Volume 5

RAPTOR

RESEARCH

NEWS

Number 2
March-April 1971

Editors: Byron E. Harrell,
Donald V. Hunter, Jr.

Raptor Research Foundation, Inc.
c/o Biology Department
University of South Dakota
Vermillion, South Dakota 57069 U.S.A.

NOTES, NEWS, AND QUERIES 50

Protection Bill Introduced in Congress 50

Quiet for Condors 50

DDT and the Court Squeeze 51

New Jersey Hawks Thoroughly Explored

in State Museum Bulletin 13 51

SPBP Pamphlet 52

Owl Sanctuary 53

A Source of New Members 53

CAPTIVE BREEDING OF PEREGRINES:

Suggestions from their Behaviour in the

Wild (R. Wayne Nelson) 54

SURVIVAL OF THE PEREGRINE FALCON:

PROTECTION OR MANAGEMENT? (Tom J. Cade) 83

NOTES, NEWS, AND QUERIES

Protection Bill Introduced in Congress. “A bill to extend
to hawks and owls the protection now accorded to bald and
golden eagles,” (H.R. 5821) was introduced in the House of
Representatives on March 10 and was referred to the
Committee on Merchant Marine and Fisheries. The bill was
introduced by Rep. Dingell (D-Mich.), along with Reps.
Conte (R-Mass.), William D. Ford (D-Mich.), Karth
(D-Minn.), McCloskey (R-Calif.), Moss (D-Calif.), Nedzi
(D-Mich.), Obey (D-Wis.), Saylor (R-Pa.), and Udall (D-Ariz.).

The Society for the Preservation of Birds of Prey is asking
groups to help sponsor the distribution of 20,000 fliers in
support of the bill. RRF was asked but declined since it is
general policy not to take a Foundation position on
controversial issues. It is policy, however, to provide as much
information as possible on both sides to our members.

Elsewhere in this issue there is a paper by Tom Cade
which incidentally was prepared and received before we
learned about this bill. He believes “that total protection of
the Peregrine will only hasten its total extinction in North
America,” and that falconry can have an important role in
the management of populations. That falconry is not
provided for in the bill is indicated by the S.P.B.P. material:
“When asked about the future of falconry in the United
States, Dingell somewhat reluctantly admitted ‘it doesn't
look too good.’ He said that under the bill, all holders of
valid falconry licenses would be allowed to retain their birds.
However, no harvesting of raptors from the wild would be
permitted after the passing of the bill and there would be no
specific provision for the practice of falconry. The transfer
and sale of native raptors would also be prohibited. In twenty
or thirty years, few captive raptors will still be living, so the
legal possession of hawks and owls by private ownership
would become non-existant.”

We will include more information and comments as they
become available.

Quiet for Condors. Interior Secretary Rogers C. B. Morton
has refused to extend an oil drilling permit in the Los Padres
National Forest, a principal nesting area of the California
Condor.

The condor, the nation’s largest bird with a wingspread of

50

51

up to nine feet, is extremely sensitive to noise. The slightest
amount of noise may drive the bird permanently from its
nest. Since there are estimated to be only 60 to 80 condors
left in California and since the majority of them nest in the
Los Padres Forest’s Sespe Sanctuary, Morton’s refusal to
allow the U. S. Royalty Oil Corporation to continue to drill
for oil there is good news indeed. [From Conservation News
36(4): 13, Feb. 17, 1971.]

DDT and the Court Squeeze. The U. S. Court of Appeals
for the District of Columbia Circuit has tightened the squeeze
to ban DDT by ordering William D. Ruckelshaus,
administrator of the new Environmental Protection Agency,
to issue cancellation notices on all of its remaining uses. The
January 7 court decision also ordered Ruckelshaus to further
exercise the new agency’s pesticide regulatory authority
which it assumed from Agriculture and decide if DDT is
enough of an “imminent hazard” to public health to ban all
interstate shipments.

The court made it clear that the public does indeed have a
say in determining what pesticides are safe or not safe to
use— decisions that the Agriculture Department and pesticide
manufacturers conveniently made in the past. Judge David
Bazelon, part of the three-judge panel which arrived at the
decision, added that though courts previously “treated
administrative policy decisions with great deference,” they
no longer will “bow to the mysteries of administrative
expertise.”

The decision is the result of a suit filed against the
Agriculture Department and its Secretary, Clifford Hardin,
by the Environmental Defense Fund, the Sierra Club, and
West Michigan Environmental Action Council and the
National Audubon Society in October 1969. Conservationists
are hoping that Ruckelshaus will yield to the overwhelming
evidence documenting DDT’s tragic effects on fish and
wildlife and take the kind of constructive action which
Agriculture stubbornly resisted. [From Conservation News
36(3):8, Feb. 1, 1971.] [On March 17, Ruckelshaus
announced that he did not consider the health hazard as
proved.]

New Jersey’s Hawks Thoroughly Explored in State
Museum Bulletin 13. From the dawn of recorded
history— and no one knows how many milleniums

52

before— hawks and other birds of prey have awed and
inspired men.

In “The Hawks of New Jersey,” the New Jersey State
Museum’s Bulletin 13, author Donald S. Heintzelman briefly
outlines the history of man’s relation with hawks and tells
much more about birds of prey. Though completely
protected in our state, some species face extinction.

In 104 pages, “The Hawks of New Jersey” includes two
maps, four tables and 86 of the finest available hawk
photographs and drawings as well as a glossary of special
terms and selected references for further reading.

State Museum Bulletin 13, in clear, readable language,
stresses the ecological role of hawks in nature, particularly
emphasizing the role of predators in food chains and food
webs.

Besides exploring the fossil record of hawks, it explains
how they are affected by pesticides, habitat destruction, and
shooting. It provides a guide to hawk migrations in New
Jersey, explaining where and why they occur, and presents
life history sketches of all hawk species recorded in New
Jersey.

A key and other aids to hawk identification, along with
copious illustrations, also enhance the Bulletin’s value to the
general public.

Author, Donald S. Heintzelman, Curator of Ornithology
at the State Museum since April 1969, formerly served as
Associate Curator of Natural Science at the William Penn
Memorial Museum, in Harrisburg, Pennsylvania. He holds an
A.B. degree from Muhlenberg College and has done graduate
work at Lehigh University.

Much of his professional life has been devoted to the
study of birds of prey, and many of his explorations
searching for birds have been recorded on color slides and
films.

Bulletin 13, “The Hawks of New Jersey,” is available for
$2.00 (postpaid). Make check or money order payable to
Treasurer State of New Jersey and mail order to New Jersey
State Museum, W. State Street, Trenton, New Jersey 08625,
Attention Publications. [News release from N. J. State
Museum, April 1, 1971.)

SPBP Pamphlet. A six page pamphlet entitled “Birds of
Prey, Valuable Members of the Wildlife Community” has
been published by the Society for the Preservation of Birds

53

of Prey (P. O. Box 293, Pacific Palisades, Calif. 90271). They
sell for $4/100 ($1.50 Resource Dept, rate; $5 Foreign rate).

Owl Sanctuary. Florida Atlantic University gives a hoot.
Next week, The Audubon Society will officiate when the
campus becomes a Burrowing Owl sanctuary.

“Our owl population has grown and prospered along with
the university,” said Roger Miller, vice president for
administrative affairs. (AP, Boca Raton, Fla Mitchell (S.D.)
Daily Republic, April 19, !97L)

A Source of New Members. Fran Hamerstrom has hit
upon a source of contacts for potential members. She saved
up the request cards for reprints of a raptor paper she had
written and sent them on to the office to have a brochure
sent to those not already members. Perhaps others who have
published papers on raptors recently could help in this way.

CAPTIVE BREEDING OF PEREGRINES:
Suggestions from their Behaviour
in the Wild.

by R. Wayne Nelson
Department of Biology
The University of Calgary
Calgary 44, Alberta, Canada

INTRODUCTION

The breeding of Peregrine Falcons ( Falco peregrinus ) in
captivity is not yet easily accomplished. While perhaps
somewhat over one-half dozen successful efforts (yielding
captive-bred fledglings) have been made, many other efforts
have been unsuccessful. As the declines in breeding falcons in
the wild continue and spread (Cade and Fyfe, 1970) the
urgency to develop and perfect captive breeding techniques
with these birds becomes ever greater.

The successful efforts with captive breeding of the large
falcons to this time have indicated some of the conditions
under which the birds will breed. The conditions that those
birds were kept in obviously provided the essential features
that stimulated those birds to breed, but the lack of success
by other pairs of birds held under broadly similar conditions
suggests that perhaps the successful pairs to date represent
only the very tolerant extreme, and that the birds that did
not breed were deprived of features of the natural
environment essential for reproduction. If we attempt to
duplicate more closely those features of the wild falcons’
environment which appear important to them, we might be
able to establish a captive environment in which a greater
number of the captive pairs would be able to carry out the
full sequence of behaviour patterns that precede the laying of
fertile eggs.

It is in the hopes of hastening the perfection of captive
breeding techniques that my observations on F ' p. pealei
breeding in the wild on the British Columbia coast are
reported here, and suggestions that derive from them are
made.

The behaviour of the various species of birds of prey in
the wild should be indicating to us what features of the wild
environment we should be trying to duplicate in the hawk
house. The behaviour of the birds in captivity, if we take the

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55

time to observe them to any extent, should also indicate to
us at what stage in the breeding cycle breakdown in breeding
actually occurs. Why the behaviour of the birds of prey in the
wild and in captivity has been largely ignored to date is
something of a mystery, especially when the behaviour can
apparently tell us such a great deal about the birds.

Many of the following observations are based on a
continuing study of the behaviour of British Columbia coast
Peregrines (Nelson, 1970). I have studied the ‘courtship’
behaviour closely only in one wild pair to date, but the
activities of that pair can be considered reasonably ‘normal’
since they led to the production of fertile eggs and to the
fledging of a young falcon. I will briefly describe some of the
important behaviour patterns during the two months prior to
egg-laying, and will indicate how I think that the captive
breeding situation might be made more stimulating for the
birds. The fact that the falcons I have studied are coastal
birds may have some bearing on what behaviour they exhibit
and what environmental factors are important to their
breeding in the wild and in captivity. Despite this possibility,
I think that when the non-coastal falcons are studied in
detail, great similarities will be seen between the general
behaviour of the coastal birds and those elsewhere. Some of
the behaviour patterns (e.g. ‘courtship feeding’) are found in
many many species of birds.

The first portion of the breeding cycle may best be
termed the “pre-incubation phase.” All the essential
behaviour sequences of this phase must be carried out
successfully if fertile eggs are to be laid, just as the essential
parts of incubation must occur if the eggs are to hatch.
Because the acquisition of fertile eggs from captive falcons
appears to be a (if not the) major difficulty in captive
breeding of the large falcons at present, my remarks will
mainly concern the 2-3 month period that preceeds
egg-laying.

PRE-INCUBATION PHASE

By considering the courtship behaviour of the falcons in
the wild, we may be able to understand more clearly what
factors are necessary to ‘force’ falcons to breed in captivity.
As was said by Enderson (1967), it will be by providing the
correct conditions for captive birds that they will be literally
forced to breed.

Lighting. Various people have experimented with artificial

56

lighting to induce moult in raptors at different times of the
year, and considerable success has been seen (Mihalovits,
1965; Simonyi, 1968 (BPIE 6); Hunter, 1970 (BPIE 16); and
others).

Similarly, Willoughby and Cade (1964) were able to
stimulate American Kestrels ( F. sparverius ) to breed, and
produce fertile eggs, in December to February at Syracuse ,
N.Y. (when temperatures were sometimes below freezing in
the unheated buildings) by changing only one factor in the
buildings: the daylength (photoperiod) for the Kestrels was
suddenly increased from 8 hours light and 1 6 hours dark, to
18 hours light and 6 hours dark. Fyfe (1968 (BPIE 4))
induced his captive arctic Peregrines to “migrate north” by
increasing their daylength. Kendall (1968), using artificial
light to lengthen the daylight period by about one hour, was
able to bring his captive Prairie Falcons (F, mexicanus ) into
breeding condition slightly earlier than otherwise might have
been expected. It is obvious that photoperiod is an important
‘lever’ in trying to bring the captive birds to breed. There is
another aspect of the lighting that appears to be equally
important, however.

Beebe (1967) and Schramm (Peterson, 1968) obtained
fertile eggs from Peale’s Peregrines in naturally-lighted
buildings, and Waller’s (1968) Peregrines were also
(apparently) in naturally-lighted buildings when they
produced young falcons. But, although these efforts with
natural lighting have “let nature take its course,” they have
certainly not been duplicating nature very closely. While the
length of the day has an effect in stimulating the falcons to
breed, in buildings with sky-lights or windows it is likely that
the effective daylength is shortened considerably in the
darkened interior. Also, the brightness of the light in the
enclosures in which the falcons were living certainly could
not have been as great as that out of doors. A simple test
with a camera lightmeter in most buildings will tell us that
the indoor illumination is greatly inferior to that outside,
even in overcast conditions.

Koehler (1969) records that the brightness of the
enclosures had an effect on the laying dates and fertility of
her American Kestrels’ clutches, and, moreover, pointed out
that while clutches in the outdoor pens were fertile—

“in 1963 and 1964 only the second clutches of the
pairs breeding indoors were fertile. Those first
clutches, which were forceably delayed about four
weeks by putting the pair together too late . . . were
fertile too.”

57

Koehler (1969) also noted that there is a considerable
difference in the preference for sunshine exhibited by wild
males and females of various raptor species:

“The birds in the wild, however, especially the males,
spend many hours soaring during the display
season. . .far more in contact with the sun’s rays than
in the pens. . . The females tend to spend much of
their time sitting by the selected nest site.”

“The urge to fly of the captive males during this
period is greatly intensified and their restlessness a
trial to the observer. In normal day length, there
appears to be a threshold of light necessary for
attaining full reproductive capacity— especially of the
males. This threshold seems to vary from species to
species.”

In coastal Peregrines the same thing seems true. I have
observed the male soaring much more often than the female,
and the male is also more often seen to be Prominent
Perching on a snag or in an exposed treetop. While such
behaviour of the male may also have an ‘on guard’ function,
this behaviour largely ceases once incubation is underway, at
a time when it might be thought that ‘guarding’ in this way
would be even more important than earlier. Instead, when
not incubating, the male takes up rather inconspicuous
positions on the cliff, or in nearby trees. There seems,
therefore, to be some other function for this Prominent
Perching behaviour in which the male selects exposed and
brightly lit areas during the pre-incubation phase.

Unpaired captive females of a number of species of birds
of prey have laid eggs when fed very well and left relatively
undisturbed on natural day lengths— even in buildings (Beebe,
1967). The fact that females of a number of captive pairs are
laying eggs that are infertile suggests that the males are not
stimulated sufficiently to carry out their part of the
courtship and copulation requirements. By removing the first
clutches soon after they have been completed, and causing
the female (at least) to recycle, and lay again, sometimes
fertile clutches have been obtained (Beebe, 1967; Kendall,
1968; Koehler, 1969; and others). Probably the extra two
weeks or more of increasing daylengths (by natural lighting),
and perhaps additional brightness, have stimulated the males
into the necessary sexual development, so that the second
clutches have been fertile. Or, possibly the ‘broody’ activities
of the female with the first clutch stimulates the male to
develop pair-bond behaviour.

The fact that Peregrines in the wild do not as a rule lay

58

infertile clutches should be sufficient to tell us that some
factor(s) are not operating correctly for the males in many of
the captive situations in which infertile clutches are being
laid. Apparently when first clutches are infertile there is
inadequate stimulation for the males.

While positive proof may be difficult to obtain at present,
the evidence from coastal Peregrines and American and
European Kestrels (F. tinnunculus ) strongly suggests that
while the female is triggered into breeding condition
primarily by increasing daylength, the male requires both
sufficient day length and sufficiently bright light stimulation
before he comes into complete breeding condition.

Very bright lighting (but with some areas of shade) in the
breeding quarters would seem to be a logical (and simple)
step toward creating an environment in which the falcons’
basic requirements for breeding would be better satisfied. A
white interior (see Kendall’s photos) would aid this end. It
would be wise to try to subject the male to brighter light
than the female, by rigging extra lights near his favourite
perches, which could be turned on (possibly automatically)
when he perched there.

Willoughby and Cade (1964) brought their Kestrels into
breeding condition with single 150 watt bulbs in the center
of the birds’ 12’ X 6’ X 8’ high rooms. Upon putting their
Kestrels suddenly onto the long daylengths (16 or 18 hours),
it took from 43 days to 63 days for the first eggs to be laid
by the pairs of Kestrels— and many were fertile. This shows
that for Kestrels that illumination was adequate.

With larger falcons (and those of more northern origin) in
larger enclosures, we should be giving the birds daylengths
considerably longer, and the lighting should be reasonably
bright— at least resembling that found out of doors. Birds
should not be exposed to heavy doses of ultraviolet light
because of the possibilities of developing skin cancers and
‘snowblindness.’ Incandescent bulbs should be sufficient.

Automatic timers (some with automatic dimmers) have
been used by Fyfe, Kendall, and others, with considerable
success. Willoughby and Cade (1964) kept a 7.5 watt bulb
burning constantly in their Kestrels’ rooms so that the birds
could regain their perches at night, because if the artificial
day ended very suddenly the birds could become quite
alarmed at being caught away from their night perches. A
dim light should be left on for at least fifteen minutes after
the main lights in the falcon room are extinguished for the
night, so that the birds might easily regain their night perches
before total darkness sets in.

59

Temperature. As mentioned above, Willoughby and Cade
(1964) had Kestrels breeding in rooms that had temperatures
“frequently below freezing.” The air temperature apparently
does not greatly affect the laying of fertile eggs. One might,
however, expect a great likelihood of egg or nestling chilling
at low temperatures and it is unlikely that nestlings could
survive very long at temperatures below or near freezing.

Depending on the number of nestlings in a brood, at some
point between one and 2 l /i weeks of age the adult female
Peregrine is physically no longer capable of covering her
offspring. At this age severe chilling could kill them. One
should attempt to give the birds conditions approximately
the same as those found during the natural incubation and
nestling phases where the birds originated. Those were the
conditions which the individual birds had evolved to tolerate
and survive in.

Overheating may be more of a problem than chilling, with
the adult birds at least, and possibly with nestlings as well.
On the B.C. coast I have watched an incubating female
Peregrine suffering greatly in bright sunshine while covering
her eggs. The temperature in my blind (which was also in the
sunlight on the cliff-front) reached a maximum of only 68° F
that day, but the falcon panted strongly, fluffed her head and
wing feathers, spread her wings slightly, and occasionally
placed one foot out to the side— all these (apparently) being
means by which she was attempting to cool herself. Her
incubating activities were also interesting, for during this time
of heat stress on these few ‘warm’ days, she appeared to be
treating the eggs much more roughly than she normally did.
So, pealei , at least, suffers in the direct sunlight when
incubating. It should be noted, however, that most of the
ledges chosen by pealei seem to be shaded for most, if not all,
of the day. On the particular ledge at which the female was
seen to be stressed, the incubating bird was exposed to direct
sunlight from about 9:30 a.m. until 3:00 p.m. if the sun was
shining.

Size of Quarters and Courtship Activities. The breeding of
American Kestrels at the Patuxent Wildlife Research Center
was mostly carried out in large (50’ X 20’ X 6’) wire mesh
netting outdoor pens (Porter and Wiemeyer, 1970). Kestrel
reproduction has also been brought about in rooms of 12’ X
6’ X 8’ high with one 150 watt bulb as the illumination,
although only two young were fledged from 1 8 eggs hatched
(Willoughby and Cade, 1964)— possibly due to a poor quality
food supply.

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For larger falcons, Kendall’s (1968) quarters for his Prairie
Falcons in 1968 was about 10’ X 14’, X 8’ high, and Beebe’s
(1967) quarters for Peregrines was about 12’ X 18’, X 8’
high.

While there must be some size of an enclosure below
which courtship will be inhibited, apparently nobody has
attempted to determine what such size requirements might
be. Some of the present facilities are probably too small to
allow the behavioural interactions between the male and
female which seem to be important in bringing about
reproduction. The sizes of the quarters in which successes
have been obtained give some indications of what is needed.

The courtship activities of wild falcons suggest that a great
deal of space is required. One cannot expect a captive tiercel
to safely carry out Power-diving displays (also termed
Sky-dancing), nor expect the male and female to be both
airborne to allow Charging of one bird at the other in pretend
attacks, when they are confined in a small room. Buildings of
adequate size to allow such aerial displays are beyond most
people’s means. So, while we must utilize small buildings, we
should keep in mind that the falcons do exhibit such aerial
behaviour during the period of courtship, and that the
significance or importance of such (presumed) courtship
behaviour patterns in successful breeding are inadquately
appreciated at present. The successes to date show that
enormous quarters are not absolutely essential, but the
quarters should be as large as possible without creating
difficulties in other areas such as providing adequate
illumination.

Courtship activities in the wild falcons are not performed
very frequently during any one day. Although activity can be
exceedingly rapid, there is a very great deal of total
inactivity. For this reason it is not surprising that captive
falcon breeders have not yet recorded many details of the
behaviour of their falcons during this phase, although
Olendorff (1968) described in detail the behaviour of his
captive American Kestrels. Beebe (1967) has noted an
interesting display exhibited by the male Peregrine shortly
before egg-laying, and Kendall (1968) recorded some
posturing by his Prairie Falcons. These writers and others
have mentioned various calls given by the birds in this phase.

As day length increases from February through April, the
wild falcons on the B.C. coast progress through several
obvious phases of activity as they approach the time of
egg-laying. I will first outline the more obvious and seemingly
important of these activities, and will then suggest how they

61

may be important factors to consider in the designing of
breeding quarters.

At six weeks before the eggs were laid, the pair of pealei
that I studied in 1969 began flying about together near the
nest cliff. The male began Prominent Perching and
occasionally Power-diving nearby, and the pair began
attacking intruding eagles as a pair.

Four weeks before eggs were laid the male’s interest in
nesting suddenly became very evident. Cliff-racing by the
male involved flying at a fairly rapid speed close to and along
the length of the cliff, and often he turned back to race in
the other direction along the cliff. This might be seen two or
three times in a 4-6 hour observation period. At this time
too. Food- transferring (the so-called “courtship feeding”)
began, with the female slightly in advance of the male in her
interest in this activity, for on the first few times it was seen
to occur, the female was seen chasing the male when he had
food, and he did not seem to be willing to give it up to her.

Male-ledge Displays also began about four weeks before
egg-laying. In these displays the male flies to a prospective
nest ledge and gives Eechip calls (he may go to other ledges
on occasion, but he seems to have a favourite ledge). He also
settles onto the scrape and shuffles about, but these actions
seem to be totally ignored by the female for a few days. At
this time the male also begins Passing and Leading (he usually
chooses a time when the female is perching in the general
area of the cliff-front, or when she is flying towards the cliff
area). In this display, the male races close past the female at
high speed, and continues on towards the prospective nest
ledge. Sometimes she actually follows him to the ledge which
is probably exactly what the male intends her to do. If she
does not follow him, the male lands at the ledge and usually
carries out actions of the Male-ledge Display. If she does
follow him to the ledge, sometimes he departs immediately,
and sometimes he seems to give the actions of the Male-ledge
Displays in her presence. From this time onwards the female
spent considerable time on or immediately beside the
prospective nest ledge.

I observed Male-ledge Displays for several days before the
first Passing and Leading. On the first day that Passing and
Leading was observed, the female followed the male to the
chosen ledge once. Passing and Leading ceased once the
female was spending some time at the ledge, on and off
during the day. However, the male continued to perform his
Male-ledge Displays at times when the female was not at the
ledge, until close to the date of egg-laying.

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About a week prior to egg-laying, the male began
Mock-attacking the female. At this time the female was
spending much of the day on the ledge. In Mock-attacking,
the male would suddenly come into the nest ledge vicinity at
an incredible speed, aiming roughly horizontally at the
female on the nest ledge. A split-second before he might have
‘pan-caked’ himself onto the cliff or the female, he would
suddenly pull steeply out of his ‘attack’ and veer off along
the cliff and out of sight. The female, during this very brief
encounter, would utter a few Eechip calls as the male
appeared racing at her. Such Mock-attacks could be
performed either a few minutes or a few hours apart. They
probably function to synchronize the pair in their sexual
development.

The actions observed by Beebe (1967:68) in his captive
Peregrines very shortly prior to egg-laying, seem to have been
an amalgamation of Male-ledge Displays (Eechip calling,
Head-rotating, Bowing, and shuffling about in the scrape) and
either or both of Passing and Leading and Mock-attacking
(“This was followed by a quick take-off and rapid flight
around the room, past the female, and back to the nest ledge
where the entire procedure would be repeated”). Both of
Olendorffs (1968:81) Kestrels, about one month prior to
egg-laying, were observed to enter the nestbox for a very
short period of time, and “upon leaving, each bird would fly
directly at the other and turn at the last minute to another
perch.” This activity seems to be somewhat similar to the
Dive Display mentioned by Willoughby and Cade (1964) in
which the wild male Kestrel dives close to the female as she
perches in a tree. The similarity between the observed
behaviour of the wild and captive Peregrines and Kestrels
suggests that there is some necessity that these behaviour
patterns be carried out for normal breeding to occur.

Behavioural observations of this type should be put to use
in the captive breeding projects. They are not “curiosities”
but instinctive patterns that the birds are highly motivated to
perform. They can tell us what stage of the cycle the birds
are at. And the behaviour patterns can indicate to us what
aspects of the captive environment may be inhibiting the
birds from progressing in sequence through the rest of the
breeding cycle.

To allow for Passing and Leading, and for Cliff-racing and
Mock-attacking to occur (even if only at slow speeds in the
confines of a room) the best place for nest ledges would seem
to be half way along a long wall— not in a comer. If the ledges
are placed in corners of the falcon room, the smaller male

63

could be ‘trapped’ by the stronger female if she came to the
ledge while he was there. Also, a ledge in a corner would
make it difficult for the male to Mock-attack the female on
the ledge and turn at the last second to avoid collision with
her or the ledge or wall. By placing ledges in the middle of a
wall, at least the male could fly past the ledges, from one end
of the room to the other.

It is desirable that the falcon room should be as tall as
possible. Richard Fyfe has mentioned to me how a pair of
birds placed in a room with a higher ceiling seems to be much
calmer— especially with perches which are placed quite high
in the room. Aside from giving the birds a greater ‘peace of
mind,’ a room with height may aid in giving the male added
speed and stimulus in his courtship flights.

The larger the quarters, the more maneuverability the
birds will have, espcially if they are large falcons.

Dividing the Quarters. One aspect of Peregrine courtship
that I have not yet seen in pealei in the wild is that of Mutual
Roosting, perching of the pair side-by-side, mentioned by
Cade (1960) for arctic Peregrines. This is not to say that it
never occurs in pealei in the wild, but it seems to occur very
seldom, if ever. In the coastal falcons it is not common that
the pair spends many hours in close proximity to one
another.

Early in the pre-incubation phase especially, it would
seem advantageous to offer the captive pair the alternative of
not having to be in the immediate presence of the mate all
day long. A simple means of offering the birds some sort of
solitude if they ‘desire’ it would be to place a partition (like a
broad, thin pillar) in the middle of the breeding chamber,
with perches placed on it and on the surrounding walls so
that the birds could perch out of sight of each other if they
so desired. Such visual isolation might also be stimulatory to
both birds by giving them the chance of a ‘sudden’ and
‘surprise’ approach to the mate around the corner. Brehm
(1969) partitioned his Goshawk ( Accipiter gentilis ) breeding
quarters, (if the birds wished it) and a means of
exercising. . .and success. Another important consideration is
that a central partition would allow a circular flight path in
the room and an illusion of greater available space than there
actually is.

Placement of Perches to Facilitate Courtship. The
positioning of perches in the falcon room may not be as
insignificant a matter as one first might think. If there is any

64

kind of dominance relationship established in captivity, it
will probably be in favor of the larger female. In the wild it
seems to be in favor of the male, except when the pair is
close together at the ledge or at copulation. Various authors
in Raptor Research News and elsewhere have noted how the
females of various species seem to actually harass the males
early in the season or when first introduced to each other,
but eventually tolerate them in the room. Placement of
perches might be done so as to enable the male to establish a
dominant or equal relationship with the female, for example
by placing perches for him just the exact distance down from
the ceiling that they would be attractive and ‘safe’ for the
smaller male, but so that the female would find them
uncomfortable to use because of lack of head-room. Some
perches should be in shadow, others in bright light.

Also, the positions of perches in the room could permit
the male to fly past the nest ledges, from a perch high at one
end of the room to a perch at the other end of the room.
People should keep all of these factors in mind when
contemplating how best to ‘force’ the birds to behave
naturally in the room.

Types of Ledges, their Placement and Sanitation.
Traditionally, a table or bench covered with some material
has been offered as a nest ledge for the captive falcons. In the
wild, such exposed ledges (and floor-level sites) would very
seldom be used. Have you ever seen an eyrie of a wild falcon
in which the sun could pour fully onto the ledge for the full
length of the day? The falcons seldom, if ever, choose such
sites if there are any alternatives. In fact, various authors have
noted how many ledges are overhung, even in pot-holes or
small caves. We should be offering the captive birds just such
alternatives so that they can do the choosing, so that they
can choose the ledge which to them offers the best situation,
the best feeling of security.

In a brightly lit room, several nest ledges should be
offered to the birds— some fully exposed to the bright lights,
some entirely shaded, and some very shaded and even
cave-like. It may be that such a simple thing as a dark and
‘private’ nest ‘cave’ might be sufficient extra stimulus to
trigger the male and/or female into the appropriate breeding
behaviour and condition. Willoughby and Cade (1964) found
that the blocking of captive Kestrels’ nestbox holes depressed
their development somewhat. We may be accidentally causing
similar inhibition of the larger falcons by providing the birds
with ledges which are just not ‘right’— hence the birds do not

65

come into proper breeding condition.

If a person had a reasonably large room, it might be most
interesting to give the birds very real choices by providing
them with a variety of high, middle-elevation, and floor-level
ledges, of three types at each level— (1) open ledge with sod
and grass; (2) open ledge with dirt and/or sand; and (3) a
recessed, shaded, ‘cave-like’ ledge with dirt and/or sand. Since
the birds sometimes dig deep scrapes, four or five inches of
packed material should be placed on the ledges. Such a set of
alternatives would probably show us what types of ledge
material and ‘privacy’ the birds prefer (fine sand is probably
too loose and dirty a material on which to rear tiny
nestlings).

Ledges should measure a minimum of about two feet
from front to back, and three feet wide, on the basis of ones
I have seen in the wild. Enderson (1968 (BPIE 3)) noted that
captive falcons, in landing at the ledge, can cut the bottoms
of their feet by skidding on the ledge material against the
solid floor of the ledge. Falcons in the wild often seem to
land at a grassy or mossy part of the ledge, and walk to the
scrape from there, or, less often, land rather gently by
dropping almost straight down the last few inches onto the
ledge. Enderson has suggested that the fronts of ledges should
be provided with a cushioned landing pad of some cushioning
fabric (see also Kendall’s photos). Sod and grass, or moss,
might be used as well, instead of the landing area being
simply of solid wood or rock.

There is a suggestion (Porter and Wiemeyer, 1970; Porter,
in letter, Oct. 1970) that contaminated nestboxes or nestbox
material of Kestrels from one year may be the cause of death
of embryos in eggs the following year. In many reports in the
literature it is stated that a number of species of birds of prey
either build onto their stick nests, or use different nest sites
from one year to the next. It is possible that digestive tract
contaminants (bacteria) from the nestlings in the nest one
year may be able to survive overwinter and kill embryos in
eggs laid at the same ledge the following year (or on the same
nestbox litter, or in contact with the nestbox walls, in the
case of captive Kestrels). The frequent use of alternative
ledges of nestholes by various raptors, and the building upon
the tops of old stick nests each year by others, may have
evolved because of the selective advantage to the birds of
avoiding this sort of mortality factors. So, as a precaution,
ledge material should be removed at the end of each season
and fresh material provided. A simple matter such as this
could be critical in avoiding loss of eggs in later years.

66

Feeding and Caching. Falconers tend to feed their birds
very well through cold weather, but to cut down slightly on
the food when warmer weather arrives. In the spring, in the
wild, this is exactly the opposite of what happens, especially
for the female.

The behaviour of wild falcons suggests, as Beebe (1967)
postulated, that it is essential that the female be very well fed
if she is to lay eggs. In fact, as egg-laying nears, it is quite
evident in wild pealei that the female is doing none of the
hunting, and that the male is catching enough food for both
himself and his mate. Also of possible importance is the fact
that the male usually eats the heads of the prey items before
presenting them to the female for her (or later, for the
nestlings) to eat. In other words, the female receives few, if
any, heads duiing that time prior to egg-laying (as long as two
weeks prior to laying) when she is being supported by the
male, and also on through incubation and into the nestling
phase. Since it is known for chickens that extra calcium in
the diet (in the form of crushed oystershell) yields eggshells
of greater thickness, there may be a connection between a
diet of chicken heads and/or necks for captive birds and the
observations a few people have made that captive bred
nestlings have had great difficulty getting free of the
eggshells.

Since the female in the captive situation is usually
dominant over the male, the partitioning of the breeding
quarters may enable the male to be fed without his feeding
being seen by the female. If he is slipped food through a
small trap-door that is out of view of the female, he could eat
it before the female knew he had any food that she could
steal from him.

The male must be allowed the opportunity to take food
to the female, in ‘courtship feeding,’ when he is ready to, an
option open to the male in the wild. If the birds are given
food in an undivided room, the female may get and eat the
food first, and the male will be deprived of the stimulus to be
gained from presenting food to her. A partitioned room, with
small trap-doors by ‘feeding ledges’ would allow the human
being some choice as to how and when to present the food to
the birds. The birds could be fed if the male and female were
in the different sections of the room. Or the food could be
given to the male first, and if he did not take the extra to the
female when he finished eating, then the female could be
slipped some food through the other small door into the
section she was in— or she could simply be allowed to find the
extra food later where the male had left it in his area.

Peregrines seem to cache a fair proportion of their food in
the wild, and later retrieve it. The male pealei often goes to a
cache to get some food, eats a bit of it, and only then flies to
and offers the rest to the female. Waller (1968) noted that his
Peregrines cached excess food in different parts of the room,
and Kendall (1968) mentioned that his Prairies cached food
in a hole in a log, from which they could not retrieve it!
There is room for experimentation here, to try to devise a
way of giving the birds a chance to cache food in a place
from which the human being can retrieve it if it gets very
‘high.’ It may be possible to get the birds to use a short
hollow pipe, placed by a ledge against an outside wall of the
room, for caching or disposing of old or unwanted food
items, or to use a ledge (possibly with rocks or very long dry
grass on it for concealing the food) for caching food which
the birds wish to use later. Ingenuity could devise other
methods of getting old food items out of the bird’s room.
There should be no necessity for one to have to enter the
room to take the food in view of the birds.

In any event the birds should be provided with a great
deal of food, preferably whole birds of natural origin, and
reasonably clean of biocide contamination. Berry (1968) has
suggested caution be used in feeding frozen food, although
changes his Goshawk underwent during laying (rapid weight
loss, and weakness) were “more probably from lack of fresh
water immediately before laying.”

The Lethargy Near Egg-laying. Olendorff (1968) may have
been the first to detect the astonishing lethargy which besets
female falcons in the few days prior to egg-laying. In
Peregrines the period may extend for as long as a week prior
to laying. During this time the female appears to be ill, as she
dozes for a great deal of the day and spends very little time
doing anything active. Even after having read Olendorffs
(1968) account of the “withdrawal” of his female Kestrel
just prior to egg-laying, when I first observed this behaviour
in a wild female Peregrine I felt certain she was ill.

Olendorff noted that his female Kestrel, when she became
lethargic, “was subdued enough to take food from my hand
which she had not done for several weeks; the nest
defense. . .was entirely absent as far as the female was
concerned.” The wild Peregrine showed a similar lack of
defense of the cliff area in this period. Approach by the male
in Mock-attacking or for Copulation, however, would
suddenly (although only briefly) bring the female Peregrine
into an alert condition.

68

Female lethargy is mentioned because people engaged in
captive breeding may become greatly alarmed by the female’s
lack of activity, thinking that she may be ill when in fact she
probably is not. Very close watch must be taken during this
time, however, to be certain whether her dullness is due to
impending egg-laying or some other reason such as acutal
illness. If she has been eating well, if the pair (or at least the
female) has been observed engaging in some of the courtship
activities such as nest-scraping, and if the male is healthy, one
could assume that she was, in fact, readying to lay eggs.

Water. Berry (1968) has suggested that ample fresh water
may be very necessary for egg-laying to proceed without
difficulties. He noted that his Goshawk drank a great deal
during laying.

At hatching, moisture seems to be critical. Schramm (in
Peterson, 1968) wrote regarding his Peregrines (pealei ):
“There is a very noticeable change in attitude during
the last couple of days before the eggs hatch. The
parents are very much more aggressive at this time
and the falcon (female) takes many more baths in the
always available water.”

There is considerable evidence from other wild species that
the moisture on or immediately around the eggs is extremely
important at hatching: for example— for Mallard ( Anas
platyrhynchos ) (Mayhew, 1955:46); Bobwhite Quail ( Colinus
virginianus) (Johnson, 1968:85); Sharp-tailed Grouse
( Pedioecetes phasianellus) (R. L. Brown, pers. comm.);
murres (Uria spp.) (Tuck, 1960); and Osprey ( Pandion
haliaetus ) (Welty, 1962:302). For the latter, Welty states:
“The Osprey. . .is known to shake water from its wet
feathers over its eggs in warm weather. This action
may function both to cool the eggs and to prevent
excessive water loss.”

It would seem extremely important to offer the captive
birds of prey ample clean water. Some sort of siphoning
system could be easily arranged to allow the person caring for
the birds to change their water daily without entering the
falcon room. Some effort should be made to ensure that the
birds do bathe. In artificial incubating of raptor eggs, these
factors should also be kept in mind.

Age at First Breeding. In 1969 I saw two pairs of wild
pealei in which the males were adult and the females were
only one year old. This implies that it is possible for pair
bonding to occur prior to a Peregrine’s first birthday. Neither

69

of these two pairs laid eggs or raised young in 1969 but at the
same two sites in 1970 there were only adult birds present,
and I am fairly sure that at one of the two cliffs the female
was the same bird as in 1969 when she was moulting from
immature into adult plumage. Each of the sites produced two
flying young in 1970. This suggests very strongly that female
Peregrines in the wild WILL breed successfully around their
second birthday.

I mention these two instances of wild Peregrine females
breeding successfully when apparently only two years old,
because I know that many think that it may take up to four
or five years for Peregrines to come into breeding condition.

We should have realized years ago that the plumage of the
Peregrine should indicate when the bird will be of breeding
age. Since the immature plumage is mostly, if not entirely,
lost when the bird is about one to one and one-half years old,
the bird should be capable of breeding in the season of its
second birthday, when it first has the adult plumage. But I do
not know whether the same holds true for the other large
falcons in which plumages seem to be more alike between
adults and immatures. I would suggest, then, that everyone
attempting to breed any of the large falcons should have the
quarters and the birds entirely prepared to breed as they near
their second birthday.

Introduction of the Pair. I have only a few remarks to
make about this rather important aspect of the captive
breeding program.

In wild Peregrines (at least in times prior to usage of
DDT), various writers (e.g. Green, 1916; Hickey, 1942) noted
that if a member of a pair died, a new mate was acquired
almost immediately (apparently from a local floating surplus
of birds, which may no longer exist), and the incubating of
the eggs or the raising of the young proceeded almost as if
nothing had happened. It seems that if the two members of a
prospective pair are in the same daylength in the breeding
season, they can and will pair up without too much
difficulty. In a room, however, there may be some difficulty
at first, in that the two strange birds cannot retreat very far
from each other if they wish to.

Willoughby and Cade (1964) acquired a “new wild pair”
of Kestrels in late November, put them into a room with a
long photoperiod, and had them lay eggs in late January— and
one egg hatched in late February. Porter and Wiemeyer
(1970) have noted that they have successfully paired Kestrels
“when both sexes were placed together simultaneously in a

70

pen new to both of them,” and also when a new male was
placed into a female’s pen and vice versa. Kendall’s (1968)
Prairie Falcons were introduced to each other, free in their
room, in November, and produced a fertile second clutch in
the following April. The suggestion from all this is that a long
acquaintance of the pair with each other and with the room
is not imperative, as long as the conditions in the room are
reasonably correct. If the birds are not imprinted to human
beings (see below), and if they are both subjected to
adequate illumination (as well as increasing daylength or long
daylength), pairing should not be difficult. In fact, the birds
should almost welcome the arrival of a member of the
opposite sex of the same species!

Imprinting and Disturbance. A considerable number of
raptors have been held in captive breeding projects but have
not laid eggs. In addition there are some pairs which have
produced only infertile eggs, even when caused to recycle and
relay several times. Aside from the numerous aspects
discussed earlier, disturbance of the birds which we are
hoping will breed in our falcon rooms seems to be of great
importance in many cases. Few of those who have written on
the subject of captive breeding have mentioned disturbance
as being critical— possibly because these writers have had
some success, and so their birds were not overly disturbed.
Yet the risk that the birds will become imprinted onto
human beings instead of their companions as mates is very
real and serious.

It has been mentioned above, and elsewhere, that at
certain stages of the ‘courtship’ proceedings the male will
begin presenting food to the female, and that this is critical
for egg production. If a human being goes into the falcon
room to provide food, which is the female falcon to consider
as her mate— the person who has fed her every day since she
was taken from the wild— or the male falcon which has never
fed her before in her life? She might well be confused by it
all, and imprinted onto the human being as her mate,
considering the tiercel to be just a companion of no sexual
significance. Equally, the tiercel could treat the human being
as being a parent falcon which still continues to feed him.

Some writers on raptors, most notably Hamerstrom (1968
(BPIE 5)) have mentioned how a female bird of prey will
consider the human food-provider as its mate, and how even
some tiercels consider the human being as the mate. When (as
with her Golden Eagles, Aquila chrysdetos ) the two birds,
one male and one female, both imprinted to a human being

71

are put together, they may attempt to kill each other. In my
own experience I have known a silent, apparently
non-imprinted female Prairie Falcon that became a classical
‘screamer’ when one year old, and eventually she became
sexually imprinted to her trainer, preferring to defnd the
place where she was usually flown against other raptors (even
at great distances) instead of hunting, even though she was
not exceedingly well fed. Yet, when offered a nest ledge, this
Prairie Falcon did not lay or even form a scrape. It appears as
if we must be extremely careful not to get the captive
breeding birds used to human beings as food providers.

Those who are seriously attempting to breed these birds in
captivity should attempt to determine just what upbringing is
best for creating a pair of falcons which will breed in
captivity. First, Beebe (1967) has suggested that it may be
best to raise eyasses in an environment similar to that in
which they will be expected later to breed -that is, raise them
in a breeding chamber, possibly with the aid of foster parent
birds of prey. Second, it would appear to be best if the
association with human beings is minimal from the beginning.
The success of the Patuxent researchers with Kestrels— many
of them totally untamed— suggests that there are advantages
in leaving the captive breeding birds alone.

It may be argued that most of the efforts with the large
falcons which have been successful to date have involved
birds which were trained in falconry, and hence the birds had
an attachment to men. While this may be true, the proper
testing of the other alternative— that of breeding birds which
have never been tamed or trained in falconry— does not yet
seem to have been seriously tried.

The Kestrels at Patuxent, some of which were themselves
bred in captivity, seem to have done extremely well at
breeding without any vigorous exercising (and, of course, the
attendant risk of being lost) as in lure-flying. The problem to
date seems to have been that those people fortunate enough
to have Peregrines, thinking that the birds would not breed
until three, four or five years of age, have desired to fly them
for the first year or two. Few people have tried to test the
very obvious likelihood that birds which have not been flown
in falconry will breed as (or more) easily in captivity, and at
much younger ages. The intense desire of the holders of
falcons to at least exercise them out of doors (and I share
that desire, too) may well be holding back the success of the
captive breeding efforts by simply making the birds too
reliant (imprinted) on human beings.

Actual disturbance of the birds in their breeding quarters

72

may also be critical. It is true that the successful efforts to
breed falcons in captivity to date have apparently involved
some, or considerable, intrusion by human beings into the
quarters, and Beebe (1967), Waller (1968), and Schramm
(Peterson, 1968) all mention how they were vigorously
attacked by their captive Peregrines at some stage of the
breeding cycle. At some point, if the birds are in breeding
condition, they seem to take on a very aggressive and
protective attitude against human beings, that is, they seem
to ‘resent’ the intrusions.

There has been little mention of how frequently the birds
were disturbed in their quarters in most of the written
accounts of the successful and unsuccessful efforts. It does
not seem to have occurred to most people that it might be
important whether the human beings simply left the falcons’
food on a perch— or actually hand-fed them, or whether the
human beings spent long hours with the birds (to ensure that
they remained ‘tame’). In the successful efforts, it may well
be that the birds were allowed just enough solitude and
privacy (i.e. were almost ignored), that they actually became
‘wild,’ and as a result of this solitude they came into breeding
condition.

Brehm’s (1969) and Herren’s (1970) successes at breeding
Goshawks and European Sparrowhawks (A, nisus )
respectively were with birds which were virtually undisturbed
by human beings in their breeding quarters.

The birds of prey in the wild can suggest how much
disturbance they can withstand. In two different seasons I
observed that Bald Eagles ( Haliaeetus leucocephalus )
attempting to nest quite close to pealei sites failed to even
reach the incubation phase, let alone produce any young,
apparently because of the frequent harassment by the
falcons. I have learned that by visiting the top of a Peregrine’s
nest cliff in the weeks just prior to egg-laying, the human
visitor can sufficiently disturb the falcons as to cause them to
shift to another nest cliff as much as half a mile away
(although their actions at the time of the visit to the cliff-top
would not suggest that they were being disturbed). And I
have also found that visiting a nest ledge before the clutch is
complete can cause the falcons to shift to another ledge and
lay the remainder of the clutch there. In summary, wild
falcons (and eagles) actively respond to intrusions upon their
domain prior to and during laying by seeking another nest
site (or by failing to reproduce at all because all adjacent sites
were occupied). If disturbed in a falcon room, with nowhere
to retreat to, the risk of the breeding cycle coming to a halt

would seem to be high.

Porter and Wiemeyer (1970) suggest that frequent
inspection of nestbox contents was the cause of many of
their captive Kestrels laying eggs in both of their nestboxes
and incubating poorly in 1966. They (and Dr. Porter, in
letter, Oct. 1970) have also noted that some Kestrels in pens
near peripheral fences (hence, subject to disturbance by the
passage of people nearby) layed few or no eggs in some
seasons.

If the birds in breeding projects are not already imprinted
to human beings, but are actually trying to pair up with their
feathered mates, is it really very surprising if the birds do not
progress quite to the egg-laying stage if human beings enter
the quarters? With no alternative nest sites elsewhere to shift
to, the captives may simply halt their seasonal sexual
development before laying eggs. The birds must be extremely
motivated to breed if they will do so concomittantly with the
frequent intrusion of human beings into their rooms. Unless
the birds are relying on the human in a direct way (e.g.
feeding from the hand), they may flee or attack, suggesting
that they ‘resent’ the intrusion. It would be better to leave
the birds entirely alone through this part of the season, so
that they could develop a relationship with each other rather
than continuing an ambivalent relationship with people, and
so that they could have an undisturbed ‘territory’ of their
own.

How to Effect Isolation. Such a situation of total isolation
for the captive breeding birds is not at all impossible to
create. The few disadvantages should be viewed as challenges
to be overcome. The probable advantages of such isolation
for the birds far outweigh any disadvantages which might be
pointed out.

Some of the innovations which are needed for equipping
an isolated falcon room have already been mentioned. Small
trap-doors at several places in the room, placed adjacent to
padded ‘feeding ledges,’ would allow placing of food into the
room without any human being being seen by the falcons. A
large piece of fabric might be placed on the inside of the
trap-doors so that in opening the small door and placing food
onto the ledge, the keeper’s hand and the food would be
hidden, the food only becoming visible as the fabric ‘fringe’
was falling back into place. In this way the falcons would
associate no human being, and not even human hands or a
glove, with food. Small drop-chutes could be improvised so
that even trap-doors would not be necessary— so that all the

74

falcon could see would be the sudden (and preferably silent)
appearance of food on the feeding ledges.

Water could be presented and cleaned by means of hoses
and siphons placed through the walls into the basin. A
low-level trap-door could be provided adjacent to the water
basin so that if it became excessively fouled it could be
discretely removed, cleaned, and carefully placed back into
the falcon room.

There may be no fool-proof method of retrieving old and
foul food remains from the falcon room. The wild falcons
seem to simply fly off with, and drop, prey items which have
been picked clean. They may sometimes also cache them and
never retrieve them. Some form of ‘drop-chute’ into which
the falcons could cache old food items, and which would
convey the remains outside the falcons’ room, would be most
convenient if it could be devised.

Observing the falcons in their room is a rather simple
matter. I have found that one-way glass, or two-way mirrors,
are indispensible in blinds in the field, and Herren (1970)
used such means to observe his captive European
Sparrowhawks. From the brightly illuminated side of the
glass (the falcons’ side) it appears opaque or as a mirror, but
viewed from the observer’s side (which should be poorly lit)
the glass appears as a slightly darkened window. The birds
can be viewed with ease, yet are quite undisturbed. Several
such windows could be placed into the walls of a falcon room
to allow the human observers to see the entire interior of the
room. Because the falcons might attack their own images in
the small mirrors (about 4X8 inches is adequate), they sould
be placed at positions and angles so that a perched bird
cannot see its own image or that of its mate; i.e., the only
chance a bird should have of seeing a ‘foreign’ bird in a
mirror should occur when the bird is in flight. Such mirrors
offer many advantages over tiny peep-holes, are fairly
inexpensive, and might even allow careful photography of the
birds if the interior was reasonably brightly lit. Usually such
mirrors require the area on the mirror side to be illuminated
about twice as brightly as the side from which the person
would be watching— otherwise the falcons would be looking
through glass. With a dark cloth covering one’s head and
shoulders and the window, a person can still be in a brightly
lighted area, and yet safely look into the falcon room
without being seen. With such devices, people with falcons
could learn a very great deal more about how their birds were
(or were not) behaving through the breeding season.

75

INCUBATION PHASE

Much of what has already been mentioned above applies
in this phase as well. A few observations of incubating wild
falcons should be mentioned, however.

Treatment of the Eggs. The shuffling of adult falcons on
the eggs occurs often enough to sometimes make the observer
very fearful for the safety of the eggs beneath the active
falcon. Very often through the day the incubating bird will
change position on the eggs, rapidly shuffle its feet while
incubating, and occasionally push an egg back beneath its
body with its beak. Exactly how such frequent activities of
the incubating falcon, and the resultant movements of the
eggs beneath it, relate or compare to the seemingly overly
gentle treatment of eggs in an artificial incubation machine
remains to be discovered.

It is not yet known how long eggs of the birds of prey can
safely remain uncovered at cool temperatures. Beebe (1967)
and Lawson and Kittle (1970) suggested that raptor eggs may
be very susceptible to chilling. While the adult birds are very
attentive in the wild, occasions do occur when the eggs are
left uncovered for many minutes— yet they do not appear to
suffer by it. To illustrate the point, I will list the times in
minutes for which the pealei clutch I was watching on May
17, 1969, was uncovered. The temperature ranged from a low
of about 45 °F at the beginning of the observation period
(3:00 a.m.) to about 60°F at the end of the period (noon).
Mainly the female was incubating during this time. The
durations of time for which the eggs were uncovered, due
solely to natural causes, were 3, 7, 2, 1%, 3%, 7, U/ 2 , 3%, 5,
3 J 4, 3%, 3, 3, 2%, 10, 3Va, 4H, and 1 X A minutes. It does not
appear as if brief uncovered spells are of serious consequence
to Peregrine eggs. (Is it possible that the difficulties Lawson
and Kittle reported in artificial incubation could have been a
result of daily candling— that the bright light passing through
the eggs could have caused mortality?)

Disturbance. Wild Peregrines on the coast, when
incubating, do not seem perturbed by constant very loud
sounds such as the pounding of surf and the noises of high
winds. But they become alert and alarmed at distant strange
sounds such as clanking noises made by people on board a
ship half a mile away from the nest ledge in thick fog.
Unusual sounds will bother them; but they seem capable of
habituating to common sounds, even loud ones.

76

Captive falcons can still have their eggs candled for
fertility when held in ‘isolation’ without being disturbed
greatly. Herren (1970) has mentioned how, when the adult
birds were feeding, he removed a broken egg from his
European Sparrowhawks’ nest by reaching in through the
space where the one-way glass rested. Apparently the birds
did not observe his actions as they were feeding. Small doors
at the back of each nest ledge might prove adequate for
removing eggs for candling when necessary, and for returning
them to the scrape. The timing and method of actually doing
so would have to be precise to avoid alarming the birds
(possibly, at a moment when both birds were away from the
ledge, the rooms could be blackened and the eggs removed by
such a small door for immediate candling, then replaced and
the lights turned back on). Alternatively, the birds might be
visited at ‘night’ in the dark, and the eggs might be carefully
removed from under the incubating female for candling and
replacing.

NESTLING PHASE

Dividing the Quarters and Harassment of Adults. In the
wild, when the nestling Peregrines are nearing flying age,
adult pealei literally ‘make themselves scarce.’ The reason for
this is fairly obvious whenever they bring food to the nest
ledge— they are mobbed by the well-grown young. If the
adults perch nearby the nest ledge, they are screamed at
almost continuously by the nestlings. And once the young
falcons are flying, the adult birds effectively hide themselves
from them for long periods. Here is an additional reason for
having a partition or wide pillar in the middle of the falcon
room— it would allow the adult falcons a chance to get out of
view of the large and screaming young. Though they will
occasionally feed the young through the day, or at least give
them food at the ledge for the young birds to rip up for
themselves, the adults should be able to ‘hide’ for part of the
day, and this they can be enabled to do if they are provided
with some perches out of view of the nest ledge on which the
noisy youngsters will be.

It would be best if young falcons were removed (possibly
by night) from the parents shortly before they are capable of
flying, to prevent undue harassment of the adults by
fledglings screaming and chasing them about all day long in
the confines of the room. Porter and Wiemeyer (in letter,
Dec., 1968) and Dr. Koehler (in letter, Dec., 1968) have
pointed out to me that fledgling kestrels do not seem to

77

harass their parents a great deal, and the former have
mentioned that the fledgling American Kestrels learn to take
food from the feeding tray in their enclosures within a few
days of first flying, and hence do not chase and beg from the
parents a great deal. The larger falcons may be somewhat
different. It hardly needs stating that during the nestling and
fledgling phase, just as earlier in the season, the captive
falcons should be provided with great quantities of food to
ensure that food shortage does not cause any conflict
between adults and young.

THE FUTURE

Secrecy and Sharing. While Raptor Research News, Hawk
Chalk , and the NAFA Journal have published much
information on the captive breeding efforts of a number of
people, there is still a dearth of information on the
conditions necessary for successful and repeated breeding of
the various birds of prey in captivity. Of course the
perfection of the techniques will take time, but it appears as
if, for various reasons, valuable time is actually being wasted
at present. There are more than a few people attempting the
captive breeding of Peregrines, and other large falcons, who
have (for various reasons) not felt inclined to present their
methods, ideas, or findings for the aid of others who are
struggling toward the same end.

Failures (as much as successes) should be written up and
distributed as soon as possible as a warning to other people
what conditions to avoid. The printing of such information
will aid everyone involved with these birds by saving
time— other people will not repeat the same mistakes.
Comparison of the failures with the successes can teach us a
great deal.

There is not yet a positive and fool-proof method of
raising and then breeding in captivity any of the large falcon
species or subspecies. Those few people who have succeeded
must be considered at present to have been very
fortunate— ( 1 ) fortunate in having tolerant birds which would
breed in conditions (of space, lighting, disturbance, etc.) in
which most others would not breed, or (2) fortunate in,
largely by chance, having duplicated the natural conditions
which allowed instinctive behaviour patterns to be performed
adequately— but not yet able to determine exactly what the
correct conditions in fact were. If the methods were simple
and uncomplicated, and known, a number of people would
be breeding and raising a number of birds each year. This is

78

not yet occurring. I have a great deal of respect for the
pioneer work of those who have tried to breed birds of prey
in captivity. These birds can be bred and raised in captivity.

In this article I have tried to apply my observations on the
behaviour of wild Peregrine Falcons to the question of how
to best produce captive-bred Peregrines. I hope that those
with Peregrines in captivity will achieve greater success by
trying out these suggestions from the behaviour of the wild
falcons, and that this article will encourage others to share
their experiences so that very shortly we all may know how
to breed successfully these magnificent birds and save them
for posterity.

CONCLUSIONS AND SUMMARY

Because a majority of the efforts at captive breeding of
Peregrine Falcons, and other large falcons, are not meeting
with success, it is suggested that we consider the behaviour of
the falcons in the wild, and compare it with the behaviour
seen in the captive falcons. By doing this, it may be possible
to determine at what point(s) in the breeding cycle the
breakdowns are occurring.

It appears to be true that those few pairs of falcons which
have bred successfully in captivity either (1) represented a
tolerant extreme of the species, or (2) were subjected to
certain specific conditions which allowed them to
breeds conditions which have not yet been fully recognized
and described. It will be many years before the correct set of
conditions are placed together by chance if we change only
one factor each year in our efforts to get the birds to breed
reliably: we could change lighting one year, humidity the
next year, divide the quarters the next, and so on, looking for
the ‘correct’ set of conditions with which to ‘force’ the birds
to breed. By using the behaviour of the species in the wild as
a guide, the captive breeding efforts should now aim toward
all at once presenting the captive falcons with the maximum
possible stimulation to breed.

In the wild, the male seems to lead the female on through
much of the courtship phase. In captivity, the opposite is
often the case: the male is inhibited or slowed in his sexual
development. Infertile first clutches are occasionally found in
captivity.

The brightness of the falcon room may be critical to the
development of the male as ‘spring’ comes near. The captive
falcons should receive light stimulation (intensity and
daylength) similar to that found where the birds would breed

79

in the wild.

A number of factors should be provided so as to give
greater stimulation to the prospective breeding pair of captive
falcons:

(1) A long photoperiod; at the end of the day the lights
should dim gradually, or a small bulb should burn through
the night, to allow the birds to take their perches for the
night.

(2) Bright illumination, resembling that found out of
doors, with some areas of shade for the birds if they wish to
use it.

(3) A reasonably spacious breeding quarters to allow for
some of the courtship flights of the tiercel.

(4) A partition in the middle of the quarters to allow the
pair to be out of view of each other or out of sight of the
nestlings if they so desire. Such a partition would provide
some solitude, a means of ‘surprise’ for the birds (by enabling
one to suddenly come into the view of the other), and a
circular flight route around the quarters.

(5) Perches should be placed in such a way as to allow
courtship flights past the ledges. Placement of perches may
also aid in equalizing the dominance relationship within the
pair.

(6) Ledges of various types and at various elevations
should be offered, some brightly illuminated, some in dark
recesses, to allow the birds to make the choice of which
might be most stimulating to them. Some ledges should be
placed along the middle portion of a wall to allow flights to
go past the ledges from one end of the room to the other.

(7) Food should be provided in such a way that the male
might be allowed to feed first, out of sight of the female.
This would permit him to take the food to the female if he
was so motivated. Ample food should be provided so that the
birds can feed when they wish throughout the day.

(8) Imprinting of the birds to human beings should be
avoided at all costs (unless artificial insemination of the birds
is intended). Imprinting to the human food-provider may be
one of the major factors preventing many pairs from
breeding.

(9) Isolation of the falcons from disturbances (especially
from people entering the breeding quarters) should, in itself,
prove to be very stimulating for the birds. Intrusions by
people may be responsible for lack of laying or improper
development of courtship in falcon pairs. The breeding
quarters can be fitted with adequate means for feeding,
watering, and viewing the birds, and probably could also be

80

fitted with devices for removing old and unused food, and for
removing eggs for candling.

Several other factors should be borne in mind:

(1) Peregrines, and possibly the other large falcons also,
appear to breed successfully in the wild by their second
birthday.

(2) The introduction of the members of the pair to one
another and to their room need not be a dangerous
undertaking— if the two birds are not imprinted to human
beings, and if they are both on increasing or long
photoperiods.

(3) The lethargy of the female, as laying nears, should be
viewed with hope, and not treated with fear.

(4) Water for bathing and drinking appears to be
important near the time of laying and hatching. The water
should be clean.

(5) The ledge material should be changed at the end of the
season so that fecal contaminants from one brood cannot
damage a clutch the following season.

To date, while there have been some very important
discoveries made by a number of those involved with captive
breeding, much time has been wasted through a certain
degree of lack of communication— and people are repeating
the same techniques that have already been proved
unsuccessful by others. The people involved with captive
breeding should be making greater efforts to use the available
channels (especially RRN ) for communicating their ideas and
discoveries to others, so that as soon as possible a majority of
the pairs set up for breeding will be producing young
Peregrines each season.

ACKNOWLEDGEMENTS

I wish to thank the many people who have helped me in
my field studies of the falcons, and those who have discussed
with me and written to me concerning the falcons, their
problems, and their propagation in captivity. Dr. M. T, Myres
has been very helpful in supervising my studies, and this
paper has benefited from his advice.

REFERENCES CITED

Beebe, F, L„ 1967. Experiments in the husbandry of the

Peregrine. Raptor Research News 1 (4) :6 1 -86.

Berry, R. B. 1968. Captive breeding behavior: American

Goshawk— Part I. Raptor Research News 2(3):58-72.

81

Brehm, H. 1969. Successful breeding experiments with
Goshawks. Hawk Chalk 8(3):47-54.

Cade, T. J. 1960. Ecology of the Peregrine and Gyrfalcon
populations in Alaska. Univ. of Calif. Publ. Zool
63(3) : 1 5 1 -290.

Cade, T. J., and R. Fyfe. 1970. The North American
Peregrine Survey, 1970. Canadian Field-Naturalist
84(3): 23 1-245.

Enderson, J. 1967. Some ideas concerning the breeding of
Peregrines in captivity. Raptor Research News l(3):43-45.

Green, C. deB. 1916. Notes on the distribution and nesting
habits of Falco peregrinus pealei Ridgway. Ibis
58:473-476.

Herren, H. 1970. The European Sparrow-hawk— breeding in
captivity. Raptor Research News 4(2): 60-67.

Hickey, J. J. 1942. Eastern population of the Duck Hawk.
Auk 59:176-204.

Johnson, R. A. 1969. Hatching behavior of the Bobwhite.
Wilson Bulletin 81(1 ):79-86.

Kendall H. 1968. Breeding Prairie Falcons in captivity. J.
North Amer. Falconers’ Assoc. 7:57-64.

Koehler, Amelie. 1969. Captive breeding of some raptors.
Raptor Research News 3(1 ):3-l 8. (translation by Frances
Hamerstrom of Koehler, 1968. Uber die Fortpflangzung
einiger Griefvogelarten in Gefangenschaft. Der Falkner
18:28-33.)

Lawson, P., and E. Kittle. 1970. Artificial incubation. Raptor
Research News 4(5): 136-137.

Mayhew, W. W. 1955. Spring rainfall in relation to Mallard
production in the Sacramento Valley, California. J . Wildl.
Mgmt. 19(l):36-47.

Mihalovits, J. 1965. Light-induced molt of Red-tails and
Goshawks./, North Amer. Falconers’ Assoc. 4:29-30.

Nelson, R. W. 1970. Some Aspects of the Breeding Behaviour
of Peregrine Falcons on Langara Island, B.C. MSc. thesis.
The University of Calgary, Calgary, Alberta, Canada, xiii +
306 p.

Olendorff, R. R. 1968. A contribution to the breeding
behavior of the American Kestrel in captivity. Raptor
Research News 2(4): 77-92.

Peterson, R. 1968. The domestic raising of the Peale’s
Peregrine Falcon. J. North Amer. Falconers’ Assoc.
7:64-67.

Porter, R. D., and S. N. Wiemeyer. 1970. Propagation of
captive American Kestrels. /. Wildl. Mgmt. 34(3): 594-604.

Tuck. L. M. 1960. The Murres: their Distribution,

82

Populations and Biology. Canadian Wildlife Series: 1.
Ottawa: Queen’s Printer. 260 p.

Waller, R. 1968. A report of the first successful breeding of
Peregrine Falcons in captivity. /. North Amer. Falconers *
Assoc . 7:45-57 (translation by E. H. Spuhler of Waller,
1962. Der Wilde Falk ist Mein Gesell. Melsunger: Verl.
Neumann-Neudamm.)

Welty, J. C. 1962. The Life of Birds. Philadelphia: W. B,
Saunders Co. 546 p.

Willoughby, E. J., and T. J. Cade. 1964. Breeding behavior of
the American Kestrel (Sparrow Hawk). Living Bird
3:75-96.

And various Breeding Project Information Exchange reports
circulated by Raptor Research Foundation.

SURVIVAL OF THE PEREGRINE FALCON:
PROTECTION OR MANAGEMENT?

by Tom L Cade
Cornell University
Ithaca, New York 14850

The Peregrine Falcon has probably been affected by the
DDT-thin eggshell syndrome over its entire range in North
America. All recent samples of eggs from such diverse
populations as those in Ungava, the Canadian Barrens,
Northwest Territories, arctic Alaska, interior Alaska, Aleutian
Islands, Queen Charlotte Islands, and Baja California show
eggshell thinning that ranges from 7 to 21% below pre-DDT
averages (Cade and Fyfe, 1970; Cade et al., 1970). The larger
percentage changes are in the range of those associated with
the depleted population of Great Britain (Ratcliffe, 1970)
and with the virtually extinct falcons of California and
eastern United States (Hickey and Anderson, 1968).

Field surveys in 1969 and 1970 indicate that fewer than
20 producing pairs of anatum Peregrines remain south of the
taiga, excluding Mexico. Local disappearances of pairs at long
known aeries have occurred in the taiga and tundra in the last
two or three years. There can no longer be any serious
question that the Peregrine is an endangered species in North
America.

What can be done about the plight of the Peregrine? Some
people say we should give absolute protection to our last
remaining wild Peregrines by preventing all human
molestation and by prohibiting the taking of wild falcons for
any purpose. This protectionist strategy can only work in
ecosystems that are still capable of self-regenerating and
self-regulating adjustments to perturbations, such as those
caused by chemical pollution. Protectionists should ask
themselves whether any such ecosystem still exists. I agree
with Wayne Nelson (1970) that total protection of the
Peregrine will only hasten its total extinction in North
America.

The strategy of total protection is based on the
assumption that once we stop the use of DDT and related
compounds, organochlorine pollution will rapidly dissipate as
a critical factor in the falcons’ food-chain, and the remaining
Peregrines will recoup their losses. In their recent paper on
the decline of the Peregrine in California, Herman, Kirven,

83

84

and Risebrough (1970) give voice to this point of view: “The
premise that pollution will inevitably doom the peregrine in
California has prompted some would-be falconers to attempt
to obtain birds before their final disappearance. We refuse to
accept this premise, however, as long as the possibility exists
that environmental contamination might be reduced. The
partial recovery of the British peregrines following the sharp
reductions in the use of dieldrin (N. W. Moore, pers. comm.)
and the anticipated reductions of the inputs of DDT and
perhaps also PCB into the environment in North America
provide considerable support to the argument that it is
essential to provide complete protection to any remaining
birds that might constitute a nucleus of a future comeback.”

This is a common and increasingly strident protectionist
attitude, well exemplified in recent 1970-71 editorial
comments in The California Condor published by the Society
for the Preservation of Birds of Prey. Carried out as literally
stated, “complete protection” would exclude the taking of
Peregrines for experimental breeding or for other
management practices; therefore, the probable outcome of
protection needs to be carefully weighed against the
advantages of taking falcons into captivity.

Despite the partial recovery that has taken place in Great
Britain since 1963, from a population low equal to about
38% of the pre-war numbers to a level estimated in 1969 to
be 55% of pre-WW II (D. A. Ratcliffe, in lift.), all evidence
leads to the conclusion that a decline is still underway in
North America (Cade and Fyfe, 1970). The British Peregrine
population was never reduced as much as the population in
continental United States; furthermore, it is a geographically
restricted, insular population, one that was originally much
denser than anything we have ever known in North America,
about 650 pairs in only 88,135 square miles compared to
California, for example, with a pre-DDT figure of about 100
pairs in 158,693 square miles. There were never fewer than
240 occupied aeries in Britain. Also, the British Peregrines are
genetically more homogeneous than the North America
populations are. Given some favorable change in the
environment, recovery of such a population is more likely
than is the recovery of a sparsely distributed, genetically
heterogeneous, continental population, which has already
been reduced to less than 5% of its original numbers south of
the tiaga.

While the domestic use of DDT has been going down in
the United States for several years, there is no evidence for a
reduction in environmental levels of DDT (DDE) residues;

85

indeed, DDT residues are still increasing, in the
phytoplankton of the sea for example (Cox, 1970). No
breakdown products of DDE are known from nature, so that
the quantities present now may simply recycle through
ecosystems on an indefinite basis. There may be enough DDE
already present in the global ecosystem to render the last
wild Peregrine incapable of reproduction. Other pesticide
residues, chemical pollutants, and heavy metals will surely
loom as continuing hazards to birds of prey— not to mention
the exponentially accelerating outright destruction of habitat
and continued reduction in the number of prey animals for
raptors.

There is always a chance that the protectionist point of
view will prove to be correct. Just leave the falcons alone in
the wild, and nature will take care of her own. But do we
want to rely solely on such a tenuous hope? What if
organochlorine residues continue to persist in nature? What if
the remnant anatum populations have already passed below
the “critical size” for recovery (Ziswiler, 1967)?

While the wild, adult Peregrines should be given absolute
protection, a cogent case can be made for taking a prudent
number of young falcons into captivity, including some of
those produced in California. For those few aeries still
surviving in the United States south of Canada, the states
should immediately institute a system of falcon wardens to
guard the aeries and to prevent unlawful human disturbance.

Beyond that simple expedient, a managed “harvest” of
young falcons should be instituted for captive propagation
and as a means for increasing the survival rate of first year
birds. The immediate goal of propagation for anatum,
tundrius, and pealei should be to develop self-perpetuating
captive stocks on a scale sufficient for continued scientific
studies that hopefully will lead to practical breeding for
educational, recreational, and restocking purposes. In my
opinion every producing pair of southern anatum Peregrines
should be contributing some of their young to captive
breeding programs. This is the only way to save some of these
southern falcons, if indeed it is not already too late. While we
do still have the time, sufficient numbers of tundrius and
pealei falcons should be acquired, so that a genetically
representative sample of adaptable individuals can be
identified as captive breeders. Certainly several hundred
Peregrines will have to be screened and should be made
available to qualified breeders in the United States and
Canada— both to professional, institutional programs and to
qualified private individuals who have the demonstrated

86

expertise and facilities for attempting serious propagation.

The natural mortality of first year Peregrines is high. Band
returns indicate that 70% of the fledglings die in their first
year (Enderson, 1969); but the true natural mortality is
probably lower, perhaps around 60%, or even lower
according to Shor (1970). Band returns also suggest an adult
mortality rate of 25%, but this figure is certainly too high for
the pre-DDT period, when stable breeding numbers were
maintained with an average production of about one fledged
young per pair per year. My best estimate for adult mortality,
when breeding numbers are stable, is about 15% or a mean
adult longevity of slightly more than six years.

If 60% of the young die in their first year and 15% of the
surviving cohort in their second year, then for every 100
young fledged 34 survive to breeding age. This is slightly
more than enough to replace losses in the breeding
population with the given mortality rates. Looked at in
another way, for every 100 young fledged, 66 die before
entering the breeding population.

Nearly 20 years ago I pointed out to falconers that these
expendable young birds constitute the “harvestable surplus”
for falconry (Cade, 1954). How many of these birds of the
year can still be taken by human agency without affecting
recruitment to the adult breeding populations? It could be
argued that since the adult breeding populations are
declining, there are no surplus young. The argument is
somewhat academic, since the majority of young birds still
die in their first year.

If falconers were allowed to continue taking immature,
passage Peregrines with the proviso that the birds have to be
released at the end of their second winter, in time for spring
migration, the wild falcon populations could actually benefit
from a bonus of adult birds added to them. Falconers can
certainly keep a higher percentage of first year birds alive
than obtains in the wild. From my experience I would
estimate that for every 1 00 passagers taken in their first fall,
at least 60 and perhaps as many as 75 would still be alive at
the end of their second winter, roughly twice the number
that can be expected to survive in the wild. Diseases that are
often fatal to immature falcons in the wild are usually
curable today in captivity. Moreover, falconers can feed their
charges on foods with the least DDT contamination, so that
their birds, when released to join the wild breeders, would
have relatively low body burdens of pesticides. Thus two
benefits could accrue by holding Peregrines for falconry
during their first two years of life: (1) a greater number

87

would survive to breeding age and (2) the birds would
re-enter the wild with the least likelihood that their eggs will
be affected by DDT.

The use of falconry for increasing the survival rate of
immature falcons is a management technique that should be
given some serious thought, especially for migrant Peregrines
from northern breeding grounds. In any case, protection,
based on reason rather than hysteria, and propagation, based
on scientific methods rather than trial and error, should go
hand in hand as the two chief measures for promoting the
survival of the Peregrine and other threatened birds of prey.

References

Cade, T. J. 1954. On the biology of falcons and the ethics of
falconers. Falconry News and Notes 1 (4) : 1 2-1 9.

Cade, T. J., and R. Fyfe. 1970. The North American
peregrine survey, 1970. Canadian Field-Nat.
84(4): 23 1-245.

Cade, T. J., J. L. Lincer, C. M. White, D. G. Roseneau, and L.
G. Swartz. 1971. DDE residues and eggshell changes in
Alaskan falcons and hawks. Science (in press).

Cox, J. L. 1970. DDT residues in marine phytoplankton:
increase from 1955 to 1969. Science 170:71-73.

Enderson, J. H. 1969. Peregrine and prairie falcon life tables
based on band-recovery data. Pp 505-509 in: Peregrine
falcon populations their biology and decline , J. J. Hickey
ed. Univ. Wisconsin Press.

Herman, S. G., M. N. Kirven, and R. W. Risebrough. 1970.
The peregrine falcon in California I, A preliminary review.
Audubon Field Notes 24:609-613.

Hickey, J. J., and D. W. Anderson. 1968. Chlorinated
hydrocarbons and eggshell changes in raptorial and
fish-eating birds. Science 162:271-273.

Nelson, R. W. 1970. Observations on the decline and survival
of the peregrine falcon. Canadian Field-Nat.
84(4):313-319.

Ratcliffe, D. A. 1970. Changes attributable to pesticides in
egg breakage frequence and eggshell thickness in some
British birds. /. Apprl. Ecol 7:67-115.

Shor, W. 1970. Peregrine falcon population dynamics
deduced from band recovery fata. Raptor Research News
4(2):49-59.

Ziswiler, V. 1967. Extinct and vanishing animals.
Springer-Verlag.

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