Temple 1990, Gawlik and Bildstein
1993). Based on reports of high nest success
throughout the species’ range, Maddox and
Robinson (2004) considered it fortuitous that
habitat degradation had not resulted in elevat-
ed rates of nest predation or decreased pro-
ductivity. Our observations, and the results of
some, more recent studies (DeGeus 1990,
Yosef 1994, Collins 1996, Esely and Bollinger

1 Dept, of Natural Resources and Environmental
Sciences, Univ. of Illinois, Urbana, IL 61801, USA.

2 Current address: Illinois Natural History Survey,
One Natural Resources Way, Springfield, IL 62702,
USA.

3 Current address: Inst, for Wildlife Studies, 2515
Camino del Rio South, Ste. 339, San Diego, CA
92108, USA.

4 Corresponding author; e-mail:
jwalk@dnrmail.state.il. us

2001) , suggest there are landscapes and nest-
site contexts in which this presumption does
not apply. Our objectives were to measure
nest success of Loggerhead Shrikes in a re-
gion of intensive agriculture with marginal
habitat, and to determine whether land use
near nests, or nest-site context, influenced nest
fate.

METHODS

From 1998 through 2000, we monitored
Loggerhead Shrike nests within a 125-km2 3 4
area of southern Jasper County, Illinois. The
study was centered on Prairie Ridge State Nat-
ural Area (88° 12' W, 38° 57' N) and included
most of Smallwood Township and adjacent
portions of Wade and Fox townships. Jasper
County’s landscape is composed of 71% row
crop (corn, Zea mays ; and soybeans. Glycine
max), 6% wheat ( Triticum aestivum\ most
double-cropped to soybeans after harvest), 6%
rural grassland (hay, pasture, roadsides, and
idle grass), 13% woodland, and 1% roads, res-
idential/urban areas, and small amounts of
open water and other land covers (Illinois In-
teragency Landscape Classification Project

2002) . Our study area differed from the coun-
ty as a whole by having greater row crop cov-
er (>85%) and less woodland cover (<5%;
JWW unpubl. data).

Between 1966 and 2000, North American
Breeding Bird Survey results suggested de-
clining abundance of Loggerhead Shrikes in
Illinois (-4.5%/year) and the Midwest
(—0.3%/year in the eight states of U.S. Fish
and Wildlife Service Region 3; Sauer et al.
2005). From 1994 to 1996, roadside searches

Walk et al. • LOW NESTING SUCCESS OF SHRIKES

within 49 km2 of the center of our 1998-2000
study area documented 12 (1996) to 16 (1994)
shrike territories annually (roughly 0.25-0.33
shrike territories/km2; JWW unpubl. data, re-
ported to the Illinois Department of Natural
Resource’s Natural Heritage database). During
our 1998-2000 study, the densities of nesting
shrikes were similar to, or lower than, that re-
ported during the 1994 to 1996 roadside sur-
veys.

From March through June, we located
shrike nests by locating adults or food caches,
searching nearby suitable nest sites, observing
nest building, or observing provisioning of in-
cubating females and nestlings. Because the
study area was almost entirely private land,
initial searches were limited to roadsides.
When shrikes were located, we often were
permitted to search for, and monitor, nests on
private land. We checked nests every 3-5 days
until their fate was determined, and we cal-
culated nest and egg success based on expo-
sure days (Mayfield 1975, Johnson 1979).
When nests failed, we assumed failure oc-
curred at the midpoint between nest checks.

We recorded nest context and visually es-
timated the percentage of land-use types with-
in 100 m (3.1 ha) of nest sites (after Gawlik
and Bildstein 1993). Land-use categories were
(1) row crop; (2) hay or pasture; (3) idle grass-
land; (4) woody vegetation (forest and shrub
areas combined); (5) small grains; (6) road-
ways, including grassy rights-of-way; and (7)
residential (yards and farmsteads). We com-
pared measurements at nest sites with 20 ran-
dom locations, each also 100 m in radius and
selected by overlaying a map of the study area
with a numbered grid. Because shrike nest
sites are limited to woody vegetation, we cen-
tered random locations on the tree or shrub
closest to each randomly selected point. We
characterized the context of nest sites and ran-
dom trees as follows: fencerows, farmsteads/
yards, watercourses, woodland edges, or iso-
lated trees (>20 m from another tree). Be-
cause the proportions of land uses were not
normally distributed across the study area, we
used Mann- Whitney U- tests to compare land
use between random sites and nest sites, and
between successful and depredated nests.
Contexts of nest trees and random trees, and
trees with successful and depredated nests,
were compared using a chi-square test. Unless

otherwise noted, values are reported as means
± SE.

RESULTS

We monitored 34 shrike nests from 1998
through 2000. Ten nests (29%) fledged >1
young, 21 nests (62%) were depredated, 2
(6%) were abandoned during egg laying, and
1 (3%) was dislodged from a tree during a
thunderstorm. Nest failures attributed to pre-
dation included 6 empty nests with no evi-
dence of the predator, 4 tilted or compressed
nests, and 1 1 highly disturbed nests (lining re-
moved, nest shredded, or completely dis-
lodged). At one depredated nest on a farm-
stead, the cooperators reported to us that their
domestic cat ( Felis cattus ) had killed one of
the adults. Shrike nests appeared to be more
vulnerable to predation near hatching. Of 22
nests surviving to at least the 14th day of in-
cubation, 8 were eventually lost to predators
before the nestlings were 4 days old.

From the beginning of egg laying to fledg-
ing, egg success was 20.5% and nest success
was 25.6% (95% Cl = 19.4-33.8%). Clutch
size was 5.7 ± 0.2 eggs ( n = 30 nests). In
nests that survived until at least the second
nest check after hatching, 87.5 ± 3.6% of
eggs hatched successfully (n = 10 nests). Al-
though 4.4 ± 0.4 young fledged per successful
nest, only 1.3 ± 0.4 young fledged per nest
attempt.

Land use within 100 m of shrike nests in-
cluded more hay and pasture than randomly
located points (Mann-Whitney U = 241.0; P
= 0.049), but no other variable that we mea-
sured differed between nest and random lo-
cations (Table 1). Land use did not differ sig-
nificantly between successful and depredated
nest sites. The majority of the nests we mon-
itored (87%) were located in small (<3 ha)
pastures (including the enclosing fences) or
yards/farmsteads, and were within 50 m of
county roads. Although shrike nests were
placed in fencerows more frequently than ex-
pected (x2 = 25.69, df = 4, P < 0.001), nests
in fencerows were more likely to be depre-
dated (x2 = 10.94, df = 3, P = 0.012; Table
2). Daily nest survival was 0.957 ± 0.012 in
fencerows and 0.973 ± 0.013 in yards/farm-
steads.

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

TABLE 1. Percent land use (± SE) within 100 m (3.1 ha) of random trees and Loggerhead Shrike nest
locations in Jasper County, Illinois, 1998-2000.

Land use

Random sites
(n = 20)

Nest sites

All

(« = 33)

Successful
(n = 10)

Depredated
C n = 21)

Row crops

58.6 ± 6.9

51.0 ± 4.9

51.3 ± 9.2

54.4 ± 6.1

Hay and pasture

7.5 ± 4.7

19.4 ± 4.9a

18.5 ± 9.5

19.3 ± 5.9

Idle grassland

10.5 ± 6.0

5.9 ± 2.6

6.0 ± 5.1

6.4 ± 3.5

Woodland

7.2 ± 2.9

2.6 ± 0.9

3.0 ± 1.9

1.8 ± 0.5

Small grains

2.8 ± 1.6

3.2 ± 1.6

0.0 ± 0.0

2.9 ± 2.0

Roadway

5.8 ± 1.4

9.5 ± 1.3

7.5 ± 2.0

10.2 ± 1.8

Farmstead, yard

7.3 ± 2.2

8.8 ± 2.4

13.0 ± 5.4

7.6 ± 2.8

a Significantly more hay and pasture at nest sites than random sites (Mann- Whitney U = 241.0, P = 0.049). There were no other significant (all P >
0.08) differences in land use between random and nest sites or between successful and depredated nests.

DISCUSSION

Reproductive success of Loggerhead
Shrikes in this agricultural landscape (25.6%
nest success, 20.5% egg success) is among the
lowest reported for the species. Graber et al.
(1973) reported 80% nest success in south-
eastern Illinois in 1967 and, in Jasper and
nearby counties, Anderson and Duzan (1978)
observed 72% nest success in 1971-1972. By
1991-1992, Collins (1996) found that the pro-
portion of fledglings to number of eggs laid
had dropped to 25% in southern Illinois. Our
methods for measuring nest success (Mayfield
1975) differ from that used by Collins (1996),
but the results are similar and suggest a sub-
stantial reduction in shrike nesting success in
the region.

Clutch size (5.7 eggs) in our study was sim-
ilar to those of recent Midwestern studies
(5. 3-5. 7 eggs; Burton 1990, DeGeus 1990,
Collins 1996, Esely and Bollinger 2001). Our
measure of 4.4 fledglings per successful nest

TABLE 2. Proportions of Loggerhead Shrike nests
and random tree locations within various land-use con-
texts in southeastern Illinois, 1998-2000.

Nest sites

Context

Random

sites

(n = 20)

All

(n = 34)

Successful
(n = 10)

Depredated
(n = 21)

Yard, farmstead

0.35

0.24

0.40

0.14

Fencerow

0.20

0.53a

0.30

0.62a

Watercourse

0.15

0.20

0.14

Woodland edge

0.15

0.00

Isolated tree

0.15

0.09

0.10

a Loggerhead Shrike nests were placed in fencerows more frequently than
expected (x2 = 25.69, df = 4, P < 0.001), and nests in fencerows were
more likely to be depredated (x2 = 10.94, df = 3, P = 0.012).

was the same as the mean reported from 14
studies compiled by Esely and Bollinger
(2001). Toxicological problems affecting egg
viability are not implicated; an analysis of or-
ganochlorine residues in shrike eggs, includ-
ing several eggs collected in our study area in
1995 and 1996, indicated that DDE levels had
decreased 79% in the region since the early
1970s (Anderson and Duzan 1978, Herkert
2004). Roughly 88% of fully incubated eggs
hatched successfully during our study.

Intensified agricultural land use and a con-
comitant increase in the abundance of gener-
alist predators are likely the causes for a de-
crease in shrike nesting success in this land-
scape. Predation was implicated in 88% of the
nest failures and in 62% of all nesting at-
tempts in our study. From 1970 to 2000, acre-
age of row crops increased by 26% in Jasper
County, while hay acreage decreased by 85%
and pasture decreased by about 47% (Illinois
Department of Agriculture 1971, National Ag-
ricultural Statistics Service undated). Potential
nest sites in this landscape are few and most
occur in linear habitats, often limiting shrikes
and other birds to nesting situations in prey-
rich corridors that are easily searched by pred-
ators (Major et al. 1999). Furthermore, human
structures and agricultural waste may subsi-
dize populations of generalist predators
(Warner 1985, Dijak and Thompson 2000).
Road-kill surveys conducted by the Illinois
Department of Natural Resources from 1975
through 1998 documented increases in the
abundance of raccoons ( Procyon lotor) and
opossums ( Didelphis virginiana ) of more than
250% and 100%, respectively (Gehrt et al.
2002; S. D. Gehrt pers. comm.).

Walk et al. • LOW NESTING SUCCESS OF SHRIKES

Successful shrike nests were more likely to
be in yards, whereas depredated nests were
more likely to be in fencerows. Yards are not
benign breeding habitat, however. Gawlik and
Bildstein (1990) recognized the potential
threat of predation by domestic cats on adult
shrikes and their young, and during our study,
a cat killed at least one yard-nesting adult
shrike. Row crops were the most common
land use near nests, reflecting the ubiquitous-
ness of cropland in the landscape, but shrikes
preferentially selected nest sites in or near
pastures (Table 1). Most pastures in our study
area were small (<3 ha) horse pastures adja-
cent to residences, which were located pri-
marily along county roads. Shrikes elsewhere
also frequently nest near roadsides, and the
shorter grasses and utility lines along road-
sides may be superior hunting areas (Luuk-
konen 1987, DeGeus 1990, Gawlik and Bild-
stein 1990, Smith and Kruse 1992). The vis-
ibility of shrikes on utility lines (i.e., along
roads) may have contributed to high represen-
tation of pasture habitat near the shrike nests
that we monitored, but little suitable nesting
habitat was available to Loggerhead Shrikes
away from roadways in our study area. Al-
though widely used, roadways and other linear
habitats may be ecological sinks for nesting
shrikes, given the low nesting success we
found and that has been reported elsewhere.
Yosef (1994) found lower nest success among
shrikes nesting in fencerows (36%) than for
those nesting within pastures (54%) in Flori-
da. Likewise, roadside-nesting Loggerhead
Shrikes had 39% nest success in Missouri
(compared with 76% success for interior
nests; Esely and Bollinger 2001), 35% nest
success in Iowa (DeGeus 1990), and 31% egg
success in Indiana (Burton 1990).

Pasture and hay acreage has declined by
50% in the Midwest over the past 50 years
(Herkert et al. 1996). At the same time,
shrikes have declined or disappeared from
much of the region (Cade and Woods 1997,
Sauer et al. 2005). Our results — documenting
a sharp decrease in nesting success in a county
with recent land-use changes typical of the
Midwest — suggest that nesting success, often
thought to be relatively high for shrikes (Yos-
ef 1996, Maddox and Robinson 2004), will
need to be re-evaluated as land-use changes

result in a less optimal environment for Log-
gerhead Shrikes.

ACKNOWLEDGMENTS

We thank the many private landowners of Jasper
County, Illinois, who permitted us to access their prop-
erties to search for and monitor nests. This project was
supported by an S. Charles Kendeigh Award from the
Champaign County Audubon Society, and the Univer-
sity of Illinois. R. Yosef, C. P. Woods, and anonymous
reviewers suggested several improvements to the man-
uscript.

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dues and eggshell thinning in Loggerhead Shrikes.
Wilson Bulletin 90:215-220.

Brooks, B. L. and S. A. Temple. 1990. Dynamics of
a Loggerhead Shrike population in Minnesota.
Wilson Bulletin 102:441-450.

Burton, K. M. 1990. An investigation of population
status and breeding biology of the Loggerhead
Shrike ( Lanius ludovicianus) in Indiana. M.A. the-
sis, Indiana University, Bloomington.

Cade, T. J. and C. P. Woods. 1997. Changes in dis-
tribution and abundance of the Loggerhead
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Collins, J. A. 1996. Breeding and wintering ecology
of the Loggerhead Shrike in southern Illinois.
M.Sc. thesis. Southern Illinois University, Carbon-
dale.

DeGeus, D. W. 1990. Productivity and habitat prefer-
ences of Loggerhead Shrikes inhabiting roadsides
in a Midwestern agroenvironment. M.Sc. thesis,
Iowa State University, Ames.

Dijak, W. D. and F. R. Thompson, III. 2000. Land-
scape and edge effects on the distribution of mam-
malian predators in Missouri. Journal of Wildlife
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Esely, J. D. and E. K. Bollinger. 2001. Habitat se-
lection and reproductive success of Loggerhead
Shrikes in northwest Missouri: a hierarchical ap-
proach. Wilson Bulletin 113:290-296.

Gawlik, D. E. and K. L. Bildstein. 1990. Reproduc-
tive success and nesting habitat of Loggerhead
Shrikes in north-central South Carolina. Wilson
Bulletin 102:37-48.

Gawlik, D. E. and K. L. Bildstein. 1993. Seasonal
habitat use and abundance of Loggerhead Shrikes
in South Carolina. Journal of Wildlife Manage-
ment 57:352-357.

Gehrt, S. D., G. F. Hubert, Jr., and J. A. Ellis. 2002.
Long-term population trends of raccoons in Illi-
nois. Wildlife Society Bulletin 30:457-463.
Graber, R. R., J. W. Graber, and E. L. Kirk. 1973.
Illinois Birds: Laniidae. Illinois Natural History
Survey Biological Notes, no. 83.

Haas, C. A. and S. A. Sloane. 1989. Low return rates
of migratory Loggerhead Shrikes: winter mortal-

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ity or low site fidelity? Wilson Bulletin 101:458-
460.

Herkert, J. R. 2004. Organochlorine pesticides are not
implicated in the decline of the Loggerhead
Shrike. Condor 106:702-705.

Herkert, J. R., D. W. Sample, and R. E. Warner.
1996. Management of Midwestern grassland land-
scapes for the conservation of migratory birds.
Pages 89-116 in Management of Midwestern
landscapes for the conservation of migratory birds
(F. R. Thompson, III, Ed.). General Technical Re-
port NC-187, USDA Forest Service, North Cen-
tral Forest Experiment Station, St. Paul, Minne-
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Illinois Department of Agriculture. 1971. Illinois
annual farm census. Illinois Department of Agri-
culture, Division of Agricultural Statistics, Spring-
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Illinois Interagency Landscape Classification Pro-
ject. 2002. Land cover of Illinois statistical sum-
mary, 1999-2000. USDA National Agricultural
Statistics Services, Washington, D.C.; Illinois De-
partment of Agriculture, Springfield; and Illinois
Department of Natural Resources, Springfield.
www.agr.state.il.us/gis/stats/landcover/ (accessed
1 1 February 2005).

Johnson, D. H. 1979. Estimating nest success: the
Mayfield method and an alternative. Auk 96:651-
661.

Luukkonen, D. R. 1987. Status and breeding ecology
of the Loggerhead Shrike in Virginia. M.Sc. the-
sis, Virginia Polytechnic Institute and State Uni-
versity, Blacksburg.

Maddox, J. D. and S. K. Robinson. 2004. Conserva-
tion assessment for Loggerhead Shrike ( Lanius lu-

dovicianus). USDA Forest Service, Eastern Re-
gion, Milwaukee, Wisconsin.

Major, R. E., F. J. Christie, G. Gowing, and T. J.
Iverson. 1999. Elevated rates of predation on ar-
tificial nests in linear strips of habitat. Journal of
Field Ornithology 70:351-364.

Mayfield, H. 1975. Suggestions for calculating nest
success. Wilson Bulletin 87:456-466.

National Agricultural Statistics Services. Undat-
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USDA National Agricultural Statistics Services,
Washington, D.C. www.nass.usda.gov/QuickStats/
(accessed 1 1 February 2005).

Sauer, J. R., J. E. Hines, and J. Fallon. 2005. The
North American Breeding Bird Survey: results
and analysis 1966-2004, ver. 2005.2. USGS Pa-
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cessed 19 August 2005).

Smith, E. L. and K. C. Kruse. 1992. The relationship
between land-use and the distribution and abun-
dance of Loggerhead Shrikes in south-central Il-
linois. Journal of Field Ornithology 63:420-427.

U.S. Fish and Wildlife Service. 2002. Birds of con-
servation concern 2002. U.S. Fish and Wildlife
Service, Division of Migratory Bird Management,
Arlington, Virginia.

Warner, R. E. 1985. Demography and movements of
free-ranging domestic cats in rural Illinois. Journal
of Wildlife Management 49:340-346.

Yosef, R. 1994. Effect of fencelines on the reproduc-
tive success of Loggerhead Shrikes. Conservation
Biology 8:281-285.

Yosef, R. 1996. Loggerhead Shrike, Lanius ludovici-
anus. The Birds of North America, no. 231.

The Wilson Journal of Ornithology 1 1 8( 1 ):75 — 80, 2006

NEST INTERFERENCE BY FLEDGLING LOGGERHEAD SHRIKES

ERIC L. KERSHNER12 AND ERIC C. MRUZ1

ABSTRACT. — Using video cameras, we documented at least two fledgling Loggerhead Shrikes ( Lanius lu-
dovicianus) visiting their parent’s second active nest. We recorded 70 visits during a 10-day period, with visits
averaging 7 min. We observed the fledglings sitting on the nest contents on 21 occasions. We concluded that
these visits were not indicative of cooperative breeding behavior, because the fledglings were destructive to the
nest structure and contents, and the adult female exhibited aggressive behavior toward the fledglings. An early
reduction in post-fledging parental care by their father (who was of captive-bred origin) and slow development
of the fledglings’ hunting skills might have caused them to seek food resources from their mother. However,
this is the first time that we have observed these behaviors in this intensively managed population. Received 27
December 2004, accepted 24 October 2005.

The presence of extra individuals at nests
has been observed in many groups of birds
(Skutch 1961, Stacey and Koenig 1990).
Many of these extra individuals have been
considered “helpers” in cooperative breeding
systems. Helpers have been documented in a
variety of species, including members of the
Corvidae (Woolfenden and Fitzpatrick 1984),
Hirundinidae (Myers and Waller 1977, Fraga
1979), Furnariidae (Skutch 1969), and a few
raptors (Faaborg et al. 1980, James and Oli-
phant 1986). These extra individuals are con-
sidered to place the good of the species over
the good of the individual, contrary to the ba-
sic tenets of natural selection (Wynne-Ed-
wards 1962). In these systems, the extra in-
dividuals help a breeding pair maximize an-
nual productivity by assisting with nest build-
ing, attendance, and post-fledgling care.

However, not all extra nest visitors can be
classified as helpers. Lombardo (1986) noted
that the sole purpose of extra Tree Swallows
( Tachycineta bicolor ) visiting a breeding
pair’s nest was to obtain food resources.
House Wrens ( Troglodytes aedon) and Acorn
Woodpeckers (Melanerpes formicivorus) have
been observed using their non-active natal
nests for night roosting (Preble 1961, Koenig
et al. 1995), and fledgling Carolina Wrens
(Thryothorus ludovicianus ) have used an ac-
tive Northern Cardinal ( Cardinalis cardinalis)
nest during a period of inclement weather (Ja-
wor and Gray 2003). Thus, the motivation for

‘Inst, for Wildlife Studies, 2515 Camino del Rio
South, Ste. 334, San Diego, CA 92018, USA.

2 Corresponding author; e-mail: kershner@iws.org

visiting the active nests of parents or unrelated
adults likely varies by species.

As part of a larger study assessing the nest-
ing behavior of Loggerhead Shrikes ( Lanius
ludovicianus) on San Clemente Island (SCI),
California, we documented at least two fledg-
lings from a first brood visiting and interfering
at their parent’s second nest. We believe this
is the first record of fledgling shrikes returning
to their parent’s subsequent active nest. We
document the nest visitation by these fledg-
lings, and explore the reasons for these visits.

METHODS

We collected our fledgling interference data
during a larger study on the nesting behavior
of Loggerhead Shrikes on SCI (32° 50' N,
118° 30' W), which is located approximately
109 km northwest of San Diego, California.
SCI is administered by the U.S. Navy and is
used for active military training as part of the
Southern California Offshore Range; the U.S.
Navy also has an environmental program on
the island for the protection and conservation
of natural resources (U.S. Department of the
Navy 2002).

From 23 May to 27 June 2003, we video-
taped a pair of shrikes nesting in Norton Can-
yon, located on the west side of SCI. The
breeding territory at this site is at the bottom
of a steep canyon, where there are several
small trees and shrubs. As part of the recovery
program for this endangered population, two
captive-born shrikes were released into the
wild in 1999 (male) and 2001 (female) as
hatch-year birds. In 2002, the male bred suc-
cessfully in this same territory, whereas the
female bred successfully with another male in

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

a nearby canyon in 2002. As part of the larger
recovery effort to improve reproductive out-
put and survival of adults and offspring, we
provided supplemental food to these birds ev-
ery other day during the breeding season (i.e.,
1 February— 15 July; feeding began when birds
took up occupancy at this site). We provided
a diet of mealworms ( Tenebrio sp.), crickets
{Gryllus sp.), mice ( Mus musculus), and liz-
ards ( Anolis sp.) in plastic tubs that we low-
ered by rope into the canyon bottom, where
they remained for the adults to use for a 1-hr
period. During this 1-hr period, we recorded
data on the identity, health, and behavior of
all shrikes present; the amount of supplemen-
tal food taken; and what each individual did
with the supplemental food (e.g., cached the
food, fed themselves, male fed the fledglings
or the female on the nest).

To assess the behavior of nesting shrikes,
we used miniature video cameras (model
MVC2000-WP-LED, Micro Video Products,
Bobcaygeon, Ontario, Canada; 7.5 X 4 cm)
placed within 30 cm of the nest. We set up
cameras during the egg-laying stage. Each
camera was equipped with infrared light-emit-
ting diodes to allow data collection during
night hours. We used coaxial cable to connect
each camera to a time lapse VCR located
—500 m from the nest tree. We powered the
VCR and camera with a series of 12-volt
deep-cycle marine batteries and used solar
panels to maintain battery charge. We pro-
grammed each VCR to record five frames/sec,
and we changed the video tape every 24 hr.
We reviewed video tapes later to record nest-
ing activity. We also recorded any unusual
events at the nest, such as the presence of
predators or competitors and the interactions
(aggressive or not) between the male and fe-
male. We considered behaviors such as bill
snapping and physical contact as aggressive
behaviors (Yosef 1996). We collected other
nesting behavior data from this site by ob-
serving the territory from the canyon rim dur-
ing supplemental feeding sessions (i.e., every
other day). All results are presented as means
± SE.

RESULTS

Five young fledged from the first nest on
~6 May. All fledglings were color banded pri-
or to fledging for individual identification.

Both adults provided care to the fledglings un-
til —23 May, when the female began incubat-
ing her second clutch in a different tree within
the same territory. Data collected during sup-
plemental feeding observations indicated that
three to four fledglings were present at the
second nest site during the period we collected
video data. We also found that the male allo-
cated more time to feeding the female on the
second nest than to caring for the first-nest
fledglings.

During the second nest attempt (23 May-
27 June), from which five young fledged, we
observed at least two different first-nest fledg-
lings visiting the second nest on 10 different
days. Color bands were indistinguishable on
black-and-white video footage, but we had
verified the identity of first-nest fledglings re-
maining in the territory during supplemental
feeding sessions. The first visit was made on
24 May and the last took place on 8 June,
although we detected at least three fledglings
from the first nest attempt in the general area
until 1 1 July. We do not know whether fledg-
lings were regularly present in the nest tree
during this period, as the camera was focused
on the nest and immediate surroundings. On
numerous occasions, the adult female was ob-
served vocalizing at something in the nest
tree, probably fledglings that may have spent
considerable time in the nest tree and out of
camera view.

We recorded 70 visits (mean visits/day =
7.0 ± 2.4, range = 1-22) during the 10 days
when first-nest fledglings appeared at the nest
(Fig. 1). During these visits, fledglings spent
a total of 6 hr 48 min at the nest (mean min/
visit = 7.0 ± 1.7, range = 3-21). On 24 May,
two first-nest fledglings were present at the
nest at the same time on three separate occa-
sions. Subsequently, we witnessed only one
fledgling at the nest at any one time.

On 21 occasions, we observed a first-nest
fledgling sitting on the nest while the adult
female was away. This occurred 16 times dur-
ing the egg stage and 5 times during the nest-
ling stage. When the female left the nest, the
fledgling would move into the nest cup im-
mediately. The total time spent sitting on the
nest contents by first-nest fledglings was 1 hr
12 min, averaging 3.0 ± 1.0 min per occasion.
On two occasions when a fledgling was sitting
on the nest, the female tried to evict the fledg-

Kershner and Mruz. • NEST INTERFERENCE BY SHRIKES

0:25

0:23

0:21

0:19

0:17 e
E

0:15 its
0:12 ?

0:10 §

0:08

0:06

0:04

0:02

0:00

FIG. 1. Number of visits and mean time per visit for fledgling Loggerhead Shrikes returning to their parents’
second active nest on San Clemente Island, California, 2004. Asterisks indicate dates when we provided sup-
plemental food.

ling by pecking at it. During one visit, the
female sat on top of the fledgling for 15 min,
poking underneath the fledgling as if to check
on her eggs. On several occasions, the fledg-
ling would act destructively while sitting on
the nest. These behaviors included pulling up
the nest lining, pulling sticks out of the nest
structure, breaking open an egg and eating the
eggshell, pecking at newly hatched nestlings,
and stealing food from the female. Other be-
haviors exhibited by fledglings included con-
stant begging to the female, sleeping on the
rim of the nest, and blocking the female from
entering the nest cup. Fledglings would block
the female by getting in the nest and moving
so that the female could not resume incubation
or brooding.

We observed the adult female feeding first-
nest fledglings on 18 occasions (Fig. 2), not
including when fledglings stole food from the
female or consumed food laying in the nest.
More often, however, the female was aggres-
sive toward fledglings at the nest. We recorded

215 aggressive acts between the female and
fledglings, with the number of aggressive acts/
min ranging from 0.25 to 1.16 (Fig. 2).

DISCUSSION

We believe this is the first report of fledg-
ling shrikes returning to an active nest of their
parents. The actual number of different fledg-
lings visiting the nest (we know of at least
two) was uncertain. It does seem clear, how-
ever, that the observations made at this nest
are not behaviors associated with a coopera-
tive breeding system. In cooperative breeding
systems, helpers are present to assist the nest-
ing pair increase productivity (Skutch 1961).
Assisting with nest building, nest defense,
nest attendance, and post-fledging care allows
the nesting pair to focus their energy on pro-
ducing multiple clutches. Some species would
not be capable of double-clutching without a
cooperative breeding system (Poiani and Jer-
miin 1994). Although Loggerhead Shrikes on
SCI are frequently double-brooded, in this

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

FIG. 2. Number of times fledglings were fed by their parents while visiting their second nest, and the number
of aggressive acts per minute exhibited by the adult female toward visiting fledglings while at the nest, San
Clemente Island, California, 2004.

case, the destructive nature of these fledglings
(e.g., nest and egg destruction, attacking nest-
lings, stealing food) suggests that they were
not attempting to increase their parent’s an-
nual productivity, despite their incidental nest
attendance.

We believe first-nest fledglings visited the
nest and begged from the female to extend
parental care. In Loggerhead Shrikes, post-
fledging care is generally the duty of the male
(Yosef 1996). During this period, the male
provisions the young, who often follow the
male around, presumably learning how to hunt
for food. This period extends to independence,
which occurs 40 days after hatching (Scott
and Morrison 1990). The first-nest fledglings
in our study should have become independent
on 29 May. However, it appears that when the
female began incubating her second clutch on
23 May, the male turned his attention to pro-
visioning the female on the nest and reduced

his feeding of the first-nest fledglings. There-
fore, it appears that the amount of parental
care might have been reduced earlier than nor-
mal, although how and when parental care is
terminated remains unclear. Trivers (1974)
suggests that there is a conflict between adults
and offspring regarding how long the depen-
dency period should be. There should be se-
lective pressure for young to try to receive
more parental care than is optimal for the par-
ents to give.

Why males might reduce parental care early
is unknown. The male we observed was cap-
tive-bred and may have exhibited some be-
havioral abnormalities associated with being
reared in captivity. Selection pressures in cap-
tivity are vastly different from those in the
wild, and, as a result, changes in important
life-history behavioral traits may occur (Curio
1996, McPhee 2003). For example, Woolaver
et al. (2000) found that over-dependence on

Kershner and Mruz. • NEST INTERFERENCE BY SHRIKES

food provisioning resulted in behavioral
changes in captive-bred and released Echo
Parakeets ( Psittacula echo), and Harvey et al.
(2002) found abnormal nesting behavior in
captive Hawaiian Crows ( Corvus hawaiien-
sis ). Thus, since the male we observed was
reared in captivity before being released into
the wild, there could have been some behav-
ioral deficiency causing the male to terminate
parental care prematurely. We do not believe
this to be the case, however, as this male was
released into the wild as a juvenile, and young
birds are better at assimilating into new wild
environments than adults (Swinnerton et al.
2000, Robert et al. 2004, Turner et al. 2004).
In addition, this male bred each year after his
release and successfully raised four fledglings
to independence prior to 2003. During nest
monitoring of his prior breeding attempts, we
did not detect any abnormal behavior (Insti-
tute for Wildlife Studies unpubl. data).

A more plausible explanation for our un-
usual observation could be the presence of
supplemental food provided as part of the re-
covery program. Supplemental food is meant
to increase survival and productivity; howev-
er, it is unknown to what extent released birds
rely on this food. If the male shrike relied on
supplemental food for provisioning the female
and fledglings, he may have foraged less for
natural food than birds that do not receive
supplemental food. It is also possible that the
presence of supplemental food slowed the
first-nest fledglings’ learning process in ac-
quiring natural food. Wheelwright and Tem-
pleton (2003) suggest that the speed at which
juveniles acquire foraging skills might deter-
mine the length of parental care. By feeding
regularly from the food tubs, the fledglings
may not have observed many wild foraging
tactics by the male. Thus, they needed more
time to develop these skills and continued to
beg for food from both adults — despite the po-
tential cost to the adults (Trivers 1974).

Our supplemental feeding observations re-
vealed that first-nest fledglings learned to for-
age from the food tubs rather quickly and reg-
ularly took supplemental food when we of-
fered it. This may explain why the fledglings
did not visit the second nest every day. We
provided supplemental food on 6 days during
the period when the fledglings were observed
at the nest (24 May-8 June). They did not

visit the nest on 4 of those days (25 May, 27
May, 2 June, 6 June), and visited only two or
three times on each of the other 2 days we
provided supplemental food (31 May and 4
June; Fig. 1). Fledglings visited the nest on 8
of 10 days when food was not provided, sug-
gesting that the fledglings sought provisioning
from the female.

Differences in the number of visits each day
could also be explained by the abrupt reduc-
tion in food provisioning. The first day the
female ceased parental care for her first brood
was 24 May. The fledglings were unaccus-
tomed to not being fed by her, potentially ex-
plaining the 18 visits to the nest on that day
(Fig. 1), On 7 June, the second clutch of eggs
began to hatch, and there was a spike in ac-
tivity surrounding the nest as the female re-
moved eggshells and began feeding newly
hatched chicks. This increase in activity, es-
pecially with food deliveries to the nest, may
have caused the high number of visits record-
ed ( n = 22; Fig. 1) that day.

In general, we believe that the visits of
these fledgling shrikes to their parent’s second
nest were motivated by hunger, possibly due
to early reduction of parental care or the re-
tardation of foraging skills due to the presence
of supplemental food. On SCI, all captive-
reared pairs released into the wild received
supplemental food. Since 2003, we have
placed small video cameras at 10 shrike nests
to study nesting behavior, and have not ob-
served nest visits by first-nest fledglings at
any other time (Institute for Wildlife Studies
unpubl. data).

Despite the potential benefit provided by
fledglings “tending” the nest when the adult
female was away from the nest, the first-nest
fledglings likely interfered with the success of
the second nesting attempt, as one egg was
destroyed by a visiting fledgling, food was
stolen from the female, and visiting fledglings
constantly pecked at newly hatched young.

ACKNOWLEDGMENTS

We thank D. M. Cooper, R. Dempsey, and C. Camp-
bell for assisting with the implementation of the cam-
era systems and initial review of video tapes. We thank
the Shrike Working Group, consisting of the U.S.
Navy, U.S. Fish and Wildlife Service, PRBO Conser-
vation Sciences, and the Zoological Society of San Di-
ego, for their input regarding the initial use of the vid-
eo cameras at shrike nests. We thank the biologists

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118 , No. 1 , March 2006

from PRBO Conservation Sciences for their assistance
in monitoring shrike nests before and after the instal-
lation of nest cameras. We also thank the shrike release
crew of the Institute for Wildlife Studies for monitor-
ing shrikes at our camera site during supplemental
feeding sessions. E. M. Russell and two anonymous
referees provided comments on an earlier draft of the
manuscript.

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The Wilson Journal of Ornithology 1 1 8( 1 ): 8 1 — 84, 2006

FIRST BREEDING RECORD OF A MOUNTAIN PLOVER IN
NUEVO LEON, MEXICO

JOSE I. GONZALEZ ROJAS,1 3 MIGUEL A. CRUZ NIETO,2
OSCAR BALLESTEROS MEDRANO,1 2 3 AND IRENE RUVALCABA ORTEGA1

ABSTRACT. — We document the first breeding record of Mountain Plovers ( Charadrius montanus) in the
state of Nuevo Leon, Mexico. On 9 July 2004, we located a nest with two eggs and one chick in a colony of
Mexican prairie dogs ( Cynomys mexicanus). Mean height of vegetation near the nest was 7.1 cm, and bare
ground cover was 41.2% (30 m2 sampled). Although this record represents the second nesting for this species
in Mexico, it is the first to document successful breeding. Received 21 January 2005, accepted 5 November
2005.

The Mountain Plover ( Charadrius montan-
us) is a species of North America’s grasslands.
It is classified as vulnerable on the IUCN Red
List (Birdlife International 2004), endangered
in Canada (Committee on the Status of En-
dangered Wildlife in Canada 2004), and
threatened in Mexico (Diario Oficial de la
Federacion 2002). In the United States, the
Mountain Plover was proposed for listing as
a threatened species in 1999 (U.S. Fish and
Wildlife Service 1999), but the proposal was
withdrawn in 2003 (U.S. Fish and Wildlife
Service 2003). The U.S. Shorebird Conser-
vation Plan rates the species as highly imper-
iled (Brown et al. 2001). Between 1966 and
1991, the entire population of Mountain Plo-
vers declined by 63% (Knopf 1994); current-
ly, the population is estimated at 1 1 ,000-
14,000 individuals (Plumb et al. 2005). The
population decline has been attributed to loss
of nesting habitat due to cultivation, urbani-
zation, livestock management, and declines in
native herbivores, mainly black-tailed prairie
dogs ( Cynomys ludovicianus) and North
American bison ( Bison bison ; Wiersma 1996,
BirdLife International 2004).

The Mountain Plover’s primary breeding
range includes eastern Colorado, central Wy-
oming, eastern Montana (Graul and Webster
1976), northeastern New Mexico, and the

1 Lab. de Ornitologia, Fac. de Ciencias Biologicas,
Univ. Autonoma de Nuevo Leon, A.P. 25-F, Cd. Univ-
ersitaria, San Nicolas de los Garza, Nuevo Leon
66450, Mexico.

2 Pronatura Noreste, A. C. Loma Larga 331, Mon-
terrey, Nuevo Leon 25268, Mexico.

3 Corresponding author; e-mail:
josgonza@fcb.uanl.mx

Oklahoma and Texas panhandles (Knopf
1996). An isolated breeding population, which
may be resident year-round, occurs in the Da-
vis Mountains, Texas (Knopf 1996). In the
United States, the plover’s winter range ex-
tends from Sacramento, San Joaquin, and the
Imperial Valley in California east to the Lower
Colorado River Valley, and from Yuma east
to Phoenix and the Chandler area in southern
Arizona (Rosenberg et al. 1991, Knopf and
Rupert 1995). In Mexico, the winter distri-
bution has not been well studied, but it is be-
lieved to extend along the U.S./Mexico border
south through Baja California, Sonora, Chi-
huahua, and Tamaulipas into Zacatecas and
San Luis Potosf (Phillips et al. 1964, Wilbur
1987, Howell and Webb 1995, Gomez de Sil-
va et al. 1996). More surveys are needed to
document wintering as well as year-round res-
ident populations.

Mountain Plovers nest in shortgrass and
mixed grass prairies (Graul and Webster 1976,
Knowles et al. 1982, Knopf and Miller 1994,
Knopf and Rupert 1999b). They typically oc-
cur in areas characterized by short vegetation
(<8 cm high; Graul 1975) and >30% bare
ground (Knopf and Miller 1994), and they are
commonly associated with prairie dog colo-
nies ( Cynomys spp.; Knowles et al. 1982).
Vegetation at nest sites varies throughout the
breeding range, but is usually dominated by
blue grama ( Bouteloua gracilis ), buffalograss
( Buchloe dactyloides), needle-and-thread (Sti-
pa comata), and sagebrush (Artemisia sp.;
Finzel 1964, Graul 1975, Knowles et al. 1982,
Knopf and Miller 1994). Plovers often nest
near cow manure, rocks, or clumps of vege-
tation (Graul 1975, Olson and Edge 1985,
Knopf and Miller 1994).

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

During the breeding period, Mountain Plo-
vers have been observed in colonies of Mex-
ican prairie dogs ( Cynomys mexicanus)
around San Juan del Prado, Galeana, Nuevo
Leon. These observations have included in-
dividuals in breeding plumage and birds ex-
hibiting reproductive behavior (calls, displays,
etc.; Knopf and Rupert 1999a). On 5 July
1994, observers found six widely spaced pairs
and one single individual; on 16 June 1997,
seven individuals (including a pair) were de-
tected in three unspecified prairie dog colonies
in the same area; and on 24 April 1998, seven
more individuals (including two pairs) were
observed. Mountain Plovers were also detect-
ed on 25 April 1998 at Galeana between El
Cristal and La Paz (two pairs and two terri-
torial males) and on 26 April 1998 at La He-
diondilla (one pair and one single) and Llano
La Soledad (two pairs), where unsuccessful
attempts were made to document nesting
(Knopf and Rupert 1999a). During 5-1 1 May
1999, Desmond and Chavez-Ramirez (2002)
observed 30 Mountain Plovers, including
eight pairs and two groups of three individuals
each at Rancho Los Angeles and La India, in
Saltillo, Coahuila de Zaragoza, and at La Ca-
sita in Galeana, Nuevo Leon. On 9 May 1999,
Desmond and Chavez-Ramirez (2002) found
a nest with three eggs near La India, the only
previous nest documented in Mexico. The La
India nest was not monitored and therefore,
its outcome is unknown. Previous nest search-
es conducted in Mexico during the plover’s
known reproductive period (based on obser-
vations in the Great Plains) yielded no other
nesting records; however, Desmond and Cha-
vez-Ramirez (2002) suggested that the breed-
ing season in northeastern Mexico might be
later than it is farther north so that hatching
coincides with the rainy season and the period
of greatest insect availability (June-July).

On 9 July 2004, around 17:00 CST, we ob-
served a Mountain Plover pair at Llano La
Soledad, a gypsophile grassland (7,607 ha)
within ejido San Rafael, Galeana, Nuevo Leon
(24° 48' 50" N, 100° 41 ' 54" W). Llano La So-
ledad contains the largest known colony of
Mexican prairie dogs (Trevino-Villarreal and
Grant 1998). As we approached the pair, one
individual feigned wing injury, while the oth-
er emitted alarm calls and flew around us. Af-
ter a few minutes, one individual “squatted”

on the ground, placed its bill under its body,
and remained motionless. When we ap-
proached within 2 m of what appeared to be
a nest, the bird again feigned wing injury. We
subsequently located the nest, which con-
tained two eggs and one chick. The chick re-
mained motionless while the adults called (as
described by Graul 1974).

Relative to the plover’s nest, the nearest
Mexican prairie dog burrow was approximate-
ly 15 m away. There was also a small cluster
of Atriplex shrubs ( n = 28; estimated mean
height = 60 cm) 40 m from the nest. Live-
stock (cattle, goats) were nearby, but the area
was not overgrazed, nor was cow manure
found near the nest. We photographed and
video-recorded the nest. This record repre-
sents the first Mountain Plover nest in Nuevo
Leon, and the first record of successful nesting
for Mountain Plovers in Mexico.

As part of another study at Llano La Sole-
dad, we had characterized the vegetation a few
days prior to finding the plover nest. After
finding the nest, we selected three of our 1 X
10-m quadrats that were closest to the nest —
200, 1,000, and 1,500 m away — to character-
ize the vegetation. We recorded height, cover
diameter, and species of each plant. We then
calculated mean height, relative density (RD
= number of individuals of a given species as
a proportion of the total number of individuals
of all species), relative frequency (RF = fre-
quency of a given species as a proportion of
the sum of the frequencies for all species), rel-
ative coverage (RC = coverage for each spe-
cies expressed as a proportion of the total cov-
erage for all species), and importance value of
each species (IV = RD + RF + RC, which
provides an overall estimate of the influence
or importance of a plant species in the com-
munity; Brower et al. 1990; Table 1). We
identified 1 1 plant species, with a mean height
of 7.1 cm. The most common forbs were sum-
mer bluet ( Hedyotis purpurea ; n = 725, RD
= 37, RF = 15.9) and McVaugh’s bladderpod
(. Leonsquerella mcvaughiana ; n — 273, RD =
13.9, RF = 15.9); Muhlenbergia sp. ( n = 654,
RD = 33.3, RF = 15.9) and Karwinski’s
grama ( Bouteloua karwinskii ; n = 140, RD =
7.1, RF = 10.5) were the most common grass-
es. Muhlenbergia sp. had the greatest RC
(43.3%) and IV (92.3), and the IV of summer

Gonzalez Rojas et al. • MOUNTAIN PLOVER NEST IN NUEVO LEON

TABLE 1. Vegetation composition and structure in three 1 X 10-m quadrats, placed 2(X), 1,000, and 1,500 m

away from a Mountain Plover nest, in the grassland at
2004.

Llano La Soledad,

Galeana,

Nuevo Leon, Mexico, July

Species

No.

Ha (cm)

RDb (%)

RFC (%)

RCd (%)

IVe

Forbs

Summer bluet ( Hedyotis purpurea)

725

2.5

37.0

15.9

12.4

65.2

McVaugh’s bladderpod ( Lesquerella mcvaughiana)

273

3.3

13.9

15.9

19.0

48.8

Desert zinnia ( Zinnia acerosa)

4.5

4.0

5.3

5.7

15.0

Woody crinklemat {Tiquilia canescens)

5.8

2.4

5.2

3.7

11.3

Houston machaeranthera ( Machaeranthera aurea)

5.1

1.7

5.2

0.5

7.4

Texas sundrops ( Calylophus tubicula)

8.6

0.3

10.5

0.7

11.5

Slimpod fiddleleaf ( Nama stenophyllum )

3.0

0.1

5.2

0.1

5.4

Grasses

Muhly ( Muhlenbergia sp.)

654

5.3

33.3

15.9

43.3

92.3

Karwinski’s grama ( Bouteloua karwinskii)

140

1.7

7.1

10.5

13.0

30.6

Havard’s threeawn ( Aristida havardii )

25.0

0.1

5.2

1.2

6.5

Buffalograss ( Buchloe dactyloides)

13.0

0.1

5.2

0.4

5.7

a H = mean height.

b RD = relative density (number of individuals of a given species as a proportion of the total number of individuals of all species).
c RF = relative frequency (frequency of a given species as a proportion of the sum of the frequencies for all species).
d RC = relative coverage (coverage for each species expressed as a proportion of the total coverage for all species).
e Importance value = RD + RF + RC (Brower et al. 1990).

bluet was 65.2. The sampled area comprised
41.2% bare ground.

The continued documentation of Mountain
Plover nests in northeastern Mexico further
confirms that a breeding population of Moun-
tain Plovers exists in northeastern Mexico
(Knopf and Rupert 1 999a, Desmond and Cha-
vez-Ramirez 2002). Desmond and Chavez-
Ramirez (2002) proposed that the breeding
season in northeastern Mexico may be later
than that known for northern populations, but
a more accurate hypothesis might be that the
breeding period in northeastern Mexico is pro-
tracted because the earliest observation of
pairing occurred in late April (Knopf and Ru-
pert 1999a) and the latest nest with eggs was
observed in early July.

Vegetation characteristics near the nest we
found corresponded with those reported by
Graul (1975; height <8 cm), Knopf and Mill-
er (1994; bare ground >30%), and Desmond
and Chavez-Ramirez (2002; height = 2.3 cm,
bare ground = 86.4%). The presence of a
shading element near the nest is considered
important in nest-site selection (Graul 1975,
Olson and Edge 1985, Knopf and Miller
1994); the nearest shade we found was 40 m
from the nest (a cluster of Atriplex sp.). Dom-
inant plant species differed from those report-
ed in association with Mountain Plover nest

sites: blue grama, buffalograss, needle-and-
thread, and sagebrush (Finzel 1964, Graul
1975, Knowles et al. 1982). In Llano La So-
ledad, however, Muhlenbergia sp. and Kar-
winski’s grama were the dominant grasses,
and summer bluet and McVaugh’s bladderpod
were the dominant forbs; buffalograss occurs
in the area but was not common (RD = 0.1,
RF = 5.2; Table 1).

The presence of a disjunct Mountain Plover
breeding population in northeastern Mexico —
and its association with colonies of Mexican
prairie dogs — has strong conservation impli-
cations for grasslands in that region. However,
the last remnants of northeastern Mexico’s na-
tive grasslands and Mexican prairie dog hab-
itats are being lost, which could have negative
effects on the region’s population of Mountain
Plovers. Other avian species that commonly
occur in association with Mexican prairie dog
colonies include Long-billed Curlew ( Numen -
ius americanus ), Ferruginous Hawk ( Buteo
regalis). Burrowing Owl {Athene cunicular-
ia ), and an endemic, Worthen’s Sparrow (Spi-
zella wortheni ); they, too, could be at risk of
declines due to habitat loss.

ACKNOWLEDGMENTS

We thank F. L. Knopf, C. C. Farquhar, E. Inigo-
Elias, and two anonymous referees for their comments
and suggestions on the manuscript.

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

LITERATURE CITED

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Brown, S., K. Hickey, B. Harrington, and R. Gill
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vation Sciences, Manomet, Massachusetts.

Committee on the Status of Endangered Wildlife
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gered Wildlife in Canada, Environment Canada,
Ottawa, Ontario.

Desmond, M. J. and F. Chavez-Ramirez. 2002. Nest
documentation confirms the presence of a breed-
ing population of Mountain Plovers ( Charadrius
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Diario Oficial de la Federacion. 2002. Norma Ofi-
cial Mexicana NOM-O59-SEMARNAT-2001 .
Proteccion ambiental-Especies nativas de Mexico
de flora y fauna silvestres-Categorias de riesgo y
especificaciones para su inclusion, exclusion o
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Finzel, J. E. 1964. Avian populations of four herba-
ceous communities in southeastern Wyoming.
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Graul, W. D. 1974. Vocalizations of the Mountain
Plover. Wilson Bulletin 86:221-229.

Graul, W. D. 1975. Breeding biology of the Mountain
Plover. Wilson Bulletin 87:6-31.

Graul, W. D. and L. E. Webster. 1976. Breeding
status of the Mountain Plover. Condor 78:265—
267.

Howell, S. N. and S. Webb. 1995. A guide to the
birds of Mexico and northern Central America.
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Knopf, F. L. 1 994. Avian assemblages on altered grass-
lands. Studies in Avian Biology 15:247-257.

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tanus: montane, grassland, or bare-ground plover?
Auk 1 1 1 :504-506.

Knopf, F. L. and J. R. Rupert. 1995. Habits and hab-
itats of Mountain Plover in California. Condor 97:
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Knopf, F. L. and J. R. Rupert. 1999a. A resident pop-
ulation of Mountain Plover Charadrius montanus
in Mexico? Cotinga 11:17-19.

Knopf, F. L. and J. R. Rupert. 1999b. Use of culti-
vated fields by breeding Mountain Plovers in Col-
orado. Studies in Avian Biology 19:81-86.

Knowles, C. J., C. J. Stoner, and S. P. Gieb. 1982.
Selective use of black-tailed prairie dog towns by
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Olson, S. L. and D. Edge. 1985. Nest site selection
by Mountain Plovers in northcentral Montana.
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Phillips, A. R., J. T. Marshall, and G. Monson.
1964. The birds of Arizona. University of Arizona
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Plumb, R. E., F. L. Knopf, and S. H. Anderson. 2005.
Minimum population size of Mountain Plovers
breeding in Wyoming. Wilson Bulletin 117:1 5—
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Rosenberg, K. V., R. D. Ohmart, W. C. Hunter, and
B. W. Anderson. 1991. Birds of the lower Colo-
rado River Valley. University of Arizona Press,
Tucson.

Trevino- Villarreal, J. and W. E. Grant. 1998. Geo-
graphic range of the endangered Mexican prairie
dog ( Cynomys mexicanus). Journal of Mammalo-
gy 79: i 273-1 287.

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and threatened wildlife and plants: proposed
threatened status for the Mountain Plover. Federal
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and threatened wildlife and plants: withdrawal of
the proposed rule to list the Mountain Plover as
threatened. Federal Register 68( 1 74):53083-
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The Wilson Journal of Ornithology 1 18( I ):85-90, 2006

BREEDING BIOLOGY OF THE DOUBLE-COLLARED SEEDEATER
(SPOROPHILA CAERULESCENS)

MERCIVAL R. FRANCISCO1

ABSTRACT. — The Double-collared Seedeater ( Sporophila caerulescens ) is the most common seedeater in
southern South America. Because information on its breeding biology is mostly limited to descriptions of nests
and eggs, I studied the reproductive biology of the Double-collared Seedeater in southeastern Brazil. I found 41
active nests during seven breeding seasons (1997-2003). Nesting occurred from December to May. All nests
found during incubation contained two eggs, eggs were laid on consecutive days, and incubation started the
morning the female laid the last egg. Incubation and nestling periods were 12 and 12-15 days, respectively.
Only females incubated the eggs. Mean time spent incubating/hr was 52.3 min, and incubation recesses averaged
6.6 min. Nestlings were fed 7.6 times/hr, and although both males and females fed the young, the participation
of females was significantly greater than that of males. Predation was the major cause of nest failure. Daily
survival rates during the incubation (0.990) and nestling (0.935) stages differed. Overall nesting success was
36%. Although studies conducted in disturbed areas can reveal greater rates of nest predation than those found
in undisturbed areas, some Sporophila species seem to benefit from habitat disturbance. The conversion of native
habitats to agricultural lands in Brazil, as well as the spread of exotic grasses, has resulted in the expansion of
the Double-collared Seedeater to previously forested areas. Received 14 February 2005, accepted 16 November
2005.

The genus Sporophila (Emberizidae) com-
prises a diverse group of small finches widely
distributed in the Neotropics. The greatest di-
versity is reached in interior South America,
where most species inhabit grassy semi-open
areas (Ridgely and Tudor 1994, Sick 1997).
However, detailed information on breeding bi-
ology is lacking for most of these species.
Furthermore, the melodious songs of these
seedeaters make them vulnerable to pursuit
for the illegal pet trade. As a result, many spe-
cies have been locally extirpated, and some
are severely threatened (Collar et al. 1992,
Willis and Oniki 1992, Ridgely and Tudor
1994, Sick 1997, Willis 2003).

The Double-collared Seedeater ( S . caeru-
lescens) is the most common seedeater in
southern South America. It inhabits grasslands
and agricultural areas (Ridgely and Tudor
1994), commonly near populated locations.
Recently, it has expanded its distribution in
response to the destruction of forested areas
and the consequent spread of exotic grass spe-
cies (Sick 1997). Although not endangered,
entire populations of the Double-collared
Seedeater have been lost to the illegal pet
trade, being one of the most popular cage

1 Depto. de Genetica e Evolut^ao, Univ. Federal de
Sao Carlos, Rodovia Washington Luis, km 235, P.O.
Box 676, CEP 13565-905, Sao Carlos, SP, Brazil;
e-mail: mercivalfrancisco@uol.com.br

birds in Brazil. Information on its breeding
biology is limited to descriptions of nests and
eggs (Euler 1900, Ihering 1900, Pereyra 1956,
De La Pena 1981, Alabarce 1987) and the
length of the nestling period — obtained from
a single nest observed in Argentina (Pereyra
1956). More information on the species’ ecol-
ogy is needed before meaningful conservation
objectives can be developed for the species.
Herein, I describe the reproductive biology of
the Double-collared Seedeater in southeastern
Brazil. Phenology and duration of the breed-
ing season, length of incubation and nestling
periods, egg mass, nest success, and infor-
mation on parental care are reported.

METHODS

Study area. — I conducted my study on the
campus of Sao Carlos Federal University, lo-
cated in the central region of Sao Paulo state,
southeastern Brazil (21° 58' S, 47° 52' W).
The campus is subdivided into a semi-urban-
ized portion and an adjacent non-urbanized,
disturbed cerrado area (savanna that ranges
from open grasslands to forested areas, such
as gallery forests that grow alongside water-
courses; Eiten 1972). The semi-urbanized area
totals 187 ha, and is composed of extensive
lawns, orchards, gardens, and Eucalyptus spp.
and Pinus spp., with regenerating cerrado un-
dergrowth. Buildings and streets are widely
spaced and compose only 23 ha (12%). The

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

non-urbanized area is a 529.6-ha mosaic com-
posed of sensu lato cerrado (125 ha), gallery
forest (3.6 ha), regenerating cerrado (84 ha),
an abandoned Eucalyptus spp. plantation with
regenerating cerrado undergrowth (94 ha),
and active Eucalyptus spp. silviculture (223
ha) (Paese 1997). The climate in this region
is tropical, with two well-marked seasons: a
humid, hot season from October through
March and a dry, cold season from April
through September. In both the semi-urban-
ized and non-urbanized areas, grass seeds are
abundant during the wet season.

During seven breeding seasons (1997-
2003), I conducted nest searches from early
November, when males started to sing and de-
fend territories, to May, when males stopped
singing. All habitats were searched for nests.
Although I conducted nest searches weekly,
the number of habitats covered and search ef-
fort varied on each field survey. Nests were
located by searching the areas defended by
males and by following females observed near
these territories. Using a metal caliper (accu-
rate to 0.01 mm), I measured nests and eggs,
and I used a spring scale (accurate to 0.1 g)
to weigh eggs.

Using a 7 X 35 binocular, I observed nests
during 60-min periods to calculate the fre-
quency of feeding visits and to estimate the
proportion of time that females spent incubat-
ing the eggs. These observations were always
made early in the morning (06:00-10:00
UTC — 3) and while maintaining a minimum
distance of 20 m from the nests. During the
nestling stage, only nests containing two
young (the most frequent brood size) were
considered for observations. The nestling
stage was subdivided into three observation
periods: early (1—4 days after hatching), mid-
dle (5-9 days after hatching), and late (10-13
days after hatching; Roper and Goldstein
1997). I used the Kruskal-Wallis test to com-
pare the frequencies of feeding trips among
these periods. To compare the number of
times that males and females fed the young, I
used the Mann-Whitney £/-test.

1 checked nests every 1—3 days. Predation
was assumed to have occurred when eggs or
nestlings younger than fledging age disap-
peared from a nest. Abandonment was as-
sumed if adults were not seen on or near the
nest and the eggs were cold or the nestlings

were dead (Pletschet and Kelly 1990). When-
ever possible, I checked nests from a distance.
By using binoculars, I was able to see eggs
and young through the thin nest walls, thus
avoiding observer disturbance (see Roper and
Goldstein 1997). I estimated rates of daily
nest survival during the incubation and nest-
ling stages by using the Mayfield method
(Mayfield 1961), and compared them accord-
ing to Sauer and Williams (1989) by using
program CONTRAST (Hines and Sauer
1989). One to six nests of each stage were
analyzed per year in order to calculate surviv-
al rate, but because of small sample sizes,
years were pooled. Means of daily survival
rate are presented ± SE; all other means are
presented ± SD. I calculated standard errors
according to Johnson (1979). Nesting success
(probability of survival) from incubation
through fledging was also estimated following
Mayfield (1961).

RESULTS

I found 41 active nests, 26 in the semi-ur-
ban area and 15 in disturbed cerrado. Nests
were found in all habitats except gallery forest
and active Eucalyptus spp. plantations. Males
started defending territories in early Novem-
ber, and I found the earliest nest on 18 De-
cember 1999. The nest contained two eggs in
the late stage of incubation, suggesting that
breeding activities had started in early Decem-
ber. The latest nesting activity was recorded
on 9 May 1997, when I observed the last
young in a nest.

Nests were cup-shaped and built of thin
grass roots and spiderweb silk. The walls were
thin, as the eggs and young could be seen
through them. The eggs were white or slightly
greenish, with dark and light brown spots,
sometimes concentrated at the large end of the
egg (Euler 1900, Ihering 1900, De La Pena
1981). The height of nests above ground
ranged from 0.6 to 6 m (2.4 ± 1.2, n = 25).
I also measured outside diameter (6.7 cm ±
0.8, n — 19), inside diameter (5.2 cm ± 0.7,
n = 19), inside height (4.0 cm ± 0.6, n — 18),
and outside height (4.8 cm ± 0.7, n — 19) of
the nests. Egg measurements were length =
17.7 mm ± 0.5, n — 11; width =13 mm ±
0.5, n = 11; and weight = 1.4 g ± 0.5, n —
11.

Double-collared Seedeaters did not appear

Francisco • BREEDING BIOLOGY OF SPOROPH/LA CAFRULESCENS

to select any particular plant species for nest
construction. Eighteen species belonging to 1 1
different families were identified, including
the exotic Pinus spp. (Pinaceae), Cupressus
spp. (Cupressaceae), Eriobotrya japonica
(Rosaceae), Michelia champaca (Magnoli-
aceae), Ligustrum lucidum (Oleaceae), Mur-
raya exotica , Citrus sp. (Rutaceae), and Eu-
patorium sp. (Asteraceae). Native plant spe-
cies included Piptocarpha rotundifolia , Ver-
nonia sp. (Asteraceae), Didymopanax vinosum
(Araliaceae), Miconia albicans , Tibouchina
granulosa (Melastomataceae), Machaerium
acutifolium, Caesalpinia peltophoroides,
Sweetia elegans, Sibipiruna sibipiruna (Fa-
baceae), and Casearia silvestris (Flacourti-
aceae).

All nests observed during incubation con-
tained two eggs ( n = 27). Eggs were laid on
consecutive days and incubation started the
morning the female laid the last egg (first day
of incubation). Hatching occurred on the
morning of the 13th day (n — 4 nests). During
33 hr of focal observations at seven different
nests, I observed only females incubating the
eggs. Males did not feed females on the nests.
The mean time spent incubating/hr was 52.3
min ± 5.8 (range = 41.2-60 min), and incu-
bation recesses were 6.6 min ± 4.4 (range =
0.3—18.7 min, n = 23).

Nestlings fledged in 12-15 days (mean =
13.3 ± 1.2, n = 8), and invariably, nestlings
from the same nest fledged on the same day
(n = 4 nests). They left the nests with poorly
developed feathers and weak flight capabili-
ties. In 34 hr of focal observations at 1 1 dif-
ferent nests, nestlings were fed an average of
7.6 ± 4.3 times/hr. The number of feeding vis-
its/hr increased throughout the nestling period
(Fig. 1), and although both males and females
fed the young, the participation of females
(4.8 visits/hr ± 2.4) was significantly greater
than that of males (2.7 ± 2.5; U = 341.0, P
= 0.001).

Females regularly brooded nestlings after
feedings (until the young were up to 7 days
old), and both males and females removed fe-
cal sacs. In one territory, adults fed one fledg-
ling and young nestlings at the same time,
suggesting that the nestlings represented at
least a second brood for that breeding season.
On several occasions, one or both adults of a

Nestling stage

FIG. 1 . Average number of feedings/hr in the early
(n = 14 hr at eight different nests), middle (n = 9 hr
at five different nests), and late (n - 1 1 hr at six dif-
ferent nests) nestling stages. Error bars are SDs. The
frequency of feedings differed among the stages (Krus-
kal-Wallis H = 16.38, P < 0.001).

pair were observed chasing intruding Double-
collared Seedeaters that approached nests.

Apart from one nest that fell down during
a storm, predation was the only cause of nest
failure. No nests were abandoned and no eggs
were infertile. Daily survival during incuba-
tion was 0.990 ± 0.010 (one predation event
in 104 nest days, n = 12 nests). Survival dur-
ing the nestling stage was 0.935 ± 0.024 (sev-
en predation events in 107 nest days, n = 13
nests). Nest survival was higher during incu-
bation (11 of 12) than during the nestling
stage (6 of 13; x2 = 4.5, df = 1, P = 0.033).
Nesting success from incubation to fledging
was 36%.

The mean number of female arrivals and
departures from nests during the incubation
stage was 1.9 ± 2.0/hr ( n = 33 hr). During
the nestling stage, the mean number of paren-
tal arrivals and departures was 15.7 ± 9.2 (n
= 34 hr). The mean number of parental de-
partures and arrivals per hr was greater during
the nestling stage than it was during incuba-
tion (U = 31.5, P < 0.001).

DISCUSSION

The nesting season of Double-collared
Seedeaters began in December, which is late
compared with the onset of breeding season
for most passerine birds inhabiting cerrado
(i.e., they usually start in September; Sick
1997). Nesting in Double-collared Seedeaters

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

coincided with the fruiting period of exotic
Gramineae species, seeds of which are fed to
nestlings. Entire seeds of Brachiaria sp. were
observed in the crops of nestlings. Other seed-
eaters found in the study region, such as S.
lineola and S. leucoptera, shared the same
breeding period (MRF pers. obs.).

The nests were similar to those described
for other Sporophila species (e.g., S. collaris,
S. ruficollis, S. albogularis, S. nigricollis, and
S. lineola; Alderton 1961; ffrench 1965; De
La Pena 1981; Marcondes-Machado 1982,
1997), and the cup shape and thin walls were
typical of those constructed by congeners
(Sick 1997). The use of spiderwebs in nest
construction has also been recorded for S. ruf-
icollis (De La Pena 1981) and S. nigricollis
(ffrench 1965). Nests were not reused, as pre-
viously reported for S. nigricollis (Alderton
1961), S. albogularis , and S. lineola (Marcon-
des-Machado 1982, 1997), but females re-
used the material of old nests to build new
nests.

The incubation period of 12 days was sim-
ilar to that of S. nigricollis and S. americana
(it lasts 13 days for S. torqueola). For S. cae-
rulescens, Pereyra (1956) reported a nestling
period of 13—14 days, and I observed a mean
of 13.25 days. The nestling period is 8-9 days
for S. nigricollis, 11—13 days for S. ameri-
cana, 1 1 days for S. torqueola , and 9 days for
S. lineola (Skutch 1945, Gross 1952, Alderton
1961, Marcondes-Machado 1997). Overall,
both the incubation and nestling periods re-
ported for the Sporophila species are among
the shortest of Neotropical, open-cup nesting
Passeriformes. Although some nests of S.
americana, S. lineola (Skutch 1945, Gross
1952, Marcondes-Machado 1997), and S. cae-
rulescens (De La Pena 1981), have been
found containing three eggs or young, two
seems to be the usual brood size for Sporo-
phila species.

Predation was by far the major factor lim-
iting nesting success in S. caerulescens, sim-
ilar to reports for many other open-cup nesting
Neotropical passerines (Skutch 1949, 1985;
Snow 1976; Oniki 1979; Roper and Goldstein
1997; Martin et al. 2000; Mezquida and Ma-
rone 2000). My data support the hypothesis
that parental activity may increase the risk of
nest predation (Skutch 1949, 1985). The num-
ber of adult departures from, and arrivals to.

nests were much greater, and daily survival
was lower during the nestling stage. Skutch’s
hypothesis predicts that the primary predators
should be diurnal and visually oriented. How-
ever, in addition to parental activities, nests
containing nestlings may be more conspicu-
ous due to the noise (Haskell 1994, 1999;
Dearborn 1999) and odor of the young, which
would attract nocturnal mammalian predators
that use olfaction. Nestlings vocalized only
when parents were feeding them, and the beg-
ging calls were audible from 15 m when
broods were 7-8 days old, and from about 20
m when young were in the late nestling stage.

Although little is known about nest preda-
tors in the Neotropics, preliminary observa-
tions and video data have shown diurnal birds
to be the most important predators in environ-
ments other than wet forests (Martin et al.
2000, Mezquida and Marone 2002). Potential
predators in the study area included Burrow-
ing Owl {Athene cunicularia; Mezquida and
Marone 2000), Guira Cuckoo {Guira guira;
Mason 1985), Squirrel Cuckoo {Piaya cay-
ana), and anis {Crotophaga spp.; Telleria and
Diaz 1995). During my study, I observed a
Great Kiskadee {Pitangus sulphuratus ) prey-
ing upon a Double-collared Seedeater nest. I
have also observed Plush-crested Jays ( Cyan -
ocorax chrysops) feeding on Common Quail
{Coturnix coturnix) eggs placed in artificial
cup-shaped nests (MRF unpubl. data), which
suggests their potential as a predator of seed-
eaters, as well. Potential nocturnal mammalian
predators occurring in the study area included
white-eared opossum ( Didelphis albiventris),
crab-eating raccoon {Procyon cancrivorus),
grison (Galictis vittata ), striped hog-nosed
skunk ( Conepatus semistriatus), tayra ( Eira
barbara), jaguarundi ( Herpailurus yaguaron-
di ), and house cats ( Felis catus ).

Studies conducted in disturbed areas can re-
veal greater rates of nest predation than those
in undisturbed areas due to the increased
abundance of mesopredators in disturbed ar-
eas (Martin 1996, Martin et al. 2000). How-
ever, some Sporophila species seem to benefit
from habitat disturbance. Before its expansion
into anthropogenic habitats, the niche occu-
pied by the Double-collared Seedeater was
probably limited to non-forested areas, such
as forest borders, cerrados, and wetlands
where native grasses occurred. Today, the in-

Francisco • BREEDING BIOLOGY OF SPOROPHILA CA FRIJLESCFNS

creasing extension of agricultural areas in
Brazil, as well as the spread of exotic grasses,
has resulted in the expansion of Double-col-
lared Seedeaters to areas previously covered
by forests. Gross (1952) and ffrench (1965)
provide additional records of the expansion of
S. americana and S. nigricollis into anthro-
pogenic habitats.

ACKNOWLEDGMENTS

I am grateful to N. Arguedas, H. L. Gibbs, M. Ro-
drigues, M. A. Pizo, M. Galetti, and three anonymous
referees for their important suggestions on previous
versions of this manuscript, and M. I. S. Lima for iden-
tifying plant species. This study was supported by
Coordenagao de Aperfeigoamento de Pessoal de Nivel
Superior (CAPES), Conselho Nacional de Desenvol-
vimento Cientifico e Tecnologico (CNPq) and Funda-
gao de Amparo a Pesquisa do Estado de Sao Paulo
(FAPESP).

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Skutch, A. F. 1949. Do tropical birds rear as many
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The Wilson Journal of Ornithology 1 18(l):91-98, 2006

SMALL MAMMAL SELECTION BY THE WHITE-TAILED HAWK IN

SOUTHEASTERN BRAZIL

MARCO A. MONTEIRO GRANZINOLLI1 2 AND JOSE CARLOS MOTTA-JUNIOR1 2

ABSTRACT. — We analyzed diet and prey selection of the relatively unknown albicaudatus subspecies of the
White-tailed Hawk ( Buteo albicaudatus). Our study was based on an analysis of 259 pellets collected from
September 2000 to September 2001 in the municipality of Juiz de Fora in southeastern Brazil. We also assessed
the abundance of small mammals with pitfall traps (2,160 trap-nights). Small mammals composed 52.5% of the
estimated biomass consumed by the hawks, and selection appeared to be mediated by abundance. The Bonferroni
confidence intervals procedure revealed that when abundance of small mammals was higher, the hawks were
selective, preying on Calomys tener more than would be expected by chance (P < 0.05); other rodents were
consumed less than expected. Oligoryzomys nigripes, Oxymycterus sp., and Gracilinanus spp. were taken in the
same proportion as they were found in the field. During reduced prey abundance (October-March), White-tailed
Hawks preyed opportunistically on small mammals. Differences in habits and vulnerability of small mammals
may explain prey selectivity in the White-tailed Hawk. Received 5 October 2004, accepted 3 October 2005.

The White-tailed Hawk {Buteo albicauda-
tus) is a poorly known species ranging from
southern Texas to northern Argentinean Pata-
gonia (Farquhar 1992, Thiollay 1994). Infor-
mation on its ecology is scarce and largely
descriptive or anecdotal, with most studies
having been conducted in North America
(Stevenson and Meitzen 1946, Kopeny 1988,
Farquhar 1992). Data on type and number of
prey have received some attention in Texas
(see Farquhar 1992), but prey selection rela-
tive to prey abundance remains unknown.
Only three studies report on the diet of this
raptor in the Neotropics. Schubart et al. (1965)
examined contents of two stomachs contain-
ing mainly insects; Brasileiro et al. (2003) re-
ported predation on a snake, and Motta- Junior
and Granzinolli (2004) observed consumption
of a Ringed Kingfisher {Megaceryle torqua-
ta ). The species is thought to be an opportu-
nistic predator (Stevenson and Meitzen 1946,
Kopeny 1988), and in Texas, half of the prey
biomass comprises mammals (Farquhar
1986).

Opportunistic predators generally take prey
in accordance with their abundance in the
field, whereas selective predators consume
prey in proportions that differ from those
available (Jaksic 1989). This selectivity or op-
portunism may be explained in relation to the
energy costs and benefits involved in the cap-

1 Depto. de Ecologia, Instituto de Biociencias, Univ.
de Sao Paulo, 05508-900 Sao Paulo, SP, Brazil.

2 Corresponding author; e-mail: mgranzi@usp.br

ture and handling of prey. Predators may con-
sume the most profitable, but not necessarily
the most abundant, prey (Schoener 1971, Kor-
pimaki 1985, Stephens and Krebs 1986, Iriarte
et al. 1989, Jaksic 1989). According to opti-
mal foraging theory, predators behave to max-
imize their fitness, which is done by maxi-
mizing their net rate of energy intake (Emlen
1966, 1968; Schoener 1971; Stephens and
Krebs 1986). Thus, prey selection by a pred-
ator not only depends on prey energy content,
but also on the predator’s success in three ba-
sic stages: finding, handling, and consuming
prey. Selectivity can be assessed by observing
differences among the prey species at any of
these steps. Prey selectivity may be a result of
both prey and predator morphology and be-
havior (Corley et al. 1995). Emlen (1966,
1968) hypothesized that predators will exhibit
a greater degree of dietary selection when
their prey are abundant, but will be more op-
portunistic when food is scarce. Additionally,
a predator may eat more abundant prey at
greater frequencies than expected in relation
to abundance (Emlen 1966). Here, we analyze
prey selection by the White-tailed Hawk rel-
ative to prey abundance, evaluating previous
assertions about the opportunistic feeding be-
havior of this species (Stevenson and Meitzen
1946, Farquhar 1986, Kopeny 1988).

METHODS

Study site. — We conducted fieldwork on pri-
vate farmlands in northern Juiz de Fora (21°
41' S, 43° 27' W), in the state of Minas Gerais

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118 , No. 1 , A/c/rc/? 2P06

in southeastern Brazil (Fig. 1). The elevation
of our study area (17,537 ha) ranged from 670
to 800 m; the topography is mountainous. The
climate is Humid Subtropical, winters are dry,
and annual rainfall averages 1,536 mm. The
wet season extends from October to April
(192 mm rainfall, mean temperature = 20.2°
C), and the dry season occurs from May to
September (37 mm rainfall, mean temperature
= 16.8° C). Originally, the dominant vegeta-
tion was semi-deciduous forest; now the area
is primarily farmland, pastures, patches of
second-growth vegetation, and plantations of
exotics (e.g.. Eucalyptus spp. and Pinus spp.;
Juiz de Fora 1996).

General diet. — The analysis of the White-
tailed Hawk’s diet was based on 259 pellets,
which we collected from seven nesting and six
roosting sites of approximately seven pairs.
We collected and identified (by size and
shape) all pellets from perches used exclu-
sively by White-tailed Hawks. We oven-dried
the collected material and treated it with a
10% NaOH aqueous solution (Marti 1987).
Prior to chemical treatment, we removed re-
mains of scales, fur, and feathers, and later
added them to other remains, such as mandi-
bles, teeth, and invertebrate exoskeletons. We
identified remains by comparing them to a ref-
erence collection from the study area. Inver-
tebrates were generally identified to family
and order, whereas vertebrates were identified
mostly to genus or species. Prey biomass was
estimated by counting the minimum number
of individuals in pellets and then multiplying
this number by the mean body mass of each
species at the study site (Marti 1987).

Prey selection. — We estimated the relative
abundance of small mammals in the field by
monitoring five sets of drift-fence pitfall traps
(Friend et al. 1989). Traps were distributed
systematically around most of the hawks’
hunting sites (Fig. 1), determined before and
during the study period through observations
of foraging individuals. We collected pellets
during small mammal trapping. Each set of
pitfall traps consisted of 12 buckets (36 1
each), totaling 60 traps. From September 2000
to September 200 1 , we operated traps monthly
for 3 consecutive days, totaling 2,160 trap-
nights. Captured mammals were identified,
weighed, sexed, earmarked, and released. An
index of small mammal abundance for each

month was based on the total number of in-
dividual first captures (recaptures were not
counted).

Indices of prey abundance are assumed to
reflect prey availability, but this may not nec-
essarily be true (Jaksic 1989). Traps should be
efficient, nonselective, and catch the entire
range of small mammal prey. Moreover, traps
should be placed in patches where and when
the predator hunts. Our procedures fulfilled
these assumptions, in terms of both time and
place of foraging. Our traps were open 24 hr
per day, so that both diurnal and crepuscular
activities of White-tailed Hawks were ac-
counted for by the trapping procedures. Pitfall
traps appear to be less selective and more ef-
ficient, capturing larger numbers of species,
individuals, and age classes compared with
traditional live traps (Williams and Braun
1983; MAMG unpubl. data).

Analyses. — We conducted G-tests to test the
goodness-of-fit of the frequency distributions
of prey in the diet and in the field (Zar 1984).
We interpreted nonsignificant results to mean
that White-tailed Hawks exploited prey in
proportion to their abundance in the field; sig-
nificant differences suggested that the hawks
“preferred” or “avoided” some small mam-
mal species, hence apparently selecting or
avoiding prey. To confirm selection or avoid-
ance of prey, we used the Bonferroni confi-
dence intervals procedure for each prey spe-
cies (Neu et al. 1974, Byers et al. 1984,
Plumpton and Lutz 1993, Martinez and Jaksic
1997, McLoughlin et al. 2002). If the expect-
ed proportion of consumption was not includ-
ed in the confidence interval, then the ob-
served and expected consumption differed
significantly. If the confidence interval includ-
ed the expected proportion of consumption,
then the hypothesis that prey species were pre-
ferred or avoided was rejected. All tests were
considered significant at P < 0.05.

RESULTS AND DISCUSSION

General diet. — Numerically, the main prey
were insects, followed by small mammals,
reptiles, and birds (Fig. 2). Small mammals
composed the bulk of biomass, followed by
insects, reptiles, and birds. Our results are
similar to those of Stevenson and Meitzen
(1946), Farquhar (1986), and Kopeny (1988).

Only 5 of 12 genera of small mammals

Granzinolli and Motto-Junior • PREY SELECTION BY THE WHITE-TAILED HAWK

7617814

7613814

7609814

7605814

7601814

7597814

662845 666845 670845

7617814

7613814

7609814

7605814

7601814

7597814

1 g g 1_9 3_9 5_8 7_8 km

Scale 1:97000

FIG. I. Satellite image (LANDS AT 7/ETM, 27 June 2000) of study area in Juiz de Fora municipality, Minas
Gerais, southeastern Brazil. Coordinate grid system is UTM (Zone 22, Corrego Alegre). White squares are sites
of pitfall traps; white circles are nest and perch sites of White-tailed Hawks.

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

Insecta Other Reptilia and Aves Mammalia

Arthropoda Amphibia

FIG. 2. Number of individuals and estimated biomass of prey groups consumed by White-tailed Hawks
from September 2000 to September 2001, Juiz de Fora municipality, Minas Gerais, southeastern Brazil.

( Calomys , Akodon, Oligoryzomys, Oxymycte-
rus, Gracilinanus) found in the study area
(Appendix) were identified in White-tailed
Hawk pellets. The genus Akodon was repre-
sented mostly by A. lindberghi, with some A.
cursor ; both were found in pellets and in pit-
fall traps. The seven genera whose remains
were not found in pellets were uncommon:
only 12 individuals (4.6% of total captures)
were trapped in pitfalls (Appendix). Prey be-
havior or habitat choice may explain the ab-
sence of some genera in the diet of White-
tailed Hawks. Rhagomys , Oryzomys, and Ju-
liomys {—Wilfredomys) have arboreal or scan-

sorial habits, whereas Thaptomys , Bibimys ,
Bolomys , and Blarinomys display subterra-
nean or fossorial habits, and all but Bolomys
and A. lindberghi inhabit mostly forests (Em-
mons 1990, Eisenberg and Redford 1999, No-
wak 1999; JCM-J pers. obs.). Furthermore, al-
though the genus Oxymycterus was as uncom-
mon as the seven genera not recorded in
White-tailed Hawk pellets, its habitat is most-
ly open vegetation (MAMG unpubl. data).

Prey selection. — White-tailed Hawks exhib-
ited differential predation on small mammal
species when both seasons were combined (G
= 32.54, P < 0.001; Table 1). The same pat-

TABLE 1. Small mammal prey selection by White-tailed Hawks in Juiz de Fora municipality, Minas Gerais,
southeastern Brazil, from September 2000 to September 2001. Observed values (Obs) are actual frequencies in
the diet; expected values (Exp) are frequencies calculated from proportions obtained in the field by pitfall
trapping.

Species

Dry season

Wet season

Total diet

Obs

Exp

Obs

Exp

Obs

Exp

Akodon spp.

1 1

33.5

7.5

40.8

Calomys tener

59.1

23.7

113

83.1

Oligoryzomys nigripes

41.3

6.8

47.9

Oxymycterus sp.a

0.7

—

0.7

Gracilinanus spp.a

1.4

2.0

3.5

Total

136

136.0

40.0

176

176.0

52.07

7.68

32.54

<0.001

0.054

<0.001

a Oxymycterus sp. and Gracilinanus spp. were grouped for G-tests.
b G-test, df = 3.

Granzinolli and Motta-Junior • PREY SELECTION BY THE WHITE-TAILED HAWK

tern was observed during the dry season (G
= 52.07, P < 0.001), but not in the wet
months (G - 7.68, P = 0.054; Table 1).

The Bonferroni confidence intervals pro-
cedure revealed that in the dry season, the
hawks preyed more on Calomys tener and less
on Akodon spp. than expected based on trap-
ping data (Table 2). Conversely, in wet
months, there were no differences in small
mammal predation compared with the avail-
ability of small mammals in the study area
(Table 2). Oligoryzomys nigripes, Oxymycte-
rus sp., and Gracilinanus spp. were always
consumed in the same proportion that they
were found in the environment (Table 2).
Hence, our findings are not entirely congruent
with those of Stevenson and Meitzen (1946)
and Kopeny (1988).

Other studies on small mammal populations
in southeastern Brazil indicate peaks of abun-
dance during the dry season (e.g., Motta-Ju-
nior 1996, Vieira 1997, Talamoni and Dias
1999). The same pattern was observed in our
study (Fig. 3).

The high frequency of C. tener (sometimes
considered a subspecies of C. laucha\ Eisen-
berg and Redford 1999) in the White-tailed
Hawk’s diet may be due to its higher vulner-
ability. A similar suggestion was proposed by
Corley et al. (1995) for other rodent and pred-
ator species in Patagonia. A less vulnerable
species ( Eligmodontia typus, better escape
ability) was preyed upon less than expected
by the culpeo fox ( Dusicyon culpaeus ), while
the behaviorally and morphologically vulner-
able Akodon spp. were consumed more fre-
quently than expected. Other diet studies of
owls (Motta-Junior 1996, Motta-Junior and
Bueno 2004, Motta-Junior et al. 2004) in
southeastern Brazil have revealed that C. tener
is one of the main prey species, despite not
being the most abundant in the field, suggest-
ing higher vulnerability. C. tener is apparently
mainly terrestrial and does not dig burrows
(Eisenberg and Redford 1999, Nowak 1999);
thus, it is more vulnerable because it is likely
to be more conspicuous to the hawks. In con-
trast, species of Akodon travel in tunnels un-
der the leaf litter and nest in burrows (Em-
mons 1990); thus, Akodon spp. may be able
to escape White-tailed Hawk predation more
efficiently than C. tener.

Our results suggest that prey selection by

Akodon spp. 0.081 0.304 0.020 < Pl , < 0.141 (-) 0.150 0.187 0.004 < Pi < 0.295 (0)

Calomys tener 0.699 0.435 0.597 < Pi < 0.799 ( + ) 0.450 0.593 0.247 < P, < 0.652 (0)

Oligoryzomys nigripes 0.176 0.246 0.092 < Pi < 0.260 (0) 0.350 0.170 0.155 < Pi ^ 0.544 (0)

Oxymycterus sp. 0.015 0.005 0.000 < p, < 0.041 (0) 0.025 0.000 0.000 < p, < 0.088 (0)

Gracilinanus spp. 0.029 0.010 0.000 < Pi < 0.066 (0) 0.025 0.050 0.000 < Pi < 0.088 (0)

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 1 18, No. J, March 2006

FIG. 3. Small mammal abundance from September 2000 to September 2001, Juiz de Fora municipality,
Minas Gerais, southeastern Brazil. Data were not available for November 2000.

White-tailed Hawks was mediated by prey
abundance. When the abundance of small
mammals was higher (dry season), the hawks
selected the more abundant prey, Calomys te-
ner (Table 2). However, during a period of
lower abundance of prey (wet season), White-
tailed Hawks were opportunistic relative to
small mammal species. Our results support the
prediction of Emlen ( 1 966) that predators feed
selectively on very abundant prey, thus sug-
gesting that White-tailed Hawks exploit re-
sources depending on their availability.

In conclusion. White-tailed Hawks seem to
prey selectively on a more vulnerable small
mammal (C. tener ), which has terrestrial hab-
its and uses open habitat. The semi-fossorial
Akodon spp. were apparently less vulnerable
to the hawks. Alternatively, but not exclusive-
ly, our results support Emlen’s (1966) hypoth-
esis that predators, in times of high prey abun-
dance, will prey selectively on species that are
more abundant. Further studies of raptor diet
selection in the Neotropics should stress mor-
phological and behavioral traits of prey as a
way to understand differential vulnerability to
predators (e.g., Kotler 1985, Corley et al.
1995).

ACKNOWLEDGMENTS

We thank C. V. Rios for assistance in the field. M.
V. Vieira, R. P. Kavanagh, C. C. Farquhar. A. A.

Bueno, and two anonymous referees provided helpful
comments on previous versions of our manuscript. Fi-
nancial support was provided by the Conselho Na-
cional de Desenvolvimento Cientffico e Tecnologico
and the Fundagao de Amparo a Pesquisa do Estado de
Sao Paulo.

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food preference. American Naturalist 100:611-
617.

Emlen, J. M. 1968. Optimal choice in animals. Amer-
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Emmons, L. H. 1990. Neotropical rainforest mammals:
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cago, Illinois.

Farquhar, C. C. 1986. Ecology and breeding behavior
of the White-tailed Hawk in the northern Coastal
Prairies of Texas. Ph.D. dissertation, Texas A&M
University, College Station.

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Farquhar, C. C. 1992. White-tailed Hawk ( Buteo al-
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641-645.

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Korpimaki, E. 1985. Prey choice strategies of the Kes-
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Martinez, D. R. and F. M. Jaksic. 1997. Selective
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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

APPENDIX. Rodents and opossums ( Gracilinanus spp.) captured in pitfall traps in Juiz de Fora municipality,
Minas Gerais, southeastern Brazil, from September 2000 to September 2001. For each month, we tallied only
first captures. Data were not available for November 2000.

Species

weight (g)

Sep

Oct

Dec

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Total

Akodon cursor*

—

Akodon lindberghi a

—

•7

Bibimys labiosus

—

Blarinomys breviceps

Bolomys lasiurus

Calomys tener*

1 1

118

Gracilinanus agilis a

—

Gracilinanus spp.a

—

Juliomys sp.

Oligoryzomys cf. flavescens

Oligoryzomys nigripes a

Oryzomys cf. kelloggi

Oxymycterus sp.a

Thaptomys nigrita

—

Rhagomys rufescens

—

Total

261

a Species preyed on by White-tailed Hawks.
b — represents no captures.

Short Communications

The Wilson Journal of Ornithology 1 1 8( 1 ):99- 101, 2006

Provisioning of Fledgling Conspecifics by Males of the Brood-parasitic
Cuckoos Chrysococcyx klaas and C. caprius

Irby J. Lovette,14 Dustin R. Rubenstein,1 2-23 and Wilson Nderitu Watetu3 4

ABSTRACT. — Although post-fledging care by adult
males seems unlikely in bird species that are obligate,
interspecific brood parasites, there have been numer-
ous reports of adult male Chrysococcyx cuckoos ap-
parently feeding conspecific young. Most researchers
currently view these observations with skepticism, in
large part because Chrysococcyx and other cuckoo spe-
cies engage in courtship feeding, and it is possible that
field observers could mistake adult females receiving
food from courting males for fledglings, especially giv-
en the similar appearances of females and juveniles.
Here, we report an observation of an extended provi-
sioning bout by an adult male Klaas’s Cuckoo (C.
klaas) feeding a conspecific individual with juvenile
plumage and behavior, and we summarize our obser-
vations of similar occurrences in the Diederik Cuckoo
(C. caprius ) in Kenya. We suggest that the available
evidence indicates that male provisioning, and hence
potential parental care, is present in these brood-para-
sitic cuckoos at a higher frequency than currently rec-
ognized. The mechanism that causes males to associate
with fledglings is unknown, but warrants further study.
Received 20 December 2004, accepted 19 September
2005.

The genus Chrysococcyx comprises 15 spe-
cies of small. Old World cuckoos (Sibley and
Monroe 1990), of which all are thought to be
obligate brood parasites (Davies 2000).
Klaas’s Cuckoo (C. klaas) has a wide distri-
bution in sub-Saharan Africa, where it is
known to parasitize a large number of passer-
ine host taxa, often- — but not exclusively —
species of Sylviidae and Nectarinidae (Irwin
1988). Similarly, the Diederik Cuckoo (C. ca-
prius) breeds throughout much of sub-Saharan
Africa and has a broad range of hosts, pri-
marily species of Ploceidae (Irwin 1988).

1 Cornell Lab. of Ornithology, 159 Sapsucker
Woods Rd„ Ithaca, NY 14850, USA.

2 Dept, of Neurobiology and Behavior, Cornell
Univ., Seeley G. Mudd Hall, Ithaca, NY 14853, USA.

3 Mpala Research Centre, Box 555, Nanyuki, Ken-
ya.

4 Corresponding author; e-mail: IJL2@cornell.edu

Over the past century, there have been nu-
merous observations of male Chrysococcyx
cuckoos feeding conspecifics that were
thought to be fledglings (Moreau 1944, Fried-
mann 1968, Iversen and Hill 1983, Rowan
1983). In a literature review of provisioning
behavior in brood parasites, Lorenzana and
Sealy (1998) found 5 records of nestling or
fledgling provisioning by Klaas’s Cuckoo
males and 1 1 such records for Diederik Cuck-
oo males; Friedmann (1968) discusses 12 and
15 such records, respectively, including some
anecdotal reports. There is apparently only
one equivalent report of a female Chrysococ-
cyx cuckoo provisioning fledglings, and in that
case, both the female and young were captive
birds (Millar 1926, Lorenzana and Sealy
1998). Historically, a number of researchers
(e.g., Moreau 1944, Friedmann 1968) consid-
ered parental care to be common in African
Chrysococcyx cuckoos and believed that the
behavior might be a primitive condition as-
sociated with a relatively recent evolutionary
transition to brood parasitism. As researchers
continued to document the prevalence of
courtship feeding in these and other cuckoo
species, more recent authorities (e.g.. Rowan
1983, Irwin 1988, Lorenzana and Sealy 1998,
Davies 2000) have suggested that the behavior
is either misdirected courtship feeding or the
result of human observers misidentifying
adult females as fledglings. In practice, these
and other possibilities are difficult to exclude.
Although the plumages of adult African Chry-
sococcyx are highly sexually dimorphic, it is
difficult to distinguish females from juveniles
in the field (Rowan 1983).

Here, we report an observation of an ex-
tended provisioning bout by an adult male
Klaas’s Cuckoo feeding a conspecific individ-
ual with juvenal plumage and behavior, and
we summarize our observations of similar oc-
currences in the Diederik Cuckoo. These ob-

100

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

servations add to the body of evidence sug-
gesting that male Chrysococcyx cuckoos may
engage in intensive provisioning of juveniles.

KLAAS’S CUCKOO

Beginning at 10:08 UTC + 3 on 15 August
2004, IJL, DRR, and WNW observed an adult
male (by plumage) Klaas’s Cuckoo in Lake
Nakuru National Park, Kenya (00° 22' S, 36°
03' E). This bird was foraging at an extremely
rapid rate of movement in the open canopy of
a large yellow-barked acacia tree ( Acacia xan-
thophloea ). After watching the bird for a few
minutes, we observed it deliver food to a sec-
ond, sedentary cuckoo in the same tree. We
noted the time, and for the next 26 min, we
were able to keep both cuckoos under constant
focal observation with at least one observer
following each bird. This is apparently the
longest-duration period of potential fledgling
provisioning reported for Chrysococcyx
(Friedmann 1968).

During our observation, the adult male
cuckoo continued to forage rapidly within an
approximate 40-m radius around the second
cuckoo. The male returned to the second
cuckoo 18 times while carrying food items,
all of which appeared to be 1- to 3-cm-long
lepidopteran larvae gleaned from the foliage
and bark of the acacia. On 16 of the 18 visits,
the second, more sedentary bird accepted and
ate the caterpillar. On each visit, the adult
male presented the food with his tail slightly
cocked, but we observed no other conspicuous
postures or behaviors potentially related to
courtship. No copulations or attempted copu-
lations occurred.

During our observation, the presumed ju-
venile moved among four perches, flying 3—4
m each time. These flights were notably more
fluttery than those of the adult male and ap-
peared typical of the weak flight exhibited by
recently fledged birds. While perched, this
bird also assumed the “fluffed” posture typi-
cal of recent fledglings, and it remained sta-
tionary between most provisioning visits. The
observation ended when the presumed juve-
nile made a similar, but slightly longer flight
into denser foliage and disappeared from our
sight. Although the plumages of female and
immature Klaas’s Cuckoos are variable and
overlap (Irwin 1988), we noted at the time
that the bird being provisioned had a distinct

white patch behind the eye and a white throat
marked with substantial, dark barring — plum-
age characters more typical of juveniles (Irwin
1988).

DIEDERIK CUCKOO

On 28 May 2002 at 08:23, WNW observed
a male Diederik Cuckoo feeding an apparent
fledgling (based on plumage) at the Mpala Re-
search Centre, Laikipia, Kenya (00° 17' N,
36° 54' E). The fledgling was perched about 3
m above ground in a Balanites aegyptica tree.
During 15 min of observation, the adult fed
the fledgling at least four times and continued
to do so when the observer left the area. On
19 May 2003 at 10:15, WNW noted similar
behavior at a site 100 m from that of the first
observation. During this observation, an adult
male Diederik Cuckoo gleaned insects from
long grass and fed them to a fledgling (based
on plumage) perched on a nearby acacia. We
observed the male make six feeding trips be-
fore cattle flushed the birds.

DISCUSSION

Based on the posture, behavior, and plum-
age of the Klaas’s Cuckoo that we observed
being fed by an adult male, it seems highly
likely that it was a recently fledged bird rather
than an adult female being courted. We also
noted that the adult male engaged in intensive
(and, presumably, energetically costly) forag-
ing for an extended period in order to provi-
sion this individual. Friedmann (1968) consid-
ered provisioning bouts as long as 15 min as
“suggestive of the fact that the catering adult
was not merely indulging in courtship feed-
ing.” Our observation of an intensive provi-
sioning period of nearly twice that duration
further supports this interpretation. In contrast,
courtship feeding in Chrysococcyx typically
involves a series of stereotyped behaviors that
we did not observe: the male’s presentation of
food while simultaneously cocking his head
and vibrating his wings and tail, postural bow-
ing movements by the male, vocalizations by
the male or both individuals, or (in some cas-
es) subsequent copulation (Irwin 1988).

When considered in concert, our observa-
tions and those in dozens of previous reports
describing equivalent behaviors suggest that
males of several African Chrysococcyx cuck-
oos may provision fledglings regularly. Post-

SHORT COMMUNICATIONS

101

fledging associations of adults and offspring
also have been documented in other brood-
parasitic taxa, such as the Brown-headed
Cowbird ( Molothrus ater\ Hahn and Fleischer
1995). Indeed, previous reports have docu-
mented male Klaas’s and Diederik cuckoos
provisioning both pre-volant young and mul-
tiple fledglings (Moreau 1944, Friedmann
1968, Lorenzana and Sealy 1998), thus ex-
cluding misidentification of adult females as
sufficient explanation for this behavior. We
speculate that not only are females sometimes
misidentified as fledglings, but perhaps older
fledglings being provisioned by males are
sometimes mistaken for females being court-
ed. If earlier reports were correct and provi-
sioning of fledglings by adult males is rela-
tively common in the African Chrysococcyx,
it raises interesting questions about the genetic
relatedness of the interacting individuals and
their underlying social system.

ACKNOWLEDGMENTS

We thank M. Muchai and the many additional staff
members of the Department of Ornithology, National
Museums of Kenya who have greatly facilitated our
field research in their country. We similarly acknowl-
edge the Kenya Wildlife Service and the Mpala Re-
search Centre for allowing us to conduct this research.

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South African Journal of Natural History 6:28-29.

Moreau, R. E. 1944. Food-bringing by African
Bronze Cuckoos. Ibis 86:98-100.

Rowan, M. K. 1983. The doves, parrots, louries, and
cuckoos of Southern Africa. David Philip, Cape
Town, South Africa.

Sibley, C. G. and B. L. Monroe. 1990. Distribution
and taxonomy of birds of the world. Yale Univer-
sity Press, New Haven, Connecticut.

The Wilson Journal of Ornithology 1 1 8( 1 ): 101-104, 2006

Widespread Cannibalism by Fledglings in a Nesting Colony of
Black-crowned Night-Herons

Christina Riehl12

ABSTRACT. — I studied the diet and foraging be-
havior of fledgling Black-crowned Night-Herons (Nyc-
ticorax nycticorax ) in a mixed-species nesting colony
of Black-crowned Night-Herons and Snowy Egrets
(Egretta thula ) in New Orleans, Louisiana. In 1 of 5
years, cannibalism of nestlings that had fallen or
climbed out of nests was common, accounting for 66
of 94 (70.2%) prey items taken by fledglings. Juveniles
took younger conspecifics by both predation and scav-

1 5500 Camp St., New Orleans, LA 70115, USA.

2 Current address: Dept, of Ecology and Evolution-
ary Biology, Princeton Univ., Princeton, NJ 08544,
USA; e-mail: criehl@princeton.edu

enging. Isolated incidents of cannibalism among
Black-crowned Night-Herons have been reported pre-
viously, but not on a colony-wide scale. Received 2
December 2004, accepted 19 September 2005.

Many researchers have studied the diets of
adult and nestling Black-crowned Night-Her-
ons ( Nycticorax nycticorax ; Bent 1 926, Palm-
er 1962, Wolford and Boag 1971), but there
are few data on the diet and foraging behavior
of juveniles immediately after leaving the
nest. Here, I provide the first report of wide-

102

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 1/8, No. 1, March 2006

spread cannibalism and scavenging of conspe-
cifics among fledglings in a nesting colony of
Black-crowned Night-Herons.

METHODS

From 1 February to 18 July 2000, I moni-
tored a colony of Black-crowned Night-Her-
ons on Ochsner Island, Audubon Park, New
Orleans, Fouisiana (29° 56' N, 90° 8' W) as
part of a long-term (1997-2001) study on re-
productive success. Ochsner Island is a small
(600 m2) island in a man-made lagoon; the
distance between the island and the shore of
the mainland is approximately 6 m. The is-
land’s vegetation is dominated by Chinese tal-
lowtree ( Sapium sebiferum ) and live oak
( Quercus spp.). In 2000, 143 pairs of Black-
crowned Night-Herons and 10 pairs of Snowy
Egrets ( Egretta thula ) nested on the island.
Nest height ranged from 1 to 7 m above
ground. I recorded the diet and foraging be-
havior of approximately 70 juvenile night-her-
ons from fledging until the end of the breeding
season, when the members of the nesting col-
ony dispersed. Night-herons were considered
to have fledged when they left the nest per-
manently and were no longer fed by adults, at
which point most were capable of clumsy
flight. Prey items were identified by direct ob-
servation of foraging night-herons. Observa-
tions were made from the mainland, from
which approximately half of the nests in the
colony could be observed. I observed foraging
juveniles for 546 hr.

RESUFTS

Juvenile Black-crowned Night-Herons were
fed by parents until 45 ± 3 (SD) days after
hatching ( n = 23). However, juveniles were
able to climb out of the nest and onto sur-
rounding vegetation as early as 30 days after
hatching, returning to the nest when a parent
approached with food. At 35 days, juveniles
readily left their nests, often climbing out of
the nest to solicit food from a nearby parent
or unrelated adult night-heron.

Juveniles remained on the island for 1—3
weeks after leaving the nest permanently,
forming small groups of one to four individ-
uals from the same nest, or neighboring nests.
Each group or lone individual occupied a
small (7—9 m2) territory on the ground and
defended the area from passing adults and oth-

er fledglings (see Noble et al. 1938 for a full
description of territoriality in juvenile night-
herons). Fledglings rarely ventured into the
water to hunt; rather, they spent most of their
time foraging on the ground under active
nests. Of 94 prey items that I saw juvenile
night-herons consume, 66 (70.2%) were youn-
ger fledgling or nestling night-herons. I ob-
served juveniles feeding on both chicks that
they killed ( n = 20) and chicks that were al-
ready dead when I began observations ( n =
46). Other prey items included fish (10.6%),
frogs (8.5%), brown rats (Rattus norvegicus\
4.3%), carrion dropped from active nests
(3.2%), Wood Duck chicks ( Aix sponsa;
2.1%), and a dead Snowy Egret nestling
(1.1%).

Fledglings did not prey on chicks in nests
or chicks perched in vegetation; they limited
their attacks to nestlings on the ground that
had fallen or climbed out of nests. Adults de-
fended chicks in nests, but I never observed
adults interfering with fledglings that were
preying on chicks on the ground. Since older
night-heron nestlings often left the nest to
perch on nearby vegetation before fledging
permanently, it was not always clear whether
victims were nestlings that had fallen from
nests or younger fledglings that had just left
the nest. It is probable, however, that preda-
tion by fledgling night-herons increased mor-
tality rates of chicks that had climbed out of
the nest and would have otherwise been able
to climb to safety. Older nestlings in low nests
(<1.5 m above ground) often climbed out of
the nest onto the ground before fledging, and
were therefore more vulnerable to attacks than
nestlings in high nests.

Small, weak, and moribund chicks were at-
tacked more frequently than healthy-looking
nestlings near the age of fledging. The victims
were approximately 50-70% of the size of
fledglings and appeared difficult to kill and
consume. Fledglings killed younger conspe-
cifics by striking them with their bills for up
to 1 hr or more, and then consumed them by
repeatedly striking the carcasses and labori-
ously tugging small pieces of meat from them.

Older fledglings were particularly skilled at
preying on nestlings and appeared to focus
their foraging attempts on nestlings to the ex-
clusion of other prey. When a fledgling found
an undefended nestling and began to attack it.

SHORT COMMUNICATIONS

103

other fledglings usually came to fight over the
victim. In one case, I observed five fledglings
attack and consume a 15-day-old nestling that
had fallen from its nest.

DISCUSSION

Black-crowned Night-Herons are among
the most opportunistic of North American her-
ons. They employ several different foraging
behaviors (Kushlan 1976) and consume a
wide variety of prey, including fish, mollusks,
insects, reptiles, amphibians, rodents, birds,
eggs, carrion, refuse, and plants (Hancock and
Kushlan 1984, Davis 1993). Night-herons will
alter their foraging methods to concentrate on
locally abundant resources, including mice
(Allen and Mangels 1940), fish (Spanier
1980), and amphibians (Wetmore 1920). They
have also been reported to systematically ex-
ploit rookeries of other colonially nesting
birds, including Common Terns {Sterna hirun-
do\ Marshall 1942, Collins 1970, Shealer and
Kress 1991) and Franklin’s Gulls {Larus pi-
pixcan\ Wolford and Boag 1971). Kale (1965)
reported an instance of adult night-herons in
a colony preying opportunistically on White
Ibis ( Eudocimus albus ) and Great Egret ( Ar -
dea alba) chicks from the same mixed-species
rookery, noting that ibis and egret chicks from
neighboring nests constituted a major food
source for night-heron chicks. Published re-
ports of night-herons feeding on conspecifics,
however, are limited to Wolford and Boag’s
(1971) report of a night-heron nestling that
was regurgitated by another nestling. Williams
and Nicholson (1977) reported a suspected in-
stance of brood reduction in the Black-
crowned Night-Heron, but did not find evi-
dence of cannibalism.

There is virtually no information on the for-
aging behavior of night-heron fledglings dur-
ing the period immediately after they leave the
nest — after the adults have stopped feeding
them but before they become adept at catching
their own prey. Lorenz (1938) and Palmer
(1962) reported that fledglings move through
the colony and are able to beg food from any
adult; however, Finley (1906) and Noble et al.
(1938) found that adults do not feed juveniles
on the ground. Data on the composition of
fledgling diet are scarce, possibly because re-
cently fledged juveniles may forage at night
(Rockwell 1910, Davis 1993). In this study, I

found that juveniles sometimes climbed back
to the nest in the first 2-3 days after fledging,
and were usually fed by the parents. After 3
days post-fledging, fledglings on the ground
often grabbed the bills of passing adults in an
attempt to stimulate them to regurgitate food,
but were almost always unsuccessful.

Fledglings also seemed unable to fish effi-
ciently in the deep water surrounding the is-
land, at least for the first 7 or 8 days after
fledging. I frequently observed fledglings in
the water striking at floating sticks and pieces
of leaves, but they rarely captured live prey.
Fledglings occasionally picked up prey
dropped by nestlings in active nests; on one
occasion, a fledgling climbed into a low nest
and pulled a fish from the bill of the fledgling
to which it had just been delivered. Adults, by
contrast, were never observed feeding on dead
nestlings or other carrion, suggesting that they
were more skilled at catching higher-quality,
live prey.

Although I spent similar amounts of time
observing the same rookery each year ( 1 997-
2001), cannibalism among Black-crowned
Night-Heron fledglings was prevalent only in
2000. I observed night-heron fledglings feed-
ing on dead night-heron and egret chicks only
twice in 1998 and once in 2001. The species
composition of the nesting colony was fairly
constant across years, comprising 120-150
pairs of Black-crowned Night-Herons and 5—
10 pairs of Great Egrets and Snowy Egrets;
thus, the level of competition for food among
fledglings on the island should not have been
elevated in 2000. In other years, fledgling di-
ets were dominated by fish and frogs. How-
ever, it is difficult to compare prey composi-
tion across years because I observed far fewer
prey captures in other years, possibly because
juvenile Black-crowned Night-Herons may
forage mostly at night.

It is possible that cannibalism rates were
exceptionally high in 2000 because local
shortages of fish or other live prey forced
fledglings to seek alternate food resources, but
I was unable to document such a shortage. A
food shortage would have affected the diet
and foraging patterns of fledglings more than
adults and nestlings, since adults often left the
nesting colony to forage while fledglings re-
mained on the island.

104

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

ACKNOWLEDGMENTS

I am grateful to W. E. Davis, Jr., J. A. Kushlan, and

an anonymous reviewer for their helpful comments on

the manuscript.

LITERATURE CITED

Allen, R. P. and F. P. Mangels. 1940. Studies of the
nesting behavior of the Black-crowned Night Her-
on. Proceedings of the Linnean Society of New
York 50-51:1-28.

Bent, A. C. 1926. Life histories of North American
marsh birds. U.S. National Museum Bulletin, no.
135, Smithsonian Institution, Washington, D.C.

Collins, C. T. 1970. The Black-crowned Night Heron
as a predator of tern chicks. Auk 87:584-586.

Davis, W. E., Jr. 1993. Black-crowned Night-Heron
( Nycticorax nycticorax). The Birds of North
America, no. 74.

Finley, W. L. 1906. Herons at home. Condor 8:35-40.

Hancock, J. and J. A. Kushlan. 1984. The herons
handbook. Harper and Row, New York.

Kale, H. W., II. 1965. Nestling predation by herons in
a Georgia heronry. Oriole 30(March):69-70.

Kushlan, J. A. 1976. Feeding behavior of North
American herons. Auk 93:86-94.

Lorenz, K. 1938. A contribution to the comparative
sociology of colonial-nesting birds. Proceedings

of the International Ornithological Congress 8:
207-218.

Marshall, N. 1942. Night desertion by nesting Com-
mon Terns. Wilson Bulletin 54:27-31.

Noble, G. K., M. Wurm, and A. Schmidt. 1938. So-
cial behavior of the Black-crowned Night Heron.
Auk 55:7-40.

Palmer, R. S. 1962. Handbook of North American
birds, vol. I: loons through flamingos. Yale Uni-
versity Press, New Haven, Connecticut.

Rockwell, R. B. 1910. Some Colorado night heron
notes. Condor 12:113-121.

Shealer, D. A. and S. W. Kress. 1991. Nocturnal
abandonment response to Black-crowned Night-
Heron disturbance in a Common Tern colony. Co-
lonial Waterbirds 14:51-56.

Spanier, E. 1980. The use of distress calls to repel
night herons ( Nycticorax nycticorax ) from fish
ponds. Journal of Applied Ecology 17:287-294.

Wetmore, A. 1920. Observations on the habits of
birds at Lake Burford, New Mexico. Auk 37:393-
412.

Williams, M. D. and C. P. Nicholson. 1977. Obser-
vations at a Black-crowned Night-Heron nesting
colony. Migrant 48:1-7.

Wolford, J. W. and D. A. Boag. 1971. Food habits
of Black-crowned Night Herons in southern Al-
berta. Auk 88:435-437.

The Wilson Journal of Ornithology 1 18(1): 104- 106, 2006

First Report of Black Terns Breeding on a Coastal Barrier Island

Shawn R. Craik,1 3 Rodger D. Titman,1 Amelie Rousseau,1 and Michael J. Richardson2 3

ABSTRACT. — Black Terns ( Chlidonias niger suri-
namensis) breed locally in freshwater wetlands across
the northern United States and central Canada, often
building their nests over shallow water on a floating
substrate of matted marsh vegetation. Here, we report
the first nesting record of this species on a coastal bar-
rier island. The nest, which consisted of two eggs laid
in a slight scrape of sand, was located on 6 July 2004
in a large breeding colony of Common Terns ( Sterna
hirundo) on Kelly’s Island at Kouchibouguac National
Park. New Brunswick, Canada. The observation also
represents the current northeastern breeding limit for
this species in North America. Both eggs hatched, but

' Dept, of Natural Resource Sciences, McGill Univ.,
Ste-Anne-de-Bellevue, QC H9X 3V9, Canada.

2 Dept, of Biological Sciences, Bishop's Univ., Len-
noxville, QC JIM 1Z7, Canada.

3 Corresponding author; e-mail:
shawn.craik@mail.mcgill.ca

neither chick survived beyond 4 days. Received 15 De-
cember 2004, accepted 5 October 2005.

The North American subspecies of Black
Tern ( Chlidonias niger surinamensis ) breeds
locally across the northern United States and
central Canada. Black Terns are semicolonial,
typically nesting in productive, shallow fresh-
water marshes, semipermanent ponds, prairie
sloughs, and along margins of lakes and rivers
(Stewart and Kantrud 1984, Dunn and Agro
1995, Schummer and Eddleman 2003). Nests
are generally placed in areas of calm water
within stands of emergent bulrush ( Scirpus
spp.), cattail ( Typha spp.), bur-reed ( Spargan -
ium spp.), or pickerel weed ( Pontederia corda-
ta\ Cuthbert 1954, Dunn 1979, Mazzocchi et

SHORT COMMUNICATIONS

105

al. 1997). Nests are usually built over shallow
water (0.5- 1.2 m deep) on a floating substrate
of matted, dead marsh vegetation, floating root-
stalks and discarded pieces of wood, or musk-
rat feeding platforms; occasionally, nests are
built on non-floating substrates, including
muskrat lodges, flattened vegetation, and mud
(Cuthbert 1954, Bergman et al. 1970, Dunn
1979). Nests often consist of dead vegetation
arranged in a compressed pile with a shallow
depression at the top (Dunn and Agro 1995).

Black Terns use coastal habitats during mi-
gration, winter, and in summer when non-
breeding birds aggregate in large flocks (100+
birds) on saltpans, marshes, estuaries, and
brackish wetlands (Dunn and Agro 1995). Re-
ports of Black Terns breeding in marine areas
are extremely rare (Sirois and Fournier 1993).
In the mid-1990s, a single nest was found at
Seal Island National Wildlife Refuge (NWR),
Rockland, Maine (C. S. Hall pers. comm.),
and in both 2003 and 2004, two nests were
located at Machias Seal Island, New Bruns-
wick (C. M. Develin pers. comm.). The nests
at these marine sites consisted of a small
amount of dead vegetation in sparse common
sheep sorrel ( Rumex acetosella) and grasses,
or they were placed on a granite rock surface.
Nests were located in large, mixed colonies of
Common ( Sterna hirundo) or Arctic ( S . par-
adisaea ) terns. The nest at Seal Island NWR
was ~30 m from the high-tide line, whereas
the nests at Machias Seal Island were —100
m from water. All five Black Tern nests in
marine areas failed to fledge young.

The Canadian Maritime breeding popula-
tion of Black Terns was estimated to be 150
pairs (Erskine 1992), with southern New
Brunswick representing the species’ north-
eastern breeding limit in North America
(Dunn and Agro 1995). Since 2000, however.
Black Terns (<4 birds annually) have been
observed in mid- to late June with breeding
Common Terns on four coastal barrier islands
of Kouchibouguac National Park, New Bruns-
wick. Surveys conducted from 2000 to 2003,
however, did not confirm breeding (Christie et
al. 2004; E. Tremblay pers. comm.).

Here, we report the first evidence of Black
Terns breeding on a coastal barrier island. Kel-
ly’s Island (46° 50' N, 64° 55' W), 2 ha in size,
is part of a 26-km crescent of barrier spits and
islands that separate Kouchibouguac Bay of the

Northumberland Strait from the shallow estu-
ary-lagoon system of Kouchibouguac National
Park (Beach 1988). The island is composed of
sand and is vegetated by extensive stands of
marram grass ( Ammophila brevdigulata ); the
island’s outer edge consists of a gently sloping
intertidal beach zone. The island supports a
large breeding colony of Common Terns,
which included 1,041 nests counted in 2004
(Parks Canada Tern Survey 2004).

On 6 July 2004 at approximately 17:00
AST, after the entire tern colony at Kelly’s Is-
land had flushed and taken flight, we identi-
fied a pair of adult Black Terns flying above
the center of the island. One of the Black
Terns descended and landed, and we subse-
quently identified a Black Tern nest with two
eggs laid in a slight scrape of sand. The long,
oval eggs were noticeably smaller (—34 X 24
mm) than the subelliptical eggs in nearby
Common Tern nests (—42 X 31 mm; SRC
pers. obs.). The Black Tern eggs were dark
olive and marked with dark brown dots and
blotches, the density of which was greater
near the large end. Nearby Common Tern eggs
were generally cream colored and finely
marked with brown and black dots. The Black
Tern nest and many of the Common Tern nests
consisted of a small amount of dead vegeta-
tion loosely lining a scrape made in the sand.
Both species nested in areas of the island
where cover was sparse (5-15% marram
grass). Whereas Common Tern nests were
0.5-30 m from the high-tide line, the Black
Tern nest was 26.5 m from the water. Two
Common Tern nests were within 3 m of the
Black Tern nest.

On 20 July at 17:20, we returned to the nest
and found a newly hatched chick and a pip-
ping egg. The hatchling’s down was predom-
inantly cinnamon and black, except for a
white belly and a white mask over the eye and
cheek. A single adult Black Tern was ob-
served flying 5-10 m directly above the nest.
On 24 July, we checked the nest again and
found both chicks dead at the nest; one adult
Black Tern was flying 10-15 m above the is-
land. The young were necropsied, but the
cause of death was undetermined (S. McBur-
ney pers. comm.).

Adult Common Terns at Kelly’s Island
readily exhibited aggressive displays toward
the smaller Black Tern adults. Overt aggres-

106

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

sion typically involved brief aerial chases and
attack by Common Terns as a Black Tern
adult approached and descended toward its
nest. Common and Black terns occasionally
form mixed-breeding colonies elsewhere
(Snow and Perrins 1998), and Common Terns
have been known to defend nesting territories
against other tern species, including Roseate
Terns ( Sterna dougallii ; Burger and Gochfeld
1991, Nisbet 2002). Aggressive displays by
Common Terns, and the close proximity of
tern nests at Kelly’s Island, may have com-
promised the survival of the Black Tern
chicks by preventing the adults from provid-
ing sufficient food resources to their young,
resulting in dehydration or malnutrition (S.
McBurney pers. comm.). Nevertheless, our
observations represent the first confirmed
breeding of Black Terns on the barrier islands
of Kouchibouguac National Park and repre-
sent the northeastern breeding limit for this
species in North America.

ACKNOWLEDGMENTS

We are grateful to Kouchibouguac National Park,
especially E. Tremblay, for providing logistical and
field support. We appreciate information on Black
Terns provided by the National Audubon Society’s
Seabird Restoration Program, the University of New
Brunswick, and I. C. T. Nisbet. S. McBurney willingly
performed necropsies. Observations and preparation of
this manuscript were conducted during SRC’s graduate
studies of Red-breasted Mergansers ( Mergus serrator)
supported by Bishop’s University, the Canadian Wild-
life Federation, the New Brunswick Wildlife Trust
Fund, and the Province of Quebec Society for the Pro-
tection of Birds. We thank M.-A. Hudson and three
anonymous reviewers for helpful comments on this
manuscript.

LITERATURE CITED

Beach, H. (Ed.). 1988. The resources of Kouchiboug-
uac National Park: resource description and anal-

ysis. Kouchibouguac National Park, Environment
Canada-Parks, New Brunswick, Canada.

Bergman, R. D., P. Swain, and M. W. Weller. 1970.
A comparative study of nesting Forster’s and
Black terns. Wilson Bulletin 82:435-444.

Burger, J. and M. Gochfeld. 1991. The Common
Tern: its breeding biology and social behaviour.
Columbia University Press, New York.

Christie, D. S., B. E. Dalzell, M. David, R. Doiron,
D. G. Gibson, M. H. Lushington, P. A. Pearce,
S. I. Tingley, and J. G. Wilson. 2004. Birds of
New Brunswick: an annotated list. New Bruns-
wick Museum monographic series (natural sci-
ence), no. 10. Saint John, New Brunswick, Can-
ada.

Cuthbert, N. L. 1954. A nesting study of the Black
Tern in Michigan. Auk 71:36-63.

Dunn, E. H. 1979. Nesting biology and development
of young in Ontario Black Terns. Canadian Field-
Naturalist 93:276-281.

Dunn, E. H. and D. J. Agro. 1995. Black Tern (Chli-
donias niger). The Birds of North America, no.
147.

Erskine, A. J. 1992. Atlas of breeding birds of the
Maritime Provinces. Nimbus Publishing and Nova
Scotia Museum, Halifax, Nova Scotia, Canada.

Mazzocchi, I. M., J. M. Hickey, and R. L. Miller.
1997. Productivity and nesting habitat character-
istics of the Black Tern in northern New York.
Colonial Waterbirds 20:596-603.

Nisbet, I. C. T. 2002. Common Tern ( Sterna hirundo).
The Birds of North America, no. 618.

Schummer, M. L. and W. R. Eddleman. 2003. Effects
of disturbance on activity and energy budgets of
migrating waterbirds in south-central Oklahoma.
Journal of Wildlife Management 67:789-795.

Sirois, J. and M. A. Fournier. 1993. Clarification of
the status of the Black Tern ( Chlidonias niger) in
the Northwest Territories, Canada. Colonial Wa-
terbirds 16:208-212.

Snow, D. W. and C. M. Perrins. 1998. Black Tern
( Chlidonias niger). Pages 796-799 in The birds of
the Western Palearctic, vol. 1. Oxford University
Press, Oxford, United Kingdom.

Stewart, R. E. and H. A. Kantrud. 1984. Ecological
distribution and crude density of breeding birds
on prairie wetlands. Journal of Wildlife Manage-
ment 48:426-437.

SHORT COMMUNICATIONS

107

The Wilson Journal of Ornithology 1 18(1): 107— 108, 2006

First Observation of Cavity Nesting by a Female Blue Grosbeak

Thomas S. Rischu and Thomas J. Robinson12

ABSTRACT. — On 21 May 2003, we discovered a
completed Blue Grosbeak ( Passerina caerulea ) nest in
an Eastern Bluebird ( Sialia sialis ) nest box. On 28
May, the nest contained four whitish-tan eggs with
light-brown, streaky and spotty markings, an unusual
color pattern for Blue Grosbeak eggs. Species’ iden-
tification was confirmed by capturing the breeding fe-
male in the nest box, and confirmed again later with
identification of the chicks as Blue Grosbeaks. To our
knowledge, this is the first published account of cavity
nesting, artificial or otherwise, for this species. Re-
ceived 27 September 2004, accepted 31 May 2005.

The Blue Grosbeak ( Passerina caerulea ) is
a large bunting in the family Cardinalidae and
is relatively common in the southeastern Unit-
ed States. However, little is known of the
breeding ecology of this species (Ingold
1993). The nest is typically cup-shaped and
composed of twigs, rootlets, and bark, is often
lined with grass and/or fine hair, and some-
times contains artificial debris, such as card-
board, cellophane, or newspaper (Stabler
1959, Bent 1968, Ingold 1993). Blue Gros-
beaks commonly build their nests in riparian
thickets, fallow fields, open woodlands, and
hedgerows, usually from 1 to 4 m above the
ground (Stabler 1959, Bent 1968, Ehrlich et
al. 1988).

Here, we detail an observation of cavity
nesting by a pair of Blue Grosbeaks. We dis-
covered the nest during an ongoing study of
Eastern Bluebirds ( Sialia sialis) in Craighead
County, Arkansas. During the winter of 2002,
we erected approximately 200 Eastern Blue-
bird nest boxes at 2 m above ground, with
each box being at least 100 m from adjacent
boxes. The site is composed mostly of pas-

1 Dept, of Biological Sciences, Arkansas State
Univ., P.O. Box 599, State University, AR 72467,
USA.

2 Current address: Dept, of Biological Sciences, 331
Funchess Hall, Auburn Univ., Auburn, AL 36849,
USA.

3 Corresponding author; e-mail: trisch@astate.edu

tures and fallow fields, with some nest boxes
located along mixed-hardwood forest edge.

We checked all nest boxes at least once per
week to monitor nesting activity. On 21 May
2003, we discovered an unidentified, but com-
plete, nest without eggs in a nest box in an
area of open woodland dominated by northern
red oak ( Quercus rubra ) and bordered on one
side by a thin stand of privet ( Ligustrum spp.).
The nest was an open cup composed of grass,
fine sticks, and several interwoven pieces of
cellophane. Cellophane is commonly incor-
porated within nests of Blue Grosbeaks (In-
gold 1993), possibly as a substitute for shed
snakeskin, a common item in grosbeak nests
(Strecker 1926). It is unclear why snakeskins
are incorporated into grosbeak nests (Ingold
1993), but their addition to nest boxes with
artificial nests may decrease predation (E. C.
Medlin and TSR unpubl. data). This behavior
is common in some obligate cavity-nesting
species, including Tufted Titmouse ( Baeolo -
phus bicolor ) and Great Crested Flycatcher
( Myiarchus crinitus ). We did not measure the
nest, but the nesting material entirely covered
the floor of the nest box (10 cm wide X 15
cm deep), and the nest cup covered the rear
70% of the nest-box floor. We estimated the
inside diameter of the nest cup to be ~6— 7
cm, which is similar to grosbeak nest-cup di-
ameters reported by others (Ingold 1993).

On 28 May, we checked the nest again and
it contained four oval eggs with light-brown,
streaky and spotty markings, and a light, whit-
ish-tan background color. Although Blue
Grosbeak eggs are typically light blue to white
and unmarked (Ingold 1993), some are lightly
spotted with brown (Ingold 1993) or “dis-
tinctly marked with dots and spots of chestnut
and subdued lilac” (Davie 1898:404). The
size, color, and markings of the eggs we ob-
served were similar to those of Brown-headed
Cowbirds ( Molothrus ater), so much so that
we could not distinguish them from cowbird
eggs. Although Blue Grosbeaks are frequent

108

THE WILSON JOURNAL OF ORNITHOLOGY • Vol 118, No. 1, March 2006

hosts of Brown-headed Cowbirds, and cow-
birds are known to parasitize hosts nesting in
nest boxes (Whitehead et al. 2000, 2002), we
did not observe nest parasitism in any of our
nest boxes during our 2-year study.

Prior to the discovery of the nest, we had
observed a pair of Blue Grosbeaks near the
nest box several times over a 2-week period.
We suspected that the pair was nesting nearby,
but not in the nest box. On 8 June, however,
we captured a female Blue Grosbeak in the
nest box by using a nest-box trap (Robinson
et al. 2004); she was incubating the four eggs
described above, which appeared to be pip-
ping. When we revisited the nest again on 13
June, we found four nestlings approximately
5 days old and apparently in good condition.
We identified the nestlings as Blue Grosbeaks
(and not cowbirds) by virtue of their large
conical bills and yellow rictal flanges. Al-
though Brown-headed Cowbirds also have
conical bills, grosbeaks’ bills are obviously
larger. In addition, Blue Grosbeak chicks have
yellow rictal flanges (Baicich and Harrison
1997), whereas those of Brown-headed Cow-
bird chicks are cream-colored in the eastern
subspecies (Baicich and Harrison 1997).

On 27 June, the nestlings were no longer in
the nest. We assumed they fledged success-
fully because there were no obvious signs of
nest predation, and predation at our field site
is generally low (13% Eastern Bluebird nest
predation; TJR and TSR unpubl. data).

Our observation of Blue Grosbeaks nesting
in a nest box is unique for two reasons: (1) to
our knowledge, this is the first record of cavity
nesting by Blue Grosbeaks, and (2) the color
pattern of the eggs was unusual. We know of
few previously published reports of female
Blue Grosbeaks laying eggs with brown spot-
ty markings — a rare color pattern for Blue
Grosbeak eggs (Davie 1898, Ingold 1993).
Avian ecologists should be aware that cavity

nesting occasionally occurs in this species; the
behavior may merit closer examination.

ACKNOWLEDGMENTS

We extend our thanks to J. C. Bednarz, H. B. Fok-
idis, J. L. Ingold, M. A. Whitehead, and an anonymous
reviewer for comments on previous versions of this
manuscript. Additionally, we appreciate J. Cassady and
C. Robertson for their invaluable assistance in the
field. This research was funded by an ASU Faculty
Improvement Grant to TSR in 2003 and 2004, an Ar-
kansas Audubon Society grant to TJR in 2003 and
2004; TSR further benefited from reassignment time
from the Environmental Sciences Program at ASU.

LITERATURE CITED

Baicich, P. J. and C. J. O. Harrison. 1997. A guide
to the nests, eggs, and nestlings of North Ameri-
can birds, 2nd ed. Academic Press, San Diego,
California.

Bent, A. C. 1968. Eastern Blue Grosbeak. Pages 67-
75 in Life histories of North American cardinals,
grosbeaks, towhees, finches, sparrows, and allies
(part 1) (O. L. Austin, Jr., Ed.). U.S. National Mu-
seum Bulletin, no. 237, part 1. [Reprinted 1968,
Dover Publications, New York.]

Davie, O. 1898. Nests and eggs of North American
birds. Landon Press, Columbus, Ohio.

Ehrlich, P. R., D. S. Dobkin, and D. Wheye. 1988.
Blue Grosbeak. Page 556 in The birder’s hand-
book: a field guide to the natural history of North
American birds. Simon and Schuster, New York.
Ingold, J. L. 1993. Blue Grosbeak ( Guiraca caerulea).

The Birds of North America, no. 79.

Robinson, T. J., L. M. Siefferman, and T. S. Risch.
2004. A quick, inexpensive trap for use with nest
boxes. North American Bird Bander 29:115-116.
Stabler, R. M. 1959. Nesting of the Blue Grosbeak
in Colorado. Condor 61:46—48.

Strecker, J. K. 1926. On the use, by birds, of snakes’
sloughs as nesting material. Auk 43:501-507.
Whitehead, M. A., S. H. Schweitzer, and W. Post.
2000. Impact of brood parasitism on nest survival
parameters and seasonal fecundity of six songbird
species in southeastern old-field habitat. Condor
102:946-950.

Whitehead, M. A., S. H. Schweitzer, and W. Post.
2002. Cowbird host interactions in a southeastern
old-field: a recent contact area? Journal of Field
Ornithology 73:379-386.

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109

The Wilson Journal of Ornithology 1 18(1): 109-1 12, 2006

A New Record of the Endangered White-winged Nightjar ( Eleothreptus

candicans) from Beni, Bolivia

Tomas Grim1 3 and Radim Sumbera1 2 3

ABSTRACT. — The ecology of the White-winged
Nightjar ( Eleothreptus candicans) is poorly known.
Only three breeding populations (one from Brazil and
two from Paraguay) are known, and populations are
decreasing due to continuing destruction of cerrado
habitat. On 14 September 2003, we took several pho-
tos of an unidentified nightjar in Beni Biosphere Re-
serve, Departmento Beni, Bolivia. The bird was later
determined to be an adult male White-winged Nightjar.
Interestingly, the only previous record for Bolivia was
a male collected in 1987 at the same locality and time
of year. Because the White-winged Nightjar is non-
migratory and secretive, we hypothesize that there may
be a sustainable population of White-winged Nightjars
in Bolivia, and the paucity of sightings may be due to
the species’ low detectability. Received 16 December
2004, accepted 1 1 October 2005.

The White- winged Nightjar ( Eleothreptus
candicans ), a member of the Caprimulgidae
(Cleere 1999, Pople 2004), was recently re-
classified from the genus Caprimulgus to the
genus Eleothreptus (Cleere 2002). Its known
range and population size are very small, and
its ecology has received attention only re-
cently (Pople 2003). Parker et al. (1996) as-
signed the species High Conservation Priority
and the IUCN lists the species as Endangered
(IUCN Red List; Pople 2004). E . candicans is
threatened by ongoing loss of its cerrado hab-
itat (heavy grazing, trampling, invasive grass-
es, habitat conversion to plantations, and
large-scale, uncontrolled grass fires; Cleere
1999, Pople 2004).

Until the 1980s, White-winged Nightjars
were known only from two museum speci-
mens collected at the beginning of the 19th
century in Or^anga, Sao Paulo state, and Cu-
iaba, Mato Grosso state, Brazil (Sclater 1866).
Only three populations have been found, all

1 Dept, of Zoology, Palacky Univ., Tr. Svobody 26,
771 46 Olomouc, Czech Republic.

2 Dept, of Zoology, Univ. of South Bohemia, Bran-
isovska 31, 37005 Ceske Budejovice, Czech Republic.

3 Corresponding author; e-mail: grim@prfnw.upol.cz

in southern Brazil and eastern Paraguay: Emas
National Park, Brazil (Rodrigues et al. 1999);
Aguara Nu, Mbaracayu Forest Nature Re-
serve, Paraguay (Lowen et al. 1996, Clay et
al. 1998); and a recently discovered popula-
tion at Laguna Blanca, Departmento San Pe-
dro, central Paraguay (Anonymous 2002). Ad-
ditionally, in 1987 a single male was captured
and collected at the Beni Biological Station,
Departmento Beni, Bolivia (Davis and Flores
1994). Despite specific searches for the spe-
cies in subsequent years, however, it has not
been relocated at Beni (Brace et al. 1997,
Brace 2000, Pople 2004; R. Brace and J.
Hornbuckle in lift.).

Surveys in Aguara Nu have resulted in a
population estimate of 40—150 individuals
(Clay et al. 1998, Pople 2003) at that location.
The number of birds observed in Emas Na-
tional Park was 12 in September 1985 and
only 1 in October 1990 and in November
1997 (Rodrigues et al. 1999). Although there
are no other recently published records from
Emas, the national park probably supports a
sizeable population of E. candicans (Pople
2004) because Emas encompasses a large ex-
tent of apparently suitable habitat. The re-
cently discovered population at Laguna Blan-
ca in Paraguay is estimated to include a min-
imum of 30 birds (R. P. Clay in litt.).

On 14 September 2003 at 22:00 EDT, we
photographed an unidentified nightjar on a ter-
mite mound between the Beni Biological Sta-
tion (Estacion Biologica del Beni; 14° 50' S,
66° 17' W) and Laguna Normandia (—1.5 km
northwest of the station; see Fig. 3 in Brace
et al. 1997), Departmento Beni in northern
Bolivia. Later the bird was unambiguously
identified as a male E. candicans (Fig. 1). Be-
cause it lacked visible wear on the remiges
and pale flecking in the contour plumage, it is
probable that the individual had recently com-
pleted a molt. If the species undergoes the
same pattern of molt in both Beni Biosphere

110

THE WILSON JOURNAL OL ORNITHOLOGY • Vol. 118, No. 1, March 2006

LIG. 1. Adult male White-winged Nightjar ( Eleothreptus candicans ) photographed on 14 September 2003
in Beni Biosphere Reserve, Departmento Beni, Bolivia. Photo by R. Sumbera.

Reserve and Paraguay (i.e., replacement of
flight feathers in a single post-nuptial molt), it
suggests that the species may breed consid-
erably earlier in Bolivia than in Paraguay
(where it breeds mainly between September
and December).

Beni Biological Station is 180 km west of
Trinidad and 50 km east of San Borja on El
Porvenir Estancia. El Porvenir Estancia lies in
the Llanos de Mojos, which is a lowland plain
(—200 m elevation) characterized as savanna
with forest islands. The habitat where we ob-
served the White-winged Nightjar is a season-
ally inundated savanna with a high density of
termite mounds (Fig. 2).

Ours is only the second record of White-
winged Nightjar in Bolivia, the first having
been made in September 1987 (Davis and Flo-
res 1994). Interestingly, both observations
were made near Beni Biological Station at the
same time of year (1 1 September 1987 and 14
September 2003). Despite a number of re-
search programs that have been conducted at
the station (A. B. Hennessey in lift.), there had
been no additional records of White-winged
Nightjar after 1987. R. C. Brace and J. Horn-

buckle (in lift .), for example, searched for
White-winged Nightjars and conducted mist-
netting from mid-July through the end of Au-
gust every year from 1992 to 1999, but re-
corded no White-winged Nightjars. Although
the White-winged Nightjar is considerably
less conspicuous than many other sympatric
nightjar species common in Bolivia (R. G. Po-
ple in litt.), it seems unlikely that there would
be so few observations of the species if the
area supported a small resident population.
Rather, the two individuals recorded during
the last 2 decades may have come from an
undiscovered population elsewhere in the
northern Bolivian lowlands. However, E. can-
dicans is presumed to be a resident species.
Indeed, radio-tracking work in Paraguay (Po-
ple 2003) revealed that White-winged Night-
jars are year-round residents, and a study of
captive birds revealed a post-nuptial molt pat-
tern typical of a nonmigratory species. There-
fore, the occurrence of the two individuals at
Beni Biological Station during the same time
of year may indicate that some birds make
local movements, possibly in response to fires
(Pople 2004).

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1 1 1

FIG. 2. Typical habitat of the White-winged Nightjar — wet savanna with termite mounds providing perches
above the surrounding young vegetation. The forest in the background is Florida Fragment south of Laguna
Normandia, 1.5 km northwest of Beni Biological Station, Departmento Beni, Bolivia. The photo in Figure 1
was taken within this area. Photo by T. Grim.

Neotropical savannas are under increasing
human pressure due to large-scale conversion
of grassland habitats to pastures (Marris
2005). Although the White-winged Nightjar is
a typical savanna dweller and is adapted to
irregular and small-scale fires, it likely has
been negatively affected by regular and large-
scale burning in recent years (Brace et al.
1997, Pople 2004). Conservation of savanna
habitats — including cerrado, the primary hab-
itat for E. candicans — has been neglected thus
far. Because savanna habitats are facing great-
er threats than Amazonian rainforests, the
conservation of cerrado habitat should be-
come a top priority in the Neotropics (Marris
2005).

Our observation highlights the importance
of Beni Biosphere Reserve for threatened ( n
~ 4) and near-threatened {n = 15) bird species
in Bolivia (Brace et al. 1997). Among these
19 species are 1 1 that rely wholly or partially
on savanna habitat. So far, 500 bird species
have been reported from Beni Biosphere Re-

serve (Brace et al. 1997, Brace 2000). We add
to this list one more species: on the same day
(14 September 2003) that we observed the
White-winged Nightjar, we also recorded one
Black-throated Saltator ( Saltator atricollis).

We hypothesize that Departmento Beni in
northern Bolivia holds a resident population
of E. candicans , and that the paucity of re-
cords from Bolivia reflects the lack of inten-
sive searches during the correct season and the
low detectability of this species. We concur
with Brace et al. (1997) that more information
on the White-winged Nightjar’s status is re-
quired, and we hope that our observation pro-
vides an impetus for further research on this
elusive species.

ACKNOWLEDGMENTS

We are grateful for the detailed and helpful com-
ments and suggestions by R. R Clay and two anony-
mous referees. We thank R. C. Brace and A. B. Hen-
nessey for their comments on the manuscript and G.
Dryden for reviewing our translation to English.

112

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118 , No. 1, March 2006

LITERATURE CITED

Anonymous. 2002. A new population of the White-
winged Nightjar. World Birdwatch 24:5.

Brace, R. C. 2000. The avifauna of the Beni Biolog-
ical Station: records to 1999. Estacion Biologica
del Beni, Bolivia.

Brace, R. C., J. Hornbuckle, and J. W. Pearce-Hig-
gins. 1997. The avifauna of the Beni Biological
Station, Bolivia. Bird Conservation International
7:117-159.

Clay, R. R, D. R. Capper, J. Mazar Barnett, I. J.
Burfield, E. Z. Esquivel, R. Farina, C. P. Ken-
nedy, M. Perrens, and R. G. Pople. 1998. White-
winged Nightjars Caprimulgus candicans and cer-
rado conservation: the key findings of Project
Aguara Nu 1997. Cotinga 9:52-56.

Cleere, N. 1999. Family Caprimulgidae (nightjars).
Pages 302-386 in Handbook of the birds of the
world, vol. 5: barn-owls to hummingbirds (J. del
Hoyo, A. Elliott, and J. Sargatal, Eds.). Lynx Ed-
icions, Barcelona, Spain.

Cleere, N. 2002. A review of the taxonomy and sys-
tematics of the Sickle-winged and White-winged
nightjars (Caprimulgidae). The Bulletin of the
British Ornithologists’ Club 122:168-179.

Davis, S. E. and E. Flores. 1994. First record of
White-winged Nightjar Caprimulgus candicans
for Bolivia. The Bulletin of the British Ornithol-
ogists’ Club 1 14:127-128.

Lowen, J. C., L. Bartrina, T. M. Brooks, R. P. Clay,
and J. Tobias. 1996. Project YACUTINGA ’95:
bird surveys and conservation priorities in eastern
Paraguay. Cotinga 5:14-19.

Marris, E. 2005. The forgotten ecosystem. Nature
437:943-944.

Parker, T. A., Ill, D. F. Stotz, and J. W. Fitzpatrick.
1996. Ecological and distributional databases for
Neotropical birds. Pages 1 1 8-407 in Neotropical
birds: ecology and conservation (D. F. Stotz, J. W.
Fitzpatrick, T. A. Parker, III, and D. K. Moskov-
its). University of Chicago Press, Chicago, Illi-
nois.

Pople, R. G. 2003. The ecology and conservation of
the White-winged Nightjar Caprimulgus candi-
cans. Ph.D. dissertation, University of Cambridge,
United Kingdom.

Pople, R. G. 2004. White-winged Nightjar Eleothrep-
tus candicans. In Threatened birds of the world
2004. CD-ROM. BirdLife International, Cam-
bridge, United Kingdom.

Rodrigues, F. H. G., A. Hass, O. J. Marini-Filho, M.
M. GuimarAes, and M. A. Bagno. 1999. A new
record of White-winged Nightjar Caprimulgus
candicans in Emas National Park, Goias, Brazil.
Cotinga 11:83-85.

Sclater, P. L. 1866. Additional notes on the Capri-
mulgidae. Proceedings of the Zoological Society
of London 1866:581-590.

The Wilson Journal of Ornithology 1 18(1): 1 12-1 13, 2006

Predation of Eared Grebe by Great Blue Heron

James W. Rivers' 2 and Michael J. Kuehn1

ABSTRACT. — Great Blue Herons ( Ardea herodias)
typically prey upon fish and other aquatic organisms,
and they occasionally take small mammals and birds.
We observed a Great Blue Heron attack, kill, and at-
tempt to consume an Eared Grebe ( Podiceps nigricol-
lis). The heron was unable to swallow the grebe, and
it abandoned the carcass after approximately 30 min.
An examination of the carcass showed that the grebe
lacked obvious physical deformities. Our observation,
coupled with a similar one nearby, indicates that Great
Blue Herons attack and kill birds larger than reported
previously. Received 11 January 2005, accepted 19
September 2005.

1 Dept, of Ecology, Evolution, and Marine Biology,
Univ. of California, Santa Barbara, CA 93106. USA.

2 Corresponding author; e-mail:
rivers @ lifesci .ucsb.edu

On the morning of 14 November 2004, we
witnessed an adult Great Blue Heron {Ardea
herodias) attack, kill, and attempt to consume
an Eared Grebe {Podiceps nigricollis ) at Oso
Flaco Lake (35° 00' N, 120° 30' W) in San
Luis Obispo County, California. The incident
occurred shortly after the heron landed near
the grebe and began foraging in shallow (~30
cm deep) water. At approximately 11:25 PST,
the heron caught the grebe with a stabbing
motion as the grebe swam underwater. The
heron then proceeded to subdue the grebe by
grasping its neck, shaking it, and submerging
it intermittently. After approximately 15 min,
the grebe appeared to be dead. At this point,
the heron briefly released the grebe to deliver
several sharp blows to its head and chest area.

SHORT COMMUNICATIONS

1 13

The heron attempted several times to swal-
low the grebe, but it had difficulty maneuver-
ing the grebe into its mouth. During one at-
tempt, it was able to maneuver the carcass into
position, but the grebe’s diameter, its limp
wings, or both prevented the heron from swal-
lowing it. After attempting to swallow the
grebe for approximately 15 min, the heron
abandoned the carcass, preened briefly, and
then flew off. The grebe weighed 255 g
(weighed after the grebe was frozen and then
thawed), and although that is low body weight
for this species (Cullen et al. 1999), it is typ-
ical of grebes arriving on a wintering area af-
ter a migratory flight (Jehl 1997; J. R. Jehl,
Jr. pers. comm.). When we examined the
grebe, we found no deformities or obvious in-
dications of poor condition (e.g., loss of pec-
toral muscle).

On the day previous to our observation (13
November 2004), H. R. Pedersen (pers.
comm.) observed a Great Blue Heron at Lake
Cachuma in Santa Barbara County, California
(—130 km southeast of Lake Oso Flaco), cap-
ture an Eared Grebe. The heron was foraging
and caught the grebe in shallow water, grasped
it by the neck in the same manner we wit-
nessed, and submerged it several times. After
a brief struggle, the grebe escaped and ap-
peared unharmed (H. R. Pedersen pers.
comm.).

We know of no previous reports of Great
Blue Herons capturing, killing, and attempting
to consume Eared Grebes, or any other bird
species of that size; however, McCanch
(2003) reported a Grey Heron ( Ardea cinerea)
that had choked to death while attempting to
ingest a Little Grebe ( Tachybaptus ruficollis ).
Great Blue Herons have a diverse diet that
includes songbirds and mammals of various
sizes (Peifer 1979. Butler 1992), and they
have been observed abandoning large prey
items that they were unable to swallow (R. W.

Butler pers. comm.). Thus, it is possible that
the herons may have targeted the grebes as
potential prey items, but were unable to suc-
cessfully consume them because of their size.
Alternative explanations are (1) that the her-
ons mistook the grebes for fish or (2) that the
herons were acting to defend a foraging area.
Indeed, an observer at Lake Cachuma report-
ed seeing a foraging heron attack and kill an
American Coot ( Fulica americana) with no
attempt to eat it (L. R. Mason pers. comm.).
The heron we observed, however, expended a
substantial amount of effort subduing and at-
tempting to consume the grebe, indicating a
deliberate act of predation. Evidently, small
grebes are potential prey items for Great Blue
Herons, and herons may attack and kill large
birds more commonly than is recognized.

ACKNOWLEDGMENTS

We thank K. E. Jirik, the students of the Terrestrial
Vertebrate Ecology Laboratory course at the Univer-
sity of California-Santa Barbara, and members of the
Pomona Valley and Golden Gate Audubon Societies
for their assistance with observations. H. R. Pedersen
and L. R. Mason kindly shared their observations of
foraging herons; R. W. Butler provided helpful discus-
sion; and J. R. Jehl, N. V. McCanch, and an anony-
mous reviewer provided valuable comments on the
manuscript.

LITERATURE CITED

Butler, R. W. 1992. Great Blue Heron {Ardea hero-
dias ). The Birds of North America, no. 25.
Cullen, S. A., J. R. Jehl, Jr., and G. L. Nuechter-
lein. 1999. Eared Grebe {Podiceps nigricollis).
The Birds of North America, no. 433.

Jehl, J. R., Jr. 1997. Cyclical changes in body com-
position in the annual cycle and migration of the
Eared Grebe Podiceps nigricollis. Journal of Avi-
an Biology 28:132-142.

McCanch, N. 2003. Grey Heron choking on Little
Grebe. British Birds 96:86.

Peifer, R. W. 1979. Great Blue Herons foraging for
small mammals. Wilson Bulletin 91:630-631.

114

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

The Wilson Journal of Ornithology 1 18(1): 1 14-1 16, 2006

Abnormal Eggs and Incubation Behavior in Northern Bobwhite

Fidel Hernandez,1 2 Juan A. Arredondo,1 Froylan Hernandez,1 Fred C. Bryant,1 and

Leonard A. Brennan1

ABSTRACT. — A long-term (>5 years) study of
Northern Bobwhite ( Colinus virginianus) provided the
first record of runt eggs and two observations of pro-
longed incubation. During 2004, we located two
clutches (n = 11 and 9 eggs) — laid by the same hen —
consisting entirely of runt eggs. Mean length, width,
and mass were 18.8 mm, 15.4 mm, and 2.0 g, respec-
tively, 26% of the volume and 24% of the mass of
typical bobwhite eggs. Based on our long-term data
set for bobwhites ( n = 3,566 eggs), runt eggs occur at
a frequency of 0.56%, within the range (0.02-4.32%)
reported for other avian species. The two records of
prolonged incubation behavior represented 75 days
(326%) and 47 days (204%) beyond the normal incu-
bation period (23 days) of bobwhites. This prolonged
incubation behavior is in excess of the time frame re-
ported for most birds exhibiting prolonged incubation
(50-100% beyond normal incubation). Received 31
January 2005, accepted 3 October 2005.

Documenting anomalies in avian behavior
often is an opportunistic endeavor given the
rarity of such behavior and the short-term na-
ture (<2 years) of most studies. An ongoing,
long-term (>5 years) radiotelemetry project
(The South Texas Quail Research Project;
STxQRP) on Northern Bobwhite ( Colinus vir-
ginianus) provided us with the opportunity to
monitor bobwhite behavior over seven breed-
ing seasons (1998-2004) on the Encino Di-
vision of the King Ranch, Inc.. Brooks Coun-
ty, Texas. We provide the first record of runt
eggs for Northern Bobwhite and two addition-
al records of prolonged incubation behavior.

First record of runt eggs. — Runt eggs, also
referred to as dwarf, cock, wind, and witch
eggs (Rothstein 1973), are those noticeably
smaller than the smallest expected for a given
species (Mulvihill 1987; for suggested crite-
ria, see Koenig 1980a). Although runt eggs
have been reported for several avian species

1 Caesar Kleberg Wildlife Research Inst., Texas
A&M Univ., Kingsville, TX 78363, USA.

2 Corresponding author; e-mail:
fidel.hernandez@tamuk.edu

(e.g., Canada Goose, Branta canadensis
[Manning and Carter 1977]; woodpeckers [Pi-
cidae, Koenig 1980b]; and Eastern Bluebird,
Sialia sialis [Mulvihill 1987]), they normally
occur at low frequencies (~1 per 1,000 to
2,000 eggs; Koenig 1980b. Mallory et al.
2004). Furthermore, runt eggs usually repre-
sent only a small proportion of a clutch (Roth-
stein 1973, Ricklefs 1975, Bartel 1986). Entire
clutches consisting solely of runt eggs are ex-
tremely rare and have been reported only for
Song Thrush ( Turdus philomelos; M’Wiliiam
1927), Gray Catbird ( Dumetella carolinensis ;
Rothstein 1973), and Eastern Bluebird (Ze-
leny 1983). We report the first record of runt
eggs for Northern Bobwhite and provide es-
timates of the frequency of such eggs.

On 21 June 2004, we located a radiomarked
hen on a nest at the base of brownseed pas-
palum ( Paspalum plicatulum ). The clutch
consisted entirely of runt eggs ( n = 11). We
monitored the hen for several days thereafter,
but never located her at the nest site again.
We concluded that she had abandoned the nest
and we collected the eggs. During the follow-
ing 5 weeks, the hen again paired with a male,
and on 30 July, we documented a second
clutch of runt eggs (n = 9) in a nest con-
structed in red lovegrass ( Eragrostis secun-
diflora). The hen also abandoned this nest, and
we collected the clutch on 2 August.

None of the runt eggs was viable (i.e., none
contained yolk). Mean length, width, and
mass of the runt eggs {n = 20) were 18.8 mm,
15.4 mm, and 2.0 g, respectively. The smallest
reported measurements for bobwhite eggs are
26 mm (length) and 22.5 mm (width) (Bent
1932), and 8.2 g (Case and Robel 1974). Koe-
nig (1980a) defined runt eggs as those with a
relative volume (length X width2 X tt/6)
<75% of the average. Mean length, width,
and mass of bobwhite eggs are 30 mm, 24
mm, and 8.3 g, respectively (Bent 1932, Case
and Robel 1974). Thus, the volume and mass

SHORT COMMUNICATIONS

of the runt eggs we found were only 26% and
24%, respectively, of the average.

We used data from STxQRP and Hernandez
(1999) to estimate the frequency of runt eggs
in Northern Bobwhite. During 1999-2004 of
the STxQRP, we located 392 nests and deter-
mined clutch size for 297 nests ( n = 3,161
eggs). Hernandez (1999) located 83 bobwhite
nests in Shackelford County, Texas during
1997-1998 and determined clutch size for 35
nests ( n = 385 eggs). Based on these com-
bined data (3,546 normal-sized eggs + 20 runt
eggs), runt eggs in bobwhites occur at a fre-
quency of 0.56%, which is within the range
(0.02-4.32%) reported for other avian species
(Koenig 1980b, Mallory et al. 2004).

The mechanisms underlying the production
of runt eggs are not entirely understood (Mul-
vihill 1987). However, runt eggs often are pro-
duced after temporary disturbance or damage
(e.g., injury or infection) to the reproductive
organs (Pearl and Curtis 1916, Romanoff and
Romanoff 1949). Instances of entire clutches
being composed of runt eggs suggest a con-
genital defect or permanent injury to the re-
productive system (Mulvihill 1987). We pre-
sume the bobwhite hen that laid the runt eggs
may have suffered from some type of per-
manent injury to her reproductive organs.

Prolonged incubation behavior. — Pro-
longed incubation beyond the normal time re-
quired for hatching has been reported for
many avian species, including Killdeer ( Cha -
radrius vociferus'. Powers 1978), Common
Loon ( Gavia immer\ Sutcliffe 1982), and
Long-eared Owl ( Asio otus\ Marks 1983).
Most birds that exhibit prolonged incubation
appear to incubate for at least 50-100% lon-
ger than necessary to hatch a clutch (Skutch
1962). Prolonged incubation (56 days) has
been reported only once for Northern Bob-
white (Stoddard 1931), which is 33 days
(143%) beyond the average incubation period
(23 days). We report two additional records of
prolonged incubation for Northern Bobwhite.

During our first observation of prolonged
incubation, a bobwhite hen exhibited normal
incubation behavior during a first nesting, and
the eggs successfully hatched on 7 July 2003.
However, the hen exhibited prolonged incu-
bation of a second clutch. We discovered the
nest on 1 1 August, and by 8 September, only
1 of 10 eggs had hatched. The female was not

1 15

observed on the nest between 9 and 25 Sep-
tember, but on 26 September, the hen returned
to the nest and resumed incubation until 5 De-
cember. Thus, the hen incubated the eggs for
28 days, abandoned the nest for 17 days, and
then resumed incubation for another 70 days.
The 98 days of incubation was 75 days
(326%) beyond the normal incubation period
for bobwhites.

We documented the second occurrence of
prolonged incubation during the 2004 nesting
season. On 18 June, we accidentally flushed
an un-radiomarked hen from a nest. We re-
turned to the nest site on 12 July, presuming
the clutch had hatched, and found her still in-
cubating the clutch. The hen continued incu-
bating until 27 August, when the clutch was
depredated. Assuming the hen had just begun
incubation when we first found the nest, she
incubated for at least 70 days, or 47 days
(204%) beyond the normal incubation period
for bobwhites.

Although only 1 of 10 eggs hatched in our
first observation of prolonged incubation,
Murray and Frye (1957) suggest that the
hatching of even one egg is sufficient to sat-
isfy the nesting instinct. In our observation,
however, the hen continued incubation even
though only one egg hatched. Hurst (1978)
observed a similar phenomenon, during which
a bobwhite hen continued incubation of par-
tially hatched, dead chicks. The clutch con-
sisted of 10 eggs: 1 infertile, 1 completely
hatched, and 8 partially hatched. The eight
partially hatched eggs contained fully devel-
oped chicks that had pipped and partially
ringed their eggshells but had become “en-
tombed.” Hurst (1978) did not report the
length of time that the hen remained on the
partially hatched eggs.

Prolonged incubation is thought to provide
a safety margin for eggs that take longer than
normal to hatch (Skutch 1962, Holcomb
1970). However, Holcomb (1970) suggested
that prolonged incubation would be maladap-
tive for species capable of renesting. Bob-
whites commonly renest two or three times
per breeding season, regardless of previous
nest fate (Stoddard 1931). Given that the two
records of prolonged incubation occurred to-
ward the end (July-August) of the normal
nesting season for bobwhites (May-August),
the opportunity for renesting was limited and

116

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

may have contributed to prolonged incuba-
tion.

ACKNOWLEDGMENTS

This research was supported by the George and
Mary Josephine Hamman Foundation; Amy Shelton
McNutt Charitable Trust; William A. and Madeline
Welder Smith Foundation; Bob and Vivian Smith
Foundation; Robert J. Kleberg, Jr., and Helen C. Kle-
berg Foundation; Texas State Council of Quail Unlim-
ited; the South Texas, Houston, East Texas, and Alamo
Chapters of Quail Unlimited; the South Texas Celeb-
rity Weekend; Quail Associates; private contributions;
King Ranch, Inc.; and San Tomas Hunting Camp. We
thank B. M. Ballard, D. G. Hewitt, and three anony-
mous reviewers for providing helpful comments on an
earlier version of this manuscript. Data for this re-
search were provided by the South Texas Quail Re-
search Project. This manuscript is Caesar Kleberg
Wildlife Research Institute Publication Number OS-
Ill.

LITERATURE CITED

Bartel, K. E. 1986. Another record of runt eggs for
the Tree Swallow. North American Bird Bander
1 1:3-4.

Bent, A. C. 1932. Eastern, Florida, and Texas Bob-
white. Pages 9-36 in Life histories of North
American gallinaceous birds. U.S. National Mu-
seum Bulletin, no. 162. [Reprinted 1963, Dover
Publications, New York.]

Case, R. M. and R. J. Robel. 1974. Bioenergetics of
the Bobwhite. Journal of Wildlife Management
38:638-652.

Hernandez, F. 1999. The value of prickly pear cactus
as nesting cover for Northern Bobwhite. Ph.D.
dissertation, Texas A&M University, Kingsville
and College Station.

Holcomb, L. C. 1970. Prolonged incubation behaviour
of Red-winged Blackbird incubating several egg
sizes. Behaviour 36:74-83.

Hurst, G. A. 1978. Unusual incubation behavior in
Bobwhite. Wilson Bulletin 90:290-291.

Koenig, W. D. 1980a. The determination of runt eggs
in birds. Wilson Bulletin 92:103-107.

Koenig, W. D. 1980b. The incidence of runt eggs in
woodpeckers. Wilson Bulletin 92:169-176.

Mallory, M. L„ L. Kiff, R. G. Clark, T. Bowman,
P. Blums, A. Mednis, and R. T. Alisauskas.
2004. The occurrence of runt eggs in waterfowl
clutches. Journal of Field Ornithology 75:209-
217.

Manning, T. H. and B. Carter. 1977. Incidence of
runt eggs in the Canada Goose and Semipalmated
Sandpiper. Wilson Bulletin 89:469.

Marks, J. S. 1983. Prolonged incubation by a Long-
eared Owl. Journal of Field Ornithology 54:199-
200.

Mulvihill, R. S. 1987. Runt eggs: a discovery, a syn-
opsis, and a proposal for future study. North
American Bird Bander 12:94-96.

Murray, R. W. and O. E. Frye, Jr. 1957. The Bob-
white quail and its management in Florida. Game
Publication 2, Florida Game and Fresh Water Fish
Commission, Tallahassee, Florida.

M’William, J. M. 1927. Some abnormal eggs of wild
birds. Scottish Naturalist 66:108-110.

Pearl, R. and M. R. Curtis. 1916. Studies on the
physiology of reproduction in the domestic
fowl — XV. Dwarf eggs. Journal of Agricultural
Research 6:977-1042.

Powers, L. R. 1978. Record of prolonged incubation
by a Killdeer. Auk 95:428.

Ricklefs, R. E. 1975. Dwarf eggs laid by a starling.
Bird Banding 46:169.

Romanoff, A. L. and A. J. Romanoff. 1949. The avi-
an egg. John Wiley and Sons, New York.

Rothstein, S. I. 1973. The occurrence of unusually
small eggs in three species of songbirds. Wilson
Bulletin 85:340-342.

Skutch, A. F. 1962. The constancy of incubation. Wil-
son Bulletin 74:115-152.

Stoddard, H. L. 1931. The Bobwhite quail: its habits,
preservation and increase. Charles Scribner’s
Sons, New York.

Sutcliffe, S. 1982. Prolonged incubation behavior in
Common Loons. Wilson Bulletin 94:361-362.

Zeleny, L. 1983. Miniature bluebird eggs. Sialia 5:
127-128.

The Wilson Journal of Ornithology 1 18(1): 1 17-1 19, 2006

Once Upon a 1 lime in [American Ornithology

George Bird Grinnell, the “father of Amer-
ican conservation,” was born in 1849. He ul-
timately would spearhead a movement for the
preservation of North American waterfowl,
lay the foundation for the national park sys-
tem, lead the way in ending the commercial
taking of wildlife, and help found the Amer-
ican Ornithologists’ Union, Boone and Crock-
ett Club, and Audubon Society. Schooled for
a time by Lucy Bakewell Audubon, John
James Audubon’s widow, Grinnell grew up in
Audubon Park, the former 12-ha Audubon es-
tate on Manhattan Island in New York City.
“Grandma” Audubon’s tutelage, hunting ex-
periences with Audubon’s grandson. Jack, and
frequent visits to the homes of Audubon’s
sons, Victor and John Woodhouse Audubon —
where rifles and shotguns, powder horns and
shot, animal trophies, bird paintings, and box-
es of bird skins were always about — were for-
mative, and predisposed Grinnell’s future as a
naturalist and conservationist. At the age of
25, four years after receiving a B.A. from Yale
University in 1870, Grinnell was asked by pa-
leontologist O. C. Marsh, head of the Peabody
Museum in New Haven, Connecticut, to ac-
company him on an army-sponsored expedi-
tion of the Black Hills, South Dakota. Com-
manded by Col. George Armstrong Custer, the

60-day expedition set out on 2 July 1874 from
Fort Abraham Lincoln, just across the Mis-
souri River from Bismarck, North Dakota. Be-
cause trouble was expected from hostile In-
dians, the military command consisted of 10
companies of the 7th Calvary, 2 companies of
Infantry, and a battery of 3 Gatling guns. In
all, there were 1,200 men and their horses,
wagons, a beef herd, and Indian scouts (Fig.
1). Military goals were to explore unmapped
Indian Territory and investigate rumors of
gold; the scientists, or “bug hunters” as the
military called them, were along to collect
specimens and fossils.

The following ornithological event was re-
corded by Grinnell as he accompanied Cus-
ter’s exploration of the Black Hills, about 22
months before the battle of Little Bighorn
(Greasy Grass). The incident took place in late
August as the troops were on their return trip
to Fort Abraham Lincoln from the west. Grin-
nell was subsequently invited to accompany
the inglorious 1876 expedition as naturalist,
but he had a professional conflict that kept
him home. The original reference is Grinnell,
G. B. 1875. Zoological Report. Pages 79-102
in Report of a reconnaissance of the Black
Hills of Dakota made in the summer of 1874.
(W. Ludlow). U.S. Army Department of En-
gineers.—FRITZ L. KNOPF

August 28. — About 6.30 a.m., while we were halting for a short time on a little
knoll, a most interesting and exciting chase came under my observation. The ground
was wet from the rain that had but just ceased to fall, and the men were, most of
them, standing by their horses, instead of lying asleep on the ground, as is usually
the case when a halt is made. I was looking out over the plain, when I observed
two birds in rapid flight, approaching the hill where we were standing. They flew
with astonishing velocity, and it was but a short time before they were quite near
us. From the manner of their flight, I at first thought they were two falcons engaged
in play, but a nearer view showed me that the foremost bird was much the smallest,
and that it was making most strenuous efforts to escape from its pursuer by darting
and twisting from one side to the other, up or down, or by straightforward flight.
In one of its turnings it came quite close to the column, and, forgetting in its intense
fear its natural shyness, it darted in among the men and horses. The larger bird, a
peregrine falcon, as I could now see, hesitated not an instant, but dashed after,
following the object of its pursuit in every cut and twist that it made, now passing
under the horses, now low over their backs or close to the men’s heads. After,
perhaps, a minute of rapid pursuit, the smaller bird by a quick double put a group
of men and horses between itself and the falcon, and then darted swiftly along the
ground to where I was standing, an interested observer. Here, almost exhausted, it

117

118

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

FIG. 1 . The 1 874 Custer Expedition returning from the Black Hills of South Dakota, photographed by
William H. Illingworth. The expedition included 1,200 men and 1 10 wagons, here seen between the Black Hills
and Fort Abraham Lincoln, Dakota Territory, near the modern day South Dakota and North Dakota border.
Photograph taken in the vicinity of George Bird Grinnell’s account of a Peregrine Falcon ( Falco peregrinus )
pursuing a Passenger Pigeon ( Ectopistes migratorius). Custer is on horseback in the foreground with his wagon
behind him; in the distance, the expedition is aligned in four columns. Grinnell is believed to be one of three
individuals (in the middle on a mule) mounted and slightly forward of the expedition. Photo courtesy of the
South Dakota State Historical Society-State Archives.

alighted on the saddle of a horse standing within arm’s length of me, and I was
able to distinguish that it was a passenger pigeon, ( Ectopistes migratoria). Mean-
while, the falcon, baffled for a moment, had risen 30 feet in the air, and was
hovering over the group, looking for his prey. Hardly ten seconds had elapsed since
the pigeon alighted, when he saw his pursuer above him, and, terror-stricken by
the sight, the luckless bird darted away again over the open prairie. The falcon
followed, and the doubling and twisting recommenced before they had gone a
quarter of a mile. The pigeon once tried to regain the shelter of the command, but
his relentless pursuer cut him off and drove him toward the plain, and, in a few
seconds, by a tremendous burst of speed, caught up to his victim, and, throwing
out his powerful feet, seized him, and, without checking his flight, bore him off to

ONCE UPON A TIME IN AMERICAN ORNITHOLOGY

1 19

a neighboring butte, there to devour him. It was a splendid sight, and I can compare
it to nothing unless it be a scene of ancient falconry, the only difference being that
the birds were so much more evenly matched than in the old-time sports. It would,
I think, be difficult to name a harder bird to catch than the pigeon, and, perhaps,
the only bird that can do it in a straight-away chase is the peregrine falcon. I should
mention that the soldiers made efforts to frighten the hawk away by shouting and
throwing their hats at it, but it paid no attention to their demonstrations, except
once to stretch out its feet as if to grasp a hat that sailed close by it.

The Wilson Journal of Ornithology 1 18(1): 120-127, 2006

Ornithological Literature

Compiled by Mary Gustafson

THE NORTH AMERICAN BANDERS’
MANUAL FOR BANDING SHOREBIRDS
(CH ARADRHFORMES , SUBORDER CHA-
RADRII). By Cheri L. Gratto-Trevor. North
American Banding Council, Point Reyes Sta-
tion, California. 2004: 45 pp., 4 color plates, 15
figures, 1 table, 8 appendices. Available at no
charge from www.nabanding.net/nabanding/
pubs.html. — This manual, intended to be an in-
tegral part of the North American Banding
Council Study Guide, should be required read-
ing for anyone capturing shorebirds (waders).
After introductory sections on the ethics of
banding and some of the factors to consider
when devising a study program, this publica-
tion offers a synthesis of the various methods
used to capture shorebirds in their breeding,
passage, and wintering habitats. This group of
species has tested human ingenuity; thus,
many of the 1 80 references from the published
literature included in this manual are about
trapping techniques. There is also useful ma-
terial on marking techniques, including bands,
color bands, dye-marking, radio tracking, and
so on. Although much of this material is avail-
able elsewhere, it was scattered in many
sources, and it is well worthwhile having it
compiled in one publication. The many per-
sonal communications add to the book’s val-
ue, including many of the little tricks that are
often passed on by word of mouth.

The manual also includes a useful table that
summarizes all that a bander needs to know
for each species: American Ornithologists’
Union code. Birds of North America refer-
ence, band size, methods for determining age
and sex, and any problems often encountered
when trapping, handling, and banding the spe-
cies.

As an English ringer of wading birds (albeit
with experience in banding shorebirds on four
continents), I was struck by the different ap-
proach taken in this publication. In many oth-
er countries, extensive long-term studies of
waders carried out primarily by volunteers
have provided ample opportunities to develop
methods for safely handling hundreds, and oc-

casionally thousands, of birds at a time. The
target audience of this manual, however, is
North American banders, who often are pro-
fessional ornithologists — but inexperienced in
studying shorebirds — usually undertaking
short-term studies, often of small numbers of
birds. Capturing shorebirds can indeed be a
specialized art, at times potentially dangerous
for birds and for banders, and should not be
undertaken lightly. The exceptionally detailed
and thorough treatment here, of all aspects of
the process, should help ornithologists maxi-
mize the scientific value of their work on
shorebirds, and minimize the danger to them-
selves or their subjects. The emphasis
throughout is on safe methods of capturing
and handling. Given the international knowl-
edge base on these birds — many of which are
themselves great international travelers — the
author has succeeded in pulling together in-
formation from around the world to develop
this manual, and all banders can probably
learn something from reading it.

There is, unfortunately, one significant fail-
ing in the publication — an Appendix on age-
ing calidrid shorebirds in which the photo-
graphs are the worst that I have ever seen pub-
lished. The birds’ feathers are so disheveled
that, not only do they reflect poorly on band-
ing, they make it very difficult to discern the
plumage characters that the photographs are
intended to illustrate. These days, with pho-
tographic equipment so easy to use, and, in-
deed, with so many high-quality images ap-
pearing on Web sites and elsewhere, there is
no excuse for publishing such poor photo-
graphs. The flawed appendix should not de-
tract from the value of this publication, but
users of the manual should obtain other ref-
erence materials for ageing shorebirds. This
useful manual should surely be obligatory
reading for all who capture shorebirds.

— DAVID NORMAN, Merseyside Ringing
Group, England, and Carnegie Museum of
Natural History, Powdermill Avian Research
Center, Pennsylvania; e-mail: david.norman@
physics.org

120

ORNITHOLOGICAL LITERATURE

121

A PASSION FOR WILDLIFE: THE HIS-
TORY OF THE CANADIAN WILDLIFE
SERVICE. By J. Alexander Burnett. UBC
Press, Vancouver, British Columbia. 2003: 331
pp., numerous photos. ISBN: 0774809604,
C$85.00 (cloth). ISBN: 0774809612, C$27.95
(paper). — In 1947, in what appears to be an
endless series of reorganizations, the Canadian
government reorganized the Department of
Resources and Government and gave birth to
the Dominion Wildlife Service, which carried
much of the responsibility for wildlife in Can-
ada. Initially, the agency was staffed by fewer
than 30 people, but it included several sea-
soned ornithologists, including George Boyer
and Oliver Hewitt. The early years were chal-
lenging— in 1949, Newfoundland and Labra-
dor joined the Canadian Confederation, bring-
ing with them segments of their population
that traditionally harvested vast numbers of
seabirds and their eggs. In 1950, the Wildlife
Service became a division of the National
Parks Branch, and chief Harrison secured per-
mission to rename the division the Canadian
Wildlife Service (CWS) — the name it still
holds today. This book recounts the nearly
half-century history of the CWS.

The book is divided into 10 chapters and
an epilogue. The first chapter covers the gen-
esis of the CWS and provides an historical
context through a synopsis of Canadian wild-
life policy up to the 1940s. The remaining
chapters are topical, each focusing on an as-
pect of the CWS’s diverse agenda. Chapter 2
describes the CWS involvement in enforcing
the Migratory Birds Convention Act of 1917.
This included the difficult and sensitive task,
conducted by Leslie Tuck and others, of
bringing some level of enforcement to the ru-
ral populations of Newfoundland and Labra-
dor who depended on seabird harvest for sub-
sistence. Managers required information, and
surveys and other scientific research became
an integral part of the CWS. Chapter 3 em-
phasizes working with birds — during the first
50 years of the CWS, ornithology was the pre-
eminent scientific concern. In the early years,
waterfowl research tended to dominate the
agenda, but seabird research became, and re-
mains, important, and research has been di-
rected at a broad spectrum of problems (e.g.,
bird strikes at airports). The contributions of
prominent CWS seabird biologists (e.g., Les-

lie Tuck, David Nettleship, Hans Blokpoel,
Kees Vermeer, Rob Butler, Tony Gaston, and
many others) are chronicled in the chapter.

Chapters 4 and 5 cover mammals and fish,
and chapter 6 describes the shift in conser-
vation strategy — from a focus on species to
habitat preservation and continental-scale
thinking — that began in the 1970s. The chap-
ter also traces changes in the CWS with re-
gionalization of administrative control. Chap-
ter 7 describes efforts to foster public aware-
ness and understanding of wildlife values and,
hence, securing public support for conserva-
tion initiatives. This involved the cooperation
of CWS personnel with filmmakers and the
establishment of wildlife interpretation cen-
ters. This chapter also tells the painful story
of consolidation during the late 1970s and ear-
ly 1980s, when federal budget cuts caused a
thorough reexamination of CWS priorities, as
the government cut off funds, for example, for
the wildlife interpretation centers.

Chapter 8 deals with the growing field of
wildlife toxicology, precipitated by the dev-
astating effects of DDT. It describes programs
designed to investigate avian ingestion of
crude oil, as well as problems with pesticide
use in agriculture and forestry. Chapter 9 cov-
ers endangered species, including many birds.
Chapter 10, Defining the Rules: Wildlife Gov-
ernance, describes a series of initiatives that
had come to fruition by the 1990s (e.g.,
amendments to the Canadian Wildlife and Mi-
gratory Birds Convention acts, Ramsar des-
ignation for suitable wetlands sites in Canada,
and the Western Hemisphere Shorebird Re-
serve Network). The Epilogue, The Canadian
Wildlife Service: A Work in Progress, high-
lights important aspects of the CWS and
brings closure to this historical account.

This book is thoroughly researched and
very well written. The author does not shy
away from, or gloss over, problems that have
been part of the CWS (e.g., federal versus pro-
vincial authority, research versus management
mandates, or the disastrous budget cuts of the
early 1980s). He has managed to provide an
even-handed history of the CWS. I am sure
that many people who have had careers in the
CWS would disagree on details and, perhaps,
emphasis, but I find this a well-balanced his-
tory of an important North American conser-

122

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 1 18, No. 1, March 2006

vation institution. It should be of interest to
any historically oriented ornithologist.
—WILLIAM E. DAVIS, JR., Boston Univer-
sity, Boston, Massachusetts; e-mail: wedavis@
bu.edu

WHALES & DOLPHINS OF THE
WORLD. By Mark P. Simmonds, photogra-
phy by seapics.com. The MIT Press, Cam-
bridge, Massachusetts. 2004: 160 pp., 180
full-color photographs, 1 color map. ISBN
0262195194. $29.95 (cloth).— This book
takes on the challenging task of introducing
80-plus species of whales and dolphins to the
general public, while at the same time provid-
ing many spectacular photographs to get
across the author’s conservation message.
This large-format book (9.5' X 12.5') takes
advantage of its size by including lots of pho-
tos. The photos come from seapics.com, an
image library containing the works of over
200 marine and underwater photographers,
many of whom are internationally known.
This is the marine wildlife equivalent of the
bird photo archives provided by VIREO (Vi-
sual Resources for Ornithology), and enables
the author to illustrate his book with some tru-
ly stunning photos, including some of very
rare species like that of a breaching Blain-
ville’s beaked whale {Mesoplodon densiros-
tris). The text is easy to read and clearly writ-
ten to introduce whales and dolphins to the
general public so that people will become
more informed about the conservation issues
affecting cetaceans. At the same time, the
book includes some of the latest scientific
findings and taxonomic changes.

The book is divided into 5 chapters. The
first 2 chapters cover whale biology, behavior,
and some general information for each of the
14 cetacean families. Because some families
are poorly known or include fewer species,
the general accounts can vary in length from
just 2 pages (porpoises and beaked whales) to
12 pages (marine dolphins). The family ac-
counts include both general descriptive infor-
mation and detailed information, such as
breeding biology, habitat, prey, and feeding
strategies if known. Each account also in-
cludes information on current and past con-
servation threats, such as whaling and habitat

disturbances. There are also short sections on
cetacean physiological adaptations, migration,
intelligence, and echolocation. The first 2
chapters compose two-thirds of the book
(—100 pp.), while the final third (60 pp.) in-
cludes a chapter on interactions between man
and whales and 2 chapters on conservation
threats and current measures being taken to
protect cetaceans. At the end of the book is a
rather uninteresting 2-page color map of the
world showing cetacean habitats; however, it
does not include much detail other than basic
ocean temperature zones and river dolphin
ranges. There is also a nice comprehensive list
of all the cetacean species, subdivided by fam-
ilies, that includes Latin names, a bibliogra-
phy of Web sites and book titles, a very gen-
eral and basic 1-page glossary, and a page of
interesting facts and figures on cetaceans (e.g.,
the longest-lived mammal — the bowhead
whale, Balaena mysticetus — can live more
than 200 years).

The 180 photographs are what really make
this book interesting, especially since it is just
160 pages long. Included are some incredible
action shots like an orca ( Orcinus orca ) just
about to make a meal of a mako shark ( Isurus
oxyrinchus ) and another of copulating Atlantic
spotted dolphins ( Stenella frontalis ). My fa-
vorite was a photo of a snorkler alongside a
sperm whale ( Physeter macrocephalus ) that
fills two full pages, although it is somewhat
ruined by a large chapter heading on one of
the pages. By using photos from seapics.com,
the author is able to draw from an almost lim-
itless collection of quality images. Many of
the photos appear to be published for the first
time in this book, although some have previ-
ously appeared in other publications. None-
theless, the quality of the reproductions is
good.

This is an easy book to recommend to any-
one with an even slight interest in marine
mammals. As stated in the introduction, the
book “is intended as both a celebration of the
whales and dolphins of the world and an in-
troduction to their diversity, biology and con-
servation.” It certainly meets that goal. The
author is the Director of Science at the Whale
and Dolphin Conservation Society, and the
book is written to promote their conservation
views; in fact, the royalties from the book are
donated to the society. Whereas several other

ORNITHOLOGICAL LITERATURE

123

recent books serve as excellent marine mam-
mal field guides, this book was intended for a
wider audience and would make a nice addi-
tion to any library. You will probably find
yourself looking through and marveling at the
photos again and again, as I did. — MICHAEL
FRITZ, See Life Paulagics, Seaville, New Jer-
sey; e-mail: mike@paulagics.com

PARTNERS IN FLIGHT: NORTH AMER-
ICAN LANDBIRD CONSERVATION
PLAN. By Terrell D. Rich, Carol J. Beard-
more, Humberto Berlanga, Peter J. Blancher,
Michael S. W. Bradstreet, Greg S. Butcher,
Dean W. Demarest, Erica H. Dunn, W. Chuck
Hunter, Eduardo E. Inigo-Elias, Judith A.
Kennedy, Arthur M. Martell, Arvind O. Pan-
jabi, David N. Pashley, Kenneth V. Rosen-
berg, Christopher M. Rustay, J. Steven Wendt,
and Tom C. Will. Cornell Lab of Ornithology,
Ithaca, New York. 2004: 84 pp. Available at
no charge from www.partnersinflight.org. —
The long-awaited Partners in Flight [PIF]
Landbird Conservation Plan arrived with
much fanfare, and deservedly so. This broad
plan will serve as the starting point for bird
conservation planning throughout the U.S.
and Canada. A future planned revision will
incorporate Mexican species, expanding the
utility of the plan to the continental scale.

The plan starts with a description of how it
was created and how it should be implement-
ed, in addition to definitions of terms and var-
ious ranking factors. A total of 448 species
that nest in North America are included.
Landbirds are defined to include species in 45
families. These families include Cathartidae
plus those within the following orders: Galli-
formes, Falconiformes, Columbiformes, Psit-
taciformes, Cuculiformes, Strigiformes, Ca-
primulgiformes, Apodiformes, Trogoniformes,
Coraciiformes, Piciformes, and Passeriformes;
13 more families (including Tinamidae) will
be added when the plan is revised to include
Mexico. The plan also provides guidance on
Conservation Issues and Recommendations
for seven Avifaunal Biomes: Arctic, Northern
Forest, Pacific, Intermountain West, South-
west, Prairie, and Eastern.

At the core of the plan are the PIF Species
of Continental Importance, composed of 100

Watch List Species and 91 Stewardship Spe-
cies. The Watch List Species were determined
through Assessment Scores (from 1 to 5) of
the Population Size, Breeding Distribution,
Non-breeding Distribution, Threats to Breed-
ing Population, Threats to Non-breeding Pop-
ulation, and Population Trend for each indi-
vidual species. The Combined Score is deter-
mined by summing Population Score, the
highest of the Distribution and Threats scores,
and the Population Trend score, for a maxi-
mum of 20.

Species with Combined Scores of 14 and
up comprise the Watch List; species with a
Combined Score of 13 and a Population Trend
of 5 were also added to the Watch List. Six
species had Combined Scores of 12 and Trend
Scores of 5, including Northern Bobwhite
( Colinus virginianus ), Loggerhead Shrike
( Lanius ludovicianus ), Field Sparrow ( Spizella
pusilla), Lark Sparrow ( Chondestes gramma-
cus ), Black-throated Sparrow ( Amphispiza bil-
ineata ), and Grasshopper Sparrow (Ammodra-
mus savannarum ). One species, the Eastern
Meadowlark ( Sturnella magna), had a Com-
bined Score of 11 and a Trend Score of 5, but
no species had a lower Combined Score and
a Trend Score of 5. A whopping 43 species
that had Combined Scores of 13 and Trend
Scores of less than 5 did not make the Watch
List.

Several species rated the maximum score,
including Gunnison Sage-Grouse ( Centrocer -
cus minimus ), Lesser Prairie-Chicken ( Tym -
panuchus pallidicinctus ), California Condor
( Gymnogyps californianus ), Thick-billed
( Rhynchopsitta pachyrhyncha) and Red-
crowned parrots ( Amazona viridigenalis ), Ivo-
ry-billed Woodpecker ( Campephilus princi-
palis), Black-capped Vireo ( Vireo atricapilla ),
Florida Scrub-Jay ( Aphelocoma coerules-
cens), and Bachman’s ( Vermivora bachmanii)
and Kirtland’s warblers ( Dendroica kirtlan-
dii ). This varied group includes species absent
from the USFWS endangered species list
(Gunnison Sage-Grouse, Lesser Prairie Chick-
en, Thick-billed and Red-crowned parrots),
two species that were previously all but writ-
ten off as extinct but present on the endan-
gered species list (Ivory-billed Woodpecker
and Bachman’s Warbler), and species that are
heavily managed endangered species (Califor-

124

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

nia Condor, Black-capped Vireo, Florida
Scrub-Jay, and Kirtland’s Warbler).

The Population Size Ranking Factor in-
cludes a Global Population Estimate, a number
difficult to determine for most bird species. I
find these estimates to be interesting and
thought provoking, though I continue to be
puzzled by the disparity in population esti-
mates among species. The percentage of the
population residing in the U.S. and Canada is
also estimated, and, for many species included
in the plan, < 1 % of the global population nests
in the U.S. or Canada. Expansion of the plan
to Mexico will be critical to future conserva-
tion efforts. Although Population Trend infor-
mation for each species is used as a part of the
Combined Score, the information in the Trend
Score is qualified by using the Monitoring
Needs information. The Monitoring Needs
identifies species for which trend data are lack-
ing or imprecise, as well as species affected by
poor survey coverage (e.g., those in boreal for-
ests and far northern areas). The remainder of
the species that lack an identified Monitoring
Need have a qualifier, that while monitoring is
considered adequate “some issues, such as
bias, may not have been accounted for.”

While it is easy to find fault with individual
data points or certain aspects of the plan, the
utility of the ranking process is evident in the
results. Without debating which species are
facing threats, what effect those threats might
have on a population, or whether a Ranking
Factor should be increased or decreased, the
plan will be useful for achieving bird conser-
vation at the biome, BCR, state, or habitat lev-
el. The plan is a starting point for all future
bird conservation efforts. Partners in Flight
has recently released revised ranking data for
landbirds covered in this plan on the PIF Web
site (www.partnersinflight.org). The Landbird
Conservation Plan should be required reading
for biologists and land managers as well as
those interested in bird conservation. —
MARY GUSTAFSON, Texas Parks and Wild-
life Department, Mission, Texas; e-mail:
Mary.Gustafson@tpwd.tx. state. us

FLIGHT IDENTIFICATION OF EURO-
PEAN SEABIRDS. By Anders Blomdahl,
Bertil Breife, and Niklas Holmstrom. Chris-

topher Helm, London, United Kingdom. 2003:
374 pp., over 690 color photos. ISBN:
0713660201. £35.00 (paper). — Field guides to
bird identification are no longer restricted to
general guides on the birds of a particular re-
gion. Although this guide’s coverage is re-
stricted to the European region, it covers the
specialized topic of flight identification of sea-
birds, a group defined here as including loons,
grebes, tubenoses, cormorants, waterfowl,
skuas, jaegers, gulls, terns, alcids, etc. The au-
thors state that they were inspired by their
study of large numbers of migrating seabirds
along the Baltic coast of Sweden, but much
of the information pertains to almost any non-
tropical coast along the North Atlantic.

The guide opens with a solid Basics of
Field Identification section. It is a good over-
view of the challenges inherent to watching
fast-flying birds in oftentimes difficult condi-
tions, and contains many cautions for the less
experienced birder. The book stresses the
shape, size, and flight style of birds in flight.
The discussion of weather, wind, and light is
helpful for those not used to scanning vast
stretches of ocean. Although the next section
listing 87 seabird watching sites in Western
Europe is not very useful on the U.S. side of
the “pond,” it is a good guide for traveling
North American birders.

Species are organized by functional groups:
some by family, such as those in the section
entitled “ Divers Gaviidae others more in-
formally, such as those in the section entitled
“ Diving Ducks and Sawbills .” An overview
of identification points is provided in each
section, including marks that separate species
from other groups or from other species with-
in groups, and marks related to age and molt.
A blue box on the overview page contains a
bulleted list of field marks to note when at-
tempting to separate species within the group.
It stands out well for easy reference in the
field as that fast-flying seabird goes whizzing
past.

The individual species accounts are unique
among field guides in that they stress identi-
fication in flight. A short opening paragraph
describes the species’ range and includes oth-
er commentary. The accounts contain the
more-expected information under the head-
ings Size and Plumage and Bare Parts. Size
information is often presented with a compar-

ORNITHOLOGICAL LITERATURE

125

ison to other species covered by the guide.
The accounts also contain the headings Sil-
houette and Flight and Flocking. These key
features make this guide particularly suited for
seabird watching. Again, comparatives are
used liberally throughout these sections.

A nice touch is that the authors apparently
were not enslaved by format. A Note, Voice,
Subspecies, and/or Geographical Variation
section appears at the end of each species ac-
count, as warranted. For example, it would not
have been very useful to include a description
of Fea’s Petrel ( Pterodroma feae ) vocaliza-
tions, but it is very appropriate that one is in-
cluded for Canada Goose ( Branta canaden-
sis). Notes include information such as addi-
tional identification points, the possibility of
hybrids, the possibility of escapees, and com-
parisons with other species that, while very
rare to the region and not covered in the book,
are still possible.

Multiple photographs, all of birds in flight,
of course, accompany almost every species
account. For those who have become used to
the stellar bird photos that have cropped up
everywhere these days, some of the photos
might seem to be of substandard quality.
Many are quite good, but even the more-dis-
tant photos do an excellent job of illustrating
how the birds actually appear when seabird
watching. Photos also include images of birds
in various plumages.

This book will be particularly useful as
more birders become aware of the massive
bird migrations that can be witnessed in many
places along the Atlantic coastline. Its empha-
sis on flight identification complements the
more standard field guides available. Use of
this guide will speed birders’ abilities and
confidence as they spend time in the field
watching seabirds.

Because this book was written by Europe-
ans for the purpose of identifying European
seabirds, North American birders should be
aware that some of the book’s approaches may
be a bit confusing, or less helpful, to them.
For example, the common names used in Eu-
rope do not always match the names used in
North America (e.g., Slavonian Grebe [ Podi -
ceps auritus] rather than Homed Grebe, Arctic
Skua [ Stercorarius parasiticus ] rather than
Parasitic Jaeger). In addition, comparisons are
often made to European species. For example,

“Red-necked Grebe lacks the abnormally
elongated appearance of Great Crested Grebe
and is a more compact and chubbier bird,”
but many North American birders are not fa-
miliar with Great Crested Grebe ( Podiceps
cristatus). Finally, some species that are fairly
regular on the U.S. side of the Atlantic are
treated with minor descriptions and no photos
(e.g., Canvasback [Aythya valisineria ] and
Redhead [A. americana ]) or descriptions are
missing altogether (e.g., Black Skimmer
[Rhynchops niger]). Overall, however, this
book is worthwhile to those who spend time,
or would like to spend time, watching the
spectacle of seabird migration along the At-
lantic coast. — PAUL A. GURIS, See Life
Paulagics, Green Lane, Pennsylvania; e-mail:
info@paulagics.com

THE SINGING LIFE OF BIRDS: THE
ART AND SCIENCE OF LISTENING TO
BIRDSONG. By Donald E. Kroodsma, illus-
trated by Nancy Haver. Houghton Mifflin
Company, Boston, Massachusetts and New
York, New York. 2005: 482 pp., 68 figures,
CD of recordings. ISBN: 0618405682, $28
(cloth). — “Somewhere, always, the sun is
shining, and somewhere, always, the birds are
singing.” So begins Don Kroodma’s celebra-
tion of birdsong, The Singing Life of Birds.
On every page, Kroodsma reveals his passion
for birds, his infatuation with birdsong, and
his desire to unravel the mysteries of avian
singing behavior. More than a celebration, the
book is Kroodsma’s attempt to answer the
“why” questions of birdsong. Why do some
species learn their songs? Why are the songs
of other species innate? Why do some species
have dialects, where birds match the songs of
their neighbors? Why would other species be
unable to learn neighboring songs? Why do
mockingbirds mimic? Why do females of
some species sing? Kroodsma attempts to an-
swer such questions with 30 different adven-
tures— 30 accounts of birds singing their sto-
ries— and shares three decades of recording
and analyzing songs. Traveling widely across
the Americas — from the eastern to the western
U.S. and from Saskatchewan to Central and
South America — often enlisting the aid of
countess colleagues and students, Kroodsma

126

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006

takes us along on his exploits as he recounts
his recording experiences.

The common thread running throughout the
book is an emphasis on the combination of
listening to (songs on the CD) and seeing
(sonagrams) bird songs. It is the sight of
sound that excites Don Kroodsma, and he in-
fects the reader with his enthusiasm (“. . . I
can’t imagine a world without sonagrams, as
I can’t imagine listening without also see-
ing”). Using sound spectrograms and the ac-
companying CD of bird songs, he considers
how birds acquire their songs, what makes
their songs unique, what functions songs
serve, and “how the pieces of this singing
continent fit together.”

Chapter 1 introduces readers to the ele-
ments of sonagrams — how to interpret the
time-frequency displays of sonagrams; how to
distinguish noisy, complex sounds from pure-
toned, whistled sounds; how to recognize the
rhythm and amplitude evident in sonagrams;
and how to learn to listen (“How do I hear
with my eyes?”). Kroodsma also shares his
personal beginnings and interest in birdsong
in this chapter, crediting the Bewick’s Wren
( Thryomanes bewickii ) as the bird that first
taught him how to listen. He ends the chapter
by outlining the kinds of questions he asks,
and attempts to answer, throughout the book:
How, where, when, and from whom do birds
acquire their singing vocabulary? What are
the functions of different bird sounds? How
do a bird’s life history features and its evo-
lutionary background influence song? How do
the brain, syrinx, and hormones control and
influence birdsong?

As Kroodsma takes readers on his pre-dawn
vigils, he reflects on the music of nature and
the journeys on which birds have taken him.
He bikes across Martha’s Vineyard, aston-
ished to hear and record improbable sweetie-
heys from Black-capped Chickadees ( Poecile
atricapillus ) (across the continent, nearly all
other chickadees sing hey-sweetie). He traips-
es across, canoes through, flies to, and criss-
crosses, visits, and revisits Illinois, South Da-
kota, New York, North Carolina, Michigan,
California, Colorado, Saskatchewan, Iowa,
and Nebraska — all to identify “The Great
Marsh Wren Divide” that distinguishes what
are almost certainly two different species of
Marsh Wren ( Cistothorus palustris). Kroods-

ma spends an entire early-May night (20:10-
05:04), following one male Whip-poor-will
(Caprimulgus vociferus), and counts 20,898
tuck-wHip-poor-WILLs — 2,300 songs/hr and
40 songs/min in just under 9 hr. And then he
asks “Why so much song?” (Because the
moon was full? Because the weather was
warm? Because Whip-poor-wills had just re-
turned from migration? Do high song rates re-
flect genetic superiority or good territories?).
Relentlessly curious, always intrigued,
Kroodsma is continually searching for an-
swers.

Kroodsma’s enthusiasm is one of the most
notable and enjoyable features of his book. I
offer only a few examples: (1) “Hear the
DNA of this flycatcher speak. . . ”; (2) “I love
the way song ‘G’ begins. . . ”; (3) “There’s
something universal in the quality of these
sounds [of Sooty Shearwaters, Pujfinus gri-
seus], and it seems fitting that the birds them-
selves have the final comment about the sheer
wonder and joy of birdsong”; (4) “. . . I can’t
help but. . . admir[e] how the black images of
songs against the white paper reveal the magic
in the singing bird”; and (5) “. . . songs of
some [Fox Sparrows, Passerella iliaca, are]
so beautiful that they can bring tears to the
eyes.”

Kroodsma shares many of his discoveries
about birdsong with readers. For example,
there are two birdsong vocabularies and two
species (eastern and western) of Marsh Wrens,
not just one. The songs of Eastern Phoebes
{Sayornis phoebe) and Willow ( Empidonax
traillii) and Alder ( E . alnorum) flycatchers are
innate, not learned. Sedge Wrens ( Cistothorus
platensis ) improvise (make up their songs)
and they do not imitate (learn songs from)
their neighbors as other wrens do — because
Sedge Wrens are nomadic due to the unpre-
dictability of their sedge-meadow breeding
habitats. Song Sparrows ( Melospiza melodia)
that match and share songs with their neigh-
bors keep their territories longer — and may
live longer. A young Bewick’s Wren learns his
father’s songs early in life, but in the follow-
ing years, after occupying a territory of his
own, he replaces his father’s songs by match-
ing those of neighboring males. Kroodsma
also lets us in on the fact that the meetcha
song “switch” of a male Chestnut-sided War-
bler ( Dendroica pensylvanica ) is “off” if he

ORNITHOLOGICAL LITERATURE

127

has a female, but it is “on” if he is without a
female (males sing several meetcha songs,
e.g., wheedle wheedle wheedle wheedle sweet
sweet MEETCHA).

There are 68 figures, nearly all of which are
sonagrams; these are flawless and impeccably
prepared and presented. Some sonagrams are
presented at an expanded time scale to show
greater detail, and songs of these sonagrams
can also be heard on the CD, but are played
at a correspondingly slower pace. Figure cap-
tions offer straightforward explanations about
how to interpret the notes and “read” the son-
agrams; Kroodsma points out the intricate de-
tails and encourages readers to follow along
on the CD — to hear, and see, birdsong at the
same time. The CD (98 tracks, —73 min) con-
tains superlative recordings of more than 50
species — to aid readers in the interpretation of
the sonagrams or for sheer listening enjoy-
ment.

Appendix I {Bird Sounds on the Compact
Disc) provides detailed, colorful descriptions
of the bird sounds on the accompanying CD.
Appendix II {Techniques) offers useful advice
on how to listen to and record birdsong, on
the recording equipment needed to do so, and
on the software for making sonagrams. At the

end of Appendix II, Kroodsma notes that
“There’s no longer any mystique to what I
have done all these years. Anyone can do this
kind of stuff. And anyone should.” The Notes
and Bibliography chapter provides a short
section on recommended readings, an anno-
tated list of readings for the key topics dis-
cussed in text, and a formal, extensive bibli-
ography. A well-organized, all-inclusive in-
dex— referencing key topics, CD tracks, the
locations of sonagrams in text, and the most
important information for the key species dis-
cussed— completes the volume.

Cautious, meticulous, thoroughly prepared,
objective, and determined to know, Kroodsma
takes the reader, with lively, often stirring
prose, on 30 fascinating journeys. No matter
what your level of ornithological expertise, af-
ter reading this book you will have learned to
listen to, and to look at, birdsong in a different
way, and you will have broadened your un-
derstanding of avian singing behavior. As
Kroodsma reminds us (quoting Shakespeare),
“The earth has music for those who listen.”
I highly recommend this book. — JAMES A.
SEDGWICK, USGS Fort Collins Science
Center, Fort Collins, Colorado; e-mail:
jim_sedgwick@usgs.gov

THE WILSON JOURNAL OF ORNITHOLOGY

Editor JAMES A. SEDGWICK
U.S. Geological Survey
Fort Collins Science Center
2150 Centre Ave., Bldg. C.

Fort Collins, CO 80256-8118, USA
E-mail: wjo@usgs.gov

Editorial Board KATHY G. BEAL
CLAIT E. BRAUN
RICHARD N. CONNER
KARL E. MILLER

Review Editor

Managing Editor
Copy Editor
Editorial Assistant

M. BETH DILLON
CYNTHIA P. MELCHER
ALISON R. GOFFREDI

MARY GUSTAFSON
Texas Parks and Wildlife Dept.

2800 S. Bentsen Palm Dr.

Mission, TX 78572, USA
E-mail: WilsonBookReview@aol.com

GUIDELINES FOR AUTHORS

Consult the detailed “Guidelines for Authors” found on the Wilson Ornithological Society Web site (http://
www.ummz.lsa.umich.edu/birds/wilsonbull.html).

NOTICE OF CHANGE OF ADDRESS

If your address changes, notify the Society immediately. Send your complete new address to Ornithological
Societies of Norht America, 5400 Bosque Blvd., Ste. 680, Waco, TX 76710.

The permanent mailing address of the Wilson Ornithological Society is: %The Museum of Zoology, The
Univ. of Michigan, Ann Arbor, MI 48109. Persons having business with any of the officers may address them
at their various addresses given on the inside of the front cover, and all matters pertaining to the journal should
be sent directly to the Editor.

MEMBERSHIP INQUIRIES

Membership inquiries should be sent to James L. Ingold, Dept, of Biological Sciences, Louisiana State Univ.,
Shreveport, LA 71115; e-mail: jingold@pilot.lsus.edu

THE JOSSELYN VAN TYNE MEMORIAL LIBRARY

The Josselyn Van Tyne Memorial Library of the Wilson Ornithological Society, housed in the Univ. of
Michigan Museum of Zoology, was established in concurrence with the Univ. of Michigan in 1930. Until 1947
the Library was maintained entirely by gifts and bequests of books, reprints, and ornithological magazines from
members and friends of the Society. Two members have generously established a fund for the purchase of new
books; members and friends are invited to maintain the fund by regular contribution. The fund will be admin-
istered by the Library Committee. Terry L. Root, Univ. of Michigan, is Chairman of the Committee. The Library
currently receives over 200 periodicals as gifts and in exchange for The Wilson Journal of Ornithology. For
information on the Library and our holdings, see the Society’s web page at http://www.ummz.lsa.umich.edu/
birds/wos.html. With the usual exception of rare books, any item in the Library may be borrowed by members
of the Society and will be sent prepaid (by the Univ. of Michigan) to any address in the United States, its
possessions, or Canada. Return postage is paid by the borrower. Inquiries and requests by borrowers, as well as
gifts of books, pamphlets, reprints, and magazines, should be addressed to: Josselyn Van Tyne Memorial Library,
Museum of Zoology, The Univ. of Michigan, 1109 Geddes Ave., Ann Arbor, MI 48109-1079, USA. Contri-
butions to the New Book Fund should be sent to the Treasurer.

This issue of The Wilson Journal of Ornithology was published on 6 March 2006.

130

Continued from outside back cover

104 First report of Black Terns breeding on a coastal barrier island

Shawn R. Craik, Rodger D. Titman, Amelie Rousseau, and Michael J. Richardson

107 First observation of cavity nesting by a female Blue Grosbeak
Thomas S. Risch and Thomas J. Robinson

109 A new record of the endangered White-winged Nightjar ( Eleothreptus candicans ) from Beni, Bolivia
Tomas Grim and Radim Sumbera

112 Predation of Eared Grebe by Great Blue Heron
James W. Rivers and Michael J. Kuehn

114 Abnormal eggs and incubation behavior in Northern Bobwhite

Fidel Hernandez, Juan A. Arredondo, Froylan Hernandez, Fred C. Bryant, and Leonard A. Brennan

1 17 Once Upon a Time in American Ornithology

120 Ornithological Literature

The Wilson Journal of Ornithology

(formerly The Wilson Bulletin)

Volume 118, Number 1 CONTENTS March 2006

1 Message from the Editor
Major Articles

3 Variation in mass of female Prothonotary Warblers during nesting
Charles R. Blem and Leann B. Blem

13 The rediscovery and natural history of the White-masked An third {Pithys castaneus)

Daniel F. Lane, Thomas Valqui H., Jose Alvarez A., Jessica Armenta, and Karen Eckhardt

23 Nesting ecology of Lesser Prairie-Chickens in sand sagebrush prairie of southwestern Kansas

James C. Pitman, Christian A. Hagen, Brent E. Jamison, Robert J. Robel, Thomas M. Loughin, and Roger
D. Applegate

36 A comparative behavioral study of three Greater Sage-Grouse populations
Sonja E. Taylor and Jessica R. Young

42 First known specimen of a hybrid Buteo : Swainson’s Hawk ( Buteo swainsoni) x Rough-legged Hawk
(B. lagopus) from Louisiana
William S. Clark and Christopher C. Witt

53 Nocturnal hunting by Peregrine Falcons at the Empire State Building, New York City
Robert DeCandido and Deborah Allen

59 Field experiments on eggshell removal by Mountain Plovers
Tex A. Sordahl

64 Seed-size selection in Mourning Doves and Eurasian Collared- Doves
Steven E. Hayslette

70 Low nesting success of Loggerhead Shrikes in an agricultural landscape
JeJfery W. Walk, Eric L. Kershner, and Richard E. Warner

75 Nest interference by fledgling Loggerhead Shrikes
Eric L. Kershner and Eric C. Mruz

81 First breeding record of a Mountain Plover in Nuevo Leon, Mexico

Jose I. Gonzalez Rojas, Miguel A. Cruz Nieto, Oscar Ballesteros Medrano, and Irene Ruvalcaba Ortega

85 Breeding biology of the Double-collared Seedeater ( Sporophila caerulescens )

Mercival R. Francisco

91 Small mammal selection by the White-tailed Hawk in southeastern Brazil
Marco A. Monteiro Granzinolli and Jose Carlos Motta-Junior

Short Communications

99 Provisioning of fledgling conspecifics by males of the brood-parasitic cuckoos Chrysococcyx klaas and
C. caprius

Irby J. Lovette, Dustin R. Rubenstein, and Wilson Nderitu Watetu

101 Widespread cannibalism by fledglings in a nesting colony of Black-crowned Night-Herons
Christina Riehl

Continued on inside back cover

Wilson Journal

ofO rnithology

Volume 118, Number 2, June 2006

\ ■ '

Published by the
Wilson Ornithological Society

THE WILSON ORNITHOLOGICAL SOCIETY
FOUNDED DECEMBER 3, 1888

Named after ALEXANDER WILSON, the first American ornithologist.

President — Doris J. Watt, Dept, of Biology, Saint Mary’s College, Notre Dame, IN 46556, USA; e-mail:
dwatt@saintmary s . edu

First Vice-President — James D. Rising, Dept, of Zoology, Univ. of Toronto, Toronto, ON M5S 3G5,
Canada; e-mail: rising@zoo.utoronto.ca

Second Vice-President — E. Dale Kennedy, Biology Dept., Albion College, Albion, MI 49224, USA;
e-mail: dkennedy@albion.edu

Editor — James A. Sedgwick, U.S. Geological Survey, Fort Collins Science Center, 2150 Centre Ave.,
Bldg. C, Fort Collins, CO 80526, USA; e-mail: wjo@usgs.gov

Secretary — Sara R. Morris, Dept, of Biology, Canisius College, Buffalo, NY 14208, USA; e-mail:
morriss@canisius.edu

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FRONTISPIECE. Bachman’s Sparrows ( Aimophila aestivalis) occupy fire-dependent, longleaf pine ( Pinus pa-
lustris) ecosystems of the southeastern United States. Tucker et al. (p. 131) found that both densities and
reproductive indices were greater during the first 3 years after burning than in older burns; they recommend a
2-3 year burn regime to maintain healthy populations. Similarly, Stober and Krementz (p. 138) report that home-
range size increases with habitat succession: home ranges in mature habitats often were twice the size of those
in regeneration habitats. Original painting (watercolor) by Don Radovich.

rft>e Wilson Journal

of Ornithology

Published by the Wilson Ornithological Society

VOL. 118, NO. 2 June 2006 PAGES 131-280

The Wilson Journal of Ornithology 118(2): 131-137, 2006

BREEDING PRODUCTIVITY OF BACHMAN’S SPARROWS IN
FIRE-MANAGED LONGLEAF PINE FORESTS

JAMES W. TUCKER, JR.,1-3 4’5 W. DOUGLAS ROBINSON,14 AND JAMES B. GRAND2

ABSTRACT. — Bachman’s Sparrows ( Aimophila aestivalis) occupy fire-dependent, longleaf pine ( Pinus palustris)
ecosystems of the southeastern United States. Their populations have declined, due, in part, to fire suppression
and degradation of longleaf pine forests. Populations decline when longleaf stands go more than 3 years without
fire. The influence of fire on breeding productivity, however, is poorly understood because territories are large
and it is difficult to find the well-hidden nests of this ground-nesting sparrow. In an earlier study, densities of
Bachman’s Sparrows were similar across pine stands burned 1 to 3 years previously, but declined significantly by
the 4th year since burning. To assess whether the decline in density might be associated with a decline in breeding
success, in 2001 we used a reproductive index to estimate breeding productivity of 70 territorial males, and from
1999 to 2001 we monitored 28 nests. We examined the influence of (1) season (growing versus dormant) when
last burned and (2) years since burning on breeding productivity of Bachman’s Sparrows in longleaf pine stands
in the Conecuh National Forest, Alabama. Reproductive indices were greater (Z = 1.99, P = 0.047) during the
first 3 years after burning (mean = 3-8, SE = 0.4, n = 10) than they were 4 years after burning (mean = 2.0, SE
= 0.5, n = 3), similar to the pattern of change in Bachman’s Sparrow density. We found no effect of burn season
on the breeding productivity index (Z = 0.075, P — 0.94). The parallel patterns of declining density and lower
breeding success suggest that Bachman’s Sparrow density may be positively correlated with habitat quality. We
conclude that burning longleaf pine forests on a 2-3 year rotation will best maintain populations of Bachman’s
Sparrows. Received 8 February 2005, accepted 25 November 2005.

Bachman’s Sparrow (. Aimophila aestivalis ) is
one of the bird species most characteristic of

1 Dept, of Biological Sciences, 331 Funchess Hall,
Auburn Univ., AL 36849, USA.

2 USGS, Alabama Coop. Fish and Wildlife Research
Unit, School of Forestry and Wildlife Sciences, Au-
burn Univ., AL 36849, USA.

3 Current address: Archbold Biological Station, 475
Easy St., Avon Park, FL 33825, USA.

4 Current address: Dept, of Fisheries and Wildlife,
104 Nash Hall, and Oak Creek Lab. of Biology,
Oregon State Univ., Corvallis, OR 97331, USA.

5 Corresponding author; e-mail:
jtucker@archbold-station.org

longleaf pine ( Pinus palustris) forests and it
ranks high among species of management con-
cern in the southeastern United States (Hunter
et al. 1994). It is classified as threatened or en-
dangered in several states (Dunning 1993) and
in 2002 it was red-listed (i.e., one of most at-
risk species) by the National Audubon Society
on its WatchList (see http://audubon2.org/
webapp/watchlist/viewSpecies.jsp?id = 18).
Loss and degradation of habitat are the most
probable causes for the species’ population de-
cline (Haggerty 1988). Prescribed fire has been
identified as a key tool for managing Bach-
man’s Sparrow habitat (Plentovich et al. 1998,

131

132

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

Tucker et al. 1998). Until recently, however,
prescribed fire has been used mainly during
the winter (dormant season) to minimize its
negative effects on sparrow reproductive suc-
cess, despite evidence that historically, natural
fires occurred most often during late spring
and summer (growing season; Robbins and
Myers 1992). Growing-season fires are most
beneficial to native plant communities (e.g.,
Platt et al. 1988, Waldrop et al. 1992, Streng et
al. 1993), but the way in which fire timing in-
fluences sparrow breeding success is un-
known.

Similarly, evidence from botanical studies in-
dicates that frequent fires are needed to main-
tain dense, herbaceous ground cover preferred
by Bachman’s Sparrows (e.g., Platt et al. 1988,
Dunning and Watts 1990, Waldrop et al. 1992,
Streng et al. 1993, Plentovich et al. 1998, Tuck-
er et al. 1998). Engstrom et al. (1984) followed
changes in bird species composition through
15 years of fire exclusion in a stand of “oldfield
pines” (mostly loblolly, P. taeda\ and shortleaf,
P. echinata, pines) in northwestern Florida that
had previously been burned annually during
the dormant season; Bachman’s Sparrows dis-
appeared from the stand after 5 years of fire
exclusion. In studies on Florida dry prairies,
Bachman’s Sparrow densities increased on
sites burned in mid-June relative to those on
control sites (>2.5 years since burning; Shriver
et al. 1999), but there were no differences in
density or reproductive success during the first
three breeding seasons following winter fires
(Shriver and Vickery 2001). Yet, no data are
available to evaluate directly the influence of
time since burning and season of burning on
breeding productivity of this elusive sparrow
species.

In a previous study, we examined the influ-
ence of burn season and fire frequency on the
density of Bachman’s Sparrows in longleaf
pine forests in southern Alabama and north-
western Florida (Tucker et al. 2004) and found
that density was unaffected by burn season.
Furthermore, density was similar within the
first 3 years after burning, but declined precip-
itously in stands 4 or more years after a fire
(Tucker et al. 2004). We hypothesized that re-
duced breeding success in stands unburned for
4 or more years might explain this decline in
density. To test this hypothesis, we compared
the breeding productivity of Bachman’s Spar-

rows across burned units of longleaf pine hab-
itat that differed in time since burning. We also
evaluated the potential influence of fire timing
within the growing season on nesting success
by comparing daily survival rates between
nests initiated early and late in the growing
season.

METHODS

We estimated breeding success by monitor-
ing nests and using a reproductive index based
on behavioral observations (Vickery et al.
1992b). The reproductive ecology of Bach-
man’s Sparrows is poorly known because nests
are hidden on the ground, usually below tufts
of overhanging grasses, and are therefore ex-
ceptionally challenging to locate (Weston 1968,
Harrison 1975, Haggerty 1986). In response to
the difficulties of finding ground-nesting spar-
row nests, Vickery et al. (1992b) developed a
reproductive index based on readily observ-
able behaviors that reduces the necessity of lo-
cating nests to measure breeding success
(Vickery et al. 1992a, Dale et al. 1997). During
the breeding season of 2001, we monitored the
territories of 70 male Bachman’s Sparrows in
longleaf pine stands of the Conecuh National
Forest, Alabama. To complement this intensive
study of focal individuals, we monitored nests
found in the same habitat units from 1999
through 2001.

Between 22 April and 12 May 2001, we lo-
cated territories within 13 habitat compart-
ments (a group of adjacent stands managed as
a prescribed burn unit), which varied from 387
to 700 ha in size and comprised four treatment
combinations of burn season (dormant [1 Oc-
tober-31 March] or growing [1 April-30 Sep-
tember]) and time since burning (1—3 years or
4 years). We sampled two compartments for
each treatment but one: there was only one
compartment that had been burned during the
growing season 4 years earlier (i.e. , 1997). No
stands were burned during the 2000 growing
season, so territories within stands the 1st year
after growing-season burning could not be in-
cluded. Because the number of compartments
was small and the study design was unbal-
anced, we grouped compartments burned ^3
years earlier to test our hypotheses that repro-
ductive success would parallel trends in den-
sity (Tucker et al. 2004) and be greater during

Tucker et al. • FIRE AND BACHMAN’S SPARROWS

133

the first 3 years (n = 10) than 4 years (n = 3)
post-burning.

Female and juvenile Bachman’s Sparrows
are very secretive and difficult to observe, so
we concentrated our efforts on searching in-
dividual territories, rather than mapping terri-
tories within habitat compartments, to increase
our chances of observing evidence of repro-
duction. Furthermore, Bachman’s Sparrow ter-
ritories are relatively large (see Dunning 1993)
and densities are relatively low, especially in
stands not burned for >4 years (Tucker et al.
2004); thus, monitoring individual territories
also allowed us to sample a sufficient number
of territories to characterize breeding produc-
tivity within each burn treatment (i.e., each
combination of burn season and years since
burning). Within each compartment, we se-
lected territories for monitoring by visiting an
area known to contain several Bachman’s
Sparrows and selecting the first four or six
singing males encountered within each com-
partment. Although unmated males of many
species sing more frequently than mated males
(Best 1981), the territories that we monitored
within habitat compartments were adjacent to
each other (although often separated by ^100
m) and we did not observe evidence (e.g., ap-
pearance of additional territories) that would
suggest that we overlooked mated birds during
selection of the territories. We monitored 10
territories within each burn treatment, but we
divided territories unequally between the two
habitat compartments within treatments to al-
low a team of two observers traveling together
to efficiently monitor two habitat compart-
ments (i.e., 5 territories per observer) each day.
We marked singing perches for each male with
plastic flagging and noted the territorial bound-
aries and location of adjacent territories not se-
lected for study. We also used mist nets to cap-
ture most of the males (53 of 70) and marked
them with unique combinations of colored leg
bands. All 70 territories were monitored once
per week from 21 May to 12 July 2001, span-
ning the peak of breeding activity at our study
site.

Behavioral evidence of reproductive activity
was monitored during 45-min visits to each ter-
ritory once per week. A visit began when we
arrived on a territory, and entailed recording
all evidence of reproductive activity — the pri-
mary objective being the discovery of an active

nest. In addition, we marked new song perch-
es to delineate more accurately territory
boundaries. Each territory was assigned a cu-
mulative score indicating increasing evidence
of breeding success, slightly modified from the
method of Vickery et al. (1992b). The scores
for evidence of reproductive success were as-
signed as follows: 1 = presence of the territo-
rial male, 2 = presence of a mated pair, 3 =
evidence of an active nest, 4 = adults carrying
food to presumed nestlings, 5 = direct obser-
vation or evidence of fledglings, 6 = evidence
of an active nest after successful fledging of a
first brood, 7 = evidence of successful fledging
for two broods, 8 = evidence of an active nest
after successful fledging of two broods, and 9
= evidence of successful fledgling for three
broods. Bachman’s Sparrows are not known to
attempt more than three broods within one
breeding season (Stober and Krementz 2000).

A cumulative reproductive score corre-
sponding to the maximum evidence of breed-
ing success was assigned to each of the 70 ter-
ritories. Because individual territories within
habitat compartments were not independent
sampling units, we calculated median repro-
ductive scores for each compartment and treat-
ed individual compartments as our sampling
units. The reproductive scores were ranked
(i.e., ordinal) data, so we used a nonparametric
normal approximation to the Mann- Whitney U-
test (Zar 1984) to compare median reproduc-
tive scores in compartments burned <3 versus
4 years previously and compartments burned
in the growing versus dormant season.

All Bachman’s Sparrow nests found from
1999 through 2001 were monitored according
to standard methods (Martin and Geupel 1993)
on a 2-3 day schedule until the nests failed or
the offspring fledged. We calculated daily sur-
vival rates (DSR) of nests (Mayfield 1961, 1975)
to evaluate the influence of burn season, years
since burning (<3 versus 4), and timing of fire
within the growing season on nesting success.
For Mayfield calculations, we used our obser-
vations for length of the incubation period (13
days) and nestling period (9 days), which were
similar to those reported by Haggerty (1986,
1988). Overall nest success (i.e., the probability
of a completed clutch producing ^1 fledgling)
was calculated by raising daily nest survival to
the 22nd power. We calculated variances in
DSR and evaluated effects by examining 95%

134

THE WILSON JOURNAL OL ORNITHOLOGY • Vol. 1 18, No. 2, June 2006

<3 4 Growing Dormant

Years since burned Season last burned

LIG. 1 . Mean (± SE) reproductive scores of Bach-
man’s Sparrows calculated using median scores from
individual habitat compartments at the Conecuh Na-
tional Lorest, Alabama, during 2001 were greater in
the first 3 years after burning (n = 10) than 4 years
after burning (n = 3) but did not differ between sea-
sons when last burned (n = 5 and n = 8 for growing
and dormant seasons, respectively). Reproductive
scores were collected using methods modified from
Vickery et al. (1992b).

confidence intervals (±2 SE) around the DSR
(Johnson 1979).

RESULTS

Breeding productivity. — Of the 70 Bach-
man’s Sparrow territories monitored, we found
evidence of successful reproduction (i.e.,
fledglings observed) within 30 and evidence of
two successful broods within 4 territories.
Overall, 28% (14/50) of territorial males in

compartments burned ^3 years earlier re-
mained unpaired, and 50% (10/20) of territorial
males in compartments burned 4 years earlier
remained unpaired (x2 = 3.07, P = 0.080). Fur-
thermore, 52% (26/50) of territories in com-
partments burned ^3 years earlier successfully
produced young, but only 20% (4/20) of ter-
ritories burned 4 years earlier successfully pro-
duced young (x2 = 5.97, P — 0.015). Repro-
ductive scores of Bachman’s Sparrows were
greater (Z = 1.99, P = 0.047) in the first 3 years
after burning (mean = 3.8, SE = 0.4, n = 10)
than 4 years after burning (mean = 2.0, SE =
0.5, n = 3) but did not differ (Z = 0.075, P =
0.94) between stands burned in the growing
season (mean = 3.3, SE = 0.7, n — 5) versus
those burned in the dormant season (mean =
3.4, SE = 0.5, n = 8; Fig. 1).

Nesting success. — We found 34 nests during
the study: 2, 12, and 20 in 1999, 2000, and
2001, respectively. Two nests were found the
day of fledging, two were destroyed during
construction, and two were burned during egg
laying, leaving 28 nests for calculating DSR.
Overall, 13 of the 28 (46%) nests fledged
young. All nest failures resulted from depre-
dation; no parasitism by Brown-headed Cow-
birds ( Molotbrus ater) was observed.

DSR of early-season nests (found in April
and May) were slightly greater than those of
late-season nests (found June and July), al-
though the 95% confidence intervals over-
lapped (Table 1). In addition, DSR of nests dur-

TABLE 1. Exposure days (number of nests), number of nest failures, daily survival rates (DSR), and 95%
confidence intervals (95% Cl) by nesting stage and time within the breeding season (nest cycle) for 28 Bachman’s
Sparrow nests in the Conecuh National Forest, Alabama, from 1999 through 2001.

95% CIa

Stage

Nest cycleh

Exposure days

Failures

DSR

Lower

Upper

IncubatioiT

Early

66.0 (8)

0.970

0.928

1.012

Late

52.5 (8)

0.981

0.943

1.019

Total

1 18.5 (16)

0.975

0.946

1.004

Nestlingd

Early

64.5 (13)

0.923

0.856

0.989

Late

46.5 (12)

0.850

0.745

0.954

Total

1 11.0 (25)

0.892

0.833

0.951

Combined1'

Early

130.5 (15)

0.946

0.907

0.986

Late

99.0 (13)

0.919

0.864

0.974

Total

229.5 (28)

0.935

0.902

0.967

a Calculated as mean ± 2 SE (Johnson 1979).

b Early nest cycle included nests found in April and May; late nest cycle included nests found in June and July.
c Incubation stage included a 13-day period from laying of the penultimate egg until the first egg hatched.
d Nestling stage included a 9-day period from 1st day of hatching until fledging.
e Includes the sum of incubation and nestling periods.

Tucker et al. • FIRE AND BACHMAN’S SPARROWS

135

ing the incubation period tended to be greater
than during the nestling period, but again the
95% confidence intervals overlapped (Table 1).
DSR of all nests from the beginning of incu-
bation through fledging was 0.935 (Table 1),
and the probability of a completed clutch pro-
ducing at least one fledgling was 0.226. DSR
was similar between the first 3 years (DSR =
0.94, 95% Cl = 0.90-0.97, n = 22 nests) and
the 4th year (DSR = 0.93, 95% Cl = 0.86-1.00,
n — 6 nests) after burning and between sites
burned in the growing (DSR = 0.89, 95% Cl =
0.81-0.97, n = 7 nests) and dormant (DSR =
0.95, 95% Cl = 0.92-0.99, n = 21 nests) sea-
sons.

DISCUSSION

Nesting success averaged across all our hab-
itat compartments was 23%, which falls within
the range previously reported for Bachman’s
Sparrows in Arkansas pine forests (25%; Hag-
gerty 1988), South Carolina dear-cuts (8-34%;
Stober and Krementz 2000), and Florida dry
prairies (7-38%; Perkins 1999). Neither burn
season nor time since burning had a large ef-
fect on nest survival rates at our study sites.
Although our sample size of nests was one of
the largest yet obtained in a Bachman’s Spar-
row study, the sample was nevertheless rela-
tively small, indicating that only large effects
could be detected (Johnson 1979). In contrast,
our results from the reproductive scores (i.e.,
70 territories; Fig. 1) suggested that breeding
productivity was greater the first 3 years after
burning than in older burns. The latter result is
consistent with our hypothesis that reduced
breeding success in older burns may help ex-
plain the lower densities of Bachman’s Spar-
rows in those burns (Tucker et al. 2004).

Although logistic constraints prevented us
from simultaneously measuring density and
breeding productivity of Bachman’s Sparrows,
our results suggest a positive correlation be-
tween the two measures in our study area. We
acknowledge that these results only are sug-
gestive of a positive association between den-
sity and breeding productivity, but our consis-
tent results among the 3 years of our studies —
1999 and 2000 for density of Bachman’s Spar-
rows (Tucker et al. 2004) and 2001 for this
study of breeding productivity — strongly sup-
port the conclusion that a regime of burning
every 2-3 years will best maintain healthy pop-

ulations of Bachman’s Sparrows in longleaf
pine forests. Bock and Jones (2004) reviewed
studies that examined the association between
avian density and reproductive success and
found that a preponderance of studies in rel-
atively undisturbed areas reported a positive
association between the two measures; most
studies that reported a decoupling between the
two measures were conducted in disturbed
habitats. Our study area was within the largest
remaining extent of longleaf pine forest (Out-
calt and Sheffield 1996), and habitats were rel-
atively natural and managed under a paradigm
of ecosystem management. Thus, a positive
correlation between density and breeding pro-
ductivity of Bachman’s Sparrows in the area
would be expected.

Why do density and breeding success de-
cline in older burns? Previous studies suggest
that percent coverage by herbaceous ground
cover, particularly grass (Dunning and Watts
1990, Plentovich et al. 1998, Haggerty 2000,
Tucker et al. 2004), is a primary factor influ-
encing habitat occupancy by Bachman’s Spar-
rows. Herbaceous ground cover and, thus,
habitat suitability decreases with time since
burning (Engstrom et al. 1984, Tucker 2002).
Haggerty (1998) found that territory sizes were
inversely correlated with percent coverage of
herbaceous ground cover. Thus, higher spar-
row densities are facilitated by smaller territo-
ries in high-quality habitat.

It should be noted that small territory sizes
could have an effect on detectability of repro-
ductive status, as well. The stealthy behavior
of female and juvenile Bachman’s Sparrows
makes them difficult to detect, but they may be
easier to detect in smaller territories (i.e., high-
er quality habitat) because their activities are
confined to a smaller area. Despite a potential
bias in detectability resulting from territory
size, the scores for reproductive success nev-
ertheless would be positively correlated with
habitat quality.

Future studies should address the effects of
timing of fires within the breeding season. We
were unable to examine breeding productivity
immediately before and after growing-season
fires. Although we did not find differences in
sparrow reproductive success between burn
seasons, timing of fire within the growing sea-
son may be an important factor and needs ad-
ditional study. For example, both our study

136

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

(Table 1) and one in South Carolina (Stober
and Krementz 2000) revealed that early-season
nests tended to be more successful than late-
season nests. Fires during late April and early
May could destroy a large percentage of the
nestlings or young fledglings from the first
nesting cycle and result in low annual recruit-
ment from those nesting attempts. Further-
more, we do not yet know whether territory
holders move to unburned sites and breed
elsewhere or quit all reproduction efforts for a
given year when their territories are burned
early in the growing season (Seaman and Kre-
mentz 2000). Alternatively, productivity of food
resources (i.e., seed production and inverte-
brates) may be enhanced sufficiently by early-
season fires to compensate for the loss of nests
early in the season; if vegetation re-grows
quickly enough, it could provide cover for
nests that season. Although Seaman and Kre-
mentz (2000) found that Bachman’s Sparrows
abandoned stands burned in the growing sea-
son and failed to return within 50 days after
the fires, anecdotal observations (JWT unpubl.
data, J. B. Dunning pers. comm.) suggest that
Bachman’s Sparrows often return and/or estab-
lish territories in burned stands within a few
days after fire and remain there through the
remaining breeding season. Shriver et al.
(1996, 1999) found that burning Florida dry
prairies during mid-June resulted in an extend-
ed breeding season for Florida Grasshopper
Sparrows ( Ammodramus savannarum flori-
danus) but fires in July did not.

In conclusion, results of this study on breed-
ing productivity and our earlier study on den-
sity of Bachman’s Sparrows (Tucker et al.
2004) suggest that land managers interested in
providing habitat for Bachman’s Sparrows in
longleaf pine forests should burn at least every
3 years, regardless of burn season. Sites left un-
burned for >4 years host few to no breeding
Bachman’s Sparrows (Tucker et al. 2004) and
it appears that breeding productivity is low
among birds that do settle in those habitats.
Thus, low breeding productivity may be a
plausible explanation for the low densities of
sparrows in pine stands unburned for more
than 3 years. Because most natural fires histor-
ically occurred during the growing season
(Robbins and Myers 1992), prescribed burning
during the growing season probably will be
most beneficial for longleaf pine communities

overall. Our study, based on one of the largest
sample sizes of reproductive success yet ob-
tained for this elusive sparrow, suggest that
burn season may be of little consequence to
the reproductive output of Bachman’s Spar-
rows; however, the effects of fire timing within
the growing season still need to be evaluated.

ACKNOWLEDGMENTS

This research was supported by funds from the U.S.
Geological Survey, State Partnership Program; a J. L.
Landers Research Award of the Gopher Tortoise Coun-
cil; grants from the U.S. Geological Survey, Biological
Resource Division, Species at Risk Program; a F. M. Pea-
cock Scholarship from the Garden Club of America ad-
ministered through the Cornell Laboratory of Ornithol-
ogy; and the W. F. Coxe Research Fund of the Birming-
ham Audubon Society. The research benefited from
partnerships among the following organizations and
agencies: Department of Biological Sciences, Auburn
University; Solon Dixon Forestry Education Center,
School of Forestry and Wildlife Sciences, Auburn Uni-
versity; Alabama Cooperative Fish and Wildlife Re-
search Unit; USDA Forest Service, Conecuh National
Forest; Alabama Department of Conservation and Nat-
ural Resources, Division of Wildlife and Freshwater
Fisheries; and The Longleaf Alliance. R. Johnson, G.
Morgan, R. Lint, P. Brinn, and R. Mullins provided lo-
gistical support during fieldwork. Help from the follow-
ing field assistants is gratefully acknowledged: C. Kriss-
man, C. Romagosa, J. Stratford, R. Peters, A. Sorenson,
and M. Hershdorfer. Reviews by J. B. Dunning, Jr., C.
A. Haas, L. A. Powell, P. C. Stouffer, P. D. Vickery, and
an anonymous reviewer greatly improved this manu-
script.

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The Wilson Journal of Ornithology 1 1 8(2): 138— 144, 2006

VARIATION IN BACHMAN’S SPARROW HOME-RANGE SIZE AT
THE SAVANNAH RIVER SITE, SOUTH CAROLINA

JONATHAN M. STOBER1 35 AND DAVID G. KREMENTZ24

ABSTRACT. — Using radiotelemetry, we studied variation in home-range size of the Bachman’s Sparrow
( Aimophila aestivalis ) at the Savannah River Site (SRS), South Carolina, during the 1995 breeding season. At
SRS, sparrows occurred primarily in two habitats: mature pine habitats managed for Red-cockaded Woodpecker
{Picoides borealis) and pine plantations 1 to 6 years of age. The mean 95% minimum convex polygon home-
range size for males and females combined {n = 14) was 2.95 ha ± 0.57 SE, across all habitats. Mean home-
range size for males in mature pine stands (4.79 ha ± 0.27, n = 4) was significantly larger than that in 4-year-
old (3.00 ha ± 0.31, n = 3) and 2-year-old stands (1.46 ha ± 0.31, n = 3). Home-range sizes of paired males
and females (n = 4 pairs) were similar within habitat type; mean distances between consecutive locations differed
by habitat type and sex. We hypothesize that a gradient in food resources drives home-range dynamics. Received
16 December 2004, accepted 28 November 2005.

The Bachman’s Sparrow {Aimophila aesti-
valis) is a species of concern due to its pop-
ulation decline (Sauer et al. 2004) and large
reductions in range (Dunning 1993). The im-
pact of prescribed fire and timber management
on Bachman’s Sparrow abundance (Dunning
and Watts 1990; Gobris 1992; Plentovich et
al. 1998; Tucker et al. 1998, 2004) and habitat
occupancy (Wan A. Kadir 1987; Haggerty
1998, 2000) have been well documented. The
sparrow’s secretive nature, however, makes it
difficult to obtain basic information on its re-
production, survival, movement, and home-
range dynamics (Dunning 1993).

Bachman’s Sparrow home-range sizes have
been estimated using spot mapping of un-
marked (McKitrick 1979, Meanley 1990) and
color banded (Haggerty 1998) males, but this
approach is problematic in some habitats be-
cause detecting Bachman’s Sparrows is diffi-
cult in dense, early successional stands (Bibby
et al. 1992). Bachman’s Sparrows are ex-
tremely cryptic in dense vegetation, particu-
larly after 3-4 years of vegetative succession
in rapidly growing pine plantations. Males are

1 Warnell School of Forest Resources, Univ. of
Georgia, Athens, GA 30602, USA.

2 USGS Patuxent Wildlife Research Center, Warnell
School of Forest Resources, Univ. of Georgia, Athens,
GA 30602, USA.

3 Current address: J. W. Jones Ecological Research
Center, Rte. 2, Box 2324, Newton, GA 39870, USA.

4 Current address: USGS Arkansas Coop. Fish and
Wildlife Research Unit, Dept, of Biological Sciences,
Univ. of Arkansas, Fayetteville. AR 72701, USA.

5 Corresponding author; e-mail:
jonathan.stober@jonesctr.org

often only seen while perched on singing
posts; such observations do not accurately re-
flect their entire home range. Because females
do not sing, it is impossible to consistently
follow or locate their movements. Using spot
mapping, mean estimates of home-range size
ranged from 5.1 ha ± 1.2 SD (range = 4-6.7,
n = 6) in mature Florida pine flatwoods
(McKitrick 1979) to 2.5 ha ± 0.2 SE (range
= 0.7— 4.5, n — 25) in several Arkansas clear-
cuts during the initial 3 years of succession
(Haggerty 1998). How home-range sizes vary
across the species’ range or habitat types is
unknown (Dunning 1993). Because of wide-
spread conservation concern for Bachman’s
Sparrows, wildlife managers require a better
understanding of the species’ natural history.
We estimated home-range size using radiote-
lemetry in early and late successional longleaf
pine ( Pinus palustris ) stands, examined how
home-range size varied with habitat type, and
monitored movements within territories by
habitat type and sex.

METHODS

During the 1995 breeding season, we stud-
ied Bachman’s Sparrows at the Savannah Riv-
er Site (SRS) (33° 14' N, 81° 31' W), an 800-
km1 2 3 4 5 National Environmental Research Park
managed by the U.S. Department of Energy.
The SRS is located in western South Carolina
along the Savannah River in Aiken, Barnwell,
and Allendale counties and lies in the Upper
Coastal Plain physiographic province. At the
SRS, Bachman’s Sparrows inhabit understory
grass and grasslands found in mature loblolly

138

Stober and Krementz • BACHMAN’S SPARROW HOME-RANGE SIZE

139

( Pinus taeda) and longleaf pine stands (40-
98 years old) managed for Red-cockaded
Woodpeckers ( Picoides borealis ); they also
occur in regenerating pine stands during the
initial 6-10 years after planting (Dunning and
Watts 1990, Gaines et al. 1995, Kilgo and
Bryan 2005). Mature pine stands were man-
aged with periodic prescribed fires on a 3- to
5-year rotation during both the growing and
dormant seasons. All mature stands in which
we monitored sparrows had been burned 1-2
years previously and were on a 3-year burn
rotation. Both the mature and regenerating
stands were characterized by understories
dominated by Andropogon spp. and Panicum
spp. grasses, rather than native wiregrass (Ar-
istida spp.; Stober 1996). Regeneration stands
consisted of areas recently clear-cut and ma-
chine planted with bare-root longleaf pines at
densities of 1,400-1,700 trees/ha; site prepa-
ration generally included a prescribed burn
before planting. Patches of shrubs within un-
derstories of grasses and forbs occurred in
both regeneration and mature stands. We ran-
domly selected five stands from groups with
similar management histories: one 2-year-old
stand (19.2 ha), one 4-year-old stand (15.0
ha), and three mature stands (17.6, 16.7, and
5.2 ha). Selected stands were >1 km apart.

To capture Bachman’s Sparrows, in each
stand we placed 25 12-m-long (30-mm mesh)
mist nets in a 5 X 5 grid with nets 50 m apart
(Krementz and Christie 1999). Captured birds
were weighed, sexed, aged, and banded with
a federal leg band. We categorized sparrows
as either hatch-year or after-hatch-year and
determined sex by the presence or absence of
a brood patch (Pyle et al. 1987). Using the
Rappole and Tipton (1991) thigh-harness
method, we attached radio transmitters to 20
sparrows in five stands: 6 sparrows (4M:2F)
in 2-year-old longleaf pine habitat, 6 sparrows
(4M:2F) in 4-year-old longleaf habitat, and 8
sparrows (6M:2F) in three mature pine habi-
tats. The radio with harness weighed 1.1 — 1.2
g (Advanced Telemetry Systems, Isanti, Min-
nesota), about 6% of body mass relative to all
captured birds (females: 18.6 g ± 0.24 SE, n
= 36; males: 18.2 g ± 0.31 SE, n = 69; Sto-
ber 1996, Krementz and Christie 1999). With-
in a few hours after release, all radio-tagged
sparrows resumed normal activities, and we

observed no unusual behaviors associated
with the radio-attachment method.

We located radio-marked sparrows daily,
and made observations on each sparrow
throughout the day, from sunrise to twilight,
throughout the breeding season. We recorded
status (live, dead, or lost radio), location, and
any reproductive, foraging, or other behavior.
Occasionally, we monitored individuals twice
a day, with a minimum of 2 hr between ob-
servations. Sparrows readily traversed their
home ranges within this time period; there-
fore, consecutive observations likely did not
result in autocorrelation problems (Swihart
and Slade 1985) that would have yielded un-
derestimates of home-range size (Cresswell
and Smith 1992).

To provide an index of Bachman’s Sparrow
density, we also conducted spot mapping three
times in each stand by using playback tapes
of the Bachman’s Sparrow’s primary song and
counting all males (Bibby et al. 1992, Dun-
ning et al. 1995, Stober 1996). While record-
ing daily locations of marked sparrows, we
also mapped the locations of unmarked spar-
rows within each stand. Counter-singing ex-
changes between unmarked and marked indi-
viduals were recorded as well.

We marked sparrow locations with flagging,
and we used a Trimble Pathfinder Pro GPS (3-
D mode) unit to establish benchmark Univer-
sal Transverse Mercator (UTM) coordinates
within each territory. All GPS locations were
differentially corrected and were accurate to
<5 m. Individual locations were then refer-
enced to an established UTM location using a
survey laser. The survey laser was used to cal-
culate distance (±0.10 m) and azimuth (±0.01
degrees) between locations, which were then
converted into UTM coordinates. Once an in-
dividual’s locations were mapped, we used
program HOME RANGE (Ackerman et al.
1990) to estimate the 95% minimum convex
polygon (MCP) for home range (Mohr 1947).
We attempted to collect 35 observations per
bird (Ackerman et al. 1990). We recognize
that the 95% MCP has certain limitations, but
all other breeding season home-range sizes for
Bachman’s Sparrows described in the litera-
ture were estimated using this metric (Dun-
ning 1993). Distances moved between loca-
tions were calculated for each individual, as
were distances from each location to the arith-

140

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

TABLE 1. Home-range size estimates and densities of male Bachman’s Sparrows in pine habitats, by stand
age, during the 1995 breeding season at the Savannah River Site, South Carolina.

Stand age (years)

Stand size (ha)

No. marked
sparrows

95% MCP3 (SE)

Range

Male density/
10 hab

19.2

1.46 (0.31)

0.99-2.04

2.59

15.0

3.00 (0.31)

2.80-3.37

4.65

Mature

17.6

—

3.41

Mature

Mature (both stands)0

16.7

4.79 (0.27)

4.23-5.69

1.79

a Mean 95% minimum convex polygon estimates.

b Includes both radio-marked and unmarked singing males; densities determined using spot mapping technique within each stand.
c Home-range estimate for mature stands is pooled across the two stands.

metic center of each home range, defined as
the mean distance from the estimated central
coordinate to each observation within the
home range.

Only 14 of the 20 radio-marked sparrows
were included in the analysis of home-range
size. We obtained <35 locations for two fe-
males and one male, and three males were
treated as outliers and excluded from analyses.
The outliers included ( 1 ) a bird with two dis-
tinct home ranges (a combined total of 20.9
ha) in a mature stand, (2) one whose home
range (1.63 ha) ended up outside the study
stand in an adjacent 33-year-old stand of
planted pine, and (3) one (in the 2-year-old
habitat) that behaved like a floater and used
part of an adjacent 43-year-old stand of pine
(5.46 ha). Due to these exclusions, we used
only two (the 17.6- and 16.7-ha stands) of the
three mature pine stands in our analyses.

FIG. 1 . Home-range size, by habitat age (2 years,
4 years, mature), using 95% minimum convex polygon
estimates for Bachman’s Sparrows (« = 4 females, 10
males) during the 1995 breeding season. Savannah
River Site, South Carolina. Pairs designated by similar
alpha characters (A-D); F = female. M = male.

We used a general linear model procedure
(PROC GLM; SAS Institute, Inc. 1987) to
conduct three pre-planned tests comparing
home-range sizes of males by habitat type. We
included only males because all marked fe-
males were paired to marked males. Once we
determined differences in home-range sizes by
habitat type (F-test), we used Tukey tests to
compare the least-squares means. Due to in-
sufficient sample sizes, we did not test for the
effect of sex (female n = 4) or conspecific
density (/? = 4) on home-range size. We also
used the GLM procedure and Tukey tests to
compare the least-squares means for mean
distance moved and distance from home-range
arithmetic center by habitat type and sex. All
statistical tests were one-tailed. The level of
statistical significance was set at 0.05 and
means are reported ± SE.

RESULTS

For the 14 radio-marked individuals in our
analyses, we recorded an average of 63 loca-
tions (range = 45—81) per individual over an
average of 50 days of observation (range =
38—62 days). Ten birds were monitored in the
2-year-old (3M:2F) and the 4-year-old (3M:
2F) stands, and four males were monitored in
the two mature stands (3M:0F and 1M:0F).
The mean 95% minimum convex polygon
home-range size for males and females com-
bined ( n — 14) across all habitats was 2.95 ha
± 0.57. Mean 95% MCP home-range size
across all habitats was 3.26 ha ± 0.49 for
males ( n = 10; Table 1) and 2.20 ha ± 0.48
(n = 4) for females. For males, home-range
size increased with habitat age (F27 = 33.9, P
< 0.001; Fig. 1). Home-range sizes differed
between 2-year-old (mean = 1.46 ha ± 0.31,
n = 3) and 4-year-old (mean = 3.00 ha ±

Stober and Krementz • BACHMAN’S SPARROW HOME-RANGE SIZE

141

0.31, n — 3) regeneration habitat (r = 3.54, P
= 0.009), and were significantly larger in ma-
ture pine habitats than in the 2- and 4-year-
old habitats (t = 8.18, P < 0.001; t = 4.40,
P = 0.003, respectively).

Home ranges were always adjacent to a
stand edge. Conspecific density was highest
(4.65 males/ 10 ha) in the 4-year-old stand (Ta-
ble 1) and lower in the 2-year-old stand and
one mature stand, both of which were isolated
with no suitable adjacent sparrow habitat. Of
the four sparrow pairs in which both the male
and female were marked, two inhabited the 2-
year-old stand and two inhabited the 4-year-
old stand. In one pair, the female had a larger
home-range size than the male (pair B; Fig.
1); otherwise, male and female home ranges
were roughly similar.

Mean distance moved between consecutive
observations was 83.9 m ± 12.78 ( n = 14);
distance moved differed among habitat types
(F211 ~ 14.66, P < 0.001) and was marginally
different between sexes (FU2 = 3.73, P =
0.077). Mean distance moved in mature stands
(106.6 m ± 6.4) was not different from that
in the 4-year-old stand (88.8 m ± 5.7), but
differed from the distance moved in the 2-
year-old stand (61.0 m ± 5.7). The mean dis-
tance from the arithmetic center of an individ-
ual’s home range to each location differed by
habitat type (F211 = 12.69, P — 0.001), but
not by sex (F, 12 = 0.78, P = 0.40). Mean
distance from arithmetic center in mature
stands (81.8 m ± 4.7) was not different from
that in the 4-year old stand (73.6 m ± 4.2, t
= 1.32, P = 0.21) but differed from that in
the 2-year-old stand (51.9 m ± 4.2, t - 4.77,
P < 0.001). The longest movement between
daily observations was 824 m by a male, and
most long-distance movements were about
200 m. In one case, a male crossed a riparian
area 200 m wide to an adjacent regeneration
stand, remained there for 2 days, and then re-
turned to the original stand.

DISCUSSION

Because we located birds through radiote-
lemetry rather than by visual documentation
at singing posts, our estimates of home-range
size were slightly larger and more precise than
those reported by Haggerty (1998). Home-
range estimates of McKitrick (1979) and Hag-
gerty (1998) were biased by their dependence

on visual records of males (color banded or
unmarked) perched in conspicuous locations.
Nonetheless, home-range sizes of male spar-
rows in our study were similar to those re-
ported by Haggerty (1998), with the smallest
territories found in the 1- and 2-year-old pine
regeneration habitat and home range increas-
ing with succession of habitat. Radiotelemetry
also allowed us to obtain the first estimates of
female home-range size, which were similar
to male home-range size {n = 4 pairs). Home-
range size between paired birds is probably
influenced by the mate-guarding behavior that
males exhibit during the breeding season
(Haggerty 1986). Some locations for the fe-
male whose home range was larger than the
male’s (2-year-old stand) were recorded after
her brood had fledged, which may explain the
larger size of her home range.

We recorded few instances of direct conflict
between adjacent sparrows defending home
ranges. The persistent use of primary song and
counter-singing (Meanley 1990, Dunning
1993) apparently mediated the need for direct
conflict in establishing and maintaining home
ranges. Spot mapping revealed the highest
density of sparrows in the 4-year-old stand.
Similarly, spot mapping conducted by Stober
(1996) in regeneration habitats 1-6 years of
age revealed that Bachman’s Sparrow densi-
ties were greatest in 3- to 4-year-old habitats.
Overlap of sparrow home ranges was limited
to three instances and occurred in grassy
patches in mature pine stands or in regenera-
tion habitats where trees and shrubs were sup-
pressed and grasses dominated the vegetation.

Although Haggerty (1986) reported that
sparrow density was inversely related to
home-range size, we were unable to corrobo-
rate this. Stober (1996) found more sparrows
in stands with suitable adjacent habitat than in
isolated, disjunct stands. Dunning et al. (1995)
also found that areas connected by corridors
of suitable habitat had a greater probability of
sparrow occupancy than isolated patches of
suitable habitat. Greater conspecific density
may constrict the size of home ranges in
breeding season, but this hypothesis needs to
be tested by removing territorial individuals
and monitoring the behavior of adjacent in-
dividuals. Vegetation succession and arthro-
pod food resources also may play important
roles in determining home-range size.

142

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 1 18, No. 2, June 2006

We found that home-range size increased
with habitat succession: home ranges in ma-
ture habitats often were twice the size of those
in regeneration habitats. We hypothesize that
the distribution of resources within home
ranges may explain this pattern. Bachman’s
Sparrows are omnivorous, foraging exclusive-
ly from the ground for insects (orthopterans,
arachnids, lepidopteran larvae, coleopterans,
hemipterans) and grass seeds, especially those
of Panicum spp. (Allaire and Fisher 1975,
Haggerty 1992, Dunning 1993). Early succes-
sional habitats have greater arthropod produc-
tivity than mature pine stands in the Southeast
(Menhinick 1963, Landers and Mueller 1986,
Hurst 1992). Cross (1956) surveyed a range
of upland habitats at the SRS for Orthoptera
and found >40 species in early successional
habitats compared with only 7 species in ma-
ture loblolly pine stands. In contrast, ground-
level arthropod communities in mature pine
stands managed for Red-cockaded Woodpeck-
ers at the SRS include an abundance of spi-
ders and ants, but few grasshoppers (New and
Hanula 1998). Stober (1996) found that, as a
percentage of total vegetation cover, Panicum
spp. were more abundant in regeneration
stands (0.8— 1.3%) than in mature pine stands
(0. 1-0.4%); thus, differences in home-range
size between habitats may be a reflection of
greater seed resources and arthropod produc-
tivity in early regeneration habitats than in
mature pine habitats managed for Red-cock-
aded Woodpeckers. In examining previous
studies on Bachman’s sparrows across their
range (Wan A. Kadir 1987; Dunning and
Watts 1990; Gobris 1992; Haggerty 1998,
2000; Plentovich et al. 1998; Tucker et al.
1998, 2004), we observed that, in general,
sparrow densities and arthropod communities
were reduced with succession of understory
vegetation.

Despite the differences we observed in
home-range sizes by habitat type and the dif-
ferences in male densities among stand ages,
Stober and Krementz (2000) detected no sig-
nificant differences in survival rates between
sexes or habitat types. Apparently, the larger
home-range sizes of Bachman’s Sparrows in
mature pine stands do not predispose those
birds to lower survival rates, as might be ex-
pected from longer movements throughout
their territories. Breeding season survival rates

were high (0.905, 95% Cl = 0.794-0.992),
with only 2 mortalities (raptor and mammal
depredations) out of 20 individuals radio-
tagged.

We found that Bachman’s Sparrows did not
move far (~100 m/day) between consecutive
observations, as was also found for radio-
marked Eastern Towhees (. Pipilo erythroph-
thalmus ) at the Savannah River Site (Kre-
mentz and Powell 2000). Like towhees, Bach-
man’s Sparrows moved among adjacent
stands, but unlike towhees, Bachman’s Spar-
rows used middle-aged (—20- to 35-year-old)
stands infrequently (Stober 1996). Not sur-
prisingly, we found that daily movements re-
flected home-range sizes: smaller home ranges
among habitat types were associated with
shorter daily distances moved.

Management for Bachman’s Sparrow pop-
ulations in forested habitats often involves
prescribed fire and reduced pine densities. If
small home-range size is a surrogate for hab-
itat suitability, managers should maintain a
continuous matrix of herbaceous understory
vegetation. Clear-cuts should be managed for
perches (Dunning and Watts 1990), abundant
herbaceous vegetation (Mills et al. 1991, Dun-
ning 1993), and connectivity with nearby suit-
able habitat (Dunning et al. 1995). Although
it is known that mature stands of pine become
more suitable for sparrows with frequent pre-
scribed fire and moderate basal areas of pine,
further research should ascertain whether
home-range size in mature pine stands is de-
pendent on the distribution of herbaceous un-
derstory, as arthropod communities in mature
pine stands are a function of primary produc-
tivity occurring on the forest floor (Cross
1956). Additional information on Bachman’s
Sparrow reproduction and survival across the
range of occupied habitats is needed to deter-
mine the viability of populations inhabiting
intensively managed industrial forests versus
forests managed on longer logging rotations
with fire management.

ACKNOWLEDGMENTS

This project was funded by the USGS Biological
Resources Division and by the U.S. Department of En-
ergy— Savannah River Operations Office through the
U.S. Forest Service — Savannah River under Interagen-
cy Agreement DE-AI09-00SR221 88 (Cooperative
Agreement contract no. 12-11-008-876). J. C. Kilgo,
G. O. Ware, J. B. Dunning, Jr., J. Blake, and two anon-

Stober and Krementz • BACHMAN’S SPARROW HOME-RANGE SIZE

143

ymous reviewers commented on the manuscript.

Thanks to J. S. Christie, A. Allen, H. McPherson, C.

E. Moorman, and J. B. Dunning, Jr., for assistance in

the field.

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The Wilson Journal of Ornithology 1 18(2): 145— 15 1 , 2006

NESTING SUCCESS AND BREEDING BIOLOGY OF CERULEAN

WARBLERS IN MICHIGAN

CHRISTOPHER M. ROGERS1

ABSTRACT. — The Cerulean Warbler ( Dendroica cerulea ) is a Nearctic-Neotropical migratory bird species
that has declined significantly over the long-term. Poor reproductive success may be an important factor con-
tributing to the observed decline, but reproductive output has been measured for very few breeding populations.
From 2003 to 2005, I intensively monitored 22-23 breeding territories/year in each of two large forest habitats
in southwestern Michigan: oak- ( Quercus spp.) hickory ( Carya spp.) (2003: Barry State Game Area) and black
locust- ( Robinia pseudoacacia) black cherry ( Prunus serotina ) (2004-2005: Fort Custer U.S. Army Michigan
National Guard Reservation). I also gathered descriptive data on nonsong vocalizations and age of territorial
males. I describe four distinctive call notes, by sex, including the social and environmental contexts in which
they were used. Using two independent methods of aging, there was a strong preponderance of after-second-
year males at both study sites. Only 9 {n = 7 nests), 12 (n = 14), and 30 (n = 25) fledglings were produced
during the 2003, 2004, and 2005 breeding seasons, respectively. Nest heights were the highest recorded for this
species (mean = 19-20 m). During the same period, male reproductive success was 0.30, 0.32, and 0.80 male
fledglings/breeding male and 0.60, 0.63, and 1.58 fledglings/breeding pair. Productivity estimates, not thought
to be self-sustaining, were even lower than those of a well-studied Cerulean Warbler population in southern
Ontario. Thus, reproductive output was low in two geographic regions — representing three different forest
types — in the northern portions of the Cerulean Warbler’s breeding range. The preponderance of after-second-
year males at the Michigan study sites and in southern Ontario suggests a need for regional models of Cerulean
Warbler population dynamics. Received 21 March 2005, accepted 22 December 2005.

The population declines and conservation
status of Nearctic-Neotropical migratory bird
species are the subjects of much debate (As-
kins 1993, Martin and Finch 1995, Robinson
et al. 1995, James et al. 1996, Faaborg 2002).
The Cerulean Warbler {Dendroica cerulea) is
a Nearctic-Neotropical migratory bird species
that has declined significantly over the long-
term throughout its breeding range, prompting
a recent petition to the U.S. Fish and Wildlife
Service to assign the species threatened status
under the Endangered Species Act (U.S. Fish
and Wildlife Service 2002). Breeding Bird
Survey data (1966-2000) indicate a popula-
tion decline of 3. 04 %/year (Link and Sauer

2002) . In Canada, the Cerulean Warbler is a
Species of Special Concern (Committee on
the Status of Endangered Wildlife in Canada

2003) .

Populations of Cerulean Warblers may be
negatively affected by numerous alterations to
their breeding habitats, including the loss of
large tracts of mature deciduous forest, forest
fragmentation and associated negative factors
(e.g., increased brood parasitism and nest pre-

1 Dept, of Biological Sciences, Wichita State Univ.,
Wichita, KS 67260, USA; e-mail:
chris.rogers@wichita.edu

dation), increasing forest immaturity via ac-
celerated harvest cycles, and loss of key tree
species (Robbins et al. 1992, Hamel 2000).
Despite a recent increase in studies of breed-
ing Cerulean Warblers (Oliamyk and Robert-
son 1996; Jones et al. 2000, 2001, 2004; Gab-
be et al. 2002), critical information concerning
nest success and breeding biology in different
parts of the breeding range remains scarce.
Because the Cerulean Warbler is apparently
expanding its range along a northeastern front
(Hamel 2004), northern populations may be
important to its continued persistence. My ob-
jectives were to (1) gather data on nesting suc-
cess in two distinct forest habitats (oak-hick-
ory, locust-cherry) in southwestern Michigan,
and (2) describe the age structure of breeding
populations and the social context of nonsong
vocalizations, both poorly known for this pa-
rulid species. Because certain vocalizations
may be given near the nest by breeding adults,
the study of nonsong vocalizations is impor-
tant in evaluating nest productivity (Barg
2002).

METHODS

Study sites and periods. — I studied nest suc-
cess and breeding biology in two large forest
tracts in southwestern Michigan known to har-

145

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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

bor breeding populations of the Cerulean War-
bler (Barrows 1912, Brewer et al. 1991, Ro-
senberg et al. 2000). Site 1 is a 1,813-ha tract
of largely unfragmented oak- ( Quercus spp.)
hickory (Cary a spp.) and black walnut (Jug-
lans nigra ) forest in the Barry State Game
Area (BSGA), Barry County, Michigan (42°
35' N, 85° 26' W). BSGA is currently man-
aged for multiple wildlife conservation pur-
poses, including the production of game and
nongame species. The site was originally
abandoned farmland purchased piecemeal by
the state of Michigan in the 1940s; because of
natural succession, the forest at BGSA is now
relatively mature. The topography is low roll-
ing hills and depressions. Site 2 is a 2,849-ha
black locust ( Robinia pseudoacacia ) and
black cherry ( Prunus serotina ) forest in the
Fort Custer U.S. Army Michigan National
Guard Reservation (FTCU), Kalamazoo
County, Michigan (42° 18' N, 85° 19' W). The
site was obtained as farmland and scattered
homesteads by the U.S. government in 1917.
The topography is gentle hills with little relief.
BSGA and FTCU are 35 km apart, separated
by a landscape of small towns, small wood-
lots, marshes, lakes, and farmland. Both sites
are characterized by maturing forest with large
trees, occasional gaps, and an open understo-
ry— all habitat features preferred by Cerulean
Warblers. I studied Cerulean Warblers at
BSGA from 2 June to 27 July 2003, and at
FTCU from 15 May to 23 July 2004, and from
19 May to 25 July 2005.

Territory mapping, nest monitoring, and
nest-site characteristics . — In 2003 and 2004,
I mapped Cerulean Warbler territories accord-
ing to Bibby et al. (2000), whereby foci of
territorial male activity are the primary means
of identifying individual breeding territories.
At each site, males were often recognized by
song type (several frequently gave a distinctly
less-buzzy ending to their typical song), plum-
age variation (several had a distinct white su-
percilium), and differences in their stage of
the reproductive cycle. I marked locations of
male song perches on USGS 1:24,000 topo-
graphic maps that were enlarged (by comput-
er) 3X; enlarged maps showed topographic
detail clearly, including specific recognizable
ridges, depressions, small wetlands, and roads.
Mapping revealed preferred (tall) trees from
which individual males repeatedly sang

throughout the breeding season, usually in the
center of the territory. I gained additional in-
formation on territory boundaries by follow-
ing males as they patrolled and sang through-
out their territories, and by observing bound-
ary disputes (counter-singing and direct fights
involving male-male contact). I color-banded
14 territorial males in 2005 at FTCU, 10 of
which subsequently aided me in determining
territory boundaries that year; the remainder
were on territories that I did not monitor. All
males captured and banded were used in an
analysis of age structure. Established territory
boundaries were evident by mid- June at both
sites. Global Positioning System coordinates
were determined for estimated territory cen-
ters and plotted on topographical maps.

I intensively searched territories every 2—6
days (0. 5-2.0 hr/visit) for the presence of ac-
tive nests or newly fledged young; I observed
territories from 06:00 to 16:00 EST, with oc-
casional evening visits from 16:00 to 21:30.
Each territory check involved a complete tra-
verse through the entire territory, with stops
in and near all forest gaps to search for active
nests and adults giving contact calls. I moni-
tored nests every 2—4 days early in the nesting
cycle, and every day as fledging neared. I de-
fined successful nests as those from which > 1
warbler young fledged; failed nests were those
from which no warblers or only Brown-head-
ed Cowbirds (Molothrus ater ) fledged. Most
nests were very high (19—20 m) in the canopy
and nest contents could not be observed di-
rectly. I used a spotting scope (20-60X) to
observe female incubation and brooding be-
havior, and to count warbler and cowbird nest-
lings as they grew large enough to be seen
above the nest rim. As fledging approached,
large cowbird young were easily distinguished
from the much smaller warbler young by
plumage features, size, and vocalizations.
Fledglings recently fledged from previously
undiscovered nests (n — 9) were counted di-
rectly when they emitted loud begging calls.
To minimize underestimating Cerulean War-
bler reproduction, I identified to species and
recorded the locations of all begging fledg-
lings and alarm-calling adults of all avian spe-
cies in all foliage layers of each Cerulean
Warbler territory.

After each nest had failed or the young had
fledged, I recorded the following nest-tree and

Rogers • CERULEAN WARBLER BREEDING BIOLOGY

147

nest characteristics: nest-tree species; nest
height (distance from ground to nest bottom);
nest-tree height (distance from ground at stem
base to highest foliage); trunk distance (dis-
tance from nest to central tree axis, measured
from the ground); foliage distance (distance
from nest to nearest foliage below it); nest-
tree diameter at breast height (dbh); and gap
distance (distance from nest to any obvious
forest discontinuity >25 m2). Height ratio was
calculated as nest height/nest-tree height. All
heights were measured with a rangefinder ex-
cept foliage distance, which was estimated by
eye (nearest meter). 1 measured trunk distance
and gap distance with a transit.

Estimating age of territorial males. — Age
of breeding male Cerulean Warblers was es-
timated using two methods. Method 1 (2004-
2005), which provides a general estimate of
male age-class frequency, entailed using 10 X
32 binoculars to observe whether the bird had
a distinct white supercilium, purportedly pre-
sent only in second-year (SY) males and ab-
sent in after-second-year (ASY) males (Dunn
and Garrett 1997); nearly all males were ob-
served from <15 m. Method 2 (2005) was
conducted by an experienced bird bander, who
relied on a combination of molt limits and the
colors of flight and body contour-feathers
(Pyle 1997) to age the 14 captured territorial
males while they were in hand. The two in-
vestigators using the two different aging
methods recorded ages independently of one
another.

Nonsong vocalizations. — When monitoring
nests and territories for reproductive output, I
described nonsong vocalizations emitted by
both sexes of Cerulean Warblers and docu-
mented the social and environmental context
of those vocalizations. The resulting set of de-
scriptions likely represents the most common
nonsong vocalizations that this species makes
on the breeding grounds. I did not make audio
recordings and sonograms of these vocaliza-
tions; rather, I described them with previously
established terminology used for describing
vocalizations of wood warblers (Nolan 1978,
Getty 1993).

RESULTS

Territory defense. — From mid- to late May
each year, I often observed male Cerulean
Warblers at FTCU engaged in territorial chas-

ing and occasional physical fights (n = 5 ob-
served). Observations of the BSGA popula-
tion began in early June, when males had al-
ready established territories and were no lon-
ger chasing one another. Throughout June and
much of July at both sites (and in mid- to late
May at FTCU), males sang prodigiously, often
within 10-30 m of one another during bouts
of intense counter-singing at their territorial
borders; counter-singing sometimes involved
three males.

Nonsong vocalizations. — Adult Cerulean
Warblers emitted four distinct nonsong vocal-
izations over the 3-year study. (1) Both sexes
gave a metallic, buzzy zzee call note, singly
or in series of 1-6 notes. I heard female zzee
calls 127 times, and knew the behavioral con-
text of 87: 23 occurred when females were
foraging alone or with the male or a fledgling
nearby; 33 when near, leaving, or approaching
an active nest; 29 when at an active nest; and
2 (a series of loud zzees) occurred when my
presence near the female’s nest apparently
caused alarm. Males gave only 24 zzee calls,
with the behavioral context known in 23 in-
stances: 13 were given shortly after counter-
singing near a territorial border; 6 while ap-
parently foraging alone or with a fledgling
nearby; 3 when near, leaving, or approaching
an active nest; and 1 when my presence
caused apparent alarm. The zzee call is prob-
ably the metallic call note described as a flight
and contact call (Oliarnyk and Robertson
1996). (2) Both adults frequently gave long
series of sweet, nonmetallic chip notes when
I was near a nest containing nestlings or fledg-
lings; in three cases, a female with a nest un-
der construction engaged in extensive chip-
ping when I was in the territory. (3) A high-
pitched, nonmetallic alarm tchip was heard six
times: twice from females, apparently alarmed
by a nearby Turkey Vulture ( Cathartes aura)
or a female Brown-headed Cowbird (the latter
near an active nest); once from a territorial
male, apparently alarmed by a nearby Red-
tailed Hawk ( Buteo jamaicensis); and three
times from three different females when I was
near a nest with nestlings. (4) On 10 occa-
sions, I heard territorial males — always ac-
companying a female with an active nest
(eggs or young) or a nest under construction —
give a series of very soft, almost warbled
notes; apparently, this was the Cerulean War-

148

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

TABLE 1. Nest-tree and nest-location variables (mean ± SE) for Cerulean Warblers at Barry State Game
Area (BSGA; n = 6 nests in 2003) and Fort Custer (FTCU; n = 12 nests in 2004, n = 18 nests in 2005). All
values are in meters, except dbh (cm) and nest height/tree height (proportion). See methods for definitions of
variables.

Nest-tree Nest height/ Distance Distance Distance

Site

Nest-tree dbh

height

Nest height

tree height

to bole

to foliage

to gap

BSGA

FTCU

45.5 ± 6.6
38.1 ± 2.9
41.9 ± 1.0

21.8 ± 2.0
26.0 ±1.1
26.6 ± 4.0

18.7 ± 2.1

19.0 ± 1.4

20.1 ± 0.2

0.84 ± 0.04
0.73 ± 0.04
0.75 ± 0.37

3.5 ± 0.6
3.8 ± 0.5
4.1 ± 0.2

4.9 ± 1.9
5.8 ± 1.1
7.2 ± 0.4

17.7 ± 7.2
1.5 ± 0.8
2.9 ± 0.3

bier’s whisper “song.” I describe this vocali-
zation as nonsong, as it differed strongly from
the typical song.

Nest placement and tree species. — Nests
usually were placed on a horizontal limb with
a bifurcation immediately distal to the nest,
but occasionally they were placed on a lateral
branch in a cluster of small, upright shoots
with leaves. One nest was inside a spherical
mass of Virginia creeper (P arthenocissus
quinquefolia) vines at the end of a short lateral
branch. Mean nest-tree dbh exceeded 38 cm,
and nest-tree height exceeded 21 m in all 3
years; at both sites, nest height averaged 19-
20 m (Table 1). Trunk and foliage distances
were essentially similar at the two sites,
whereas gap distance differed strongly; nests
tended to be found near roads (unpaved sand
and gravel) at FTCU, but not at BSGA, where
roads were fewer and narrower (Table 1). At
BSGA, the closest gap for one nest was a dirt
road, and for five nests the closest gaps were
natural forest openings (one small marsh and
four light gaps where trees had fallen, allow-
ing light to reach the forest floor); at FTCU
(years pooled), the closest gaps were roads
(13 nests) and natural forest openings (appar-
ently all light gaps; 17 nests). Nest height as
a percentage of tree height was slightly greater
at BSGA than at FTCU (Student’s t = 2.60,
P = 0.014, df = 32; Table 1). At BSGA, four
tree species were used for nesting: black oak
( Q . velutina; n = 3), northern red oak ( Q . rub-
ra; n = 1), white oak ( Q . alba ; n = 1), and
black walnut {n = 1). At FTCU (years

pooled), six tree species were used for nest-
ing: black locust ( n = 17), black walnut ( n =
7), black cherry ( n = 3), sugar maple ( Acer
saccharum\ n — 1), and American sycamore
( Platanus occidentalis\ n = 1).

Male age. — Most males lacked a white su-
percilium (visible through binoculars) at

BSGA (9 of 10), FTCU in 2004 (14 of 16),
and FTCU in 2005 (16 of 20). The frequency
distributions of the two male plumage types
did not differ between sites in 2004 (x2 —
0.04, df = 1, P = 0.85). Pooling all years,
84.8% (39 of 46) of males lacked a white su-
percilium. In 2005 at FTCU, 10 of the 14
males captured and aged in the hand were
identified as ASY males, and 4 were identified
as SY males.

Pairing, nest success, and brood parasit-
ism.— Fifteen females were found on 23 ter-
ritories at BSGA, and 19 females were found
on 23 (2004) and 22 (2005) territories at
FTCU. The relative frequency of paired and
unpaired males did not differ between study
sites (2003 versus 2004, x2 = 1.80, df = 1, P
= 0.18). Apparent nest success was 43% at
BSGA and FTCU in 2004 and 52% at FTCU
in 2005. (As most nests were high in the can-
opy, exact hatching dates could not be deter-
mined, and Mayfield estimates of nest surviv-
al could not be calculated.) At FTCU, two
nests were found for each of three females in
2004, and two nests were found for each of
four females in 2005, indicating renesting af-
ter nest failure; no confirmed renests were re-
corded at BSGA. Despite an appreciable rate
of nest failure, the exact cause of nest failure
could be determined for only 12 nests: 3 failed
due to brood parasitism, (one cowbird young
fledged in each case), 2 failed due to exposure
(initial nest superstructure destroyed by heavy
rain or nest branch broken off by high winds),
and 7 failed due to predation. In the last case,
the nest’s rim was torn and/or the entire nest
was tipped. In 2004, Cerulean Warbler pairs
at BSGA and FTCU fledged 0.1 cowbird/
breeding pair and 0.1 cowbird/nest; in 2005,
warbler pairs at FTCU fledged 0.2 cowbird/
breeding pair and 0.1 cowbird/nest.

In 23 territories intensively monitored at

Rogers • CERULEAN WARBLER BREEDING BIOLOGY

149

BSGA in 2003, six nests and one recently
fledged brood were found, and nine fledglings
(3.0/successful nest) were produced. In 23 ter-
ritories monitored at FTCU in 2004, 12 nests
and 2 recently fledged broods were found, and
12 young fledged (2.0 per successful nest). In
22 territories monitored at FTCU in 2005, 19
nests and 6 recently fledged broods were
found, and 30 fledglings (2.3 per successful
nest) were produced.

Male reproductive success. — At BSGA,
male reproductive success was 0.20 (all
males) and 0.30 (paired males only) male
fledglings/male. Corresponding values at
FTCU were 0.26 and 0.32 male fledglings/
male in 2004, and 0.68 and 0.79 in 2005. The
number of fledglings/breeding pair was 0.60
at BSGA, and 0.63 (2004) and 1.58 (2005) at
FTCU.

DISCUSSION

Nest placement. — As previous workers have
found in other parts of the species’ breeding
range (Oliarnyk and Robertson 1996, Hamel
2000, Jones and Robertson 2001, Jones et al.
2001), Cerulean Warblers in Michigan chose
a diversity of tree species for nest placement.
Nests at BSGA and FTCU averaged 19-20 m
in height; typical (pre-ice storm) nest height
in a southern Ontario population was 1 1 .6—
11.8 m (Oliarnyk and Robertson 1996, Jones
et al. 2001) and the range-wide mean nest
height (excluding the present study) is 1 1 .4 m
(Hamel 2000). Nest height/nest-tree height of
nests in the Ontario population (0.61) was
lower than in southern Michigan (0.73-0.84).
Thus, not only did Michigan Cerulean War-
blers choose high nest sites, they also nested
relatively high within a given nest tree. Given
the intensive season-long nest searches con-
ducted throughout all territories studied, it is
unlikely that any low nests were missed.

Nonsong vocalizations. — The zzee call note
appears multifunctional, as it was used by
both sexes in a variety of situations. It was
given more often by females, which appar-
ently used the note as a contact call when they
were at, or close to, the nest; the call may also
function as an alarm note. Therefore, I used
female zzee calls as cues for finding nests;
when heard, I attempted to watch the female
return to an active nest, or to find the nest if
the call was thought to have been given by a

sitting female. The relatively few occurrences
of male zzees were nearly all associated with
active territorial defense against a nearby rival
male, but several were given near an active
nest. The sweet chip notes — given in response
to my presence near nests containing older
nestlings or fledglings — were alarm notes gen-
erally resembling the alarm chips of other
North American parulids (Getty 1993). The
higher-pitched tchip alarm note was rarely
heard, and only in response to either a poten-
tial predator, a cowbird near the nest, or my
presence in the territory. I heard the whisper
“song” 10 times, all in the context of a male
interacting with a female near an active nest.
Intersexual behavior was difficult to observe,
as birds generally remained high in the forest
canopy, but males may give this vocalization
as a “song cue” to nesting females (Barg
2002).

Male age. — Cerulean Warbler males with a
white supercilium (SY males, Dunn and Gar-
rett 1997) composed 10-20% of all territorial
males at my study sites. Only 4 of the 14
banded males in 2005 were in the SY age
class. Although aging by supercilium alone is,
at best, an approximation, general agreement
between the two aging methods used suggests
that a significant majority of the breeding ter-
ritorial males were in their second or a sub-
sequent breeding season. In southern Ontario,
15% of males are thought to be SY birds
(Jones et al. 2004). Thus, at least two popu-
lations in the northern part of the breeding
range are biased toward older males. The two
southwestern Michigan populations I studied
are approximately 774 km from the southern
Ontario study site. Within the range of another
Dendroica species, the Black- throated Blue
Warbler ( D . caerulescens ), Graves (1997)
found latitudinal segregation among males, by
age class. Furthermore, first-year American
Redstart ( Setophaga ruticilla ) males are
forced into marginal breeding habitat by older
males (Ficken and Ficken 1967, Sherry and
Holmes 1989). Further field study is required
to investigate possible habitat-specificity and/
or broader geographical extent of age-struc-
tured breeding populations of Cerulean War-
blers.

Population productivity. — Excluding un-
paired males, male reproductive success was
0.30-0.32 male fledglings/breeding male at

150

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

BSGA (2003) and FTCU (2004) and 0.79
male fledglings/breeding male at FTCU
(2005). Reproductive output in southwestern
Michigan was, therefore, poor in two distinct
habitat types in 2 of 3 years, and in all 3 years
it was lower than the productivity of a south-
ern Ontario population (0.94 male fledglings/
breeding male) — thought to be a sink popu-
lation requiring 1.7 male fledglings/breeding
male for sustainability (Jones et al. 2004).
Survival estimates for the Michigan study
populations are needed, however, before de-
termining whether they are self-sustaining or
not.

A previous study of passerine populations
in southwestern Michigan (Rogers and Caro
1998) indicated that corvid nest predators
(American Crow, Corvus brachyrhynchos;
Blue Jay, Cyanocitta cristata ) and brood par-
asites (Brown-headed Cowbird) are regular in-
habitants of all habitat types, including the in-
terior of large forest tracts, as well as subur-
ban, exurban, and agricultural areas. Avian
nest predators and cowbirds were frequently
observed in both forest edge and interior on
annual point counts from 1993 to 2004 (CMR
unpubl. data). Corvids, therefore, are candi-
dates for causing nest failure in Cerulean War-
blers at BSGA and FTCU. Nest predation also
may have been caused by eastern fox squirrels
(, Sciurus niger), which were common at both
study sites, and eastern chipmunks ( Tamias
striatus ), which were abundant at BSGA.
Both sciurid species were observed in trees at
heights exceeding 10 m. Effects of cowbird
parasitism were low in all 3 years; however,
>60% of the Hooded Warbler ( Wilsonia ci-
trina ) nests at FTCU were parasitized by cow-
birds in 2004-2005 (R. Adams pers. comm.).
The Cerulean Warbler’s status as a poor cow-
bird host deserves further attention.

A possible source of error in my study was
the failure to detect fledglings in all territories.
Although this cannot be completely discount-
ed, any error was probably negligible, as Ce-
rulean Warbler adults feeding older nestlings
or fledglings typically became excited, and
gave frequent and obvious alarm calls (chips);
in addition, all fledged broods and adults (of
all species) emitting alarm-chips were identi-
fied to species. It is unlikely that enough
fledglings were missed to bias my estimates
of (low) reproductive output. Some territories

yielded no fledglings for an entire breeding
season. This is not necessarily surprising, as
the breeding season is short: no July nest
starts were found in 2 years, and the species
begins breeding after spring migration in mid-
May. At BSGA in 2003, females were not de-
tected on 8 of 23 territories (35%); thus, some
females may have been missed. However,
Holmes et al. (1996) found a similar percent-
age (27%) of unpaired males among Black-
throated Blue Warblers.

Low reproductive output among Cerulean
Warblers may be a factor contributing to their
long-term population decline. To test this hy-
pothesis more rigorously, additional studies of
this species are needed. Specifically, repro-
ductive output should be measured in more
regions. In addition, longer-term studies
would be useful for assessing temporal vari-
ation in reproduction within individual sites.
Finally, age structure strongly biased toward
older males suggests a need for regional, as
opposed to local, models of the Cerulean War-
bler’s population dynamics.

ACKNOWLEDGMENTS

The able field assistance of staff members of the
Kalamazoo Nature Center is gratefully acknowledged,
particularly that of B. Nelson, who captured and aged
male Cerulean Warblers. The U.S. Army Fort Custer
Reserve unit and the Michigan Department of Natural
Resources kindly permitted access to the study sites,
and Kellogg Biological Station provided important lo-
gistical support. J. Jones and two anonymous referees
provided useful comments on an earlier version of the
manuscript. This is contribution number 1210 of Kel-
logg Biological Station.

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The Wilson Journal of Ornithology 1 18(2): 152— 163, 2006

MIGRANT SHOREBIRD PREDATION ON BENTHIC
INVERTEBRATES ALONG THE ILLINOIS RIVER, ILLINOIS

GABRIEL L. HAMER,1 246 EDWARD J. HESKE,12 JEFFREY D. BRAWN,23 AND

PATRICK W. BROWN15

ABSTRACT. — We evaluated the effect of shorebird predation on invertebrates at a wetland complex along
the Illinois River, west-central Illinois, during spring migration. Using a new exclosure experiment design adapted
to the shifting nature of foraging microhabitat of interior wetlands, we found that shorebird predation did not
significantly deplete total invertebrate density or total biomass in open (no exclosure) versus exclosure treatments.
Chironomids and oligochaetes were the most common invertebrates occurring in substrate samples. The density
of oligochaetes was lower in open treatments, though the degree of difference varied both spatially and tem-
porally. Shorebird density was positively correlated with the amount of invertebrate biomass removed from the
substrate during the late-May sampling period. Our results suggest that shorebirds use an opportunistic foraging
strategy and consume the most abundant invertebrate prey. The dynamic hydrology at our study site likely
played a role in preventing invertebrate depletion by continually exposing new foraging areas and prey. Received
16 February 2005, accepted 30 December 2005.

Migrating shorebirds (Charadriiformes) re-
quire stopover resources for rest and rapid ac-
cumulation of energy to fuel their transconti-
nental migration (Myers et al. 1987). As fresh-
water wetlands in the United States continue
to be converted to agriculture and develop-
ment (Dahl 2000), the reduction in stopover
areas is believed to have negative effects on
shorebird populations (Sutherland and Goss-
Custard 1991, Harrington et al. 2002). Con-
sequently, many North American shorebirds
are listed as threatened, endangered, or species
of special concern (Brown et al. 2001, Mor-
rison et al. 2001), including Greater Yellow-
legs ( Tringa melanoleuca ), Short-billed Dow-
itcher ( Limnodromus griseus), and Buff-
breasted Sandpiper ( Tryngites subruficollis ) in
the Mississippi Alluvial Valley and Great
Lakes region.

1 Center for Wildlife and Plant Ecology, Illinois Nat-
ural History Survey, 607 E. Peabody Dr., Champaign,
IL 61820, USA.

2 Dept, of Natural Resources and Environmental
Sciences, Univ. of Illinois, W-503 Turner Hall, 1102
S. Goodwin Ave., Urbana, IL 61801, USA.

3 Dept, of Animal Biology, Univ. of Illinois, Shel-
ford Vivarium, 606 E. Healey, Champaign, IL 61820,
USA.

4 Current address: Dept, of Fisheries and Wildlife,
Michigan State Univ., 13 Natural Resources, East Lan-
sing, MI 48824, USA.

5 Current address: Michigan Natural Features Inven-
tory, Michigan State Univ. Extension. P.O. Box 30444,
Lansing. MI 48909. USA.

6 Corresponding author; e-mail: ghamer@msu.edu

While migrating through the interior United
States, shorebirds are faced with unpredictable
habitats that are much different from coastal
systems (Skagen and Knopf 1994a). The pre-
dictability of tidal cycles and blooms of food
resources in the intertidal zones of coastal sys-
tems support large concentrations of shore-
birds and high levels of site fidelity in loca-
tions such as Delaware Bay along the north-
east Atlantic coast and the Copper River Delta
in the Gulf of Alaska. In contrast, shorebirds
using interior flyways are more dispersed and
occur at stopover habitats in smaller numbers
than those using coastal flyways (Skagen and
Knopf 1993). Some shorebirds undertake
long, nonstop flights; many other species do
not depart with enough fuel to reach their final
destinations and must make multiple stops to
refuel during migration (White and Mitchell

1990, Skagen and Knopf 1994b, Farmer and
Wiens 1999) — a less energetically challenging
strategy (Piersma 1987).

Shorebirds are opportunistic feeders and
readily shift their diet to exploit locally abun-
dant invertebrate resources (Skagen and Oman
1996). Studies of shorebird diet among inte-
rior stopover habitats indicate that chironomid
larvae are the dominant prey items (Helmers

1991, Mihue et al. 1997). Much less is known
about the importance of oligochaetes — often
the most abundant invertebrates in freshwater
mudflats in the Mississippi Alluvial Valley
(Elliott-Smith 2003, Hamer 2004, Mitchell
and Grubaugh 2005) — as prey (Safran et al.

152

Hamer et al. • SHOREBIRD PREDATION ON BENTHIC INVERTEBRATES

153

1997). The importance of oligochaetes may be
underestimated because they are small, frag-
ile, sensitive to post-mortem digestion in
esophageal, proventricular, and gizzard con-
tents, and are thus often ignored in analysis
(Rundle 1982, Safran et al. 1997). However,
oligochaetes are comparable to chironomids in
caloric value (5,575 and 5,424 calories/g dry
weight, respectively), crude protein, and gross
energy (Cummins and Wuycheck 1971, An-
derson and Smith 1998).

Observational studies, esophageal analyses,
and exclosure experiments have been used to
assess the interactions between shorebirds and
their prey (Brooks 1967, Schneider 1978,
Evans et al. 1979, Rundle 1982, Swennen
1990). Food consumption has been measured
using indirect visual methods in many studies
of the foraging ecology of Palearctic, coastal
shorebirds (Evans et al. 1979, Moreira 1997).
These indirect methods, however, are often
challenging to use in inland systems where
prey are small and successful and unsuccess-
ful foraging pecks and probes are not distin-
guishable. Collecting individual shorebirds for
esophageal analysis provides valuable infor-
mation on diet, but it does not determine the
effect of shorebird predation on the inverte-
brate community and may produce bias
caused by missing soft-bodied invertebrates
(Rundle 1982). A less invasive technique for
investigating shorebird-prey relationships is to
use exclosure experiments, also termed caging
experiments, which entail structures that pre-
vent shorebirds from feeding on invertebrates
within the enclosed substrate. The invertebrate
community within the exclosure can be com-
pared with that in equivalent substrate outside
the exclosure for an indirect measure of shore-
bird predation on invertebrates.

Recently, researchers have implemented ex-
closure experiments at freshwater shorebird
stopover sites (Mihue et al. 1997, Ashley
2000, Mitchell and Grubaugh 2005), but pre-
viously the majority had been conducted in
marine intertidal systems (Wilson 1991, Mer-
cier and McNeil 1994, Weber and Haig 1997).
Results of these exclosure experiments are
varied; some studies have revealed up to 90%
reductions in prey densities due to shorebird
predation (Schneider and Harrington 1981,
Szekely and Bamberger 1992), whereas other
studies document no measurable effect (Raf-

faelli and Milne 1987, Mitchell and Grubaugh
2005). During migration in the interior fly-
ways, the extent of shorebird predation on dif-
ferent invertebrate taxa at stopover areas is not
clear.

We conducted an exclosure experiment at a
shorebird stopover location in the Upper Mis-
sissippi Alluvial Valley. Our primary objec-
tives were to evaluate (1) whether shorebird
predation depletes invertebrate prey during
migration along an interior flyway, (2) which
invertebrates and size classes are removed
from the substrate, (3) the chronology in
abundance and biomass of benthic inverte-
brates, and (4) a new exclosure-experiment
design adapted to the unpredictable nature of
interior shorebird foraging habitats.

METHODS

Study area. — Our study was conducted at
Chautauqua National Wildlife Refuge (NWR)
(40° 38' N, 89° 99' W) and Emiquon NWR
(40° 32' N, 90°09'W), which are part of a
large wetland complex along the Illinois River
in west-central Illinois near Havana (Fig. 1 A).
The 1,816-ha refuge at Chautauqua NWR was
established in 1936 and consists of large back-
water lakes, and bottomland and upland for-
est. Chautauqua also has been designated a
stopover of international importance by the
Western Hemisphere Shorebird Reserve Net-
work (Harrington and Perry 1995). The late
drawdown in July and August at this refuge
creates extensive, shallow-water mudflats at-
tracting an estimated 100,000 to 250,000
shorebirds each fall (Bailey 2003). Compara-
tively little shorebird habitat is available at
Chautauqua in the spring, when water levels
are elevated to prevent encroachment of ex-
otic invasives — black willow ( Salix nigra ) and
cocklebur ( Xanthium strumarium ) — that inter-
fere with moist-soil plant production.

Emiquon NWR is an 856-ha refuge com-
posed of backwater lakes, sloughs, forested
wetlands, and a variety of other terrestrial hab-
itats. Because Emiquon was only just acquired
in 1993, much of the refuge comprises newly
established wetland, and portions will remain
in agriculture until leases with private land-
owners expire. The refuge is divided into two
main units: Wilder Tract (197 ha) and South
Globe (288 ha). The Wilder Tract was taken
out of agricultural production in 1998 and is

154

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

FIG. 1 . (A) Location of the three study sites near

Havana, Illinois (Chautauqua South Pool, Emiquon
South Globe, Emiquon Wilder Tract) where shorebird
predation was studied from February to June 2004.
White squares show approximate location of study
plots. (B) Depiction of a plot (1 ha) containing one
exclosure and one open (no exclosure) treatment used
in this study. The dashed lines indicate approximate
location of the shoreline (mud/water interface where
shorebirds foraged).

managed as a moist-soil unit. The South
Globe unit was taken out of production for the
first time in 2004, when the remaining corn
and bean stubble were flooded to create ex-
tensive shallow water habitat.

Field methods. — The exclosure experiment
was conducted during spring shorebird migra-
tion from March through June 2004. Three
plots were established at each of the three field
sites (Chautauqua South Pool, Emiquon Wil-
der Tract, Emiquon South Globe) for a total
of nine plots (Fig. 1A). Each plot was 1 ha in
size (100 X 100 m, designated by flags at each
corner) and contained both an exclosure treat-
ment and an open treatment. The exclosure
consisted of a sheet (16 X 1 m) of metal fenc-
ing (mesh = 5X10 cm) positioned horizon-
tally and supported 10 cm above the substrate
by metal stakes at each corner and at 5-m in-
tervals along both sides (Fig. IB). The long
axis of the exclosure was placed perpendicular

to the shoreline so that the shoreline always
remained within some part of the exclosure as
water levels fluctuated. Because the fence
sagged between the metal stakes, small sec-
tions of black willow branches were used to
prop up the fence to maintain the entire unit
at a 10-cm height. Few predators of benthic
invertebrates — other than shorebirds, largely
predatory invertebrates, and crayfish — occur
in this inland system. The lack of sides on the
exclosure, however, allowed access by other
predators and excluded only avian predators.
The open treatment lacked any fencing but
was marked by flags to the same dimensions
of the exclosure. The open and exclosure
treatments were placed 40 m apart and 30 m
from the edges of the plot (Fig. IB). Because
of the changing hydrology and changing lo-
cations of shorebird habitat, plots were not es-
tablished at the same time. The first plot was
established on 27 February and the last on 29
April.

We determined shorebird use of the plots
by conducting censuses twice per week at
each plot during the peak of migration (mid-
April to the end of May) and once per week
during the remainder of spring migration.
Means were calculated for each 2-week period
for each plot to determine average shorebird
density in the 2-week period before inverte-
brate sampling. The first survey was on 6
March and the last was on 16 June. During
each census, we identified and counted all
shorebirds in the 1-ha plot (from a vehicle or
on foot) using 8 X 42 binoculars or a 15-45X
spotting scope. We recorded water levels dur-
ing each census using a PVC pipe (vertical
pole) marked at 1-cm intervals; a pole was
placed permanently outside each plot in water
that was deeper than it was inside the plot. We
determined change in water level by compar-
ing the water level from each 2-week sam-
pling period at each plot. The absolute value
of the change in water level was used in the
analysis.

We sampled for benthic invertebrates in
both treatments when each plot was estab-
lished and then at 2-week intervals throughout
spring migration. The first samples were taken
on 27 February and the last on 6 June. Each
treatment was sampled at the shoreline (where
edge of surface water meets mudflat), which
was the primary shorebird foraging zone.

Hamer et al. • SHOREBIRD PREDATION ON BENTHIC INVERTEBRATES

155

Only one core sample per 2-week interval was
taken from each treatment to avoid potential
resampling of the same area in subsequent
sampling periods and to avoid sediment dis-
turbance. Ashley et al. (2000) conducted a
study in which two cores were sampled in
each treatment; they found no difference be-
tween the subsamples and recommended elim-
inating them in future exclosure studies. We
used core samplers, similar to those developed
by Swanson (1978), that were modified by us-
ing metal conduit piping with a sharpened
edge. We extracted core samples 5 cm in di-
ameter to a depth of 5 cm (Sherfy et al. 2000).
After inserting the core sampler into the sub-
strate, we placed a plumber’s stopper plug in
the end of the core sampler to aid in removal
of the core. Contents of the sampler were
placed in a resealable plastic bag containing
95% ethyl alcohol, stained with Rose Bengal,
and kept cool until sorted.

Laboratory methods. — Invertebrates were
removed from the preserved sample using a
number 30 mesh sieve and identified to order
or family according to Pennak (1989) and
Merritt and Cummins (1996). All samples
were sorted by one observer to reduce bias.
Chironomids and gastropods were sorted into
two size classes: <5 mm and >5 mm. All
invertebrates, excluding gastropods, were
dried at 70° C for 24 hr on pre-dried and pre-
weighed glass microfiber filters. To determine
biomass, we weighed samples to the nearest
0.0001 g using a Mettler balance. Invertebrate
densities (no. individuals) and biomasses (g)
are reported per m2.

Statistical analysis. — To determine whether
differences existed between the two treat-
ments prior to the experiment, we used paired
r-tests to compare measures of invertebrate
density and biomass before we established the
plots. To analyze invertebrate density and bio-
mass, we used a repeated measures mixed-
model analysis of variance using PROC
MIXED (Littell et al. 1998, Sherfy and Kirk-
patrick 2003) in SAS 8.0 (SAS Institute, Inc.
2000). Fixed factors in the model included
sampling period, site, predation, and all two-
way and three-way interactions. Predation
(defined as the number of invertebrates re-
moved) was determined by subtracting the
values for invertebrates in the open treatment
from values for invertebrates in the exclosure

treatment, for each pair. Values above zero in-
dicate greater invertebrate densities in the ex-
closures, suggesting that shorebirds removed
invertebrates from outside the exclosure treat-
ment. The random factor of plot (site) was in-
cluded as an error term in the model; site rep-
resents the main blocking factor. To avoid
problems with different initiation dates for the
plots, we used samples only from early May,
late May, and early June in the PROC MIXED
analysis, which matched the timing of shore-
bird migration. We also included shorebird
density (log10 [X + 1 ]-transformed) and
change in water level as covariates in the
model.

A separate analysis was performed for all
eight invertebrate density (individuals/m2)
variables (oligochaete, total chironomid, small
chironomid, large chironomid, total gastropod,
small gastropod, large gastropod, total inver-
tebrate) and for invertebrate biomass (g/m2).
Data on large chironomids included many
zero values that resulted in an infinite likeli-
hood error; therefore, they are not reported.
To meet assumptions of normality, we trans-
formed all invertebrate data (log10 [X + 1])
prior to analysis.

PROC MIXED allows specification of the
covariance structure of the R matrix (Littell et
al. 2000). We used the compound-symmetry
structure, which has constant variance and co-
variance between repeated measures and as-
sumes that all repeated measures on a subject
(i.e., plots) are equally correlated regardless of
their temporal relationship. We used linear re-
gression to analyze correlations between
shorebird density and invertebrate density, and
between shorebird density and biomass re-
moved, in the nine plots for the early May and
late May sampling periods. Statistical signifi-
cance was set at P < 0.05 and all means are
presented ± SE.

RESULTS

We found no difference in oligochaete den-
sity ( t = 0.25, df = 15, P = 0.81) or inver-
tebrate biomass ( t = 0.02, df = 15, P = 0.98)
between the exclosure and open treatments
from the initial samples taken just before the
plots were established. Differences in chiron-
omid density (t = 2.15, df = 15, P — 0.048)
and invertebrate density ( t = 2.22, df = 15, P
= 0.043) between the exclosure and open

156

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

treatment indicated a heterogeneous inverte-
brate community at the onset of the experi-
ment.

We conducted 116 shorebird surveys and
observed 15 shorebird and 11 waterfowl spe-
cies foraging inside the plots. We observed
838 shorebirds, 89% of which consisted of
Least Sandpiper ( Calidris minutillcr, n = 309),
Pectoral Sandpiper ( Calidris melanotos’, n =
268), Lesser Yellowlegs ( Tringa flavipes', n =
118), and Killdeer ( Charadrius vociferus; n =
49). We observed 463 waterfowl, 94% of
which were Green- winged Teal {Anas crecca\
n = 145), Northern Shoveler (A. clypeata\ n
= 110), Blue-winged Teal (A. discors\ n =
105), and Mallard (A. platyrhynchos\ n = 76).
During the early-May to early- June sampling
periods used in the PROC MIXED analysis,
only 22 waterfowl and 677 shorebirds were
observed in the plots. Mean shorebird density
across all sites from late March to early June
was 6.3/ha ± 1.5 (n = 36); peak density oc-
curred in early May (12.3/ha ± 2.8, n = 9;
Fig. 2). The highest shorebird density (39.8/
ha) occurred at Chautauqua on 20 May.

We collected 108 benthic core samples, but
not all of these were used in the analysis due
to the dynamic hydrology. Oligochaete den-
sity (all sites combined) from late March to
early June was 15,137.5/m2 ± 3,005.1 in ex-
closure treatments ( n — 36; Fig. 2) versus
11,798.8/m2 ± 3,131.4 {n = 36) in open treat-
ments. Chironomid density was 2,291.9/m2 ±
461.1 ( n = 36) in exclosure treatments and
2,306.0/m2 ± 573.0 ( n = 36) in open treat-
ments. Oligochaete density peaked in late
May (22,975.1/m2 ± 8,999.8; n = 36) and chi-
ronomid density peaked in early May
(5.715.5/m2 ± 1,548.5; n = 36). The greatest
oligochaete density observed in a single sam-
ple occurred on 20 May in an open treatment
at Emiquon Wilder Tract (88,618.2/m2), and
the greatest chironomid density was recorded
on 7 May from the same site (16,297.6/m2).

Oligochaete density (F126 = 7.20, P =
0.013) and large gastropod density {Fx 26 =
0.21, P = 0.049) differed between treatments,
indicating a significant predation effect (Table
1); a significant predation X period X site in-
teraction for oligochaetes indicated that the ef-
fect varied both spatially and temporally (F426
= 3.19, P = 0.029). The grand mean for oli-
gochaete density was 1.2X greater in the ex-

closure than in the open treatments. Based on
the total of mean invertebrate densities for all
the plots, shorebirds removed 18.9% of the
total invertebrates from the substrate. Density
of chironomids, total invertebrate density, and
total invertebrate biomass did not differ be-
tween treatments.

Mean change in water level (all sites com-
bined) was 10.33 ± 2.23 cm {n = 36). The
change in water level influenced only oligo-
chaete density (F126 = 4.45, P = 0.045);
shorebird density had no influence on any re-
sponse variables (Table 1). Shorebird density
was positively correlated with invertebrate
biomass removed (r2 = 0.64, P = 0.010) and
invertebrate density removed (r2 = 0.39, P =
0.071) in late May (Fig. 3). Chautauqua con-
tributed the most to the positive correlation
between shorebird density and invertebrate
biomass removed.

DISCUSSION

Exclosure design. — A concern with exclo-
sure experiments in soft sediments is the pres-
ence of artifacts produced by the exclosure
structure (Vimstein 1978). Many of these ar-
tifacts, however, are associated with marine
intertidal systems, where the influences of ex-
closure structure appear greater than in non-
intertidal systems. Hulberg and Oliver (1980)
found that exclosures alter the level of sedi-
mentation, which in turn influences popula-
tions of polychaetes. Their study was per-
formed on a wave-exposed coastal beach that
is a very different environment from our sys-
tem, which lacked wave perturbations and a
diurnal tide. Quammen (1981) established an
exclosure design to separate the effects of
multiple predators within a system: a floating
exclosure without sides prevented access by
shorebirds while allowing fish to enter the ex-
closure during high tide. This design, how-
ever, is not as appropriate for a system without
tides and with fewer predators of benthic in-
vertebrates. Although common carp {Cyprinus
carpio ) were observed in our impoundments,
no fish were observed foraging at the soil/wa-
ter interface where core samples were taken.
Even if other predators of benthic inverte-
brates went unnoticed, the lack of sides on our
exclosure should have allowed normal access.
We also had no evidence that the exclosure

Hamer et al. • SHOREBIRD PREDATION ON BENTHIC INVERTEBRATES

157

C\J

70,000 n

60,000 -

50,000 -

40,000 -

30,000 -

20,000 -

-C

10,000 -

0 -

70,000 -|

■0

60,000 -

50,000 -

c/5

40,000 -

30,000 -

20,000 -

10,000 -

0 -

70,000 n

60,000 -

O 10,000 H

b o

♦ Exclosure

Chautauqua South Pool

I i

Emiquon Wilder Tract

" T

A o

►

I l

Emiquon South Globe

□ Open a Shorebird density (ind/ha)

Chautauqua South Pool

5 l

14 Mar 3 Apr 23 Apr 13 May 2 Jun 22 Jun

T 25

CsJ

14,000 n

- 20

12,000 -

10,000 -

- 15

c/5

8,000 -

- 10

6,000 -

4,000 -

- 5

2,000 -

- 0
T 25

1—

C\l

0 -
14,000 -|

12,000 -

- 20

10,000 -

- 15

8,000 -

- 10

6,000 -

4,000 -

- 5

2,000 -

- 0
T 25

C\l

0 -

14,000 -,

12,000 -

- 20

10,000 -

- 15

8,000

- 10

6,000 -

4,000 -

-- 5

2,000 -

— 0

0 -

Emiquon Wilder Tract

Emiquon South Globe

25
- 20
- 15
10
5
0

25
- 20

- 15

- 10

- 5
0

T 25

- 20

15
10

14 Mar 3 Apr 23 Apr 13 May 2 Jun 22 Jun

FIG. 2. Mean density of oligochaetes and chironomids (mean ± SE) in exclosure and open (no exclosure)
treatments at three study sites: Chautauqua South Pool ( n = 15), Emiquon Wilder Tract ( n = 12), and Emiquon
South Globe ( n = 9) in Havana, Illinois, from late March to early June 2004. Shorebird density (filled triangles;
individuals/ha; n = 36) shown without error bars for clarity.

represented either shelter or obstruction for
larger predators, such as crayfish.

A potential problem with exclosure exper-
iments is the build-up of algae on the cage
structure (Vimstein 1978). Algae grew on sev-
eral of our exclosures, but only where the
fence was immersed in deeper water (>10
cm), and algae were never present at the sam-
pling locations. If water levels had dropped

quickly at an exclosure with algal growth, the
physical nature of the soil/water interface
could have been influenced; however, this did
not occur during our study.

Exclosure structures are often used as avian
roosts, which could influence the nutrient lev-
els in the exclosure through the addition of
feces. Weber and Haig (1997) reduced tern
and gull roosting on wooden stakes by sharp-

158

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

TABLE 1. Results of repeated measures mixed-model analysis of variance for shorebird predation effects
on invertebrate density (individuals/m2) and biomass (g/m2) in mudflats at Chautauqua and Emiquon NWR near
Havana, Illinois, during early May, late May, and early June, 2004.

Oligochaete density

Total chironomid
density

Small chironomid
density

Effect

Site

2,6

0.05

0.95

2.44

0.17

1.08

0.40

Period

2,11

0.89

0.44

5.69

0.020

3.47

0.068

Period X Site

4,11

2.40

0.11

1.20

0.37

0.63

0.65

Predation

1,26

7.20

0.013

0.08

0.79

0.00

0.97

Predation X Site

2,26

5.20

0.013

0.06

0.95

0.22

0.80

Predation X Period

2,26

4.47

0.022

0.15

0.86

0.08

0.92

Predation X Period X Site

4,26

3.19

0.029

1.09

0.38

0.62

0.65

Shorebird density

1,26

0.00

0.98

1.20

0.28

0.61

0.44

Change in water level

1,26

4.45

0.045

1.09

0.31

0.42

0.52

a Indicates mixed-model error to an infinite likelihood from too many zero values in the data.

ening their ends. Our metal stakes were oc-
casionally used as roosts by Red-Winged
Blackbirds (. Agelaius phoeniceus ), and feces
at the base of some stakes were present in
small amounts. Core samples, however, were
taken from the middle of the exclosure and
the open treatments, thus avoiding the base of
stakes by at least 0.5 m.

Interior freshwater wetlands are challenging
environments for exclosure experiments be-
cause of their unpredictable hydrology. The
zone of shorebird foraging habitat constantly
shifts as water levels fluctuate. The exclosure
design commonly used in marine intertidal
systems consists of 1-m2 treatments, which is
not appropriate in an interior system because
the exclosure would not be long enough to
ensure that the fluctuating shoreline foraging
zone would always remain within the exclo-
sure. Mitchell and Grubaugh (2005) used the
traditional square exclosure design and estab-
lished 113 plots in the Lower Mississippi Al-
luvial Valley. The plots were repeatedly sam-
pled over the course of two summer/fall mi-
grations, but only the plots representing shore-
bird foraging habitat (wet substrate or water
depth <10 cm) were sampled. As a result,
many plots were never sampled during their
study. Our new design was implemented to
compensate for the dynamic hydrology by es-
tablishing each treatment as a linear transect
perpendicular to the shoreline. This allowed
repeated sampling as water levels changed
throughout the migration period. However,
even with this modified design, only 9 of 16
plots originally established were used in our

study; the water level changed so dramatically
in the other 7 plots that the shoreline did not
remain within the treatments.

When the height of the exclosure structures
was maintained at 10 cm above the substrate,
prevention of shorebird predation was accom-
plished. On two occasions, however, we found
evidence that shorebirds had been inside the
exclosure (presence of tracks and feces). This
occurred when the fence sagged below 5 cm
(shorebirds walked over the fence), or was
above 15 cm (shorebirds walked under fence).

We believe that the only major factor ac-
counting for differences in the response vari-
ables (e.g., invertebrate density) between the
two treatments was the exclusion of avian
predators. We observed 22 waterfowl and 677
shorebirds inside plots during the sampling
period used in the analysis. Most of the wa-
terfowl observed foraged in deeper water and
likely did not influence the benthic inverte-
brates at the shoreline. Therefore, most differ-
ences between the treatments were likely at-
tributed to shorebird predation.

Exclosure experiments continue to be valu-
able tools for studying predator-prey interac-
tions. Future studies in non-intertidal, soft
sediments may benefit from implementation
of an experimental design similar to the one
used in this study. Researchers are well aware
of exclosure artifacts in marine systems, but
little is known about the influences of exclo-
sure structures in interior wetlands. A third
treatment (in addition to the exclosure and
open control) used in many marine studies is
the use of a “cage control” that has a top

Hamer et al. • SHOREBIRD PREDATION ON BENTHIC INVERTEBRATES

159

TABLE 1. Extended.

Total gastropod
density

Small gastropod
density

Large gastropod
density

Invertebrate

density

Invertebrate

biomass

1.23

0.36

0.84

0.48

1.01

0.42

0.68

0.43

0.67

3.34

0.073

2.18

0.16

0.14

0.87

0.51

0.61

2.79

0.10

2.63

0.092

3.09

0.062

0.66

0.63

1.47

0.28

1.23

0.35

0.26

0.62

0.02

0.90

4.21

0.049

0.32

0.58

1.20

0.28

6.76

0.014

3.32

0.049

1.20

0.31

1.29

0.29

0.01

0.99

5.65

0.024

1.17

0.29

1.77

0.19

0.31

0.74

2.34

0.12

— a

—

1.18

0.34

2.35

0.081

0.17

0.68

0.40

0.53

0.14

0.71

0.17

0.69

0.86

0.36

0.39

0.54

0.34

0.56

0.11

0.75

0.32

0.58

0.26

0.62

cover and two sides, which is designed to
identify the effects of the cage structure while
allowing normal predation to occur (fish or
crabs could enter the cage from the two open
sides). The presence of the exclosure cover,
however, is likely to influence normal shore-
bird foraging. Weber (1994) attempted to ac-
count for this effect by establishing a cage
control identical to the exclosure treatment but
without the cover, which evaluated the influ-
ence of the stakes but not the potential effects
of the exclosure cover.

Predator— prey interactions. — Our results
indicate that migrating shorebirds did not lo-
cally deplete invertebrate populations at our
study sites, and only oligochaete density was
reduced by shorebird foraging. We were sur-
prised to find that shorebirds affected oligo-
chaete densities, but not chironomid densities.
Chironomids are known to be important
shorebird prey throughout interior stopover lo-
cations (Eldridge 1987, Helmers 1991, Skagen
and Omen 1996, Mihue et al. 1997), but our
results suggest that shorebirds did not select
chironomids over other prey. Oligochaetes are
often the most abundant freshwater inverte-
brate in mudflats in the Mississippi Alluvial
Valley (Elliott-Smith 2003, Mitchell and Gru-
baugh 2005), and they were the most abun-
dant prey at our study sites (Hamer 2004). Our
results support Skagen and Omen’s (1996) as-
sertion that dietary flexibility allows shore-
birds to exploit variable resources. The effect
of shorebird predation varied spatially, and we
identified at least four factors that could have

influenced shorebird predation pressure on
benthic invertebrates.

First, the energy demands of shorebirds are
highly variable. Different intensities of shore-
bird predation occurring seasonally on the
coast of Venezuela were explained by the dif-
ferent energy demands of molt, fat deposition,
and foraging habitat (Mercier and McNeil
1994). Wilson (1991) compared episodic
shorebird predation at the Bay of Fundy, Nova
Scotia, and at Grays Harbor, Washington, and
found a significant reduction of major prey at
the Bay of Fundy but no effects of predator
exclusion at Grays Harbor. The difference in
the intensity of predation was explained by
differing migration strategies at these two
sites. Shorebirds using Grays Harbor tend to
migrate in short hops (Iverson et al. 1996,
Warnock and Bishop 1998) and do not need
to accumulate the massive fat reserves re-
quired for a transoceanic migration strategy
like shorebirds departing from the Bay of Fun-
dy. The short hop migration strategy of inte-
rior shorebirds (Skagen and Knopf 1994b,
Farmer and Wiens 1999) may explain why
other studies of shorebird predation in the in-
terior U.S. also show little effect of predator
exclusion on invertebrate prey (Mihue et al.
1997, Ashley et al. 2000, Mitchell and Gru-
baugh 2005). Multiple stops reduce the need
to accumulate large amounts of fuel at one
location.

Second, shorebird territoriality may influ-
ence the degree of episodic predation on in-
vertebrates. As shorebird densities increase.

160

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

0 Chautauqua South Pool x Emiquon Wilder Tract + Emiquon South Globe

Early May

Late May

FIG. 3. Relationship between invertebrate biomass removed (g/m2) and density removed (individuals/m2)
versus shorebird densities (individuals/ha) at Chautauqua South Pool, Emiquon South Globe, and Emiquon
Wilder Tract near Havana, Illinois, in early May and late May of 2004. Values for biomass and density removed
were calculated by subtracting open from exclosure values. A value of zero (dashed line) represents equal
biomass (or density) in the exclosure and open treatments. Values >0 indicate greater biomass (or density) in
the exclosure. Note difference in scales.

interference (fighting, kleptoparasitism, distur-
bance) between territorial birds limits the de-
pletion of resources (Goss-Custard 1980).
Duffy et al. (1981) studied shorebird compe-
tition for prey resources at a wintering ground
in Peru and did not find depletion of inverte-
brate prey; one factor reducing the importance
of competition may have been territoriality
among the wintering birds. Migrant shorebirds
at our stopover location are mostly nonterri-
torial (Hamer 2004); thus, territorial interac-

tions likely did not play a role in the shore -
bird/prey dynamics at our study sites.

Third, shorebird predation pressure is great-
er in locations with greater densities of for-
aging birds. Shorebird densities observed dur-
ing our study averaged 6.3/ha, peaking at
39.8/ha. Coastal flyways receive much greater
concentrations of shorebirds where densities
can approach 100/ha (in coastal South Caro-
lina; Weber and Haig 1997) to 4,500/ha (in
coastal Venezuela; Mercier and McNeil 1994).

Hamer et al. • SHOREBIRD PREDATION ON BENTHIC INVERTEBRATES

161

The dispersed migration through interior hab-
itats results in lower shorebird densities and
possibly reduces predation pressure.

Finally, the dynamic water levels recorded
during our study may have been an additional
factor that reduced the effect of shorebird pre-
dation on benthic invertebrates. Water levels
fluctuated an average of 8.9 cm during 2-week
intervals. Gradual drawdown or flooding con-
tinuously shifts the location of foraging hab-
itat and exposes new invertebrate prey (Run-
dle and Fredrickson 1981). Even though man-
agers at Chautauqua’s South Pool attempted
to maintain a stable water level over the
course of the spring, the average fluctuation
over each 2-week period was 7.6 cm. Much
of this variation can be explained by wind-
driven seiches (wind fetch), which can expose
previously unexploited foraging habitat in
large, shallow wetlands (Laubhan and Fred-
rickson 1993). Without this phenomenon,
shorebird reduction of invertebrates at Chau-
tauqua may have been greater.

Because shorebirds are size-selective when
preying on invertebrates, they can influence
the invertebrate community structure in soft
sediments (Peterson 1979, Kent and Day
1983, Wilson 1989). Shorebird predation on
marine polychaetes often targets large (adult)
individuals, which can lead to increased re-
cruitment of juveniles and increased densities
of smaller invertebrates. As a consequence,
exclosure experiments in which only prey
densities are measured may fail to account for
the interactions of size-class predation and
size-dependent competition. Our results, how-
ever, do not suggest that such episodic shore-
bird predation influenced the invertebrate
community structure in our study. There was
no evidence of size-selection of chironomids,
but the mean density of large gastropods was
more than seven times greater in the exclosure
than the open treatment (106.1/m2 versus 14.1/
m2, respectively). Thus, it seems likely that
shorebirds selected large gastropods, which
has been observed elsewhere in the Mississip-
pi Alluvial Valley (Brooks 1967, Rundle
1982).

Competition for prey resources at migration
stopover locations may result when early mi-
grants deplete prey resources and reduce the
successful foraging rate of later-arriving
shorebirds, thus increasing the length of stay

for later arrivals (Wilson 1991). Although this
occurs at some locations (Schneider and Har-
rington 1981), later migrants at our study site
were not likely disadvantaged by reductions
in prey density by early migrants because the
dynamic hydrology constantly exposed pre-
viously unexploited food resources.

Our results suggest that migrating shore-
birds along the Illinois River may have re-
duced oligochaetes and larger gastropods.
Flexible and opportunistic foraging strategies
are beneficial to shorebirds facing the unpre-
dictable nature of interior flyways. The re-
moval of oligochaetes, the most abundant in-
vertebrates at our study sites, suggests that
shorebirds fed opportunistically on the most
available prey. The dynamic hydrology, and
the resulting continuously renewing availabil-
ity of invertebrate prey, likely offer sufficient
invertebrate resources for migrating shore-
birds in the Illinois River valley.

ACKNOWLEDGMENTS

This research, conducted as part of a master’s thesis,
was funded by the Illinois Natural History Survey, the
Illinois Department of Natural Resources Wildlife
Preservation Fund, The Nature Conservancy, and the
Champaign County Audubon Society. We thank the
staff at the Forbes Biological Field Station, D. J. Sou-
cek, and J. M. Levengood for their assistance with the
project; M. J. Wetzel and R. E. Dewalt for aid in iden-
tification of invertebrates; J. Dassow, B. J. O’Neal, A.
Bartlett, and B. T. Kapusta for their assistance in the
field and lab; and the staff at the Illinois River National
Wildlife and Fish Refuge and Rice Lake State Fish and
Wildlife Area. Comments on earlier drafts by G. O.
Batzli and three anonymous reviewers greatly im-
proved this paper.

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The Wilson Journal of Ornithology 1 18(2): 164— 172, 2006

COMPOSITION AND TIMING OF POSTBREEDING MULTISPECIES
FEEDING FLOCKS OF BOREAL FOREST PASSERINES IN

WESTERN CANADA

KEITH A. HOBSON1 2 AND STEVE VAN WILGENBURG1 2

ABSTRACT. — The aggregation of nonbreeding insectivorous songbirds into multispecies feeding flocks dur-
ing migration and on their wintering grounds is a well-known and important aspect of their ecology. The
establishment of multispecies feeding flocks on the temperate breeding grounds of North American Neotropical
migrants, however, remains poorly known or understood. To address this gap, we investigated the composition
and timing of flocking behavior among several species occurring in the southern boreal mixed-wood forest of
western Canada. Of 67 species observed in 216 flocks, the most abundant were Tennessee Warbler ( Vermivora
peregrina ) and several resident species: Black-capped Chickadee ( Poecile atricapillus ), Red-breasted Nuthatch
(Sitta canadensis ), and Boreal Chickadee ( Poecile hudsonica). Consistent with previous work on Eurasian boreal
species, residents appeared to play a pivotal role in flock occurrence and cohesion. Flocking tended to begin in
late June, and flock sizes increased throughout the summer. This suggests that unsuccessful breeders, early
breeders, and early migrants are the first to join flocks, whereas later-nesting species may delay joining flocks
until after their young fledge. We also investigated the propensity of several species to display flocking behavior
in areas with and without a superabundant food source — the spruce budworm ( Choristoneura fumiferana). These
data provided some support for the hypothesis that flocking facilitates foraging, as species tended to flock in
areas where food abundance was lower. Received 24 January 2005, accepted 14 December 2005.

The aggregation of individual insectivorous
songbirds into multispecies feeding flocks is a
phenomenon that has been noted for some
time (e.g., Newton 1896, Sharpe 1905) and
has received considerable attention recently
(Hutto 1994, Latta and Wunderle 1996,
Monkkonen et al. 1996). Such flocking be-
havior is interesting from several perspectives,
and a number of hypotheses have been put
forth to explain the evolution of such inter-
specific associations, primarily focusing on
the avoidance of predation (Pulliam 1973, El-
gar 1989) and the facilitation of food finding
(Morse 1970, 1977). The establishment and
maintenance of hierarchies within flocks and
the role of interspecific competition in struc-
turing these aggregations also are areas of
considerable interest (Munn and Terborgh
1979, Powell 1979, Hutto 1994).

To date, research on multispecies feeding
flocks involving forest passerines has focused
primarily on the wintering grounds, particu-
larly in the Neotropics (reviewed by Monk-
konen et al. 1996; see also Buskirk et al. 1972;
Hutto 1987, 1994; Ewert and Askins 1991;

1 Prairie and Northern Wildlife Research Centre, Ca-
nadian Wildlife Service, 1 15 Perimeter Rd., Saskatoon,
SK S7N 0X4, Canada.

2 Corresponding author; e-mail:

Keith. Hobson@ec.gc.ca

Latta and Wunderle 1996). This is in spite of
the fact that mixed-species flocks of North
American songbirds are conspicuous on their
breeding grounds or during the early post-
breeding migration period. In the continental
United States, Morse (1970) was the first to
conduct a quantitative study on ecological as-
pects of mixed-species foraging flocks of
songbirds during late summer through winter,
but virtually no studies of foraging flocks have
been conducted on North American breeding
grounds since then. Research by Monkkonen
et al. (1996) on mixed-species foraging aggre-
gations and heterospecific attraction in boreal
bird communities in Finland represents an im-
portant advance in the study of flocking be-
havior among temperate-breeding songbirds.
These authors determined that feeding asso-
ciations occurred during the breeding season
and that titmice ( Parus spp.) seemed to play
a focal role in the occurrence of these flocks.
They also suggested that flocking might pro-
duce variation in species numbers, local abun-
dances, and spatial patterns, both within and
between communities in boreal forests. To ad-
dress the paucity of information on multispe-
cies aggregations of boreal forest songbirds on
their breeding grounds in North America, we
investigated the composition and timing of
flocking behavior among several species.

164

Hobson and Van Wilgenburg • BOREAL MULTISPECIES FEEDING FLOCKS

165

Within the boreal forest of North America,
the southern boreal mixed-wood ecozone sup-
ports one of the most diverse breeding bird
assemblages of any forest type in the conti-
nent (Robbins et al. 1986, Price et al. 1995).
Most of the breeding birds are Neotropical or
short-distance migrants. In addition, much of
the forest occurring in this region is contigu-
ous primary forest that has not yet been al-
tered by logging (but see Stelfox 1995). This
is in contrast to Scandinavian boreal forest,
which has less complex avian communities
with fewer migrants (see Schmiegelow and
Monkkonen 2002). The first objective of our
study was to establish the timing and impor-
tance of flocking throughout the breeding and
immediate postbreeding periods. To accom-
plish this, we aimed to document occurrences
of flocking in relation to overall breeding phe-
nology of the avian community. Second, we
sought to document flock composition and ev-
idence of associations among flock members;
specifically, we were interested in identifying
species integral to flock formation and wheth-
er species associations were random or based
on foraging guilds or taxonomic affinities. Our
third objective was to determine whether
flocking was associated with areas where food
resources were superabundant — areas with in-
festations of spruce bud worm ( Choristoneura
fumiferana). If flocking was a response to in-
creased foraging efficiency, we expected that
species occurring in areas where food is su-
perabundant might be less likely to participate
in foraging flocks.

METHODS

Study area and field observations. — The
study was conducted from mid-May to mid-
September 1992-1996, in the southern boreal
mixed-wood forest of west-central Saskatch-
ewan, Canada, primarily in the vicinity of
Prince Albert National Park (53° 35' N, 106°
00' W), a 387,500-ha block of contiguous pri-
mary forest. The dominant tree species in this
region were trembling aspen ( Populus tremu-
loides ), white spruce ( Picea glauca ), jack pine
( Pinus banksiana ), black spruce ( Picea mari-
ana ), and paper birch ( Betula papyrifera). The
majority of the study area burned in 1919;
therefore, it is largely uniform in age structure
(Weir and Johnson 1998). Forest west of the
park had undergone an outbreak of spruce

budworm, providing us with an opportunity to
sample similar forest habitats in budworm-in-
fested (hereafter “infested”) and uninfested
(i.e., no budworm infestation) areas. By 1993,
approximately 30,000 ha were infested and
classified as moderately to severely defoliated
(i.e., >50% defoliation; Saskatchewan Natural
Resources Forest and Lands Branch 1993).
From mid-May to mid-July in >30 mature
forest stands, we opportunistically recorded
all feeding flocks encountered. For the pur-
poses of this study, we defined a flock as any
assemblage of individuals composed of more
than one species clearly moving together. We
did not include single family groups; however,
we did include amalgamations of single-spe-
cies flocks composed of more than one family
group. After mid-July and until mid-August,
when flocks became more common, one ob-
server spent at least 6 hr per day searching for
flocks along forest trails and riparian edges.
Thereafter, observations were again made op-
portunistically during the course of other
fieldwork.

In total, we observed 215 flocks, distributed
relatively equally amongst infested ( n = 102)
and uninfested sites ( n = 113). Upon encoun-
tering a flock, we followed it for -20—30 min
while counting or estimating the number of
individuals of each species and noting the
presence of family groups — as evidenced by
begging or feeding of young. Flock height,
forest type, and location were also recorded.

As part of another study in the same area,
from 31 May to 1 July 1992-1996, we also
conducted 395 point counts across spruce- or
aspen-dominated mixed-wood stand types
(Hobson and Bayne 2000). Points were rough-
ly equally distributed among infested ( n =
204) and uninfested (n = 191) forest. Six
highly skilled observers with at least 6 years
experience conducted 10-min point counts
from 04:00 to 08:30 CST, during which ob-
servers recorded all birds heard or seen within
an unlimited-distance radius. Two visits were
made to each station during the survey period,
once prior to 15 June, and once after 15 June.
Relative abundance estimates were based on
the maximum count for a species during these
two visits. Because these data were collected
prior to the routine use of methods to correct
for detectability biases, we do not have de-
tectability functions to correct these data;

166

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

therefore, estimates of flocking propensity
should be interpreted with caution. However,
this dataset allowed us to quantify relative
abundances as determined by point counts and
contrast them with the relative occurrences of
species in mixed-species flocks at the regional
scale.

Statistical analyses. — Basic descriptive sta-
tistics were used to examine the magnitude
and frequency of species’ occurrences in
flocks; values are reported as means ± 1 SD.
To examine the probability of species co-oc-
curring in flocks, we conducted tests of in-
dependence using G-tests with Williams’ cor-
rection for continuity. Using 2X2 contingen-
cy tables, we contrasted the number of flocks
(frequency of occurrence) in which species
co-occurred and the number of flocks in which
one species occurred but the others did not.
We used Fisher’s exact test of independence
when expected frequencies were <5 (Zar
1996). To evaluate flocking propensity (the
occurrence of a species more or less frequent-
ly than expected due to chance) of the most
abundant species in both infested and unin-
fested forests, we used a 2 X 2 Yate’s-cor-
rected chi-square test for independence; this
test contrasted a given species’ abundance in
flocks and on point counts with the total abun-
dance of all species in flocks and on point
counts.

To compare estimated flock size in infested
versus uninfested forests, we used analysis of
covariance (ANCOVA) on rank-transformed
data and included Julian date as the covariate.
Shannon Evenness, species richness, and
Simpson’s, McIntosh, and Shannon diversity
indices were used to evaluate flock composi-
tion (Magurran 1988). Flock-size estimates
were log-transformed and we used linear re-
gression to analyze change in flock size
throughout the season. Finally, temporal pat-
terns of flock composition were depicted
graphically and Mann-Whitney G-tests were
employed to test for significance of change
through time and between infested and unin-
fested areas. We set statistical significance at
a < 0.05; however, Bonferroni adjustments
were used for multiple comparisons, resulting
in species co-occurrence being assessed at a
< 0.0004 (0.05/120 pairwise comparisons)
and flocking propensity being assessed at a <

0.001 (0.05/52 tests). Scientific names of all
bird species are given in Table 1.

RESULTS

We recorded 5,753 individuals representing
67 species in 216 flocks (Table 1). The mean
number of species per flock was 6.6 ± 3.3 and
the mean number of individuals per flock was
41.1 ± 60.4. The six species occurring most
frequently in flocks included a long-distance
migrant (Tennessee Warbler), two short-dis-
tance migrants (Yellow-rumped Warbler,
Chipping Sparrow), and three resident species
(Black-capped Chickadee, Red-breasted Nut-
hatch, Boreal Chickadee).

We evaluated the probability of the 15 most
commonly observed (i.e., number of flock oc-
currences >30) species co-occurring in flocks.
Of the 120 possible pair-wise comparisons, we
found only 5 significant (positive or negative)
associations. Black-capped Chickadee co-oc-
curred with Bay-breasted Warbler 1.6 times
less frequently than expected by chance (G =
15.03, P < 0.001), and there was also a neg-
ative association between Boreal Chickadee
and American Redstart (2.6 times; G = 10.66,
P < 0.001). Red-breasted Nuthatch associated
positively with Brown Creeper 1 .4 times more
frequently than expected by chance (G =
15.44, P < 0.001). Among migrants, Ameri-
can Redstart was positively associated with
Red-eyed Vireo 1 .9 times more frequently
than expected by chance (G = 18.06, P <
0.001) and with Bay-breasted Warbler 7.8
times less frequently than expected by chance
(G = 12.14, P < 0.001).

In both infested and uninfested stands, we
compared the abundances of species in flocks
with their relative abundances, as determined
by regional point counts (Table 2). This pro-
vided us with another measure of flocking ten-
dency and whether it changed with resource
availability. Controlling for Julian date, flock
size was larger in uninfested sites (61.1 ±
78.0 individuals) than in infested areas (20.1
± 15.6 individuals; Fu52 = 13.23, P < 0.001).
In the infested sites, seven species occurred in
flocks more than expected and seven less than
expected on the basis of their regional relative
abundances; 12 species showed no significant
association (Table 2). Of the same 26 species
considered above, only 9 occurred more fre-
quently in flocks than expected on the basis

Hobson and Van Wilgenburg • BOREAL MULTISPECIES FEEDING FLOCKS

167

of their relative abundances, all but 1 of which
(Brown Creeper) showed a similar tendency
in uninfested sites (Black-capped Chickadee,
Yellow-rumped Warbler, Red-breasted Nut-
hatch, Boreal Chickadee. Dark-eyed Junco,
Yellow Warbler). Nine species avoided flocks
in uninfested areas and, of these, five species
also avoided flocking in the infested sites.
Pine Siskin showed less tendency to flock in
the infested than in uninfested sites. Six spe-
cies showed a significant tendency to either
avoid or join flocks in one of the two habitats,
with no significant trend in the other habitat
(Chipping Sparrow, Bay-breasted Warbler,
Magnolia Warbler, Black-and-white Warbler,
Solitary Vireo, and Dark-eyed Junco).

Flock size and the number of species in
flocks generally increased through the season;
however, the trend was only significant for
flock size (F{ 152 = 40.305, P < 0.001; Fig.
1). For all years combined, we compared flock
attributes before and after 29 July — the mid-
point of our observation period and the date
by which most, if not all, nests were expected
to have fledged. The number of individuals
detected in flocks after 29 July (61.8 ± 77.8,
n = 79 flocks) was greater than that detected
before (19.4 ± 14.8, n — 75 flocks; Mann-
Whitney U = 1,221.0, two-tailed P < 0.001).
The number of species per flock was similar
in the first (6.0 ± 2.7, n = 111 flocks) and
second periods (7.4 ± 3.8, n — 103 flocks;
Mann-Whitney U = 4,892.5, two-tailed P =
0.067). We also compared indices of flock di-
versity by infested versus uninfested areas and
time period (before and after 29 July). The
McIntosh diversity index (Magurran 1988)
was higher in uninfested (Me U = 15.5 ±
14.6, n = 114) than in the infested sites (Met/
= 9.1 ± 7.3, n = 100; Mann-Whitney U =
3,568.5, two-tailed P < 0.001), but no signif-
icant difference was found for Simpson or
Shannon diversity measures. Shannon Even-
ness, however, was greater in the infested {J'
= 0.90 ± 0.09) than in uninfested sites ( J ' =
0.87 ± 0.12; Mann-Whitney U = 4,522.0,
two-tailed P = 0.021). The McIntosh index
was also higher for flocks observed after 29
July (Met/ = 15.9 ± 15.2) compared with
those observed earlier (Mcf/ = 9.3 ± 7.0, n
= 214; Mann-Whitney U = 3,842.5, two-
tailed P < 0.001); again, however, we detect-
ed no difference in the other measures of di-

versity. Shannon Evenness was greater in
flocks observed before 29 July ( J ' = 0.90 ±
0.09) compared with those observed later ( J '
= 0.87 ± 0.12; Mann-Whitney U = 4,244.0,
two-tailed P = 0.003).

DISCUSSION

The tendency for species to flock in our
study area was widespread among migrants
and residents. Tennessee Warbler was one of
the migrants most frequently observed flock-
ing, a phenomenon that may be related to its
relatively earlier breeding and dispersal in the
boreal forest, as well as to its high abundance
(Rimmer and McFarland 1998). This species
is one of the earliest fall migrants to be re-
corded at Delta Marsh Bird Observatory
(DMBO), a constant-effort mist-netting sta-
tion just south of our study area (DMBO un-
publ. data). Among residents, Black-capped
Chickadee, Red-breasted Nuthatch, and Bo-
real Chickadee were among the most fre-
quently observed flocking species. Similarly,
other studies in temperate North America and
Europe have revealed that parids and nut-
hatches occur frequently in multispecies for-
aging flocks; parids, in particular, have been
classified as nuclear species in these aggre-
gations (Morse 1970, Berner and Grubb 1985,
Monkkonen et al. 1996). In our study area,
resident boreal species typically breed earlier
than migrants and are observed moving in
family groups during June when most mi-
grants are still incubating. This phenology
may predispose them to serving as catalysts
for flocking, similar to their roles in forming
fall and winter flocks.

Despite many thousands of hours of field-
work in the southern boreal mixed-woods
from May through September, we observed no
mixed-species foraging aggregations until late
June. Thereafter, the probability of encounter-
ing flocks increased as birds dispersed beyond
their territory boundaries. Additionally, flocks
tended to be larger later in the season; thus,
even though flocks of resident species would
move through the territories of migrant spe-
cies, the migrants apparently did not tempo-
rarily join the residents as they passed through
(Monkkonen et al. 1996). Rather, failed breed-
ers or birds in dispersing family groups likely
constituted the earliest migrants joining
flocks.

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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

TABLE 1. Summary of flocking data for avian species recorded in the southern boreal mixed- wood forest
of Saskatchewan, Canada, 1992-1996.

Species

No. individuals
(%)

No. flocks
in which
present (%)

Mean no. per
flock (SD)

Tennessee Warbler ( Vermivora peregrina)

952

(16.55)

146

(67.59)

6.5

(9.1)

Black-capped Chickadee ( Poecile atricapillus )

854

(14.84)

142

(65.74)

6.0

(7.8)

Yellow-rumped Warbler ( Dendroica coronato )

635

(11.04)

132

(61.11)

4.8

(6.3)

Red-breasted Nuthatch (Sitta canadensis )

383

(6.66)

122

(56.48)

3.1

(2.7)

Boreal Chickadee ( Poecile hudsonica )

378

(6.57)

(37.50)

4.7

(5.1)

Chipping Sparrow ( Spizella passerina)

355

(6.17)

(41.20)

4.0

(3.0)

American Redstart ( Setophaga ruticilla )

238

(4.14)

(16.20)

6.8

(9.9)

Red-eyed Vireo ( Vireo olivaceus )

207

(3.60)

(36.11)

2.7

(2.2)

Pine Siskin ( Carduelis pinus)

178

(3.09)

(12.04)

6.8

(6.2)

Ruby-crowned Kinglet ( Regulus calendula )

171

(2.97)

(26.39)

3.0

(2.3)

Blackburnian Warbler {Dendroica fused)

161

(2.80)

(20.83)

3.6

(2.6)

Bay-breasted Warbler {Dendroica castanea )

150

(2.61)

(22.22)

3.1

(2.5)

White-throated Sparrow {Zonotrichia albicollis )

127

(2.21)

(15.28)

3.8

(4.6)

Chestnut-sided Warbler {Dendroica pensylvanica)

111

(1.93)

(9.72)

5.3

(5.9)

Brown Creeper {Certhia americana)

104

(1.81)

(21.76)

2.2

(1.2)

Magnolia Warbler {Dendroica magnolia )

(1.27)

(18.52)

1.8

(1.3)

Black- throated Green Warbler {Dendroica virens)

(0.96)

(10.19)

2.5

(1.5)

Black-and-white Warbler {Mniotilta varia )

(0.90)

(7.41)

3.3

(3.5)

Cape May Warbler {Dendroica tigrina )

(0.89)

(12.04)

2.0

(1.2)

Blue-headed Vireo {Vireo solitarius)

(0.87)

(7.41)

3.1

(3.4)

Ovenbird {Seiurus aurocapilla )

(0.66)

(12.50)

1.4

(0.8)

Dark-eyed Junco {Junco hyemalis )

(0.63)

(6.48)

2.6

(2.0)

Cedar Waxwing {Bombycilla cedrorum )

(0.56)

(1.85)

8.0

(8.1)

Yellow Warbler {Dendroica petechia)

(0.52)

(5.09)

2.7

(2.1)

Golden-crowned Kinglet {Regulus satrapa)

(0.52)

(2.78)

5.0

(5.5)

Rose-breasted Grosbeak {Pheucticus melanocephalus)

(0.50)

(4.17)

3.2

(3.0)

Canada Warbler {Wilsonia canadensis )

(0.47)

(6.94)

1.8

(1.1)

American Robin {Turdus migratorius )

(0.43)

(2.31)

5.0

(8.4)

Yellow-bellied Sapsucker {Sphyrapicus varius)

(0.40)

(6.94)

1.5

(0.6)

White-winged Crossbill {Loxia leucoptera)

(0.30)

(1.39)

5.7

Swainson’s Thrush {Catharus ustulatus )

(0.24)

(2.78)

2.3

(2.0)

Flycatcher spp. {Empidonax spp.)

(0.24)

(2.78)

2.3

(0.4)

Hairy Woodpecker {Picoides villosus )

(0.21)

(5.09)

1.1

(0.3)

Mourning Warbler {Oporornis Philadelphia)

(0.21)

(4.17)

1.3

(0.7)

Philadelphia Vireo {Vireo philadelphicus)

(0.19)

(3.24)

1.6

(0.5)

Palm Warbler {Dendroica palmarum)

(0.16)

(1.85)

2.3

(1.9)

Purple Finch {Carpodacus purpureus)

(0.16)

(1.39)

3.0

Least Flycatcher {Empidonax minimus)

(0.14)

(2.31)

1.6

(0.9)

Northern Flicker {Colaptes auratus)

(0.14)

(2.31)

1.6

(0.9)

Downy Woodpecker {Picoides pubescens)

(0.12)

(2.78)

1.2

(0.4)

Gray Jay {Perisoreus canadensis)

(0.10)

(1.39)

2.0

Western Tanager {Piranga ludoviciana)

(0.10)

(1.39)

2.0

Alder Flycatcher {Empidonax alnorum)

(0.09)

(0.46)

5.0

Connecticut Warbler {Oporornis agilis)

(0.07)

(1.39)

1.3

Wilson’s Warbler {Wilsonia pusilla)

(0.07)

(1.39)

1.3

Evening Grosbeak {Coccothraustes vespertinus)

(0.07)

(0.93)

2.0

Blue Jay {Cyanocitta cristata)

(0.07)

(0.46)

4.0

Kinglet spp. {Regulus spp.)

(0.07)

(0.46)

4.0

Ruby-throated Hummingbird {Archilochus colubris)

(0.07)

(0.46)

4.0

Song Sparrow {Melospiza melodia)

(0.07)

(0.46)

4.0

Common Yellowthroat {Geothlypis trichas)

(0.05)

(0.93)

1.5

Pileated Woodpecker {Dryocopus pileatus)

(0.05)

(0.93)

1.5

Swamp Sparrow {Melospiza georgiana)

(0.05)

(0.93)

1.5

Warbling Vireo {Vireo gilvus)

(0.05)

(0.93)

1.5

Blackpoll Warbler {Dendroica striata)

(0.03)

(0.93)

1.0

Northern Waterthrush {Seiurus noveboracensis)

(0.03)

(0.93)

1.0

Hobson and Van Wilgenburg • BOREAL MULTISPECIES FEEDING FLOCKS

169

TABLE 1 . Continued.

No. flocks

No. individuals

in which

Mean no. per

Species

(%)

present (%)

flock (SD)

Thrush spp. ( Catharus spp.)

2 (0.03)

2 (0.93)

1.0

Traill’s Flycatcher ( Empidonax traillii)

2 (0.03)

2 (0.93)

1.0

American Three-toed Woodpecker ( Picoides dorsalis )

2 (0.03)

2 (0.93)

1.0

American Goldfinch ( Carduelis tristis)

2 (0.03)

1 (0.46)

2.0

Winter Wren ( Troglodytes troglodytes )

2 (0.03)

1 (0.46)

2.0

Common Grackle ( Quiscalus quiscula)

1 (0.02)

1 (0.46)

1.0

Eastern Phoebe (Say o mis phoebe)

1 (0.02)

1 (0.46)

1.0

House Wren (Troglodytes aedon )

1 (0.02)

1 (0.46)

1.0

Orange-crowned Warbler (Vermivora celata)

1 (0.02)

1 (0.46)

1.0

Olive-sided Flycatcher (Contopus cooperi)

1 (0.02)

1 (0.46)

1.0

White-breasted Nuthatch (Sitta carolinensis )

1 (0.02)

1 (0.46)

1.0

Total

5,753 (100.00)

216

Overall, we found relatively few significant
(positive or negative) species co-occurrences
in flocks. Brown Creeper was positively as-
sociated with Red-breasted Nuthatch; this
likely reflects common foraging habitats. Sim-
ilarly, the strong negative association between
American Redstart and Bay-breasted Warbler
likely reflects the very different habitats that
these species prefer (i.e., deciduous understo-
ry versus coniferous canopy). Instead of
strong tendencies for species to associate with
others during flocking, we observed random
associations of individuals and species more
often.

Our flocking propensity results suggest that
some species show stronger tendencies to
flock than others. In both infested and unin-
fested sites. Black-capped and Boreal chick-
adees, Yellow-rumped Warbler, Red-breasted
Nuthatch, and Yellow Warbler consistently
showed high tendencies to flock, whereas
Red-eyed Vireo, White-throated Sparrow, Ov-
enbird. Cape May Warbler, and Black-throated
Green Warbler consistently showed negative
tendencies to flock, based on their abundance.
There appear to be no strong underlying pat-
terns other than an increased propensity for
residents to flock. The flocking propensity
trends we observed could have been biased by
the low detectabilities of a few species with
high-pitched songs (e.g., Brown Creeper,
Black-and-white Warbler, Cape May Warbler,
and Bay-breasted Warbler); if that were the
case, however, our estimates of flocking pro-
pensity should have been greater instead of
lower because high-pitched species would

likely be more detectable in flock surveys (vi-
sual) than during point counts (largely audi-
tory).

The two primary hypotheses explaining the
occurrence of mixed-species foraging flocks
are (1) the reduction of per capita predation
risk and (2) greater facilitation of successful
foraging due to decreased need for vigilance
or insect flushing (Morse 1977, 1980; Krebs
and Davies 1981). At sites in Ohio, Berner
and Grubb (1985) sought evidence for each
hypothesis by experimentally manipulating
food abundance during winter and examining
the tendency for resident species to flock.
They found less flocking in a food-supple-
mented site versus a control site and so argued
that flocking was related more to foraging
than to antipredator strategies per se. Al-
though we did not manipulate food abundance
on our sites, we were able to examine flock
composition in uninfested and infested forests
of similar composition. Forests infested with
spruce budworm are known to provide a su-
perabundant food source for many forest
songbirds, including budworm specialists and
non-specialists (Zach and Falls 1975, Morse
1989). Flocks in budworm-infested areas were
less diverse (i.e., greater community even-
ness) than those outside of infested areas, like-
ly because flocks in the infested stands were
dominated by budworm specialists, such as
Cape May Warbler, Tennessee Warbler, and
Bay-breasted Warbler. However, we found no
general pattern of a greater propensity to flock
in uninfested versus infested areas: nine spe-
cies showed a greater flocking propensity in

TABLE 2. Avian flocking propensity (FP) in sites with and without spruce budworm infestation. Relative abundance, from point-count data and within flocks,
is given for each species. FP denotes trend ( + , 0 = no trend) in flocking propensity — the occurrence of a species in flocks more or less than expected (based

on its relative abundance) due to chance.

170

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

Hobson and Van Wilgenburg • BOREAL MULTISPECIES FEEDING FLOCKS

171

FIG. 1. Temporal patterns in avian flocking, by
species richness and flock size, for all species observed
in the southern boreal mixed-wood forest of Saskatch-
ewan, Canada, 1992-1996.

uninfested sites and seven had a higher pro-
pensity in the infested sites. Flock size, how-
ever, tended to be much larger in uninfested
sites than in the infested sites. While our re-
sults are not entirely unequivocal, they are
congruent with the findings of Berner and
Grubb (1985) in linking flocking propensity
to relative food availability.

Combined, the few trends in species co-oc-
currences, the inconsistent trends in flocking
propensity for most species examined, and the
contrasting diversity measures between infest-
ed and uninfested sites suggest that flocks are
largely representative of local avian commu-
nities. Other than resident species, flock struc-
ture appears little affected by species’ migra-
tory patterns or foraging and nesting guilds.
This suggests that the advantages of flocking
extend to most species, despite different life-
history strategies.

Although we found little structure in pat-
terns of flocking on the breeding grounds, it
is well established that flocking does occur in
boreal forest bird communities immediately
after the young fledge (i.e., as soon as birds

are no longer constrained by nesting). The ex-
istence of mixed-species flocks during south-
bound migration suggests that this behavior
continues for migrants, possibly until they
reach their wintering grounds (Morse 1970).
Whether resident or migrant, species that join
flocks may engage in non-flocking behavior
only during the relatively short breeding pe-
riod in their life cycle. Additional studies on
the breeding grounds as soon as multispecies
feeding flocks begin to form are now needed
to investigate how flocking relates to other de-
mands, such as post-fledging parental care and
molt.

ACKNOWLEDGMENTS

We thank the numerous field assistants who helped
collect field data on mixed-species flocks over the
course of our investigations, in particular, E. Cum-
ming, who also provided additional data. Our work
was funded by the Canadian Wildlife Service and the
Prince Albert Model Forest (Project No. 211). We
thank M. Monkkdnen and two anonymous reviewers
for constructive comments that improved the manu-
script.

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The Wilson Journal of Ornithology 1 18(2): 173— 177, 2006

VARIATION IN SIZE AND COMPOSITION OF BUFFLEHEAD
(. BUCEPHALA ALBEOLA) AND BARROW’S GOLDENEYE
( BUCEPHALA ISLANDICA) EGGS

JENNIFER L. LAVERS,1 35 JONATHAN E. THOMPSON,24
CYNTHIA A. PASZKOWSKI,1 AND C. DAVISON ANKNEY2 3 4 5

ABSTRACT. — We investigated the relationships between egg nutrient constituents and fresh egg mass in
Bufflehead ( Bucephala albeola) and Barrow’s Goldeneye ( B . islandica ). We found consistently positive rela-
tionships between egg mass and yolk, albumen, lipid, mineral, and water (absolute amounts); however, the
proportions of nutrient components to fresh mass were highly variable in the eggs of both species (allometric
relationships). In Bufflehead eggs, all components except mineral exhibited negative allometry with fresh egg
mass. In Barrow’s Goldeneye eggs, only mineral exhibited negative allometry, whereas yolk, lipid, and water
all exhibited positive allometry with fresh egg mass. Overall, larger eggs of both species contained greater
absolute amounts of nutrients; therefore, larger eggs were of better quality than smaller eggs. Nutrient content,
however, was more highly correlated with mass in Barrow’s Goldeneye eggs than in Bufflehead eggs. We propose
that this may be due to the source of egg nutrients: because of their smaller body size, Buffleheads typically
rely more on exogenous nutrients than Barrow’s Goldeneyes. Received 5 January 2005, accepted 16 December
2005.

For many bird species, nutrient content is
positively correlated with egg size. Conse-
quently, egg size is often used as an indicator
of egg and hatchling quality (Birkhead 1984,
Sotherland and Rahn 1987, Pelayo and Clark
2002). There are many potential benefits to
laying larger, and presumably better quality,
eggs, including increased hatchling size (Ali-
sauskas 1986, Dawson and Clark 1996, An-
derson and Alisauskas 2001, Pelayo and Clark
2002), increased growth rate of both embryos
and hatchlings (Martin 1987, Badzinski et al.
2002), and higher probability of survival after
hatching (Dawson and Clark 1996). Such ben-
efits may lead to selective pressure for females
to produce larger eggs with greater protein
and lipid stores (Lack 1967). However, the se-
lective pressure to produce larger eggs is con-
strained by a number of factors, including he-
redity (Martin 1987), the female’s metabolic
and physiological capabilities (Rohwer 1988,

1 Univ. of Alberta, Dept, of Biological Sciences, Ed-
monton, AB T6G 2E9, Canada.

2 Univ. of Western Ontario, Ecology and Evolution
Group, Dept, of Zoology, London, ON N6A 5B7, Can-
ada.

3 Current address: Memorial Univ. of Newfound-
land, Dept, of Biology, St. John’s, NL A1B 3X9, Can-
ada.

4 Current address: Ducks Unlimited Canada, #200,
10720-178 St., Edmonton, AB T5S 1J3, Canada.

5 Corresponding author; e-mail: b06jll@mun.ca

Thomson et al. 1998), and nutrient availability
(Alisauskas and Ankney 1992).

The eggs of species with precocial young,
such as waterfowl (Anseriformes), have larger
yolks than do those of species with altricial
young (Ricklefs 1977). Newly hatched Buffle-
head (. Bucephala albeola ) and Barrow’s Gold-
eneye (. B . islandica) ducklings often struggle
to exit their nest cavity, and, once out, they
follow the female to the nearest body of water,
which may be located immediately below the
nest or up to 2 km away (Savard et al. 1991,
Gauthier 1993, Eadie et al. 2000). Ducklings
must rely on stored yolk reserves until they
reach the water and begin to feed (Birkhead
1985). Barrow’s Goldeneye and Bufflehead
ducklings can experience high mortality rates
in the 1st week after hatch due to their inex-
perience in foraging (Savard et al. 1991).
Thus, ducklings with large yolk reserves like-
ly survive for longer periods with little or no
food than do those with relatively small yolk
reserves.

In some species, nutrient content does not
depend on egg size, and the benefits of laying
larger eggs may not exist. In the European
Starling ( Sturnus vulgaris), for example, larg-
er eggs contained proportionately less yolk
and lipid than smaller eggs (Ricklefs 1984),
suggesting that in some species, the chicks
that hatch from larger eggs may not experi-

173

174

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

ence the advantages of proportionately larger
yolk reserves.

The primary objective of this study was to
determine the relationship between size and
nutrient composition in the eggs of Bufflehead
and Barrow’s Goldeneye breeding in British
Columbia. The two species nest sympatrically
and have a similar diet (Thompson and An-
kney 2002), but they exhibit significant dif-
ferences in body and egg size.

METHODS

Study area. — The study area included ap-
proximately 250 km2 of the Cariboo Parklands
in central British Columbia, Canada (52° 07'
N, 122° 27' W, approximate center point).
Montane and boreal wetlands used by breed-
ing Bufflehead and Barrow’s Goldeneye were
typically too alkaline and/or too shallow to
support fish, and had well developed and di-
verse aquatic invertebrate communities (for a
more detailed description of the study area,
see Thompson 1996).

Egg collection and preparation. — Buffle-
head (n = 21) and Barrow’s Goldeneye (n =
40) clutches were collected in 1993 and 1994
in conjunction with a broader study investi-
gating nutritional strategies for reproduction
in these species (Thompson 1996). Digital cal-
ipers were used to measure egg length and
width (breadth) to the nearest 0.1 mm, and a
Mettler balance was used to weigh fresh eggs
to the nearest 0.1 g. Eggs were then boiled
and frozen, pending analysis. Later, the boiled
eggs were thawed and separated into their
component parts: yolk, albumen (including
egg membranes), and shell. Egg components
were dried to a constant mass at 80° C and
measured to the nearest 0.01 g. Because egg
lipid is confined to the yolk, the dried yolk
was washed with petroleum ether in a modi-
fied Soxhlet apparatus to extract the lipid
component (Dobush et al. 1985).

Statistical analyses. — High rates of intra-
specific brood parasitism, particularly for Bar-
row’s Goldeneye, precluded reliable discrim-
ination between eggs of the host and parasite;
therefore, within-clutch analyses of variation
in egg size and composition were not con-
ducted. For each variable, we inspected a scat-
ter plot to identify eggs that were significantly
larger or smaller than average (outliers). Us-
ing Principle Component Analyses (PCA),

outliers were identified as points on the scatter
plot that lay distinctly apart from all others
(McGarigal et al. 2000). Outliers exert undue
pull on the direction of the component axes,
strongly affecting the ecological efficacy of
the ordination (McGarigal et al. 2000). A few
eggs that deviated noticeably from the norm
were removed from the data set. Final sample
sizes for Bufflehead and Barrow’s Goldeneye
(after eliminating outliers) were 123 and 226
eggs, respectively.

Preliminary analysis indicated that the re-
siduals were normally distributed and the data
did not exhibit any nonlinear trends. We used
linear regression to determine the relationship
between absolute amounts of individual egg
components (dependent variables: dry yolk,
dry albumen, lipid, mineral, and water) and
fresh egg mass (independent variable). We ex-
amined proportional nutrient content by log10
— log10 (hereafter log-log) regressions of egg
components versus fresh egg mass (Alisaus-
kas 1986). A regression slope of unity ( b =
1.0) signifies that a component makes up a
constant fraction of the total egg mass. Slopes
significantly <1 or > 1 imply that components
make up a decreasing or increasing fraction of
the total egg as egg mass increases. For each
species, we tested both absolute and propor-
tional variation in egg composition. We used
analysis of covariance (ANCOVA) to test
whether there was differential partitioning of
egg nutrients between the two species. Means
and slopes are reported ± SE, and significance
was set at P — 0.05. All analyses were con-
ducted using MINITAB (Minitab, Inc. 2003).

RESULTS

Dimensions and composition of Bufflehead
and Barrow’s Goldeneye eggs are presented in
Table 1. Fresh mass of Bufflehead eggs con-
sisted of 42% wet yolk, 40% wet albumen,
and 9% mineral. Overall, water composed ap-
proximately 52% of fresh egg mass. Similarly,
the composition of Barrow’s Goldeneye eggs
averaged 40% wet yolk, 45% wet albumen,
and 9% mineral. Water composed approxi-
mately 57% of fresh egg mass.

There was a consistently positive relation-
ship between fresh egg mass and absolute
amounts of dry yolk, dry albumen, lipid, min-
eral, and water in the eggs of both species
(Table 2). In Bufflehead eggs, all components

Lavers et al. • EGG VARIATION IN BUFFLEHEAD AND BARROW’S GOLDENEYE

175

TABLE 1. Dimensions (mm) and composition (g) of Bufflehead ( n
226) eggs collected in central British Columbia, 1993-1994.

= 123) and Barrow’s

Goldeneye ( n =

Variable

Bufflehead

Barrow’s Goldeneye

Mean ± SE

CVa (%)

Mean ± SE

CVa (%)

Length

50.20 ±0.15

3.33

61.69 ± 0.13

3.06

Breadth

36.22 ± 0.07

2.13

43.76 ± 0.06

2.10

Fresh egg mass

36.68 ±0.19

5.89

66.41 ± 0.22

5.04

Mineral

3.36 ± 0.03

9.82

6.24 ± 0.02

6.09

Wet albumen

14.71 ± 0.22

16.93

30.17 ± 0.23

1 1.60

Dry albumen

2.66 ± 0.02

9.77

4.94 ± 0.02

7.09

Wet yolk

15.46 ± 0.23

16.24

26.00 ± 0.27

15.65

Dry yolk

7.60 ± 0.06

8.55

13.31 ± 0.06

6.99

Yolk lipid

5.14 ± 0.04

8.95

8.94 ± 0.04

7.27

Yolk protein

2.45 ± 0.02

8.57

4.31 ± 0.02

7.19

Water

19.91 ± 0.14

7.89

37.92 ± 0.21

8.47

a Coefficient of variation.

except mineral exhibited negative allometry
with egg mass (Table 3). The log-log regres-
sion slope for mineral did not differ from uni-
ty ( b = 0.96 ± 0.11), indicating that mineral
mass made up a constant proportion of total
egg mass. In Barrow’s Goldeneye, yolk, lipid,
and water all exhibited positive allometry,
whereas mineral exhibited negative allometry
and albumen exhibited isometry with egg
mass (Table 3). Results of the ANCOVA in-
dicated that the nutrients of Bufflehead and
Barrow’s Goldeneye eggs are partitioned in
different ways; the slopes of the regression
lines for each nutrient differed (all P < 0.001)
between species.

DISCUSSION

The percentages of wet yolk in Bufflehead
(42%) and Barrow’s Goldeneye eggs (40%)
were similar to those reported by Lack (1967)
for other waterfowl, such as Common Gold-

eneye ( Bucephala clangula\ 44%) and Mus-
covy Duck ( Cairina moschata\ 40%), but
were greater than those reported for Greater
Snow Goose ( Anser caerulescens atlanticus;
36%) and Mute Swan ( Cygnus olor, 34%). In
Bufflehead and Barrow’s Goldeneye, yolk, al-
bumen, lipid, mineral, and water (absolute
amounts) all exhibited a positive relationship
with egg size. Log-log regression analysis of
component masses versus fresh egg mass in-
dicated interspecific differences. In Bufflehead
eggs, all components except mineral exhibited
negative allometry with egg mass. In Barrow’s
Goldeneye eggs, only mineral exhibited neg-
ative allometry, whereas yolk, lipid, and water
exhibited positive allometry with egg mass.
Thus, on average, large Bufflehead eggs do
not contain proportionately more nutrients
than small eggs, whereas large Barrow’s
Goldeneye eggs do contain more nutrients
than small eggs. The results for Bufflehead are

TABLE 2. Summary of linear regression analyses (egg components versus fresh egg mass; absolute amounts;
all P < 0.001) for Bufflehead ( n = 123) and Barrow’s Goldeneye ( n = 226) eggs collected in central British
Columbia, 1993-1994.

Component

Bufflehead

Barrow’s

; Goldeneye

b (SE)a

Intercept

b (SE)a

Intercept

Mineral

0.09 (0.01)

-0.04

0.37

0.06 (0.01)

2.45

0.26

Dry albumen

0.04 (0.01)

0.95

0.15

0.07 (0.00)

-0.01

0.51

Dry yolk

0.15 (0.02)

1.76

0.28

0.23 (0.01)

-1.93

0.69

Yolk lipid

0.11 (0.02)

1.12

0.27

0.16 (0.01)

-1.71

0.67

Yolk protein

0.04 (0.01)

0.83

0.21

0.07 (0.01)

-0.23

0.53

Water

0.32 (0.06)

8.03

0.20

0.67 (0.05)

-6.55

0.49

a Slope of regression ± SE.

176

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

TABLE 3. Summary of allometric regression analyses (egg components versus fresh egg mass; all P <
0.001) for Bufflehead (n = 123) and Barrow’s Goldeneye (n = 226) eggs collected in central British Columbia,
1993-1994.

Component

Bufflehead

Barrow’s Goldeneye

b (SE)a

Intercept

b (SE)a

Intercept

Mineral

0.96 (0.11)

-0.98

0.35

0.60 (0.06)

-0.29

0.26

Dry albumen

0.61 (0.13)

-0.54

0.14

1.00 (0.06)

-1.13

0.52

Dry yolk

0.81 (0.12)

-0.38

0.27

1.12 (0.05)

-0.92

0.68

Yolk lipid

0.80 (0.12)

-0.54

0.25

1.16 (0.05)

-1.16

0.67

Yolk protein

0.68 (0.01)

-0.67

0.20

1.03 (0.05)

-1.25

0.54

Water

0.58 (0.11)

0.39

0.18

1.16 (0.08)

-0.54

0.45

a Slope of regression ± SE; a regression slope of unity (b = 1 .0) signifies that a component makes up a constant fraction of the total egg mass. Slopes
significantly <1 or >1 indicate that components make up a decreasing or increasing fraction of the total egg as egg mass increases.

similar to those of Jager et al. (2000), who
found that larger Eurasian Oystercatcher
(Haematopus ostralegus ) eggs contained more
lean dry matter and lipid (absolute amounts)
than smaller eggs, but the proportion of both
constituents decreased with egg size.

In several bird species, hatchlings from
large eggs have a higher probability of sur-
vival to fledging than do hatchlings from
small eggs (Payne 1978). Bufflehead and Bar-
row’s Goldeneye hatchlings were not mea-
sured or monitored in this study, therefore it
is not known whether large eggs of these spe-
cies do indeed produce larger ducklings. How-
ever, larger Ruddy Duck ( Oxyura jamaicensis )
eggs produced larger, more mature ducklings
that were provisioned with greater energy re-
serves and exhibited greater survival rates
than ducklings from smaller eggs (Pelayo and
Clark 2002).

Overall, larger eggs in both species con-
tained more nutrients, although nutrient con-
tent of Barrow’s Goldeneye eggs was more
highly correlated with egg mass than it was in
Bufflehead eggs (Table 2). This suggests that
nutrients in Bufflehead and Barrow’s Gold-
eneye eggs are partitioned differently. A pos-
sible mechanism for this difference is the
source of egg nutrients: because Buffleheads
have a smaller body size, they rely more on
exogenous nutrients, whereas the larger Bar-
row’s Goldeneyes can rely more on endoge-
nous nutrients (Thompson 1996, Hobson et al.
2005). This may explain the higher CVs for
the constituents of Bufflehead eggs, as they
are less able to buffer the effects of variable
food supplies by drawing on endogenous re-
serves.

Our results show that larger eggs of Buffle-
heads and Barrow’s Goldeneyes contain more
nutrients than smaller eggs, which may in-
crease the survival of their hatchlings during
the 1st crucial week of life. This is especially
important given that Buffleheads and Bar-
row’s Goldeneyes nest in boreal and montane
regions where food typically is less available
than in, for example, the prairie wetlands of
North America, used by many temperate nest-
ing ducks (Thompson 1996, Thompson and
Ankney 2002). Further studies should be con-
ducted on these species to examine variation
in egg composition within and between
clutches and to determine whether hatchlings
from larger eggs are larger and have lower
mortality than those from smaller eggs.

ACKNOWLEDGMENTS

Funding for this project was provided by the Na-
tional Science and Engineering Research Council of
Canada (NSERC) through an operating grant awarded
to C. D. Ankney. Additional financial support was pro-
vided through a joint Canadian Wildlife Service and
NSERC grant awarded by the Pacific Wildlife Re-
search Network Program. We thank the University of
Western Ontario and University of Alberta for further
financial support for this project as well as use of com-
puter and research labs for data analysis and sample
preparation. This research was facilitated by generous
cooperation and logistical support provided by M.
Clarke, B. Arner, D. Regier, and E. Hennan of Ducks
Unlimited Canada, and A. Breault and D. Dockerty of
the Canadian Wildlife Service. Permission to work in
portions of the study area was kindly granted by the
Canadian Department of National Defense (Chilcotin
Military Training Area) and B. Durrell of the Wine
Glass Ranch. Dedicated field and lab assistance for this
project was provided by T. Matthews and S. A. Lee.
Finally, we thank G. Robertson and three anonymous

Lavers et al. • EGG VARIATION IN BUFFLEHEAD AND BARROW’S GOLDENEYE

177

reviewers for their constructive feedback on previous

versions of this manuscript.

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The Wilson Journal of Ornithology 1 18(2): 178-186, 2006

SITE-SPECIFIC SURVIVAL OF BLACK-HEADED GROSBEAKS
AND SPOTTED TOWHEES AT FOUR SITES WITHIN THE
SACRAMENTO VALLEY, CALIFORNIA

THOMAS GARDALI1 2 AND NADAV NUR1 2

ABSTRACT. — We estimated apparent annual survival and recapture probabilities for adult Black-headed
Grosbeaks ( Pheucticus melanocephalus ) and Spotted Towhees ( Pipilo maculatus) at four sites along the Sacra-
mento River, California. To calculate our estimates, we used capture-recapture mist-net data collected over two
time periods at four study sites: from 1993 to 1995 at Flynn, Ohm, and Sul Norte, and from 1995 to 2000 at
Ohm and Phelan Island. Our primary objective was to determine whether there were site-specific differences in
adult survival and recapture probabilities for each species. Such differences are rarely investigated, yet, if present,
suggest site-specific differences in habitat quality, with important implications for source/sink dynamics. We
found site-specific variation in Black-headed Grosbeak survival within both the 1993-1995 dataset (Flynn =
0.797 ± 0.496, Ohm = 0.158 ± 0.191, Sul Norte = 0.773 ± 0.131) and the 1995-2000 dataset (Ohm = 0.088
± 0.090, Phelan Island = 0.664 ± 0.111). For Spotted Towhees (1993-1995 data), the most supported model
assumed constant survival across sites (0.602 ± 0.240), but there was some support for site variation in survival,
as well (Flynn = 0.653 ± 0.365, Ohm = 0.214 ± 0.253, Sul Norte = 0.632 ± 0.258). These results clearly
suggest site variation for Black-headed Grosbeaks, and weak evidence of site variation for Spotted Towhees.
For both species, the general pattern was low survival at Ohm, suggesting low-quality habitat there and/or
reduced site fidelity. The magnitude of site-to-site variation in survival observed in the Black-headed Grosbeak,
and suggested for Spotted Towhee, has strong implications for determining source versus sink population status.
To determine source versus sink status, we conclude that investigators must not only take into account site
variation in reproductive success, but also consider site-specific estimation of adult survival. Received 28 March
2005, accepted 4 January 2006.

Measuring adult survival — the probability
that an adult will survive from one year to the
next — is a critical step toward understanding
population dynamics, as low survival rates
may be responsible for population declines for
some species (Nur and Sydeman 1999). It has
been hypothesized that tropical deforestation
has led to decreases in over-winter survival
(e.g., Askins et al. 1990, Rappole and Mc-
Donald 1994), and several recent studies sug-
gest that events at migratory stopover areas
also may have significant consequences (e.g.,
Moore et al. 1995, Yong et al. 1998, Sillett
and Holmes 2002). Few researchers, however,
have examined the potential role of the breed-
ing grounds in affecting annual survival
(Chase et al. 1997, Powell et al. 2000, Sillett
and Holmes 2002).

Many factors that are related to a particular
species’ life-history characteristics operate to
influence adult survival at various periods in
the annual cycle. Survival of migratory spe-
cies, for example, may be regulated primarily

1 PRBO Conservation Science, 4990 Shoreline
Hwy., Stinson Beach, CA 94970, USA.

2 Corresponding author; e-mail: tgardali@prbo.org

by events during migration or on their win-
tering grounds in the tropics (e.g., habitat
loss). In contrast, all factors influencing the
survival of resident species occur on their
year-round home ranges. Survival also may be
influenced by events during the breeding sea-
son in the temperate zone. Reproductive effort
can affect survival rates for some species (Nur
1988a, 1988b), and individuals that must
make repeated nesting attempts due to high
levels of nest depredation may pay a greater
cost in terms of survival. For example, female
Common House-Martins ( Delichon urbicum )
that double-brooded experienced lower rates
of survival than single-brooded females (Bry-
ant 1979). Additionally, environments where
the predator community is rich and abundant
and habitat cover is poor could negatively in-
fluence survival rates.

Despite the widely recognized assumption
that survival plays a critical role in regulating
populations, few studies of passerines have
been designed to specifically look for site- or
habitat-specific differences (Peach 1993),
though several researchers have examined site
fidelity in relation to various indices of site
quality (e.g., Bollinger and Gavin 1989, Sedg-

178

Gardali and Nur • SITE-SPECIFIC SURVIVAL

179

wick 2004). This is likely because survival is
relatively difficult to measure; it requires sev-
eral years of study, and often-small sample
sizes from individual sites prohibit proper
analyses. However, site-specific estimates of
survival can provide insight into habitat qual-
ity, and differences in survival could alert land
managers to potential problems.

Here, we present site-specific survival es-
timates for two species that differ in life his-
tory characteristics — the migratory Black-
headed Grosbeak ( Pheucticus melanocephal-
us ) and the resident Spotted Towhee ( Pipilo
maculatus). Our estimates were based on data
collected during a multi-site, multi-year, con-
stant-effort mist-netting program (Nur and
Geupel 1993) conducted along the Sacramen-
to River. We also investigated differences in
recapture probability — the probability that an
individual that has survived from year jc to
year x + 1 is also recaptured in year x + 1
(Nur and Clobert 1988). As is often the case
in attempting to estimate survival, we could
not distinguish mortality from permanent dis-
persal (that is, we measured “local survival”;
Lebreton et al. 1992); thus, our estimates are
conservative (Lebreton et al. 1992). Site dif-
ferences in the survival estimates we present
may be explained by variation in survival
probability from one year to the next, varia-
tion in permanent emigration, or both. How-
ever, local movements of individuals from
year to year (e.g., in some years individuals
may have nested closer to, or farther from the
array of mist nets) should not have biased our
survival estimates; such local dispersal (af-
fecting recapture from one year to the next) is
incorporated into our recapture probability
calculations (Nur and Clobert 1988).

METHODS

Study sites. — Our four study sites were in
the Sacramento Valley, California: Flynn (40°
06' N, 122° 12' W), Sul Norte (39° 46' N,
121° 99' W), Ohm (40° 09' N, 122° 12' W),
and Phelan Island (39° 69' N, 121° 97' W).
Ohm and Flynn were the northern-most sites
(3.4 km from each other), Phelan Island was
south of these sites by —50 km, and Sul Norte,
located —100 km south of Ohm and Flynn,
was the southern-most site (see map in Gar-
dali et al. in press). Sites ranged in elevation
from 39 to 70 m. Dominant trees included

Fremont cottonwood ( Populus fremontii), val-
ley oak ( Quercus lobata ), and willow ( Salix
spp.) with varied understory communities
consisting of mugwort ( Artemesia douglasi-
ana ), Santa Barbara sedge ( Carex barbarae),
blue wildrye ( Elymus glaucus ), California
blackberry ( Rubus ursinus), and various ex-
otic, weedy species (e.g., Johnson grass [Sor-
ghum halepense], Bermuda grass [ Cynodon
dactylon ], Himalayan blackberry [Rubus dis-
color]). Flynn and Sul Norte (in Tehama and
Glenn counties, respectively) were riparian
remnants of relatively old forests. Ohm (in Te-
hama County) was also a remnant forest, but
differed in that it was grazed by cattle for the
duration of the study; thus, the density of the
shrub community was diminished in compar-
ison (TG pers. obs.). Ohm also had more
black walnut ( Juglans californica ) trees than
the other sites (TG pers. obs.). Phelan Island
(in Glenn County) was a riparian restoration
site planted in 1991 and 1992 (see Alpert et
al. 1999 for details). Land use surrounding all
sites was primarily agricultural (orchards). Al-
though all sites were broadly similar in plant
species composition, landscape context, and
climate, there were likely some differences in
habitat structure/complexity and flooding fre-
quency.

Field methods. — Black-headed Grosbeaks
and Spotted Towhees were sampled through
standardized effort mist netting (Monitoring
Avian Productivity and Survivorship protocol;
DeSante et al. 2000). Sampling occurred at
Flynn, Ohm, and Sul Norte during 1993-1995
and at Ohm and Phelan Island during 1995-
2000. Ten 12-m, 36-mm-mesh mist nets were
operated at each study site for 5 (morning) hr
per day for 1 day during each of 10 consec-
utive 10-day periods (—500 net-hr/site). Start-
ing dates were approximately 1 May and op-
eration continued through the 10— day period
ending 8 August. Nets were opened 15 min
after sunrise and kept open for 5 hr during
each day of net operation. Nets were checked
every 20 to 45 min, depending on weather
conditions, and were closed when water ac-
cumulated on them, or when wind caused net
pockets to consistently billow. Because of
these standardized protocols, effort (net hr)
was similar among sites and years. Captured
birds were banded with federal bands, mea-
sured, and released immediately.

180

THE WILSON JOURNAL OF ORNITHOLOGY • Vol 118, No. 2, June 2006

Statistical analyses. — We used capture/re-
capture data of adult birds to estimate annual
survival, and we used program SURGE 4.3 to
calculate recapture probabilities (Lebreton et
al. 1992, Cooch et al. 1996). Recapture prob-
abilities of transients can be lower than recap-
ture probabilities of site-faithful individuals in
most species (Peach et al. 1991, Chase et al.
1997, Pradel et al. 1997), and such heteroge-
neity in recapture probabilities violates an as-
sumption of capture-recapture methodology
(see Lebreton et al. 1992 for discussion). Var-
ious methods have been used to identify site-
faithful individuals, such as identifying indi-
viduals captured at least twice during any
breeding season and/or captured in more than
one year (e.g., Chase et al. 1997, Gardali et
al. 2000, Nur et al. 2000). In our study, how-
ever, we did not recapture enough individuals
meeting these criteria to allow such analyses
except for (1) Black-headed Grosbeaks at Sul
Norte in 1993-1995 and (2) Black-headed
Grosbeaks at Phelan Island in 1995-2000. In
these two cases, individual Black-headed
Grosbeaks captured at least twice during any
breeding season and at least 7 days apart, and/
or those captured in more than one year were
considered site-faithful breeders. We com-
pared survival estimates from this “high site
fidelity” subset with those from the full da-
taset, to determine whether the inclusion of
transient Black-headed Grosbeaks biased our
survival estimates. All other analyses were
based on the full dataset (site-faithful breeders
and transients).

For both species and each dataset (i.e.,
1993-1995 and 1995-2000), we evaluated
four models with time-constant survival (phi)
and recapture (p) probabilities to test for po-
tential site-specific variation: ( 1 ) constant sur-
vival and recapture probability across sites,
(2) variable survival but constant recapture
probability across sites, (3) variable survival
and recapture probability across sites, and (4)
constant survival but variable recapture prob-
ability across sites. To select the most appro-
priate model, we employed Akaike’s Infor-
mation Criterion (AIC) and chose the model
with the lowest AIC value (Lebreton et al.
1992, Burnham and Anderson 2002). We used
differences in AIC between that model and
other models to evaluate the evidence in sup-
port of particular models. Models with AAIC

TABLE 1. Total numbers of Black-headed Gros-
beaks and Spotted Towhees captured, by site and time
period, Sacramento Valley, California, 1993-2000.

Years

(dataset)

Site

Black-headed
Grosbeak («)

Spotted
Towhee (n)

1993-1995

Flynn

Ohm

Sul Norte

1995-2000

Ohm

Phelan Island

150

<2 can be said to exhibit moderately strong
support relative to the preferred model; those
with 2-4 have less support and those with
>10 have none (Burnham and Anderson
2002).

We analyzed the data as a partial time series
because we did not collect data at all netting
sites in all years. Ohm was the only site where
mist netting was conducted over the course of
the entire study; Llynn and Sul Norte were run
from 1993 to 1995 and Phelan Island was op-
erated from 1995 to 2000.

RESULTS

Overall, more Black-headed Grosbeaks
were captured than Spotted Towhees (Table
1 ), but a slightly higher percentage of towhees
was recaptured (17.1% versus 12.3%); most
of our captures were presumed to be tran-
sients. Captures were greatest for both species
at Sul Norte (1993 to 1995 data); during 1995
to 2000, we captured more grosbeaks at Phe-
lan Island but more towhees at Ohm (Table
1).

Black-headed Grosbeak. — The model
where survival differed across sites while re-
capture probability was constant performed
best (AAIC = 0) among the four models
(1993 to 1995 dataset; Table 2). Model 3 (both
survival and recapture probabilities differed
across sites) did not produce maximum-like-
lihood estimates; boundary estimates were 1 .0
for either survival or recapture probability due
to the small sample size (Cooch et al. 1996).
There was also support for model 4 (constant
survival, recapture probability differed across
sites; AAIC = 0.4; Table 2). The best model
from the 1995 to 2000 dataset (model 2) was
also the one that supported site-specific vari-
ation in survival; there was some support for
model 4 as well (AAIC = 1.14; Table 2).

Gardali and Nur • SITE-SPECIFIC SURVIVAL

181

TABLE 2. Survival and recapture probabilities for Black-headed Grosbeaks, 1993-1995 (Flynn, Ohm, and
Sul Norte) and 1995-2000 (Ohm and Phelan Island), Sacramento Valley, California. Models were (1) constant
survival and recapture probability across sites, (2) variable survival but constant recapture probability across
sites, (3) variable survival and recapture probability across sites, and (4) constant survival but variable recapture
probability across sites. All = all sites combined. AICM. = AIC weights.

Model

Survival estimate
(phi)

Recapture probability
estimate (p)

AIC

AAIC

AIC„,

1993-

-1995

All: 0.813

0.327

All: 0.136

0.040

126.63

1.77

0.172

Flynn: 0.797

0.496

All: 0.181

0.102

124.86

0.417

Ohm: 0.158

0.191

NAa

Sul Norte: 0.773

0.131

Flynn: 1.000

Flynn: 0.1 18

0.090

128.42

3.56

0.070

Ohm: 0.031

0.053

Ohm: 1.000

—

Sul Norte: 0.692

0.470

Sul Norte: 0.216

0.134

All: 0.762

0.624

Flynn: 0.173

0.280

125.26

0.40

0.341

Ohm: 0.032

0.077

Sul Norte: 0.189

0.172

1995-

2000

All: 0.642

0.088

All: 0.166

0.046

264.99

13.80

0.001

Ohm: 0.088

0.090

All: 0.205

0.054

251.19

0.510

Phelan: 0.664

0.111

Ohm: 0.020

0.030

Ohm: 1.000

—

253.06

1.87

0.200

Phelan: 0.666

0.139

Phelan: 0.204

0.054

All: 0.659

0.349

Ohm: 0.017

0.020

252.33

1.14

0.289

Phelan: 0.208

0.077

a NA = not applicable.

b Boundary estimates were 1 .0 for either survival or recapture probability due to small sample size.

Black-headed Grosbeak l l Spotted Towhee

1.00

0.75

| 0.50
03

0.25

0.00

FIG. 1. Site-specific survival estimates for Black-
headed Grosbeaks and Spotted Towhees at four sites
in the Sacramento Valley, California, over two time
periods, 1993—1995 and 1995—2000. For both species,
survival estimates from Model 2 (variable survival, but
constant recapture probability across sites) are pre-
sented (see Tables 2 and 3). Error bars are ± SE.

Flynn Ohm Sul Norte Ohm Phelan Island

Site

Overall, we found site-specific variation in
survival for Black-headed Grosbeaks within
the 1993-1995 dataset (Flynn = 0.797 ±
0.496, Ohm = 0.158 ± 0.191, Sul Norte =
0.773 ± 0.131) and the 1995-2000 dataset
(Ohm = 0.088 ± 0.090, Phelan Island =
0.664 ±0.111; Fig. 1, Table 2).

To investigate whether including transients
would bias the full datasets (i.e., those includ-
ing both transient and site-faithful individu-
als), we analyzed the subset of data that met
our requirements for site-faithful birds. For
this, we only estimated constant survival and
constant recapture probabilities. At the Sul
Norte site (1993-1995 data), the estimate for
the site-faithful subset (0.700 ± 0.271) was
similar to that of the full dataset (0.773 ±
0.131; Table 2). If transients were biasing re-
sults, the survival estimate for the site-faithful
subset would have been greater than that for
the full dataset, but this was not the case. For
Phelan Island (1995-2000), however, the dif-
ferences in survival estimates (site-faithful

182

THE WILSON JOURNAL OF ORNITHOLOGY • Vol 118, No. 2, June 2006

TABLE 3. Survival and recapture probabilities for Spotted Towhees, 1993-1995 (Flynn, Ohm, and Sul
Norte) and 1995-2000 (Ohm and Phelan Island), Sacramento Valley, California. Models are (1) constant survival
and recapture probability across sites, (2) variable survival but constant recapture probability across sites, (3)
variable survival and recapture probability across sites, and (4) constant survival but variable recapture proba-
bility across sites. All = all sites combined. AIC*, = AIC weights.

Model

Survival estimate
(phi)

Recapture probability
estimate (p)

AIC

AAIC

AIC*,

1993-

1995

All: 0.602

0.240

All: 0.317

0.173

85.06

0.512

Flynn: 0.653

0.365

All: 0.340

0.180

86.56

1.50

0.242

Ohm: 0.214

0.253

NAa

Sul Norte: 0.632

0.258

Flynn: 0.557

0.501

Flynn: 0.431

0.366

90.18

5.12

0.040

Ohm: 0.083

0.140

Ohm: 1.000

Sul Norte: 0.752

0.470

Sul Norte: 0.256

0.212

All: 0.626

0.532

Flynn: 0.375

0.482

86.87

1.81

0.207

Ohm: 0.104

0.261

Sul Norte: 0.324

0.377

1995-

2000

All: 0.245

0.11 1

All: 0.496

0.271

68.98

0.508

Ohm: 0.248

0.165

All: 0.496

0.272

70.97

1.99

0.188

Phelan: 0.238

0.241

Ohm: 0.296

0.244

Ohm: 0.378

0.373

72.13

3.15

0.105

Phelan: 0.138

0.170

Phelan: 1.000

—

All: 0.237

0.241

Ohm: 0.472

0.453

70.85

1.87

1.990

Phelan: 0.598

0.596

a NA = not applicable.

b Boundary estimates were 1.0 for either survival or recapture probability due to small sample size.

subset = 0.739 ± 0.276; full dataset = 0.664
± 0.1 1 1) were consistent with the supposition
that transients could have biased our survival
estimates, but we could not conclude with
confidence that this was the case (Table 2).

Spotted Towhee. — Model 1 (constant sur-
vival and recapture probabilities) from the
1993 to 1995 dataset received the most sup-
port (Table 3). Models assuming site differ-
ences for either survival or recapture proba-
bilities (but not both) also received some sup-
port (models 2 and 4). The magnitude of site
variation with respect to survival (model 2;
Table 3) was large (a difference of 0.41 to
0.43, when comparing Ohm with the other
two sites), but the standard errors were large
and overlapping (Fig. 1, Table 3).

Model 1 (constant survival and constant re-
capture probability) was also best (AAIC = 0)
in the 1995 to 2000 dataset (Table 3). Like
those of the earlier dataset (1993-1995), mod-
els with site-specific differences in either sur-
vival or recapture probabilities (models 2 and

4) could not be ruled out (Table 3). The sur-
vival estimates for both Ohm and Phelan Is-
land were very low (model 2; Fig. 1, Table
3). Furthermore, the survival estimates for
Ohm were similar in both the 1993-1995 and
1995-2000 time periods, indicating within-
site consistency, but Phelan Island also had a
low survival rate. Overall, the pattern of site-
specific Spotted Towhee survival observed in
the 1993 to 1995 data was not manifest in the
1995 to 2000 data.

DISCUSSION

In addition to the site-specific variation we
found in survival rates, our survival estimates
differed from those published elsewhere.
Based on the best-supported models, our sur-
vival estimates for Black-headed Grosbeaks at
Flynn, Sul Norte, and Phelan Island (0.664 to
0.797) were greater than those calculated
(with a modified Cormack-Jolly-Seber meth-
od) by DeSante and O’ Grady (2000) from
1992-1998 data collected at 51 mist-net sta-

Gardali and Nur • SITE-SPECIFIC SURVIVAL

183

tions in northwestern North America (0.573 ±
0.046 SE) and 28 mist-net stations in south-
western North America (0.576 ± 0.05 1 SE).
Survival estimates from the Ohm site (0.088
and 0.158) were considerably lower. Of mod-
els assuming constant survival across sites,
the best model for all sites combined (model
4; both time periods) also estimated notably
higher survival rates than those reported by
DeSante and O’ Grady (2000). For Spotted To-
whees, our 1993 to 1995 survival estimate
(0.602) was greater than those found by
DeSante and O’ Grady (2000) for the north-
western (34 sites) and southwestern (17 sites)
regions (0.519 ± 0.047 SE and 0.486 ± 0.043
SE, respectively), whereas our 1995 to 2000
estimate (0.245) was lower.

Site variation in survival was indicated for
Black-headed Grosbeaks. There was also
some evidence that Spotted Towhee survival
varied by site, although the variation around
several of these estimates was large and over-
lapping. For both species, survival estimates
at the Ohm site were low; this site differs from
the others in that cattle were grazed there dur-
ing the entire study period. Grazing has the
potential to affect habitat quality in several
ways, which may influence survival and em-
igration probabilities (Saab et al. 1995). For
example, grazing appeared to have reduced
the amount of low shrubby vegetation cover
that serves as protection from predators.
Heightened predation pressure could negative-
ly affect survival directly via adult mortality,
and/or indirectly via nest predation, whereby
there is a fitness cost for individuals that re-
nest relatively more than other individuals. In-
deed, reproductive effort can affect adult sur-
vival rates in some landbird species (Nur
1988a, 1988b; McCleery et al. 1996; Cichon
et al. 1998). An additional cause of reduced
survival at the grazed site could be related to
food resources: fewer insects may have been
available because of diminished or modified
foraging substrates (but see Haas 1998).

In general, the few past studies conducted
to examine over-summer survival (i.e., during
the breeding period itself) have revealed rel-
atively high survival rates during this period
(Smith 1995, Lahti et al. 1998, Powell et al.
2000, Sillett and Holmes 2002). There is,
however, some evidence that subordinate in-
dividuals (e.g., young birds) experience higher

rates of mortality during this period — primar-
ily due to predation (Geer 1982, Smith 1995,
Powell et al. 2000). Additionally, recent evi-
dence suggests that events during one stage in
the annual cycle may influence the subsequent
stage (Marra et al. 1998, Sillett et al. 2000),
and that conditions in one year may affect re-
productive performance in a subsequent year
(Nur 1988a). Hence, differences in survival
caused by differences in conditions on the
breeding grounds would not be captured in
those studies limited to estimating survival
during the summer/breeding season months
(Smith 1995, Lahti et al. 1998, Powell et al.
2000, Sillett and Holmes 2002).

Spotted Towhee survival was low at both
Ohm and Phelan Island, whereas Black-head-
ed Grosbeak survival was low at Ohm but rel-
atively high at Phelan Island. Although we do
not know why towhee survival was low at
Phelan Island, this is a restoration site and
some vegetation features, or other component
of the ecosystem, may have reduced survival.

We could not distinguish true mortality
from permanent dispersal. Therefore, ob-
served differences in apparent survival rates
may reflect site-specific differences in site fi-
delity instead of true survival. Such differenc-
es also suggest that habitat conditions at Ohm
were relatively poor for grosbeaks, and per-
haps towhees, because individuals did not re-
main faithful to that site for multiple years.
Several studies have shown that individuals
are less likely to return to a territory or site if
reproductive performance at that location was
poor (e.g., Harvey et al. 1979, Haas 1998,
Porneluzi 2003). Interestingly, Haas (1997)
found that Brown Thrashers ( Toxostoma ruf-
um) return significantly more to grazed sites
than to ungrazed sites and speculated that
thrashers in grazed sites were able to forage
more effectively (e.g., preferred substrate) and
maintain better body condition.

It is possible that transients may have dom-
inated captures at Ohm, but not at other sites.
Perhaps the habitat configuration or net loca-
tions at Ohm were more suitable for capturing
migrating grosbeaks. However, Spotted Tow-
hees are year-round residents, yet they had
low survival estimates at Ohm as well. Also,
the Ohm and Flynn sites are only 3.2 km
apart, making it difficult to imagine that more
migrants would be captured at Ohm. Further-

184

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

more, the differences in survival rates be-
tween these two sites were so large that it
seems unlikely that the cause would have been
a preponderance of transients at Ohm (Table
2). Although transient composition may have
explained part of the site differences in sur-
vival, we believe that the differences are pri-
marily due to true differences in survival. The
fact that survival estimates of both species
were low at Ohm makes this argument more
compelling, and it is likely that both species
are being affected by the same mortality fac-
tors at that site.

The large differences we found in our sur-
vival estimates have strong implications for
source-sink dynamics (Pulliam 1988). Wheth-
er a site is a source or a sink depends on a
combination of adult survival and juvenile re-
cruitment. The low survival rates of Spotted
Towhees at Ohm suggest that Ohm is a sink
population. Population growth rate (lambda)
is equal to the sum of adult survival and net
recruitment rate of offspring, which itself is a
product of the number of female offspring
produced per adult female and the survival of
fledged offspring to breeding age (Pulliam
1988, see also Nur and Sydeman 1999).
Therefore, a difference in adult survival of
0.40 (such as that found for Spotted Towhees)
will lead to a difference in lambda of 0.40 if
the other parameter values are the same; thus,
if a population is growing at 10% per year at
a favorable site (lambda = 1.1), the popula-
tion would be declining at 30% per year at an
unfavorable site, such as Ohm (lambda =
0.70).

For Black-headed Grosbeaks, the differenc-
es in apparent survival between Ohm and the
other sites were even greater. Adult survival
rates of 0.77 to 0.80 at Flynn and Sul Norte
(Model 2, 1993 to 1995) may be consistent
with those of a source population. At Ohm,
with an adult survival rate of 0.19, it would
not be possible for a population to yield a
lambda of 1.0 or greater (Model 2, 1993 to
1995), even using the most optimistic param-
eter values for reproductive success and off-
spring survival. As a result, the Ohm popu-
lation may be a sink due to low adult survival,
irrespective of reproductive success. Alterna-
tively, emigration rates may be high at Ohm
because it is a reproductively inferior site re-
sulting in a high turnover of individuals. In

this case, survival could be as great at Ohm
as at the other sites and Ohm would contribute
to the overall metapopulation (Howe et al.
1991).

It is common for researchers modeling site-,
treatment-, or habitat-specific lambda to use a
single survival estimate in combination with
several reproductive estimates (e.g., Donovan
et al. 1995, Manolis et al. 2002). The practice
has been to use a single survival estimate from
one site (not necessarily derived from the
study area), regional estimates that combine
several sites, or a mean of published esti-
mates. This is understandable because site-
specific survival is difficult to estimate,
whereas estimating nest survival is relatively
easy. Our results, however, emphasize the
need to combine site-, treatment-, or habitat-
specific estimates of adult survival with com-
parable estimates of nest survival when mod-
eling population viability.

ACKNOWLEDGMENTS

We are indebted to the many biologists that helped
to collect these data, especially A. M. King and S. L.
Small. We would like to thank PRBO staff; G. R. Geu-
pel and G. Ballard both contributed to this study in
important ways. Funds for this monitoring project
came from several sources: The Nature Conservancy,
U.S. Fish and Wildlife Service, the David and Lucile
Packard Foundation, the William and Flora Hewlett
Foundation, the National Fish and Wildlife Founda-
tion, CALFED Bay/Delta Program, the U.S. Bureau of
Reclamation, the Natural Resource Conservation Ser-
vice, and River Partners. We are deeply grateful to all
of them. We especially thank our many partners for
long-term support: J. Carlon, D. Efseaff, G. Golet, S.
Lawson, G. Mensik, S. Phelps, J. Silveira, R. Vega, T.
Zimmerman, and D. Zeleke. We thank G. H. Golet, C.
A. Haas, and two anonymous reviewers for helpful
comments on this manuscript. This is PRBO contri-
bution # 1297.

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The Wilson Journal of Ornithology 1 18(2): 187— 193, 2006

PRE-MIGRATORY FATTENING AND MASS GAIN IN
FLAMMULATED OWLS IN CENTRAL NEW MEXICO

john p. Delong1 2

ABSTRACT. — Hatching-year (HY) and presumed HY Flammulated Owls (Otus flammeolus) were captured
during a period of pre-migratory activity in central New Mexico from 2000 to 2003. Mass gains were evident
through the pre-migratory period. Fat deposition was an important component of these mass gains; muscle
growth appeared to contribute to a lesser degree. Fat scores and pectoral-muscle scores were positively related
to body mass and to each other, and, from first to last capture, most recaptured owls showed increases in body
mass that were accompanied by fat deposition and growth in pectoral muscles. These data add to a growing
body of research indicating that pre-migration increases in fat and muscle mass may be interdependent, but the
magnitude of increased muscle mass may be too small to be detected at certain scales. Received 4 February
2005, accepted 26 November 2005.

Many migratory birds show substantial
gains in body mass prior to migration (King
1972, Bairlein 2002). These gains typically
represent some combination of growth in fat,
muscle, and organ tissues (King 1972, Lind-
strom and Piersma 1993, Bairlein 2002). Fat
is a major component of internal energy re-
serves and it can be catabolized during mi-
gratory flights (King 1972). The amount of fat
stored appears to vary in relation to the ex-
pected travel distance, opportunities to refuel,
and predation risk en route (King 1972, Al-
erstam and Lindstrom 1990, Bairlein 2002).
Increases in muscle size appear to have a two-
fold role: to increase the power output from
the wings (specifically for pectoral muscles)
and to provide a source of amino acids and
water as they are catabolized during flight
(Marsh 1984, Pennycuick 1998, Lindstrom et
al. 2000, Bairlein 2002). Increases in the size
of digestive organs facilitate more rapid up-
take of nutrients, aiding in fat storage and the
growth of pectoral and other muscles. When
not in use, the digestive organs themselves
may provide additional nutrient sources as
they are catabolized (Karasov and Pinshow
1998, Piersma et al. 1999).

The masses of fat and non-fat tissues often
are correlated with overall body mass, but it
is not clear that changes in masses of fat and
lean tissues are interdependent (Gosler 1991;

1 HawkWatch International, Inc., 1800 S. West Tem-
ple, Ste. 226, Salt Lake City, UT 84115, USA.

2 Current address: Eagle Environmental, Inc., 2314
Hollywood Ave. NW, Albuquerque, NM 87104, USA;
e-mail: jpdelong@comcast.net

Selman and Houston 1996; Redfern et al.
2000, 2004). Because changes in mass are re-
lated to foraging and behavioral patterns be-
fore migration and during migration stop-
overs, understanding how lean and fat tissues
contribute to changes in mass in migratory
birds may help to elucidate important aspects
of migratory bird ecology (Karasov and Pin-
show 1998, Bairlein 2002). The concurrent
study of fat deposition, muscle hypertrophy,
and mass gain prior to migration has received
little attention in field studies, probably be-
cause carcass analysis is usually required
(e.g., Redfern et al. 2000). Although carcass
analysis can provide precise measurements,
samples sizes are often small because birds
must be killed for analysis. Scoring body
composition does not require killing birds and
it confers the possibility of adequate sample
sizes (Redfern et al. 2004).

Flammulated Owls ( Otus flammeolus ) are
small, insectivorous birds that breed in the
montane forests of western North America
and Mexico (McCallum 1994). The species is
believed to winter in southern Mexico and
Guatemala; thus, it is considered by most
sources to be a Neotropical migrant, undertak-
ing potentially long flights between summer-
ing and wintering areas (McCallum 1994).
During the falls of 2000-2003, I examined the
interrelationships among mass gain, fat de-
position, and the size of pectoral muscles in
Flammulated Owls captured in central New
Mexico. My coworkers and I captured Flam-
mulated Owls from late August, when hatch-
ing-year (HY) birds become independent from
their parents (Linkhart and Reynolds 1987),

187

188

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

through October, when birds begin their
southward migration. These capture efforts
were part of a larger study on the migration
ecology of Flammulated Owls (DeLong 2004,
DeLong et al. 2005). Based on stable hydro-
gen isotope analysis of feathers and the stage
of the preformative molt, most of the owls had
not traveled far from their natal areas (De-
Long 2004, DeLong et al. 2005). During latter
stages of our field seasons, we captured some
migrants that had come from latitudes north
of central New Mexico, but they were few in
number. Hence, our sampling period was a
post-independence/pre-migration period for
owls that had summered in central New Mex-
ico. Using this sample, I tested the hypothesis
that fat and muscle tissue growth simulta-
neously contribute to overall mass gain in
Flammulated Owls prior to their southward
migration.

METHODS

The study site was located near Capilla
Peak in the Manzano Mountains of central
New Mexico (34°42'N, 106° 24' W). The
Manzano Mountains are part of an important
migratory corridor for many raptors and song-
birds that move through New Mexico during
the fall (see DeLong and Hoffman [1999] and
DeLong et al. [2005] for additional details).
My coworkers and I set up two mist-netting
stations, spaced ~200 m apart, one on each
side of the north-south trending Capilla Peak
ridge. We lured owls to the stations by broad-
casting the territorial breeding-season hoots of
the male Flammulated Owl from within arrays
of 3-6 mist nets (60-mm mesh). From 18 Au-
gust to 22 October, we opened mist nets 3—7
nights/week, depending on volunteer support
and weather. We typically began netting 0—30
min after sunset and continued until 15-30
min before sunrise. We closed the nets when
winds exceeded —24 km/hr or when precipi-
tation began to fall. We checked nets for cap-
tured owls every 40-70 min.

We banded owls with federal aluminum leg
bands, used an electronic scale to determine
their mass to the nearest 0.1 g, and used a
standard wing chord ruler to measure their un-
flattened wing chords to the nearest 1 mm. To
determine whether body mass and other pa-
rameters of males and females differed, we
obtained blood samples or feather shafts from

randomly selected HY owls and sent them to
Wildlife Genetics, Inc. (Nelson. British Co-
lumbia, Canada; www.wildlifegenetics.com)
for DNA analysis (CHD gene method; Grif-
fiths et al. 1998).

Whenever possible, we aged owls as either
HY or adult. We identified HY owls by the
presence of retained juvenal plumage (De-
Long 2004) or by uniform fault-barring (Pyle
1997). We identified adult owls by the pres-
ence of multiple generations of flight feathers.
For the analyses in this paper, I excluded
adults because their body mass was signifi-
cantly greater (HY mean mass — 53.9 g, n —
124; adult mean mass — 59.9 g , n = 13; t =
4.7, P < 0.001) and adults were not captured
frequently enough to analyze separately. The
analyses included both confirmed and pre-
sumed HY owls. I presumed that owls of un-
known age were HY birds if they were molt-
ing their contour feathers, had only a single
generation of flight feathers, and weighed less
than the mean weight for adults. Most adult
Flammulated Owls finish molting their flight
feathers by late September (Reynolds and
Linkhart 1987), in which case they too would
have had a single generation of flight feathers
during our study period; thus, it is possible
that some adult birds were misidentified as
hatching-year birds. For two reasons, howev-
er, I believe the number of adults included in
the analyses is small. First, most unknown-age
owls were captured before October (74% of
128 unknown-age owls) and thus would likely
show multiple generations of flight feathers if
adult. Second, nearly all of these birds were
captured before we were able to use the re-
tained-plumage criterion for identifying hatch-
ing-year owls; therefore, these owls were la-
beled unknown-age only because they did not
show multiple generations of flight feathers,
not because they lacked retained juvenal
plumage. We did not know to look for these
feathers in the early years, but learned to do
so as the study progressed (DeLong 2004). As
the study progressed, it became clear that
adult owls were rarely captured at our study
site (JPD unpubl. data).

We used a 5-point scoring technique to vi-
sually assess the size of pectoral muscles. The
pectoral-muscle score was based on thickness
(roughly a cross-section), as follows: 1 =
muscle very concave with keel of sternum

DeLong • PRE-MIGRATORY MASS GAIN IN FLAMMULATED OWLS

189

protruding sharply, 2 = muscle roughly tri-
angle-shaped with keel protruding sharply, 3
= rounded muscle with keel still protruding
just slightly above the muscle level, 4 = mus-
cle rounded and flush with keel, and 5 = mus-
cle depth exceeds (bulges beyond) the keel.
The cross-sectional shape of pectoral muscles
is positively correlated with the pectoral mass
in small birds (Selman and Houston 1996);
therefore, visual assessments of the cross-sec-
tional shape of pectoral muscles should pro-
vide a suitable index of pectoral-muscle size.
A similar approach has been used effectively
in studies of songbirds (Gosler 1991).

We visually assessed furcular fat deposits
(i.e., the claviculo-coracoid fat body described
by King and Famer 1965) using a 6-point
scoring technique similar to that of Helms and
Drury (1960). The furcular fat score reflected
the depth of fat in the furculum: 0 = no fat,
1 = furculum 1-5% filled with fat, 2 = 5-
33% filled, 3 = 34-66% filled, 4 = 67-100%
filled, and 5 = fat bulging above furculum.
Subcutaneous fat in this region is correlated
with overall body fat in small birds — as are
fat-scoring procedures, which are based at
least partly upon it (Krementz and Pendleton
1990; Rogers 1991; Redfern et al. 2000,
2004). We assigned pectoral-muscle and fur-
cular fat scores to recaptured birds without
reference to original capture records.

This study incorporated data from 350 cap-
tures, including 9 birds recaptured in the same
season; however, sample sizes for some anal-
yses were <350 because we did not record all
of the necessary measurements for all birds. I
used r-tests and Kolmogorov-Smimov tests to
evaluate whether males and females differed
in body composition variables. I used linear
regression to evaluate the effect of capture
date on body mass and fat and pectoral-mus-
cle scores. I used analysis of covariance (AN-
COVA) to evaluate the relationship of fat
score and body mass, with wing chord length
and pectoral-muscle score as covariates. I also
evaluated the relationship of pectoral-muscle
score and body mass, with wing-chord length
and fat score as covariates. These two analy-
ses allowed me to produce mass estimates for
each level of each score, having controlled for
the effects of the other tissue type and size.
Statistical tests were conducted with NCSS

FIG. 1 . Body mass (g) of hatching-year Flammu-
lated Owls increased in relation to capture date, show-
ing the gradual gains in body mass through the pre-
migration season. The dashed lines represent the 95%
confidence interval for the regression line (solid line).
Owls were captured during fall at Capilla Peak, New
Mexico, 2000-2003.

2004 (Hintze 2001) and considered significant
if P < 0.05.

RESULTS

The number of owls captured varied annu-
ally— 89 owls were captured in 2000, 157 in
2001, 85 in 2002, and 19 in 2003. Of these
350 owls, our first capture was on 19 August
and our last capture was on 18 October, with
a median capture date of 17 September.

Of the 88 owls whose sex was determined,
37 were female and 51 were male. Females
and males did not differ in body mass ( t =
1.04, P = 0.30, n = 88), fat score (Z = -0.66,
P = 0.51, n = 85), or pectoral-muscle score
(Z = 0.50, P = 0.62, n = 88). Therefore, I
combined data for males and females in all
further analyses.

Body mass increased through the season in
all years, but capture date explained only a
small proportion of the variation in body mass
(. R 2 = 0.06, P < 0.001, n = 350; Fig. 1). Body
mass was significantly lower in 2000 than in
2001-2003 (F3<346 = 46.4, P < 0.001, n =
350), but there was no body mass X date in-
teraction and no effect on the overall pattern
of mass change. Fat scores also increased
through the season ( R 2 = 0.19, P < 0.001;
Fig. 2). There was a drop in fat scores in mid-

190

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

FIG. 2. Mean ± SE fat scores (filled circles) and
pectoral-muscle scores (unfilled circles) in relation to
capture date for Flammulated Owls captured during
fall at Capilla Peak, New Mexico, 2000-2003. Fat
scores increased through the season, but pectoral-mus-
cle scores did not. Dates were grouped into 5-day pe-
riods from 18 August to 22 October.

September (Fig. 2), but fat scores continued
to increase after that time. Pectoral-muscle
scores did not change through the season ( R 2
- 0.0, P = 0.34; Fig. 2).

ANCOVA revealed that fat scores and pec-
toral-muscle scores were both related posi-
tively to body mass (Table 1). Wing chord
length was a strong predictor of body mass,
and fat score was a stronger predictor of body
mass than pectoral-muscle score (Table 1).
Based on least-square means of fat scores
(ANCOVA), increments in mass from one fat
score to the next ranged from 1.0 to 1.8 g and
spanned 7.0 g overall (difference in least-
square mean mass of fat scores 0 and 5; Table
2). Mass increments from one pectoral-muscle
score to the next ranged from 0.3 to 1.1 g but

TABLE 2. Least-square mean (as derived from
ANCOVA, see Table 1) body mass and body mass
gain from one score to the next for furcular fat and
pectoral-muscle scores of Flammulated Owls at Cap-
illa Peak, New Mexico, 2000-2003.

Scoring

regime

Mass (g)

Gain in
mass (g)

Fat

51.03

1.97

52.45

0.44

1.4

53.59

0.48

1.1

54.63

0.38

1.0

56.45

0.44

1.8

58.07

1.39

1.6

Muscleb

53.29

1.08

—

53.60

0.37

0.3

125

54.73

0.30

1.1

55.16

0.53

0.4

a Gain in mass not calculated for lowest fat and muscle class.
b No birds had a pectoral-muscle score of 1 .

spanned only 1 .9 g overall (difference in least-
square mean mass of pectoral-muscle scores 2
and 5).

Based on the mean body mass of the first
10% of captured owls and that of the last 10%
captured, the overall mass gain from the be-
ginning to the end of the season was 2.5 g, or
4.8% of initial body mass, and the mean fat
score increased from 1.5 to 3.2. Using the data
in Table 2, I estimated that fat mass increased
by 2 g over the sampling period, or approxi-
mately 80% of the total mass increase (i.e.,
body mass of a bird with a fat score of 3.2
[—55 g] — body mass of a bird with a fat
score of 1 .5 [—53 g] = a 2-g increase in fat).
In contrast, pectoral-muscle scores averaged

TABLE 1. Results of analyses of covariance evaluating the relationships of fat and pectoral-muscle scores
versus body mass in Flammulated Owls captured during fall at Capilla Peak, New Mexico, 2000-2003.

Analysis/Factor

Fat score as main factor

Fat score

9.45

<0.001

Pectoral-muscle score (covariate)

6.82

0.009

Wing chord length (covariate)

33.29

<0.001

Pectoral-muscle score as main factor

Pectoral-muscle score

2.54

0.057

Fat score (covariate)

44.86

<0.001

Wing chord length (covariate)

36.78

<0.001

DeLong • PRE-MIGRATORY MASS GAIN IN FLAMMULATED OWLS

191

TABLE 3. Nine within-season recaptures of Flam-
mulated Owls indicating changes in mass and body
condition indices, Capilla Peak, New Mexico, 2000-

2003.

Year

Initial

capture

date

Days to
next
capture

Change in
mass (g)

Change in
fat score

Change
in muscle
score

2000

9 Sep

+ 5.0

+ 1

— a

2000

10 Sep

+ 2.0

+ 1

—

2000

9 Sep

0.0

—

2000

30 Sep

+5.0

—

2001

2 Sep

-2.6

2001

25 Sep

+0.3

2001

30 Sep

+ 1.0

+ 1

2002

19 Aug

+ 1.7

+ 1

2003

5 Sep

+2.7

+ 1

a Data not available.

3.5 among both the first 10% and the last 10%
of birds captured.

All but two of the owls recaptured later in
the same season ( n = 9) increased in body
mass between the initial and second capture,
and three of the owls exhibited simultaneous
increases in fat and pectoral-muscle scores
(Table 3). In addition, scores for fat and pec-
toral muscle were positively correlated (r =
0.37, P < 0.001), indicating that owls with
high fat scores tended to have high pectoral-
muscle scores. Owls showed nearly every
combination of fat and pectoral-muscle
scores, except for the highest pectoral-muscle
score being paired with the lowest fat score,
or vice versa.

DISCUSSION

Body mass of Flammulated Owls increased
significantly as the migration season ap-
proached. This result is consistent with data
showing that migratory birds often increase
their total body mass prior to migration (Bair-
lein 2002). Such patterns have been shown for
songbirds, shorebirds, and even some diurnal
raptors, but little information is available on
pre-migration gain in mass among owls (Ges-
saman 1979, Bairlein 2002). In Colorado,
Linkhart and Reynolds (1987) found mass
gain in one radio-tracked adult Flammulated
Owl during the month of September. In the
present study, I confirmed this pattern for a
large number of owls, but I also found that
capture date explained only a small amount of
variation in the mass of captured owls. This

latter pattern is not surprising given the ex-
pected variation in hatching dates and that
owls of different ages likely gain mass at dif-
ferent rates.

I evaluated the relationship of pectoral-
muscle size and fat stores to the seasonal in-
crease in body mass in three ways. First, using
recapture data, I found that there were con-
current increases in fat scores, muscle scores,
and body mass for most individuals. Second,
scores of furcular fat and pectoral muscles
were closely tied to body mass, but fat scores
were better predictors of body mass than pec-
toral-muscle scores. Third, fat scores in-
creased through the season along with total
body mass, but pectoral-muscle scores did
not. Taken together, these three results indi-
cate that fat stores are an important compo-
nent of the overall mass gain in Flammulated
Owls prior to migration, but pectoral-muscle
size is not as important.

Recently, the question of whether fat stores
and muscle tissues develop independently has
been raised. For example, Redfern et al.
(2000, 2004) found a general interdependence
in fat stores and muscle mass for Sedge War-
blers (. Acrocephalus schoenobaenus ) and Red-
wings ( Turdus iliacus ). My data also support
the hypothesis that fat and pectoral-muscle
scores are interdependent because (1) there
were concurrent increases in fat scores, mus-
cle scores, and body mass for most recaptured
birds; (2) there was a positive correlation be-
tween the variables; and (3) there were no
owls having high scores for one parameter
without also having high scores for the other.

There appeared to be a non-fat component
to the season-long mass gain that was unre-
lated to pectoral-muscle size. About 20% of
the season-long mass gain was not explained
by increases in fat mass or pectoral muscle.
These increases in mass may have been relat-
ed to increased sizes of internal organs, which
may have been necessary to facilitate the ob-
served accumulation of muscle and fat re-
serves. Such changes have been observed in
other migratory birds as fat reserves were re-
plenished. For example, Karasov and Pinshow
(1998) found that internal organ size increased
and contributed to gains in body mass among
foraging Blackcaps ( Sylvia atricapilla) cap-
tured at a stopover site in Israel during north-
bound-migration.

192

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

These data add to the growing body of
work showing that both fat deposition and
muscle growth are associated with migration-
related mass gains and that the two processes
are somewhat interdependent. The implication
of these studies is that birds getting ready to
migrate or already migrating may have spe-
cific nutrient needs when foraging. This work
may help to improve our understanding of for-
aging ecology and site selection before and
during migration — two concerns becoming in-
creasingly important for the conservation of
migratory birds.

ACKNOWLEDGMENTS

Primary financial support was provided by the
USDA Forest Service (Cibola National Forest and Re-
gion 3), the New Mexico Game and Fish Department
(Share with Wildlife Program), Public Service Com-
pany of New Mexico, and the New Mexico Ornitho-
logical Society. Additional funds for the project came
from J. and J. Humber. I gratefully thank all of our
supporters for their generosity. B. G. deGruyter, H. P.
Gross, and J. P. Smith were instrumental in arranging
funding and logistical support for this project. I ben-
efited greatly from working with S. L. Stock, who in-
troduced me to, and trained me in, fat- and muscle-
scoring techniques for owls. The company and assis-
tance of the Manzano Mountains’ field crew and vol-
unteers from both HawkWatch International and Rio
Grande Bird Research were greatly appreciated. In par-
ticular, W. L. Beard, Z. M. Hurst, W. M. King, and E.
A. Snyder made significant contributions to the field
effort. I appreciate discussions with J. F. Kelly about
migration ecology and analytical techniques. Thanks
to J. V. Jewell for support in so many ways. This man-
uscript benefited from thoughtful reviews by J. F. Kel-
ly, J. P. Smith, and three anonymous reviewers.

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The Wilson Journal of Ornithology 1 18(2): 194— 207, 2006

MORPHOLOGICAL VARIATION AND GENETIC STRUCTURE OF
GALAPAGOS DOVE {ZEN AID A GALAPAGOENSIS) POPULATIONS:
ISSUES IN CONSERVATION FOR THE GALAPAGOS BIRD FAUNA

DIEGO SANTIAGO- ALARCON,1 3 SUSAN M. TANKSLEY,2 AND
PATRICIA G. PARKER1 2 3

ABSTRACT. — Island species, particularly endemics, tend to have lower genetic diversity than their continental
counterparts. The low genetic variability of endemic species and small populations has a direct impact on the
evolutionary potential of those organisms to cope with changing environments. We studied the genetic population
structure and morphological differentiation among island populations of the Galapagos Dove ( Zenaida galapa-
goensis). Doves were sampled from five islands: Santa Fe, Santiago, Genovesa, Espanola, and Santa Cruz. Five
microsatellite markers were used to determine genetic diversity, population structure, gene flow, and effective
population sizes. jFsx and Rsr values did not differ among populations; in general, populations with greater
geographical separation were not more genetically distinct than those closer to one another, and estimated gene
flow was high. There were no significant differences in allelic richness and gene diversity among populations.
Although there was extensive morphological overlap among individuals from different island populations for
both males and females, we found significant differences in overall body size only between populations on Santa
Fe and Santa Cruz (males and females) and between Espanola and Santa Fe (males only). Significant differences
in body size between populations undergoing high rates of gene flow indicate that differentiation may be due
to either phenotypic plasticity or ecotypic differentiation. Based on the results of previously conducted disease
surveys, we discuss the conservation implications for the Galapagos Dove and other endemics of the archipelago;
we also discuss the possible effects of wind currents on gene flow. Received 24 January 2005, accepted 28
November 2005.

Historically, islands are places where the
most dramatic morphological and genetic dif-
ferentiations have occurred (Grant 1998,
2001). Geographic isolation between popula-
tions is expected to promote differentiation of
both morphological and genetic characters,
due to either drift or different selective re-
gimes (Slatkin 1985, Bohonak 1999). This
may reflect population divergence due to in-
sufficient gene flow that would counteract the
effects of drift and selection (Slatkin 1985,
Hutchison and Templeton 1999, Coleman and
Abbott 2003). Isolation leads to the formation
of geographical races, which is considered one
of the initial stages of speciation (Grant 2001).
However, factors independent of geographical
isolation (e.g., microclimate, resources, habi-
tat structure) may be acting to create differ-
ences between sympatric populations or pop-
ulations undergoing high gene flow (e.g.,
Schluter 2001, Ogden and Thorpe 2002).
There is also the possibility that morphologi-

1 Dept, of Biology, Univ. of Missouri-St. Louis,
8001 Natural Bridge Rd„ St. Louis, MO 63121, USA.

2 Dept, of Animal Science, Kleberg Center, Texas
A&M Univ., College Station, TX 77843-2471, USA.

3 Corresponding author; e-mail: onca77@yahoo.com

cal differences may be observed — either im-
mediately or within a few generations — at dif-
ferent geographic locations (different popula-
tions) without corresponding genetic differ-
entiation (phenotypic plasticity; e.g., James
1983, Losos et al. 1997, Trussell and Etter
2001).

Island species have served as models for
studies of evolution due to the discrete nature
of island archipelagos and the isolation be-
tween different island populations of the same
species. Several Galapagos archipelago en-
demics have very limited inter-island move-
ment, resulting in morphological differences
(e.g., Bollmer 2000, Grant 2001). Columbi-
formes on the other hand are strong fliers able
to move long distances (Goodwin 1977, Bap-
tista et al. 1997). Because of the proximity of
several islands in the archipelago, we expect-
ed high gene flow among populations of the
Galapagos Dove {Zenaida galapagoensis ) and
no morphological differentiation.

The Galapagos Dove is an endemic species
whose biology and ecology are poorly under-
stood. Our knowledge of this species is re-
stricted to taxonomic relationships (Goodwin
1977, Johnson and Clayton 2000), morpho-
logical descriptions (Ridgway 1897, Gifford

194

Santiago-Alarcon et al. • MORPHOLOGY AND GENETICS OF THE GALAPAGOS DOVE 195

1913, Prestwich 1959), and more recently, to
some aspects of its breeding and feeding ecol-
ogy on Genovesa Island (Grant and Grant
1979). Morphological and ecological studies
of bird species in the Galapagos archipelago
have been mostly restricted to Darwin’s finch-
es (Bowman 1961; Boag 1981, 1983; Grant et
al. 1985; Grant 2001), Galapagos mocking-
birds (Nesomimus spp.; Curry 1988, 1989;
Curry and Grant 1989), and the Galapagos
Hawk ( Buteo galapagoensis’, de Vries 1973,
1975; Bollmer et al. 2003). Measurements and
a general description of Galapagos Doves are
provided by Ridgway (1897), Gifford (1913),
and Swarth (1931). Gifford (1913) suggested
that doves inhabiting the northern-most is-
lands— Wolf (formerly Wenman) and Darwin
(formerly Culpepper) — are larger than those
located within the main cluster of islands; for
this reason, dove populations were classified
as two subspecies: Z. g. exsul (on Wolf and
Darwin) and Z. g. galapagoensis (Swarth
1931, Baptista et al. 1997). To assess levels
of population structure and morphological
variation, our study focused on populations of
the southern subspecies (Z. g. galapagoensis).

Island species, particularly endemics, tend
to have lower genetic diversity than their con-
tinental counterparts, especially when such
species inhabit small islands (Frankham 1996,

1997) . Maintaining genetic diversity and un-
derstanding patterns of genetic diversity in
natural populations is a central issue in con-
servation genetics (Frankham 1996, 1997,

1998) . Populations are not equivalent in their
capacity to adapt to changing environmental
conditions, and genetic diversity maximizes
the potential evolutionary responses of con-
served populations (Petit et al. 1998, Hedrick
2001). Species inhabiting islands are consid-
ered behaviorally and physiologically naive;
thus, they might be affected more severely
than mainland species by the introduction of
predators and diseases (Mack et al. 2000). De-
mographic and environmental stochasticity
can be accentuated in small island populations
with little genetic variability, increasing their
risk of extinction (Frankham 1996, 1997,
1998).

The introduction of exotic organisms to is-
lands is one of the most important factors in
the extinction of endemic species (Wikelski et
al. 2004). Because of the negative impact of

pathogens on the avian endemics in several
other archipelagos, preventing the introduc-
tion of avian diseases is a conservation pri-
ority in the Galapagos archipelago (Padilla et
al. 2004, Wikelski et al. 2004). Some diseases
common to Columbiformes, such as Tricho-
monas gallinae, might be transmitted to Ga-
lapagos Doves by other Columbiformes, such
as the exotic Rock Pigeon ( Columba livia ) and
the transient (from South America) Eared
Dove (Z. auriculata ; Harmon et al. 1987, Cur-
ry and Stoleson 1988, McQuistion 1991, Mete
et al. 2001, Padilla et al. 2004). Padilla et al.
(2004) have reported a >85% prevalence of
Haemoproteus malaria in Galapagos Doves
and infections of Chlamydophila psittaci in
doves inhabiting the island of Espanola. Buck-
ee et al. (2004) have shown theoretically that
host spatial structure directly affects pathogen
diversity and strain structure. Thus, it is a con-
servation priority to understand the movement
patterns of those species that could serve as
vectors or reservoirs of diseases with inter-
specific infection potential. We have shown
how lice from Galapagos Doves can be trans-
mitted to Galapagos Hawks when they prey
on doves; predation may represent a route of
transmission for several infectious agents
transmitted by lice (Whiteman et al. 2004).

Among the islands sampled in this study,
only Santa Cruz was inhabited by humans,
and it holds the largest human population of
the inhabited islands in the archipelago. Es-
panola was the most isolated island, lying at
the southeastern extreme of the archipelago.
Santa Fe and Genovesa were the smallest is-
lands, and Genovesa was the northern-most
island (Fig. 1). The Galapagos islands selected
for this study — Santiago, Santa Cruz, Santa
Fe, Genovesa, and Espanola — were chosen to
represent the maximum geographic isolation
between populations (e.g., Espanola versus
Genovesa) and widest (east-west and north-
south) coverage of the archipelago that our
budget and logistical restrictions could accom-
modate. In this study, we (1) used principal
components analysis (PCA) to examine mor-
phological variation, (2) used five microsat-
ellite loci to describe the population structure
and genetic diversity, and (3) estimated effec-
tive population sizes and gene flow of Z. ga-
lapagoensis on five islands of the Galapagos
archipelago: Santiago, Santa Cruz, Santa Fe,

196

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

91° W 90“' W

t 0 20 40 60 60 km

Pin, a I i i i I i i ' I

FIG. 1 . Map of the Galapagos archipelago, Ecua-
dor, showing the five islands (in dark gray) where Ga-
lapagos Doves were sampled in 2002 and 2004. The
Galapagos Dove occurs on all the major islands of the
archipelago.

Genovesa, and Espanola. Specifically, we
asked (1) are there significant morphological
differences among island populations of the
Galapagos Dove, (2) are these populations
isolated, and (3) is there evidence of low ge-
netic variability in the Galapagos Dove?

METHODS

Field methods. — We conducted our study in
the Galapagos archipelago from May through
July 2002 and from June through July 2004.
Following the guidelines described in Ralph
et al. (1996), we captured Galapagos Doves
by using hand nets and mist nets. We took
blood samples (50 pd each) by venipuncture
of the brachial vein from 25 birds each on
Santa Cruz, Santa Fe, and Espanola, and 30
birds each on Santiago and Genovesa islands
(Fig. 1). Samples were mixed with 500-700
pj of lysis buffer (100 mM Tris pH 8.0, 100
mM EDTA, 10 mM NaCl, 0.5% SDS; Long-
mire et al. 1988). We also measured 25 birds
each from Santa Cruz, Santa Fe, and Espanola
islands and 30 each from Santiago and Gen-
ovesa islands (Fig. 1). During the 2002 study
season, we sampled doves on San Cristobal
Island, but due to the small sample size ( n =
2) they were not included in our analysis. En-
demics on San Cristobal are rare, and the Ga-
lapagos Dove seems to be among the rarest.

In order to quantify inter-population differ-
ences in morphology, we took the following
measurements to the nearest 0. 1 mm from the

right side of each individual: (1) tarsus length,
(2) tail length, (3) length of exposed culmen
(from terminus of the feathering to the bill’s
tip), (4) bill width (calipers were oriented at a
90° angle to the axis of the bill and measure-
ment was taken at the terminus of the feath-
ering), and (5) bill depth (at the terminus of
the feathering and again at a 90° angle to the
axis of the bill). Using a ruler with a brass
perpendicular stop, we also measured wing
chord length (unflattened, from carpal joint to
the tip of the longest primary) to the nearest
0.5 mm. We used Pesola scales (100 and 300
g) to measure mass to the nearest 0.1 g. Bird
measurements were taken by DSA on all the
islands but Santa Fe, where J. L. Bollmer con-
ducted the sampling.

Using plumage patterns, we identified birds
as adults or juveniles: adults have brighter col-
oration, and juveniles are much duller in color
(Ridgway 1 897). Because individual adults of
some dove species do not have completely os-
sified skulls (Pyle 1997), and because the use
of cranium calcification (pneumatization) for
aging doves is not well developed (Pyle
1997), any captured individual with incom-
plete calcification and adult coloration was
considered an adult. Although it is possible to
identify males and females in the field by their
plumage coloration and body size (males and
females have similar coloration patterns, but
males tend to be brighter than females and are
larger; Ridgway 1897, Gifford 1913; DSA and
PGP unpubl. data), this technique is not al-
ways reliable due to individual variation.
Therefore, we used a polymerase chain reac-
tion- (PCR) based technique for sexing every
individual (Fridolfsson and Ellegren 1999).
Birds were released within 40 m of capture
location.

Morphology

Statistical analyses. — We used Principal
Component Analysis (PCA) to describe mor-
phological variation among islands (SPSS,
Inc. 2001). Prior to PCA, variables were
checked for outliers (standardizing to zero
mean and unit variance); four values with
standard deviations >2.5 were eliminated. Al-
though all variables (raw data) were normally
distributed (Kolmogorov-Smirnov test, P ^
0.06) and have the same scale and dimension
(except mass), they were log-transformed in

Santiago-Alarcon et al • MORPHOLOGY AND GENETICS OF THE GALAPAGOS DOVE 1 97

TABLE 1. Microsatellite primers and number of alleles scored for Galapagos Doves from five islands
sampled in 2002 and 2004, Galapagos Islands, Ecuador (n = 134).

Locus

Primer

sequence 5 '-3'

TAa

No. alleles

WU7al 17F

CTC

AGT

GTA

AAT

ATG

GCA

GGG

AAT C

WU7al 17R

CAG

GTC

TTT

TTG

GTG

GAT

GTC

WUa38F

GGA

GGG

CAC

CAG

AGT

WUa38R

GAT

AAG

ACC

CGA

CTT

TCA

WUelF

CAG

TGT

GGC

AGG

TAC

TTC

WUelR

CTC

ATT

AGT

GGA

CCT

TGG

WUj22F

CAG

GAG

CCA

TCG

TAC

ACA

WUj22R

TGA

ATT

ACC

CCA

TCA

ACA

ClipT17

See Traxler et al. 2000

a Annealing temperature (°C).

order to examine proportional contributions of
large and small measurements equally. We
used PCA on the correlation matrix because
one of the variables (mass) did not have the
same dimension, and because a PCA on a cor-
relation matrix applied to transformed data is
equivalent to a variance-covariance matrix
analysis (McGarigal et al. 2000). Furthermore,
a PCA from a variance-covariance matrix ap-
plied to untransformed (raw) data will give
more weight to variables with large variance,
which will have a larger influence on the PCA
(McGarigal et al. 2000). Because males are
larger than females, analyses describing the
morphological variation among islands were
conducted separately for each sex to prevent
the variance due to sexual dimorphism from
masking variation among populations. For
each PCA, principal component scores were
normally distributed (Kolmogorov-Smirnov
test, P ^ 0.74). Communalities (total variation
extracted from each variable) are reported for
each PCA. All components with eigenvalues
>1 were retained for subsequent analyses. Ei-
genvectors were rotated using varimax rota-
tion and retained when the explained variance
was higher than that of unrotated components
or when the interpretation of PCs was easier.
After conducting a PCA for females, we did
not find significant differences between adult
and juvenile females (/46 = -0.69, P = 0.48);
thus, we retained both groups in the PCA.
However, we did find significant differences
between adult and juvenile males (/67 = 4.23,
P < 0.001) and removed juveniles (15) from
the male pool. We excluded female bill depth
from the analyses for inter-island comparisons
because only one such record was available

for Santiago Island. We used /-tests and AN-
OVAs on PC scores for group comparisons
and Tukey post-hoc tests any time an ANOVA
was significant. In every case, variances of PC
scores were homogeneous between and
among groups (Levene’s test, P > 0.25). All
/-tests were independent and two-tailed.

Genetics

DNA isolation and amplification. — DNA
extractions by phenol-chloroform were fol-
lowed by dialysis in IX TNE2 (10 mM Tris-
HC1, 10 mM NaCl, 2 mM EDTA) and diluted
to a working concentration of 20 ng/pl. Integ-
rity and concentration of each DNA sample
was determined by spectrophotometry and
electrophoresis in 0.8% agarose gels run in
1 X TBE. Individuals were scored at four poly-
morphic microsatellite loci (Table 1) original-
ly developed for White-winged Doves (Z.
asiatica ; accession numbers for WU7all7,
WUel, WUa38, and WUj22 are AF260574,
AF260573, AY428751, and AY428752, re-
spectively) and one locus developed for Rock
Pigeon (Traxler et al. 2000). We prepared PCR
reactions of 10 pi that included 50 ng of
whole genomic DNA, 1 mM dNTP’s, 10X re-
action buffer, 25 mM MgCl2, 0.5 pg of each
primer, 0.1 pi of DMSO, and 0.5 units of Taq
DNA polymerase (SIGMA). PCR conditions
were as follows: initial denaturation at 94° C
for 3 min followed by 35 cycles of denatur-
ation at 94° C for 30 sec; annealing from 54
to 56° C (see Table 1) for 1 min and extension
at 72 C for 1 min; and a final extension at 72°
C for 10 min. PCR products were separated
in non-denaturing 7.5% polyacrylamide gels
run on BioRad sequencing rigs. Gels were

198

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

TABLE 2. Principal component (PC) scores and communalities for seven morphological variables of male
(n = 50) and female ( n = 52) Galapagos Doves sampled from five islands in 2002 and 2004, Galapagos Islands,
Ecuador. PC scores represent the correlations of each variable with the principal components; communalities
represent the sums of squares of correlation coefficients on the first two PCs or the proportion of variance
extracted from each variable.

Males

Females

Variable

PCI

PC2

Communalities

PCI

PC2

Communalities

Culmen

0.626

-0.212

0.508

0.614

0.515

0.678

Bill width

0.331

0.734

0.762

0.172

0.639

0.918

Bill depth

0.492

0.272

0.550

—

Tarsus

0.367

0.644

0.888

0.720

0.331

0.629

Tail

0.786

-0.101

0.692

0.421

-0.642

0.820

Wing

0.674

-0.256

0.604

0.790

-0.006

0.739

Weight

0.779

-0.294

0.696

0.606

-0.644

0.787

a Not included.

stained with 0.05% ethidium bromide (EtBr)
and visualized using a Kodak UV digital im-
ager (KODAK image station 440CF).

Statistical analyses. — We calculated genetic
diversity using Nei’s unbiased estimator (Nei
1973), which is the probability that two alleles
randomly sampled from a population are dif-
ferent. We analyzed allelic richness through
rarefaction analysis as implemented by El
Mousadik and Petit (1996) and Petit et al.
(1998).

^ST estimates outperform RSJ counterparts
under some circumstances (e.g., when there
are allele size constraints in a microsatellite
marker, size differences cannot be used to re-
flect distances among alleles), even under the
stepwise mutation model (SMM). Further-
more, Rst can be less accurate at reflecting
population differentiation due to its greater as-
sociated variance. Even a small number of
random mutation events tends to erase part of
the memory of the mutation process that is the
base of the SMM, which makes RSJ estimates
superior to ^ST only when the mutation pro-
cess follows the SMM exactly (Gaggiotti et
al. 1999, Balloux et al. 2000, Balloux and Lu-
gon-Moulin 2002). Due to the uncertainty of
the mutation process of microsatellites (Prim-
mer and Ellegren 1998, Goldstein and Schlot-
terer 1999), we decided to use F-statistics
(Weir and Cockerham 1984) for our analysis.
For the sake of comparison, we also calculat-
ed RSJ across samples, and the significance of
population differentiation based on ^ST was
evaluated using a G-test and 1,000 randomi-
zations (Goudet et al. 1996). We used pairwise

^ST values and geographic distance matrices
to test for isolation by distance (Slatkin 1993,
Hutchison and Templeton 1999); significance
was evaluated with a Mantel test (Mantel
1967) and distance was log-transformed be-
fore analysis. Geographical distance was mea-
sured as the closest distance between islands.

Data were analyzed for linkage disequilib-
rium and Hardy-Weinberg equilibrium using
FIS, and testing was conducted via G-test and
randomization procedures (Goudet et al. 1996,
Goudet 1999). Bonferroni corrections were
applied when appropriate (Rice 1989). Loci
proved to be in linkage equilibrium after 200
permutations ( P > 0.08, Bonferroni corrected
P-value at a = 0.05 was 0.005). Samples were
under Hardy-Weinberg equilibrium after 500
randomizations, except for one locus/popula-
tion (WU7all7, P = 0.002 for Santiago Is-
land, Bonferroni corrected P-value at a =
0.05 was 0.002). Therefore, we tested for pop-
ulation differentiation without assuming H-W
equilibrium. Analyses were conducted using
FSTAT (Goudet 2002).

Because gene flow and effective population
size estimates based on ^ST depend on many
unrealistic assumptions (Waples 1998, Whit-
lock and McCauley 1999), we used a coales-
cent-based approach to calculate migration
rates (Nm) and theta (0 = 4Nep,, which is a
genetic diversity parameter related to the ef-
fective population size [Ne] from which Ne
can be estimated) using the program MI-
GRATE (Beerli and Felsenstein 1999, 2001).
Unlike Fsx, this program accounts for direc-
tional gene flow and for differences in popu-

Santiago-Alarcon et al. • MORPHOLOGY AND GENETICS OF THE GALAPAGOS DOVE 199

PCI

FIG. 2. (A) Morphological ordination space be-

tween islands for adult male Galapagos Doves. PCI is
an axis of overall body size and PC2 is a vector re-
flecting bill size and tarsus length ( n = 50). Sample
sizes per island were as follows: Santiago (18), Santa
Cruz (15), Espanola (11), Santa Fe (15), and Genovesa
(20). (B) Morphological ordination space between is-
lands for female Galapagos Doves. PCI is an axis of
overall body size and PC2 is a vector reflecting bill
size and tarsus length ( n = 52). Sample sizes per island
were as follows: Santiago (12), Santa Cruz (10), Es-
panola (14), Santa Fe (10), and Genovesa (10). Ellip-
ses represent the 95% confidence interval for the dif-
ferent islands.

lation size. We ran the program five times us-
ing the estimates of each run as starting pa-
rameters for the next one. We assumed equal
mutation rates among loci, which is an unre-
alistic assumption (Goldstein and Schlotterer
1999); however, it provides better estimates of
parameters than when using variable mutation
rates among loci, which increase the variance
(Beerli and Felsenstein 1999). We estimated
parameters for the first run, since using an ^ST
initial estimate produced an attraction to the
area of the likelihood surface of the generated
Fst values, thus preventing the program from

searching efficiently throughout the likelihood
surface (P. Beerli pers. comm.). Ten short
chains and two long chains were used to cal-
culate parameters. We sampled 500 genealo-
gies for each short chain and 5,000 for each
long chain; increments were set to 20 for the
short chains and to 100 for the long chains;
an initial stabilizing period (burn-in) was set
to 10,000 genealogies. We computed multiple
estimation of parameters using the two long
chains of each run. Because MIGRATE cal-
culates historical migration rates, we used the
assignment/exclusion method of Comuet et al.
(1999), implemented in the program GENE-
CLASS (Piry et al. 2004), to estimate current
levels of gene flow. This method is appropri-
ate to use when all possible sources of mi-
grants (populations) have not been sampled
(Comuet et al. 1999, Berry et al. 2004). We
used the “leave one out” criterion, which re-
moves the individual for which probabilities
of assignment/exclusion to a specific popula-
tion are calculated (Berry et al. 2004). We
used the simulation algorithm of Paetkau et
al. (2004) to estimate assignment/exclusion
probabilities (a = 0.05, 10,000 simulated in-
dividuals).

RESULTS

Morphological variation of males among
islands. — We retained the first two principal
components. PCI, representing an overall size
dimension, explained 36% of the variance.
PC2, a bill- (width and depth) and tarsus-
length component, explained 17% of the var-
iance. The variance extracted from each var-
iable was >50% (Table 2). There were sig-
nificant differences among islands in the
doves’ overall body size (PCI, F4A5 = 4.99,
P = 0.002; Fig. 2a), but not bill size (PC2,
F445 = 1.53, P = 0.21). Based on PCI, Santa
Cruz and Espanola doves were significantly
larger than Santa Fe doves (Tukey-test, HSD
= 1.16, P = 0.033 and HSD = 1.23, P =
0.019, respectively). There is overlap, how-
ever, among individuals of these three islands,
as well as those from the other islands (Fig.
2a).

Morphological variation of females among
islands. — We retained the first two principal
components. PCI, which represents an overall
size dimension, explained 37% of the variance
(Table 2). PC2, a bill- (culmen length and

200

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

TABLE 3. Genetic diversity (Nei 1973) and allelic richness for Galapagos Dove, as estimated by rarefaction
analysis (Petit et al. 1998) per locus and population. Samples were collected from five islands in 2002 and 2004,
Galapagos Islands, Ecuador.

Locus

Genetic diversity

SFb

Wu7al 17

0.75

0.73

0.66

0.69

0.72

Wua38

0.56

0.71

0.52

0.55

0.67

Wuel

0.35

0.42

0.24

0.31

Wuj22

0.49

0.55

0.62

0.56

0.61

Cli|xT17

0.79

0.84

0.78

0.84

0.79

Mean ± SD

0.59 ±0.18

0.65 ± 0.16

0.56 ± 0.20

0.58 ± 0.22

0.62 ±0.18

a /?t = estimated allelic richness for all islands.

b SF = Santa Fe, E = Espahola, SC = Santa Cruz, S = Santiago, G = Genovesa.

width) and tarsus-length component, ex-
plained 23% of the variance. The variance ex-
tracted from each variable was >62% (Table
2). There were significant differences among
islands in overall body size (PCI, F441 = 3.14,
P = 0.023; Fig. 2b), but not in the second
component (PC2, F441 = 0.84, P = 0.51). Dif-
ferences in overall body size were found only
among doves from Santa Cruz and Santa Fe,
where Santa Cruz females were larger than
those from Santa Fe (Tukey-test, HSD = 1.53,
P = 0.005); otherwise there was extensive
overlap among individuals from the different
islands (Fig. 2b).

Population structure and genetic diversi-
ty.— We scored 33 alleles for five polymorphic
microsatellite loci from 25 doves on Santa
Cruz, Santa Fe, and Espanola, 30 on Santiago,
and 29 on Genovesa. Santa Fe doves had the
fewest alleles (23); Espanola and Santiago had
29 each, Genovesa had 25, and Santa Cruz
had 26. The populations with the richest al-
lelic composition (Santiago and Espanola) had
86% ([29 - 5]/[33 - 5]) of the allelic diver-
sity (excluding the five alleles that were au-
tomatically present because there are five
loci). Rarefaction analysis showed the same
tendency in allelic richness among popula-
tions; allelic richness across loci and samples
was 27 (Table 3). Genetic diversity was great-
est among doves from Espanola and lowest
among those from Santa Cruz; however, there
were no significant differences among islands
for either allelic richness or genetic diversity
(both P > 0.19).

Estimates of Fsx (0.01, P > 0.43) and RSJ
(0.0057, P > 0.43) across samples showed no
genetic structure. The 95% bootstrap confi-

dence intervals of the overall F ST estimate
were —0.001 and 0.02. No pairwise F ST values
were significantly different (all P > 0.025,
Bonferroni corrected P-value at a = 0.05 was
0.005; Table 4), and we failed to detect iso-
lation by distance in our data set (Mantel test
after 2,000 randomizations, P > 0.25).

We estimated high levels of historical gene
flow between populations of the Galapagos
Dove (Table 5). The highest estimated number
of migrants per generation was 71 (Espanola
to Genovesa), which was surprising consid-
ering that they are separated by the largest
geographic distance (—200 km) compared
with distances between the other islands sam-
pled. Genovesa Island had the highest theta
value (1.91) and Santa Fe had the lowest
(0.18). The high theta for Genovesa is sur-
prising because it is the smallest island of
those included in the study; however, Santa
Cruz, the largest island, had the second lowest
theta value (0.4). If we assume that microsat-
ellite markers have a mutation rate of 10 4
events per locus per generation (Goldstein and
Schlotterer 1999), and that this mutation rate
is the same for each locus, the effective pop-
ulation sizes are as follows: Santa Fe 463; Es-
panola 3,600; Santa Cruz 1,000; Santiago
4,600; and Genovesa 4,775. The current high
rate of gene flow, as estimated with GENE-
CLASS, suggests that doves are moving
among islands. The assignment analysis cor-
rectly allocated 27.6% (37) of the individuals
(P < 0.009), but most (34 of 37) had likeli-
hoods lower than the threshold value of being
assigned to another population. The difficul-
ties of assigning individuals suggest high cur-
rent gene flow among populations. Analyses

Santiago-Alarcon et al. • MORPHOLOGY AND GENETICS OF THE GALAPAGOS DOVE 20 1

TABLE 3.

Extended.

Allelic richness

/?Ta

6.75

4.98

6.1 1

3.97

4.96

5.46

2.99

2.00

2.56

4.97

4.98

4.61

9.63

7.70

8.25

4.6 ± 1.67

5.8 ± 2.38

5.2 ± 2.58

5.8 ± 2.77

5.0 ± 2.12

5.4 ± 2.08

to detect first generation (F0) migrants detect-
ed 15 migrants (P < 0.05; Table 6).

DISCUSSION

In this study, we present evidence that pop-
ulations of Galapagos Doves are morpholog-
ically and genetically similar, which must be,
in part, the result of high rates of gene flow
among islands. However, our results also in-
dicate that there are morphological differences
between doves from some island pairs. This
might be due to different abiotic and biotic
pressures operating on different islands (see
below) and to the degree of connectedness
(gene flow) between some island pairs (Table
5). For example, Santa Cruz and Santa Fe
doves differ in body size (both males and fe-
males) and gene flow estimates for these is-
lands are low (see Table 5) even though they
are the closest among all the island pairs (17.5
km). Genovesa, the island with the largest ef-
fective population size, is the smallest island
of those sampled and is also the one receiving
the largest number of migrants from the other
islands. In addition, it is remarkable that the
lowest F ST value and highest numbers of mi-
grants coming to Genovesa are from Espan-

ola, which is the island most distant from
Genovesa (Fig. 1, Tables 4 and 5). Dove pop-
ulations on both Genovesa and Espanola,
which are small and relatively isolated com-
pared with the central islands (Fig. 1), are the
two populations with the greatest genetic di-
versities, largest estimated population sizes,
and highest rates of gene flow (Tables 3 and
5).

Environmental factors such as wind cur-
rents might be influencing the travel routes se-
lected by doves from different islands, thus
affecting the degree of connectivity among is-
land populations. Several phylogeographic re-
constructions of other vertebrate endemics of
the archipelago have shown that present and
historical wind and ocean currents have had a
south-southeast to north-northeast effect on
the evolutionary history of organisms (e.g.,
Caccone et al. 1999, 2002; B. S. Arbogast un-
publ. data). However, it is difficult to believe
that wind currents are the main reason for
movements of Galapagos Doves among is-
lands. Even though there is a high rate of gene
flow in a south-to-north direction (e.g., Espan-
ola to Genovesa [71.4], Espanola to Santa
Cruz [17.85]), gene flow is also high in the

TABLE 4. Estimates of genetic differentiation for Galapagos Doves sampled from five islands in 2002 and
2004, Galapagos Islands, Ecuador. Pairwise Fst values are above, and P- values are below, the dashes (geographic
distances in km are given in parentheses). No values were significant (Bonferroni corrected P-value at a = 0.05
was 0.002).

Island

Santa Fe

Espanola

Santa Cruz

Santiago

Genovesa

Santa Fe

—

0.0028

0.0033

-0.0036

0.0090

Espanola

0.22 (74)

—

0.0264

0.0159

-0.0003

Santa Cruz

0.42 (18)

0.16 (99)

—

-0.0096

0.0372

Santiago

0.10 (76)

0.34 (161)

0.66 (24)

—

0.0160

Genovesa

0.035 (135)

0.20 (204)

0.025 (103)

0.095 (100)

—

TABLE 5. Bi-directional gene flow estimates and theta values (95% Cl), estimated with MIGRATE (Beerli and Felsenstein 1999, 2001), for Galapagos Doves
from five islands, 2002 and 2004, Galapagos Islands, Ecuador.

202

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118 . No. 2, June 2006

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opposite direction (e.g., Santa Cruz to Espan-
ola [36.9], Santa Fe to Espanola [29.2], Gen-
ovesa to Santiago [21.5], Genovesa to Espan-
ola [14.2]; Table 5). Hence, wind currents
might not completely account for movements
among islands. Perhaps the lack of any clear
pattern in dove movement among islands is
due to the strong flight capabilities of Co-
lumbiformes and the short distances between
some islands (<20 km). Doves may simply
move between islands to track food resources
and suitable environmental conditions. The
lack of any pattern in isolation by distance
among populations supports the idea that
doves can move in any direction.

Low genetic differentiation among dove
populations might also be accounted for either
by a recent population expansion or by the
presence of alleles shared due to common an-
cestry (e.g.. Grant et al. 2005), rather than by
frequent dispersal between populations. Rapid
population expansion could explain reduced
within-population diversity (versus global di-
versity linked to founder events; Hedrick
2000, McCoy et al. 2003). In our study, esti-
mates of genetic diversity were similar among
populations, which would support a gene flow
explanation instead of a recent expansion. The
possible effect of shared alleles due to com-
mon ancestry might be ruled out by the results
obtained with GENECLASS, which estimated
that current rates of gene flow are high. More-
over, if the Galapagos Dove colonized the ar-
chipelago between 2.5 and 3 mya, as proposed
by Johnson and Clayton (2000), we should
have detected a genetic signature of diver-
gence, given isolation (by distance) between
populations.

Morphological variation among islands. —
Altitudinal and latitudinal patterns of morpho-
logical variation within islands have been con-
firmed for Darwin's finches, but some patterns
are not consistent among islands (Grant et al.
1985). For a given finch species, individuals
are larger at higher elevations within any one
island, but size variation among island popu-
lations is not systematically related to either
latitude or longitude. However, this is not the
case for other endemic species of the archi-
pelago, such as Galapagos Hawks, where
there is a clear north- (smaller size) to-south
(larger size) trend in morphological variation
(Bollmer et al. 2003). Body size variation in

Santiago-Alarcon et al. • MORPHOLOGY AND GENETICS OF THE GALAPAGOS DOVE 203

TABLE 6. Gene flow estimates of first generation migrants (F0), calculated with GENECLASS (Piry et al.
2004), for Galapagos Doves on five islands, 2002 and 2004, Galapagos Islands, Ecuador. P-values are given in
parentheses.

Island

Santa Fe

Espanola

Santa Cruz

Santiago

Geneovesa

1 to Xa

2 to X

3 to X

4 to X

5 to X

1: Santa Fe

—

1 (0.039)

1 (0.028)

2: Espanola

1 (0.025)

—

1 (0.016)

3: Santa Cruz

2 (0.027)

1 (0.003)

—

1 (0.002)

4: Santiago

1 (0.026)

2 (0.026)

—

1 (0.004)

5: Genovesa

1 (0.006)

1 (0.035) 1

(0.012)

a The population receiving migrants = x, and the number preceding x is the population from where migrants come. For example, in row 1 : Population
2 (Espanola) provides 1 migrant per generation to Population 1 (Santa Fe); Population 3 (Santa Cruz) provides 1 migrant; Population 4 (Santiago) provides
0 migrants; and Population 5 (Genovesa) provides 0 migrants per first generation to Population 1 .

the Galapagos Dove, however, did not show
geographical patterns among the group of is-
lands studied here, most likely because (1) en-
vironmental characteristics on the different is-
lands do not vary geographically in a simple
manner (Grant et al. 1985), and (2) gene flow
for doves among islands is greater than it is
for finches or hawks (see below). Moreover,
the dove’s omnivorous diet (see Grant and
Grant 1979) could further impede extensive
morphological differentiation between island
populations — a situation similar to that of Ga-
lapagos mockingbirds (B. S. Arbogast unpubl.
data) and Hawaiian thrushes ( Myadestes spp.;
Lovette et al. 2001).

Population structure and conservation. —
The lack of population structure and the high
levels of gene flow and genetic variation are
in stark contrast with results reported for other
species in the archipelago, which are charac-
terized by divergence among different island
populations and low genetic diversity (e.g..
Grant 2001, Bollmer 2000, Bollmer et al.
2003). Allelic richness of the Galapagos Dove
for the five microsatellite loci genotyped in
this study was similar to the values reported
for its continental relatives. White-winged
Dove (Tanksley 2000) and Mourning Dove (Z.
macroura ; L. M. Reichart unpubl. data), and
in some cases it was greater.

Tanksley (2000) used microsatellite mark-
ers and reported no genetic structure in White-
winged Doves sampled at a broader geograph-
ic scale in North America; mtDNA revealed
slight differentiation between populations ac-
cording to a historical east-west division of its
distribution (Pecos River in Texas) that is cur-
rently disappearing due to the species’ range

expansion (Pruett et al. 2000). Pruett et al.
(2000) suggested that the White-winged
Dove’s range expansion is due to urban de-
velopment, which provides water, food, and
nesting sites. Urban development also might
be affecting Galapagos Dove populations, at
least on the two inhabited islands visited in
this study (Santa Cruz and San Cristobal).
Santa Cruz doves had the third lowest number
of alleles, second lowest effective population
size, and the lowest genetic diversity. On San
Cristobal, extensively surveyed for 3 days, we
saw and captured only two doves. Population
declines of other endemic bird species on San
Cristobal have been reported (Vargas 1996).
The rarity of doves and population declines of
other endemic bird species on San Cristobal
seem to be due to the large number of intro-
duced species and to the longer history of hu-
man settlement (Vargas 1996). These results
provide some support for a negative impact of
urban development on Galapagos Doves.

Harmon et al. (1987) reported Galapagos
Doves infected with Trichomonas gallinae
(believed to have been transmitted by Rock
Pigeons) on Santa Cruz Island, and Padilla et
al. (2004) reported infected Rock Pigeons, but
no infected Galapagos Doves. Galapagos
Doves on Espanola were infected with Chla-
mydophila psittaci. The prevalence of Hae-
moproteus spp. in Galapagos Doves was
found to be >85% on five islands (Padilla et
al. 2004). The presence of infectious diseases
and mosquitoes of the genus Culex (Wikelski
et al. 2004, Whiteman et al. 2005) — the vector
of some malaria species — poses serious
threats to endemic species. The fact that in-
fectious diseases have resulted in epidemics or

204

THE WILSON JOURNAL OL ORNITHOLOGY • Vol. 118, No. 2, June 2006

epizootics (e.g., C. psittaci and T. gallinae ) in
Columbidae and other bird taxa suggests that
regular population and disease surveys are
needed for Galapagos Doves. High rates of
gene flow in Galapagos Doves could contrib-
ute to the endangerment of native and endem-
ic species prone to the effects of introduced
pathogens that can be transmitted across spe-
cies (e.g., Galapagos Dove lice being trans-
mitted to Galapagos Hawks during predation;
Whiteman et al. 2004). We recommend that
the Galapagos Dove be considered a focal
species for disease research in the archipelago
because it could serve as a reservoir/vector for
some infectious diseases (Padilla et al. 2004).

Morphology and dispersal. — That we found
morphological differences between some is-
land pairs is not congruent with low genetic
differentiation and high rates of gene flow
among islands. Lack of concordance between
morphology and genetics, however, is not un-
common; through the use of mtDNA markers,
it has been reported for other groups, such as
reptiles (Schmitt et al. 2000, Brehm et al.
2001), mollusks (Mukaratirwa et al. 1998), in-
sects (Baranyi et al. 1997), and birds (Seutin
et al. 1993, 1994; Zink and Dittmann 1993;
Freeman-Gallant 1996).

One might expect that morphological dif-
ferences would have been erased by the con-
nectedness between populations. However, be-
cause genes under selective pressure likely
control morphological traits, and because ^ST
assumes neutral markers, selectively neutral
markers might not track morphological differ-
ences among populations. We do not believe
that processes such as genetic drift are impor-
tant in determining the morphological differ-
ences in Galapagos Doves, since they require
that gene flow be restricted among popula-
tions. Alternatively, morphological characters
can be very plastic and might vary within spe-
cies, depending on the environmental charac-
teristics of an area. Many studies have shown
that environmental factors are sufficient to
produce morphological changes, either im-
mediately or within a few generations (James
1983, Losos et al. 1997, Trussed and Etter
2001). In other words, environmentally in-
duced differences among populations are in-
dependent of genetic differences. Another
possibility is that even where dove popula-
tions are sympatric and/or affected by high

rates of gene flow, there may be an ecotypic-
differentiation process driven by divergent se-
lection (Schluter 2001). This has been report-
ed in several studies and for different taxa
(Schluter 2001, Ogden and Thorpe 2002).
Based on the estimated effective population
sizes for the different islands (from —400 on
Santa Fe to —4,800 on Genovesa), the migra-
tion rates (0 to —70 individuals per genera-
tion) represent —2% of the effective size of
the population on the different islands. At this
level of migration, the genetic influx might
not completely counteract the effects of selec-
tion (Conner and Haiti 2004), which could ac-
count for the morphological differences ob-
served in our study.

ACKNOWLEDGMENTS

We thank all who provided help during the different
stages of the field season, particularly N. K. Whiteman,
J. L. Bollmer, G. Jimenez, J. Merkel, J. Rabenold, and
N. Gottdenker. We thank the staff of the Charles Dar-
win Research Station for their invaluable help and lo-
gistical support during the course of this study, espe-
cially P. Robayo. We also thank N. Freire and J. Mi-
randa who helped with dove sampling at Tortuga Bay,
Santa Cruz. Permits for sample collection were pro-
vided by Galapagos National Park. We thank B. A.
Loiselle, R. E. Ricklefs, B. T. Ryder, A. Cohen, and J.
L. Bollmer for helpful comments and suggestions on
earlier versions of this manuscript. We thank H. Vargas
for sharing his knowledge of Galapagos Doves from
islands not visited in this study. We thank P. Beerli
who provided guidance on using program MIGRATE.
We thank R. L. Curry and two anonymous reviewers
for comments that greatly improved the manuscript.
Financial support was provided by The International
Center for Tropical Ecology, The Saint Louis Zoo, and
E. Des Lee Collaborative Vision in Zoological Re-
search.

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The Wilson Journal of Ornithology 1 18(2):208— 217, 2006

BREEDING ECOLOGY OF AMERICAN AND CARIBBEAN
COOTS AT SOUTHGATE POND, ST. CROIX:

USE OF WOODY VEGETATION

DOUGLAS B. McNAIR1’34 AND CAROL CRAMER-BURKE2 3 4

ABSTRACT. — American ( Fulica americana ) and Caribbean ( F . caribaea) coots nested colonially at brackish
Southgate Pond, St. Croix, United States Virgin Islands (USVI), following a 50-year rainfall event in mid-
November 2003. Breeding occurred during three time periods: seven pairs bred from 6 December to 2 January
(early), seven from 17 January to 15 February (middle), and eight from 26 April to 19 May (late) (range of
clutch initiation dates = 165 days). Hatching success was high (65.3%), but overall reproductive success was
low (27%) owing to poor brood survival. Coots built all but 2 of 22 nests at the water line in sturdy crotches
of small, live white mangroves ( Laguncularia racemosaf two late nests were built on remnant stubs of dead
white mangroves after water levels had sharply declined. Early pairs nested in manglars (islets of one or more
mangroves without solid land) farther away from shore and in deeper water than middle or late pairs (65.6
versus 42.1 and 29.0 cm, respectively). Southgate Pond remains the preferred breeding site for coots on St.
Croix and the USVI. Coots have also recently nested on St. Croix at seven semi -permanent or permanent, man-
made, freshwater ponds where they have probably been overlooked, as coots respond rapidly to changes in
water levels at semi-permanent or permanent wetlands. Predominance of non-assortative pairing at Southgate
Pond suggests that American and Caribbean coots are morphs of one species. Received 7 February 2005,
accepted 7 November 2005.

The Caribbean Coot ( Fulica caribaea) is
not globally threatened (Taylor 1996), but the
species is listed as locally endangered in the
United States Virgin Islands (USVI; Indige-
nous and Endangered Species Act of 1990)
and is considered threatened throughout the
West Indies, especially breeding populations
(Raffaele et al. 1973, 1998). Caribbean and
American (F. americana) coots are two of the
rarest bird species that nest in wetlands of the
USVI, including St. Croix (Beatty 1930, Raf-
faele 1989), and their breeding ecology in the
Caribbean is poorly known (Taylor 1996,
Brisbin et al. 2002). In North America, Amer-
ican Coots are associated with freshwater
marshes and low-salinity brackish wetlands
(Kantrud 1985).

Following the largest rainfall event in over
50 years, we studied the breeding ecology of
Caribbean and American coots at Southgate
Pond, the largest seasonal brackish pond on
St. Croix. Although degraded by previous

1 Div. of Fish and Wildlife, Dept, of Planning and
Natural Resources, 45 Mars Hill, Frederiksted, St.
Croix, USVI 00840, USA.

2 St. Croix Environmental Assoc., Arawak Bldg.,
Ste. #3, Christiansted, USVI 00820, USA.

3 Current address: Sapphos Environmental, Inc., 133
Martin Alley, Pasadena, CA 91 105, USA.

4 Corresponding author; e-mail:
dmcnair@sapphosenvironmental.com

coastal development, Southgate Pond is still
one of the most productive mangrove wet-
lands for birds on St. Croix (Scott and Car-
bonell 1986, Sladen 1992; DBM and CCB un-
publ. data). We describe coot breeding adap-
tations in use of woody vegetation as nest
sites (Sugden 1979), and provide information
on phenology, clutch size, and breeding suc-
cess. We also present recent breeding infor-
mation (since 2002) on coots for seven other
sites on St. Croix, formulate management
strategies (especially for Southgate Pond), and
assess the taxonomic significance of pairing
between the two species.

METHODS

During 2003-2004, we studied American
and Caribbean coots at Southgate Pond, a
17.9-ha wetland (17° 45' 29.6" N, 64° 39'
45.9" W) on St. Croix, USVI. We used the cri-
teria of Roberson and Baptista (1988) to dis-
tinguish American (types A and B) from Ca-
ribbean coots (types C, D, and E) in the field.
A small percentage (<1.4%) of the males with
broad, high, and bulbous shields may be
white-shielded morphs of American Coots
(Roberson and Baptista 1988). Types A and B
have a dark chestnut or red-brown corneous
callus, whereas types C, D, and E lack a cal-
lus. After becoming familiar with vocal dif-

208

McNair and Cramer-Burke • COOTS AT SOUTHGATE POND, ST. CROIX

209

ferences between the sexes (Gullion 1950), we
also identified the genders of some coots at
their nests. Males were larger than females
and had larger shields and bills, regardless of
species, which agrees with expectations based
on size and hormonal differences between the
sexes (Gullion 1951; Fredrickson 1968, 1970).

We visited Southgate Pond twice a week
after the first nest was discovered in early Jan-
uary 2004. Nests were marked with numbered
flagging and the location of each nest was re-
corded with a Global Positioning System
(GPS) unit and plotted on a map using
Arc View 3.2. We recorded the coot species
associated with each nest and coot behavior
during each nest visit. Some individuals were
not identified to species because of their elu-
sive behavior. Dates of clutch initiation for
nests found during laying were calculated by
backdating and assuming that one egg was
laid per day (Gorenzel et al. 1982, Brisbin et
al. 2002). Assuming a 23-day incubation pe-
riod (Brisbin et al. 2002), initiation dates for
nests found after laying were estimated based
on hatch dates minus 1 day (the day on which
the first egg hatched). For failed nests, we ad-
justed hatch date for incomplete or under-re-
corded clutch sizes based on the mean clutch
size and backdating from the midpoint be-
tween the first and last egg dates. Because our
potential renest intervals were long, renests
were not assigned to any one pair of coots
(based on criteria in Arnold 1993).

We used the method of Mayfield (1975), as
modified by Johnson (1979), to calculate
hatching success (based on a 23-day incuba-
tion period). To determine reproductive suc-
cess, we followed the fate of individuals and
broods until they were fully grown and inde-
pendent (60-70 days; Taylor 1996). Young
coots leave the nest on the day of hatching
and broods are difficult to count accurately
when young birds hide in emergent vegetation
(Gullion 1956); however, emergent vegetation
was scarce at Southgate Pond. As young ac-
quired juvenal plumage (~3 weeks old) they
left the breeding area for deeper water along
the northwestern shore of Southgate Pond,
where different broods coalesced into larger
flocks and were easier to see and count. All
nesting attempts had known outcomes and we
calculated reproductive success (number of
young fledged/number of eggs laid) by (1)

multiplying the number of active nests by
mean clutch size to derive an estimate of the
total number of eggs laid, and (2) dividing the
number of fully grown and independent young
(not broods per se) by eggs laid. Fledging suc-
cess (number of young fledged/number of
eggs hatched) was determined by dividing re-
productive success by hatching success. The
number of breeding pairs was based on the
number of active nests. Coot nest density at
Southgate Pond and the seven man-made
freshwater ponds was calculated based on
pond area and the number of nests or pairs
simultaneously active at each pond. Assess-
ment of intraspecific brood parasitism (“nest-
dumping”) followed the criteria of Post and
Seals (2000).

We recorded the following parameters at
each active nest and nest site: nest height from
the water line to the top of the nest rim (cm),
length and width of outer nest cup (cm),
length and width of inner lining (cm), water
depth below the nest (cm), above-water height
(cm) and greatest breadth (m) of the white
mangrove, distance to nearest white mangrove
(m), distance to nearest shoreline (m), distance
to nearest active nest (m), and distance to
nearest active or inactive nest (m). For each
pair of coots, four variables (water depth be-
low the nest, distance from the water line to
the top of the nest rim, height of white man-
grove above water, distance to nearest shore-
line) were adjusted to the date of clutch ini-
tiation. We also noted whether white man-
groves that contained nests were isolated
manglars (islets of one or more mangroves
without solid land) or formed a line of con-
nected manglars away from the shoreline. We
used a bathymetric map of Southgate Pond to
adjust distances between nests and the shore-
line by taking the mean value of four distance
measurements from the —15.25 to 30.5 cm
contour (—0.5 to 1 foot) centered on the main
breeding area. We then used sine/cosine func-
tions to calculate an angle of 0.026 degrees,
which translated to a 1.9-m change in shore-
line distance per cm drop (or rise) in water
levels. Baseline water level data (in cm) were
recorded in situ from several 2-m sticks
placed in the lowest bed of the flat-bottomed
pond. The water level decline was nearly con-
stant throughout the study period (mean of
0.58 cm/day), except for one heavy rainfall

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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

event when water levels rose 17 cm from 16
to 18 April. We obtained monthly measure-
ments of salinity at Southgate Pond using a
temperature-compensated refractometer (ac-
curate to within ± 1 ppt). From December
2003 through July 2004, salinity increased
from 4 to 32 ppt as water levels dropped.

To systematically sample coot breeding
habitat, we established a grid of 56 line tran-
sects, spaced 8 m apart along north-south car-
dinal directions from 15 m west of the south-
western shoreline and extending to the eastern
point of Southgate Pond just beyond the main
coot colony. We randomly selected sample
points ( n = 436) every 8 m along each tran-
sect. The last point along each transect was a
point in open water beyond the vegetation far-
thest from shore. Water depth (cm), vegetation
present or absent (open water), and species
composition (if vegetation present) were sam-
pled at each point. We used a random number
generator to assign numbers 1 to 22 (i.e., cor-
responding to the number of coot nests we
found) to sample points of water depth. Water
depth at each sampled point that contained
vegetation was then adjusted to reflect water
depth at the observed or estimated date of
clutch initiation for each coot nest represented
by each random number (e.g., random number
one represents coot nest one, which initiated
incubation on 6 December). This procedure
removed the effects of declining water levels
so that vegetation data would be comparable
to nest data.

To assess differences in water depths be-
tween vegetation and open water and among
species of plants, we used two-tailed f-tests
and one-way ANOVA (Zar 1999, StatSoft
2002). Because the sample sizes for five of
the eight vegetative species/types recorded
were small (total n = 15), we did not include
them in the ANOVA. We used simple linear
regression to assess the relationship between
water depth below nests and the date of clutch
initiation. We used a Mann-Whitney U- test to
assess whether water depths at coot nests dif-
fered from random and to examine whether
phenological or habitat variables were related
to hatching outcome (success/fail). We used
nonparametric tests (Mann-Whitney U , Krus-
kal-Wallis //, and Spearman’s rank correlation
rs ) when sample sizes were small and data did
not otherwise meet assumptions of the normal

distribution, including homogeneity of vari-
ances and distribution of residuals. For all
tests, we used an a value of 0.05. Means are
reported ± SD.

RESULTS

We located 22 active coot nests at South-
gate Pond during winter and spring of 2003-
2004. Dates of clutch initiation ranged from 6
December to 19 May (165 days), with breed-
ing occurring during three periods: early (6
December to 2 January; 27 days), middle (17
January to 15 February; 29 days), and late (26
April to 19 May; 23 days). One nesting at-
tempt during the late period was overlooked
(see below). We identified one pair of Carib-
bean Coots and five Caribbean X American
coot pairs (hereafter mixed pairs) during the
early period, two pairs of Caribbean Coots
and four mixed pairs during the middle period
(two male American and two female Carib-
bean coots were sexed in two of these four
mixed pairs), and three pairs of Caribbean
Coots and two mixed pairs during the late pe-
riod (both males were American and both fe-
males were Caribbean coots). One of the
American Coots of one mixed pair during
each of the first two periods was type B (in-
termediate, sensu Roberson and Baptista
1988). The other American Coots appeared to
be type A birds. Of the three coots whose
mates were not identified, two were Caribbean
and one was American.

Clutch size decreased as the nesting season
progressed ( rs = —0.56, P = 0.025) and av-
eraged 6.88 ± 1.41 eggs (range = 5-9, n —
16). Seventeen of 22 nests (77%) hatched at
least one chick, and only 5 of the 130 eggs
(3.8%) that remained unbroken in the nest
bowl throughout the normal incubation period
failed to hatch. Daily nest survival (5) was
0.982 ± 0.008 SE and hatching success was
65.3% (Mayfield method). Hatching success
was not related to clutch initiation dates (U =
26, Z = 1 .29, P = 0.20) or any other pheno-
logical or habitat variable, although successful
nests generally began earlier and had larger
clutches, greater water depths, and were far-
ther away from shore than failed nests. Forty-
one young became fully grown and indepen-
dent 60-70 days after hatching. This excludes
three young — attended by a pair of Caribbean
Coots — that fledged from a ninth nest over-

McNair and Cramer-Burke • COOTS AT SOUTHGATE POND, ST. CROIX

21 1

TABLE 1. Measurements of 14 nest and nest-site parameters for 22 coot nests built in white mangroves at
Southgate Pond, St. Croix, U.S. Virgin Islands, during winter and spring of 2003-2004.

Parameter

Mean ±

Range

Nest height from water line to top of nest rim (cm)

13.5

6.9

4.8-35.5

Length of outer nest cup (cm)

35.9

8.8

25.4-61.0

Width of outer nest cup (cm)

28.6

4.2

20.3-36.2

Length of inner lining (cm)

19.8

2.2

15.5-25.4

Width of inner lining (cm)

18.0

2.1

14.0-22.9

Water depth below nest (cm)

44.8

17.6

15.0-78.5

Above-water height of white mangrove (m)a

1.9

0.6

1. 0-3.7

Greatest breadth of white mangrove (m)b

3.9

1.1

1.5-5. 8

Distance to nearest white mangrove (m)c

3.2

-t-

2.4

0.0-8. 5

Distance to nearest shoreline (m)

48.4

-t-

26.0

10.4-98.1

Distance to nearest active nest (m)

60.4

59.6

18.7-308.2

Distance to nearest active nest (m)d (excluding three isolated nests)

42.7

-4-

13.5

18.7-60.2

Distance to nearest active or inactive nest (m)

42.3

59.9

10.2-283.9

Distance to nearest active or inactive nest (m)d (excluding three isolated nests)

23.1

-I-

11.3

10.2-50.5

a One outlier excluded (dead white mangrove: nest 17; height <20 cm).

bTwo outliers excluded (one dead white mangrove and one live white mangrove: nests 17, 21; breadth not measured and = 55.7 m, respectively).
c One outlier excluded (live white mangrove: nest 22; distance = 127.9 m).

d One isolated nest excluded from each of early, middle, and late nesting periods (nests 7, 13, and 17).

looked during the late period (date of clutch
initiation was later than 19 May). The largest
single brood observed comprised five young
(from a mixed pair), and there were six broods
(from four mixed pairs and two Caribbean
Coot pairs) with four young. Reproductive
success was 27%, and fledging success was
41.3%.

Nests were built along the water line in par-
tially submerged, small, live white mangroves
( Laguncularia racemosa\ Table 1). Most nests
were placed either in the central crotch (early
and middle periods) or in smaller crotches of
outside branches (late period); two nests dur-
ing the late period were also placed either on
remnants of dead white mangroves under live
vegetation or on unconcealed dead white man-
groves. All nests during the early and middle
periods had short or long ramps, while only
two nests during the late period had ramps.
Nests were in isolated manglars (n = 18) or
in rows of manglars {n = 4), but away from
mangroves that formed the outer fringes of
Southgate Pond’s vegetated shoreline. Nests
were located close to nest materials, the bulk
of which (excluding sticks and twigs of man-
groves) consisted of shoreline sea purslane
( Sesuvium portulacastrum ), a perennial suc-
culent forb also used to construct most of the
ramps. Seed pods of Sesbania sericea, a short-
lived shrub, composed the inner nest lining of
several nests. The dominant submerged plant

(forb) of Southgate Pond was widgeon grass
( Ruppia maritima), but this species was not
used as nest material. Most manglars, both
white and black ( Avicennia germinans ) man-
groves, were located at the east end of the
pond, where most nests were concentrated
(Fig. 1). Two rather isolated nests (7, 13) were
near the southwestern shoreline, and the most
isolated nest (17) was near the northwestern
shoreline. The density of coot nests during the
three periods was 0.39-0.45 nests/ha.

Mean water depth at nests was 44.8 cm (Ta-
ble 1) and declined throughout the breeding
season (early period: 65.6 cm ± 11.0; middle
period: 42.1 cm ± 3.8; late period: 29.0 cm
± 9.5; Kruskal-Wallis H = 15.14, P < 0.001;
Fig. 2). Early nests were also farther away
from the shoreline than middle or late nests
(early period: 70.0 m ± 29.7; middle period:
49.6 m ± 11.2; late period: 28.5 m ± 15.8;
Kruskal-Wallis H = 8.81, P = 0.010). Other
comparisons of nest or nest-site variables be-
tween early, middle, and late periods were not
significantly different.

Vegetation sampled at random points along
line transects composed 34.6% (n = 151) of
breeding habitat; the remainder was open wa-
ter ( n = 285), where mean water depth was
significantly greater than in vegetated areas
(open water: 45.8 cm ± 27.3; vegetation: 37.4
cm ± 26.2; t = 3.11, df 434, P = 0.002).
Live white and black mangroves and dead

212

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

60 120 180 240 300 360 420 Meters

FIG. 1 . The location of 22 coot nests at Southgate Pond, St. Croix, U.S. Virgin Islands, during winter and
spring of 2003-2004.

white mangroves dominated vegetation types
within breeding habitat, and mean water
depths at dead and live white mangroves were
significantly deeper than at black mangroves
(F2134 = 8.28, P < 0.001; Table 2). Mean wa-
ter depths at live white mangroves with and

90:

80: .
70:*

y = 61 .84 - 0.23x, r2 = 0.68, P < 0.001

60:

20:

10 1 — -

0 20 40 60 80 100 120 140 160 180

Date of clutch initiation (1=6 December)

FIG. 2. Relationship between water depth below
22 coot nests and the date of clutch initiation at South-
gate Pond, St. Croix, U.S. Virgin Islands, during winter
and spring of 2003-2004.

without coot nests were similar (without nests:
39.3 cm ± 25.7; with nests: 44.8 cm ± 17.6;
Mann-Whitney U = 434.5, P = 0.24).

Freshwater ponds. — Since 2002, 1—3 pairs
of Caribbean Coots and mixed pairs have bred
intermittently year-round at seven man-made,
freshwater ponds on St. Croix, which range in
size from 0.1 to 2.9 ha. The mean coot density
at all sites combined for all breeding sequenc-
es over the 4 years was 4.2 pairs/ha (range =
0.3-10.0, n = 17) and apparent hatching suc-
cess was high (16 of 24 nests based on hatch
rates of the proportion of nests found). Most
breeding records occurred after the 50-year
rainfall event of mid-November 2003 filled
the ponds. This event followed a dry period,
when a variety of plant species had colonized
the bottom of many dry, or nearly dry, ponds.
In addition, the Virgin Islands Agricultural
Station Middle Pond (see McNair 2006 for list
of pond names and their locations on St.
Croix) was deliberately drained during winter
2002-2003. Water levels varied between years
at several sites when nesting occurred, espe-

McNair and Cramer-Burke • COOTS AT SOUTHGATE POND, ST. CROIX

213

TABLE 2. Mean water depth (cm) for eight vegetation

types at

Southgate Pond, St. Croix, U.S. Virgin

Islands, during winter and spring of 2003—2004.

Vegetation type

Mean ± SDh

Dead Laguncularia racemosa

45.4 ± 26.9 A

Live Laguncularia racemosa

39.3 ± 25.7 A

Live Avicennia germinans

23.2 ± 21.2 B

Dead Avicennia germinans

38.6 ± 20.6C

Sesbania sericea

43.9 ± 17.0C

Sesuvium portulacastrum

27.8 ± 28. 8C

Sesuvium portulacastrum on dead L. racemosa

52.7 ± 20.2C

Sporobolus virginicus a

6.8 ± 29. lc

All vegetation

151

37.4 ± 26.2

Open water

285

45.8 ± 27.3

a Seashore rush grass.

b Overall ^2,134 = 8.28, P < 0.001; rows with different letters (A, B) are significantly different (Tukey’s unequal n HSD post-hoc tests: P = 0.026 for
live Avicennia germinans versus live Laguncularia racemosa', P < 0.001 for live A. germinans versus dead L. racemosa).
c Sample size too small to test.

cially at the Virgin Islands Agricultural Sta-
tion Middle Pond. Live creeping burrhead
(Echinodorus berteroi ) was almost absent
there in 2004, when the pond was not used by
coots and emergent vegetation was restricted
to the shoreline when the water level was
higher. Although coots nested in a variety of
live (five species) and dead (two species) veg-
etation, woody (especially remnant S. sericea,
at four ponds) vegetation rather than perennial
herbaceous vegetation was the predominant
nest substrate (18 of 27, 67%). Nests ranged
from 4 to 33.5 m away from the shoreline,
and water depths below nests were generally
greater for nests built in woody vegetation,
especially S. sericea (usually 1.25-2.25 m).
The bulky, conspicuous nests composed of
sticks of S. sericea (—90 X 65 cm) were su-
perficially shaped like the above-water portion
of a beaver lodge. Anthropogenic disturbance
at these seven ponds was negligible except
around Carlton North Pond, where all vege-
tation except that fringing the shoreline was
cleared for a housing development in early
October 2004; however, coots continue to
breed at Carlton North Pond.

DISCUSSION

Because of a drought on St. Croix that be-
gan in 2002, the bottom of Southgate Pond
was dry in 2003 until water from heavy rains
began to fill the pond in late August. None-
theless, the basin was only about one-quarter
full until a 50-year rainfall event during 10-
14 November 2003 caused Southgate Pond to

overflow. Coots colonized the pond and began
laying eggs within 2-3 weeks after this sea-
sonal wetland filled with water, typical of
coots after arrival on their breeding grounds
(Alisauskas and Arnold 1994).

When conditions are suitable, Southgate
Pond is probably the preferred breeding site
for coots on St. Croix (and in the USVI;
McNair 2006), even though freshwater ponds,
each with a small number of birds, support
higher breeding densities (this study). Al-
though Southgate Pond is brackish, the num-
ber of breeding pairs during three consecutive
periods from December to May did not de-
cline as salinity increased from low to mod-
erately brackish; elsewhere, breeding densities
typically decline as salinity increases (Kantrud
1985, Arnold 1993). Regardless, semi-per-
manent or seasonal wetlands are generally
preferred habitat for American Coots in North
America (Kantrud 1985, Arnold 1993, Ali-
sauskas and Arnold 1994). Nests at Southgate
Pond, which generally lacked emergent her-
baceous vegetation, were built in woody veg-
etation. In Saskatchewan, small, isolated, par-
tially submerged willow ( Salix spp.) clumps
were used as nest sites for a substantial per-
centage (22%) of American Coot nests during
a wet year (Sugden 1979), although willows
were not used as nest materials. This is dif-
ferent from what we observed at Southgate
Pond, where white mangroves served as nest
sites and as nest-building material; remnant or
live woody plants (especially remnant S. ser-
icea) at freshwater ponds on St. Croix were

214

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

used similarly. In another Saskatchewan
study, coot nests were composed of the same
plant species that provided support for the nest
(cf. Sutherland and Maher 1987).

Water depths below many nests in fresh-
water ponds on St. Croix were much deeper
than water depths below nests in white man-
groves at Southgate Pond. Apart from South-
gate Pond, the most suitable freshwater breed-
ing site for coots on St. Croix has been Gran-
ard South Pond, where three pairs nested in
remnant Sesbania and other nest sites. Unlike
mangroves at Southgate Pond, suitable rem-
nant woody vegetation at freshwater ponds
usually becomes available only when these
ponds dry up and then refill with water, which
kills the colonizing shrubs. Emergent vegeta-
tion suitable for nests at some of these ponds
can be scarce, even when water levels are low.
Nests in perennial emergent forbs were float-
ing platforms built amongst this vegetation,
which is typical of coot nests in marshes
(Fredrickson 1970, Sugden 1979, Gorenzel et
al. 1982, Kantrud 1985, Post 1990, Alisauskas
and Arnold 1994, Frost and Massiah 2001).

At Southgate Pond, water depths at coot
nests during each period were typical of those
observed at American Coot nests on the North
American mainland (Sugden 1979, Gorenzel
et al. 1982, Sutherland and Maher 1987, Post
1990, Arnold 1993), although depths during
the third period were rather shallow. Even
though coots on the North American mainland
frequently nest in residual emergent vegeta-
tion (Gorenzel et al. 1982, Alisauskas and Ar-
nold 1993), in our study they probably avoid-
ed using dead white mangroves as nest sites
in deeper water at Southgate Pond because
nests in these sites would have been exposed.
Were it not for the effects of hurricanes Hugo
and Marilyn in 1989 and 1996, which killed
many white mangroves farther from shore,
several more pairs of coots may have used
these mangroves as nest sites. Coots also
avoided nesting in black mangroves, which
are generally located closer to shore than the
live white mangroves they used. Water depths
at nests in white mangroves during the late
period were similar to mean depths at black
mangroves, suggesting that water depth at
black mangroves was otherwise acceptable to
coots. However, coots generally prefer deeper
water farther from shore (Sutherland and

Maher 1987, Post 1990, Arnold 1993). Fur-
thermore, white mangroves offer superior
structural support for nests (black mangroves
lack the sturdy bowl-shaped central crotch and
low lateral branches) and greater concealment.
For similar reasons, American Coots in Sas-
katchewan nested in live willows but not
quaking aspens ( Populus tremuloides ) (Sug-
den 1979).

As water levels declined, nest-site selection
changed; by the late period, the central crotch-
es of white mangroves were no longer suitable
(too far above water). Nonetheless, inter-nest
distances remained similar during all three pe-
riods, suggesting that territory sizes (which
were not measured) also remained similar. In-
ter-nest distances between simultaneously ac-
tive (or inactive) nests during all three periods
were typical of those observed for coots else-
where, although published data are unavail-
able for nests limited to woody vegetation.
Unlike what has been observed at many North
American sites characterized by emergent
vegetation, coots at our study site built few
non-nesting platforms (six in white man-
groves), and the distribution and structure of
nesting cover at Southgate Pond did not
change over the breeding season. Given the
fixed number of live white mangroves as po-
tential nest sites for coots at Southgate Pond,
territorial behavior probably prevented any
additional coot pairs from breeding at the site.
The location of coot nests is mainly controlled
by territorial spacing, distance from shore, and
the distribution and structure of nesting cover
(Gullion 1953, Sugden 1979, Sutherland and
Maher 1987). Water depth, although correlat-
ed with distance from shore in this study, was
probably a less important factor in nest-site
selection.

Nest concealment in woody vegetation
must have been effective because hatching
success at Southgate Pond was high. Apparent
hatching success was also high at freshwater
sites, which is typical of American Coots
(Gorenzel et al. 1982, Alisauskas and Arnold
1994, Brisbin et al. 2002). Intraspecific nest
parasitism was not observed at Southgate
Pond or at the freshwater ponds. Fledging suc-
cess at Southgate Pond, although not consis-
tently associated with differences in water
depth, was low (<41%). This contrasts with
apparent fledging success at freshwater sites

McNair and Cramer-Burke • COOTS AT SOUTHGATE POND, ST. CROIX

215

(this study), and that in North America, which
is generally high (>50%; Alisauskas and Ar-
nold 1994). Most broods observed at South-
gate Pond consisted of 2-3 birds, lower than
the number typically observed at freshwater
ponds (7 of 13 broods had >4 fledged young).
Thus, we speculate that brood losses within 5
days after hatching exceeded 50% at South-
gate Pond. Low survivorship of young also
occurred during the early brood period for
White-cheeked Pintails {Anas bahamensis ) at
Humacao, Puerto Rico (F. J. Vilella pers.
comm.), where most losses were attributed to
rats ( Rattus spp.), Great Egrets (Ardea alba),
and Black-crowned {Nycticorax nycticorax )
and Yellow-crowned {Nyctanassa violacea )
night-herons. All of these potential predators
were present at Southgate Pond.

Despite low reproductive success at South-
gate Pond, the long intervals between breed-
ing periods and the similar number of pairs
breeding during each period suggest that some
middle and late period nests were probably
second or third broods rather than renests.
Presumed success of second nesting attempts
also occurred at three of the seven freshwater
ponds. Nesting during the late period at
Southgate Pond appeared to be possible be-
cause of heavy rainfall that occurred from 16
to 17 April, when water levels rose 17 cm,
allowing coots to reset their breeding clock
despite an overall drop in water level (14 cm)
since the middle breeding period. Before the
50-year rainfall event of mid-November 2003,
coots probably last nested at Southgate Pond
in 2001, following the previous torrential rain-
fall event of 8 May when water filled the pond
(CCB unpubl. data). This opportunistic, multi-
brooded breeding response to aquatic periods
resulting from torrential vernal and autumnal
rainfalls in an otherwise semi-arid environ-
ment may allow coots to overcome generally
low reproductive success on St. Croix. Nev-
ertheless, three breeding periods during one
aquatic phase is probably exceptional (DBM
and CCB unpubl. data). How frequently and
successfully coots breed at Southgate Pond
and freshwater sites on St. Croix in the future
is currently being determined through an on-
going wetlands bird-monitoring scheme.

Management recommendations. — South-
gate Pond (now part of the Southgate Coastal
Reserve owned by the St. Croix Environmen-

tal Association) remains favorable habitat for
nesting coots, even though environmental
degradation has diminished this brackish pond
to <50% of its original size (Gaines 2004,
Gaines and Gladfelter 2004). The most diffi-
cult task at Southgate Pond is to maintain ap-
propriate water levels for coot nest initiation
during seasons and years when rainfall is in-
sufficient. We endorse Gaines and Gladfelter’s
(2004:54-56) two major recommendations for
water management to prolong the aquatic
phase of Southgate Pond: (1) divert water into
the pond, and (2) raise the maximum water
depth from —103 to —138 cm. Manipulation
of water levels should favor nesting coots and
other wetland birds, although it may eliminate
species that nest in terrestrial sites. During its
dry phase, two species of conservation con-
cern on St. Croix may nest at Southgate Pond:
Wilson’s Plover {Charadrius wilsonia) and
Least Tern {Sterna antillarum). However, both
species breed at more than 10 sites and are
not as rare as coots. Furthermore, Southgate
Pond is the best-documented site for coots in
the eastern Caribbean (McNair 2006). When
water levels are sufficient, the brackish habitat
at Southgate Pond may be similar to that of
brackish impoundments along the northern
Gulf coast of the United States (e.g., an abun-
dance of sea purslane and widgeon grass),
where coots are abundant (Swiderek et al.
1988).

At the seven man-made, freshwater ponds,
piped water is generally the best management
option to maintain stable, generally high water
levels. The most suitable freshwater site in the
eastern Caribbean (Barbados) is man-made
Marshall’s Pond, which is dominated by Echi-
nodorus berteroi (Frost and Massiah 2001; M.
D. Frost pers. comm.), the herbaceous species
used most frequently for nest sites on St.
Croix. Maintaining stable water levels at the
best site on St. Croix (Granard South Pond),
as well as at the other ponds, should generally
favor E. berteroi and other species with sim-
ilar vegetative characteristics. Woody vegeta-
tion would no longer compose the dominant
nest sites because stable water levels would
generally prevent woody plants such as S. ser-
icea from becoming established except along
the immediate shorelines of these ponds.

Caribbean Coot systematic s. — The taxo-
nomic status of the Caribbean Coot requires

216

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

further investigation (Roberson and Baptista
1988; also Gullion 1951, Phillips 1967, Payne
and Master 1983, Clark 1985, Taylor 1996).
Apparent non-assortative pairing of coots pre-
vailed at Southgate Pond, where both types of
coots occurred. One-half of the pairs at fresh-
water sites on St. Croix were paired non-as-
sortatively. Furthermore, at least some mixed
pairs successfully raised young, especially at
Southgate Pond, indicating that the two types
of coots can produce viable offspring (Gill
1964, Payne and Master 1983, Bond 1984).
Thus, American and Caribbean coots may
compose one species with variant, intergraded
phenotypes of which A and E birds represent
the extreme types. Although some birds can
be individually recognized in the field, an ac-
curate assessment of phylogenetic relation-
ships and the taxonomic status of American
and Caribbean coots will require studies based
on morphological and genetic analyses along
with observations of mating behavior and pair
bonds of marked birds. This will also require
confirming identification of shield character-
istics and correlating them with other mor-
phological measurements.

ACKNOWLEDGMENTS

The U.S. Fish and Wildlife Service provided partial
financial support to the Division of Fish and Wildlife,
U.S. Virgin Islands (Federal Aid Program, Pittman-
Robertson Wetlands Project, W15). S. L. Fromer and
L. D. Yntema shared their bird observations; A. G.
Gaines contributed data on salinities at Southgate Pond
and provided a digitized bathymetric map of this site;
D. B. Nelthrop and D. M. Schuster, among other land-
owners, provided access to their freshwater ponds; J.
A. Collazo and F. J. Vilella reviewed a penultimate
draft of the manuscript, and T. W. Arnold, F. E. Hayes,
and an anonymous individual reviewed earlier versions
of the paper.

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The Wilson Journal of Ornithology 1 1 8(2):2 1 8 — 224, 2006

INSULAR AND MIGRANT SPECIES, LONGEVITY RECORDS,
AND NEW SPECIES RECORDS ON GUANA ISLAND,
BRITISH VIRGIN ISLANDS

CLINT W. BOAL,1 4 FRED C. SIBLEY,1 2 TRACY S. ESTABROOK,3 4 AND

JAMES LAZELL2

ABSTRACT. — We conducted mist netting each October from 1994 to 2004 on Guana Island, British Virgin
Islands, and recorded bird sightings to develop a more complete inventory of the island’s resident and migrant
species. During our study, we recorded four new species for the British Virgin Islands: Magnolia Warbler
{Dendroica magnolia ; 1996), Golden-winged Warbler ( Vermivora chrysoptera\ 1997), Swainson’s Thrush ( Ca -
tharus ustulatus ; 2000), and Red-necked Phalarope ( Phalaropus lobatus ; 2004). Blackpoll Warbler ( Dendroica
striata) was the most frequently captured Neotropical migrant landbird, despite only being first detected in the
region in 1989. Captures and detections of other Neotropical migrant landbirds suggest that many species may
be more common in the region than previously believed, or, as speculated by other researchers, that migrant
routes may be shifting eastward due to habitat degradation on western Caribbean islands. We also used recapture
data to establish longevity records of resident species, including Caribbean Elaenia ( Elaenia martinica\ >7
years), Bananaquit ( Coereba flaveola-, 7 years), Black-faced Grassquit ( Tiaris bicolor, >9 years), and Zenaida
Dove {Zenaida aurita\ 5 years). Longevities of other resident species were similar to, or slightly less than, those
reported elsewhere. Received 22 February 2005, accepted 30 November 2005.

Ornithological research conducted in the
West Indies has covered an array of topics,
including avian species occurrence and distri-
bution, ecology of individual species, effects
of hurricanes on island bird populations, mi-
gration patterns, and community dynamics
(Wiley 2000). In the Virgin Islands region, re-
searchers have addressed avifaunal occurrence
and distribution (LaBastille and Richmond
1973, Mirecki et al. 1977, Norton et al. 1989),
and species ecologies (Askins and Ewert
1991, Chipley 1991, Mayer and Chipley 1992,
McNair et al. 2002); however, considerably
less ornithological study has been conducted
in the Virgin Islands — especially the British
Virgin Islands (BVI) — than in other areas of
the West Indies. In a bibliography consisting
of 1 1 ,648 entries for ornithological work con-
ducted in the West Indies from 1750 to 1994,
only 7.5% of the entries included information
for the Virgin Islands; only the extralimital is-
lands of San Andres, Providencia, and the

1 U.S. Geological Survey, Texas Coop. Fish and
Wildlife Research Unit, Dept, of Range, Wildlife and
Fisheries Management, Texas Tech Univ., Lubbock,
TX 79409-2120, USA.

2 The Conservation Agency, 6 Swinburne St.,
Jamestown, RI 02835, USA.

3 5529 90th St., Lubbock, TX 79424, USA.

4 Corresponding author; e-mail: clint.boal@ttu.edu

Swans have received less attention (Wiley

2000).

We conducted mist netting on Guana Is-
land, BVI, each October from 1994 to 2004.
To our knowledge, the Guana Island station is
the only current and consistently operated
banding station in the British Virgin Islands
and one of only three in the eastern Caribbean
(St. Martin and Barbados being the others).
Previously, information from the island has
proven important in developing a better un-
derstanding of Neotropical migrant bird use of
the region during the autumn migration
(McNair et al. 2002). However, our data on
species frequency of occurrence, which could
be helpful in this effort, have not been made
available until now. For example, Faaborg and
Terborgh (1980) considered the Red-eyed Vir-
eo ( Vireo olivaceus ) as a rare transient mi-
grant encountered only in the Greater Antilles.
In a status review of migrant landbirds in the
Caribbean, Arendt (1992) did not list Red-
eyed Vireos as even occurring in the British
Virgin Islands. Indeed, Norton (1996) noted
an account of a Red-eyed Vireo in Puerto Rico
as one of only a few confirmed records for the
species on the Puerto Rico Bank. The regular
occurrences of Red-eyed Vireos at Guana Is-
land (CWB and FCS unpubl. data), however,
suggest that the species uses the Virgin Is-
lands as a migration stopover more than pre-
viously believed.

218

Boal et al. • BIRD SPECIES AND LONGEVITY ON GUANA ISLAND, BVI

219

Here, we present an account of resident and
migrant species banded during October each
year for 1 1 years on Guana Island. For some
species, we report longevity records based on
recaptures of banded individuals. Additional-
ly, we provide accounts of new or rarely re-
ported species based on both banding and site
records.

METHODS

The Virgin Islands, including both the U.S.
Virgin Islands and the BVI, are a chain of
approximately 76 islands and cays located
100-150 km east of Puerto Rico. Guana Is-
land (18° 30' N, 64° 30' W) lies immediately
north of Tortola, the largest of the BVI is-
lands. Within the BVI, Guana Island is rela-
tively small (3 km2) compared with other in-
habited islands, such as Tortola (54 km2). Vir-
gin Gorda (21 km2), and Jost Van Dyke (10
km2). The BVI has a subtropical climate tem-
pered by northeasterly trade winds, with tem-
peratures normally ranging from 28 to 33° C,
and fairly constant humidity levels (—78%)
throughout the year (Lazell 2005). Annual
mean rainfall for Guana Island is estimated at
92 cm (Lazell 2005), but data are limited and
the long-term average may be lower.

Guana Island is topographically rugged,
with elevations ranging from sea level to 246
m. Approximately 90% of the island is cov-
ered by subtropical dry forest, with ghut for-
ests (mesic forest; 5%) present in some drain-
ages; miscellaneous covers include human-al-
tered areas (3%), mangroves (1%), and beach
(1%) (Lazell 1996; CWB unpubl. data). Lazell
(1996) lists the primary native vegetation on
Guana Island as tabebuia ( Tabebuia hetero-
phylla ), gumbo-limbo ( Bursera simaruba),
loblolly ( Pisonia subcordata), buttonwood
{Conocarpus erectus), frangipani ( Plumeria
alba), acacia {Acacia muricata ), and sea grape
{Coccoloba uvifera). Tam-tam {Leucaena leu-
cocephela) is common in disturbed areas. In-
troduced species include coconut {Cocos nu-
cifera), tamarind {Tamarindus indica), and
royal poinciana {Delonix regia).

We operated a mist-netting station each Oc-
tober from 1994 to 2004. Nets were located
primarily along a northeast-southwest ridge
and southeast-facing slope of a mountain on
the island’s west side. The majority of nets
were in subtropical dry forest areas, but each

year we placed 2—3 nets in human-altered ar-
eas along the ridge, all at approximately 100-
m elevation. For one afternoon each year, we
also netted along the shore of a salt pond to
sample the shorebirds present. We attempted
to use the same net locations each year, but
during the earlier years of the project we con-
ducted some “exploratory netting” in other
areas. Duration of mist-netting operations and
number of nets operated were subject to local
weather conditions, the number of assistants
available, and the amount of time we were
allowed access to the island by its owners;
thus, the number of nets used (mean = 8.1 ±
0.9 SE) and mist-netting days (mean = 8.8 ±

1 .3 SE) varied annually. Weather permitting,
nets were opened at 06:30 AST and closed
between 10:00 and 11:00; occasionally, mist-
netting was also conducted in the afternoon.

We identified all birds captured to the spe-
cies level, and, when possible, determined
their sex and age (Raffaele 1989, Pyle 1997,
Raffaele et al. 2003). We recorded weight (g),
length of wing chord (mm), and banded each
bird with a federal aluminum leg band. We did
not conduct systematic avian surveys (e.g.,
point counts), but we did record species en-
countered while engaged in other studies and
activities on the island. Combined, our obser-
vation records and mist-netting efforts al-
lowed us to compile an annual species list for
the island and document occurrences of spe-
cies previously unrecorded on the island and /
or the BVI. We compiled recapture records to
determine longevity for both resident and mi-
grant species. We considered all after-hatch-
ing-year birds (AHY) to be 1 year old at time
of initial capture.

RESULTS

Banding. — We conducted mist netting for a
mean of 252 ± 53 SE net-hr each October
from 1994 through 2004. During the study pe-
riod, we captured 1,410 birds, 188 (13%) of
which were recaptures of birds banded in pre-
vious years (Table 1). These numbers do not
include captures of birds that we did not band,
such as the Green-throated Carib {Eulampis
holosericeus) and the Antillean Crested Hum-
mingbird {Orthorhyncus cristatus). We cap-
tured 44 species, the most common of which
was the resident Bananaquit {Coereba flav-
eola; 676 captures). Other frequently captured

220

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

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Boat et al. • BIRD SPECIES AND LONGEVITY ON GUANA ISLAND, BVI

221

TABLE 2. Longevity records for species

years old on Guana Island, British Virgin Islands,

1994-2004.

Species

Agea

Sex

Year

captured

Last

recapture

No. of
recaptures

Minimum
age (years)

Wilson’s Plover

AHY

1996

1999

AHY

1996

1999

AHY

1996

1999

AHY

1996

1999

Black-necked Stilt

AHY

1997

2001

Spotted Sandpiper

1998

2004

Common Ground-Dove

AHY

1998

2001

Zenaida Dove

AHY

1997

2001

AHY

1998

2001

AHY

2001

2004

Caribbean Elaenia

Unk

1996

2003

Unk

1996

2001

Pearly-eyed Thrasher

AHY

1998

2001

Black-faced Grassquit

AHY

1996

2004

AHY

1998

2004

AHY

1998

2003

1998

2003

AHY

2000

2004

AHY

1996

2000

Bananaquit

AHY

1995

2001

AHY

1997

2003

1998

2004

AHY

1998

2002

AHY

1997

2001

AHY

1997

2001

1998

2003

AHY

2001

2004

AHY

1997

2000

AHY

1995

1998

AHY

1995

1998

1997

2001

AHY

2000

2004

AHY

2001

2004

AHY

1994

1997

1998

2002

1998

2002

AHY

1998

2001

AHY

1998

2001

a AHY = after-hatching-year, HY = hatching-year, Unk = unknown age.

resident species were Black-faced Grassquit
(Tiaris bicolor, 148 captures) and Pearly-eyed
Thrasher ( Margarops fuscatus\ 93 captures).
These three species are among the most abun-
dant residents on Guana Island. We also cap-
tured 20 species of Neotropical migrant land-
birds, the majority of which were warblers
(Table 1). The Neotropical migrant captured
most frequently was the Blackpoll Warbler
C Dendroica striata ; 185 captures), followed
by the Red-eyed Vireo (12 captures, multiple
additional sightings). Other Neotropical mi-
grants encountered included many species

(e.g., Yellow-throated Vireo, Vireo flavifrons;
Table 1) previously reported only from the
western Greater Antilles or for which there
were no records from the BVI or the Lesser
Antilles (Faaborg and Terborgh 1980, Arendt
1992).

Longevity. — We determined longevity for
all species recaptured on the island, and pro-
vide data for those older than 3 years (Table
2). Among shorebirds, the longevity records
were 5 years for Black-necked Stilt ( Himan -
topus mexicanus ), 6 years for Spotted Sand-
piper ( Actitis macularius ), and 4 years for

222

THE WILSON JOURNAL OL ORNITHOLOGY • Vol. 118, No. 2, June 2006

Wilson’s Plover ( Charadrius wilsonia ); how-
ever, our recapture rate for these species was
low and we suspect that our longevity esti-
mates, especially for the resident Wilson’s
Plover, may be substantially lower than actual
longevity. Among Columbiformes, our lon-
gevity records were 4 years for Common
Ground-Dove ( Columbina passerina) and 5
years for Zenaida Dove ( Zenaida aurita).
Among resident passerines, we recaptured Ca-
ribbean Elaenias ( Elaenia martinica ) that
were >7 and >5 years old, and we recaptured
a 4-year-old Pearly-eyed Thrasher. Among the
19 recaptured Bananaquits, two were 7 years
old, one was 6 years old, and the others were
5 and 4 years old. The oldest bird recaptured
was a >9-year-old female Black-faced Grass-
quit; we also recaptured one 6-year-old and
three 5-year-old grassquits.

New species records. — During the course of
our netting operations and surveys, we ob-
tained species records for Guana Island and,
in some cases, the British Virgin Islands. Our
captures of a Magnolia Warbler ( Dendroica
magnolia) in 1996 and a Golden-winged War-
bler ( Vermivora chrysoptera ) in 1997 were
first records for the BVI. More significant,
however, was our capture of a Swainson’s
Thrush ( Catharus ustulatus) in 2000, the first
record for the Virgin Islands and only the sec-
ond from east of Cuba (McNair et al. 2002).
In 2003, we captured another Swainson’s
Thrush and obtained a visual sighting of a sec-
ond, unbanded individual. Finally, our obser-
vation of a hatching-year Red-necked Phala-
rope ( Phalaropus lobatus ) on the salt pond of
Guana Island in October 2004 represented a
first record for that species in the Virgin Is-
lands.

DISCUSSION

Deriving longevity estimates from survi-
vorship models is preferable to using simple
longevity records (Krementz et al. 1989). The
reliability of survival estimates, however, de-
pends upon robust recapture data (e.g., Burn-
ham et al. 1987), which often are not available
for many species. Longevity records, there-
fore, are still valuable for providing some ba-
sic life-history information on little-studied
species. This may be especially true for island
settings, where longer-lived species are at
lower risk of localized extinction (Newton

1998). Although longevity records have been
reported for many North American bird spe-
cies (e.g., Kennard 1975, Klimkiewicz et al.
1983), little information is available on the
life spans of tropical birds (Snow and Lill
1974, Faaborg and Winters 1979, Johnston et
al. 1997). The few Caribbean bird species for
which there are longevity records are primar-
ily Puerto Rican (Faaborg and Winters 1979,
Woodworth et al. 1999), and there is virtually
no published information on the longevity of
birds in the eastern Caribbean. Thus, our data
provide new age records for several Caribbean
species. In Puerto Rico, Faaborg and Winters
(1979) recaptured 36 of 219 Bananaquits, the
oldest of which was 4 years and 7 months.
Outside of the Caribbean, de Souza Lopes et
al. (1980) reported a 4-year, 8-month-old Ba-
nanaquit from their study in Brazil. Our lon-
gevity record of 7 years for Bananaquits ex-
ceeds previous reports by a minimum of 2
years. Furthermore, our Bananaquit data sug-
gest that ages of 4 and 5 years are not uncom-
mon. Perhaps most unusual is our 9-year-old
age record for a Black-faced Grassquit, with
additional individuals aged 6 and 5 years.
These far exceed the previous report of 2
years and 1 1 months (Faaborg and Winters
1979). The 4-year-old Common Ground-Dove
in our study is similar to the longevity records
of 4 years and 4 years and 1 month from
Puerto Rico (Faaborg and Winters 1979).
However, the 5-year, 5-month-old Pearly-eyed
Thrasher reported by Faaborg and Winters
(1979) exceeds our oldest known thrasher by
1 to 2 years. We found no reports of longevity
for Caribbean Elaenia with which to compare
our records; however, our records of 7- and 5-
year-old Caribbean Elaenia are similar to
those reported for unspecified Elaenia spp. in
Brazil (6 years and 3 months, and 5 years; de
Souza Lopes et al. 1980) and substantially ex-
ceed ages recorded for Yellow-bellied Elaenia
(E. flavogaster ; 2 years and 1 1 months) and
Mountain Elaenia ( E . frantzii ; 3 years and 9
months) in Panama (Loftin 1975). We believe
that the 5-year-old Zenaida Dove from our
study also represents a longevity record for
that species, as we could find no reports with
which to compare our data.

Many of the Neotropical migrants captured
or sighted during our study are known to oc-
casionally occur in the BVI. Some of our

Boat et al. • BIRD SPECIES AND LONGEVITY ON GUANA ISLAND, BVI

223

sightings and captures, such as Hooded War-
blers ( Wilsonia citrina ) and Worm-eating
Warblers ( Helmitheros vermivorum), are un-
usual for the BVI. Still others, including Mag-
nolia Warbler, Golden-winged Warbler,
Swainson’s Thrush, and Red-necked Phala-
rope, provide new records for the BVI. De-
tections of Swainson’s Thrush and Red-
necked Phalarope were particularly interest-
ing. Within the Caribbean region, Raffaele et
al. (2003) indicated that Swainson’s Thrush
was found only rarely in the western Greater
Antilles and only during migration; thus, de-
tections of Swainson’s Thrush in 2 different
years on Guana Island was notable. Raffaele
et al. (2003) also indicated that Red-necked
Phalarope is a very rare migrant in the Ba-
hamas, Cuba, and Hispaniola (e.g.. Greater
Antilles); in Puerto Rico, the species has been
recorded only twice (Raffaele 1989). In Sep-
tember 2003, however, a Red-necked Phala-
rope was reported on Guadaloupe Island (Nor-
ton et al. 2003), which lies 400 km southeast
of Guana Island.

Our detections of Blackpoll Warbler and
Red-eyed Vireo, and our consistent detections
of other, less common species — such as Yel-
low-throated Vireo, Swainson’s Thrush, Indi-
go Bunting ( Passerina cyanea ), and numerous
warbler species — indicate that they may be
more common in the eastern Caribbean during
migration than previously believed due to a
lack of searching or banding efforts in that
region. For example, Blackpoll Warbler, the
most common warbler encountered on Guana
Island and the second-most frequently cap-
tured species overall, was not reported in the
BVI until 1989 (Norton 1990); it had been
considered a common Neotropical migrant
through the Greater Antilles but uncommon to
rare on other islands (Arendt 1992, Raffaele
et al. 2003). Similarly, Red-eyed Vireo was
thought to be very uncommon or vagrant in
the Lesser Antilles (Faaborg and Terborgh
1980, Arendt 1992, Norton 1996, Raffaele et
al. 2003); however, our regular sightings and
captures of Red-eyed Vireos suggest that the
species may be a more common migrant in
the BVI than previously believed.

Overall, our detections of species previous-
ly believed to be uncommon or not present
within the BVI may have been due to a lack
of field surveys and banding efforts through-

out most of the Virgin Islands and Lesser An-
tilles. Alternatively, our detections may be re-
lated to changes in habitat conditions in the
western Caribbean islands. As habitat avail-
ability decreases in the western islands, some
migrant species might be shifting their migra-
tion routes eastward (Arendt 1992). Regard-
less of possible shifts in migration routes, it
appears that Guana Island — a functional eco-
system protected as a nature preserve (Lazell
1996) — provides important habitat for both
resident and transient migrant species. A low-
occupancy, private resort occupies less than
2% of the surface area of Guana Island; the
remainder of the island is almost completely
free of direct human impacts and exists in a
near-natural state (Lazell 1996). Furthermore,
exotic herbivores and carnivores, which are a
severe problem throughout much of the Ca-
ribbean, occur at very low densities and are
heavily controlled on the island.

As larger islands in the Virgin Islands (e.g.,
Tortola, St. John, Virgin Gorda) continue to
undergo deforestation and development (e.g.,
Arendt 1992), smaller islands maintained in
primarily natural states are likely to become
increasingly important for conservation of
both resident and migrant birds. However,
small islands, such as Guana Island, may not
provide a full range of landscape characteris-
tics required for some migrant or wintering
Neotropical songbirds. For example. Northern
Parula ( Parula americana ) and American
Redstart ( Setophaga ruticilla), both common
nonbreeding residents in the Virgin Islands
(Raffaele et al. 2003), are seldom detected on
Guana. Further examination of resource use
and spatial needs of Neotropical songbirds mi-
grating through or wintering in the BVI is
needed to facilitate conservation efforts.

ACKNOWLEDGMENTS

We give our sincere thanks to G. Jarecki, H. Jarecki,
and the staff of Guana Island for their support and
facilitation of this research. We thank W. J. Arendt, A.
Olivieri, G. Perry, O. Perry, J. Richardson, P. Sibley,
A. Sutton, S. Valentine, and T. Willard for assisting
with banding operations and other logistics. Support
for the study was provided by The Conservation Agen-
cy through a grant from the Falconwood Foundation,
and by the U.S. Geological Survey Texas Cooperative
Fish and Wildlife Research Unit. This manuscript ben-
efited from the reviews and constructive comments of
G. Perry, R. L. Norton, and three anonymous reviewers.

224

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

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The Wilson Journal of Ornithology 1 1 8(2):225-236, 2006

REPRODUCTIVE BEHAVIOR OF THE YELLOW-CROWNED
PARROT C AMAZONA OCHROCEPHALA) IN WESTERN PANAMA

ANGELICA M. RODRIGUEZ CASTILLO1 3 AND JESSICA R. EBERHARD245

ABSTRACT. — We studied the breeding biology of the Panamanian subspecies of the Yellow-crowned Parrot,
Amazona ochrocephala panamensis, during 1997—1999 in the province of Chiriqm, Panama, to provide basic
information regarding the breeding behavior and reproductive success of these parrots in their natural habitat.
We recorded parrot behaviors throughout the reproductive period, monitored nest success, and characterized
occupied and non-occupied tree cavities. All breeding attempts involved a male-female pair. Clutch size ranged
from 2 to 4 eggs, which were incubated only by the female, beginning when the first egg was laid. Incubation
averaged 25 days and the eggs hatched asynchronously. During the incubation period, females remained inside
the nest for long periods of time, though they often departed from the nest area during early mornings and late
afternoons, presumably to forage; during this period, males were not observed entering the nest, though they
often remained nearby. During the nestling period, males contributed significantly to feeding the offspring. Pairs
nested in trees that were in good or fair condition, and did not favor cavities in any one tree species. As found
in many other field studies of parrots, breeding success was low. Only 10% (1997-1998) and 14% (1998-1999)
of the nests survived poaching and natural predation. Because nest poaching was the primary cause of breeding
failure and poses a serious threat to population viability, we also present data on poaching techniques and the
local trade of nestling parrots. Overall, the pool of breeding adults is likely made up of aging individuals that
are not being replaced, setting the stage for a rapid population decline. Received 13 January 2005, accepted 23
November 2005.

The genus Amazona consists of 3 1 species
distributed throughout the Neotropics (Juniper
and Parr 1998); however, the breeding biology
of only a few species has been studied (see
below). Nest poaching and the capture of
adult birds for the pet trade, together with hab-
itat loss due to deforestation, have contributed
to the precipitous decline of Amazona popu-
lations in Central America, South America,
and the Caribbean region (Forshaw 1989, Ju-
niper and Parr 1998, Wright et al. 2001). Like
many of the eight other subspecies that form
the Yellow-crowned Parrot complex (Juniper
and Parr 1998, Eberhard and Bermingham
2004), Amazona ochrocephala panamensis
has not escaped these pressures (Asociacion
Nacional para la Conservacion de la Natural-
eza 1995, Autoridad Nacional del Ambiente
1995a). In Panama, the population of this sub-
species has declined considerably due to nest

1 Escuela de Biologia, Univ. Autonoma de Chiriqm,
David, Panama.

2 Smithsonian Tropical Research Inst., Apdo. 2072,
Balboa, Panama.

3 Current address: Estafeta Universitaria, UNACHI,
David, Panama.

4 Current address: Biological Sciences Dept, and
Museum of Natural Science, 202 Life Sciences, Lou-
isiana State Univ., Baton Rouge, LA 70803, USA.

5 Corresponding author; e-mail: eberhard@lsu.edu

poaching (Ridgely 1981) and the loss of nest-
ing habitat to agricultural and cattle-grazing
activities (Autoridad Nacional del Ambiente
1995a, 1995b).

The breeding biology of a few Amazona
species has been studied in the wild; many of
these studies occurred on Caribbean islands
(Snyder et al. 1987, Gnam 1991, Rojas-Suarez
1994, Wilson et al. 1995) while others provide
information on mainland species (Enkerlin-
Hoeflich 1995, Enkerlin-Hoeflich and Hogan
1997, Renton and Salinas-Melgoza 1999, and
Seixas and Mourao 2002). Additional data on
breeding behavior come from studies of cap-
tive A. albifrons (Skeate 1984) and A. viridi-
genalis (Wozniak and Lanterman 1984). Over-
all, the studies have revealed that females typ-
ically spend long periods inside the nest dur-
ing the incubation and early nestling periods,
and depend, at least to some degree, on being
fed by their mates. Four Amazona species in
Mexico apparently select nest sites based on
tree species, size, cavity height, and entrance
size (Enkerlin-Hoeflich 1995, Renton and Sa-
linas-Melgoza 1999).

Wright et al. (2001) summarized data from
many field studies and showed that nest
poaching is a principal cause of reproductive
failure in Neotropical parrots, with poaching
rates being higher at mainland sites than on

225

226

THE WILSON JOURNAL OL ORNITHOLOGY • Vol. 118 , No. 2, June 2006

islands, and lower in protected areas (e.g., na-
ture reserves). While the impact of nest
poaching on parrot reproductive success is
clear, there are few studies that provide infor-
mation on specific techniques used by poach-
ers.

To date, there have been no published stud-
ies of the reproductive behavior of A. ochro-
cephala in Panama or other parts of its range.
Here, we report our observations of the spe-
cies’ breeding behavior, describe the charac-
teristics of nest sites and nest trees, and quan-
tify reproductive success during two breeding
seasons. We also present data regarding the
poaching techniques used in the study area.

METHODS

Study area. — Fieldwork was conducted dur-
ing the dry season (December-April) of
1997-1998 and 1998-1999 in the lowlands of
Corregimiento de San Juan (San Lorenzo dis-
trict) of the province of Chiriquf in western
Panama. The natural vegetation in the area is
tropical dry forest (following Holdridge’s
[1967] life zone classification) and mangrove,
but in many places it has been cleared for ag-
riculture and cattle grazing. Annual rainfall is
~ 1,000 mm; mean annual temperature is
—30° C, with mean temperatures of 35° and
28° C during the dry and rainy seasons, re-
spectively (Instituto de Recursos Hidraulicos
y Electrificacion 1998, 1999). The study area
was located at ~8° 17' 15" N, 82° 3' 10" W
and encompassed an area of ~8,800 ha;
~3,875 ha had been partially cleared for ag-
riculture and cattle grazing (on haciendas Mir-
aflores, El Tekal, and Los Asentamientos de
San Juan), and the remaining 4,925 ha were
mangrove. The partially cleared areas still
contained remnant patches of tropical dry for-
est dominated by Gliricidia sepium and Ery-
thrina fusca trees, the lower-statured Curatel-
la americana , and palms belonging to the gen-
era Roystonea and Acrocomia (Acosta 1996).

Characterization of nest sites. — During the
first breeding season (1997-1998), we only
studied nests found in the mangrove habitat;
in the following season (1998-1999), we ex-
tended our nest monitoring to include those
found in the partially cleared dry forest hab-
itat. We found 21 active nests during the 1st
year and 42 during the 2nd year. Of the nests
found in the 2nd year, 14 had been used by

parrots during the previous breeding season;
therefore, to avoid pseudoreplication, our data
on cavity and nest-tree characteristics repre-
sent 49 (and not 63) active nests. In the sec-
ond breeding season, 20 of the nests were
found in mangrove habitat, and the remaining
22 in the partially cleared dry forest.

To find nest cavities, we searched for trees
with cavities, observed parrots flying and vo-
calizing in the area, and interviewed local res-
idents and field laborers for information about
nesting parrots. Nests were considered active
if they contained A. o. panamensis eggs or
nestlings.

To determine the availability of cavities, we
searched for additional tree cavities near nest
trees. By searching the area surrounding an
occupied nest tree, we attempted to control for
larger-scale habitat variation (e.g., vegetation
density, canopy height, distance to feeding ar-
eas) that might have influenced cavity choice.
All trees within 100 m of each nest tree were
examined for the presence of large cavities
(i.e., cavities similar in size to those occupied
by parrots). For a given nest tree, two of the
surrounding trees found to contain cavities
were selected at random for inclusion in the
sample of unoccupied cavities. If a selected
tree contained more than one cavity, we se-
lected one of them at random to provide data
on cavity location and orientation. In the par-
tially cleared dry forest habitat, we extended
two of these searches beyond 100 m (108 and
1 16 m) in order to find trees with large cavi-
ties. Determining that a cavity was similar in
size to occupied cavities was admittedly sub-
jective; therefore, we do not present any anal-
yses comparing the dimensions of occupied
versus unoccupied cavities.

We used leaf, flower, and/or fruit samples
to identify the genus and species (where pos-
sible) of trees containing cavities. For each
cavity we measured horizontal and vertical
width of the cavity opening, inside vertical
depth and cavity diameter (measured at the
cavity floor), and distance from the ground to
the lower edge of the cavity opening (see
Saunders et al. 1982). Measurements were
made using a 30-m tape to a precision of 0.5
cm, and were used to calculate the areas of
the cavity entrance and cavity floor. For each
cavity, we noted its location relative to the
tree’s structure — branch (cavity completely

Rodriguez and Eberhard • REPRODUCTIVE BEHAVIOR OF AMAZONA OCHROCEPHALA 227

contained within a branch), trunk (cavity com-
pletely contained within the main trunk), and
branch/trunk (cavity at the intersection of a
branch and the trunk). We determined the ori-
entation of the cavity opening using a com-
pass, and measured each tree’s height using a
clinometer. We classified the physical condi-
tion of each tree — good, fair, poor, or dead —
using the scheme outlined by Sauad et al.
(1991; see also Saunders et al. 1982).

Behavioral observations. — We monitored
63 nests during the two breeding seasons: 21
during 1997-1998 and 42 during 1998-1999.
Of the 63 nests, 5 were selected each year for
detailed behavioral observations of parrots
(hereafter referred to as focal nests). In the
first field season, focal nests were chosen at
random; during the second field season, nests
were selected on the basis of their accessibil-
ity.

We made preliminary observations early in
the breeding season (prior to egg-laying) at
each of the focal nests. An observation period
lasted 13 hr (06:00 to 19:00 UTC-5). Each
year, we watched three of the five focal nests
for two preliminary observation periods, and
the other two were watched for a single ob-
servation period. In most cases (9 of 16 ob-
servation periods), we conducted preliminary
observations prior to capture of the focal in-
dividuals.

To identify the sex of focal individuals, we
used nets (set up at dawn) to capture one or
both members of each focal pair early in the
field season (prior to the onset of breeding).
We used nylon (4.5 X 15 m) and cotton (6 X
8 m) fishing nets (mist nets were not avail-
able) and suspended them using ropes and/or
poles over the nest opening or across a flyway
used by the birds. In both years, the sex of
each captured individual was identified in the
field by a veterinarian (R. De Obaldia) using
a laparoscope. We then marked the female on
the upper chest with Rhodamine B, so that she
could be distinguished from the male in sub-
sequent observations. Because the Rhodamine
B marks faded after several weeks, the birds
were subsequently marked passively by ap-
plying dye to the nest opening (see Eberhard
1998). This passive marking was done before
the prior markings had faded completely, so
that the identity of the newly marked birds
was known. With this technique, the birds in-

variably marked themselves on different parts
of the body with unique patterns, so the male
and female could be distinguished from one
another.

For the remainder of each focal pair’s
breeding attempt, we made behavioral obser-
vations at ~3-day intervals. We observed dur-
ing 3-hr periods when the parrots were most
active (either 06:30-09:30 or 15:45-18:45),
following the methodology used in other par-
rot studies (e.g., Eberhard 1998, Renton and
Salinas-Melgoza 1999). The results reported
here are based on 859 hr of nest observation
(208 hr were preliminary observations). We
observed nests with the aid of binoculars from
a distance of —15 m (the parrots quickly ha-
bituated to the observer’s presence). During
each observation period, we noted the follow-
ing: time spent by the adults inside the nest;
time spent in the nest area (defined as being
in visual range of the observer, which was ap-
proximately 50-75 m in the mangrove habitat
and approximately 100 m in the partially
cleared dry forest areas); number of other par-
rots traveling with the focal individual when
approaching or departing; and presence of
other humans in the nesting area. Other gen-
eral observations (allofeeding, allogrooming,
vocal and plumage displays, appearances of
nestlings at the cavity opening, age at which
young left the nest) were noted ad lib. When
adults made short visits to the nest, presum-
ably to feed young, we recorded total time in
the nest cavity. Focal nest observations were
made until 6 days after the last chick fledged,
or 6 days after a nest was depredated or
poached.

Three of the focal nests observed during the
first breeding season (1997-1998) were in
cavities that were re-occupied in the following
breeding season, and were considered focal
nests during the 2nd year of the study. Be-
cause it is possible that pairs used the same
cavity in consecutive years, our data might in-
clude some year-to-year pseudoreplication in
the focal-nest behavioral observations. The
adults were not permanently marked, so it was
impossible to determine whether this oc-
curred.

For the analysis of behavioral data, we di-
vided the breeding season into four stages:
pre-laying, laying, incubation, and nestling
periods. The laying period began with the lay-

228

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

ing of the first egg and extended until the last
egg was laid; the incubation period began with
the laying of the last egg and extended until
the last egg hatched (in fact, incubation began
when the first egg was laid, but for our data
presentation and analyses, we defined the in-
cubation period as described here to avoid
overlap of data from the laying and incubation
periods); the nestling period began with the
hatching of the last egg and extended until the
last nestling had fledged, or the nest was
poached or depredated.

Nest checks. — During the laying and incu-
bation periods, each focal and nonfocal nest
was checked daily and its contents inspected;
during the nestling period, we reduced the fre-
quency of checks to once per week. On days
when a focal nest was the object of behavioral
observations, the nest was checked at the con-
clusion of the observation period, or at least
2 hr before the start of an observation period.
This was done to minimize disruption of the
adults’ behavior. At each nest check, we noted
the presence of any new eggs (eggs were
numbered with a pencil), used calipers to
measure the dimensions (length and width) of
new eggs, and noted laying and hatching
dates. During the nestling period, we noted
morphological characteristics of the hatch-
lings and the emergence and locations of new
feathers, and recorded fledging dates. We also
noted evidence of cavity enlargement by the
parrots and presence of a nest lining. Al-
though the frequency of nest checks was re-
duced during the nestling period, we visited
nest trees 2 to 3 times per day in order to
maintain a presence that, we hoped, would re-
duce the likelihood that our study nests would
be poached.

Poaching interviews. — We obtained infor-
mation on the techniques used by parrot
poachers in the San Juan area through anon-
ymous interviews of individuals actively en-
gaged in the capture and sale of A. o. pana-
mensis. Poachers were contacted with the help
of an area resident who is familiar with the
parrot trade around San Juan. A consistent set
of questions or talking points was included in
each interview, but the respondents were en-
couraged to offer any information that they
might have regarding the parrots. The inter-
view questions focused on the poaching of A.
o. panamensis ; however, additional informa-

tion on other species was noted whenever
mentioned by the respondents. All interviews
were conducted by AMRC.

Statistical analyses. — Descriptive statistics
(mean ± SD, range, percentage) are presented
for nest site and behavioral data. Data from
the 2 years are presented separately in tables,
since the 2nd year included data from nests in
both partially cleared dry forest and mangrove
habitats; however, the descriptive statistics
presented in text summarize both years’ data.
We used the Lilliefors (Kolmogorov-Smirnov)
test to check for normality prior to performing
parametric tests. We performed chi-square
tests of independence to test the hypothesis
that parrots prefer cavities in certain tree spe-
cies. For each habitat, we compared the num-
ber of nests (occupied cavities) in different
tree species with the number of unoccupied
cavities in those species. Chi-square tests of
independence were also used to determine
whether parrots showed a preference for trees
in relatively good condition. We used circular
statistics (Batschelet 1981) to analyze the ori-
entation of nest-cavity openings, and per-
formed Rayleigh tests to determine whether
the orientations of occupied and unoccupied
cavities were random. These tests were per-
formed using R (R Development Core Team
2005); cavity openings facing upward were
excluded from the orientation analyses. We
performed a discriminant function analysis to
determine whether there were significant dif-
ferences between the dimensions of trees and
cavities containing successful nests versus the
dimensions of those with nests that were
poached or depredated. Discriminant function
analysis determines which variables (in our
case, nest dimensions) discriminate between
two or more groups (successful versus unsuc-
cessful nests), and identifies those variables
that contribute most to the differences be-
tween groups (Huberty 1994, Silva and Stam
1995). We employed a forward stepwise pro-
cedure to select among nine nest dimensions
(see Table 1), with entry and removal P-v al-
ues of 0.05. We used linear regression to as-
sess the degree to which time spent by the
females in the nest changed through the nest-
ling period. For analyses of data that were not
normally distributed, we used Mann- Whitney
U- tests and Wilcoxon tests. Statistical analy-
ses (with the exception of circular statistics)

Rodriguez and Eberhard • REPRODUCTIVE BEHAVIOR OF AMAZONA OCHROCEPHALA 229

TABLE 1. Dimensions of occupied cavities ( n —
of San Juan, Chiriqui, western Panama, 1997-1999.

49) of Amazona ochrocephala panamensis in the lowlands

Measurement

Mean ± SD

Range

Vertical depth (cm)

99.2 ±71.2

34.8-445.0

Internal width (cm)

26.8 ± 4.3

18.1-34.0

Internal length (cm)

26.8 ± 4.5

16.5-36.0

Area of cavity floor (cm2)

575.9 ± 175.1

257.3-907.9

Area of cavity entrance (cm2)

229.7 ± 63.0

149.8-380.1

Horizontal diameter of cavity entrance (cm)

15.6 ± 2.7

10.9-19.8

Vertical diameter of cavity entrance (cm)

17.2 ± 2.8

12.0-22.5

Height of cavity entrance (m)

12.4 ± 2.7

9.2-16.5

Height of nest tree (m)

19.2 ± 3.1

10.7-26.1

were performed using Statistica 6.0 (StatSoft,
Inc. 1998). For all tests, statistical significance
was set at a = 0.05 and means are presented
± SD.

RESULTS

Characterization of nest sites. — In our
study area, A. o. panamensis used a diversity
of tree species for nesting. In mangrove hab-
itat, active nest cavities were found in five tree
species: Rhizophora mangle, R. brevistyla,
Avicennia bicolor , Pelliciera rhizophorae,
Mora oleifera. In partially cleared dry forest
habitat, parrots were found nesting in two spe-
cies of palms, Roystonea regia. Cocos nuci-
fera, and in Ficus insipida trees. The most fre-
quently used tree species were R. regia (18 of
49 nests) and R. mangle (13 of 49 nests). The
tree species used least frequently were A. bi-
color and F. insipida, each of which was used
only once. Overall, parrots showed no pref-
erence for nesting cavities in any one tree spe-
cies in either mangrove or dry forest habitat
(mangrove: x2 = 0.813, df = 4, P = 0.94, n
= 27 nests; dry forest: x2 = 0.039, df = 2, P
= 0.98, n = 22 nests). Rather, the use of tree
species for nesting was proportional to cavity
availability in those species. We found no ev-
idence in either habitat type that any one tree
species is more likely to develop cavities than
the others (mangrove: x2 = 0.257, df = 4, P
= 0.99, n = 41 cavities; dry forest: x2 =
0.666, df = 2 ,P = 0.72, n = 25 cavities).

Characteristics of occupied and unoccupied
cavities. — Breeding pairs preferred cavities
that were relatively high above the ground and
with dimensions similar to those reported for
other Amazona species (see Table 1). The ori-
entation of occupied cavity openings was non-

random (Rayleigh test: r = 0.4408, P < 0.001,
n = 39), with a bias toward the northeast
quadrant (25 of 39 occupied nests had orien-
tations between 250° and 360°). In contrast,
the orientations of unoccupied cavities were
randomly distributed (Rayleigh test; r —
0.1495, P = 0.26, n = 61).

In both habitat types, we found that A. o.
panamensis preferred trees with single cavi-
ties (x2 = 41.49, df = 2, P < 0.001), possibly
because trees with more than one cavity were
in poorer condition than those with single cav-
ities. Indeed, parrots preferred trees in rela-
tively good condition. Forty-two of 49 (86%)
occupied trees were in good or fair condition,
while 56 of 98 (57%) unoccupied trees were
in poor condition or they were dead (x2 —
24.5, df = 1, P < 0.001). Comparing the lo-
cation of cavities (branch, branch/trunk, or
trunk) in occupied versus unoccupied trees in-
dicated that the parrots had no preference for
any particular cavity location (x2 — 0.807, df
= 2 , P = 0.67).

Pre-laying period. — We observed pairs of
A. o. panamensis prospecting for nest sites
early in each field season (13-30 December
1997, 21 December 1998-5 January 1999).
Both members of the breeding pair participat-
ed in nest prospecting. On four occasions, we
observed one of the two birds apparently take
the lead in cautiously approaching and inves-
tigating the cavity while its partner remained
perched in a nearby tree. Once a nest tree was
selected, but before egg-laying began, the fe-
male (sex was known for focal pairs once they
had been captured and marked) spent long pe-
riods of time within the nest cavity, while the
male remained perched at the entrance or
nearby. On two occasions in the mangrove

230

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

habitat, a focal female was seen taking a twig
into her nest cavity. In a third instance, an
individual (sex unknown) took a leafy twig
into its nest cavity in a M. oleifera tree. Inside
6 of the 49 monitored, occupied cavities, we
found wood chips and leaves — materials that
were a result of the parrots’ chewing activities
and/or brought in from outside the cavity.

Throughout the breeding season, pairs often
perched together, grooming each other’s neck,
head, and wings. We observed no copulations
or copulation attempts during our study. Prior
to the onset of egg-laying, the male occasion-
ally entered the nest cavity with the female
and remained inside for several minutes
(mean time inside = 3.40 ± 0.44 min, n =
17). During these visits, it is likely that he was
feeding the female, but it is also possible that
copulations occurred. As the egg-laying peri-
od approached, the female increased the
amount of time that she spent inside the nest
cavity, emerging for a few minutes at intervals
of 1. 5-2.5 hr to stretch her wings and legs
before returning to the cavity. During this pe-
riod, we observed eight instances in which the
male presented his mate with flowers of Ery-
thrina fusca or Gliricidia sepium, which the
female subsequently consumed.

Egg-laying and incubation periods. — Egg-
laying in the monitored nests (focal and non-
focal) occurred from 15 December to 3 Jan-
uary (1997-1998) and 24 December to 13
January (1998-1999). Clutch size averaged
3.08 ± 0.77 eggs over both years of the study
(Table 2), with no significant difference be-
tween years (Mann-Whitney (7-test: Z =
-0.584, P = 0.56, n = 63 clutches). The
mean laying interval was 2.16 ± 0.92 days
(Table 2). Incubation began when the first egg
was laid and was conducted exclusively by the
female. The incubation period lasted 25.14 ±
1.77 days.

During egg-laying and incubation, females
spent most of their time inside the nest or
perched nearby, and males were never seen
entering the nest cavity, although they often
remained perched nearby (Fig. 1). The amount
of time the male spent with the female during
the egg-laying period (the female’s fertile pe-
riod) versus during the incubation period did
not differ (Wilcoxon test: Z = 1.48, P = 0.14,
n = 10 breeding attempts). During incubation,
the female occasionally emerged from the nest

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Rodriguez and Eberhard • REPRODUCTIVE BEHAVIOR OF AMAZON A OCHROCEPHALA 23 1

■ Inside nest 0 Inside nest area □ Outside nest area

Laying Incubation Nestling

FIG. 1. Mean time (out of 180 min) spent by adult
Amazona ochrocephala panamensis parrots inside or
near the nest, by nesting stage. Data are presented sep-
arately for males (M) and females (F); error bars cor-
respond to standard deviations. Sample sizes refer to
the number of 3-hr observation periods. The number
of pairs observed was as follows: 1997-1998, n — 5
during laying, incubation, and nestling stages; 1998-
1999, n — 5 during laying and incubation stages, and
n = 4 during the nestling stage. Total observation
times were 27, 219, and 405 hr during the laying, in-
cubation, and nestling stages, respectively.

for a short time (8—17 min) to perch at the
cavity entrance or on a nearby branch, some-
times engaging in allogrooming with the male.
On 10 occasions, the male was observed feed-
ing the female near the nest. Males spent
much of their time in the nest area, and typi-
cally departed on two foraging trips per day —
one in the morning and the other in the late
afternoon. Early in the morning and late in the
afternoon, the female often left the nest area —
possibly to forage with the male (Fig. 1) — and
remained out of the nest area for 85.6 ± 11.5
min (range = 61-110 min). For 27 of 83 de-
partures, the pair departed with small groups
of two to four other parrots — conspecifics
and/or Amazona autumnalis. Upon their re-
turn, the pairs often flew in the company of
other parrots (30 of 83 arrivals). At the end
of the day, the male usually departed from the
nest area (65% of late afternoon observation
periods in 1997-1998, and 76% in 1998-
1999), either alone or with other parrots as
they passed by. On 1 1 occasions (involving
10 different nests), we made nocturnal nest
checks during the incubation period and ex-
amined the nest area with a flashlight; on only
three (27%) of the checks did we see the male
perched in the nest tree.

Nestling period. — Chicks hatched with their

eyes closed, and their bodies were covered
with a sparse white down that was later re-
placed by a gray down, as described by For-
shaw (1989). Nestlings spent just over 2
months in their nests before fledging, varying
somewhat between the 2 years of the study
(mean age at fledging in 1997-1998 = 68.6
± 5.36 days, n = 5 fledglings; mean age at
fledging in 1998-1999 = 78.3 ± 3.88 days, n
= 7 fledglings). Young fledged between 22
March and 5 April in 1998, and between 6
and 24 April in 1999; those hatched during
the 1 st year fledged in less time than did those
hatched during the 2nd year (Mann-Whitney
U-test: Z = —2.94, n = 12 fledglings, P =
0.003).

We made six nocturnal visits to nests and
on five of the visits (83%) the male was found
in the nest area, but never inside the nest cav-
ity; in three cases, he was perched near the
nest entrance, and twice he was perched a few
meters away in a nearby tree. On all six visits,
the female was inside the nest (on four of
these occasions, the female briefly came to the
nest entrance to look out and then quietly
went back inside; on the other two visits, she
exited the nest and returned —30 min later).

During the nestling period, we typically
found the female inside the nest as we began
each observation period (114 of 135 obser-
vation periods). She would spend much of her
time brooding recently hatched young, but as
the nestling period progressed, she decreased
the amount of time spent in the nest (linear
regression: Fl l32 = 419.08, P < 0.001, R2 =
0.76, b = -2.44). When outside of the nest,
she perched nearby and engaged in allo-
grooming with her mate and/or she left the
nest area, presumably to forage (Fig. 1). Each
day during this period, both the male and fe-
male would follow their foraging trips with
two to four short visits to the nest cavity, pre-
sumably to feed the nestlings (males: mean
duration - 5.5 ± 1.3 min, range = 2. 2-8. 3,
n = 135 observation periods; females: mean
duration = 5.1 ± 1.2 min, range - 2.4-7. 5,
n — 135 observation periods).

Nestlings acquired their plumage rather
slowly. The flight feathers were the first to
appear, with pin feathers for the remiges be-
ginning to emerge when nestlings were 16 to
28 days old. Green contour pin feathers on the
wings and yellow contour feathers on the head

232

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

began to unsheath at 26-30 days, and contour
feathers on the legs and back began to un-
sheath at 35-38 days. At —40-42 days, the
green feathers on the head and red feathers at
the bend of the wing began to unsheath. Fi-
nally, at —49-52 days, the tail feathers were
completely unsheathed. About 2 weeks before
leaving the nest, the nestlings began to perch
at the cavity opening. Fledging was asynchro-
nous, and the age at which young left the nest
ranged from 59 to 86 days (see Table 2). We
observed the nestlings’ first flight from the
nest on seven occasions; five flights occurred
in the morning and two in the late afternoon.
The first flights were relatively short (mean
distance = 34.6 ± 8.0 m, range = 25.0-48.5,
n = 1 fledglings), low, and quiet, and the
young were accompanied by one or both
adults. After the last chick in a clutch had
fledged, neither the young nor the adults en-
tered the nest cavity again; for at least 6 more
days, however, the adults continued to visit
the nest area. Breeding pairs whose nests were
poached by humans or failed due to natural
predation did not make a second breeding at-
tempt in the same cavity that year; however,
they continued to visit the nest area for at least
6 days following nest failure.

Breeding success. — We obtained productiv-
ity data for 63 breeding attempts (Table 2).
Overall, breeding success of A. o. panamensis
was very low. Over both breeding seasons,
only 12.7% (8 of 63) of nests fledged young.
Of the remaining nests, 9.5% (6 of 63) failed
due to natural predation at the nestling stage,
all of which we visually confirmed as preda-
tion by boas ( Boa constrictor). The principal
cause of breeding failure was nest poaching
by humans. A total of 77.8% of nests (49 of
63) were poached or presumed to have been
poached. Poachers accessed nest contents by
chopping holes in trunks at the level of the
nest cavity (17 of 49 poached nests), climbing
trees to reach nests (27 of 49), and less fre-
quently by felling trees (5 of 49). The disap-
pearance of nestlings often coincided with ev-
idence of machete cutting of understory veg-
etation near the nest tree (17 of 49 poached
nests).

Fourteen of the 19 cavities (74%) contain-
ing nests that failed due to predation or poach-
ing during the 1st year were reused during the
following breeding season. Only 8 of 49 cav-

ities monitored during one or both breeding
seasons housed nests that successfully fledged
young, but we found no evidence of a rela-
tionship between breeding success and the di-
mensions of nest trees or nest cavities. Dis-
criminant function analysis indicated that the
dimensions of trees and cavities containing
successful versus failed (poached or depredat-
ed) nests did not differ (Wilks’ Lambda =
0.7468, F9>39 = 1.47, P = 0.19, n = 49 nests);
only cavity depth contributed significantly to
the discriminant function (Wilks’ Lambda =
0.8953, P = 0.008).

Poaching techniques and illegal trade. —
Eighteen parrot poachers were interviewed,
and they described a range of poaching strat-
egies that included the removal of unhatched
eggs, newly hatched nestlings, fully feathered
nestlings, and the capture of recently fledged
juveniles. The majority of poachers (13 of 18)
preferred fully feathered nestlings —40 days
old and only one of the poachers took newly
hatched young (3 to 8 days old). Relatively
few poachers (2 of 18) took eggs from the
nest, and the remainder (2 of 1 8) preferred to
capture juveniles that had already fledged.
None of the poachers targeted adult parrots.

More than three quarters of the poachers
(14 of 18) considered the demand for A. o.
panamensis nestlings to be very high, and said
that they always had customers lined up to
purchase birds even before they had been tak-
en from their nests. Many of the poached birds
are sold locally to customers in Chiriqui, but
poachers indicated that vacationers from Pan-
ama City and truck drivers involved in the
transport of merchandise between Panama and
Costa Rica pay the highest prices (as much as
US$100 for a fully feathered and healthy par-
rot chick). Half of the poachers said that they
typically sold parrot nestlings for $40 or more;
most of the others (8 of 18, 44.4%) sold nest-
lings for $30-39, and only one of the poachers
sold nestlings for $20-29. Poachers were not
asked to reveal total annual earnings from
poaching, but five volunteered this informa-
tion: four indicated that they typically made
$200-350 per year and one said that he never
earned less than $200 annually and sometimes
made as much as $750 per year. For compar-
ison, the typical monthly salary for a farm la-
borer in the area is $130. According to a 1990
census (Direccion General de Estadistica y

Rodriguez and Eberhard • REPRODUCTIVE BEHAVIOR OF AMAZONA OCHROCEPHALA 233

Censo de Panama 1991), the human popula-
tion in the study area was approximately
2,358, but the number of people involved in
poaching activities is difficult to estimate.
Poaching of parrot nestlings is punishable by
fines of up to $1,000, but poachers indicated
that if they were caught, the authorities typi-
cally seized the nestlings and did not impose
any further punishment.

Fifteen of the poachers interviewed (83%)
said that they usually collected 6-9 nestlings
per breeding season, and the remaining indi-
viduals typically collected 2-5 nestlings per
season. Most of the poachers (13 of 18) said
that they have been collecting and selling par-
rot nestlings for 7-13 years, and the others
have done so for 1-6 years. Eleven poachers
(61%) noted that, in the past, they had also
taken A. autumnalis nestlings, but no longer
did so because this species is not a good im-
itator of human speech and therefore is much
less marketable than A. o. panamensis. Eight
poachers said that both of these species were
hunted for food in eastern Chiriqui, but five
of the men indicated that this practice is no
longer common, especially in the case of A.
o. panamensis , which could be sold for a rel-
atively high price. Recently, some poachers
have begun to use yellow dye on the forehead
feathers of A. autumnalis and even Aratinga
pertinax (both of which are less desirable than
A. ochrocephala in the pet trade), in order to
sell them to unsuspecting buyers as A. och-
rocephala (AMRC pers. obs.). These data in-
dicate that poaching of A. o. panamensis is not
a new phenomenon and has likely impacted
resident populations of the species by reduc-
ing recruitment of juveniles.

DISCUSSION

Characterization of nesting habitats and
cavities used for breeding. — Breeding pairs of
A. o. panamensis preferred relatively large
cavities high up in trees and palms. The di-
mensions of the cavities used by these parrots
was within the range of those reported for oth-
er Amazona species, such as A. vittata (Snyder
et al. 1987), A. leucocephala bahamensis
(Gnam 1991) and A. barbadensis (Rojas-Sua-
rez 1994).

We found no evidence that A. o. panamen-
sis prefers to nest in any one species of tree;
the frequency of nests in different tree species

reflected the frequency of cavity occurrence in
those species. Saunders (1979) found a similar
lack of preference in a study of Calyptorhyn-
chus baudinii latirostris\ in three of four nest-
ing areas studied, the dominant tree species
housed the majority of nests. Snyder et al.
(1987) found that most A. vittata nests are in
palo Colorado ( Cyrilla racemiflora ), but this
was due to the scarcity of cavities in other tree
species found in the parrots’ habitat. In our
study, breeding pairs preferred trees in good
or fair condition. This contrasts with the find-
ing of Sauad et al. (1991), who found that
72% of A. aestiva nests were in trees that were
in poor condition or dead. Similarly, Calypto-
rhynchus magnificus tended to nest in dead
trees more often than expected by chance
(Saunders et al. 1982).

In our study area in western Panama, we
found that openings of cavities occupied by
breeding A. o. panamensis tended to be ori-
ented toward the northeast. A similar prefer-
ence for certain orientations has been docu-
mented for several other parrots (Rodrfguez-
Vidal 1959, Saunders 1979; but see Saunders
et al. 1982, Sauad et al. 1991).

Breeding behavior. — The breeding behavior
of A. o. panamensis is similar to that reported
for other psittacids. Pairs are socially monog-
amous and both members of the pair contrib-
ute significantly to nest defense and caring of
young. Allofeeding of the female by her mate,
which we observed on several occasions, is
typical of breeding parrots (Skeate 1984, Sny-
der et al. 1987, Gnam 1991, Eberhard 1998),
especially early in the breeding cycle (Snyder
et al. 1987, Eberhard 1998). Nevertheless, fe-
male A. o. panamensis did not appear to de-
pend on their mates for food; they regularly
left the nest area with their mates, presumably
to forage.

Females typically laid eggs at 2-day inter-
vals, as reported for other congeners (A. vit-
tata, Snyder et al. 1987; A. leucocephala ba-
hamensis, Gnam 1991; and A. barbadensis,
Rojas-Suarez 1994), though they occasionally
laid eggs on successive days or at intervals of
up to 5 days. Clutch size varied from two to
four eggs, as reported for A. vittata (Snyder
et al. 1987), and the duration of incubation
was similar to that reported for other Amazona
parrots (Low 1972, Skeate 1984, Snyder et al.
1987, and Rojas-Suarez 1994). As in many

234

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

other parrots (Forshaw 1989), incubation be-
gan when the first egg was laid, resulting in
asynchronous hatching, and the female was
responsible for incubation. During incubation,
the female occasionally emerged from the nest
for a few minutes at a time to stretch, groom,
and participate in nest defense; in the early
morning and late afternoon she often departed
for longer times, possibly to forage. The sub-
stantial proportion of time spent outside of the
nest during this period was greater than that
reported for other Amazona parrots (e.g., Sny-
der et al. 1987, Wilson et al. 1995, Renton and
Salinas-Melgoza 1999). In A. vittata, low nest
attendance and long recesses by female par-
rots were associated with failed nesting at-
tempts (Wilson et al. 1997); we observed sim-
ilar behaviors in A. o. panamensis, but they
did not appear to negatively impact breeding
success, and the duration of incubation and
the number of eggs hatched per clutch in our
study were similar to those reported for other
Amazona parrots (Low 1972, Snyder et al.
1987, Gnam 1991, Rojas-Suarez 1994). The
long departures by A. o. panamensis females
might be due to habitat fragmentation in our
study area, which in turn has disrupted the
parrots’ foraging patterns, as observed by
Saunders (1990) in a study of Carnaby’s
Cockatoo ( Calyptorhynchus funereus latiros-
tris ) in agricultural areas.

During incubation, we never saw the male
enter the nest; this contrasts with observations
of A. albifrons (Skeate 1984) and A. vittata
(Snyder et al. 1987), in which males occa-
sionally enter the nest during this period. In
A. o. panamensis , the male spent much of his
time near the nest while his mate was incu-
bating, possibly to alert her to approaching
predators or prevent extra-pair copulations by
his mate with other males; however, the time
the male spent in the nest area did not differ
between the egg-laying (when the female is
fertile) and incubation periods, suggesting that
he was not mate-guarding.

The female was apparently responsible for
feeding the newly hatched chicks, but a few
days after the eggs had hatched, the male be-
gan to enter the nest regularly, presumably to
feed the young. This also has been reported
for other Amazona parrots, including A. albi-
frons (Skeate 1984), A. 1. bahamensis (Gnam
1991), and A. vittata (Snyder et al. 1987, Wil-

son et al. 1995). As the nestlings grew, the
female gradually reduced the amount of time
she spent in the nest with them. She ceased
brooding the young during the day when the
oldest nestling was 18 to 25 days old, similar
to that observed in other Amazona species
(e.g., Snyder et al. 1987, Enkerlin-Hoeflich
and Hogan 1997, Renton and Salinas-Melgoza
1999).

Chicks of a single clutch usually fledged on
different days, as reported for A. vittata (Sny-
der et al. 1987) and A. 1. bahamensis (Gnam
1991). Mean age at fledging was greater than
that reported by Snyder et al. (1987) for A.
vittata , by Rojas-Suarez (1994) for A. barba-
densis , and by Renton and Salinas-Melgoza
(1999) for A. finschi. As described for A. 1.
bahamensis (Gnam 1991), fledglings were ac-
companied by one or both parents on their
first flight, but the flights of A. o. panamensis
fledglings were shorter. After leaving the nest,
A. o. panamensis fledglings were very quiet,
probably to avoid attracting the attention of
predators; similar cryptic behavior has been
observed in A. vittata (Snyder et al. 1987).

Breeding success. — In our study area, the
breeding success of A. o. panamensis was low,
principally due to poaching, and to a lesser
extent to natural predation by boas. Habitat
loss due to deforestation, which often involves
felling of the largest trees, has been cited as
an important cause of population declines
among parrots (Juniper and Parr 1998). How-
ever, in the case of A. o. panamensis in west-
ern Panama, our results indicate that breeding
is not limited by the availability of nesting
sites, even though much of the area has been
partially cleared. The very low rate of breed-
ing success is instead due to extremely high
poaching rates fueled by demands of the local
pet trade. Low salaries and the lack of em-
ployment opportunities in the San Juan area
undoubtedly drive individuals to poach parrot
nestlings. Although the activity is illegal and
punishable by fines of up to $1,000, anti-
poaching laws are only weakly enforced. Be-
cause favored poaching techniques are fo-
cused on collecting nestlings, recruitment into
the A. o. panamensis population is severely
reduced, and the population is in danger of a
rapid and precipitous decline as the adults age
and are not replaced by individuals from
younger age classes.

Rodriguez and Eberhard • REPRODUCTIVE BEHAVIOR OF AMAZONA OCHROCEPHALA 235

ACKNOWLEDGMENTS

We thank the owners and laborers of Hacienda El
Tekal, Hacienda Miraflores, and Hacienda Los Asen-
tamientos de San Juan for their collaboration and for
allowing access to their properties. Partial financial
support was provided by the German Technical Co-
operation Agency through its Proyecto Agroforestal
Ngobe-ANAM-GTZ. We are grateful that some of the
parrot poachers were willing to reveal information
about their activities, which may help in developing
future conservation measures. We also thank the resi-
dents of the Corregimiento de San Juan, especially
those engaged in the collection and sale of parrots in
the local pet trade, for sharing information on their
poaching activities. Two poachers were helpful in lo-
cating nests as well as establishing contacts with
poachers and others involved in the local parrot trade.
We thank K. Harms for assistance with performing sta-
tistical tests in R, and F. Gomez and E. de Morris for
their comments on an early version of the manuscript;
the manuscript also benefited from extensive com-
ments provided by three anonymous reviewers.

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The Wilson Journal of Ornithology 1 1 8(2):237-243, 2006

GREGARIOUS NESTING BEHAVIOR OF THICK-BILLED PARROTS
(. RHYNCHOPSITTA PACHYRHYNCHA) IN ASPEN STANDS

TIBERIO C. MONTERRUBIO-RICO,1’3 JAVIER CRUZ-NIETO,2
ERNESTO ENKERLIN-HOEFLICH,2 DIANA VENEGAS-HOLGUIN,2
LORENA TELLEZ-GARCIA,1 AND CONSUELO MARIN-TOGO1

ABSTRACT. — We studied Thick-billed Parrot ( Rhynchopsitta pachyrhyncha) nest-site density and social nest-
ing behavior from 1998 to 2001 in Madera, Chihuahua, Mexico. The species formed high-density nesting
clusters; 45 nesting attempts (30%) involved nesting pairs sharing nest trees, with a maximum of three nesting
pairs per tree. The majority of nest trees were live or dead quaking aspens ( Populus tremuloides ). Clusters
contained a mean of 11.5 breeding pairs (5 nests/ha). The highly social nesting behavior of Thick-billed Parrots
may have important implications for management and conservation of their breeding habitat. Received 31 March
2005, accepted 8 January 2006.

Approximately 13% of all bird species nest
in colonies (Gill 1990). Colonial or gregarious
nesting behavior provides important advantag-
es for birds, including mate access, reduced
probability of nest predation, improved detec-
tion and defense against aerial predators while
feeding, and enhanced foraging efficiency
(Siegel-Causey and Kharitonov 1990, Dan-
chin and Wagner 1997, Eberhard 2002). De-
spite the advantages of colonial nesting, nest-
site availability may be a limiting factor for
social species, especially those that nest in
tree cavities (Eberhard 2002).

Colonial nesting is uncommon in tree-cav-
ity nesting species and it is particularly rare
among Neotropical parrots for two reasons:
(1) closely spaced tree cavities with suitable
characteristics for nesting are rare, and (2)
most parrot species are territorial around nest
sites (Forshaw 1989, Munn 1992, Inigo-Elias
1996). Of the 231 parrot species, Eberhard
(2002) reported that only 3 breed colonially.

In Mexico, 20 parrot species nest in tree
cavities, 4 of which (genus Aratinga ) also nest
in termitaries (Hardy 1963, Forshaw 1989,
Howell and Webb 1995, Rodrfguez-Estrella et
al. 1995). Both Maroon-fronted Parrots ( Rhyn-
chopsitta terrisi) and Military Macaws ( Ara

1 Lab. de Manejo y Conservation de Fauna Silves-
tre, Facultad de Biologfa, Univ. Michoacana de San
Nicolas de Hidalgo, Morelia, Michoacan, Mexico.

2 Centro de Calidad Ambiental, Inst. Tecnologico y
de Estudios Superiores de Monterrey, Monterrey, Nue-
vo Leon, Mexico.

3 Corresponding author; e-mail:
tiberio@zeus.umich.mx

militaris ) sometimes nest at high densities in
cliff crevices, thus forming nesting colonies
(Forshaw 1989, Macfas-Caballero 1998). Pri-
or to our study, cavity-nesting parrot species
in Mexico were not thought to nest colonially
in tree cavities, nor had there been reports of
multiple pairs nesting within the same tree
(Enkerlin-Hoeflich 1995, Renton and Salinas-
Melgoza 1999). Although most parrots are so-
cial and have been considered “suppressed
colonial breeders” (Ward and Zahavi 1973),
the relative density of suitable tree cavities is
low and competition for cavities is high
(Munn 1992, Gibbs et al. 1993).

The Thick-billed Parrot ( Rhynchopsitta pa-
chyrhyncha) is a highly social species that
breeds at elevations from 2,000 to 2,700 m in
mature and old-growth coniferous forests in
the northern portions of the Sierra Madre Oc-
cidental, northwestern Mexico. Social behav-
iors include the formation of foraging flocks,
sentinel posting during foraging, simultaneous
courtship and copulations of several pairs in
neighboring trees, loud vocalizations of neigh-
boring nesting pairs, synchronized defense
against raptors, and the formation of large, no-
madic flocks in winter (Lanning and Shiflett
1983; Snyder et al. 1994, 1999). Even when
distances among nests are substantial, males
of neighboring nesting pairs communicate and
wait for each other when forming foraging
flocks (Snyder et al. 1999, Monterrubio-Rico
and Enkerlin-Hoeflich 2004b).

After decades of intensive logging, few
large fragments of old-growth forest remain in
the Sierra Madre Occidental; thus, the number

237

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THE WILSON JOURNAL OF ORNITHOLOGY • Vol 118, No. 2, June 2006

110° 100° 90°

FIG. 1. Thick-billed Parrot study area near Madera, Chihuahua, Mexico, 1998-2001.

and quality of Thick-billed Parrot nesting ar-
eas has been reduced and the availability of
food resources has probably been altered
(Lanning and Shiflett 1983, Benkman 1993,
Lammertink et al. 1996). Only five nesting ar-
eas are known to remain in the species’ breed-
ing range, and two of them (Cebadillas de Ya-
huirachi and Madera) encompass >70% of the
known nesting trees (Monterrubio-Rico and
Enkerlin-Hoeflich 2004a). Our objectives
were to evaluate nest-site use, nest-tree distri-
bution, density of nesting pairs, and tree shar-
ing by nesting pairs.

METHODS

The study area was near Madera, Chihua-
hua, at the eastern edge of the Sierra Madre
Occidental, (29° 19' N, 108° 1 1' W; Fig. 1).
Common tree species included Douglas-fir
( Pseudotsuga menziesii ), white fir {Abies con-
color ). Mexican white pine ( Pinus ayacahui-
te), and quaking aspen {Populus tremuloides).
We monitored breeding activity from July to
late October in 1998-2001. The total area sur-
veyed for nests increased each year from 5 ha

in 1998 to 75 ha in 2001. Because time, per-
sonnel, and access to nesting areas were lim-
ited, however, we were unable to completely
sample and map the distributions of aspen
stands and nest trees.

We found nests by conducting intensive
searches during the prospecting and courtship
phases of the nesting cycle. A tree cavity was
considered a potential nest site if a nesting
pair was observed entering the cavity during
the egg-laying period (late July). When pos-
sible, we used climbing equipment to confirm
presence of eggs or nestlings; inaccessible tree
cavities were confirmed as nesting cavities
when nestlings could be heard or adult parrots
were observed feeding nestlings. A tree cavity
was considered a roost site if it was used by
the parrots but never contained eggs. Because
nesting parrots were not individually marked,
it is likely that some birds were sampled in
multiple years; thus, we report our results in
terms of nesting attempts rather than number
of pairs.

For each nest tree, we documented species,
condition (live or dead), diameter at breast

Monte rrubio-Rico et al. • THICK-BILLED PARROT GREGARIOUS NESTING

239

TABLE 1. Use of nest and roost trees by Thick-billed Parrots, Madera, Chihuahua, Mexico, 1998-2001.

Parameter

Number per year

1998

1999

2000

2001

1998-2001

Nesting pairs (attempts)

147

Nest trees

123a

Nest trees used by one pair

102

Nest trees with >1 pair

Nesting pairs sharing a tree

Trees used as roost sites

a72 different nest trees: 40 used once, 18 used twice, 9 used three times, 5 used four times = 123.

height (dbh), cavity height, and tree height.
The coordinates of each nest tree were ob-
tained with a Geographic Positioning System
(GPS), and locations were plotted on topo-
graphic maps (scale 1:50,000). Distances be-
tween neighboring nesting trees were mea-
sured with a 50-m tape or determined from
GPS coordinates (for trees >100 m apart).
Nest-tree distribution was analyzed with Geo-
graphic Information System software (GIS;
Arc View 3.3) using geographic coordinates
with six decimals. GIS was also used to gen-
erate a map and analyze nest distribution.

We defined a “colony” as an aggregation
of interacting neighboring groups of nesting
pairs. We used the minimum convex polygon
criterion to define nesting clusters, where a
cluster consisted of >3 nests, each <150 m
from any other nest; the significance level was
set at a = 0.05 and means are presented ±
SD. Statistical analyses were performed with
SAS (SAS Institute, Inc. 1985).

RESULTS

During 4 years of study, we documented
147 nesting attempts in 72 different trees; we
also documented 10 different trees used as
roost sites. We monitored 48 of the nest trees
for at least 2 nesting seasons and found that
33 (68%) were reused in subsequent years;
mean annual reuse was 62 ± 0.08% (range =
56-71%). Eighty of the 82 trees used for nest-
ing or roosting were aspen, and 2 were Mex-
ican white pine. Aspen snags (n = 39) and
live aspen ( n = 41) were used with similar
frequency, and 25% ( n = 18) of the snags
were severely deteriorated (total absence of
bark). The majority of all 147 nesting attempts
(86%) occurred in tree cavities that appeared
to be old woodpecker holes, but 20 nesting
attempts (14%) occurred in natural cavities

formed by tree decay and detachment of large
branches. We also recorded 30 cavities used
as roost sites (Table 1).

Sixty-nine percent (102) of the nesting at-
tempts involved only one pair of parrots per
nest tree. The 45 remaining attempts (30%),
however, involved more than one pair per tree:
18 attempts involved two nesting pairs using
different cavities in the same nest tree, and
three times we observed three nesting pairs
sharing different cavities in the same tree (Ta-
ble 1). We found more nesting pairs in 2001
C n = 73) than in other years (Table 1), but that
was also the year in which the greatest area
(75 ha) was searched for nests.

Overall, the parameters of trees containing
multiple cavities did not differ significantly
from those containing only one cavity. Nest
trees containing >1 active nest did not differ
in dbh (Wilcoxon Z = 0.38, P = 0.70; mul-
tiple-nest trees: 57.0 ± 12.2 cm; single-nest
trees: 57.8 ±11.9 cm) or tree height (Wilcox-
on Z = 1.82; P = 0.068; multiple nest trees:
28.0 ± 5.4 m; single nest trees: 24.7 ± 6.0
m). Vertical distance between nest cavities in
multiple-nest trees ranged from 1 to 1 1 m
(mean = 4.3 ± 2.9 m). Nest-cavity height
ranged from 6.5 to 31 m above ground in sin-
gle-nest trees and from 9 to 21 m (lowest cav-
ity) in multiple-nest trees.

Most nest trees used by Thick-billed Parrots
showed a clumped distribution pattern, form-
ing aggregations (nest clusters) in aspen
stands (Fig. 2). Mean nest cluster area was 2.3
± 1.7 ha, (range = 0.04-4.4 ha), and mean
within-cluster nest density was 20.9 ± 32.6
per ha (range = 2.4-100 nests/ha; Table 2).
Mean within-cluster distance between active
nests was 31.9 ± 26.4 m (range = 1.8-146
m, n = 147), and mean distance between clus-

240

THE WILSON JOURNAL OL ORNITHOLOGY • Vol. 118, No. 2, June 2006

1998 1999

• Single nests *

\ 500 0 500 1,000

▲ Multiple nests [\

LIG. 2. Diagram showing the distribution of nesting trees, by year, in 1 1 Thick-billed Parrot nesting clusters
in Madera, Chihuahua, Mexico. Nesting clusters were defined using the minimum convex polygon criterion.
Capital letters indicate the different clusters, filled circles represent nest trees with one nest, and triangles
represent nest trees with two or three nests.

ters was 325 ± 125 m (range = 185-458 m,
n — 11). The mean number of nesting at-
tempts per cluster was 11.5 ± 8.1 (range =
3-31).

No agonistic behavior was observed among
nesting pairs. Neighboring nesting pairs were
in permanent contact: synchronized foraging
flocks formed every morning and communi-
cation among pairs occurred with loud vocal-
izations and visual contact. We also observed
five events of collective responses to raptors,
in which parrots rapidly formed a flock after
sharp alarm calls had been emitted by the par-
rots that first detected the raptors.

DISCUSSION

Nest site density. — The Thick-billed Parrot
is a social species that tolerates other nesting
pairs, often in the same nest tree. Previously,

Lanning and Shiflett (1983) had observed two
active nests (only 2 m apart) in a pine snag.
They also observed two pairs nesting in a
large aspen within 215 m of three other nests
and within 1 km of six additional nests. How-
ever, we observed considerably greater nest
density and number of nesting pairs sharing
nest trees than those reported by Lanning and
Shiflett (1983) and Snyder et al. (1999). The
mean distance between active nests (31.9 m)
and the shortest distance (1.8 m) between
nesting pairs of Thick-billed Parrots were the
smallest values reported for any cavity-nesting
parrot species in Mexico. For example, the
same values for Lilac-crowned Parrot ( Ama -
zona finschi ) in the tropical subdeciduous for-
ests of the Chamela-Cuixmala Biosphere Re-
serve were 948 m and 25 m, respectively
(Renton and Salinas-Melgoza 1999). The

TABLE 2. Characteristics of Thick-billed Parrot nest clusters in aspen stands, Madera, Chihuahua, Mexico, 1998-2001.

Monterrubio-Rico et al. • THICK-BILLED PARROT GREGARIOUS NESTING

241

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m tn a\
— ^ ni o

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m os cn in

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T o
^ o

2 7

^ o o
non

cn in q
n d d n
— cn

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I

o it
o (N

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m «n id

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^ ni in
LJ i i
i T T
oo — < in

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o — : in

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2 S

O J3
GO

.5 c
S

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O .3

<D <D

s s

clumped nest distribution and multiple nests
per tree of Thick-billed Parrots observed in
Madera may be explained by (1) the existence
of adequate tree cavities at high densities and
(2) the species’ high level of sociality and tol-
erance of neighboring nesting pairs. It also
may be that nesting pairs experience lower
rates of predation by selecting tree cavities
near other pairs.

Conservation and management recommen-
dations.— In addition to high nest density, we
also documented >50% reuse of cavities by
Thick-billed Parrots. Lanning and Shiflett
(1983) recorded lower nest densities and a
lower level of cavity reuse (1 of 12 nesting
cavities in good condition were reused). High
nest density and reuse of cavities may indicate
a scarcity of adequate nesting cavities in the
surrounding conifer forests. Several authors
have addressed the alarming reduction in the
extent of old-growth conifer forests in the Si-
erra Madre Occidental and its negative impact
on the Thick-billed Parrot (Lanning and Shi-
flett 1983, Lammertink et al. 1996, Snyder et
al. 1999). As a result of habitat loss, most of
the nesting activity is now concentrated in two
areas (Cebadillas de Yahuirachi and Madera),
making the species vulnerable to the effects
of illegal logging, forest fires, and conifer crop
failures (Benkman 1993, Snyder et al. 1994,
Monterrubio-Rico and Enkerlin-Hoeflich
2004a).

A fundamental conservation goal for Thick-
billed Parrots should be to increase the num-
ber of nesting areas. This can be achieved by
protecting stands of old-growth in all current
and historical nesting areas, especially those
in the high-elevation (2,000-3,000 m) forests
of Durango and Chihuahua. Because trees
large enough to support suitable cavities may
take 4 decades or more to form, nest boxes
should be erected to augment nest-site avail-
ability. Although it remains unknown whether
Thick-billed Parrots will use nest boxes in the
wild, they are known to use them in captivity
(Snyder et al. 1994). Retaining old-growth co-
niferous forest will also ensure seed avail-
ability (Benkman 1993) and nesting opportu-
nities for other obligate cavity nesters, such as
Eared Quetzal ( Euptilotis neoxenus), and
Mexican Spotted Owl (Strix occidentalis lu-
cida ) — species that nest in the same habitats
as Thick-billed Parrot.

242

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

Areas managed for Thick-billed Parrots
should include tree species commonly used as
nest sites, such as Mexican white pine, Doug-
las-fir, and aspen. In addition, pine species
such as Durango pine ( Pinus durangensis ),
teocote pine ( Pinus teocote ), Chihuahuan pine
( Pinus leiophylla ), and Apache pine ( Pinus
engelmannii), should be included to provide a
constant cone crop (Snyder et al. 1999). Al-
though stands of large aspen are uncommon
in conifer forests of the Sierra Madre Occi-
dental, aspens can be planted in more humid
areas selected for restoration.

Populations of Thick-billed Parrots are rel-
atively small, even in the most important nest-
ing areas. Thus, the species’ recovery will re-
quire sustained periods of high nesting suc-
cess and productivity. This can be achieved
only by providing parrot populations with ad-
equate nesting opportunities across the land-
scape.

ACKNOWLEDGMENTS

We appreciate the help and advice of N. F. R. Sny-
der, R. B. Hamilton, K. Renton, M. S. Hafner, C. Ma-
cias, M. A. Cruz-Nieto, C. Valle, and J. Shiflett. Fi-
nancial support was provided by CONABIO (Mexico
Biodiversity Commission), Sacramento Zoo, National
Fish and Wildlife Foundation, Arizona Game and Fish
Department, USFWS/SEMARNAT program in Biodi-
versity Conservation for NAFTA initiative. Wildlife
Preservation Trust, Fondo Sectorial Ambiental SE-
MARNAT-CONACYT, Centro de Calidad Ambiental
at Instituto Tecnologico y Estudios Superiores de Mon-
terrey, and the School of Renewable Natural Resources
at Louisiana State University. We thank the Coordi-
nacion de Investigation Cientifica and Facultad de
Biologfa at Universidad Michoacana de San Nicolas
de Hidalgo for their continued logistical and economic
support, and the Direction General de Vida Silvestre
at SEMARNAT, which provided research authoriza-
tions. We also thank J. W. Wiley and two anonymous
reviewers who made important suggestions that im-
proved this manuscript.

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Short Communications

The Wilson Journal of Ornithology 1 18(2):244- 247, 2006

No Extra-pair Fertilization Observed in Nazca Booby
{Sula granti ) Broods

David J. Anderson134 and Peter T. Boag1 2 3 4

ABSTRACT. — Nazca Booby ( Sula granti) broods in
the Galapagos Islands showed 0% extra-pair fertiliza-
tion, based on multilocus band-sharing values. The
95% Cl of this estimate for all chicks was 0-0.098,
and for all broods it was 0-0.139. These are the first
data on extra-pair paternity to be reported for a mem-
ber of the family Sulidae. Received 6 September 2005,
accepted 22 February 2006.

The frequency of extra-pair paternity (EPP)
among bird species varies widely, from 0% in
some seabirds (e.g., Chinstrap Penguins, Py-
goscelis antarctica ; Moreno et al. 2000), the
Acorn Woodpecker (Melanerpes formicivo-
rus\ Dickinson et al. 1995, Haydock et al.

2001) , and other taxa (Griffith et al. 2002) to
72% in Superb Fairy-wrens ( Malurus cy-
aneus\ Mulder et al. 1994, Double and Cock-
burn 2000). Application of new molecular ge-
netic techniques has enabled the recent explo-
sion in availability of parentage data from
birds, and estimates of EPP exist for at least
186 species in at least 39 families (Griffith et
al. 2002, Spottiswoode and Mpller 2004). Of
particular interest is the minority (25%) of so-
cially monogamous taxa in which EPP is ab-
sent, or nearly so (Griffith et al. 2002). In de-
parting from the general trend in birds, these
taxa may experience selection pressures, or
phylogenetic constraints, that differ from
those of most species, and they can provide
insight into the evolution of the vast diversity
of mating systems in birds. The majority of
the diversity in EPP frequency is at or above
the family level in birds (Arnold and Owens

2002) ; thus, comparative analyses (Bennett

1 Dept, of Avian Sciences, Univ. of California, Da-
vis, CA 95616, USA.

2 Dept, of Biology, Queens Univ., Kingston, ON
K7L 3N6, Canada.

3 Current address: Dept, of Biology, Wake Forest
Univ., Winston-Salem, NC 27109, USA.

4 Corresponding author; e-mail: da@wfu.edu

and Owens 2002, Westneat and Stewart 2003)
require data from as many higher-order taxa
as possible.

Here, we present parentage data from Naz-
ca Boobies {Sula granti ), a socially monoga-
mous seabird in the family Sulidae, for which
published data on EPP frequency is lacking.
While Nazca Boobies exhibit life-history
characteristics associated with a low EPP rate
(Bennett and Owens 2002) — such as long life,
extended parental care, and small broods (An-
derson 1993, Anderson and Apanius 2003) —
they nest colonially in the presence of many
potential copulatory partners (Nelson 1978),
females spend extended periods unattended in
the colony while their mate forages at sea, and
they have unusually low hatching success
(60%) due to infertility or early embryo death
(Anderson 1990). The low hatching success
could be due to low sperm quality in some
males, which might induce females to select
for insurance sperm outside the pair bond, al-
though other aspects of their life history sug-
gest that EPP should be rare.

In 1990, we studied Nazca Boobies breed-
ing at the large colony at Punta Cevallos, Isla
Espanola, Galapagos Islands, Ecuador (1°20'
S, 89° 40' W). Huyvaert and Anderson (2004)
give details of the study site. We collected
blood samples from 10 single-chick broods
(January 1990, with unknown initial clutch
and brood sizes) and 13 two-chick broods
(December 1990) and their social parents
(adults that brooded the young). In this pop-
ulation, clutch size is either one or two (An-
derson 1990); hence, the December sample al-
most certainly represents complete families,
but we are not certain about initial clutch or
brood size of the January sample. Single-
chick broods in the first sampling effort were
the products of single chicks from one- or
two-egg clutches, or the survivor of obligate
siblicide (almost always the first-hatched

244

SHORT COMMUNICATIONS

245

chick) in a two-chick brood (Humphries et al.
2006). Two-chick broods were targeted in the
second sampling effort to determine whether
siblicide masked a high EPP rate in second-
hatched chicks. Families were chosen ran-
domly from across the colony and had typical
distances to neighboring sites (mean = 2.7 m
± 1.55 SD; Anderson 1993). Using syringes,
we drew blood samples from the brachial vein
and transferred them to vacutainers. Blood
was stored in Queens lysis buffer (Seutin et
al. 1991) at ambient temperature in the field
and later at 4° C. DNA was extracted from the
blood samples following the procedures of
Seutin et al. (1991). After testing various com-
binations of restriction enzymes and multilo-
cus probes for quality and quantity of bands,
all booby DNA was cut with Mbo I and hy-
bridized with radioactively labeled minisatel-
lite probes 33.15 (Jeffreys et al. 1985) and per
(Shin et al. 1985). Electrophoresis, Southern
blotting, and prehybridization followed Smith
et al. (1991), except that we used 5 pg of
DNA per sample, and Immobilon (Millipore)
transfer membranes. Transfer membranes
were hybridized, washed, and autoradio-
graphed following Smith et al. (1991), except
that the membranes were washed in 2X SSC,
0.1% SDS. After probing with both minisa-
tellites, the membranes were probed a third
time with lambda DNA to reveal lambda size
markers in each lane to facilitate scoring of
homologous fragments in different lanes.

We assessed parentage of nestlings by com-
paring bands in the 2- to 12-kb range of nest-
lings with those of their putative parents on the
autoradiographs. Bands were scored by mark-
ing acetate sheets, using different colors for
maternally and paternally derived bands. Bands
were considered identical if their centers were
less than 1 mm apart and they did not differ
greatly in density. We calculated the degree of
band-sharing between putative parents and off-
spring to determine whether we could exclude
a parent and, if so, which one. Band-sharing
(D) was calculated as D = 2 {nAB)/{nA + «B)>
where nAB is the number of bands shared by
birds A and B, and nA and nB are the number
of bands in birds A and B, respectively (Wetton
et al. 1987). Both Jeffreys 33.15 and per probes
produced DNA fingerprints similar to those de-
scribed for other bird species. Band-sharing
was calculated as the mean of the D values of

the two probes. We used the band-sharing of
mates as an estimate of the band-sharing of
unrelated birds, and used that estimate to eval-
uate the relationship of putative parents and
their offspring. Because the probability of a
brood having two chicks increased with in-
creasing band-sharing values (logistic regres-
sion, x2 = 4.34, df = 1, P = 0.037), we eval-
uated the January 1990 and December 1990
groups separately; generally, band-sharing was
greater in the December sample, for all pair-
wise analyses of family members. Because
there was no a priori difference in how fami-
lies were selected in the two sampling periods,
and given that the two sets of DNA fingerprints
were prepared by different lab workers at dif-
ferent times, the difference in average similar-
ity values may have resulted from methodolog-
ical differences, not biological differences in
relatedness.

In one-chick broods, band-sharing of mated
pairs averaged 0.330 ± 0.115 SD; band-shar-
ing between offspring and mothers averaged
0.617 ± 0.076 and that between offspring and
fathers averaged 0.625 ± 0.066. The smallest
band-sharing value between an offspring and
a parent (0.533) exceeded the largest value of
band-sharing in mated pairs (0.527; Fig. 1).
These non-overlapping distributions provide
no indication of extra-pair parentage in one-
chick broods.

In two-chick broods, band-sharing of mated
pairs averaged 0.418 ± 0.106; band-sharing
between offspring and mothers averaged
0.699 ± 0.073, and between offspring and fa-
thers it averaged 0.680 ± 0.117. Although
four band-sharing values between an offspring
and a parent were less than the largest value
of band-sharing in mated pairs (0.564; Fig. 1),
they do not provide reliable evidence of extra-
pair parentage. In three cases (indicated by pa-
rentheses in Fig. 1), DNA degradation in pa-
rental samples caused low band-sharing val-
ues between all members of the family, in-
cluding between the mated adults. The
offspring in this family displayed no unattrib-
utable bands, indicating that the putative par-
ents were in fact the genetic parents. This was
the lone instance of poor quality DNA among
our samples. In the remaining two cases (in-
dicated by the rotated parentheses in Fig. 1),
the identity of the social father was questioned
on behavioral grounds after blood samples

246

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

FIG. 1 . Distribution of band-sharing values in
Nazca Booby broods, expressed as cumulative per-
centages from lowest to highest values. Dotted vertical
lines show the maximum band-sharing value for un-
related adults (mated pairs). Values in parentheses are
the result of either poor quality DNA (•) or uncertain
parentage S. Blood samples were collected in January
and December 1990 at Punta Cevallos, Isla Espanola,
Galapagos, Ecuador.

had been taken from the two offspring and
two adults present at the nest site. At the time
of sampling, we had observed a male standing
near the female and offspring, and assumed
that he was the social father; on subsequent
days, however, another male consistently at-
tended this brood and the original male in-
stead appeared to be a neighbor. We were not
able to obtain a blood sample from the other
putative father. This was the one instance in
which family membership was uncertain.
Omitting these two families from consider-
ation, all band-sharing values of offspring and
putative parents exceeded the largest band-
sharing value of mated adults in two-chick
broods (0.564; Fig. 1). Excluding the four
chicks of the two questionable broods, our es-
timate of EPP frequency in the 32 chicks was
0 (95% Cl = 0-0.109), and in the 21 broods
it was also 0 (95% Cl = 0-0.162).

This low EPP frequency of Nazca Boobies
conforms to the expectations based on empir-
ical data from other long-lived seabirds (Grif-
fith et al. 2002) and theoretical considerations
of the likely selection forces acting on such
species (Mauck et al. 1999, Bennett and

Owens 2002, Westneat and Stewart 2003). It
also matches behavioral data showing that fe-
male boobies cooperate with extra-pair males
in permitting extra-pair copulation; during the
8 days preceding egg-laying, however, they
engage almost exclusively in within-pair cop-
ulations (DJA unpubl. data). Thus, while ex-
tra-pair copulation (EPC) is common in both
the Nazca Booby (61% of females had >1
EPC; DJA unpubl. data) and the related Blue-
footed Booby ( S . nebouxir, Osorio-Beristain
and Drummond 1998), EPP is not (see also
Hunter et al. 1992, Schwartz et al. 1999). The
benefits, if any, of EPC to females appear un-
related to any genetic benefits, such as fertil-
ization insurance that could result from ob-
taining extra-pair sperm. This intriguing dis-
parity between a high frequency of EPC and
a low rate of EPP places the Nazca Booby in
an unusual position in the spectrum of avian
mating systems that merits further study.

ACKNOWLEDGMENTS

We thank the Servicio Parque Nacional Galapagos
for permission to conduct this study, the Charles Dar-
win Research Station and TAME airline for logistical
support, I. von Lippke and P. R. Sievert for field as-
sistance, and D. F. Westneat and two anonymous re-
viewers for helpful comments. The University of Cal-
ifornia Agricultural Experiment Station and the Natu-
ral Science and Engineering Research Council provid-
ed financial support.

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in boobies. 1. A test of the insurance-egg hypoth-
esis. American Naturalist 135:334-350.
Anderson, D. J. 1993. Masked Booby ( Sula dactyla-
tra). The Birds of North America, no. 73.
Anderson, D. J. and V. Apanius. 2003. Actuarial and
reproductive senescence in a long-lived seabird:
preliminary evidence. Experimental Gerontology
38:757-760.

Arnold, K. E. and I. P. F. Owens. 2002. Extra-pair
paternity and egg dumping in birds: life history,
parental care and the risk of retaliation. Proceed-
ings of the Royal Society of London, Series B
269:1263-1269.

Bennett, P. M. and I. P. F. Owens. 2002. Evolutionary
ecology of birds: life histories, mating systems and
extinction. Oxford University Press, New York.
Dickinson, J., J. Haydock, W. Koenig, M. Stanback,
and F. Pitelka. 1995. Genetic monogamy in sin-
gle-male groups of Acorn Woodpeckers, Melaner-
pes formicivorus. Molecular Ecology 4:765—769.
Double, M. and A. Cockburn. 2000. Pre-dawn infi-
delity: females control extra-pair mating in Superb

SHORT COMMUNICATIONS

247

Fairy-wrens. Proceedings of the Royal Society of
London, Series B 267:465-470.

Griffith, S. C., I. P. F. Owens, and K. A. Thurman.
2002. Extra pair paternity in birds: a review of
interspecific variation and adaptive function. Mo-
lecular Ecology 1 1:2195-2212.

Haydock, J., W. D. Koenig, and M. T. Stanback.
2001. Shared parentage and incest avoidance in
the cooperatively breeding Acorn Woodpecker.
Molecular Ecology 10:1515-1525.

Humphries, C. A., V. D. Arevalo, K. N. Fischer, and
D. J. Anderson. 2006. Contributions of marginal
offspring to reproductive success of Nazca Booby
(Sula granti) parents: tests of multiple hypotheses.
Oecologia 147:379-390.

Hunter, F. M., T. Burke, and S. E. Watts. 1992. Fre-
quent copulation as a method of paternity assur-
ance in the Northern Fulmar. Animal Behaviour
44:149-156.

Huyvaert, K. P. and D. J. Anderson. 2004. Limited
dispersal in the Nazca Booby. Journal of Avian
Biology 35:46-53.

Jeffreys, A. J., V. Wilson, and S. L. Thein. 1985.
Hypervariable ‘minisatellite’ regions in human
DNA. Nature 314:67-73.

Mauck, R. A., E. A. Marschall, and P. G. Parker.
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parentage: effects on male parenting decisions.
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Moreno, J., L. Boto, J. A. Fargallo, A. de Leon,
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Mulder, R. A., P. O. Dunn, R. A. Cockburn, K. A.
Lazenby-Cohen, and M. J. Howell. 1994. Help-
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extra-pair mate choice. Proceedings of the Royal
Society of London, Series B 255:223-229.

Nelson, J. B. 1978. The Sulidae: gannets and boobies.
Oxford University Press, Oxford, United Kingdom.

Osorio-Beristain, M. and H. Drummond. 1998. Non-
aggressive mate guarding by the Blue-footed Boo-
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Schwartz, M. K., D. J. Boness, C. M. Schaeff, P.
Majluf, E. A. Perry, and R. C. Fleischer. 1999.
Female-solicited extrapair matings in Humboldt
Penguins fail to produce extrapair fertilizations.
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Seutin, G., B. N. White, and P. T. Boag. 1991. Pres-
ervation of avian blood and tissue samples for
DNA analyses. Canadian Journal of Zoology 69:
82-90.

Shin, H.-S., T. A. Bargiello, B. T. Clark, F. R. Jack-
son, and M. W. Young. 1985. An unusual coding
sequence from a Drosophila clock gene is con-
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Smith, H. G., R. Montgomerie, T. Poldmaa, B. N.
White, and P. T. Boag. 1991. DNA fingerprinting
reveals relation between tail ornaments and cuck-
oldry in Barn Swallows, Hirundo rustica. Behav-
ioral Ecology 2:90-98.

Spottiswoode, C. and A. P. M0ller. 2004. Extrapair
paternity, migration, and breeding synchrony in
birds. Behavioral Ecology 15:41-57.

Westneat, D. F. and I. R. K. Stewart. 2003. Extra-
pair paternity in birds: causes, correlates, and con-
flict. Annual Review of Ecology and Systematics
34:365-396.

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Walters. 1987. Demographic study of a wild
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The Wilson Journal of Ornithology 1 18(2):247-251, 2006

Golden-cheeked Warbler Males Participate in Nest-site Selection

Allen E. Graber,134 Craig A. Davis,1 and David M. Leslie, Jr.2 3 4

ABSTRACT. — Nest-site selection behaviors have
rarely been described for songbirds. Furthermore, male
involvement in nest-site selection is generally assumed
to be minimal among most species, especially those

1 Dept, of Zoology, Oklahoma State Univ., 430 Life
Sciences West, Stillwater, OK 74078, USA.

2 Oklahoma Coop. Fish and Wildlife Research Unit,
U.S. Geological Survey, Oklahoma State Univ., 404
Life Sciences West, Stillwater, OK 74078, USA.

3 Current address: Arizona Game and Fish Dept.,
Research Branch, 2221 W. Greenway Rd., Phoenix,
AZ 85023, USA.

4 Corresponding author; e-mail: agraber@azgfd.gov

predominantly exhibiting female nest building. This
assumption has held true for the federally endangered
Golden-cheeked Warbler ( Dendroica chrysoparia ), a
breeding resident of central Texas. We observed Gold-
en-cheeked Warbler males and females searching for
nest sites together on three separate occasions, 2001-
2003. Although rare, such observations add to our
knowledge of the life history of songbirds. Received
20 April 2005, accepted 11 January 2006.

For a breeding pair of birds, the nest-site
selection process can be a critical step in es-

248

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

tablishing a pair bond; certainly, the site se-
lected will often affect the pair’s reproductive
success (Martin 1998). The final choice of
nest placement, whether made by the male,
female, or both, will likely be influenced by
several factors (e.g., local resource availability
[presence of nesting materials, food], inter-
and intraspecific competition, and habitat fea-
tures influencing microclimate, brood parasit-
ism or predation) that contribute to the quality
and quantity of fledglings reared (Martin and
Roper 1988). Recent literature on this topic
has focused on gaining a better understanding
of the relationship between nest placement
and predation (e.g., Wilson and Cooper 1998,
Siepielski et al. 2001, Boulton et al. 2003, Da-
vis 2005) — the leading cause of reproductive
failure in birds and a significant selective
force on avian breeding behaviors (Ricklefs
1969, Martin 1992). Far less attention has
been given to how birds actually select a site.

Information on the behavioral processes in-
volved in nest-site selection for wood war-
blers, including the federally endangered
Golden-cheeked Warbler ( Dendroica chryso-
paria), is generally lacking (Morse 1989,
Ladd and Gass 1999). In a review of The
Birds of North America series, we found that
information on the nest-site selection process
is well described for only 15 of the 51 wood
warblers (families Parulidae and Peucedrami-
dae). Furthermore, among species predomi-
nantly exhibiting female nest building, the
role of the male in nest-site selection is often
assumed to be minor (Kaufman 1996, Ladd
and Gass 1999). With few exceptions (see
Ficken 1964, Meanley 1971, Nolan 1978),
males have been observed only mate-guarding
and singing subdued, infrequent songs, while
females actively engage in nest-site selection
activities (Pulich 1976, Guzy and Lowther
1997, Wright et al. 1998).

Few data exist on the nest-site selection
processes of Golden-cheeked Warblers (Ladd
and Gass 1999), although aspects of their
breeding biology and nesting characteristics
have been described in detail (Bent 1953, Pul-
ich 1976, Ladd and Gass 1999). The Golden-
cheeked Warbler is a habitat specialist with a
limited range. Its nesting habitats are closed-
canopy, low-growing woodlands dominated
by mature Ashe juniper ( Juniperus ashei) and
oaks ( Quercus spp.; Ladd and Gass 1999).

Such habitats are restricted to limestone
slopes, canyons, and adjacent uplands in the
Edwards Plateau and Llano Uplift of central
Texas (Pulich 1976, Kier et al. 1977). Nests
are constructed by the female with strips of
mature Ashe juniper bark and are typically
placed in Ashe junipers, but sometimes in
oaks or other hardwoods. Nests are usually
located in the upper two-thirds of a tree, av-
eraging 5-7 m above ground (Pulich 1976).

In the only comprehensive study of Golden-
cheeked Warblers, Pulich (1976) wrote that
the male might accompany the female in her
search for a nesting site. He described an ob-
servation made on 1 April 1961, in which a
female — paying no attention to her mate —
flew to the ground and picked at unidentified
objects, briefly investigated an old nest in a
juniper, and flew across a ravine to another
tree; the male guarded his mate, actively
chased an approaching satellite male, and sang
infrequently. Pulich (1976) concluded that the
female chooses the nest site, but he gave no
description of the behavioral repertoire in-
volved in her selection of the site. Pulich
(1976:82) did acknowledge that he had likely
missed some sexual displays that play a role
in establishing the pair bond because “the
courtship of the Golden-cheeked Warbler
seems to be carried on in utmost secrecy.” In
another study, Golden-cheeked Warbler males
were observed presenting strips of juniper
bark to their mates, but courtship displays
were not observed prior to nest building
(Lockwood 1996).

Here, we document male and female Gold-
en-cheeked Warblers actively searching for
nest sites together on Fort Hood, an active
U.S. Army installation in Bell and Coryell
counties, Texas (31° 10' N, 97° 45' W). We re-
corded these events during a 3-year study in-
volving detailed behavioral observations of
color-banded Golden-cheeked Warbler males.

On 2 April 2003 at 13:15 CST, a Golden-
cheeked Warbler male was heard singing the
“A-song,” a song-type associated with male-
female interactions (Bolsinger 2000). The pair
was observed displaying nest-site trying be-
haviors (Ficken 1964) in several tree forks
within a cluster of shin oaks ( Q . sinuata ). Try-
ing behaviors were characterized by both the
male and the female squatting simultaneously
or alternately in potential nearby sites while

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249

vigorously pivoting clockwise and counter-
clockwise. Pivots, consisting of half-rotations
(180°) and up to two full rotations (720°), in-
cluded outward and downward extension of
wings and upward elevation of the tail. Ex-
tension of the limbs may have provided tactile
information about the suitability of the site
(Nolan 1978).

Interruptions to trying pivots included
pressing the breast, belly, and sides against
limbs as if “nest-shaping,” attentively exam-
ining the site, or hopping to other prospective
sites (all within the same shin oak cluster). At
times, the female appeared to gather infor-
mation from her “advertising” mate and re-
sponded to his trying behavior by approaching
the potential nest site as soon as he left. In
general, female nest-site inspection behaviors
seemed to be more persistent than those of her
mate, who infrequently sang a muted A-song,
exhibited mate-guarding behavior, and paused
more often. These activities lasted —180 sec.

On 4 April 2003 at 1 1:05, we observed the
same female collecting juniper strips and then
flying to a nest under construction, 24 m away
from the previously observed trying location
and 4.5 m above ground in the outer branch
of an Ashe juniper. The female appeared to be
in her 1st day of nest construction, as a nest
platform was beginning to take shape. There
was no sign of her mate at that time.

Similar nest-site trying behaviors were re-
corded on two separate occasions — one in
2001 (1 April at 13:12) and one in 2002 (29
March at 10:47). In each case, we observed
females in the initial phases of nest-building
3 days following our observations of trying
behaviors. These nest-site selection activities
differed somewhat from those observed in
2003 with respect to the observation duration
(estimated mean for both observations = 70
sec), the degree of male participation (less in
2001; fewer pivot maneuvers in 2002, but a
similar proportion of time spent hopping to
prospective sites), the tree species in which
nest-site trying took place (Ashe juniper in
2001 and 2002), and the distance between the
nest-site trying site and the actual nest site
(mean distance for both observations = 23 m).

Although detailed information on the be-
havioral processes of nest-site selection is
rare, trying or sizing prospective nest sites —
by examining the site, squatting, depressing

the sternal region, nest-shaping, pivoting, el-
evating the tail, and extending the feet and
wings — is common among several warbler
species (e.g., American Redstart [Setophaga
ruticilla ; Ficken 1964], Cerulean Warbler
[Dendroica cerulea\ Oliarnyk and Robertson
1996], Prairie Warbler [D. discolor, Nolan
1978], and Swainson’s Warbler [ Limnothlypis
swainsonii ; Meanley 1971]). Reports of war-
bler males participating in these activities,
however, are highly unusual (Morse 1989).

Our three observations of trying behaviors
constitute the only such behaviors we wit-
nessed during our study, and we did not ob-
serve males or females performing trying ac-
tivities on their own. In another study, Nolan
(1978) found that male Prairie Warblers be-
haved very much like their mates in 10% of
about 300 observations. In the other 90% of
Nolan’s observations, the male followed and
watched the female, performed display flights,
and sang irregular, muted songs. Similarly,
American Redstart males have been observed
only occasionally trying sites while their mates
also perform trying activities (Ficken 1964).
Meanley (1971), Robinson (1990), and Oliar-
nyk and Robertson (1996) reported male
Swainson’s Warblers, Louisiana Waterthrushes,
and Cerulean Warblers (respectively) engaged
in similar nest-site trying behaviors with their
mates, but they did not specify the frequency
at which these behaviors occurred. Meanley
(1971) also reported that male Swainson’s War-
blers might examine nest sites alone.

Interestingly, the males of species considered
most closely related to Golden-cheeked War-
blers (e.g.. Black-throated Green Warbler [D.
virens], Hermit Warbler [ D . occidentalism,
Townsend’s Warbler [. D . townsendi], and Black-
throated Gray Warbler [ D . nigrescens]) do not
appear to participate in nest-site selection. The
females either “size” or “examine” prospective
sites (Black- throated Green and Townsend’s
warblers; Morse 1993 and Wright et. al 1998,
respectively) or settle into a fork and flit around
for 5-15 sec (Black-throated Gray Warbler;
Guzy and Lowther 1997), while the male fol-
lows closely and infrequently utters soft songs.
This apparent difference in nest-site selection
strategy and display may be a function of the
secretive behavior exhibited by these species
during pair formation; it is certainly plausible
that active male participation occurs in these

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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

species, but has simply not yet been observed.
Based on well-studied warbler species, Morse
(1989:169) reasoned that species’ repertoires are
extensive, making explicit comparisons among
species difficult to derive: . major differenc-

es may lie in the frequency with which a display
is performed, rather than the ability to perform
it.” Alternatively, males of species closely re-
lated to the Golden-cheeked Warbler may not
exhibit similar nest-site selection activities be-
cause visual displays in wood warblers are not
necessarily correlated with phylogeny (Morse
1989). Lovette and Bermingham (1999) suggest
that adaptive differences in behavioral charac-
ters exhibited by DencLroica species may have
developed long after their explosive speciation.

Male birds may exhibit varying degrees of
participation in nest-site selection by (1) se-
lecting the site alone, (2) mate-guarding to
protect their genetic investment, (3) perform-
ing displays to synchronize the pair’s repro-
ductive cycle, and/or (4) performing displays
to determine an actual location that shows the
most promise for successfully fledging young.
Hansell (2000) suggests that increased paren-
tal care by both parents can be found among
species in which both sexes build the nest to-
gether; perhaps the same holds true for species
exhibiting joint male-female nest-site selec-
tion. In a review of The Birds of North Amer-
ica species accounts, we identified 96 species
from 1 1 orders and 35 families in which both
sexes actively engage in nest-site selection.
Among these species, both sexes participate
in feeding young in 81 (98%) of the 83 spe-
cies where at least one sex feeds young. Close
relatives of the Golden-cheeked Warbler, how-
ever, all exhibit biparental feeding (as is ex-
pected in nidicolous species), but do not ap-
pear to show biparental nest-site selection
(Morse 1993, Guzy and Lowther 1997, Wright
et al. 1998, Ladd and Gass 1999). The life-
history traits (e.g., long-term pair bonds, role
of sexes in parental investment) common to
avian species that engage in joint male-female
nest-site selection deserve additional study.

ACKNOWLEDGMENTS

We thank J. L. Sterling Graber for co-observing the
2003 nest-site selection behavior and subsequently lo-
cating the nest. We also thank numerous field techni-
cians and volunteers, including M. Atkinson, V. Bump,
B. C. Cook, K. Cutrera, J. L. Granger, K. J. Moore, H.

Oswald, H. Schreiber, and R. K. Williams, who tire-
lessly spent hours in the field for our concurrent study
dealing with the tolerance of Golden-cheeked Warblers
to nonconsumptive recreation. C. M. Abbruzzesse, A.
D. Anders, P. M. Cavanagh, J. D. Cornelius, D. C. Dear-
born, T. J. Hayden, D. M. Herbert, S. Jester, D. L. Koeh-
ler, R. I. Leyva, B. Peak, C. E. Pekins, and M. M. Stake
provided assistance with project planning, initiation, and
logistical support. We thank R. T. Churchwell, S. Davis,
C. G. Ladd, S. A. McClure, T. J. O’Connell, J. H. Rap-
pole, and an anonymous reviewer for commenting on
earlier versions of this manuscript. Funding for our re-
search was provided by the Department of the Army
and was administered by the U.S. Army Construction
Engineering Research Laboratory and the Oklahoma
Cooperative Fish and Wildlife Research Unit
(Oklahoma State University, Oklahoma Department of
Wildlife Conservation, U.S. Geological Survey, and
Wildlife Management Institute cooperating). Informa-
tion contained in this manuscript does not necessarily
reflect the position or policy of the government, and no
official endorsement should be inferred.

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havior. Cambridge University Press, Cambridge,
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Kaufman, K. 1996. Lives of North American birds.

Houghton Mifflin, Boston, Massachusetts.

Kier, R. S., L. E. Garner, and L. F. Brown, Jr. 1977.
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Ladd, C. and L. Gass. 1999. Golden-cheeked Warbler
( Dendroica chrysoparia). The Birds of North
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Lockwood, M. W. 1996. Courtship behavior of Golden-
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ries B 266:1629-1636.

Martin, T. E. 1992. Interaction of nest predation and

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Nolan, V., Jr. 1978. The ecology and behavior of the
Prairie Warbler ( Dendroica discolor). Ornitholog-
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Oliarnyk, C. J. and R. J. Robertson. 1996. Breeding
behavior and reproductive success of Cerulean

Warblers in southeastern Ontario. Wilson Bulletin
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Pulich, W. M. 1976. The Golden-cheeked Warbler: a
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The Wilson Journal of Ornithology 1 18(2):25 1-254, 2006

Provisioning of Magellanic Woodpecker ( Campephilus magellanicus)
Nestlings with Vertebrate Prey

Valeria S. Ojeda12 and M. Laura Chazarreta1 2

ABSTRACT.— During the 2003-2004 and 2004-
2005 nesting seasons, we studied parental behavior at
seven Magellanic Woodpecker ( Campephilus magel-
lanicus) nests in Argentine Patagonia. Food items de-
livered to nestlings included wood-boring larvae
(57.6%), arachnids (13.1%), and vertebrates (4.6%, in-
cluding a bat, lizards, and avian eggs and nestlings).
Less frequent items were adult insects, caterpillars, and
pupae. Small, unidentified invertebrate prey made up
19.8% of the observations. Males delivered most of
the large prey (wood-boring larvae and vertebrates;
61.7%), while females brought most of the small prey
(arachnids and small, unidentified invertebrates;
79.6%), suggesting differences in foraging strategies
between sexes. This is the first published account of
Magellanic Woodpeckers provisioning nestlings with
vertebrates. The frequency of Magellanic Woodpecker
predation on vertebrates outside of the breeding sea-
sons is unknown. Received 26 January 2005, accepted
5 December 2005.

1 Univ. Nacional del Comahue, Depto. de Zoologia
y Ecologia, 8400 Bariloche, Argentina.

2 Corresponding author; e-mail:
campephilus @bariloche.com.ar

Although several woodpecker species (es-
pecially melanerpine species) regularly prey
on the nestlings and eggs of other birds, and
a small number of species occasionally cap-
ture lizards or even mice, picids are generally
not considered to be important predators of
vertebrates (Short 1982, del Hoyo et al. 2002).
The diet of the Magellanic Woodpecker ( Cam-
pephilus magellanicus ), the largest Neotropi-
cal picid, remains largely unstudied; the spe-
cies is considered a specialist predator of
large, wood-boring larvae (Short 1970, 1982).
There is only one record of a Magellanic
Woodpecker capturing vertebrate prey (a liz-
ard, Liolaemus sp.; Ojeda 2003), and, based
on what was known about the species’ diet,
the event was reported as opportunistic. Re-
cent observations, however, suggest that ver-
tebrate predation by the Magellanic Wood-
pecker may be more common than previously
believed. Here, we present data on food

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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

items — including vertebrates — delivered to
nestlings.

METHODS

From November to January (2003-2004
and 2004-2005 nesting seasons), we studied
parental behavior of Magellanic Woodpeckers
in native lenga ( Nothofagus pumilio ) forests
near Bariloche (41° 08' S, 71° 12' W) in Na-
huel Huapi National Park, Argentine Patagon-
ia. The area is characterized by lakes, glacial
valleys, and mountain slopes covered by for-
ests dominated by southern beech {Nothofa-
gus spp.). Elevations range from 400 to 3,480
m, the mean annual temperature is 8° C, and
winds are predominantly westerly. Annual
rainfall ranges from 500 to 2,000 mm and oc-
curs primarily in winter (Paruelo et al. 1998).

The study was carried out at two forested
sites (Challhuaco Valley and Otto Mount) lo-
cated 15 km apart. Forest composition was
similar between the two sites, but Otto Mount
was being intensively logged at the time of
our observations. Throughout the nesting sea-
son, we observed the woodpeckers’ daily rou-
tine at seven nests once per week, from dawn
to dusk (—06:00-21:00 UTC-3). We found
one nest at the Otto Mount site and six at the
Challhuaco Valley site. We made our obser-
vations from ground blinds 10-20 m from
nest trees, and observed woodpeckers with 8X
binoculars and a 25 X spotting scope. Nests
were watched for a total of 654 hr (41 days;
5-9 days/nest).

Because of marked sexual dimorphism
(Short 1970) and strong territoriality (VSO
pers. obs.), adults did not need to be marked.
Magellanic Woodpeckers normally made one
or more stops before going to the nest en-
trance, and once there, they perched for a few
seconds before feeding nestlings. This per-
mitted identification of the more conspicuous
prey items to at least the level of class. Iden-
tification of prey to the species level was
made via direct observation of predation
events or during laboratory analysis of prey
items found at the bottom of nest cavities (in-
spected every 5—10 days).

During the first 3 weeks of the nestling pe-
riod, the adults normally entered the nest cav-
ity either without prey or with items too small
to be detected (Ojeda 2004). Because we saw
no vertebrate prey delivered during this time,

we assumed that vertebrate prey were not de-
livered to nestlings until they were older.
Hence, the provisioning data analyzed in this
paper correspond to the middle and last parts
of the nestling period (nestlings 20-48 days
of age, on average), when prey were large
enough to be detected.

RESULTS AND DISCUSSION

We recorded 852 deliveries of conspicuous
prey at seven nests. Total deliveries per nest
ranged from 72 to 180. Males made 52.6%
(range = 38.0-74.6%) of all prey deliveries,
while females delivered 47.4% (range =
23.4-62.0%).

Most identified prey were wood-boring lar-
vae, arachnids, and vertebrates (Table 1). Ver-
tebrate prey was delivered to all nests, pri-
marily by males; most “vertebrates” deliv-
ered by females were birds’ eggs (n = 4). Al-
though small sample sizes precluded statistical
testing for differences in feeding behavior
among pairs or sexes, large prey (wood-boring
larvae and vertebrates) were mostly (61.7%)
brought by males, while small prey (arachnids
and unidentified small invertebrates) were
mostly (79.6%) brought by females, suggest-
ing potential differences in foraging strategies
between sexes. Short (1970) proposed such
differences in foraging behavior based on the
species’ sexual dimorphism in bill size.

Based on their slender shape and dark col-
oration, the lizard prey we observed were
most likely Liolaemus sp. (N. Ibargiiengoytia
pers. comm.). The eggs delivered to the nests
varied in coloration from white, to pink, to
Niagara-green and were small- to medium-
sized. Although we did not identify many of
the nestling prey items (n = 14) delivered to
woodpecker nestlings, at least one individual
of seven species (mostly passerines) was iden-
tified: Patagonian Sierra-Finch ( Phrygilus pa-
tagonicus ), Austral Thrush ( Turdus falcklan-
dii ), House Wren {Troglodytes aedon), Thom-
tailed Rayadito {Aphrastura spinicauda ),
Striped Woodpecker {Picoides lignarius).
White-throated Treerunner {Pygarrhichas al-
bogularis), and Fire-eyed Diucon {Xolmis py-
rope). On several occasions, lizards and nest-
lings brought by adults were so large that they
could not be swallowed by the woodpecker
nestlings. In such cases, after several failed
feeding attempts, the prey was left at the bot-

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253

TABLE 1. Percentages of 852 prey items delivered by male ( n =
Woodpeckers ( Campephilus magellanicus ) to nestlings in seven nests
2004 and 2004-2005 nesting seasons.

= 448) and female ( n = 404) Magellanic
in Argentine Patagonia during the 2003-

Prey type (n)

Both sexes

Male

Female

Invertebrates

Wood-boring larvae (491)

57.6

65.6

48.8

Arachnids (112)

13.1

9.6

17.1

Adult insects (31)

3.6

3.3

4.0

Caterpillars (4)

0.5

0.7

0.2

Pupae (6)

0.7

1.3

0.0

Unidentified invertebrates (169)

19.8

12.0

28.5

All invertebrates (813)

95.4

92.5

98.6

Vertebrates

Lizards (13)

1.5

2.7

0.2

Nestlings (14)

1.6

3.1

0.0

Avian eggs (8)

0.9

1.0

Bats (1)

0.1

0.2

0.0

Unidentified vertebrates (3)

0.4

0.2

All vertebrates (39)

4.6

7.4

1.5

tom of the nest cavity; on one occasion, how-
ever, an attending male flew to a nearby tree
with the prey and ate it (a lizard).

The identity of avian prey or potential avian
prey also was determined in several additional
ways. In one case, a woodpecker provisioned
its nestling with four similar, small nestlings,
each brought individually. Between these de-
liveries, the woodpecker flew away from, and
returned to, its nest from the same direction.
On the last three return trips, the woodpecker
was followed by a pair of Thorn-tailed Ray-
aditos that were vigorously harassing it, but
with no effect. We interpreted this event as
woodpecker predation on a brood of rayaditos.
On another occasion, we witnessed a male
woodpecker vigorously pecking on, and chis-
eling out, the bark wall that protected a House
Wren nest in a natural crevice; however, the
woodpecker was suddenly interrupted by his
mate’s arrival and he discontinued his peck-
ing. When we examined the half-opened wren
cavity, we found three small hatchlings. The
adult wrens were not present during the pre-
dation attempt.

We also recorded the characteristic foraging
signs of Magellanic Woodpeckers at several
(n = 11) small woodpecker cavities that had
been partially destroyed. Below some cavities,
we observed a row of Magellanic Woodpecker
feeding holes that descended from the lower
lip of the cavity entrance to the floor level of

the nest chamber. In other cases, it appeared
that Magellanic Woodpeckers had pecked
only at the level of the nest chamber’s floor,
where a hole about the size of the nest en-
trance had been drilled. Originally, these small
cavities had been excavated by Striped Wood-
peckers or White-throated Treerunners, and
some contained the cup nests of secondary
cavity nesters. Due to differences in body size
and feeding habits between the Magellanic
Woodpecker and these much smaller species
(Short 1970, 1982), competition is not a likely
explanation for the destructive behavior ob-
served. It appears that such cavities were de-
stroyed to reach the nest chamber at the bot-
tom of the cavity.

This is the first published account of Ma-
gellanic Woodpeckers provisioning their nest-
lings with vertebrates. Though wood-boring
larvae may be the primary food of this wood-
pecker throughout its range, there is increas-
ing evidence that Magellanic Woodpeckers
are opportunistic foragers that will take a wide
variety of prey. In addition to insects, verte-
brates, and eggs, they have also been recorded
feeding on vegetable matter (including sap) at
locations throughout much of their range
(Ojeda 2003, Schlatter and Vergara 2005).

ACKNOWLEDGMENTS

We are indebted to J. M. Karlanian, M. Gelain, A.
Ortiz, P. Taccari, Y. Sasal, and C. Bacchi for their in-

254

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

dispensable assistance during the fieldwork and to N.
Ibargiiengoytia for her assessment concerning Pata-
gonian reptiles. We are grateful to IDEA WILD (Fort
Collins, CO, USA), Birders’ Exchange (Colorado
Springs, CO, USA), and J. Masello for their donations
of equipment fundamental to this study. This research
was supported by CANON USA through its National
Parks Science Scholars Program for the Americas. We
thank R. N. Conner, L. L. Short, and K. Franzreb for
constructive comments that helped improve this man-
uscript.

LITERATURE CITED

del Hoyo, J., A. Elliott, and J. Sargatal (Eds.).
2002. Handbook of the birds of the world, vol. 7:
jacamars to woodpeckers. Lynx Edicions, Barce-
lona, Spain.

Ojeda, V. 2003. Magellanic Woodpecker frugivory and
predation on a lizard. Wilson Bulletin 115:208-
210.

Ojeda, V. 2004. Breeding biology and social behaviour
of Magellanic Woodpeckers ( Campephilus magel-
lanicus ) in Argentine Patagonia. European Journal
of Wildlife Research 50:18-24.

Paruelo, J. M., A. Beltran, E. Jobbagy, O. E. Sala,
and R. A. Golluscio. 1998. The climate of Pa-
tagonia: general patterns and controls on biotic
processes. Ecologia Austral 8:85-101.

Schlatter, R. P. and P. Vergara. 2005. Magellanic
Woodpecker ( Campephilus magellanicus ) sap
feeding and its role in the Tierra del Fuego forest
bird assemblage. Journal of Ornithology 146:188-
190.

Short, L. L. 1970. The habits and relationships of the
Magellanic Woodpecker. Wilson Bulletin 82:115-
129.

Short, L. L. 1982. Woodpeckers of the world. Dela-
ware Museum of Natural History Monographs,
no. 4.

The Wilson Journal of Ornithology 1 18(2):254— 256, 2006

Reverse Mounting and Copulation Behavior in Polyandrous Bearded
Vulture ( Gypaetus barbatus) Trios

Joan Bertran1 2 and Antoni Margalida12

ABSTRACT. — We present the first report of reverse
mounting in the Bearded Vulture ( Gypaetus barbatus).
The reverse mounting, which occurred in the Pyrenees
of northeastern Spain, took place between the female
and the alpha male in a polyandrous trio. The function
of reverse mountings is discussed in relation to the
previously reported high frequency of male-male
mountings in this raptor species. Received 25 April
2005, accepted 17 January 2006.

Reverse mounting, in which the female
mounts the male, has been described in a
number of bird species (see James 1983,
Nuechterlein and Storer 1989). This behavior
has been rarely documented in raptors, how-
ever, except for a few isolated cases in species
such as American Kestrel ( Falco sparverius'.
Bowman and Curley 1986) and Egyptian Vul-
ture {Neophron percnopterus\ Donazar 1993).

1 Bearded Vulture Study and Protection Group,
Apdo. 43, E-25520 El Pont de Suert (Lleida) Spain.

2 Corresponding author; e-mail:
margalida@gauss.entorno.es

We describe a case of reverse mounting in
a polyandrous trio of Bearded Vultures {Gy-
paetus barbatus). Bearded Vultures are terri-
torial and socially monogamous (Hiraldo et al.
1979); however, in the Pyrenees (in both
Spain and France), where the species’ largest
European population occurs, polyandrous co-
alitions are relatively common (Heredia and
Donazar 1990). The birds in this population
maintained 104 breeding territories (R. Here-
dia and M. Razin pers. comm.), 18 of which
were occupied by polyandrous trios. Before
egg-laying. Bearded Vultures in the Pyrenees
engage in their copulations for an average of
67 days (range = 50-90; Bertran and Mar-
galida 1999), during which male-male mount-
ings in trios occasionally occur (Bertran and
Margalida 2003).

Between 2004 and 2005, we monitored a
polyandrous trio of Bearded Vultures in the
central Pre-Pyrenees mountains in Catalonia,
northeastern Spain, during their courtship pe-
riod (200 hr of observation). We sexed and
identified the individuals by observing their

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255

TABLE 1. Number of male-female, male-male, and reverse mounting copulation attempts observed in mo-
nogamous pairs ( n = 8) and polyandrous trios ( n = 5) of Bearded Vultures in the Pyrenees, northeastern Spain,

2004-2005.

Male-Female

Male-Male

Female-Male

Source

Pairs

189

—

Bertran and Margalida (1999)

Trios

356

This study

copulatory activities and specific plumage pat-
terns. On 30 October 2004 at 12:19 UTC+1
(84 days before egg-laying), the female
mounted the alpha male after she had been
mounted unsuccessfully by the beta male. Fol-
lowing the female’s mount, the alpha male
drove the beta male off the perching site. The
duration of the reverse mounting (8 sec) was
similar to that of behaviorally successful
male-female copulations recorded in other
polyandrous groups (mean = 10.49 sec ±
1.30 SD, range = 8-14, n = 37; Bertran and
Margalida 2004).

Previously, researchers have studied reverse
mounting in the context of pair formation, de-
gree of sexual motivation, or reversal of sex-
ual dominance (Nuechterlein and Storer 1989,
Bowen et al. 1991, Ortega-Ruano and Graves
1991). Due to their physical and behavioral
characteristics, it has been suggested that fe-
male Bearded Vultures can dominate males
(see Negro et al. 1999); in the Cattle Egret
C Bubulcus ibis), reverse mounting has been as-
sociated with establishing dominance (Fujioka
and Yamagishi 1981). However, if reverse
mounting were of adaptive value (e.g., to
maintain female dominance or to strengthen
heterosexual couplings), it likely would be
more common. On the other hand, sexual in-
teractions outside the context of fertilization
appear to be relatively common in polyan-
drous trios (Table 1), and reverse mounting
might simply be a side effect of male-male
mountings. That is, the function of reverse
mounting may be to regulate socio-sexual ten-
sions— similar to the function of male-male
mountings (Bertran and Margalida 2003, see
also Heg and van Treuren 1990, Cockbum
2004). Further research is needed to determine
whether reverse mounting is the result of con-
frontational situations or helps to regulate
them.

ACKNOWLEDGMENTS

We thank A. Bonada, X. Macia, P. Romero, and E.
Vega for their help during fieldwork, and D. Heg and
two anonymous referees for their comments. This
study was supported by Departament de Medi Ambient
i Habitatge de la Generalitat de Catalunya and Min-
isterio de Medio Ambiente.

LITERATURE CITED

Bertran, J. and A. Margalida. 1999. Copulatory be-
havior of the Bearded Vulture. Condor 101:161 —
164.

Bertran, J. and A. Margalida. 2003. Male-male cop-
ulations in polyandrous Bearded Vultures ( Gypae -
tus barbatus): an unusual mating system in rap-
tors. Journal of Avian Biology 34:334-338.
Bertran, J. and A. Margalida. 2004. Do females
control matings in polyandrous Bearded Vulture
( Gypaetus barbatus ) trios? Ethology, Ecology and
Evolution 16:181-186.

Bowen, B. S., R. R. Koford, and S. L. Vehrencamp.
1991. Seasonal pattern of reverse mounting in the
Groove-Billed Ani ( Crotophaga sulcirostris ).
Condor 93:159-163.

Bowman, R. and E. M. Curley. 1986. Reverse mount-
ing in the American Kestrel. Wilson Bulletin 98:
472-473.

Cockburn, A. 2004. Mating systems and sexual con-
flict. Pages 81-191 in Ecology and evolution of
cooperative breeding in birds (W. D. Koenig and
J. L. Dickinson, Eds.). Cambridge University
Press, Cambridge, United Kingdom.

Donazar, J. A. 1993. Los buitres ibericos: biologia y
conservacion. J. M. Reyero (Ed.), Madrid, Spain.
Fujioka, M. and S. Yamagishi. 1981. Extramarital and
pair copulations in the Cattle Egret. Auk 98:134-
144.

Heg, D. and R. van Treuren. 1998. Female-female
cooperation in polygynous Oystercatchers. Nature
391:687-691.

Heredia, R. and J. A. Donazar. 1990. High frequency
of polyandrous trios in an endangered population
of Lammergeiers Gypaetus barbatus in northern
Spain. Biological Conservation 53:163-171.
Hiraldo, F, M. Delibes, and J. Calderon. 1979. El
Quebrantahuesos Gypaetus barbatus (L.). Mono-
grafias, no. 22, Instituto para la Conservacion de
la Naturaleza, Madrid, Spain.

James, P. C. 1983. Reverse mounting in the North-

256

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

western Crow. Journal of Field Ornithology 54:
418-419.

Negro, J. J., A. Margalida, F. Hiraldo, and R. He-
redia. 1999. The function of the cosmetic colour-
ation of Bearded Vultures: when art imitates life.
Animal Behaviour 58:F14-F17.

Nuechterlein, G. L. and R. W. Storer. 1989. Reverse
mounting in grebes. Condor 91:341-346.

Ortega-Ruano, J. and J. A. Graves. 1991. Reverse
mounting during the courtship of the European
Shag Phalacrocorax aristotelis. Condor 93:859-
863.

The Wilson Journal of Ornithology 1 18(2):256— 259, 2006

Natural Occurrence of Crowing in a Free-living Female Galliform, the

California Quail

Jennifer M. Gee12

ABSTRACT. — The vocalizations of galliform spe-
cies are typically sexually dimorphic in that only the
males crow. I observed crowing by a female California
Quail ( Callipepla californica), a galliform species that
ranges along the Pacific coast of North America. I re-
corded the female crowing during a period of the
breeding season when many other females were paired.
The female’s crow was similar in frequency to a typ-
ical male crow, though it was slightly shorter in du-
ration. I discuss possible mechanisms and conditions
that could result in female crowing. Received 28 Feb-
ruary 2005, accepted 21 December 2005.

California Quail {Callipepla californica)
show pronounced sexual dimorphism in call-
ing behavior: males crow, whereas females do
not. The California Quail’s crow is commonly
called the Male Advertisement or cow call
(Sumner 1935, Williams 1969). Males usually
crow early in the breeding season (Williams
1969), or when their mates are incubating or
die (JMG pers. obs.). Crowing males often
perch in conspicuous locations and counter-
call to each other. To my knowledge, there
have been no previous reports of female Cal-
ifornia Quail crowing under natural condi-
tions, although Genelly (1955) observed an
instance of crowing in female California Quail
that were held under captive conditions.

I observed a female California Quail crow-
ing in the foothills of the Santa Rosa Moun-

1 Dept, of Ecology and Evolutionary Biology,
Princeton Univ., Princeton, NJ 08544-1003, USA.

2 Current address: W139 Mudd Hall. Dept, of Neu-
robiology and Behavior, Cornell Univ.. Ithaca, NY
14853, USA; e-mail: jmg233@cornell.edu

tains, California (33° 22' N, 1 16° 15' W), dur-
ing the breeding season when many males
were crowing (March 2000). In that region,
the ranges of California and Gambel’s (C.
gambelii ) quail overlap and hybrids or back-
crosses compose approximately 60% of the
population (Gee 2003). From 14 to 16 March,
while conducting daily observations (>7 hr/
day) at this site with a spotting scope, I ob-
served a female California Quail crowing for
1- to 2-hr periods. This female approached to
approximately 5 m in response to calls that I
made with a quail call, and she continued
crowing from that distance for more than 10
min. Both California and Gambel’s quail are
sexually dimorphic; thus, I used field mark-
ings to identify the sex and species of the
crowing bird. I identified the individual as fe-
male by her lack of secondary sex traits (e.g.,
brown cap, black face with white margin), and
as a California Quail by the presence of scaled
breast feathers, forward-pointing crest, and
overall blue-gray body plumage (not buff).
However, backcrosses may look very similar
to pure parental types (Gee 2003). I was un-
able to trap the bird, so I could use neither
genotyping to confirm the sex or species des-
ignation nor laparotomy to examine the inter-
nal anatomical sex. Despite plumage traits,
there is potentially some ambiguity as to the
“true” sex and species of this individual.

I used Canary 1 .2.4 (www.birds. Cornell.
edu/brp/SoundSoftware.html) and Syrinx
(Burt 2005) sound analysis programs to digi-
tize recordings and prepare spectrograms from
which frequency and sound duration were

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257

0.0

Time (sec)

FIG. 1. Spectrograms (kHz/sec) of a female Cali-
fornia Quail crow (A) compared with typical male ad-
vertisement calls of California (B), hybrid (C), and
Gambel’s (D) quail in a region of range overlap (de-
scribed in detail in Gee 2003), in the foothills of the
Santa Rosa Mountains, California. Recordings were
made between 1998 and 2001.

measured. Many low-frequency noises ob-
scured the first harmonic (fundamental fre-
quency) of the call; therefore, I measured the
peak frequency of the harmonic nearest the
fundamental frequency because it was clearly
visible in all spectrograms (Fig. 1). The fe-
male’s crow was approximately the same fre-

quency as, but slightly shorter in duration
than, that of an average male California Quail
(Table 1). The female exhibited male-typical
crowing posture and behavior, calling from a
conspicuous rock outcrop to males that were
crowing in the distance. Though it was a year
of moderate reproductive success, the female
did not appear to have a mate, nor was she a
local resident based on detailed observations
of color-banded individuals at this location
(for methods see Gee 2003).

Conditions and mechanisms that could have
caused this female’s unusual behavior include
(1) elevated testosterone due to increased fe-
male competition, or (2) elevated testosterone
coupled with age-dependent decrease in ovar-
ian function and estrogen production. Note
that in both cases, I suggest a role for testos-
terone, but without examination of the gonad,
there is no way to verify the anatomical and
physiological sex of the crowing, apparently
female individual. Thus, a reproductive, pos-
sibly endocrine, pathology may have contrib-
uted to this behavior.

Intense competition may affect testosterone
levels and crowing behavior. In males, in-
creased testosterone occurs when males are
competing for mates, and it is a normal con-
sequence of reaching breeding condition. Sim-
ilarly in females, intense competition for scarce
resources, such as food or mates, could elevate
testosterone levels or its rate of conversion to
other steroids. When California Quail were
kept in female-biased pens, females became
more aggressive and began crowing, possibly
due to intense competition (reported in Calkins
et al. 1999). Although the sex ratio from Jan-
uary to June at my study site was not signifi-
cantly skewed (52:48, n = 130), local move-
ments could have created periods of unusually
intense female competition. The crowing fe-
male was unpaired and part of a wave of tran-
sient residents, many of which appeared to be
in small groups of 4-6 individuals.

Testosterone has been shown to play a role
in the crowing behavior of male Gambel’s
Quail and female Japanese Quail ( Cotumix ja-
ponica ). In Gambel’s Quail, testosterone injec-
tions administered during July (late breeding
season) caused normal adult males, but not fe-
males, to call more frequently and behave more
aggressively (Williams 1969). However, when
female Japanese Quail were both ovariecto-

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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

TABLE 1. Call duration and peak frequency (mean ± SD) of California, Gambel’s, and hybrid quail in a
region of range overlap (described in detail in Gee 2003), in the foothills of the Santa Rosa Mountains, California.
Recordings were made between 1998 and 2001. Sample sizes for call duration and frequency of different males
are as follows: Callipepla calif ornica (8, 8), hybrid (16, 8), C. gambelii (11, 8). Multiple recordings were made
of the calling female. Only the clearest recording was measured, although her crows appeared very similar to
one another.

Female

Male

C. califomica

Hybrid

C. gambelii

Duration (sec)

0.36

0.38 (0.03)

0.45 (0.02)

0.53 (0.03)

Frequency (kHz)

1.98

2.03 (0.16)

1.85 (0.17)

1.86 (0.90)

mized and treated with testosterone, they
crowed and strutted similar to males (Adkins
and Adler 1972; Adkins 1975; Balthazart et al.
1983, 1996). Thus, two factors may cause fe-
male crowing: increased levels of testosterone
and decreased ovarian function. Ovarian func-
tion appears to diminish with age in Gambel’s
and California quail, as evidenced by the ac-
quisition of partial male plumage among some
older females (Hagelin and Kimball 1997) and
the finding that sexually dimorphic plumage is
estrogen-dependent in many galliforms (Domm
1939, Owens and Short 1995). In the case re-
ported here, the age of the crowing female was
unknown, and she showed no evidence of par-
tial male plumage. Although both vocalizations
and plumage could be affected by ovarian
function, female crowing and partial male
plumage are not coupled and are likely regu-
lated by different mechanisms. Vocalizations
appear to be governed, in part, by increased
numbers of androgen receptors in the vocal
control regions or by steroid-converting en-
zymes. For example, administering the aro-
matase inhibitor, fadrazole, results in crowing
by female Japanese Quail (Marx et al. 2004).
Similarly, the crowing and strutting of male
Japanese Quail largely depend on the conver-
sion of testosterone to dihydrotestosterone and
on androgen receptors (Adkins-Regan 2005).

In the sympatric population I studied, male-
typical plumage is infrequent (but consistently
present) in female California, Gambel’s, and
hybrid quail, while male-typical vocalizations
are not. Approximately 1% of the banded fe-
male California, Gambel’s, and hybrid quail
have partial male plumage, and they may pair
and breed normally (JMG pers. obs.). In con-
trast, I observed only one female with male-
typical calling patterns. This difference sug-

gests that separate mechanisms govern sexu-
ally dimorphic plumage compared to sexually
dimorphic vocalizations, but it also suggests
that different selective pressures may act on
plumage and crowing. The consequences of
female crowing may be severe, particularly if
crowing is associated with other aggressive
and territorial behaviors, as it is in both New
World quail (Johnsgard 1988) and Japanese
Quail (Balaban 1997). Thus, female crowing
may occur only under the rare circumstances
when it and other aggressive behaviors —
which are typical among reproductive
males — do not decrease the reproductive fit-
ness of female quail.

ACKNOWLEDGMENTS

Financial support was provided by a National Sci-
ence Foundation Predoctoral Fellowship; a National
Science Foundation Doctoral Dissertation Improve-
ment Grant DEB-0073271; an Environmental Protec-
tion Agency Science-to-Achieve-Results Graduate Fel-
lowship U-9 157290 1-0; Sigma Xi Grants-in-Aid of
Research; the American Ornithologists’ Union Betty
Carnes Memorial Award; and The Reserve Commu-
nity Association of The Reserve, Palm Desert, Cali-
fornia. Carolyn Stillwell helped to draw figures. For
comments, I thank S. M. Correa, M. L. Tomaszycki,
J. C. Hagelin, and three anonymous referees.

LITERATURE CITED

Adkins, E. K. 1975. Hormonal basis of sexual differ-
entiation in the Japanese Quail. Journal of Com-
parative Physiological Psychology 89:61-71.
Adkins, E. K. and N. T. Adler. 1972. Hormonal con-
trol of behavior in the Japanese Quail. Journal of
Comparative Physiological Psychology 81:27-36.
Adkins-Regan, E. K. 2005. Hormones and animal social
behavior (Monographs in behavior and ecology).
Princeton University Press, Princeton, New Jersey.
Balaban, E. 1997. Changes in multiple brain regions
underlie species differences in a complex, con-

SHORT COMMUNICATIONS

259

genital behavior. Proceedings of the National
Academy of Sciences, USA 94:2001-2006.

Balthazart, J., M. Schumacher, and M. A. Ottin-
ger. 1983. Sexual differences in the Japanese
Quail: behavior, morphology and intracellular me-
tabolism of testosterone. General and Compara-
tive Endocrinology 51:191-207.

Balthazart, J., O. Tlemcani, and G. E Ball. 1996.
Do sex differences in the brain explain sex differ-
ences in the hormonal induction of reproductive
behavior? What 25 years of research on the Jap-
anese Quail tells us. Hormones and Behavior 30:
627-661.

Burt, J. 2005. Syrinx-PC: a Windows program for
spectral analysis, editing, and playback of acoustic
signals, ver. 2.4. www.syrinxpc.com (accessed 14
July 2005).

Calkins, J. D., J. C. Hagelin, and D. F. Lott. 1999.
California Quail ( Callipepla californica). The
Birds of North America, no. 473.

Domm, L. V. 1939. Modifications in sex and secondary
sexual characters in birds. Pages 227-327 in Sex and
internal secretions: a survey of recent research (E.
Allen, Ed.). Williams and Wilkins, Baltimore, Mary-
land.

Gee, J. M. 2003. How a hybrid zone is maintained:
behavioral mechanisms of interbreeding between
California and Gambel’s quail ( Callipepla califor-
nica and C. gambelii). Evolution 57:2407-2415.

Genelly, R. E. 1955. Annual cycle in a population of
California Quail. Condor 57:263-285.

Hagelin, J. C. and R. T. Kimball. 1997. A female
Gambel’s Quail with partial male plumage. Wil-
son Bulletin 109:544-546.

Johnsgard, P. A. 1988. The quails, partridges, and
francolins of the world. University of Nebraska
Press, Lincoln.

Marx, G., A. Jurkevich, and R. Grossmann. 2004.
Effects of estrogens during embryonic develop-
ment on crowing in the domestic fowl. Physiology
and Behavior 82:637-645.

Owens, I. P. F. and R. V. Short. 1995. Hormonal basis
of sexual dimorphism in birds: implications for
new theories of sexual selection. Trends in Ecol-
ogy and Evolution 10:44-47.

Sumner, E. L., Jr. 1935. A life history study of the
California Quail, with recommendations for its
conservation and management. California Fish
and Game 21:167-253, 275-342.

Williams, H. W. 1969. Vocal behavior of adult Cali-
fornia Quail. Auk 86:631-659.

The Wilson Journal of Ornithology 1 18(2):259— 261, 2006

Poult Adoption and Nest Abandonment by a Female Rio Grande

Wild Turkey in Texas

Steve T. Metz,1 Kyle B. Melton,1 Ray Aguirre,2 Bret A. Collier,14
T. Wayne Schwertner,3 4 Markus J. Peterson,1 and Nova J. Silvy1

ABSTRACT. — While evaluating reproductive pa-
rameters in Rio Grande Wild Turkeys ( Meleagris gal-
lopavo intermedia ) in the Edwards Plateau region of
Texas, we observed a case of poult adoption and aban-
donment of an active nest. In wild turkeys, adoption
of poults has been described previously, but during our
observation the hen also abandoned her nest at a late
stage of incubation. Most research discussing adoption
in gallinaceous birds has focused on brood abandon-
ment after hatch. Although poult adoption in conjunc-
tion with nest abandonment is probably rare, our ob-
servations indicate that it can occur, at least in Rio

1 Dept, of Wildlife and Fisheries Sciences, Texas
A&M Univ., College Station, TX 77843-2258, USA.

2 Texas Parks and Wildlife Dept., Comfort, TX
78013, USA.

3 Texas Parks and Wildlife Dept., Mason, TX 76856,
USA.

4 Corresponding author; e-mail: bret@tamu.edu

Grande Wild Turkeys. Received 7 June 2005, accepted
16 February 2006.

Species such as gulls ( Lams spp.), terns
{Sterna spp.), and geese ( Branta spp.) readily
adopt offspring (Pierottie and Murphy 1987,
Saino et al. 1994, Larsson et al. 1995). North-
ern Bobwhites {Colinus virginianus ) utilize
brood abandonment and adoption as a strategy
for increasing nesting opportunities (Burger et
al. 1995, DeMaso et al. 1997), but document-
ed cases of gallinaceous birds adopting off-
spring are rare (Martin 1989, Mills and Rum-
ble 1991). Adoption of poults by Merriam’s
Wild Turkeys ( Meleagris gallopavo merriami)
has been described (Mills and Rumble 1991),
and Healy (1992) reported nest abandonment

260

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

by a captive hen that was attracted to the calls
of another brood. In May 2005, we observed
a Rio Grande Wild Turkey (A/. g. intermedia )
hen adopt a poult and then abandon her own
nest in Kerr County. Texas. To our knowledge,
adoption in conjunction with nest abandon-
ment has not been documented before in the
wild.

As part of a study to evaluate the reproduc-
tive ecology of Rio Grande Wild Turkeys in
Texas, we tracked a radio-tagged juvenile hen
through two nesting attempts on the Kerr
Wildlife Management Area in Kerr County
(30° 04' N, 99° 20' W), Texas. On 11 April
2005, we found her first nest, which contained
13 eggs, and we estimated nest age at 3 days.
On 15 April, the nest was depredated, and the
hen subsequently renested on 28 April. After
28 April, we checked the hen’s nesting status
>5 times per week. On 7 May, the second nest
contained 12 eggs and nearby we set up an
infrared trail camera (Moultrie Game Spy®)
to monitor the nest. From 8 to 21 May, we
never observed the hen off the nest, and.
based on our intensive tracking of the hen,
there was no possibility that she hatched this
poult several days early.

At 16:00 CST on 21 May, we found the hen
incubating her second nest. On the following
day at 1 1 :00, we located the hen about 600 m
from the nest. We approached to —15 m of
the hen and observed her bedded down in a
grassy area dominated by little bluestem
(Schizachyrium scoparium ). Upon further ap-
proach. she flushed. Within about 1 min, a
poult, estimated to be 4 days old, ran from the
grassy area where the hen had been bedded.
We then examined the hen’s nest and found
all 12 eggs present and intact. We also floated
the eggs and estimated that they were at day
23 of incubation (Healy 1992).

On 23 May, we relocated the radio-tagged
hen in an effort to catch and radio-tag the
poult; however, the hen was moving and we
were unable to locate the poult. On the fol-
lowing day, the hen was relocated again, this
time with the poult. On 26 May, we captured
the poult, estimated its age as 9 days, radio-
tagged it with a 1.2-g poult transmitter (Bow-
man et al. 2002; Advanced Telemetry Sys-
tems, Isanti. Minnesota), and released it.

Other than anecdotal evidence and the ar-
ticle by Mills and Rumble (1991), there is lit-

tle available information on the frequency of
adoption in wild turkeys. Whereas Mills and
Rumble (1991) reported poult adoption by tur-
key hens both with and without existing
broods, the hen we observed had abandoned
her clutch of 12 eggs after considerable in-
vestment (>20 days of incubation) to care for
a single poult. While such cases of abandon-
ment and adoption are probably rare, our ob-
servations indicate that it can occur in Rio
Grande Wild Turkeys. Possible causes might
include hen physiological condition or chang-
es in photoperiod (Scanes et al. 1979, Youn-
gren et al. 1993. Bedecarrats et al. 1997, Sharp
et al. 1998). The hen that we observed was in
the latter stages of incubation on a second nest
when the adoption event occurred; thus, her
levels of luteinizing hormone and prolactin
may have changed sufficiently to promote be-
havioral changes (i.e., poult-rearing behavior
in preference to continued incubation). Addi-
tional research is needed to clarify what might
trigger simultaneous poult adoption and nest
abandonment in turkeys.

ACKNOWLEDGMENTS

Funding for this project was provided by the Texas
Turkey Stamp Fund through the Texas Parks and Wild-
life Department, the National Wild Turkey Federation,
and the Department of Wildlife and Fisheries Sciences,
Texas A&M University. This research was conducted
under Texas A&M University Animal Use Permit No.
2005-005. We appreciate the comments from three
anonymous reviewers that improved this manuscript.

LITERATURE CITED

Bedecarrats, G.. D. Guemene, and M. A. Richard-
Yris. 1997. Effects of environmental and social
factors on incubation behavior, endocrinological
parameters, and production traits in turkey hens
( Meleagris gallopavo). Poultry Science 76:1307-
1314.

Bowman, K.. M. C. Wallace, W. B. Ballard, J. H.
Brunjes, IV. M. S. Miller, and J. M. Hellman.
2002. Evaluation of two techniques for attaching
radio transmitters to turkey poults. Journal of
Field Ornithology 73:276-280.

Burger, L. W, Jr., M. R. Ryan, T. V. Dailey, and E.
W. Kurzejeski. 1995. Reproductive strategies,
success, and mating systems of Northern Bob-
whites in Missouri. Journal of Wildlife Manage-
ment 59:417-426.

DeMaso, S. J.. A. D. Peoples, S. A. Cox, and E. S.
Parry. 1997. Survival of Northern Bobwhite
chicks in western Oklahoma. Journal of Wildlife
Management 61:846-853.

SHORT COMMUNICATIONS

261

Healy, W. M. 1992. Behavior. Pages 46-65 in The
Wild Turkey: biology and management (J. G.
Dickson, Ed.). Stackpole Books, Mechanicsburg,
Pennsylvania.

Larsson, K., H. Tegelstrom, and P. Forslund. 1995.
Intraspecific nest parasitism and adoption of
young in the Barnacle Goose: effects on survival
and reproductive performance. Animal Behavior
50:1349-1360.

Martin, K. M. 1989. Pairing and adoption of offspring
by replacement male Willow Ptarmigan: behavior,
costs, and consequences. Animal Behavior 37:
569-578.

Mills, T. R. and M. A. Rumble. 1991. Poult adoption
in Merriam’s Wild Turkeys. Wilson Bulletin 103:
137-138.

Pierotti, R. and E. C. Murphy. 1987. Intergenera-
tional conflicts in gulls. Animal Behavior 35:435-
444.

Saino, N., M. Fasola, and E. Crocicchia. 1994.

Adoption behavior in Little and Common terns
(Aves: Sternidae): chick benefits and parent’s fit-
ness costs. Ethology 97:294-309.

Scanes, C. G., P. J. Sharp, S. Harvey, P. M. M. God-
den, A. Chadwick, and W. S. Newcomer. 1979.
Variations in plasma prolactin, thyroid hormones,
gonadal steroids and growth hormone in turkeys
during the induction of egg laying and molt by
different photoperiods. British Poultry Science 20:
143-148.

Sharp, P. J., A. Dawson, and R. W. Lea. 1998. Control
of luteinizing hormone and prolactin secretion in
birds. Comparative Biochemistry and Physiology
C: Pharmacology, Toxicology and Endocrinology
119:275-282.

Youngren, O. M., M. E. Elhalawani, J. L. Silsby,
and R. E. Phillips. 1993. Effect of reproductive
condition on luteinizing hormone and prolactin re-
lease induced by electrical stimulation of the tur-
key hypothalamus. General and Comparative En-
docrinology 89:220-228.

The Wilson Journal of Ornithology 1 1 8(2):26 1—263, 2006

Predation by a Blue-crowned Motmot ( Momotus momota)
on a Hummingbird

J. Mauricio Garcfa-C.12 and Rakan A. Zahawi1 2

ABSTRACT. — We describe predation of a Green-
crowned Brilliant ( Heliodoxa jacula) by a Blue-
crowned Motmot ( Momotus momota) in southern Cos-
ta Rica. We did not witness the capture of the hum-
mingbird, but did observe the motmot swallow the
prey whole. Although the diet of the Blue-crowned
Motmot is highly variable and can include birds, this
is the first report of predation on an adult humming-
bird. Received 27 January 2005, accepted 4 December
2005.

Members of the family Momotidae have
been observed eating a wide range of fruits,
arthropods, and small vertebrates (Meyer de
Schauensee 1964, Ridgely and Gwynne 1989,
Stiles and Skutch 1989, Karr et al. 1990, Rem-
sen et al. 1993). Although Remsen et al.
(1993) indicate that arthropods, supplemented
by fruits, are the more important component
of motmot diets, vertebrates have also been

1 Organization for Tropical Studies, P.O. Box 676-
2050, San Pedro, San Jose, Costa Rica.

2 Corresponding author; e-mail: mgarcia@ots.ac.cr

found in the stomachs of some Momotidae
species (Wetmore 1968, Stiles and Skutch
1989). Specifically, motmots have been ob-
served eating poison dart frogs (Master 1999),
snakes (Stiles and Skutch 1989), mice (Del-
gado-V. and Brooks 2003), and bats (Chacon-
Madrigal and Barrantes 2004).

The Blue-crowned Motmot ( Momotus
momota), found throughout the lowlands and
middle elevations (to —1,500 m) of Costa
Rica (Stiles and Skutch 1989), forages on
large spiders, earthworms, insects, nestling
birds, and small snakes and lizards (Stiles and
Skutch 1989, Henderson 2002). There are,
however, no known accounts of motmots eat-
ing adult birds. Here, we describe predation
on an adult hummingbird by a Blue-crowned
Motmot.

The incident occurred on the morning of 27
February 2004 at the Las Cruces Biological
Field Station (8° 47' N, 82° 57' W) of the Or-
ganization for Tropical Studies in San Vito,
Coto Brus, Puntarenas, Costa Rica (elevation

262

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

= 1,100 m, annual rainfall = 3,988 mm). (For
a full description of the site, see Mintken and
Gunther 1991 and Spencer 1991). At 07:30
CST, we observed a motmot — perched on the
cement stairs in front of a station building —
with a Green-crowned Brilliant ( Heliodoxa ja-
cula ) in its bill. The motmot held the hum-
mingbird by its body and repeatedly beat it
against the cement. The hummingbird ap-
peared freshly dead and was easily identifi-
able. As we did not witness the capture, the
hummingbird may have been dead or injured
prior to capture, although there are no ac-
counts of motmots eating prey they did not
kill.

At 07:35, the motmot flew to the ground
~7 m away and continued to beat the hum-
mingbird against the ground. At 07:40, it
moved under a building and beat the hum-
mingbird against a rock for almost 1 min. As
a result, most of the hummingbird’s feathers
were lost and its bill was broken. At 07:43,
the motmot moved out from under the build-
ing to a grassy area with some tree cover and
continued to beat the hummingbird against the
ground. At this point, the motmot was 7 m
from its mate, which was perched on a tree
branch 2 m high and present for the entire
period; it did not make any attempt to move
closer to the motmot with the hummingbird.
The motmot never used its feet to manipulate
or hold the prey; the entire time it held,
turned, and manipulated the hummingbird
only with its bill.

At 07:54, the motmot attempted, but failed,
to swallow the hummingbird whole. The mot-
mot threw the hummingbird on the ground,
picked it up again with its bill, and continued
to beat it against the ground. At 07:56, the
motmot again tried to swallow the humming-
bird and was successful. It held the humming-
bird by the back and swallowed it back end
first. The motmot then flew to a tree branch
and perched near its mate.

Reported sources of adult hummingbird
mortality include arthropods (e.g., Butler
1949, Hildebrand 1949, Carignan 1988, Gra-
ham 1997), frogs (Monroe 1957), and several
avian taxa: small raptors (e.g., Lowery 1938,
Mayr 1966, Stiles 1978), Great Shrike Tyrants
( Agriornis livida; Martinez del Rio 1992),
Baltimore Orioles {Icterus galbula ; Wright
1962), and Dusky-green Oropendolas {Psar-

ocolius atrouirens; Graves 1978). Ours is the
first report of a Blue-crowned Motmot eating
an adult bird of any kind. Our observation is
best explained as an opportunistic event and
broadens the range of predators that kill and
eat hummingbirds.

ACKNOWLEDGMENTS

We would like to thank K. G. Murray for helpful
comments on earlier drafts of the manuscript. T. L.
Master, J. V. Remsen, and an anonymous reviewer
made invaluable comments. The Organization for
Tropical Studies provided logistical support at Las
Cruces Biological Station.

LITERATURE CITED

Butler, C. 1949. Hummingbird killed by praying
mantis. Auk 66:286.

Carignan, J. M. 1988. Predation on Rufous Hum-
mingbird by praying mantid. Texas Journal of Sci-
ence 40:1 1 1.

Chacon-Madrigal, G. and G. Barrantes. 2004.
Blue-crowned Motmot {Momotus momota ) pre-
dation on a long-tongued bat (Glossophaginae).
Wilson Bulletin 116:108-110.

Delgado- V., C. A. and D. M. Brooks. 2003. Unusual
vertebrate prey taken by Neotropical birds. Omi-
tologia Colombiana 1:63—65.

Graham, D. L. 1997. Spider webs and windows as
potentially important sources of hummingbird
mortality. Journal of Field Ornithology 68:98-
101.

Graves, G. R. 1978. Predation on hummingbird by
oropendola. Condor 80:251.

Henderson, C. L. 2002. Field guide to the wildlife of
Costa Rica. University of Texas Press, Austin.
Hildebrand, E. M. 1949. Hummingbird captured by
praying mantis. Auk 66:286.

Karr, J. R., S. K. Robinson, J. G. Blake, and R. O.
Bierregaard, Jr. 1990. Birds of four Neotropical
forests. Pages 237-269 in Four Neotropical rain-
forests (A. H. Gentry, Ed.). Yale University Press,
New Haven, Connecticut.

Lowery, G. H., Jr. 1938. Hummingbird in a Pigeon
Hawk’s stomach. Auk 55:280.

Martinez del Rio, C. 1992. Great Shrike-Tyrant pre-
dation on a Green-backed Firecrown. Wilson Bul-
letin 104:368-369.

Master, T. 1999. Predation by Rufous Motmot on
black-and-green poison dart frog. Wilson Bulletin
111:439-440.

Mayr, E. 1966. Hummingbird caught by Sparrow
Hawk. Auk 83:644.

Meyer de Schauensee, R. 1964. The birds of Colom-
bia, and adjacent areas of South and Central
America. Livingston Publishers, Narberth, Penn-
sylvania.

Mintken, J. and B. Gunther. 1991. The Wilson Bo-
tanical Garden. Principes 35:124-126.

SHORT COMMUNICATIONS

263

Monroe, M. 1957. Hummingbird killed by frog. Con-
dor 59:69.

Remsen, J. V., M. A. Hyde, and A. Chapman. 1993.
The diets of Neotropical trogons, motmots, bar-
bets and toucans. Condor 95:178-192.

Ridgely, R. S. and J. A. Gwynne, Jr. 1989. A guide
to the birds of Panama with Costa Rica, Nicara-
gua, and Honduras, 2nd ed. Princeton University
Press, Princeton, New Jersey.

Spencer, D. 1991. Tropical temptation in Costa Rica.
Cornell Plantations 46:12-15.

Stiles, F. G. 1978. Possible specialization for hum-
mingbird-hunting in the Tiny Hawk. Auk 95:550-
553.

Stiles, F. G. and A. F. Skutch. 1989. A guide to the
birds of Costa Rica. Cornell University Press, Ith-
aca, New York.

Wetmore, A. 1968. The birds of the Republic of Pan-
ama, part 2. Columbidae (pigeons) to Picidae
(woodpeckers). Smithsonian Institution Press,
Washington, D.C.

Wright, B. S. 1962. Baltimore Oriole kills humming-
bird. Auk 79:112.

The Wilson Journal of Ornithology 1 18(2):264-266, 2006

Once Upon a ‘Time in American Ornithology

Alexander Wilson, namesake of The Wilson
Journal of Ornithology, was bom on 6 July
1766 in Scotland. There, he trained and worked
as a weaver (and a poet). In 1794, he emigrated
to the U.S., and for 9 years he worked as a
teacher. His own education had been sketchy,
however, and he had to study to teach. Even-
tually, North America’s birds and wilderness
held him — there were more birds and species
than in his native Scotland. Eager to begin a
life work, Wilson set out on 1 June 1803 to
draw “all the finest birds of America.” For the
next 10 years, he wrote and illustrated his sem-
inal work, American Ornithology, the first sci-
entific treatment of American birds and the first
to stress natural history and field biology. He
had an untaught skill in painting, but William
Bartram, America’s foremost naturalist and a
neighbor in his hometown of Philadelphia,
taught him how to draw. Bartram also an-
swered Wilson’s natural history queries, and in-
spired and instructed him in ornithology, bot-
any, and bird illustration.

Wilson was still teaching in 1805, but art
and science dominated his thoughts as his
drawing improved. He took a job as an assis-
tant editor with a publishing house in 1806
and ultimately convinced the publisher to sup-
port his developing work, but only if Wilson
could get commitments from 250 subscribers
at $120 each. On 7 April 1807, a brochure for
American Ornithology was sent to 2,500 of
the most eminent people in the U.S.

As time allowed, Wilson traveled exten-
sively, widening his knowledge of birdlife and
gathering information on the distribution,
nesting habits, and movements of North
American birds. He often traveled on foot or
by horseback, and while accumulating bird
lore, always equipped himself with a shotgun,
paint, paper, sketching materials, and a note-
book. Wilson made four great adventures —
through dense forests and swamps, across In-
dian territory, and in all seasons — traversing
every state in the Union, often alone, in search
of birds and subscribers. On his first trip, Oc-
tober to December 1804, he traveled 1,300

miles from Philadelphia to Niagara Falls and
back, mostly on foot, but also by stagecoach,
skiff, and sloop. Then, in September 1808, he
was off to New England in search of birds and
subscribers willing to commit $120 for his
American Ornithology. During the winter of
1808-1809, he continued his fieldwork and
search for subscribers, traveling south by
horseback to Maryland, New Jersey, Virginia,
North and South Carolina, and Georgia. Wil-
son’s longest expedition began in January of
1810, when he went from Philadelphia to
Pittsburgh, then south on the Ohio River to
Louisville in a skiff (that Wilson christened
“Ornithologist”), then overland to Natchez,
through hostile Chickasaw Indian territory,
and finally on to New Orleans.

The list of subscribers to Wilson’s American
Ornithology included some of the greatest per-
sonalities of his time: President Thomas Jef-
ferson. Robert Fulton (inventor of the first
commercial steamship), and Thomas Paine.
Wilson also enlisted the assistance of Meri-
wether Lewis, who provided bird specimens —
collected during his remarkable 1804-1806 ex-
pedition with William Clark — from which Wil-
son could draw birds of western origin.

Wilson died of dysentery at the age of 47
in 1813, just before publication of the 8th vol-
ume of American Ornithology. The 9th and
last volume was compiled by George Ord
from Wilson’s notes and drawings.

It was on a trip through the southern coastal
states that Wilson recorded the following orni-
thological observation. On 2 February 1809, 12
miles outside Wilmington, North Carolina, he
collected two Ivory-billed Woodpeckers ( Cam -
pephilus principalis ), and slightly wounded a
third (a male). Wilson’s illustrations of the Ivo-
ry-billed Woodpecker (Fig. 1) in his American
Ornithology came from drawings he made of
the injured bird while in his Wilmington hotel
room. The original reference is: Brewer, T. M.
1840. Wilson’s American Ornithology, with
notes by Jardine. Otis, Broaders, and Co., Bos-
ton, Massachusetts. — JAMES A. SEDGWICK;
e-mail: jim_sedgwick@usgs.gov

264

ONCE UPON A TIME IN AMERICAN ORNITHOLOGY

265

FIG. 1. Wilson’s Ivory-billed Woodpecker (top right, bottom center), Pileated Woodpecker (top and bottom
left), and Red-headed Woodpecker (bottom right). Illustrations of the Ivory-billed Woodpecker were drawn from
a live bird that Wilson took to his hotel room in Wilmington, North Carolina, in 1809. Color plate from: Wilson,
A. 1829. American ornithology; or. The natural history of the birds of the United States. Collins & Co., New
York. Image courtesy of the Josselyn Van Tyne Memorial Library, University of Michigan, Ann Arbor.

266

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118 . No. 2. June 2006

The first place I observed this bird at, when on my way to the south, was about
twelve miles north of Wilmington in North Carolina. There I found the bird from
which the drawing of Fig. 131 was taken. This bird was only wounded slightly in
the wing, and. on being caught, uttered a loudly reiterated and most piteous note,
exactly resembling the violent crying of a young child; which terrified my horse
so, as nearly to have cost me my life. It was distressing to hear it. I carried it with
me in the chair, under cover, to Wilmington. In passing through the streets, its
affecting cries surprised every one within hearing, particularly the females, who
hurried to the doors and windows with looks of alarm and anxiety. I drove on, and,
on arriving at the piazza of the hotel, where I intended to put up. the landlord came
forward, and a number of other persons who happened to be there, all equally
alarmed at what they heard; this was greatly increased by my asking, whether he
could furnish me with accommodations for myself and my baby. The man looked
blank and foolish, while the others stared with still greater astonishment. After
diverting myself for a minute or two at their expense, I drew my Woodpecker from
under the cover, and a general laugh took place. I took him up stairs, and locked
him up in my room, while I went to see my horse taken care of. In less than an
hour, I returned, and, on opening the door, he set up the same distressing shout,
which now appeared to proceed from grief that he had been discovered in his
attempts at escape. He had mounted along the side of the window, nearly as high
as the ceiling, a little below which he had begun to break through. The bed was
covered with large pieces of plaster; the lath was exposed for at least fifteen inches
square, and a hole, large enough to admit the fist, opened to the weather-boards;
so that, in less than another hour, he would certainly have succeeded in making his
way through. I now tied a string round his leg, and, fastening it to the table, again
left him. I wished to preserve his life, and had gone off in search of suitable food
for him. As I reascended the stairs, I heard him again hard at work, and on entering
had the mortification to perceive that he had almost entirely ruined the mahogany
table to which he was fastened, and on which he had wreaked his whole vengeance.
While engaged in taking the drawing, he cut me severely in several places, and,
on the whole, displayed such a noble and unconquerable spirit, that I was frequently
tempted to restore him to his native woods. He lived with me nearly three days,
but refused all sustenance, and I witnessed his death with regret.

The Wilson Journal of Ornithology 1 1 8(2):267-276, 2006

Ornithological Literature

Compiled by Mary Gustafson

BIRDS OF BELIZE. By H. Lee Jones, illus-
trated by Dana Gardner. University of Texas
Press, Austin. 2003: 317 pp., 56 color plates
with facing-page figure captions, 234 range
maps, 28 numbered figures. ISBN: 0292740662,
$60.00 (cloth). ISBN: 0292701640, $34.95 (pa-
per).— Being a country where English is spo-
ken, and which still retains 70% of its native
habitat, it is no surprise that Belize is an increas-
ingly popular destination for ornithologists and
birders alike. In fact, hundreds of birders visit
this tiny country annually to enjoy its rich avi-
fauna, natural beauty, and amazingly friendly
residents. For the past decade, ornithologists
and birders visiting Belize were served quite
well by Howell and Webb’s A Guide to the
Birds of Mexico and Northern Central Amer-
ica (Oxford University Press, 1995). As mas-
terful as that work is, however, the 85 1 -page
tome weighs in at a hefty 3.4 lbs., a bit much
to carry in the field. A much more portable,
but clearly outdated, option is Peterson and
Chalif’s A Field Guide to Mexican Birds
(Houghton Mifflin, 1973). Now there is a third
option: Birds of Belize is the first guide to
comprehensively cover all 574 species known
to occur in this birder-friendly country. All
regularly occurring species are illustrated, in-
cluding North American migrants that spend
only part of the year in Belize. Neither Peter-
son and Chalif nor Howell and Webb illustrate
North American migrants, and both guides in-
clude many Mexican species that do not occur
in Belize. For anyone who is not thoroughly
familiar with bird distribution in Central
America, the convenience of having only Be-
lizean birds in one volume is difficult to over-
state. Birds of Belize is also two-thirds the
weight of Howell and Webb, though still a bit
large to easily tote in the field. The guide’s
format is traditional and easy to use, with
plates and brief, facing-page text in the front;
more-comprehensive text and detailed maps
are in the back. The facing-page text covers
not only identification notes, but also the spe-
cies’ status, distribution, and habitat — incred-
ibly useful information found in few other

guides. Probably the greatest strength of this
guide is its superb, authoritative text. Lee
Jones’s knowledge about the birds of Belize
is unsurpassed. He gives excellent descrip-
tions of status, distribution, and general iden-
tification features for each species. His notes
on habitat are particularly helpful for anyone
seeking a particular species, and his descrip-
tions of vocalizations are unusually complete,
accurate, and helpful. For those seeking more
in-depth information on a particular subject, a
comprehensive bibliography is available.

For better or worse, the quality of a field
guide depends, to a large degree, on the qual-
ity of its illustrations. The illustrations in this
guide are attractive and, in most cases, more
than adequate to convey the important iden-
tifying characters. In general. Neotropical res-
ident species are better illustrated than North
American migrants; plates of antbirds, wrens,
becards, and tanagers are particularly lovely
and accurate. For some of the more difficult
ID questions, however, the illustrations fall
short and other sources may need to be con-
sulted. For example, all the raptors in flight
are misshapen and the plumage markings of
many are incorrect. Those in Howell and
Webb are far superior. Likewise, the Leptotila
doves, which are best identified by general
color pattern, look too similar; Gray-fronted
Dove (L. rufaxilla ) should be more rufous-
brown above with contrasting gray nape and
head; White-tipped Dove (L. verreauxi )
should be more gray-brown; and Gray-chested
Dove (L. cassini ) should have a more con-
trasting gray breast. Again, those in Howell
and Webb are much better.

For many of the North American migrants,
such as shorebirds, gulls, and terns, one would
be much better served by consulting some of
the better North American references such as
The Sibley Guide (Alfred A. Knopf, 2000). In-
deed, the juvenile Red-footed Booby ( Sula
sula ), the small Calidris sandpipers, the Com-
mon ( Sterna hirundo) and Roseate (S. doug-
allii) terns, the Empidonax flycatchers, the im-
mature Cape May Warbler ( Dendroica tigri-

267

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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

na ), and the basic-plumaged Palm Warbler ( D .
palmarum ) are probably not identifiable from
their illustrations in Birds of Belize ; the ju-
venile Yellow-crowned Night-Heron (Nyctan-
assa violacea ) should show pale-edged wing
coverts and a black bill; the juvenile Black-
crowned Night- Heron ( Nycticorax nycticorax )
has shorter legs than those portrayed; the
Myiarchus flycatchers are too dark and small-
headed with incorrect wing patterns (see Sib-
ley or Howell and Webb for better illustra-
tions). The shapes are a bit off on many spe-
cies; note especially that the Clay-colored
(Spizella pallida ), Chipping {S. passerina ),
Lincoln’s ( Melospiza lincolnii ), and Savannah
(Passerculus sandwichensis) sparrows are all
shown with similar proportions, including
identical tail lengths. In life, these species dif-
fer markedly in proportions (see Sibley).
Countless other small mistakes make some of
the illustrations less useful than they could be.

The text has a few minor shortcomings.
Whereas habitats are nicely described, there is
little or nothing about habits of birds; how
they move, how they feed, what they eat,
whether they are easy or hard to see, how they
nest. Although such information may be
somewhat limited for many Neotropical spe-
cies, what is known for any one species could
have been included in a few short lines with-
out making the book much larger — particular-
ly since the line spacing was larger than it
needed to be. It is also unfortunate that the
text was printed on heavy, glossy paper, which
added unnecessary weight and thickness to
the book.

Several aspects of the guide’s layout could
have been improved. Most notably, bird sizes
should have been indicated on the plates. Size,
after all, is a critical starting point in the iden-
tification process. Also, it is impossible to go
quickly from the plates to the maps. One must
go from the plates to the text to find out what
page the map is on. The maps themselves are
a bit confusing. Supposedly, range maps for
species that occur throughout Belize are not
included, which undoubtedly saves space but
may be confusing for someone not familiar
with the birds of the region. Plus, some maps
for colonial waterbirds are misleading. For ex-
ample, the Great Egret ( Ardea alba ) map is
illustrated with four dots indicating the loca-
tions of breeding colonies, yet there is no in-

dication of where foraging birds occur outside
(or during, for that matter) the breeding sea-
son. Other species, such as Red-footed Booby,
which clearly has a more limited nonbreeding
distribution than Great Egret, are mapped in a
similar way. Rarities for which there are few
records are not mapped, which is also under-
standable; however, a number of species that
occur regularly in parts of Belize, such as
Black-crested Coquette ( Lophornis helenae),
are not mapped. The migration distribution is
not mapped for any species, though it certain-
ly would have been helpful.

Although less than perfect. Birds of Belize
is still an attractive, authoritative, and very
useful guide. Its positive attributes far out-
weigh its shortcomings. It serves as a handy
reference for Belizean birds and is recom-
mended as the guide of choice to most birders
visiting this splendid country. — MICHAEL
O BRIEN, WINGS, Inc., West Cape May,
New Jersey; e-mail; tsweet@comcast.net

ARIZONA BREEDING BIRD ATLAS.
Edited by Troy E. Corman and Cathryn Wise-
Gervais. University of New Mexico Press, Al-
buquerque. 2005; 646 pp., 5 figures, 12 tables,
336 photographs (53 habitat photos, 281 bird
photos), 281 maps, 270 habitat charts, 194
phenology graphs. ISBN; 0826333796.
$45.00 (cloth). — State breeding bird atlases
get better and better. Arizona’s raises the stan-
dard once again. Authoritative species ac-
counts, illustrated with generous use of color,
make presentation of data thorough, clear, and
vivid. Atlas workers (atlasers) recorded 283
breeding species, plus 19 potential breeders.
The 270 main species accounts brim with at-
las-derived information, more than many state
atlases provide.

Each 2-page account features the usual state
map, with easy-to-discem color-coding to de-
pict the three confidence levels portraying the
likelihood of breeding within a given atlas
block. The block statistics summarize the
number of priority blocks and topographic
quads (1 ;74,000-scale maps) in which field
workers recorded the species. Color photo-
graphs supply the obligatory depiction of
birds in the species accounts. Each account
also includes two informative charts; a breed-

ORNITHOLOGICAL LITERATURE

269

ing phenology chart (for species with ade-
quate data) and a graph depicting habitat use.

Arizona’s atlas project specified 40 habitat
types within seven habitat landscapes (tundra,
forests and woodlands, scrublands, grasslands,
desert lands, wetlands, and urban/agricultur-
al). Illustrated with color photographs, a pre-
liminary chapter on habitat describes each of
the 40 habitats and reports on status and dis-
tribution. Many habitats, especially those in
desert systems, suffer declines attributable to
human activities and exacerbated by Arizona’s
burgeoning population.

Unlike some other atlases in which phenol-
ogy charts report the range of dates in which
atlasers recorded each stage of breeding (i.e.,
atlas breeding phenology codes), phenology
charts in the Arizona Atlas simply report over-
all breeding activity. The atlas also highlights
an interesting facet of Arizona bird life — the
summer “monsoon” season in July and Au-
gust. Monsoons stimulate second nestings by
such species as Canyon Towhee ( Pipilo fus-
cus ), Rufous-crowned Sparrow ( Aimophila ruf-
iceps ), Eastern Meadowlark ( Sturnella mag-
na), and maybe Common Yellowthroat
( Geothlypis trichas ), as well as the first and
only nestings by Cassin’s ( Aimophila cassi-
nii ), Botteri’s ( Aimophila botterii ) and Grass-
hopper ( Ammodramus savannarum) sparrows.
Varied Bunting ( Passerina versicolor ), and
possibly Lazuli Bunting ( Passerina amoena).

Three topics organize the species accounts:
Habitat, Breeding, and Distribution and Sta-
tus. Under Habitat, authors, referring briefly
to habitat preferences reported by previous au-
thors, analyze the principal habitats in which
atlasers found the species. The Breeding sec-
tion leads with short expositions about breed-
ing biology, often derived from the Birds of
North America series, and compares these pre-
cepts with atlas observations.

The Distribution and Status section reports
on the species’ seasonal status, and then com-
pares atlas findings with previous works on
Arizona, particularly the seminal work by Al-
lan Phillips, Joe Marshall, and Gale Monson,
The Birds of Arizona (University of Arizona
Press, 1964) and — for species occurring pri-
marily in Mexico — The Birds of Sonora by
Steve Russell and Gale Monson (University of
Arizona Press, 1990). The discussion details
where and with what frequency field workers

detected the species, provides comments on its
detectability, and concludes with an analysis
of the species status and conservation stand-
ing.

One slightly distracting theme in many spe-
cies accounts involves a small section of Ar-
izona where the Apache Nation refused atlas-
ers access to tribal lands. Their section of the
White Mountains (east-central Arizona) con-
tains one of Arizona’s few areas of high-ele-
vation habitat. Authors of species accounts
frequently lament the lack of coverage in the
missing priority blocks (30 out of 1,834) and
often project species’ likely ranges in the
missing blocks.

Some species accounts contain a unique
feature: measurements of nest-site character-
istics. Field workers measured or described
characteristics of 3,507 nests of 184 species,
including nest height and nest tree. For ex-
ample, atlasers found 121 Phainopepla
( Phainopepla nitrens ) nests in 17 tree species
(almost half in palo verde, Parkinsonia sp.) at
a median height of 2.4 m (range = 1—10 m).

Nineteen authors contributed species ac-
counts, although the editors wrote most of
them. They follow an admirably consistent
style with comparable contents, although an
editor’s eye might pick out a few grammatical
goofs (e.g., hanging participial phrases that
most readers will not notice) and a few typos.

The first part of the book discusses the de-
tails of atlas organization, methods, limita-
tions and biases, and summarizes the results.
One chapter covers geography, climate, and
habitats, and another offers a brief history of
Arizona ornithologists. (The first recorded
bird observations came from Coronado’s ex-
pedition in 1540-1542, although we do not
learn what he claimed to see.) It concludes by
quoting Elliot Coues’ sharing “a sort of char-
itable pity for the rest of the poor world, who
are not ornithologists, and have not the chance
of pursuing the science in Arizona.”

The summary of results appropriately starts
by recognizing the 710 field workers (those
who surveyed one or more atlas blocks) and
422 block helpers, who put in 51,737 hr of
field work (plus 18,119 hr of travel time).
Blocks with the most species are distributed
along a northwesterly line from the south-
eastern corner of Arizona to the center of the
state, from the Chiricahua and Huachuca

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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

mountains north to the White Mountains, and
west along the Mogollon Rim as far as Pres-
cott. Mourning Dove ( Zenaida macroura )
heads the list of species reported in the most
blocks, followed by Ash-throated Flycatcher
( Myiarchus cinerascens), House Finch ( Car -
podacus mexicanus). Common Raven ( Corvus
corax). Red-tailed Hawk ( Buteo jamaicensis ),
Northern Mockingbird ( Mimus polyglottos).
Black-throated Sparrow ( Amphispiza bilinea-
ta ), and Brown-headed Cowbird ( Molothrus
ater). Arizona specialties in the top 21 include
Cactus Wren ( Campylorhynchus brunneicap-
illus), Phainopepla, and Verdin {Auriparus
flaviceps).

In many states, atlas field workers have suc-
ceeded in surveying remote and rugged re-
gions that avian researchers ordinarily do not
study. In Arizona, their efforts have expanded,
or filled in, the known ranges of many species.
In contrast, they have also identified several
declining species, including Buff-breasted
Flycatcher ( Empidonax fulvifrons), American
Dipper ( Cinclus mexicanus), and Evening
Grosbeak ( Coccothraustes vespertinus). Many
species accounts detail declines due to habitat
destruction — especially the loss of saguaros
( Carnegiea gigantea) felled by wildfires and
urbanization. Atlas results show that a sur-
prising number of species have a limited range
in Arizona — aside from the Mexican species
that occasionally wander northward into the
southeastern mountains. Overall, this atlas
provides fascinating, thorough, accessible in-
formation about Arizona’s unique breeding
avifauna— HUGH E. KINGERY, Franktown,
Colorado; e-mail: ouzels@juno.com

NESTING BIRDS OF A TROPICAL
FRONTIER: THE LOWER RIO GRANDE
VALLEY OF TEXAS. By Timothy Brush.
Texas A&M University Press, College Sta-
tion. 2005: 245 + xiv pp., 31 color photo-
graphs, 1 1 color illustrations, 2 tables, 5 maps.
ISBN: 1585444367, $50.00 (cloth). ISBN:
1585444901, $24.95 (paper).— The Lower
Rio Grande Valley of Texas is well known to
ornithologists and birders alike who have an
interest in the avifauna of the United States.
Many species of birds with a more tropical
distribution reach the northern portion of their

range in southern Texas, and the Valley, as it
is often referred to, offers easy accessibility to
the habitats that these birds occupy. The geo-
graphic area covered includes the four south-
ern-most counties in Texas: Cameron, Hidal-
go, Starr, and Willacy. The two eastern coun-
ties— Cameron and Willacy — and southern
Hidalgo County are part of the recently
formed delta of the Rio Grande; thus, the land
use is largely devoted to row-crops. For a va-
riety of reasons, the remainder of the Valley
is less conducive to agriculture and, histori-
cally, ranching has been the primary industry.
During the past 2 decades, the human popu-
lation in these four counties has steadily in-
creased and subsequent urbanization is readily
apparent. Conservation agencies, both public
and private, have made great efforts to protect
remaining patches of native vegetation, partic-
ularly in the eastern half of the Valley. These
four counties cover approximately 1 .2 million
ha and can boast an avifauna of just over 500
documented species.

As the title states, this book focuses on the
breeding avifauna of the Lower Rio Grande
Valley of Texas. The majority of the book
takes a narrative format that is easy to read
and discusses all species that either breed reg-
ularly or occasionally within the area. At the
beginning of the book, there is a short section
that includes color photos of selected species
as well as several habitat shots. Compelling
among these are aerial photos of Santa Ana
National Wildlife Refuge taken prior to the
construction of Falcon Dam (in 1953) and in
1981 to compare changes in the condition of
the Rio Grande and surrounding land use. The
remainder of the color section includes several
paintings by Gerald Sneed depicting various
nesting birds of the Valley. These paintings
provide something that photos can’t convey,
the feeling of being in the Valley’s natural
habitats.

The introductory chapters provide a base-
line understanding of the Lower Rio Grande
Valley. There are overviews of topography
and climate, as well as an interesting historical
perspective of land use and its effect on eco-
logical diversity. Two of the remaining chap-
ters in the introductory section include a brief
discussion of the basic habitats found in the
study area and seasonal changes in the avifau-
na. A highlight of the book is the extensive

ORNITHOLOGICAL LITERATURE

271

References section, which will be a great help
to anyone working on the avifauna of South
Texas. The bulk of the book is composed of
species accounts.

The accounts include all species (171) for
which there is at least one acceptable breeding
record. At the time of writing, Eurasian Col-
lared-Doves ( Streptopelia decaocto ) were just
beginning to arrive in the Valley, but have
now taken hold and can be added to that list.
As might be expected, the lengths of species
accounts vary greatly. Brush gives extended
coverage to species that are South Texas spe-
cialties and other species that may be of par-
ticular interest due to their behavior, ecology,
or changes in relative abundance. The longer
species accounts form the heart of the book
and contain fairly detailed information about
the natural history of those species in the Val-
ley. Accounts of the remaining species vary
in length, with most including mention of the
habitats used by the specific species. Brush
specifically mentions that the style of the spe-
cies accounts is a hybrid between standard re-
gional works and other natural history writing
that relies heavily on personal experiences and
field notes. In many ways, this adds interest-
ing aspects to the species accounts in which
Brush has particular interest, such as Green
Parakeet {Aratinga holochlora ), Northern
Beardless-Tyrannulet ( Camptostoma imber-
be ), Tropical Parula ( Parula pitiayumi ), and
Altamira Oriole ( Icterus gularis).

My main quibble with the book is that some
species that are irregular breeders in the Val-
ley are covered very briefly, sometimes with
only a couple of lines. I would have liked to
see more detailed information on these occur-
rences. I also question the inclusion of Yel-
low-faced Grassquit ( Tiaris olivaceus ) as hav-
ing a breeding record in Texas. In my mind,
a single male building a “nest” does not qual-
ify as a nesting attempt, but this is a minor
point. In the introductory section of the book.
Brush does point out that there are five sub-
species endemic, or nearly endemic, to the Ta-
maulipan Biotic Province; in the species ac-
counts, however, more detailed information is
not included for all these taxa. He does dis-
cuss the “Brownsville” Common Yellow-
throat ( Geothlypis trichas insperata ) and other
subspecies that occur in the Valley, although
I would have liked a more in-depth treatment

of these taxa, such as that given to the Valley
specialties. If more research is needed on
these taxa, this would have been a good op-
portunity to point out major gaps in the cur-
rent knowledge. As mentioned previously.
Brush relies heavily on his own field experi-
ence in the Valley, thereby adding a nice di-
mension to the book for those taxa with which
he has personal experience. For other species,
however, his brief notes don’t always add to
the account. Overall, I found the book to be
very informative and would recommend it to
ornithologists and birders alike who are inter-
ested in the avifauna of Texas. — MARK W.
LOCKWOOD, Texas Parks and Wildlife De-
partment, Fort Davis, Texas; e-mail:
mark. lockwood@tpwd. state, tx. us

BIRDS OF WASHINGTON: STATUS
AND DISTRIBUTION. Edited by Terence R.
Wahl, Bill Tweit, and Steven G. Mlodinow.
Oregon State University Press, Corvallis.
2005: x + 436 pp., 285 maps. ISBN:
0870720494. $65.00 (cloth). — State avifaunal
works used to be the province of professional
ornithologists working for the U.S. Biological
Survey, other government agencies, or uni-
versities. In recent years, as ornithological re-
search has moved into physiological, molec-
ular, and evolutionary hypothesis testing, fau-
nal investigation and summarization increas-
ingly have been delegated to dedicated and
talented nonprofessionals. This volume was
developed by a team of 46 authors, including
the 3 editors. Many have biological training
and employment, but I doubt that working on
this book fit into any of their job descriptions.

Birds of Washington includes a short intro-
ductory section, followed by species accounts
for about 482 accepted species. The wrap-up
includes a brief discussion of non-established
introduced species, including accounts for
Mute Swan ( Cygnus olor ), Mandarin Duck
(Aix galericulata ), American Black Duck
( Anas rubripes ), Monk Parakeet ( Myiopsitta
monachus), and eight species of hypothetical
occurrence. Appendices include a table of oc-
currences by habitat and brief biographies of
the 46 authors.

This book serves an important function as

272

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 1 18, No. 2, June 2006

an up-to-date status check on bird occurrence,
distribution, abundance, and changes therein.
The included material appears reliable and au-
thoritative, but I am frustrated by what is not
included. This is a bare-bones treatment with
minimal analysis presented. The introductory
material includes an explanation of the species
account format, a full page of abbreviations
used, a chapter by Christopher Chappell on
Bird Habitats of Washington, one on Avian
Conservation by Joseph Buchanan, a brief dis-
cussion of the history of field ornithology in
Washington, a description of the recent infor-
mation sources used, and slightly more than a
page on changes in status and distribution
over the past half-century. The habitat chapter
provides a listing and descriptions of 30 hab-
itats and a lucid explanation of the basis for
their delimitation. All of the other sections left
me wishing for more detail. The history chap-
ter essentially begins with Jewett et al.’s Birds
of Washington State (University of Washing-
ton Press, Seattle, 1953) and does not even
mention W. L. Dawson, who wrote the mon-
umental first state bird books for Washington
and California. The Changes in Status and
Distribution section lacks a discussion of the
number of species occurring in Washington,
or the rate of addition of new species. The
treatment of increases and decreases in range
and abundance describes general classes of
causes and gives examples, but without
enough detail to really give a reader much
sense of the magnitude or prevalence of these
changes.

The species accounts for regularly occur-
ring species begin with a brief statement of
status in Washington. Abundance categories
are based on likelihood of encounter rather
than estimates of actual numbers present. A
graphic illustrating seasonal occurrence and
relative abundance follows, then a listing of
subspecies in Washington, if more than one,
and a listing of the habitats used. A section
titled Occurrence provides detail on distribu-
tion, abundance, and changes thereof. An op-
tional Remarks section is followed by Note-
worthy Records, which includes high counts
and unusual dates. Authorship is acknowl-
edged for the accounts of accepted species but
not for those of introduced and hypothetical
species. Very detailed distribution maps —
based mainly on the distribution of suitable

habitat — accompany 283 of the accounts. Sea-
sonal changes in distribution are indicated
with different shades of gray.

Vagrants receive much shorter accounts,
which list their occurrences in Washington
and sometimes a little information on the spe-
cies' normal distribution and abundance. The
term “casual vagrant” is used in place of the
traditional “accidental” for the species with
the fewest records. Inclusion as an accepted
species is based on acceptance by the Wash-
ington Bird Records Committee. Corroborat-
ing evidence is usually mentioned, but up to
30 species appear to be accepted based only
on observer descriptions (the text is not al-
ways clear on this). I imagine that most of
these records were accurate, but several (e.g..
Little Curlew, Numenius minutus ; Ruby-
throated Hummingbird. Archilochus colubris;
Mourning Warbler. Oporornis Philadelphia ;
Nelson’s Sharp-tailed Sparrow, Ammodramus
nelsoni ) present non-trivial identification is-
sues. Citations for many of the records of rar-
ities refer to the Records Committee reports
rather than the original sources. The locality
information for Washington records often
lacks county or other regional reference, so
someone not familiar with Washington geog-
raphy will need a good gazetteer to locate
Asotin, Crockett L., Stanwood, Twisp, Wal-
lula, and so on.

This book will be useful to Washington
birders interested in the status of the birds
they see. It will also be of interest to scholars
interested in dynamics of biogeography, range
expansion, range contraction, and vagrancy.
Unfortunately, the editors apparently did not
recognize this latter audience, and have not
made the information of interest to scholars as
accessible as they could have. — WAYNE
HOFFMAN, Newport. Oregon; e-mail:
whoffman @ peak.org

PEREGRINE FALCON; STORIES OF THE
BLUE MEANIE. By James Enderson. original
art by Robert Katona. University of Texas Press,
Austin. 2005: 266 pp., 18 photographs, 23 line
drawings. ISBN: 0292705905. $65.00 (cloth).
ISBN: 0292706243, $22.95 (paper).— Professor
Emeritus James Enderson of Colorado College
has written an engaging and very readable

ORNITHOLOGICAL LITERATURE

273

memoir that centers on the decline and recovery
of the Peregrine Falcon ( Falco peregrinus), a
now-revered raptor that suffered near extinction
in much of its range beginning in the mid-20th
century. The dramatic and remarkable recovery
of this species in North America, following the
banning of DDT, is certainly one of the most
significant conservation victories of the last cen-
tury, and Jim Enderson was a major player on
a team that won the game. The book’s illustra-
tions include well-chosen black and white pho-
tographs, as well as many original drawings by
artist Robert Katona, whose contributions add
significantly to the book’s success.

Enderson’s account might well be required
reading for young ornithology students; cer-
tainly, it must be that for graduate students
and established professionals. Enderson tells
his story well, and much of the ground he
covers in this book is now covered with actual
or allegorical asphalt, no longer accessible to
students currently embarking on careers. The
stars that crossed for Enderson were falconry
and science. He clearly has a passion for both,
and he was able to weave threads from each
to build a career full of adventure, scientific
puzzle-solving, and a cast of characters that
might have come from a novel.

The introductory chapter is a splendid de-
scription of the Peregrine Falcon, certainly
“one of the best-studied wild animals on the
planet.’’ ( The Birds of North America species
account lists over 300 references.) Enderson
provides us with an excellent summary of this
remarkable species’ speed, biology, sexual di-
morphism, coloration, distribution, hunting
techniques, and other critical life-history com-
ponents. The nickname “Blue Meanie” —
used throughout the book — is credited to En-
derson’s fellow peregrine researcher and good
friend, W. Grainger Hunt.

Enderson’s story begins in the early 1960s
with his searches for falcons. He focused at
first on Prairie Falcons ( Falco mexicanus),
then (like all falconers of that era) dreamed of
peregrines. His chance to engage with pere-
grines was finally realized when two falconers
invited him to visit the Queen Charlotte Is-
lands off the British Columbia coast, which at
the time was the site of the densest population
of nesting peregrines anywhere in their cos-
mopolitan range. One suspects that Enderson’s
rappelling skills might have had something to

do with the invitation, but the story of the
expedition is wonderful autobiography and
adventure. Even in his quest for falconry
birds, Enderson’s scientific orientation shines
through. For example, the expedition guide
shot a harbor seal ( Phoca vitulina) to feed
nestling peregrines recently taken from the
wild and, in describing the butchering, Ender-
son cannot resist the temptation (or obliga-
tion) to tell us why the seal’s flesh was so dark
(it relates to storing high levels of oxygen
when diving). He went home with his first
peregrine — the most highly valued species in
the world of American falconry.

By that time, Enderson was a graduate stu-
dent, and soon thereafter landed a job at Col-
orado College, in part because of his connec-
tion with Robert Stabler, a professor at the
college and a famous pioneer falconer. Pere-
grines had been declining for a decade, but
the picture was blurred in part by the secrecy
that surrounded nest sites — those who knew
the bird were not eager to tell their stories,
and most attributed local declines to egg col-
lectors or falconers. (In California, a few of
us who watched nesting peregrines knew that
eggs had been laid, but when we later returned
to cliffs, the adults defended weakly or not at
all, and the nest ledges were empty. At one
site where a friend had lavished a landowner
with canned hams and whiskey in an attempt
to exclude the reviled “eggers,’’ we conclud-
ed that the egg-collectors had come in from
the sea!) Surveys were then initiated (which
turned out to be post-decline surveys), and
Enderson was one of the first surveyors. He
checked some 50 historical nesting sites,
largely in the intercontinental West, and found
only 13 pairs. The picture would worsen be-
fore it was over.

The watershed event was the Peregrine
Conference of 1965, where peregrine scien-
tists and falconers assembled in Madison,
Wisconsin, to assess the extent of the decline
and speculate on the reasons for it. Enderson
was there and he was much impressed by
what he saw. Hypotheses explored as possible
causes of decline included: the peregrine is a
“wilderness species,’’ egg collecting, falcon-
ers, drought, and pesticides. Enderson omits
mention of Rachel Carson ( Silent Spring was
published in 1962), and fails to point out that
there was significant resistance to even dis-

274

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 2, June 2006

cussing pesticides at the conference. Roger
Tory Peterson was sitting not far from me. and
at one frustrating moment when the inevitable
discussion about pesticides was sidestepped
by a U.S. Fish and Wildlife Service represen-
tative, a frustrated and angry Peterson stabbed
the table with his wooden pencil!

But Enderson tells the DDE story well. It
was indeed like a mystery novel, with the pri-
mary culprit being DDE, not DDT. or dieldrin,
or any other of the array of biocides that
Carson had described in Silent Spring. As En-
derson describes it, there were many dead-end
roads traveled, in part because DDE was not
toxic to insects; therefore it had been little in-
vestigated. It turned out to be the primary cul-
prit that caused eggshell thinning and was re-
sponsible for most of the population decline.
The proof would not emerge until the parent
compound DDT was banned, but along the
way, experimental science provided strong ev-
idence. Enderson rightly credits David Peakall
with discovering DDE in peregrine eggshells
that were collected in 1948, only a couple of
years after the “wonder insecticide” had been
introduced into general agricultural use.

Some of the best parts of Enderson’s book
are his stories of peregrine surveys in North
America, and eventually in other parts of the
world. Enderson participated in many, if not
most, of these surveys, and his tales of ca-
noeing Arctic rivers, dangling from ropes on
500-foot cliffs, and interacting with sundry
bureaucrats make good reading. He tells won-
derful tales of remarkable characters, often
with a little spice and always with excellent
descriptions of character. For example, put in
the care of a “surly sergeant” on a Texas
beach when he is trapping migrating pere-
grines, Enderson wins the day by trapping,
banding, and releasing four birds. The surly
sergeant had been assigned to drive Enderson
(and Clayton White, another giant in the per-
egrine story) as punishment, but ended up an
enthusiastic trapper. There are tales of many
others.

Enderson was also part of the group that
managed, at long last, to breed falcons in cap-
tivity. In a chapter titled Timely Invention of
Peregrine Husbandry, Enderson describes this
technology in detail (I could have done with-
out the illustrated description of collecting
peregrine semen in the seam of a rubber gas-

ket placed on the head of the collector!). Then
(remarkably), he describes his theft of nestling
peregrines from some of the last productive
eyries in the United States and Canada. It was
a matter of the means justifying the ends, one
supposes, but it may raise some eyebrows.

Enderson — such an intimate part of the cap-
tive breeding and release program that is
widely credited with “saving the pere-
grine”— points out that what really saved the
species was the (then) controversial decision
in 1972 by William Ruckelshaus, head of the
new Environmental Protection Agency, to ban
most uses of DDT. He also asserts that the
Peregrine Falcon would have recovered on its
own from the small reservoir of functional
breeding pairs left here and there, but it would
have taken much longer, especially in those
areas from which it had disappeared entirely.
The release program was very popular, and
resulted in the elevation of the peregrine to
the status of absolute charisma. It had gone
from the reviled, often shot *'Duck Hawk” of
the mid-20th century to one of the best-loved,
wild vertebrates in the world.

Falconry is a major topic in this book, and
Enderson does it justice. He describes the
sport’s early days in North America, the col-
orful cast of characters, and the discovery of
the Arctic Peregrine’s Atlantic and Gulf of
Mexico coastal migration paths. He even in-
cludes a primer on falconry, which gives the
reader a sense of what that passion is all
about. I was especially pleased to see that En-
derson favors the correct pronunciation of fal-
con: these birds are not “phal- cons,” but “the
historically correct fall- cons,' as in the word
falling .” A “phal- con” is a car or a football
team; a “fall- con” is a bird.

In the latter passages, Enderson brings fal-
conry up to date and describes — with appro-
priate bitterness — “Operation Falcon,” a fed-
eral sting operation that, between 1981 and
1984, entrapped some 52 falconers and con-
fiscated 106 raptors. It was an unfortunate
chapter in the peregrine story.

One serious omission hangs over Ender-
son’s book — a fuller coverage of those who
sought to obfuscate the developing truth about
DDE, including pesticide company employ-
ees. Mention, perhaps, should also have been
made of the false claims that the peregrine’s
decline was faked by scientists who stood to

ORNITHOLOGICAL LITERATURE

275

benefit (in terms of professional fame and re-
search money) by reporting the precipitous
decline in numbers of peregrines.

This excellent book ends with a nicely writ-
ten memory of peregrines having returned to
two historical nesting sites from which they
had been missing for decades. The writing
here is a splendid description of emotional en-
counters with nature. The reader is put at the
spot and in the experience, and when blue
meanies appear after seemingly fruitless
searches, one shares in the relief and exulta-
tion. In an era when radiotelemetry has par-
tially replaced old-fashioned fieldwork and
modeling is thought to be a substitute for
much of what has occupied biologists for
ages, Enderson’s book reminds us of why
most of us enter wildlife-related work in the
first place. In most cases, we love the wild
things we study, we admire their beauty, and
we do all we can to guarantee that succeeding
generations will be able to do the same. —
STEVEN G. HERMAN, The Evergreen State
College, Olympia, Washington; e-mail:
hermans@evergreen.edu

HAWKS FROM EVERY ANGLE. By Jer-
ry Liguori. Princeton University Press, Prince-
ton, New Jersey. 2005: 133 pp., 68 plates, 371
photos, 2 maps. ISBN: 0691118248, $55.00
(cloth). ISBN: 0691118256, $19.95 (paper).—
In his new book, Hawks from Every Angle,
Jerry Liguori uses a new and different ap-
proach to identify 19 migratory hawk species
in flight. In the introduction, Jerry writes,
“This is primarily a visual guide; the photos
and captions are the crux of the book and are
meant to stand on their own.” Unlike previous
photo guides that offer images showing every
field mark in perfect lighting at point-blank
range, Jerry has selected high-quality images
that more accurately reflect true conditions of
field observation. He used his extensive ex-
perience studying hawks throughout North
America to select images that reflect realistic
flight profiles and structures for each species.
Through these images, Jerry represents the
full range of varying postures the birds can
show in flight when viewed from differing an-
gles and under varying environmental condi-
tions.

Multiple images are often stitched together
and presented side by side, with as many as
six images per page representing a single
“plate.” These stitched images typically show
comparative views of similar species at the
same angle, differing plumages (age, sex,
morph, race) of a given species, or different
flight profiles that illustrate the range of var-
iation for a given species under varying con-
ditions. The accompanying captions smartly
describe these comparative differences. The
author uses a holistic approach to identifica-
tion similar to that seen in Hawks in Flight by
Pete Dunne, David Sibley, and Clay Sutton
(Houghton Mifflin, 1988), except Jerry opts
for images over written descriptions as the pri-
mary focus of the guide. As such, this guide
is more useful in the field than its predecessor,
which was meant to be read at home.

The book is clearly designed for use by
hawkwatching enthusiasts at hawkwatching
sites. In the introduction, Jerry summarizes a
number of sites across North America, graphs
peak migration times by species, and adds ta-
bles that summarize high counts, by species.
The images generally cover the entire range
of expected “looks” each species may offer
as it flies by any hawkwatch site. However,
when pictures alone won’t suffice, Jerry uses
intuitive descriptions of behaviors, such as
comparative differences in wing flapping and
flight characteristics. For example, “Sharp-
shinned Hawks beat their wings in a shallow,
snappy, powerless manner, similar to a Robin.

. . . Cooper’s Hawks almost always soar with
a slight dihedral. ... In moderate to high
winds. Sharp-shinned Hawks appear hyper-
active, unstable, and hesitant, making constant
wing adjustments.” These subjective differ-
ences are used by seasoned hawkwatchers on
a daily basis to identify distant raptors, but
they are gleaned from thousands of hours of
experience and are not included in typical
guides. The author generally excludes fine de-
tails not easily seen in the field such as eye
color, and descriptions of individual feathers
that are notable only at very close range.

The text is organized by species and pre-
sented in a consistent format (the three accip-
iter species: A. striatus , A. cooperii, and A.
gentilis are treated as one group with com-
parative differences highlighted throughout).
Each species account begins with a general

276

THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118 , No. 2, June 2006

overview of the species (or species group),
followed by sections on migration and plum-
age, respectively. The remainder (and bulk) of
the account is dedicated to Flight Style with
subsections including wing beat, soaring,
head-on, gliding overhead, and wing-on/going
away. Portions of these accounts can be dif-
ficult to follow at times, particularly in the ac-
cipiter section, which continually bounces be-
tween the three species; however, the author
addresses this, to a degree, by using bold print
to accentuate key points and distinctive char-
acteristics found throughout.

As anyone familiar with raptors might ex-
pect, maximum coverage was given to the
highly variable Red-tailed Hawk ( Buteo ja-
maicensis). Jerry uses a full 14 pages of text
and images to thoroughly cover a wide range
of recognized subspecies, races, forms, and
color morphs in each age class. Jerry also cov-
ers the varying age classes of Bald Eagle
( Haliaeetus leucocephalus ) and Golden Eagle
( Aquila chrysaetos ) with detailed descriptions
of molt sequences and other plumage char-
acteristics.

This guide offers as much insightful com-
mentary on flight characteristics of raptors as
any guide ever has. It also offers a greater
range of differing perspectives and flight pro-

files than any previous guide. Unfortunately,
despite the all-encompassing title, there are
some “angles” not covered. For example,
there is no mention or images of perched
birds, and there is no coverage of general nat-
ural history other than that pertaining to mi-
gration. The exclusion of some field marks def-
initely limits the scope and usefulness of this
book as well.

Whereas this book is clearly an indispens-
able resource for anyone interested in hawk-
watching, away from the hawkwatch site it of-
fers little assistance for the observer wanting
to identify the hawk perched in their back-
yard. It also offers little for those curious
about nesting habits or breeding range of a
given species. For answers to these questions,
readers will have to turn to another guide.
However, if the backyard hawk flies from the
tree and you are able to observe it as it flaps
straight away, then Hawks from Every Angle
is likely just the ticket. Given the reasonable
price, slim profile, and the wealth of personal
wisdom packed into the pages of this book, it
deserves a spot on every birder’s bookshelf.
There is no one who can’t learn something
from this work!— JEFFREY BOUTON, Leica
Sport Optics, Port Charlotte, Florida; e-mail:
jbouton2@earthlink.net

THE WILSON JOURNAL OF ORNITHOLOGY

Editor JAMES A. SEDGWICK
U.S. Geological Survey
Fort Collins Science Center
2150 Centre Ave.. Bldg. C.

Fort Collins, CO 80256-81 18, USA
E-mail: wjo@usgs.gov

Editorial Board KATHY G. BEAL
CLAIT E. BRAUN
RICHARD N. CONNER
KARL E. MILLER

Review Editor

Managing Editor
Copy Editor
Editorial Assistant

M. BETH DILLON
CYNTHIA P. MELCHER
ALISON R. GOFFREDI

MARY GUSTAFSON
Texas Parks and Wildlife Dept.

2800 S. Bentsen Palm Dr.

Mission, TX 78572, USA
E-mail: WilsonBookReview@aol.com

GUIDELINES FOR AUTHORS

Consult the detailed “Guidelines for Authors” found on the Wilson Ornithological Society Web site (http://
www.ummz.lsa.umich.edu/birds/wilsonbull.html). Beginning in 2007, Clait E. Brain will become the new editor
of The Wilson Journal of Ornithology. As of 1 July 2006, all manuscript submissions and revisions should be
sent to Clait E. Brain, Editor, The Wilson Journal of Ornithology, 5572 North Ventana Vista Rd., Tucson, AZ
85750-7204, USA. The New Wilson Journal of Ornithology office and fax telephone number will be (520) 529-
0365, and the E-mail address will be TWilsonJO@comcast.net.

NOTICE OF CHANGE OF ADDRESS

If your address changes, notify the Society immediately. Send your complete new address to Ornithological
Societies of North America, 5400 Bosque Blvd., Ste. 680, Waco, TX 76710.

MEMBERSHIP INQUIRIES

Membership inquiries should be sent to James L. Ingold, Dept, of Biological Sciences, Louisiana State Univ.,
Shreveport, LA 71115; e-mail: jingold@pilot.lsus.edu

THE JOSSELYN VAN TYNE MEMORIAL LIBRARY

The Josselyn Van Tyne Memorial Library of the Wilson Ornithological Society, housed in the Univ. of
Michigan Museum of Zoology, was established in concurrence with the Univ. of Michigan in 1930. Until 1947
the Library was maintained entirely by gifts and bequests of books, reprints, and ornithological magazines from
members and friends of the Society. Two members have generously established a fund for the purchase of new
books; members and friends are invited to maintain the fund by regular contribution. The fund will be admin-
istered by the Library Committee. Terry L. Root, Univ. of Michigan, is Chairman of the Committee. The Library
currently receives over 200 periodicals as gifts and in exchange for The Wilson Journal of Ornithology. For
information on the Library and our holdings, see the Society's web page at http://www.ummz.lsa.umich.edu/
birds/wos.html. With the usual exception of rare books, any item in the Library may be borrowed by members
of the Society and will be sent prepaid (by the Univ. of Michigan) to any address in the United States, its
possessions, or Canada. Return postage is paid by the borrower. Inquiries and requests by borrowers, as well as
gifts of books, pamphlets, reprints, and magazines, should be addressed to: Josselyn Van Tyne Memorial Library,
Museum of Zoology, The Univ. of Michigan, 1109 Geddes Ave., Ann Arbor, MI 48109-1079, USA. Contri-
butions to the New Book Fund should be sent to the Treasurer.

This issue of The Wilson Journal of Ornithology was published on 5 June 2006.

280

Continued from outside back cover

2 47 Golden-cheeked Warbler males participate in nest-site selection
Allen E. Graber, Craig A. Davis , and David M. Leslie, Jr.

251 Provisioning of Magellanic Woodpecker ( Campephilus magellanicus) nestlings with vertebrate prey
Valeria S. Ojeda and M. Laura Chazarreta

254 Reverse mounting and copulation behavior in polyandrous Bearded Vulture ( Gypaetus barbatus) trios
Joan Bertran and Antoni Margalida

25 6 Natural occurrence of crowing in a free-living female galliform, the California Quail
Jennifer M. Gee

259 Poult adoption and nest abandonment by a female Rio Grande Wild Turkey in Texas

Steve T. Metz, Kyle B. Melton, Ray Aguirre, Bret A. Collier, T. Wayne Schwertner, Markus J. Peterson, and
Nova J. Silvy

261 Predation by a Blue-crowned Motmot ( Momotus momota) on a hummingbird
J. Mauricio Garcla-C. and Rakan A. Zahawi

264 Once Upon a Time in American Ornithology

2 67 Ornithological Literature

The Wilson Journal of Ornithology

(formerly The Wilson Bulletin)

Volume 118, Number 2 CONTENTS June 2006

Major Articles

131 Breeding productivity of Bachman’s Sparrows in fire-managed longleaf pine forests
James W. Tucker, Jr., W Douglas Robinson, and James B. Grand

138 Variation in Bachman’s Sparrow home-range size at the Savannah River Site, South Carolina
Jonathan M. Stober and David G. Krementz

145 Nesting success and breeding biology of Cerulean Warblers in Michigan
Christopher M. Rogers

152 Migrant shorebird predation on benthic invertebrates along the Illinois River, Illinois
Gabriel L. Hamer, Edward J. Heske, Jeffrey D. Brawn, and Patrick W Brown

1 64 Composition and timing of postbreeding multispecies feeding flocks of boreal forest passerines in
western Canada

Keith A. Hobson and Steve Van Wilgenburg

173 Variation in size and composition of Bufflehead {Bucephala albeola) and Barrow’s Goldeneye
(. Bucephala islandica) eggs

Jennifer L. Lavers, Jonathan E. Thompson, Cynthia A. Paszkowski, and C. Davison Ankney

178 Site-specific survival of Black-headed Grosbeaks and Spotted Towhees at four sites within the
Sacramento Valley, California
Thomas Gardali and Nadav Nur

187 Pre-migratory fattening and mass gain in Flammulated Owls in central New Mexico
John P DeLong

194 Morphological variation and genetic structure of Galapagos Dove {Zenaida galapagoensis) populations:
issues in conservation for the Galapagos bird fauna
Diego Santiago-Alarcon, Susan M. Tanksley, and Patricia G. Parker

208 Breeding ecology of American and Caribbean coots at Southgate Pond, St. Croix: use of woody
vegetation

Douglas B. McNair and Carol Cramer-Burke

218 Insular and migrant species, longevity records, and new species records on Guana Island, British Virgin
Islands

Clint W. Boal, Fred C. Sibley, Tracy S. Estabrook, and James Lazell

225 Reproductive behavior of the Yellow-crowned Parrot {Amazona ochrocephala) in western Panama
Angelica M. Rodriguez Castillo and Jessica R. Eberhard

Tbl Gregarious nesting behavior of Thick-billed Parrots ( Rhynchopsitta pachyrhyncha) in aspen stands
Tiberio C. Monterrubio-Rico, Javier Cruz-Nieto, Ernesto Enkerlin-Hoeflich, Diana Venegas-Holguin,
Lorena Tellez-Garcia, and Consuelo Marin-Togo

Short Communications

244 No extra-pair fertilization observed in Nazca Booby ( Sula granti) broods
David J. Anderson and Peter T. Boag

Continued on inside back cover

8H34

Y& Wilson Journal

of Ornithology

Volume 118, Number 3, September 2006

MCZ

LIBRARY

DEC 09 2010
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