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OF CANADA GEESE AND BLACK DUCKS
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UNITED STATES DEPARTMENT OF THE INTERIOR

FISH AND WILDLIFE SERVICE

BUREAU OF SPORT FISHERIES AND WILDLIFE

Special Scientific Report — Wildlife No. 118

UNITED STATES DEPARTMENT OF THE INTERIOR, STEWART L. UDALL, Secretary
Stanley A. Cain, Assistant Secretary for Fish and Wildlife and Parks

Fish and Wildlife Service, Clarence F. Pautzke, Commissioner
Bureau of Sport Fisheries and Wildlife, John S. Gottschalk, Director

AERIAL SURVEYS OF CANADA GEESE
AND BLACK DUCKS IN EASTERN CANADA

by

Charles F. Kaczynski and Everett B. Chamberlain

Migratory Bird Populations Station
Division of Wildlife Research

Special Scientific Report — Wildlife No. 118
Washington, D.C. • April 1968

For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, U.C. 20402 - Price 30 cents

ABSTRACT

This report summarizes results from aerial surveys of Canada geese
and black ducks in eastern Canada. Information presented is based on
data obtained during the summer of 1956, 1962-66 for Canada geese and
during the spring of 1955, 1956, 1963-66 for black ducks.

Canada geese show extreme variations in density in eastern Canada.
Density strata have been delineated. Sampling error in the stratified
sample of Canada geese exceeded + 20 percent at the 95 percent confidence
level, but estimates of optimum sample allocations indicate that it may
be reduced to less than that. The estimated number of geese in Canada
east of James and Hudson Bays approximates the number accounted for by
the Atlantic Fl37way winter survey and kill estimates. The extent to
which the two populations are the same is unknown.

The visibility from aircraft of breeding black ducks is extremely
low. Distribution of black ducks within the survey area is quite uni-
form and some apparent differences may be due to variable conditions
during observation. With the Bureau's present resources, a statistically
reliable design for sampling black ducks breeding in eastern Canada is
not feasible. Based on areas with consistent coverage and weighted
toward annual comparability in group sizes, the black duck breeding
population index appears to have been decreasing each year since 1963.
Without adjustment for visibility, the index figure equals approximately
one-eighth of the Atlantic Flyway winter survey figure.

11

CONTENTS

Page

ABSTRACT vi

INTRODUCTION 1

METHODS 1

General 1

Canada Goose Survey Methods 4

Black Duck Survey Methods 4

CANADA GOOSE SURVEY - FINDINGS 5

Canada Goose Density Strata 5

Estimates of Confidence Limits and Optimum Sample Allocation for

the Stratified Canada Goose Survey 8

Canada Goose Summer Indexes Compared With Winter Survey and Kill

Statistics 8

Canada Goose Summer Survey and Hunting Regulations 16

BLACK DUCK SURVEY - FINDINGS 17

Observed Black Duck Densities 17

Estimation of Black Duck Breeding Population Trends in Eastern

Canada 17

Comparison of Black Duck Breeding Population Trends With

Wintering Population Survey Trends 24

Approximation of the Proportion of Black Ducks Present That are

Seen From the Air (visibility rate) 27

SUMMARY AND DISCUSSION 27

Canada Goose Breeding Population and Production Survey 27

Black Duck Breeding Population Survey 28

REFERENCES 29

111

Table Page

1 Canada goose densities and population indexes taken by
aerial survey in eastern Canada, 1956 and 1962-66 ... 6

2 Computation of standard error and confidence limits

for stratified Canada goose samples 9

3 Calculation of optimum sample allocation for stratified
Canada goose sample 11

4 Estimation of improvement in confidence limits from use
of optimum sample allocation for stratified Canada goose
sample, based on years 1963-66 12

5 Winter survey and kill data compared with summer indexes

of Canada geese 13

6 Densities of black ducks determined from breeding
population surveys in eastern Canada 21

7 Comparability indexes for groupings of black ducks and
changes in density per square mile among years 1955,

1956 and 1963-66 22

8 Sources and treatment of data for comparing breeding
ground index trends and winter survey population trends

for black ducks 25

IV

List of Figures

Page

Frontispiece. Two views most typical of the area surveyed for

Canada geese vi

Figure 1. Canada goose survey transects, 1965-66 2

Figure 2. Black duck survey sampling plan 3

Figure 3. Canada goose density strata in eastern Canada . . 7

Figure 4. Summer Canada goose index from Canada east of
James and Hudson Bays compared with following
winter survey and kill data in the United
States 14

Figure 5. Summer Canada goose index from strata B, C, E and
F compared with following winter survey and kill
data in the Atlantic Fljn^iay 15

Figure 6. Observed black duck densities per square mile

based upon average of observations for 1955, 1956
and 1963-66 , 18

Figure 7. Zonal division of degree blocks sampled for black

ducks, 1955-56 and 1963-66 19

Figure 8. Black duck density per square mile by zones ... 23

Figure 9. Black duck population trend from the breeding

ground survey compared with Atlantic Flyway winter
survey trends 26

Frontispiece .

Two views most typical of the area surveyed for Canada
geese. Above, continental tundra. Below, open boreal
forest and muskeg.

VI

INTRODUCTION

This report presents results of aerial surveys of Canada geese and
black ducks nesting in eastern Canada. The aerial surveys were initiated
to obtain annual indexes to the size of the fall flight with the objective
of providing bases for determining suitable hunting season lengths and
bag limits. The history of aerial surveys in eastern Canada has been
described in an earlier report (Chamberlain and Kaczynski, 1965) and will
not be detailed here.

METHODS

General

Aerial survey transects for waterfowl are one-fourth mile wide
strips visually estimated (one-eighth mile on each side of the aircraft)
as they are flown cross-country. Division of the transect into 18-mile-
long segments is useful for statistical treatment, waterfowl distribution
delineation, and navigation. When topographic conditions permit, the
transects are flown at 200 to 300 feet above the ground. In eastern
Canada, rough terrain often makes it necessary to fly higher than the
preferred altitude. The aircraft used in eastern Canada since 1962 is
a twin-engine amphibian (Grumman Goose) . Speed on the transects is
about 120 miles per hour. Waterfowl observations are dictated into a
recorder.

Because both the duck and goose surveys were experimental and
exploratory, the pattern of aerial transects in eastern Canada was
variable. Canada goose survey transects were standardized in 1965
(fig. 1) and, except for a planned westward extension into the Churchill,
Manitoba, area in 1967, little change is foreseen. Black duck survey
transects were standardized in 1967 (fig. 2). They have been rather
evenly distributed through the survey area.

The eastern Canada survey has been conducted in two phases. The
first phase, from early May to mid-June, was a survey primarily of black
duck breeding pairs. This survey was limited in its northward extension
to about 54° north latitude because lakes further north were still ice-
covered in mid-June. Hence it was not possible to cover the northernmost
range of the black duck breeding population. The second phase, from
early July to mid-August, covered the same area as the first to obtain
a count of duck broods, and in addition continued northward to survey
Canada geese on transects up to the Hudson Strait. Beginning in 1967
that part of the survey designed to record duck broods was discontinued,
allowing all of the effort in July and August to be directed toward the
survey of Canada geese. Data from the black duck brood survey were too
limited to merit continuance.

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Canada Goose Survey Methods

Geese seen per square mile in 1956 and for the years 1962 through
1965 were plotted within one-degree-block units of latitude and longitude
to determine differences in goose density within the survey area. The
suirvey area was then divided into strata showing density differences.
Broods were given an average value of six (two adults, four young) and
combined with other geese seen. Data from earlier years were examined
but survey coverage was considered too restricted to contribute balanced
information for stratification. The turnover in aerial crew personnel
during the early years and the possibility of changes in the distribution
of goose populations with the passage of time were also considered in
this decision.

Annual indexes were based upon density strata; in each stratum,
the average density per square mile was computed and multiplied by the
number of square miles in the stratum. The figures for all strata
were then totaled. This approach seemed better than either comparing
numbers of geese seen over the total area, which was biased by non-
uniform sampling of density areas, or comparing those degree blocks of
latitude and longitude covered in consecutive years, which led to a
sharp reduction in the originally small sample.

Survey results in 1962 were too low and variable, possibly due
to crew inexperience. These data were used for stratification but were
exempted from estimates of optimum sample allocation and comparison of
population levels.

Statistical procedures described by Snedecor (1956) were used to
examine sampling error in the stratified sample and to make estimates
of optimum sample allocation and confidence limits. Since the samples
were not taken randomly and since the goose observations do not approx-
imate a normal distribution, the results are considered to be rough
estimates .

Black Duck Survey Methods

The heavily forested habitat preferred by breeding black ducks
limits the proportion of ducks that can be observed on an aerial survey.
In addition, the proportion seen is affected by the phenology of the
breeding season as determined by climatic conditions. An extreme
example of this is the "pile-up" of ducks that the survey may encounter
during a year when late ice break-up delays northward migration. While
"pile-ups" show obvious evidence of a bias in numbers of ducks observed,
less discernible variables are also probable because of local and annual
climatic variations during the time of aerial survey. This problem and
a method designed to overcome it have been described (Chamberlain and
Kaczynksi, 1965). The method, referred to as the "group-characteristic
procedure," compares similar group sizes such as singles, pairs, and

groups of three, which represent birds apparently at similar stages in
nesting phenology. In the present report, as a result of having more
data available for examination, we use some modifications of the original
method.

CANADA GOOSE SURVEY - FINDINGS

Canada Goose Density Strata

Canada goose populations in eastern Canada differed markedly in
density over their range. The six strata outlined in figure 3 are based
on the combined results of surveys in 1956 and 1962 through 1965. No
modification in strata boundaries was made after 1965. Annual indexes
per stratum for 1956 and years after 1961 are shown, together with
period averages for the strata, in table 1. The sharp irregularities
in stratum boundaries resulted from delineating strata according to
degree blocks to which the observations were assigned.

Exceptionally large numbers of geese, both flocked adults and
broods, were found each year in stratum A on the Hudson Bay side of the
Ungava Peninsula (fig. 3). Geese seen there were concentrated near the
coast and their number decreased rapidly toward the interior, so that
a low density area (stratum E) could be defined to the east and south.
Another high density area surrounded the western and southern shores of
Ungava Bay (stratum B) . The density in stratum B was only about half
as great as that in stratum A, but was much higher than in all other
strata. Here again, observations of .geese decreased quite rapidly away
from the coast, but to the south they were sufficient to designate areas
of medium density (stratum C) . Stratum F included the southern extremity
of the breeding range, where observations of geese were markedly fewer
than in areas to the north, including low density stratum E. Because
few geese were observed in the eastern margin of the surveyed area, it
was considered part of stratum F. Surveys in 1964-66 west of James Bay
(stratum D) showed a density appreciably higher than other areas of
similar latitude but lower than stratum C.

A reservation concerning the use of density strata is that obser-
vations of geese may vary with survey conditions. For example, the
lower counts obtained in the northeast extension of stratum F must result
in part from the rugged terrain which required the survey to be flown
at a higher altitude. Under these conditions, geese were less conspic-
uous because of the altitude and the increased attention required for
flying. Vegetative differences between forest and tundra probably also
effect the numbers of geese observed. Although density differences appear
great enough to reflect actual differences in the distribution of geese,
the variables mentioned undoubtedly contribute to these differences.

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Estimates of Confidence Limits and Optimum Sample Allocation for the
Stratified Canada Goose Survey

The 95 percent confidence limits of the stratified Canada goose
sample have varied from +21 percent of the mean in 1966 to + 44 per-
cent of the mean in 1962 (table 2). Calculation of the optimum sample
allocation, as indicated by the results of the last 4 years of survey
(table 3), shows that the sampling intensity should be increased in
stratum A. These data indicate that from 44 to 51 percent of the total
sample should be allotted to stratum A. The 1966 data indicate an
allotment of only 23 percent for that year because the variability of
the data from stratum A was markedly lower while that for stratum E
was markedly higher.

Table 4 shows estimates of the improvement in confidence limits
which might have resulted if optimum allocation of samples had been
made from 1963 to 1966. These estimates, based upon the average of the
estimated allotment in table 3, reveal that, with optimum allocation,
confidence limits below + 20 percent of the mean would have occurred.
Because of the apparently atypical results in the 1966 sample, the
sample taken in that year showed better confidence limits (+21 percent)
than would have resulted from optimum allocation (+ 23 percent).

Canada Goose Summer Indexes Compared With Winter Survey and Kill
Statistics

Population estimates compiled by surveys in eastern Canada may be
compared in a general manner with the winter survey and kill figures.
Sampling error in the summer index is high relative to the apparent
annual changes. The reliability of winter survey counts is unknown.
Also, there is little basis for a delineation of comparable reference
areas, summer to winter, north to south. It appears that breeding geese
from any particular northern area may distribute themselves widely in
their choice of wintering areas. For example, in the summer of 1965,
an extensive banding operation, in the vicinity of Povungnituk, Quebec,
detected that most of the banded flightless adults taken had been banded
in the Mississippi Flyway (personal communication, J. D. Heyland) . If
this trapped sample is representative of the high density area (stratum
A) on the western side of the Ungava Peninsula, it indicates that the
geese in the area, which provide about half of the total summer index,
are associated with both the Mississippi and Atlantic Flyways .

Table 5 compares summer index values from the Canada goose survey
with numbers of geese accounted for in winter surveys and kill estimates.
The summer index is compared with the following winter survey and fall
and winter kill estimate.

Figures 4 and 5 illustrate the relation of the values in table 5.
The population levels represented by the summer index east of James
and Hudson Bays were similar to those indicated in the Atlantic Flj^ay

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10

Table 3 . --Calculation of optimum sample allocation for stratified Canada
goose sample (Snedecor, 1956, p. 508)

Average

Stratum

Standard

Percent

percent

weight

deviation

allotment

allotment

Year

Stratum

(W)

(s)

Ws

Ws/Sl Ws

1963-66

1963

A

.07

63.50

4.45

44

B

.04

10.91

0.44

4

C

.11

10.62

1.17

12

E

.30

9.78

2.93

29

F

.48

2.30

1.10
10.09

11
100

1964

A

.07

72.94

5.11

51

B

.04

34.15

1.37

14

C

.11

10.14

1.12

11

E

.30

5.05

1.52

15

F

.48

1.72

0.83
9.95

8
99

1965

A

.07

68.67

4.81

45

B

.04

50.98

2.03

19

C

.11

9.67

1.06

10

E

.30

4.63

1.39

13

F

.48

2.73

1.31
10.60

12
99

1966

A

.07

39.32

2.75

23

41

B

.04

42.47

1.70

15

13

C

.11

10.75

1.18

10

11

E

.30

7.55

2.27

19

19

F

.48

8.02

3.84
11.74

33
100

16
100

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B

H

800 r

^ Eastern Canada (index)

— - — • Atlantic Flyway (winter survey and kill)

— - * Mississippi Flyway (winter survey and kill)

Eastern Canada and Atlantic Flyway

700 •-

600 I-

1963-6A

1964-65

1965-66

1966-67

800

700

600

500 L

Eastern Canada and Mississippi Flyway

I

I

/

I

1963-64

1964-65 1965-66

YEAR AND SEASON

1966-67

Figure 4. — Summer Canada goose index from Canada east of James

and Hudson Bays compared with following winter survey
and kill data in the United States.

14

-• Atlantic Flyway (winter survey and kill)
-• Strata B, C, E and F in Canada (index)

fd

a
a
o

o

CO

Q

O

X
H

800

700

600 -

500

400

300

200

_L

I

_L

1963-64

1964-65
YEAR AND SEASON

1965-66

1966-67

Figure 5. — Sununer Canada goose index from strata B, C, E and
F compared with following winter survey and kill
data in the Atlantic Flyway.

15

winter survey and kill from 1963-64 to 1965-66. However, from 1965-66
to 1966-67 the two surveys show a diverging trend (fig. 4). Comparison
of summer index values east of James and Hudson Bays with Mississippi
Flyway winter survey and kill figures shows opposition in trend every
year since 1963-64 (fig. 4). Comparison of summer index values from
strata B, C, E, and F (high density stratum A omitted) with Atlantic
Flyway winter survey and kill estimates shows agreement in trend every
year since 1963-64 (fig. 5). However, the index from this portion of
the breeding ground approximates only one-half of the Atlantic Fljrway
winter survey and kill. While it is likely that nearly all geese present
are observable on the transects in the tundra, a lesser proportion are
probably observed when forested areas are surveyed. Also, it is likely
that some geese in the western portions of strata E and F are associated
with the Mississippi Flyway. Both of the above effects may account for
the low index value from strata B, C, E, and F compared with Atlantic
Flyway winter population estimates.

Canada Goose Summer Survey and Hunting Regulations

Annual hunting regulations are set on July 15 in Canada and
August 1 in the United States. The summer survey for Canada geese is
not usually completed until mid-August. Hence, the latest data on
the Canada goose breeding population and production is not available
for consideration at regulations hearings. Completion of the summer
survey earlier than August 1 is not feasible if maximum production
figures are to be included in the index. Markedly lower brood counts
on transects 19 through 22 (fig. 1) in eastern Ungava Peninsula were
associated with early survey dates, as shown below:

Year

Dates of survey

July 20, 21
July 27 - August
August 9, 10

2

Total
broods

7
28
50

"Downy young"
broods

1965
1964
1966

2

1
1

The infrequent recording of the smallest "downy young" broods, even
at the earlier dates, suggests that surveys conducted too early will
lead to low counts not only because fewer broods have been produced, but
also because young broods are more difficult to observe than are older
broods. Unless setting the hunting regulations for Canada geese is
delayed, data adequately representing production in the highest density
area in Canada cannot be made available for current regulations hearings,

16

BLACK DUCK SURVEY - FINDINGS

Observed Black Duck Densities

Black duck densities did not differ enough between areas, and
differences between years were not consistent enough to justify strati-
fication of the sample area (Chamberlain and Kaczynski, 1965). Figure
6 shows the density per square mile within the arbitrarily selected
blocks in the survey area. These figures are based upon the average
of the years 1955, 1956 and 1963-66. Total number of square miles
sampled in all years is also shown.

The two southernmost blocks yielded below-average densities, but
this may be related to a phenological difference rather than a density
difference since, at the time of survey, nesting tends to be more
advanced in southern than in northern areas. When nesting is advanced,
hens flush less readily and drakes may have left the area. Lower than
average densities in the tier of blocks next to the St. Lawrence River
were probably related to difficult survey conditions caused by the
mountainous terrain in much of that area.

Data for the Labrador area are primarily from surveys in 1955 and
1956. For most years from 1963 to 1966, the ice-line prevented making
the survey during the required period of time. The relatively high
density of black ducks in the northernmost and easternmost blocks
indicates that the survey does not reach the northern limit of the
black duck breeding population. However, a greater proportion of the
ducks present may be counted in the more barren northern blocks than
in the heavily forested southern blocks and the importance of the more
northern areas may be exaggerated.

Estimation of Black Duck Breeding Population Trends in Eastern Canada

The group-characteristic procedure (Chamberlain and Kaczynski, 1965)
was used in estimating trends of black duck breeding populations in
eastern Canada to reduce the bias imposed by different stages of breeding
as the survey progressed northward. There is a correlation between the
progress of the breeding season and the manner in which ducks are grouped.
For example, early in the season, paired birds are most common. Later
in the season, as the hen becomes attached to the nest, more single birds
(males) are seen. Still later, the males congregate into small flocks
and fewer pairs or singles are seen. The group-characteristic procedure
divides the survey area into southern, central, and northern zones (fig.
7), and uses only the degree blocks sampled every year. For each zone
and year we computed the total number of black ducks seen per square mile
and the number of (1) singles, (2) pairs, (3) groups of three, and (4)
groups of from four to 10. Flocks larger than 10 were omitted because
their occurrence was sporadic. The sizes and occurrence, by year and
zone of the flocks omitted, are as follows:

17

-^i^-'^*^%

/— ■

,A

:£3^

)

Figure 6. --Observed black duck densities per square mile based upon

average of observations for 1955, 1956 and 1963-66. Numbers
in parentheses indicate number of square miles sampled in
all years combined.

18

Lv

r

^^«*^^

''. -^-'' /-.--N

'2^

■ /JlJfl

.^>^^'x^;;"^<:^. \l southern'^

^'' ;■■

.i^

' ' -^

■■'■■■ "■'': . f

^^ ?=•■

fe^sC,

-)

Figure 7. --Zonal division of degree blocks sampled for black ducks,
1955-56 and 1963-66.

19

Occurrence and sizes of black duck flocks larger than ten

Zone Total

Year

Southern

Centra

1

Northern

Ducks

Flocks

1955

0

11,12,

13

0

36

3

1956

0

13

15

28

2

1963

0

35

0

35

1

1964

0

0

0

0

0

1965

20

25

0

45

2

1966

0

16

30

46

2

All years:

Ducks

20

125

45

190

—

Flocks

1

7

2

••.

10

Densities in each group class were ranked as high, medium, or low
in relation to the mean density for all 6 years of survey (table 6).
Values falling within the range of the mean, plus or minus 1 standard
error, were arbitrarily considered medium, while values outside that
range were considered high or low.

In table 7, agreement or disagreement in these rankings between
any 2 years for each group of ducks is quantified by assigning a value
of two when rankings agreed (high-high, low-low, medium-medium), a
value of one for combinations of medium with either high or low, and
no value for greatest difference in combinations (high-low) . Thus
highest comparability (2) in each of the four groups would provide a
maximum agreement index of eight. Only comparisons that resulted in
an index of five or higher are shown in table 7.

For those years considered most comparable (agreement index of
five or greater, table 7) we plotted total densities (excluding flocks
larger than 10) for each zone and year (fig. 8). Lines were drawn
between the comparable points. For example, in the northern zone, 1955
data were comparable only to 1956 and 1964 data (table 7). Therefore,
in figure 8, lines are drawn from 1955 to only 1956 and 1964. With the
exception of the central zone from 1955 to 1963, every comparison, thus
selected, of an earlier year with a later year showed a decrease in
density.

An average density trend for the combination of zone-year com-
parison is shown by the doubled line in figure 8. The points on this
line were determined from the average of all points and intersects in
figure 8. In determining the average trend line, zone densities were
weighted by area.

20

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to to nj

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0)
en 0)

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U

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c

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23

Comparison of Black Duck Breeding Population Trends With Wintering
Population Survey Trends

Atlantic Flyway winter survey population data were grouped by five
areas for comparison with the breeding pair population trends indicated
by the group-characteristic procedure. These were (1) States north of
Maryland and Delaware, (2) States south of Maryland and Delaware, (3)
Maryland and Delaware plus States to the north, (4) Maryland and Delaware
plus States to the south and (5) Atlantic Flyway. Wintering population
survey figures (taken from annual Waterfowl Status Reports) for the above
areas are shown in table 8, section A. Breeding pair populations are
compared with the winter survey of the preceding winter.

All comparable (coverage) data from the breeding ground surveys are
compared with Atlantic Flyway data only, although ducks surveyed in the
more western part of the surveyed area are probably associated with both
the Atlantic and Mississippi Flyways . For those years in which there
was poor alignment in trend between the breeding ground survey and
Atlantic Flyway winter population estimates (for example, see years
1963-1964, fig. 9), examination of Mississippi Flyway winter data did
not show evidence of a compensatory effect. Also, the trial inclusions
of several segments of Mississippi FlJa^;ay winter data with the Atlantic
Flyway winter data did not provide a more credible trend relation with
the breeding ground survey than that shown by the Atlantic Flyway winter
data alone.

In comparing wintering ground trends with breeding population
trends, the selected populations on the wintering ground were expressed
in terms of their density relative to the breeding ground survey area
and then reduced to the level of breeding ground survey densities
(table 8) . The reduction was based upon the average difference between
the two surveys over all years compared.

The breeding ground survey density does not include that part of
the breeding population seen as flocks larger than 10. The density is
also underestimated because breeding populations are more difficult to
observe than are wintering populations. Data from other species and
habitats suggest that probably a small fraction of the black ducks
present are seen in the breeding ground survey.

Comparison of trends from various parts of the population wintering
in the Atlantic Flyway with the breeding population trend is shown in
figure 9. The reduction factor (value with which the winter population
density was multiplied so that it would correspond in average level with
the breeding ground density) is also shown. The best correspondence in
trend appears in the comparison between the breeding population and the
population wintering south of Maryland and Delaware.

24

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compared with Atlantic Flyway winter survey trends.

i'Density per square mile of breeding ground survey counts is based

upon group characteristics procedures.
^'Density per square mile of winter survey population relative to the

breeding ground survey area is reduced to the level of breeding ground

density to facilitate trend comparisons. The mean reduction factor is

shown.

26

Approximation of the Proportion of Black Ducks Present That are Seen
From the Air (visibility rate)

Indirect estimates of the black duck population using band recovery
and kill data indicate that the black duck winter population is much
larger than shown by winter surveys (data on file at the Migratory Bird
Populations Station). Indirect estimates of population agree with summer
and winter surveys in showing a population drop in recent years. While
the average winter population in the 1950's was estimated to be 1.5
million black ducks, a population of 870,000 was estimated for 1964. If
we accept this indirect estimate as the general population level of recent
years and estimate the part of the total black duck breeding population
that is within the survey area, it is possible to approximate the pro-
portion of black ducks present that are seen from the air (visibility
rate). It appears that 30 to 40 percent of the continental breeding
population is resident in the summer survey area (data on file at the
Migratory Bird Populations Station). We may approximate the proportion
of breeding black ducks that are seen from the air (visibility rate) as
follows :

Average breeding ground index (including flocks) 1963-66: 54,774,

Fraction of the breeding population within the summer survey
area: 0.30 to 0.40.

Indirect estimate of wintering black ducks: 870,000.

Visibility rate = 54,774 - .30 to .40 "^ 870,000 = . 16 to .21.

SUMMARY AND DISCUSSION

Canada Goose Breeding Population and Production Survey

Aerial surveys have increased our knowledge about the distribution
of Canada geese on their breeding grounds, and this will aid in inter-
preting banding data in the future. Currently, there are several
limitations to the usefulness of the summer survey as a management tool,
These limitations include high sampling error, inadequate knowledge of
seasonal distribution, and lateness of surrvey completion relative to
the time of setting regulations.

Optimum sample allocation estimates show that, with the present
resources and methods, sampling error can be reduced to a range of
+ 17 to 20 percent of the mean (95 percent confidence level) . This
degree of precision would detect, as statistically significant, changes
in the range of a 40 to 50 percent increase or of a 30 to 35 percent
decrease .

27

Administrative use of summer goose data is hindered by inadequate
knowledge of seasonal distribution, summer to winter. Comparisons of
trends between summer survey indexes and winter survey figures suggest
a relation between the summer survey area and the Atlantic Flyway.
However, this relation must be viewed critically in the light of the
degree of sampling error in the summer index (which alone may account
for changes indicated since 1963) and the unknown reliability of the
winter survey. Unless an extensive banding program can be conducted
to show a consistent relation between summer and winter goose population
by area, these relations will have to be surmised.

There is evidence that advancing the present schedule of the
summer survey to make the data available in time for hearings on regu-
lations would not be practical because it would result in greatly
reducing the number of broods that could be observed. If the summer
survey is not conducted at a time when broods can be observed, summer
survey population estimates would be of little value and a winter survey
would be preferable.

Black Duck Breeding Population Survey

Application of the group-characteristic procedure to data obtained
from eastern Canada indicates a steadily declining breeding population
since 1963 for that portion of the breeding range in Canada surveyed
repeatedly.

A downward trend is indicated also by winter survey results south
of Maryland and Delaware since 1963 and by winter survey results of the
whole Atlantic Fljrway in 1965 and 1966. We estimate that the survey
area includes about 30 to 40 percent of the total breeding black ducks.
It appears that the proportion of black ducks seen from the air is quite
low, possibly 16 to 21 percent. The combination of limited area coverage
and limited visibility provides a breeding population index that is
about 6 percent of the total black duck population as computed by indirect
estimat ion.

It is not possible to evaluate the relative effectiveness of the
breeding ground survey and winter survey in indicating population changes
because they can only be judged against each other. Knowledge of the
distribution of black ducks on the breeding ground will be needed to
interpret band recovery data properly. However, delineation of relative
black duck densities from the survey data in eastern Canada will have to
cope with a difficult problem of variable observation conditions coupled
with a small sample of black ducks observed. Tie cost in time and money
to develop and maintain a statistically reliable survey of the sparse
population of breeding black ducks in eastern Canada appears prohibitive.

28

References

Chamberlain, E. B., and C. F. Kaczynski. 1965. Problems in aerial
surveys of waterfowl in eastern Canada. U.S. Bureau of Sport
Fisheries and Wildlife, Special Scientific Report--Wildlife No. 93,
21 pp.

Snedecor, G. W. 1956. Statistical methods applied to experiments
in agriculture and biology. 5th ed. Iowa State College Press,
Ames . 534 pp .

29

« U. S. GOVERNMENT PRINTING OFFICE : 1968 O - 310-843

The Department of the Interior, created in 1849, is a Department of
Conservation, concerned with management, conservation, and develop-
ment of the Nation's water, wildlife, fish, mineral, forest, and park and
recreational resources. It has major responsibilities also for Indian and
Territorial affairs.

As America's principal conservation agency, the Department works to
assure that nonrenewable resources are developed and used wisely, that
park and recreational resources are conserved for the future, and that
renewable resources make their full contribution to the progress, pros-
perity, and security of the United States, now and in the future.

UNITED STATES

DEPARTMENT OF THE INTERIOR

FISH AND WILDLIFE SERVICE

BUREAU OF SPORT FISHERIES AND WILDLIFE

WASHINGTON. D. C. 20240