BEHAVIOR
OF
PEREGRINE
CITY
FALCONS
IN
THE
NEW
YORK
REGION
RICHARD A. HERBERT AND KATHLEEN GREEN SKELTON HERBERT
THis paper summarizesthe generalbehaviorof PeregrineFalcons
(Falco p.eregrinus)at eight nestingsitesin the Hudson River valley, at a
New York City eyrie, and at a numberof New York City winteringsites,
basedon observationsmade over a 30-year period. The more intensive
part of our study,involvingabout 1,200visitsto theseeyries,wascarried
out from 1949 to 1959. The nestingpairs alongthe Hudsonhad become
nonbreedingby the early 1950's,and by 1961 the entire populationwas
extirpated. The historyof thesepairs, their productivity,and the factors
contributingto their extirpationwill be discussed
elsewhere.
In this paperthe term eyrierefersto a cliff or seriesof cliffs and to
nest ledgeswhich are the nestingdomain of a singlepair of Peregrines
and their successors
over a periodof years. The term cli// here includes
the face of an abandonedquarry as well as a New York City skyscraper
usedas a nestingsite. Each cliff usedby the birds has at least one nest
ledgeknown to have beenusedin the years of our study. The term nest
ledgeis usedin this paperto refer to past as well as to contemporary
use.
THE
STUDY AREA AND ITS POPULATION
The sheerrock walls of the Hudson Palisades,rising to heightsof 400
feet and dominatinga majesticriver, were fitting sitesfor the eyries of the
PeregrineFalcon. The eight Hudson River eyriestreated in this paper
were distributedalong the west shoreof the river, extendingnorth from
New York City for a distanceof 55 milesin New Jerseyand New York
State, within the jurisdictionof the PalisadesInterstatePark. A ninth
HudsonRiver eyrie,about55 milesnorth of New York City on the east
sideof the river and oppositethe eyriereferredto hereafteras no. 8, has
not beenincludedin this paper,althoughit produced
youngin the 1940's
and 1950's. It is the only eyrie in this valley on the east side of the
Hudson. A tenth, marginaleyrie situatedin an abandonedquarry near
the no. 6 eyriehas beenincludedin our field observations,
althoughit
was usuallyunoccupied
after 1941.
The Hudsoneyriesare numberedfrom southto north in this paper,
1-8. Six are situatedon steeptraprockcliffs with open,exposed
ledges
Figure 1. Upper: female PeregrineFalcon at eyrie no. 1, May, 1953, when she
was at least 13 years old (seepp. 67, 87). Lower: nestingledge and banded young
Peregrinesat eyrie no. 6, showingplant growth which the birds appearedto prefer
(see pp. 77, 84)..Photographs by Richard A. Herbert.
62
The Auk, 82: 62-94. January, 1965
Jan.
]
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•.I•D
I"IERBERT,
Behavior
o]Peregrine
Falcons
63
64
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Am)HER•r, Behavior
o!Peregrine
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abovethe talus slope; two are locatedin abandonedquarries.A primary
characteristic
of the Peregrinein this regionis to dominatethe landscape,
and heightis thus an important factorin the selectionof its nest sitesand
perches.It doesnot appear,however,that extremelyhigh cliffs are preferred, nor that extremeheight is related to nestingsuccess.Indeed, the
highestcliff on the Hudson,the no. 8 eyrie, has had lessnestingsuccess
in our experiencethan the much-molested
no. 1 eyrie with its long, sheer
cliffs. More important factors in nesting successwould appear to be:
(1) suitable ledgesfor nesting, feeding, and perching; (2) absenceof
large treesthat would impedevisibility and flight; (3) length of cliff, a
long cliff with severalledgesbeing preferableto a narrow one; and (4)
inaccessibilityto disturbancefrom above. Attachmentto a traditional
site is marked; if a better territory becomesvacant, a pair of Peregrines
doesnot leaveits traditionalterritory.
Althoughonly four, or possiblyfive, of the Hudsoneyriesare firstclasseyrie sitesin the definitionof Hickey (1942)--the poorestof the
eight is locatedin a quarry havingthe dual disadvantageof only one nest
ledgeand easy accessfrom above--they have compensatory
advantages
that have madethem consistentlysoughtby the Peregrinepopulationfor
as long as its history is recorded.They might be comparedto a Park
Avenue addresswith a waiting list; in our first two decadesof observation any vacancyin the eyrieswas immediatelyfilled, a fact that led to a
falseimpressionof stability in the population.
Hickey (1942) and Cade (1960) have pointed out the attraction of
rivers for the Peregrine. Like the seabirdislandsof the Pacific Northwest
describedby Beebe (1960), one magneticattraction of the Hudson River
cliffs is a bountifulfoodsupply. Not only do the cliffs commanda migration flight line with a prodigioussupply of flickers (Colaptes auratus)
and Blue Jays (Cyanocittacristata) for severalmonthsof the year; they
are alsosituatedon a year-roundrouteof homingpigeonsspeedingup the
river. Cade (1960) also mentions,in relation to rivers, the Peregrine's
fondnessfor bathing. However, we have never seen wild Peregrines
bathe.
Another factor that has made these cliffs attractive is the protection
originallyextendedto them. Protectedfor many yearsby the no-trespass
regulationsof the large estatesalongthe Hudson,and then lesseffectively
by the sanctuarystatus of the PalisadesInterstate Park that swallowed
up theseestatesin the 1930's,the Hudsoneyriesenjoyedmore security
than many inland eyries. Althoughthe Peregrinehas been officially protected throughoutNew York and New Jerseysince 1934, protectionwas
not enforced,even in the PalisadesInterstate Park.
Peregrineswintered regularly on some 20 different New York sky-
Jan.]
1965
HERBERT
AND
HERBERT,
Behavior
o]Peregrine
Falcons
65
Figure 2. Nesting cliff of Peregrine Falcons overlooking the Hudson River. This
is one of two alternate cliffs used by the pair at eyrie no. 3. Photograph by Richard
A. Herbert.
66
HERBERT
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scrapersin midtown and downtownManhattan, on three of New York's
bridges,and on a gas tank and a high schoolin The Bronx, a northern
boroughof New York City. The apparentimpactof humaninterference
was particularly noticeablein the New York City wintering population,
which gradually increasedduring World War II, when the war effort removed many pigeon fanciers, falconers,and others normally responsible
for curtailingthis population. By 1946 the number of wintering Peregrinesin Manhattan and The Bronx had risen to 16, but by 1952 the
numberhad droppedto 7. Femalesdominatedthe New York skyscrapers
and appearedto have territorial attachmentsfor certain buildings.
In addition to the unattached,winteringPeregrines,New York City
had oneyear-roundresidentpair of Peregrines
from 1943 to 1953. This
pair, which regularlyroostedon the Grand Central Building in winter,
hatchedfour clutchesof eggson two different skyscrapersabout 1.35
miles apart in midtown Manhattan. Over a ten-year period they attempted nesting on several skyscraperswithin a one-mile radius, giving
rise to a newspaperlegend that there were severalpairs of Peregrines
nestingin midtown Manhattan. In the winter and springof 1943 two
other pairs of Peregrines
occupiedRiversideChurchand a gas tank in
The Bronx, but thesepairs did not remain.
Ratcliffe (1962) statesthat, in Great Britain, only where big cliffs are
availableis the Peregrinefound nestingcloseto human dwellings,while
Cade (1960:238) saysthat in Alaska very high cliffs seemto be avoided
by this species.In our experience
the importantfactorsappearto be the
isolationand dominanceof the air which the eyrie affords; in New York
City the successfulnestingsoccurred on the 16th and 23rd floors of the
two respectiveskyscrapers.On the Hudsonseveralof the eyrieshad recreational areasand bathing beachesbelow the talus slope; such activity
below the cliff did not disturb the birds, but any approachfrom above
was immediatelyalarming.
In the city, as on the cliffs, the Peregrineheraldsits presenceby
splashes
of "whitewash"(excrementstains) on the pinnaclesof Riverside
Church,on the statuesof the Romanathletesatop the Whitehall Building in lower Manhattan, and on outcroppings
of many older skyscrapers.
Pigeonsalso nest and rooston thesebuildings,but the excrementof such
grain-eatingbirds makes a solid, densemass. The Peregrine'smark is a
splash,its perchesloftier and more exposed.
The Peregrinehas adaptedwell to the city habitat. Attracted,doubtless,by the abundantsupplyof pigeonsand Starlings(Sturnusvulgaris),
the falconsmight have had considerablygreater nestingsuccessin the
city had it not beenfor the oppositionof pigeonfanciers(whoseflocksof
exercising
pigeons
wereraided
by thefalc,
ons),theAmerican
Society
for
Jan.]
1965
HERBERX
AND
HeRBeRX,
Behavior
ofPeregrine
Falcons
67
the Preventionof Cruelty to Animals,and the New York press,which
printedaccountsof the "murders"of pigeonsby the falconsand evenof
their supposedattacks on humans (New York Times, 25 June 1945; 17
August 1959).
FIELD
IDENTIVICATION
The Hudsonand New York City populationof Peregrines
consistsof
birds of the easternNorth Americansubspecies,
Falco peregrinusanatum.
Thesebirds are larger,richer,and darker in color than the sand-colored
falconsseenin fall coastalmigrationsin this regionand believedby the
authorsto representan arctic population. None of the numerousPeregrinesbandedas youngnestlingsin the northeastern
stateshave to our
knowledge
beenrecoveredsouthof Georgiaand Arkansas.This suggests
that Peregrines
bandedas coastalmigrantsin the fall and recoveredin
SouthAmerica are from a different population.
The Peregrine'splumageis freshand at its best in late fall after a molt
of three to four months. It appears somewhatfaded in the spring, and
the femalesare apt to appear tan-coloredon breast and belly. Over the
years several adult birds on the Hudson were identified by peculiarities
in markingsor by variationsin individualbehavior. Three of thesewere
occupantsof their respectiveeyries for many years. The male at the no.
1 eyrie,whichappearedin 1938 whenalreadyin adult plumageand which
was presentthrough1955, had a tuft of white feathersabout an inch in
diameteron hishead. His redoubtable
female(Figure1), a very darkbird
present 1942-57 (fourth to occupy the eyrie after two previous females
had beenseizedby a falconerand onehad beenshot) wasconspicuous
by
her aggressive
defenseof the eyrie, and was further identifiedby the fact
that shelaid her eggsa month earlier than the other femaleson the Hudson. The male at the no. 3 eyrie was a trim, beautifully proportioned
falcon, identified by his distinctive coloring. He was a very pale bird
with creamywhite breastbut with exceptionallydark markings. As noted
by Beebe (1960:150), contrastingmarkingsare characteristicof F. p.
anatum but this bird was the most strikingly marked of this speciesthat
we have seen. His crown and malar stripe were slate black, his back
bluish, and his belly heavily barred like that of a female--a surprising
distinctionin view of his advancedage, for the plumageof the Peregrine
tendsto becomepaler with age. This bird appearedat the eyrie in adult
plumagein 1940, and at the time of his disappearancein April, 1956, his
age must have been at least 18 years, since the Peregrine does not normally breed until two years old.
In addition, such behavioral characteristicsas the extreme "nervousness" of the female at the exposedno. 6 eyrie and certain distinctive
68
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[ Vol.Auk
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courtshiphabitsof the female at the no. 7 eyrie suggestedthat the same
female was in residencefor a number of years, but thesebirds could not
be positively identified.
From 1938 through 1944, 22 youngwere bandedin the Hudson eyries
(18 were bandedby the senior author either alone or in associationwith
others,and 4 by W. R. Spofford); yet none of the eyriesappearedto be
occupiedby a bandedbird throughoutthe period of our study. However,
the birds at the no. 8 eyrie were too distant for us to distinguishbands.
GENERAL BEXaAvmR
Althoughwe have soughtto generalizein noting the habits of the Hudson Peregrines,perhaps the most notable fact about them was that they
varied greatly as individuals. No two individualsnor pairs were the same
in behavior. No two pairs, it wouldseem,had the sameproblems.Each
eyrie was a world of its own, distinct in pattern.
THE
PAIRING BOND
Permanency.--Although
Hagar (in Bent, 1938: 44) castssomedoubt
on whether or not the Peregrinesof the Massachusettscliffs (where the
birds did not winter) mated for life, and whether or not "the female of
the previousseasonreturns directly to the cliff, if still alive (as has been
generallyassumed),"the birdsresidenton the Hudsondid appearto mate
for life, unlessone was removedfrom the cliff by somecatastrophe.(One
pair at the no. 1 eyrie remainedintact for 14 years.) This was true, not
only of the Hudson birds, but also of the pair residentin New York City
and of the pair on the Sun Life Building in Montreal (Hall, 1955: 19, 22).
Replacement of mates.--In rare casesthe catastrophethat removesone
of the pair may take the form of a battle with another Peregrinefor the
eyrie, but this is exceptional.AlthoughBeebe(1960: 163) was impressed
by the lack of intraspecificaggressiveness
among mated pairs of F. p.
pealei on Langara Island in British Columbia,in our experienceindividuals of F. p. anatum tend to respectterritorial boundaries,and territorial
behavior in Alaskan Peregrineshas been well describedby Cade (1960:
197-198). Peterson(1948: 139) relatesan incident in which two falconers trapped a breeding male at an eyrie and releasedhim a month later
at the same eyrie, after another male had taken possession
of the cliff.
Thus both birds were investedwith territorial rights, and a battle royal
ensueduntil the Peregrine that had replacedthe trapped bird was driven
from the cliff.
On 12 February 1943, two males battled for possession
of the no. 3
eyrie, one of the finest cliffs on the Hudson (Figure 2). The defending
male, the pale bird presentsince 1940, was the victor. On 1 April 1945,
Jan.]
1965
HERBERT
AND
HERBERT,
Behavior
ofPeregrine
Falcons
69
an adult female and an immature female battled for possession
of the no.
3 eyrie, the residentmale taking no part in the fight. The immature female, thought to be the defendingbird, drove the adult from the eyrie.
The immaturefemaleprovedto be a nonbreedingbird. Similar battles
took place at the Montreal eyrie, where one femalenestedcontinuously
on the Sun Life tower from 1936 through 1952 (Hall, 1955: 22). In 1944
her first mate was engagedin a battle of severaldays' duration which
endedin his death. In 1950 her secondmate disappearedand was immediately replaced (Hall, 1955: 13, 15, 18).
The primary attachmentof the male, and of occasionalfemales,appears
to be to the territory, and mating may be incidentalto this attachment.
If the femaleof a pair is killed, the male usuallycontinuespossession
of
the cliff and tries to attract a female to it; but if the male of a pair is
killed, and no replacement
appearsbeforethe breedingseason,
the female
is likely to desert. Both of theseincidentsoccurredin the winter of 195152 on the Hudson; on 7 January 1952, the male at the no. 2 eyrie was
found shot and his female desertedthe cliff in March; the female at the
no. 5 eyrie was found shot in November, 1951, but the male remainedon
the cliff and attracteda new femalethe followingspring. Hickey's report
(1942) of two femalesfighting for the same clutch of eggsalso suggests
that unsuccessful
femaleslack the site tenacity of males.
Invasion of an occupiedterritory by a wandering Peregrine does not
necessarilymean that the intruder is challengingthe resident'spossession
of the cliff. Althoughthe invaderis frequentlymet by a challengefrom
the residentmale--a seriesof aerial maneuversand threateningstoops-most wanderingPeregrinespasson their way unmolested.
On the Hudsonmost of the wanderingPeregrineswere females. Usually they were driven away from the cliff by the residentpair or by the
femalealone,but late in the breedingseasonof 1950 we saw an unusual
incident in which a strangefemale appearedto be welcomedor at least
toleratedby a residentpair (whichhad no young).
,¾isitingthe no. 7 eyrie on 28 June, we watchedthe pair perch on the
cliff after unsuccessfully
pursuinga white pigeon. At this time the in-
(ruder,a dark,moltingfemale,flewslowlyinto the eyrieterritory,too
highabovethe cliff for us to distinguish
her markings.Shecircledthe
cliff, evidentlywatchingits residents.They seemedto watch her, too,
followingher flight with rotating heads,but surprisinglythey made no
move to intercept her, nor did the residentfemale rise with her ringing
battle cry. Instead, with much conversationalee-chupping(see under
'"Calls," below) they seemedto be calling in the stranger. While the
residentfemale was perchedon the cliff "talking" to the strangefemale
flying above, the resident male executedwhat seemedto be a courtship
70
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A•BHERBERT,
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82
[ Vol.Auk
flight directedat the strangefemale,as if to enticeher in to the cliff. He
zoomedover the river, stoopingand plummetingwith foldedwingsalmost
to the surfaceof the water, then soaringinto the blue. After his flight he
perchedon the nestledge,while the strangefemalepresentlydisappeared
over the treetopsabovethe cliff. For someminutesthe male wailed, presumably calling to the resident female, who at length flew to the ledge
wherehe was concealed.Both then disappeared
from view. We heard
their conversational
notesfor sometime, this normallyindicatingcopulation. Both birds then left the cliff on brief flights. Half an hour later
they returnedwith the strangefemale flying high above them. The date
of this observationand the fact that yearling Peregrinesoften molt a
month or two earlier than adults suggestthat the strange female was a
yearling.
Althoughin our opinionthe courtshipflight is somewhatsimilar to the
challengethat the male issuesin defenseof his territory, we were convincedthat the behaviorof this residentpair toward the strangefemale
was "friendly," as evidencedby their ee-chupcalls to her and by their
return to the cliff accompanied--although
at somedistanceabove--by the
stranger.
Similarincidentsoccurredat the no. 1 eyrie and the no. 8 eyrie whena
wanderingfemale invadedeach territory. The explanationof theseoccasional incidentsmay be that the resident birds recognizedthe intruders
either as mated neighborsor as passagebirds, and knew that they were
not contendersfor, nor threats to, the eyries. On the Hudson, however,
most wandering femalesapparently were unmated birds. Mated females
from the eyriesoccasionally
wandered,whereasmalesseldomleft the cliff
excepton hunting expeditions.
WINTERING
HABITS
On the Hudson the various pairs wintered along the cliffs at or near
their eyries, in contrastto the absenceof the Peregrinesfrom the New
England eyries in winter (Hagar, in Bent, 1938: 65). This may be due
to the bountiful food supplyof the Hudsonarea.
In the past, local ornithologistsbelievedthat the Hudson birds wintered in New York City, and various spring "arrival" dates on the cliffs
were recordedin the 1930's in the minutesof meetingsof the Linnaean
Societyof New York. Further confusion
was createdby the Hudson
Peregrines'occasionalhuntingof Starlingsand pigeonsin the townsadja-
centto, or acrossthe river from,their cliffs,leadingto the beliefthat they
were wintering birds there. In the late 1930's when Great Horned Owls
(Bubo virginianus)were nestingand wintering in the immediatevicinity
of the no. 1 eyrie, the pair of Peregrinesfrequentlyflew acrossthe river
Jan.]
HERBERT
AND
HERBERT,
Behavior
ofPeregrine
Falcons
1965
71
in the late afternoonto roost on the Hunt's Point gas tank in The Bronx,
about 5.5 miles distant.
However,winter recordsfor the Hudsoneyries from the early days of
the century are in fact extant. In 1907 G. E. Hix recordedthe first winter record of a Peregrinein PalisadesPark 12 February; on 12 February
1913 Ludlow
Griscom noted the second winter
record for the Palisades
when he saw the pair at the no. 1 eyrie (Ludlow Griscom,in litt.; also
Abstr. Proc. Linn. Soc. New York, 24-25: 38). J. T. Nichols (in litt.)
recordedthe pair at the no. 1 eyrie 16 November 1915. In their unpub-
lishedmanuscript,"Birds of the Englewoodregion"(preparedin 1918),
thesetwo observersstatedthat the "Duck Hawk" was a regularpermanent resident in small numbers.
Our own numerous winter
records will
be presentedin anotherpaper.
Though an occasionalpair has wintered in New York, most of the New
York City birds were unattached,wintering females. There is little proof
of their origin, but we believe that most of thesebirds came from New
England and northeasterneyries rather than from the Hudson. Of the
banding recordsextant in 1962, only three winter recoverieswere from
New York City. The datesof theserecoveries--onein Novemberand two
in December--suggestthat the birds were wintering,yet surprisinglytwo
of the three were males. One was a first-year male, bandedas a nestling
on the Delaware River and killed 3 Decemberin Brooklyn; the second
was a first-year male banded as a nestling on the Sun Life Building in
Montreal and killed 25 December in Brooklyn; while the third was a
female,bandedas a nestlingat a Massachusetts
eyrie and killed in New
York City in November, 1952, 131/.•years later. This last bird was reported (Edward Brown, pers. comm.) to have occupiedand bred in the
sameterritory for many years. Our recordsindicatethat she was a wintering bird.
There are also three winter recoveriesfrom two nearby counties, of
Peregrinesbandedat two Vermonteyriesand onePennsylvaniaeyrie. The
reportedsex ratio of all Peregrinerecoveriesin the 1950's was almost six
to onein favor of females,suggesting
to us that femaleswandermore than
males. However, there is also an old, unprovenhypothesisthat females
outnumber
males.
Of six recoveriesfrom nestlingsbandedon the Hudson,three are winter
records(one male and two females)of birds dying in JerseyCity, New
Jersey;two wereshotand onewasfounddeadwith a partially eatenand
presumablypoisonedpigeonin January, 1944. Three other Hudsonrecoveries (two femalesand one bird of unknownsex) are of winteringbirds
taken in nearby townsof New Jersey. There is alsoone summerrecovery
from New York City, of a male bandedas a nestlingand picked up four
72
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yearslater in downtownNew York. Accordingto the agent of ,theAmerican Societyfor the Preventionof Cruelty to Animals,this bird was dying
of "a growth in its throat." The date was 20 August 1946 and the descriptionof its conditionsuggeststrichomoniasis.
THE
DAILY
CYCLE
The hunting exploitsof the Peregrinehave so captivated the human
imaginationthat one sometimesgets a picture of this swift "engineof
death" clashingand brawlingabout the skieswith unabatedfury, striking
into oblivioneveryhaplessbird of passage.On the Hudsonthe Peregrine
had no concernabout making a living. He was a bird of leisure,and at
almostany hour of the day onecouldfind him, regal and dignified,perched
on his twist of cedaror rock column,surveyinghis domain (see Figure 1).
His bright eyesmissedno movementon the cliff. With a barely perceptible movementof his head, he scrutinizedthe observerson a distant rock
or a swallowskimming the river far below.
In the spring,processions
of migrantsof many speciespassedthe Peregrine's eyrie, but except for an occasionalreconnaissance
flight after a
brazen Crow (Corvus branchyrhynchos)or a threateningstoopat a hawk
intruding near the nest ledge, the Peregrinespermitted most of these migrants to passwithout arrest. The Peregrineis not a hasty fighter. He
doeskill, but, like most predators, he kills only to eat.
The hunt.--When the Peregrine does hunt in dead earnest, his manner
is often deceptivelycasual. With no apparentintent, he will watch a pair
of homingpigeonscrossthe river half a mile north of his eyrie. When
they are almost,it would appear,to the safety of the farther shore(but
actually not more than halfway acrossthe stream) and almost a mile
distant from his perch, he takes off from the cliff on someseemingly
irrelevantimpulse,flying on a northwardcourseas casuallyas a Peregrine
can fly with his vigorous,alwayssomewhathurried flight.
Thereis a moment--justa moment--when
pursued
andpursuer,
pigeon
and Peregrine,
seemto be flyingat equalspeeds.The pigeonwill su.rely
make the farther shore. Flying at better than 45 miles an hour, a cham-
pion racer,the homingpigeonis confidentin his wings;he doesnot take
cover. Yet the hawk is still gainingspeed,quickeningand shallowinghis
wingbeatsuntil it appearsthat all of the motionis in the primaries.The
race will be neck and neck, it seems. But suddenly,it appearsthat the
pigeonis flying backwards,so great becomesthe Peregrine'shead-on
speed. In a flash, the gap is closed;the Peregrinehas overtakenthe
pigeonin a shallowstoop.Yet still the pigeonflies unharmed;the Peregrinehasnot seizedit. But--and this is the mark of a greatavianathlete
who is seldomoverextended--thePeregrinehas overtakenmerely to roll
Jan.]
1965
HERBERT
^•DHERBERT,
Behavior
o!Peregrine
Falcons
73
over and seizethe pigeonfrom underneath.Whether taken from aboveor
below,thepigeonhangslimpin thetalonsof thePeregrine.
Almostfrom
themomentof thestrike,it is dead.
It shouldbe noted,however,
that the Peregrine's
huntis not always
eitherspectacular
or successful.
Hickey (1942) describes
an occasion
whenhe and the seniorauthorsawa Peregrine
makesevenunsuccessful
attemptsto take sevendifferentracingpigeons.Much depends
on the
maneuverability
of the preyand its tendency
to take cover.Almostalone
amongthebirdsthatpassthePeregrine's
eyrie,theracingpigeondoesnot
immediately
takecover.Mostof themigrants--Blue
Jays,flickers,
swallows-andeventheBaldEagle(Haliaeetus
leucocephalus)
andthe RedtailedHawk (Butko']amaicensis)
havebeenseenby us to take cover
whenthePeregrine
salliesforthfromhispinnacle.
In thespring,whenyoungPeregrines
arein thenest,the frequency
of
huntingincreases.
BlueJaysaremoving
up theriverin numbers,
stragglingsinglefile abovethetreetops
at the topof the cliff. The malePeregrinewatches
the jaysintently,hiseyesmovingas theymove,his halfopenwingsquivering
as he waitsthe momentof pursuitwhenthe jays
reach the center of the mile-wide river and are most remote from cover.
At thismoment
helaunches
himself
intotheair. Againhisflightappears
deliberate,almostslow, as he gainsaltitude. When still far behind the
quarry,helevelsoff, toodistantandtoofar belowto threaten
the jays,
it seems.But withquickening
wingbeats
he gainsgreatspeed;yet surprisingly,
he is losingaltitudetapidlywhilethe jays are still abovehim.
Thisseems
a curious
maneuver,
but is a correct
one,for at sightof the
falcon,thejays,withfoldedwings,divefor thewater,plunlmeting
past
the falconto withina fewfeetof the river,ashe triesunsuccessfully
to
intercept
them.Thenhe singles
outonejay, pursuing
it relentlessly
just
abovethewaterandseizingit in a quick,shallowstoop.
In this fashion,
oneMay day at the no. 1 eyrie,the malebroughtin
twojaysfromhisafternoon's
hunt,givingthemwholeto the twoyoung
on thenestledge.A thirdjay wasknocked
into the water,whereit was
pounced
o.nby severalgulls,whilea fourthwhichhe pursued
escaped
to
the farther shore.
Someweekslater,whentheyoungwereseveral
dayson the wing,we
•watched
the femaleat this eyriebringin a jay. Shepursuedno such
patternOf'artistryasthemalein thehunt. WhentheBlueJaywasonly
a shortdistance
outfromthecliff,shetookoff in straightforward
pursuit,
andafterthreeor fourstoops
shestruckthejay a glancing
blow,knocking
it downmomentarily
to thewater.Asthejay thenflewweaklyabovethe
water,sheeasilypickedup thebirdandpassed
it to oneof heryoungon
the wing.Thispointsup the susceptibility
of smallcorvids
to capture
74
H•RBER:r
A• H•RB•R:r,
Behavior
ofPeregrine
Falcons
[ Vol.Auk
82
over water by Peregrines.Cade (1960) relatesa similar accountof the
captureof a Gray Jay (Perisoreuscanadensis)in the Yukon.
Feedingand night ledges.--The Peregrineusually carrieshis kill to an
establishedfeedingperch, such as a ledgeor a dead tree on the cliff.
Feedingledgesare distinct from nest ledgesand night perchesand in our
experiencethe adult birds never feed themselveson a currently usednest
ledge. On the Hudsoneach eyrie containedone or more main feeding
ledges,andwhenyoungwerepresent,twoor threeadditionalledgesmight
be set up near the nest ledge.
Although the site of a feedingledge may vary from year to year, at
someeyries the same feedingledgeswere used for many years. At the
no. 1 eyrie the main feedingsite was a fallen dead cedar (Juniperusvirginiana) bridginga chasmof rock which is within a hundredyards of the
two mostfavorednestledges.This Samedeadcedarservedas the main
feedingledgeat the no. 1• eyrie for more than 30 years and was a landmark to observersof the early 1930's.
All of the pairs on the Hudson had one or more night perches,wellmarked with whitewash,used primarily for shelter at night or during a
rainstorm. Usually the night perchwas a small, shallowledgewith an
overhang.Frequentlyit was so narrowthat the bird faced sidewiseor
inward
toward
the cliff.
Food.--The most commonprey of the HudsonPeregrineswas the homing pigeon (these being routinely banded), exceptduring spring and fall
migrationswhen Blue Jay and flicker feathersregularly floated down
the cliff. Occasionallya Starling'shead or a bandlesspigeonlay on the
feedingledge. In one year (1940) we thoughtthat the male at the no. 1
eyriehunted
Starlings,
whilethefemale
hunted
pigeons,
butin lateryears
this did not prove true. However, the male doesseem to have more success in catching small birds. Young birds often catch butterflies and
dragonflies.
In the early 1930's Cleon Garland, a pigeon fancier and game warden,
picked up more than 100 pigeonbands from feeding ledgesat the no. 1
and no. 3 eyries. One band, recoveredin February, 1932, dated back to
1897. As the feeding ledges are often difficult of access,Mr. Garland
developedan ingeniousmethod of checkingthem without climbing down
the cliff. By meansof a hook and heavily weightedfishing line he drew
up a collection
thatincluded
remains
of shorebirds,
GreenHerons
'(Buto.ridesvirescens
) , Red-headedWoodpeckers(Melanerpeserythrocephalus), Mourning Doves (Zenaidura macroura), Rufous-sidedTowhees
(Pipiloerythrophthalmus
) , CommonGrackles(Quiscalus
quiscula
) , and,
of course,flickers and Blue Jays (Cleon Garland, pers. comm.). Even a
Jan]
1965
HERBERT
AND
HERBERT,
Behavior
o!Peregrine
Falcons
75
duck (speciesunknown)was taken by a femaleat the no. 1 eyrie (Robert
Menegus,in litt., 7 March 1953).
The contentionof many pigeonfanciersthat the Peregrinepreferswhite
pigeonsmay have somefactual basis. Certainly a white pigeonoffers a
more conspicuous
target to stoopat; we often saw the falconswith white
or light-coloredpigeons.
Although the extent of the Peregrine'shunting varies somewhatwith
the season,one homingpigeon (the averageweight is about one pound)
will more than sustaina pair for a day. However,on one occasion(24
June 1953), we watchedthe femaleof a pair at the no. 7 eyrie slowly
consumean entire pigeonwhile the male wailed on a nearby ledge "asking" for a shareof the prey and occasionally
flying to her. Engrossedin
her repast,shecompletelyignoredhim, feedingfor an hour. When only
the wingsof the pigeonremained,shecarriedthemoff to anotherledge.
The male flew in to this ledgeseveraltimes,with muchconversational
eechupping,seekinga share,but eachtime he wasrouted. On his seventh
try, he emerged
with onepigeonwing--a scantdinner--whilethe female
flew about the cliff with the other wing.
This is unusual behavior. Normally the birds of a pair share a kill,
often transferringthe prey from one to another. Sometimesa portion of
the kill is left on the ledgeto be consumedlater; on one occasionwe saw
the male return to a kill 24 hours later. When young are in the nest,
remainsof partially consumedbirds are apt to be scatteredabout on
nearbyledges,but theseare usuallyfed to the youngin due courseand
the entire carcassconsumed.Normally the female doesas much hunting
as the male, but in the courtshipand early breedingseason(until the
youngare about threeweeksold) the male doesmostof the huntingand
feeds the female.
As on the Hudson,the chief prey of the city-dwellingPeregrinewas the
racing pigeon, except for such Peregrines as the Riverside Church bird.
Located near an enormouswinter Starling roost that covers three city
blockswith excrement,the Riversidebird regularly fed on Starlings.
Whether the city pigeons(feral Rock Doves) that nestedon the same
skyscraperas a winteringor nestingfalcon--usually severalfloorsbelow
--and the occasionalSparrowHawks (Falco sparverius)that nestedthere
can be termed "commensalassociates"is a moot question. By preference
the Peregrinesstruck into the flocksof racing pigeonsexercisingover the
rooftops. These pigeons offered a more accessible,vulnerable target,
while the city pigeonsfed on the ground, where the falconscould not
readily strike, and took covercloseto buildings. On occasion,however,
when there was sufficient space,the Peregrinesdid stoop at city pigeons.
In the springof 1948a New York City pair frequentedCentral Park after
76
HERBERT
.aN•)
HERBERT,
Behavior
ofPeregrine
Falcons
[ Vol.Auk
82
desertingthe eyrie on the St. RegisHotel; in the park they were often
seenstoopingat city pigeons.
Calls.--The vocalizationsof Peregrinesthrow considerablelight on
their activities. A querulouswail, drawn out and rising in pitch at the
end, is a call usedin variouscircumstances.
It is the territorialcall of the
malewhich,in early spring,doesmuchflying aboutand wailingon the
cliff. Wailingis the usualnoteof a Peregrineflushedoff the cliff when
there are neithereggsnor young. The birds alsosummoneachother by
wailing, as when the male wails to the femaleto enticeher into a nest
ledge,or whenthe femalewailsto the malefor food,or whenthe male,
carryingfoodbackto thecliff•wailsto the femaleto comeandtake the
food in an aerial transfer.
A note usedin moreintimate contextsis the ee-chupnote, describedby
Hagar (in Bent, 1938: 42) as a wichewnote. Wheneverthe birds are
closetogetheron the cliff, and particularlyduringcopulationand incubation, this is the note one usuallyhears. The ee-chupnote is neverheard
unlessthereare two birdson the cli]]. There are severalvariationsof this
call. A call alsofrequentlyheardduringnestingis a soft chirpwith which
the birds greet each other on the ledge.
The alarm note or battle cry of the Peregrineis a drawn out kaa-aa-ack,
kaa-aa-ack, kack, kack, kack, kack, kack, rising in pitch on the longdrawn openingnotesand increasingin tempoon the last syllables.When
the bird is merelyscolding(a response
of lower intensity), this is shortened to a rapid kack-kack-kack-kack-kack-kack-kack-kack.
Witherby et
al. (1939: 10-11) describethe latter as a shrill, chatteringkek-kek-kekkek; and the battle cry as "a hoarse,almostquacking'kwaahk-kwaahk,
kwaahk' of more intense excitement."
A bird (male or female) flushedoff a nestledgewherethere are eggs
or youngor evena scrapewill utter thisscoldingcry or the battle cry as
it circlesthe cliff, but if there are neither eggsnor young nor a scrapeon
the ledge,its wailingnotewill showthat it haslittle interestin the ledge.
A seldomheard note is a clucking,like the cluck of a hen (Gallus gal-
lus) or Barn Owl (Tyto alba), which the femaleusesin feedingvery
youngbirds,causingthemto opentheir bills. By the ageof two weeksor
morethe younggivea low whineas the adult approaches
with food. Hall
(1955: 13) saysthat he heardchirpingfrom the youngwhile the eggs
werestill intact, a few hoursbeforethe first egghatched.
NESTING
Courtship.--The breathtakingcourtshipflights of the Peregrinehave
beenwell describedby Hagar (in Bent, 1938: 44-46). On the Hudson,
copulationand courtshiphave beenobservedfrom 12 Februaryto late
Jan.]
1965
HERBERT
^•DHERBert,
Behavior
ofPeregrine
Falcons
77
June (in an unsuccessfulnesting season). Normally they took place in
February and March. Once incubationbeginsthere is little courtshipor
copulation;but if the nest is broken up, the cycle may build up again.
Thus there is considerablevariation in datesof courtship.
In the early stagesof nestingthe male seemsto be the dominant member of the pair and he is often seentrying to entice the female into the
recesses
of a nest ledge. Another almost invariable act in the courtship
and incubationpattern is his proffer of someportion of his kill to the
female.
Nest ledges.--Amongcasual observersof the Peregrineat these cliffs,
one sometimesheard the remark that "there are hundredsof ledgeswhere
they might be nesting." In this, evidently, the Peregrine and human
point of view are sharply divergent,for there were usually only two or
three ledgeson eachcliff that the Peregrinesusedfor nesting,and many
of theseappearedto be traditional choices.Along the Hudson the same
nestledgesof the nos.2, 3, and 4 eyrieswereusedhalf a centuryago (the
late BeecherS. Bowdish,pers.comm.).
Becauseof thesetraditional preferences,it is difficult to be categorical
in defining the requirementsof a nest ledge, for some unusedledgesappearedto us to be superiorto the chosennest site. By preferencethe nest
ledge was, like all other perches,high up on the cliff, commandingan
extensiveview. On the Hudson a physical requirementappeared to be
that it shouldhave sufficient soil or gravel to make a scrape (the hollow
or depressionin which the eggsare laid) and to provide drainage. In
addition, many preferred nest ledges had a little grass and a stunted
deciduoustree--there are few live cedarsleft on the cliffs--growing to a
height of three to eight feet, an assetin shelteringthe young (see Figure
1). One preferrednestledgeon the north cliff of the no. 3 eyrie had two
25-foot deciduoustrees above it, large enough to shade the incubating
bird and to afford a shadedperch to its mate, but this was exceptional;
in selectingnest sites the Hudson Peregrinesavoided cliffs with large
trees, although in summerthey frequently soughtshade in large trees on
nearby cliffs. Most of the ledgesfaced east, as do the cliffs, for the birds
avoided the afternoon sun; but one or two ledges faced north. Nest
ledgesvaried greatly in size and adequacy, some being as capaciousas
four feet wide and someso cramped that it would seem the young must
fall off.
Most of the Hudson cliffs had two or three known nest ledges. At the
no. 1 eyrie three nest ledgeswere regularly used, but six are known to
'have been usedover a 30-year period. However, two of thesewere used
only once, and one has not been used since the early 1930's. The two
most favored ledgeswere within 100 feet of each other and within 100
78
HERBERT
^•DHERBERT,
Behavior
ofPeregrine
Falcons
[ Vol.Auk
82
yards of the main feedingperch, the fallen cedar. Two other ledges,a
quarter of a mile to the north, were used for secondand third nesting
attempts. After a nesting failure, the birds moved to another, usually
inferior, ledge.
One of the Hudsoneyries,locatedin an abandonedquarry high up on
the river bank, had only one nest ledge. Thus the birds at this cliff were
forcedto re-neston the sameledgeif their first clutch failed to hatch. In
one year this pair successfullynestedon top of the cliff, probably in a
secondnesting. This is the only known instanceon the Hudson of Peregrinesnestingin this fashion.
Hickey (1942) stated that an absoluterequirementof the Peregrine
appearedto be "that the eggsmust be laid in a hollow which is scraped
out of dirt, gravelor similar material," while Cade (1960) stated that the
substrateof a scrape is not important or that no scrape at all may be
needed"if a containingstructurefor the eggsis presentor can be found."
Equally divergent positions have been taken abroad by Ferguson-Lees
(1951) and by Ratcliffe (1962).
The correctnessof both views is well illustrated in the history of citynestingfalconsthat have successfullynestedand reared young in New
York City without a scrape,but whosechancesof successwere greatly
increasedby a scrapeor nest box with suitable scrapematerial such as
gravel,earth, or debris. The function of a scrapeappearsto be twofold:
to prevent the eggsfrom rolling off the ledgeand to provide drainagefor
the young.
The first known nestingin New York City occurredin 1943 when a
pair of falconssuccessfully
hatchedthree youngon a coping'ofthe St.
Regis Hotel (Figure 3). In 1946 the falcons nested on this ornamental
copingon the 16th floor and hatchedthreeyoung. The ornament,in the
shapeof a shield,had a depression
aboveit in which the eggswere laid
and the young hatched. When removed from the nest at about three
weeksof age, the young were soiledand fetid with excrementbecausethe
declivity in which they were rearedhad no drainage. In 1947 three young
were again hatchedin this declivity. In 1945 the same pair of falcons
hatched three young on the roof of an abandonedbuilding at West End
Avenue and 72nd Street, about one and one-half miles distant from the
St. Regis. The nest was located23 storiesup betweena partition of the
roof and the building,in a spaceof about30 x 4 inches.It had no scrape.
The three youngwere just ready to fly when the nest site was raided by
pigeon fanciersand police (New York Times, 25 June 1945).
Thus it appearsthat, althougha scrapeor nestboxwith scrapematerial
is not an absoluteessential,it is an important factor in nest successand
is eagerly soughtby the falcons. On the Hudson the pair at the no. 2
Jan.]
196.5
HERBERT
^NO
I-I•RBœRX,
Behavior
o!Peregrine
Falcons
79
Figure 3. Nesting site of PeregrineFalconsin New York City. The St. Regis Hotel
showing the corner shield ornament between the fifteenth and sixteenth floors (arrow), where the falcons three times successfullyhatched young. Photograph by
Richard
A. Herbert.
eyrie was never successful
on one ledge that lacked drainage. The Sun
Life Building falconsof Montreal laid eggson variousoutcroppings
of the
building in 1938 and 1939 (Hall, 1955), but it was only after two nest
boxes were put out for them that they nested successfully.Groskin
(1952) hasdescribed
howa heapof debrisdeposited
by thewindenabled
Peregrinesto nest in Philadelphiain 1946.
Throughoutthe yearsof our study we could not authenticatefrequent
reportsof city- or bridge-nesting
falcons. Pigeon fanciersseveraltimes
advisedus that falconswere nestingon the Williamsburg Bridge in midtown Manhattan. Peregrineswere reported to have nested successfully
on Bear Mountain Bridge (John Orth, pers. comm.), which spans the
upper Hudsonsomethree miles north of the no. 7 eyrie herein reported.
The caretakerand engineerof the RiversideChurchin the upper part of
Manhattan Island told us that Peregrineswere nesting there. So far as
we wereable to determine,all of thesesiteswereusuallyoccupiedonly by
an unattachedfemale, the only pairs which we saw being the St. Regis
pair and an occasionalpair roostingon the GeorgeWashingtonBridge,
about three miles from the no. 1 eyrie. However, unattachedmales were
occasionallypresentin the city, and it is possiblethat nestingwas at-
temptedat the sitesreportedbut that the eggsrolledoff the ledges.
80
HERBERT
AND
HERBERT,
Behavior
o/Peregrine
Falcons
[ Vol.Auk
82
For severalyears a pair of Peregrineswas reportednestingon The
Travellers' InsuranceBuilding in Hartford, Connecticut. Aided and
abettedby a Hartford newspaper
columnist,a playful rivalry sprangup
betweenThe Sun Life AssuranceCompanyin Montreal and The Travellers'InsuranceCompanyregardingtheir respective
falcons,and the activities of the falconsbecamea feature of their house organs. When we
visitedThe Travellers'InsuranceCompanyin late July, 1949, the senior
author was allowedto ventureonto a ledgeoff the 27th floor wherethe
falconsweresaid to have nested.The adultswerepresent,but he saw no
evidenceof youngnor eggsnor prey. The date, of course,wasvery late.
Egg laying.--In a normalseasonon the Hudson,the birds beganto lay
duringthe first weekof April, the eggsbeinglaid at intervalsof approximatelytwo days. Althoughthe numberof eggsvaries,four are usualin
a first clutch in this region,while three or lessare usualin later clutches.
(On manyof the ledgesit is impossible
to seeall of the eggs.) If unsuccessfulin their initial attempt, the birdsoften lay a secondor third clutch.
The femaleat the no. 1 eyrie from 1942 to 1957 regularlylaid a month
early, beginningthe first week of March. This is the mostextremevariation from normalthat we haveknownon the Hudson,althoughone other
femalein 1939 and 1940 also had an early nestingcycle. Similar individual variationsoccurin other areas. The Sun Life Companyfalcon in
Montreal laid approximatelya month earlier than the birds in the surroundingarea (Hall, 1955). The causeof this variation is not known,
but we think it probable that the time of egg laying is geneticallycon-
trolled. Annual variation in egg-layingdatesis known to be correlated
with such factors as spring temperaturesand age of the female (Nice,
1937: 97-107), but the probability that some females are consistently
early has receivedlittle attentionfrom ornithologists,
possiblybecauseof
the failure of individual songbirdsto reach an advanced age and thus
provideadequateevidenceof the phenomenon.
Incubation.--The confusionsurroundingreportedincubationperiodsof
birds of prey (Nice, 1953) still seemsto involve the Peregrine. Hagar
(in Bent, 1938: 50) gave the periodas from 33 to 35 days amongthe
birdshe observed
in Massachusetts.
Jourdain(in Witherbyet al., 1939:
12) regardedthis as probablytoo longand listedthe periodas 28-29 days
foreachegg.Hall's(1955)average
of 39 daysfornineclutch'es
of the
SunLife falconinvolveda periodfrom the laying of the first eggto the
hatchingof the last one. His measurement
falls outsidethe tight definition of incubationperiodrecommended
by Nice (1954) and others,but
if one deductsthe sevendays usuallynecessaryfor the laying of a complete clutchof four eggs(in one year therewas a clutchof five) Hall's
Jan.]
HERBERT
Ai•D
HERBERT,
Behavior
o!Peregrine
Falcons
1965
81
measuredincubationperiod is not very disparatefrom that cited in Witherby et al.
We did not succeedin obtaining an incubationperiod on a per egg
basisas we were anxiousto avoid disturbingthe birds during the egglaying part of their nestingcycle. On the Hudson,incubationdid not
usuallybeginuntil the laying of the secondor third egg,dependingon air
temperatures.It beganmost frequentlyon the fifth day with the laying
of the third eggand averaged32-33 days from this time of commencement until the hatchingof the last egg. This period thus representsthe
incubatingtime of the adult birds and not the period requiredto hatch a
single egg, which would be slightly less. Prior to incubation it would
appearthat the eggscan stand a greaterdegreeof temperaturevariation.
However, on one occasion,20 April 1953, when the temperaturehad
droppedto 34øF with a northwestwind, we found the male incubating
one egg. If the bird, male or female, is flushed from the ledge at this
one-eggstage,desertionis a frequent result.
The male's role in incubationhas not been sufficiently documented.
The tendency to incubate is strong in the male as in the female. His
interestin the eggsand youngappearsto be as great as the female's;we
have seenhim spreadhis wingsto shieldthe eggsfrom a hot sun. The
male takesa regularpart in incubation,oftentaking shortturnswhile the
female is feeding. As the larger and heavier bird, dominanton the nest
ledge, the female incubateswhenever she chooses,whereasthe male must
often "beg" for his turn, standing on the ledge and "talking" to the female. As might be expected, the female does most of the incubating,
invariably taking over the eggsfor the night. On the Hudson,falconers
sometimestook advantage of this fact to seize the adult female on the
nestledge.
At the no. 1 eyrie,wherethe femaledid perhapsthree-quarters
of the
incubating,a typical day was recordedby the seniorauthor on 4 May
1941 as follows(the timesare basedon the 24-hourclock).
0900. Female incubating eggs. Male perchedon cliff nearby.
0935. Female turns eggs, and resumes incubating in quarter-turn counter
clockwise.
1005. Male circled cliff and disappeared.
1030. Femaleturns clockwisein quarter turn--think sheturned eggsalso.
1120. Male returnswithout food. He wails and chirps,greetingfemale. Female chirpsback and turns eggs,making two completecircles. She now
faces out to river.
•
1145. Much wailing and talk by male. Female chirps back occasionally.
1150. Several crows fly into eyrie territory, fussingaround cliff. Twice the
male seems about to pursue them, but does not. I think he wants to
incubate.
82
HERBERT
^•DHERB•aT,
Behavior
o!Peregrine
Falcons
82
[ Vol,Auk
1200. Male lands on nest ledge. Female seemsto greet him by bowing her
head. Much ee-chupping.Female doesnot get off eggs; male presently
leaves ledge and stoopsat crows.
Female turns eggs,making completecircle.
Male flies up river rapidly.
Female turns eggs. She now facesin toward cliff.
Male returns and perches.
Female turns eggs,still facing inward.
Male flies up river, landing on his regularperch of last year.
Male returns carrying rust-colored pigeon; flies twice past nest ledge
wailing to female. Female answerswith an ee-chup, but does not fly
out to take pigeon from him. Male depositspigeon on cedar feeding
perch, and percheson snagnear nest ledge.
1426. Male flies in to nest ledge and walks halfway in, but female only turns
eggsand continuesincubating.
1450. Female turns eggs. Male still waiting for her to leave.
1203.
1205.
1225.
1240.
1250.
1300.
1420.
1521. Female gets off eggs,and male takes over. He turns eggsand settles
down. Female flies up river and returns in five minutes,flying about.
1530. Femaleputs in to feedingperch,whereshebeginsfeedingon pigeon.
1700. Female returnsto nest ledgeand takes over the eggs. Her approachis
very different from the male's deferential approach to her. She lumbers
in as if she ownedthe ledge. Male getsup hastily as sheseemsabout to
step on him.
Young.--If the birdsweresuccessful
in their first clutch,normalhatching dateson the Hudsonwereapproximately
from 15 to 20 May. These
werealsothe hatchingdatesof the New York City pair. At the no. 1
eyrie the normalhatchingdate of the femalepresentfrom 1942 to 1957
was almost a month earlier.
Although
Witherby
et al. (1939:12) mention
a fledging
per!od
of five
to six weeks,30 to 35 days was the more usual period on the Hudson.
Hagar (in Bent, 1938: 50) notesa fledgingperiodof 33 to 35 days. The
young seemable to fly after a fashionat four.weeks,but they appear
reluctantto leavethe nestledgeuntil they are able to fly well, this at
about five weeks. Someyoungremainon the nestledgelongerthan five
weeks.Malesregularlyfly beforefemales
and if b•tnding
is donewhen
the youngare about four weeksold youngmales often flush off the
ledge. Young.have occasionally
fallen from the nest• ledge,but this is
exceptional
becausealmostfrom the momentof hatchingthey possess
a
markedabilityto avoidtheedgeof the ledge,however
narrowit may be.
The plumages
of the younghavebeenwell described
by Bent (1938:
52-53). They changefrom the creamywhite down of newly hatched
birdsto a coarsegray downthat beginsto appearin about10 days. Before the birds leave the ledge,they are in the streakedbuff and brown
juvenal plumageof their first year.
Both male and female feed the young,but in the early stagesthe fe-
Jan.]
1965
HERBERT
AND
HERBERX,
Behavior
ofPeregrine
Falcons
83
maledoesmostof the feeding,tearingthe prey and allowingthe youngto
pluck bits from her beak. Within a weekthey can be seentuggingat the
remainsof prey on the nest ledge,and beforethey leave the ledge they
are well initiated in tearing and pluckingthe prey for themselves.For
abouta monthafter they leavethe nestledge,the youngare fed by both
adults; on one occasionwe saw the male feed a youngbird that had been
fledgedfive weeksto the day.
DISCUSSION
NESTXNC BE•^WOR
1950-56
Detailed field observations
and the history and productivityof the
eyriesare coveredin anotherpaper now in preparation.Here it is sufficient to note that the productionof young on the Hudsonand in New
York City increased
markedlyduringthe war years,1941-45,because
of
the rationingof gasoline,the restrictedmovementsof falconersand gunners, and the total absenceof road building. In theseyears production
averagedtwo youngper eyrie per year; thereafterproductivitydecreased;
in 1951 the last younghatchedin the Hudsoneyries; and by 1961 the
populationwas extirpated.
During the yearsof the populationdecline,from 1949 to 1955, the
birds engagedin much unusualnestingbehavior,hereinreported. In
theseyearsthe birds were subjectto molestationin variousforms--road
building,seizureof youngby falconers,
and shooting.Weatherwasalsoa
deterrentin the breedingfailuresof 1950-53.
Our mostremarkable
observation
in theseyearswasthe late date at
whichthebirdsattempted
renesting.
In 1950the early-nesting
pair that
normallyincubatedduringMarch,a monthearlierthan the otherpairs,
incubateda clutchof eggsuntil 15 June; and in 1952 this samepair
appearedto haveincubateduntil mid-July.In 1953theywereincubating
on 10 June. In both 1951 and 1952 this pair incubatedfour clutches,
whichwe think is a recordfor thisspecies.In 1952 their fourth nesting
attempt was madein early July, after they had incubatedtheir third set
of eggsfor morethan two weeks.No other suchextremesin the renesting
of Peregrines
areknown•to
us.
Hickey (1942: 187) after reviewingegg collectors'
recordsof F. p..
anatumreportedthat "if the eggsare lost at a ratheradvancedstageof
incubation,no further attemptsat nestingare knownto havebeenmade."
On the basisof his own field work on F. p. p.ealei,Green(1916: 475)
concluded that "if incubation is advanced it will be more like three weeks
beforethe new set is laid." Yet our unusualfemale,havingincubateda
first clutchfor threeweeksto four weeksin March, 1951,laid eggson
84
HERBERT
^2•D
HERBERT,
Behavior
ofPeregrine
Falcons [ Vol.Auk
82
anotherledgeand commenced
incubationin the incrediblyshortspaceof
12 days. It appeared
that onlytwo eggswerelaid in the second
clutch,
and thusonly threedayswereconsumed
in laying,but as incubationdoes
not beginuntilhalf the clutchis laid, thisremarkable
femalewentthrough
the pre-eggstageof the nestcyclein oneweek,despitethe fact that her
previousnestinghad beenwell advanced.(On an earlieroccasion,
too,
the seniorauthor had known this female to renest followinga three- to
four-weekincubationof the first clutch.)
This secondclutch,discovered
on 12 April 1951,wasfoundabandoned
on 17 April. On 21 April we foundthe femaleincubating
a third clutch
of threeeggson anotherledge.On 2 May, 12 dayslater,we foundthis
third nest brokenup; three eggs,one broken,remainedon the ledge.
Within two weeks,on 14 May, we found the femaleincubatingon a
fourthnestledge;on 16 May we againsawher incubatinghere,but on
30 May we foundthe nestledgeabandoned.
At threeeyriesoh the Hudsonin the years1950-53,copulationand
courtshipwereseenuntil the late date of 26 June. At one eyrie an egg
waslaid on 5 Juneand a bird wasseenincubatingon 10 June. The lack
of success
in thesepersistent
effortssuggests
that late, repeatedrenesting
attemptshavesmallchanceof success,
evenunderotherwisefavorable
conditions.Not only were initial attemptsmore successful
than later
efforts,but early-nesting
pairs,suchas the oneat the no. 1 eyrie,had a
higher percentageof successthan late-nestingpairs. This observation
may not apply in remoteareaswherethe birdsare not subjectto human
disturbance,and whereweatheris often presumedto be the determining
factor in early nesting. However, Broley (1947: 11) notes that in Florida, where inclementweather was not a factor, there was a greater degree
of nestingsuccessamongearly-nestingBald Eagles (that lay in early
November) than among late-nestingeagles (that lay in Decemberand
have many addledeggs).
The late datesat which the birds attemptedbreedingin the years 195053 led us to speculateon how late they could successfully
breed on these
cliffs, and recalledan unverifiedstory of a young Peregrinefalling off a
nestledgeof the no. 7 eyrie in late September(S. Grierson,pers. comm.).
It seemsprobablethat young hatchedalong the Hudson River in July
might not surviveon the openledgesexposedto the midsummersun; the
heat of the rock, whichshrivelsinch wormswhenplacedthere, might be
a lethal factorto youngbirds. However,the no. 7 eyriewherethe young
were reported in Septemberhas some shadedledges. It might be of
interestto comparethe hatchingdatesof the Hudsonbirds with thoseof
cave-nesting
Peregrinesmentionedby Bent (1938: 49).
Jan.]
1965
HERBERT
^•DHERBERT,
Behavior
of Peregrine
Falcons
NATURAL
85
PREDATORS
Although predators,especiallythe raccoon(Procyon lotor), are popularly blamed for the disappearance
of eggs,even from Peregrineeyries,
their role, along the Hudsonat least,was so minor as to be negligible.In
the Hudsoneyries,the Peregrinewas well able to copewith its natural
enemiesexcept,on rare occasions,
for the formidableGreat Horned Owl.
NumerousencountersbetweenpassingRed-tailed Hawks, Ospreys (Pandionhaliaetus),and Bald Eagleshaveproducedno morethan threatening
gestureson each side, the Peregrinebeing content to stoop at but not
strike these able peers.
Ordinarily the Great Horned Owl is a bird too powerful to warrant
attack unlessthe Peregrinehas eggsor young. Enderson (1964: 340)
mentionsflushingone of theseowls which was immediatelystruck by a
pair of nestingPrairie Falcons(Falco mexicanus)and soonkilled. Broley
(1947: 17) reports that Great Horned Owls cause much disturbance
amongnestingBald Eaglesand frequentlytake over their nests. When
eaglesare displacedby hornedowls that preempttheir nests,the eagles
usuallyrebuildthat sameseasonbut do not lay.
A number of Great Horned Owls nested along the Hudson cliffs during
the 1930'sand 1940's,usuallyat somedistancefrom the Peregrines,but
in 1935 the owlshad a nestwith three younglessthan 100 yards from
the no. 1 eyriewherethe Peregrines
wereincubating.Onceduringthis dual
occupancy
of the cliff the seniorauthorvisitedthe cliff with two falconers.
They flushedthe owls,believingthat, as on previousoccasions,
the Peregrineswouldmerelystoopat themwhenthe owlswerein the open. When
flushed,one owl took cover,flying closeto the cliff; the other owl flew
out over the river and was strucka stunningblow by one of the falcons,
loud enoughto be heardby the seniorauthorwhowassomedistanceaway
on the cliff above. The owl fell, spinningslowly round and round, with
wingsset at a highangle. As it fell, the secondPeregrinestruckit, whereuponit droppedto the roadbelow.Two hikersran to capturethe harassed
creature,but the owl eludedthem,takingrefugein a smalltreebesidethe
road. Minuteslater, the owl flew slowlyout of the tree. In a lightning
stoop,the Peregrinestruckagain,and the owl fell, heavilyinert, hitting
the talus slopeand bouncingout of sight. In this secondencounter,the
owl wasthoughtto have beenkilled. But an hour or two later the senior
author saw a Great Horned Owl, thoughtto be the injured bird, fly into
the cliff from the road below,pursuinga discreetpath beneaththe level
of the treetops.
The owlssuccessfully
rearedyoungthat year (1935), but the Peregrinesabandonedtheir eggs,roostingnightly on the Hunt's Point gas
86
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[ Vol.Auk
tank in The Bronx (New York City), about 5.5 miles distant from their
eyrie, where the senior author frequently saw them. This is the only
occasionwhen the Peregrinesare thought to have abandoned their eggs
becauseof the owls, but from 1935 to 1941 the pair at the no. 1 eyrie,
which had several residentowls on its long seriesof cliffs, often roosted
on the gas tank during the fall and winter months,probably becauseof
the proximity of the owls on the cliffs. Other observers(Cleon Garland,
in litt.) also noted that the Peregrinesdepartedfrom their cliff in the late
afternoon,flying toward New York City. By 1953 the populationof
Great Horned Owls had decreasedmarkedly (there were none south of
the no. 3 eyrie), and owlswere not a factor in the nestingfailuresof the
years 1950-56.
Black snakes (black snake, Coluber constrictor,or pilot black snake,
Elaphe obsoleta)are other predatorswhich,on rare occasions,
may molest
Peregrineeyries. On 6 June 1943, the seniorauthor was watchinga nest
ledge on the south cliff of the no. 3 eyrie--a first-classcliff with a rock
wall so sheerthat it appearedimpossibleto reachthe ledgewithout wings
or rope. On the ledge was a young bird 10 days old. The female was
feedingthe youngbird, and the male was perchednearby. Their activity
at this time was entirely normal. Suddenlyboth adults darted into excited action,flying back and forth in front of the ledge,issuingthe kack~
kack-kack alarm call, diving at the ledge from a height of 20 feet, and
perchingmomentarilyat its edge. Then the female flew slowly off the
ledgedragginga hugeblack snakein one foot. Unable to carry the snake,
shelost altitude rapidly. Some30 feet out from the cliff, shedroppedthe
snake,which fell 60 feet to the talus slope. The snake,probablyElaphe,
was about six feet long and weighedprobablythree to three and one-half
pounds, or more than the falcon. This episodespeaks volumes for the
strengthand agility of the snakein reachingthe ledge,and for the courage
of the falcon in defending its young. Whether the snake would have
attacked the young in the nest is not known. Williams (1951) relates an
episodeof a rat snake (Elaphe) overpoweringand stranglingan adult
Red-shouldered
Hawk (Buteolineatus),a species
that normallypreyson
snakes.Thus the blacksnakesmay accountfor the disappearance
of eggs
at someof the Hudson eyries.
The raccoonwas conspicuous
by its absencefrom the eyries of the
Hudson. Althoughraccoons
and gray foxes(Urocyoncinereoargenteus)
wereof occasional
occurrence
on the talusslope,we neversawoneon top
of the cliff. Apart from the fact that birds'eggsare moreeasilyobtained
in treesand thicketsthan on sheercliffs,someof •he eyriesappearedto
be utterly inaccessible
to a raccoon.Further, it is difficult to imaginethat
a raccoonwouldinterferewith an incubatingPeregrineon its nestledge
Jan.]
1965
HERBER•
ANI>
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Behavior
ofPeregrine
Falcons
87
as long as other eggswere more readily available. One pair of Peregrines
is known to have attackeda Bobcat (Lynx rufus) on top of a cliff outside
of our area (Richard Thorsell, pers. comm.). As a matter of fact, in our
experienceon the Hudson the Peregrines'abandonedeggswere usually
left to bleachand whiten on the ledge, untouchedby predators.
AGE AND NESTING SUCCESS
The age and possiblesenilityof the HudsonPeregrineshave also been
consideredas factorspossiblyaffectingnestingsuccess.Hickey (1942)
suggested
that the ageof the femalesat two of the Hudsoneyriesin 1939
and 1940 may have beenthe causeof sterility, citing their failure to lay
and the fact that courtshiplasted a month past the normal period.
Our observationsdo not bear out this hypothesis,nor doesthe history
of the Sun Life Companyfalcon,a bird easilyidentifiedby a deepindentation on her chest. From 1940 through 1952 when she disappeared,she
hatched26 young,and at the age of 18 yearsor more was still producing
young (Hall, 1955). Further, in a healthy populationone may suppose
that truly senile birds would not long succeedin retaining a mate or a
nest ledge.
On the Hudson the male at the no. 1 eyrie from 1938 through 1955
(distinguishedby a tuft of white featherson his head) must have been
20 yearsor moreof age •t the time of his disappearance,
as Peregrines
do not usually breed until 2 years of age. When first observedin 1938,
he was in adult plumage. A highly productivefemalepresentat this eyrie
from 1942 to 1957 must have been 17 yearsof ageor older at the time of
her disappearance.A distinctivemale at the no. 3 eyrie appearedin 1940
and at the time of his disappearancein 1956 was at least 18 years of age.
Ratcliffe (1962) saysthat 7 years is the longestknown occupationof an
eyrie by a singlePeregrinein Great Britain, and that this occurredonly
once. Demandt (1953) acceptsHorst's (1937) conclusionthat a German
eyriewasoccupiedby the samefemalefor 18 years.
In our opinion the age of the Hudson Peregrineswas not a factor in
their nestingfailure. Broley (1952: 126) saysthat eagleshave lived for
40 yearsin zoosand may have lived•longerin the wild. Shementionsa
Bald Eagle that laid an egg after 30 years in captivity. Flower (1938)
states that the averageage for the 100 oldest Passeriformes(excluding
domesticcanaries) in captivity was 20 years and two months. Parrots,
he states,have a potential.Ofabout 50 years; an Eagle Owl (Bubo bubo)
lived for 68 years in captivity, and a Bateleur Eagle (Terathopiusecaudatus) for 55 years. Prestwich (1955: 8) notes that a Golden Eagle
(Aquila chrysaetos)beganto lay eggsafter 15 years in captivity and was
continuingto lay them at the ageof 30. A femalePeregrinethat crashed
88
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into the AmericanTelephoneand TelegraphBuilding in New York City
carrying a racingpigeonwas 131/'2
years old; she was bandedon 4 June
1939 as a nestlingin Massachusetts
and died on 13 November1952. This
is the greatestrecordedage of a wild bandedNorth AmericanPeregrine
that has come to our attention.
The known longevity recordsattained by three of the Hudson Peregrinesand the Sun Life Companyfalcon were probablydue to favored
eyrie sites and the fact that the Hudsonbirds were nonmigratory,and
further to World War II and its gasolinerationing,which temporarily
removedmany of their human persecutors.The Sun Life falconswere
alsobenefittedby the fact that the ownerof the building,The SunLife
Assurance
Company,protectedthe nestingfalconsand publicizeda favorable"image"of the predators.Had the Peregrines
in New York City had
an equally sympatheticpublic, their nestingsuccessmight have been
greatly enhanced.
In view of the advancedage attained by some of the Hudson Pere-
grines,the first-year mortality of the young may be quite high. This
conclusion
parallelsthat of Beebe(1960:173), whowas impressed
by the
very high reproductivesuccessof Peregrinesalong the British Columbian
coast. His estimateof 2.7 young fledgedper occupiedeyrie is slightly
higher than our Hudson River estimate of 2 young per eyrie fledged
during the war years.
Althoughsenilityhasnot beena factor in nestingfailure on the Hudson,
yearling femalesmay be a factor in nestingfailure. There have been no
casesof yearling malesoccupyingHudsoneyries,but in the 1940's there
were two instancesof an immature-plumagedfemale occupyingan eyrie.
In neither casewere eggslaid.
DISAPPEARANCE OF EGGS
Eggs disappearedfrom severalof the Hudson eyries,particularly in the
years 1950-53 when the six southernmosteyries were subject to extreme
disturbance. The eyrie at which this occurredmost frequently was the
exposedno. 6, where eggsdisappearedas early as 1940. This is the eyrie
situatedin a quarry with easy accessfrom above. During the year 195053 the female was missingprimaries early in the seasonand may have
been shot at. We picked up a rifle shell within 100 yards of the eyrie in
1951, and the resident park policemanadmitted that there had been
target shootingbelow the cliff. The female at this eyrie was marked by
nervousand shy behavior.
In 1940 three eggs were seen at the no. 6 eyrie on 12 April, while a
fourth egg, broken, lay on the ledge 18 inchesaway, obviouslyrolled or
kicked there by the falcons. (This ledgeis flat and capaciousso that eggs
Jan.]
1965
HERBERT
AZ'•D
HERBERT,
Behavior
o]Peregrine
Falcons
89
do not roll off; it is accessible
to a raccoon,but there was no evidenceof
raccoons.) To prevent their removal by egg collectors,these eggswere
marked, but on 18 May 1940, when the ledgewas again examined,they
had disappeared.
On 5 June 1950, from the top of this samecliff, we saw one fresh,
reddish-buffegg, probablylaid that morning,on the ledge below, and
certainly not more than one day old. There was almostno scrapeas yet.
Four dayslater this egghad disappeared.There was a better scrapethan
on our previousvisit, suggestingthat the egghad not disappearedon the
day it was laid. On 12 April 1951 we saw one fresh, unincubatedegg on
this ledge. For fear of disturbingincubationwe did not again visit the
eyrie until 21 April, when we found this egg abandoned,though still on
the ledge. On 19 April 1952 we againsawa freshlylaid eggon this ledge,
but two weekslater it had disappeared.
The eggsof the Sun Life Companyfalcondisappearedon severaloccasions(Hall, 1955: 12, 18). The Sun Life falconlaid her eggsin one of
two nest boxeson a ledge surroundingthe 26th floor of the Sun Life
Building. There being neither raccoonsnor skunks (Mep.hitismephitis)
on the Sun Life Building, Hall assumedthat the falcon herself ate her
eggs. In 1949 small piecesof shell were found in the nest box, and one
observer(Cleghorn) later saw the femaleeatingan egg (Hall, 1955: 18).
Ratcliffe (1958) also found that Peregrinesoccasionallyeat their own
eggs. A captive Barred Owl (Strix varia) at the Trailside Museum, Bear
Mountain, New York, likewise disposedof two eggs, apparently eating
them whole without leaving any tracesin the cardboardcarton which she
occupied. Likewise, a captive Barn Owl at the Trailside Museum was
thoughtto have eaten one of her eggs(John Orth, pers. comm.). It seems
possiblethat suchbirds eat their eggsor otherwisedisposeof them when
disturbed,in the same fashionas frightenedmammalsthat occasionally
eat their young. (A domesticrabbit may eat one litter becauseof "nervousness,"but may successfullyrear the next litter.)
Becauseof her proximity to frequent visitors and observers,nervousnessmay have beena factor in the disappearance
of the Sun Life falcon's
eggs. It may even have been responsiblefor the disappearance
of one
youngon 12 May 1952, four daysafter hatching;therewere no.signsof
the young bird's body in the box, althoughthe other two young were
present (Hall, pers. comm., 12 September1952). Prestwich(1955: 13)
narratesan incident of a female Kestrel (Falco tinnunculus)that hatched
five eggs,in a cage about five by two by three feet high, on alternate
days and ate eachyoung bird when it was one day old; the fifth young
was taken from her when it hatched. However, Lee S. Crandall (pers.
comm.,1953) former Curator of Birds at the New York ZoologicalPark,
90
HERBERT
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[ Vol.Auk
82
where falconsand birds of prey were kept in larger quarters, advisedus
that they had no record of thesebirds having eaten or otherwisedisposed
of eggsor young.
It might be assumedthat a bird, having oncedisposedof or eaten eggs,
doesnot thereafterhatch any young,but developsthe habit of eating all
her eggs. This was not true of the Sun Life falcon. In 1942, two.eggsof
her clutch of four disappeared,while two hatched; in 1948 her clutch was
photographed
by the seniorauthor but later disappeared;in 1949, four
eggs disappeared,one by one; in 1950 one disappearedwhile three
hatched; in 1951, three eggsdisappearedone by one during incubation,
and the embryo in the fourth died only a few days before hatching; in
1952, one egg disappearedfrom the nestingledgewhile three are reported
to have hatched (Hall, 1955: 18, 19).
In the Hudsoneyrieswe have no proof of eggshaving been eaten, but
an occasionalegg or even, on one occasion,a clutch disappearedwhen
such disappearancecould not be attributed to egg collectorsor predators.
On the Hudsonit was alwaysa fairly freshand never a long-incubated
egg that disappeared.At the no. 3 eyrie on 20 April 1953 we found the
male incubatingone freshegg. (The incubationof one egg is abnormal,
but the temperature had dropped to 34ø F with snow flurries.) Three
days later this egg was gone, only a few bits of shell remaining on the
ledge. At the no. 1 eyrie the femalewas incubatingtwo fresh eggson 16
May 1953, but a week later only one egg remainedon the ledge. Again
in 1955 at the no. 1 eyrie we found the male incubatingone fresh egg on
23 April; four days later this egg was gone. These instancessuggested
egg eating.
Usually, however,it is a bleachedor addledegg that disappears,giving
rise to speculationas to whetherthe Peregrinesmay have someknowledge
of the progressof the egg, or may notice its color and eject it from the
nest.
ABANDONMENT
OF EGGS
Even more puzzling than the disappearanceof eggswas the abandonment of partially incubatedeggs,left to whiten on the 1edgewhile the
birds were making secondand third nestingattempts on nearby ledges,
a phenomenonfrequently noted in the disastrousyears of 1959-53. We
hopeto describethis in detail in anotherpaper. Hickey (1942: 188) says
that "incompletedutches may be abandonedif exceptionallynervous
birds are molested."Birds that have beeninterruptedin their nest cycle
by such factors as blasting, shooting,road construction,visitors, or
weatherappear to build up somesort of cumulativenervousness,
so that
Jan.]
1965
HERBERT
Am)HERB•aT,
Behavior
ofPeregrine
Falcons
91
even a very slight disturbancemay subsequently
causeabandonmentof
an incompleteor evena completeclutch.
In discussing
the effectsof a Florida hurricaneon nestingBald Eagles,
Broley (1947: 18, 19) pointedout that it had far more than its immediate effect; it appearedto createa psychosisof somesort in the birds and
was calamitousto nesting, even though it occurred four to six weeks
before the nestingseason,and even though all of the nestswere rebuilt
in plenty oJ time for no.finalnesting. In 24 of the 45 rebuilt nests, no
eggswere laid; and in 21 nestswhereeggswere laid, they did not hatch,
although the birds incubated for two months.
Broley (1947: 19) also noted that the hurricaneinterferedwith the
nestingschedule
of GreatHornedOwls,and that poultryin the area had
lost their drive to incubate. In the samearticle he quotedF. B. Hutt
(then Professorof Animal Geneticsat CornellUniversity). Concerning
the chainof physiological
factorsinvolvedin the cycleof eaglecourtship
and nesting,Hutt considered
that "the role of bird psychology
in these
processesmust not be underestimated."
An analogymight be drawn with the HudsonPeregrineswhich, when
disturbedby any of severalcauses--roadconstruction,attempts to trap
the adult birds, or even weather--abandontheir eggs and attempt to
reneston anotherledge. Renestingattemptsare increasinglyunsuccessful
as the birds lose"confidence"
and becomeprogressively
morenervous,
unwillingor unablefor physiological
reasonsto incubatetheir eggs.
In the populationdeclineof the HudsonPeregrinesthe role of DDT
and other pesticidesand poisoningvia the food chain has not been determined. Ratcliffe (1963: 74) reportedthat the eating of their own eggs
by falconshas characterizedthe spectacularpopulationdeclineof the
BritishPeregrinein recentyears. Althoughaware that this behaviorpattern took placeat least occasionally
in the pre-DDT years,he regardsits
recent frequencyas the result of the birds ingestingchlorinatedhydrocarbons.We carriedout no chemicaltests,suchas the British did, either
on the eggsof thesebirds or on the birds themselves.
Mebs (1960) has noted a drasticpopulationdeclineof this speciesin
Germany,whichhe attributesto fanaticalpersecution
by carrier pigeon
fanciers.He statesthat the successful
productionof youngnotedin the
years immediatelyafter World War II has now all but ceasedin many
areas. Despite all persecutionthe breedingpairs remain at their eyries
until they, too, are eliminated.
The preciserole that continualpersecutionof the Hudsonbirds played
in clutchabandonment
and in the failure of the femalesat two eyriesto
lay an observable
clutchin the late 1950'sremainsto be elucidated.
92
HERBERT
^• HERBERT,
Behavior
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[ Vol.Auk
82
SUMMARY
Until the mid-1940's 8 to 10 pairs of PeregrineFalconsoccupiedeyries
in the lower Hudson River Valley, another pair hatched four clutcheson
two New York City skyscrapers,
and up to 16 or more birds wintered in
New York City (including its northernmostborough, The Bronx) in a
singleyear. Wintering Peregrineswere usually females,apparently from
eyries in the northeasternUnited States or southeasternCanada. The
Hudson Peregrinesappearedto mate for life, but if one of the pair was
killed, a replacementfrequentlytook place; one pair remainedintact for
14 years. Territorial defenseappearedto be intrasexual,but was particularly strongamongmales. Prey of the HudsonPeregrinestendedto be
racing pigeons,Blue Jays, and flickers,while city birds preyed on racing
pigeonsand Starlings.
On the Hudson, nest ledgesat each of the eyries were one to six in
number, renestingusuallybeing on a ledgeof inferior quality. Although
a scrapewas not essentialfor the eggs,it tended to increasenestingsuccess, and sites permitting a scrape were sought by the falcons. First
clutches usually numbered four, while secondand third clutches numbered two to three. Hatching was normally from 15 to 20 May, and
fledgingwas about five weekslater. One female regularly laid a month
early over a 16~yearperiod.
A wailing note is usually given when a Peregrinewith no eggsor young
is flushedfrom the cliff, a conversational
ee'-chupnote when two birds are
together on the cliff, and a kack-kack-kack-kack alarm or scold note
under conditionsof intense excitement. On the nest ledge the adults
sometimesgreet each other with a soft chirp note.
Productivityof this populationincreasedmarkedlyduring the war. In
1941 through1945productionat threeeyriesaveraged2 youngper year,
but thereaftera downtrendoccurred,and by 1961 the populationwas
extirpated. In theseyears the birds were subject to extremepersecution
by humans. When the birds were unduly molested,abandonmentof
clutchesand persistentrenestingoccurred. In both 1951 and 1952, one
female incubated four successiveclutches. Egg disappearancewas an
occasionalphenomenonof theseyears, and egg eating by the falconswas
inferred. As three Peregrinesin this study are known to have attained
the agesof at least 17, 18, and 20 years, respectively,senility seemsto
be without importancein nestingsuccess.
ACKNOWLEDGMENTS
The senior author made a study of the Hudson eyries and the New York City
birds from about
1930 until his death in 1960. Most
of these data have not been
published, although some statisticson the Hudson eyries for the years 1939 and 1940
Jan.
]
HERBERT
AND
HERBERT,
Behavior
o/Peregrine
Falcons
1965
93
were includedin the surveymade by Hickey (1942). In 1949 the junior author
joinedin the study,and assumed
the responsibility
of gatheringand eventuallyof
publishing
the data. Many datagathered
priorto 1940weresupplied
by Dr. Joseph
J. Hickey,withoutwhosehelpand encouragement
this manuscript
couldnot have
beenprepared.Thanksare duealsoto Dr. DeanAmadonfor hiscriticalreadingof
an earlier draft of the present manuscript.
NOTE
Publicationof this paper has beenmade possibleby a gift to the AmericanOrnithologists'Union in memory of Richard A. Herbert (1907-1960), who throughout
most of his life was an ardent and discerningstudentof the biologyand conservation
of the Peregrine Falcon.
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Liston Front Range Lighthouse,R.D. 2, Middletown, Delaware.