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

2006·4.1 MB·English

by  Robert Decandido

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The Wilson Journal ofOrnithology 1 18(1):53—58, 2006
NOCTURNAL HUNTING BY PEREGRINE FALCONS2 AT THE
EMPIRE STATE BUILDING, NEW YORK CITY
ROBERT DeCANDIDO 34 AND DEBORAH ALLEN
1
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ABSTRACT. We report on nocturnal hunting by Peregrine Falcons (Falcoperegrinus) at the Empire State
Building in Manhattan, New York City. From 4 August through 13 November 2004, we saw Peregrine Falcons
on 41 of77 nights ofobservation. During this period, they hunted migrating birds on 25 evenings, with the first
hunting attempt occurring an average of 119 min after sunset. Peregrine Falcons made 111 hunting attempts
and captured 37 birds (33% success). Hunting success was highest in September, but was most often observed
in October. Peregrines hunted migratory birds at night more frequently in autumn than in spring. Peregrines
were significantly more likely to be present on autumn nights when >50 migrants were passing by the Empire
State Building. Although the lights associated with skyscrapers are believed to disorient migrating birds and
result in many bird-to-skyscraper collisions each year. Peregrine Falcons are able to take advantage of the
situation. Skyscrapers provide hunting perches at altitudes often flown by nocturnal migrants, anddisorientation
caused by the lights sometimes results in birds circling skyscrapers and possibly becoming more vulnerable to
predation by falcons. Received26 January 2005, accepted 11 October2005.
Several diurnal raptor species, including ny 2001), Netherlands (van Dijk 2000, van
Black-shouldered Kite (Elanusaxillaris), Bald Geneijgen 2000), Poland (Rejt 2000, 2001,
Eagle (Haliaeetus leucocephalus), and Lesser 2004a), Hong Kong (Feare et al. 1995), and
Kestrel (Falco naumanni), forage at night (see Taiwan (K. Y. Huang and L. L. Severinghaus
Kaiser 1989, McLaughlin 1989, Negro et al. unpubl. data). However, direct observation
2000). Others, such as Turkey Vulture Ca and analysis ofnocturnal hunting by Peregrine
(
thartes aura). Osprey (Pandion haliaetus), Falcons, particularly during migration, is rare
Northern Harrier (Circus cyaneus), and Le- in the literature.
vant Sparrowhawk Accipiter brevipes), have In New York City, New York, the number
(
been observed flying or migrating at night and distribution of Peregrine Falcons has
(Tabor and McAllister 1988, Russell 1991, changed considerably since such observations
Yosef 2003, DeCandido et al. 2006). were first recorded in the late 1920s. Before
Peregrine Falcons (Falco peregrinus) are the era of DDT (until 1946), from autumn
considered nocturnal migrants in some parts through early spring, lone female peregrines
ofthe world (Cochran 1985, Ellis et al. 1990), were much more common at skyscrapers than
and they are known to hunt at night (Clunie males (Herbert and Herbert 1965). Peregrine
1976, Russell 1998). With increased numbers Falcons rarely nested in the city, and nocturnal
of peregrines nesting and wintering in cities, activity by these falcons was not reported in
biologists are beginning to document noctur- any season (Herbert and Herbert 1965). Be-
nal activity by these falcons in all seasons. ginning in the mid-1990s, however, more pairs
Recently, there have been reports of urban of Peregrine Falcons have begun residing
peregrines feeding young and/or hunting at year-round in Manhattan (and the metropoli-
night in North America (Cade and Bird 1990, tan area) than previously noted (B. A. Loucks
Wendt et al. 1991, Cade et al. 1996), England pers. comm., C. Nadareski unpubl. data.). To-
(Crick et al. 2003), France (Marconot 2003), day, most, if not all, ofthe seven pairs ofper-
Germany (Schneider and Wilden 1994, Klad- egrines that nest in Manhattan remain on ter-
ritory year-round. Here, we report our obser-
vations of Peregrine Falcon activity at night
Con1sHearvwaktioMnouLnetaarinningS,an4c1t0uarSyu,mmAecorpiVaalnleCyenRtde.,r Ofro-r during the 2004 southbound bird migration at
wigsburg, PA 17961, USA. one location in New York City.
2P.O. Box 1452, Peter Stuyvesant Station, New
York, NY 10009, USA. METHODS
3Current address: 1831 Fowler Ave., The Bronx,
NY 10462, USA. Most of our observations of Peregrine Fal-
4Correspondingauthor;e-mail:[email protected] cons and nocturnal migrants occurred during
53
54 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006
the southbound migration, from 4 August to if it passed south-to-north (or north-to-south)
13 November 2004; we made observations on across an imaginary east-west line at the site,
77 of 102 evenings during that period. In and continued north (or south) out of sight.
spring 2004, we observed northbound mi- On 2 evenings during southbound migration,
grants on 33 evenings from 19 April through when >100 birds simultaneously circled the
25 May. In spring 2002, we made observa- ESB, we estimated the maximum number of
tions on only 2 evenings (8 May and 15 May). birds circling per hour and recorded it as the
We made our observations from the outside number ofmigrants seen for that hour. We de-
observation deck (elevation —325 m above fined the peak of migration as the several-day
ground level) of the Empire State Building period in which we counted the highest num-
(ESB), located in midtown Manhattan in New ber of migrants. For both northbound and
York City. We arrived each evening approxi- southbound migration, total counts presented
mately 15-30 min prior to sunset. Bird mi- here do not include migrating waterfowl, her-
gration, on average, began 30-90 min after ons, or gulls.
sunset. Any Peregrine Falcon activities de- We defined a hunting attempt as one in
fined as nocturnal occurred after nautical twi- which a Peregrine Falcon approached to with-
light (1 hr after sunset). We were able to con- in 1 m of its intended prey. On a few occa-
duct our study until 22:45 EST each evening sions, peregrines made repeated stoops at the
(August through October) and until 23:45 in same prey, but did not capture or gain control
November; the observation deck of the build- of it. Each of these stoops was considered a
ing was closed to all visitors after these times. separate hunting attempt. Several times, we
In spring 2004, we observed from just before observed a peregrine strike a bird but fail to
sunset until 22:45 each evening, and in spring seize it. We classified these as unsuccessful
2002, we observed from 19:00 until 21:00. hunting attempts.
During fall migration, the northwest corner of We defined the peak period of Peregrine
the building provided the best vantage point Falcon activity as that during which we ob-
to count the greatest number of migrating served falcons at the ESB during the greatest
birds, and in spring, we observed migrants number of consecutive nights. We used cor-
from the southwest corner of the observation relation statistics (Microsoft Excel 2003) to
deck. These locations afforded unobstructed analyze data collected during this peak period.
views to the horizon and the sky above. We We compared (a) the time ofarrival ofthe first
used 10X binoculars to follow peregrines migrant after sunset with the arrival ofthe first
when they made long flights in pursuit of Peregrine Falcon, and (b) the time of arrival
prey. It was possible to observe migrating of the first migrant with the time of the first
birds and the activities of peregrines because peregrine hunting attempt. Means are present-
the upper floors of the building were illumi- ed as ± SD.
nated with (external) upward-directed halogen
RESULTS
lights, and the spire above us was illuminated
with (internal) florescent lights. We could not During southbound migration in 2004, we
identify the majority of migrants to species saw the first Peregrine Falcon at night on 4
because the external halogen lights washed August and the last one on the evening of 9
out most plumage details. However, this light- November. During this time, at least two adult
ing array permitted us to count migrants up to peregrines (male and female), as well as im-
—30-60 m above the highest point (445 m mature^), used the ESB as a hunting perch.
agl) of the ESB, and up to 30 m (perpendic- Peregrines were seen hunting or flying at night
ular) from the observation deck. We estimated on 53% (41 of 77) of the evenings we spent
that the building’s lights allowed us to see per- at the ESB (Table 1). Falcons were signifi-
egrines chasing small birds in flight up to 60- cantly more likely to be present on evenings
80 m distant. when >50 migrants were counted in migra-
Count protocols to assess nocturnal birdmi- tion (x2 = 14.7, df = 1, P = 0.001; Table 1).
gration in 2004 followed those described in Ofthe 67 nights we observed migrating birds,
Bildstein and Zalles (1995) for migrating rap- peregrines hunted migrants on 25 nights
tors. An individual was considered a migrant (37%), made 111 hunting attempts, and cap-
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DeCandido andAllen • NOCTURNAL HUNTING BY PEREGRINE FALCONS 55
TABLE 1. Summary of nocturnal hunting behavior by Peregrine Falcons in relation to the number of
migrants present after sunset in autumn 2004 at the Empire State Building. New York.
Numberclassesofmigrantpasserines
0 1-10 11-50 51-100 101-250 251+ Total
No. nights migrants counted 10 9 23 10 13 12 77
No. nights peregrines present —1 1 12 8 9 10 41
No. nights peregrines hunted — 0 8 3 7 7 25
No. hunting attempts — 0 29 17 15 50 111
No. successful hunts — —0 8 7 8 14 37
Hunting success — 28% 41% 53% 28% 33%
No. nights male observed hunting — 0 5 2 5 6 18
No. nights female observed hunting — 0 2 1 1 1 5
No. nights unknown sex observed hunting 0 1 0 1 1 3
tured prey 37 times (33% success). All of the vember (1 of8, 13%; Table 2). On 10 October
migrants we observed being captured or from 20:12 to 20:42, a male Peregrine Falcon
chased were in the warbler-to-oriole sizeclass. made 25 hunting attempts and captured 9
The peak of Peregrine Falcon activity oc- birds (36%), caching the birds on the ESB
curred from 26 Septemberthrough 14 October tower after each kill. Throughout the autumn,
2004. During that time, we conducted obser- we observed Peregrine Falcons capture only
vations on 17 nights; on 16 ofthose nights we migratory birds, although a few Rock Pigeons
observed Peregrine Falcons, and on 11 nights (Columba livia), and at least two bat species.
we observed them hunting (70 total hunts, 21 Little Brown (Myotis lucifugus) and Red (Las
prey captures, 30% success). During this pe- iurus borealis bats, were present on some
)
riod, the first migrant birds were observed 65 evenings. We could identify only two prey
± 20 min after sunset (range = 42-1 14 min); species: a Baltimore Oriole (.Icterus galbula)
Peregrine Falcons arrived 91 ±41 min after captured on 23 August, and a Yellow-billed
sunset (range = 47-190 min), and made their Cuckoo (Coccyzus americanus) taken on 9
first hunting attempt 45 ± 59 min later (range October. On 3 and 9 November, despite high
= 61-284 min), or approximately 136 min af- numbers of American Woodcocks (Scolopax
ter sunset. There was no correlation between minor migrating past the ESB tower (36
)
passage of the evening’s first migrant and the counted each night), no peregrines were ob-
arrival ofa Peregrine Falcon at the ESB (r2 = served.
0.10, P = 0.73) or between passage ofthe first In autumn 2004, most bird migration oc-
migrant and the time of a peregrine’s first curred at eye-level and above the observation
hunting attempt (r2 = 0.15, P — 0.24). deck. We counted 10,826 migrating birds, and
Nocturnal hunting success was greatest in the peak of the migration occurred from 5 to
September (12 of 27, 44%) and lowest in No- 11 October when 3,871 migrants (36% of the
TABLE 2. Summary of nocturnal hunting behavior and success by Peregrine Falcons during four autumn
months in 2004 at the Empire State Building, New York.
Aug Sep Oct Nov Total
No. hunting attempts 16 27 60 8 111
No. successful hunts 6 12 18 1 37
Hunting success 38% 44% 30% 13% 33%
No. nights one peregrine present 10 11 10 3 34
No. nights ^2 peregrines present 0 3 4 0 7
No. nights hunting observed 5 9 10 1 25
No. nights male made a hunting attempt 5 7 5 1 18
No. nights female made a hunting attempt —0 2 3 —0 5
No. nights unknown sex made a hunting attempt 1 2 3
56 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006
fall flight) were counted, averaging 1 14 birds/ constitute an abundant, easily accessible re-
hr on these 7 evenings. In spring 2004, we source for resident Peregrine Falcons, and for
counted 3,359 migrants during 33 nights of peregrines migrating through the area as well.
observation. The peak of the migration oc- In New York City in 2004, Peregrine Fal-
curred from 6 to 15 May when 1,752 migrants cons were more likely to be present and hunt-
(52% of the spring flight) were counted, av- ing at the ESB on autumn nights when >50
eraging 51 birds/hr on these 10 evenings. migrants were observed. The peak of pere-
Lone Peregrine Falcons were observed on 2 grine activity at the ESB corresponded to the
evenings: 24 April (0 migrants counted) and peak of the southbound bird migration from
22 May (79 counted), but no hunting attempts late September through mid-October. During
were observed on either night. On 15 May this time, two adult peregrines occasionally
2002, we observed an adult female peregrine perched near one another and used the ESB
make 10 unsuccessful hunting attempts on mi- as a hunting platform. More night migrants
grants from 20:15 until 21:00. were attracted to the building’s lights during
In the breeding season of 2004, a pair of autumn rather than spring migration, and
Peregrine Falcons may have attempted to nest many more circled the tower for longer time
on the ESB (B. A. Loucks pers. comm.). It is periods from August through late October. In
possible that this pair executed many of the spring, there are fewer nocturnal migrants,
hunting attempts we observed in autumn and these mostly pass higher above New York
2004. During 5 evenings between 26 Septem- City on warm air currents that override heavi-
ber and 7 October, we saw an adult male and er, cooler air near the ground (see Kerlinger
an adult female peregrine perched near one and Moore 1989). Each of these factors likely
another, each vocalizing with the “eechup” or influences a peregrine’s decision to hunt mi-
“creaking” call, and the “wailing” calls (see grants more frequently at night during au-
Ratcliffe 1980). On 3 October, we observed tumn. On the only spring night (15 May 2002)
three adults (a male, his mate, and a second during which we did see several peregrine
female) perched for <5 min within —20 m of hunting attempts, winds were —24-32 km/hr
one anotheron the ESB to—wer until the second from the northwest, and many migrants passed
female was chased away mostly by the fe- at or just above the level of the observation
male of the pair. An immature peregrine was deck.
present on 3 evenings: 9 and 14 October, and Peregrine Falcons hunted migrants in two
9 November 2004, although we could not be ways: pursuit and “still hunting” (sensu Cade
sure if it was the same bird on all 3 evenings. 1982). At the ESB, greater success occurred
On 5 October, a Peregrine Falcon passed high when they pursued prey in level flight from
overhead flying south on moderate northerly behind; however, peregrines more often em-
winds while an adult female flew back and ployed still hunting from a west- or north-fac-
forth near the ESB. It was not uncommon to ing perch on the spire above the observation
see peregrines flying high above (25-75 m) deck. When still hunting, they launched their
the top of the ESB tower at night in Septem- attacks at a 5 to 15° angle down toward in-
ber and October. coming migrants flying along a northwest-to-
southwest route past the ESB. Such direct at-
DISCUSSION
tacks were often unsuccessful, and peregrines
Tall, lighted, man-made structures present had to make additional short stoops to secure
opportunities for biologists to study nocturnal the prey. If the intended prey was able to
hunting by Peregrine Falcons that may not be dodge the initial attack, it would then fly
observed readily in remote locations. Urban straight down toward the ground, and pere-
skyscrapers provide hunting platforms that grines often made no furtherpursuits. We nev-
permit these raptors to perch at or above the erobserved targeted prey attempt to escape by
elevation of nocturnal migrants, and the lights “ringing up,” nor did we ever observe birds
used to illuminate tall buildings can disorient mass together in a flock when a Peregrine Fal-
migrating birds that may then circle these con flew among them. On some nights (e.g.,
structures, especially on evenings with over- 10 October), when many migrants passed the
cast skies and light winds. These migrants ESB and peregrines captured several birds, we
DeCandido andAllen • NOCTURNAL HUNTING BY PERLGRINE FALCONS 57
also observed unsuccessful hunting attempts in an urban-marine environment. Notornis 23:8-
that were considerably less intense than others 28.
made on the same evening. Such behavior Cochran, W. W. 1985. Ocean migration of Peregrine
may account for the low hunting success rate FinalPcrooncse:eidsinthgesaodfulHtamwakleMipgerlaagtiico?nPCaognefser2e2n3c-e22I7V
on nights when >250 migrants were counted. (M. Harwood, Ed.). Hawk Migration Association
As camera use increases for 24-hr nest sur- of North America, Rochester, New York.
veillance, it may become possible to deter- Crick, H., A. Banks, and R. Coombes. 2003. The na-
mine whether Peregrine Falcons frequently tional peregrine survey2002: results. BritishTrust
hunt at night during the nesting season, and for Ornithology News 248:8-9.
whether this varies from year to year (see Rejt DeCandido, R., R. O. Bierregaard, Jr., M. S. Mar-
2004b). Future studies at the ESB may also tell,andK. L. Bildstein. 2006. Evidenceofnoc-
determine whether nocturnal flights made to- tNuorrntahl mAimgerratiicoanabnydOsWpersetyer(nPaEnudrioopne.haJloiauertnuasl)oinf
ward conspecifics are directed at neighboring Raptor Research. In press.
Peregrine Falcons or at night-migrating fal- Ellis, D. H., A. K. Kepler, and C. B. Kepler. 1990.
cons simply passing through the area. Evidence for a fall raptor migration pathway
across the South China Sea. Journal ofRaptorRe-
ACKNOWLEDGMENTS search 24:12-18.
Feare, C. J., D. J. Haskell, and J. R. Allan. 1995.
We thank B. A. Loucks for information and kind Peregrine and Tree Sparrow feeding at night.
words ofencouragement. We also acknowledge C. A. Hong Kong Bird Report 1994:218-219.
Nadareski’s long-term work with Peregrine Falcons in Herbert, R. A. and K. G. S. Herbert. 1965. Behavior
the metropolitan area. A. Braunlich andE. J. A. Drew- ofPeregrineFalconsintheNew YorkCityregion.
itt directed us to recent literature about nocturnal Per- Auk 69:246-253.
egrine Falcon activity in Europe and Asia. We thank Kaiser, G. W. 1989. NightlyconcentrationofBaldEa-
H. Q. P. Crick for providing information about Pere- gles at an auklet colony. Northwestern Naturalist
grine Falcons in England. K. L. Bildstein, J. B. Buch- 70:12-13.
anan, and D. Panko each critically read the manuscript Kerlinger, P. and F. R. Moore. 1989. Atmospheric
and made many helpful suggestions regarding how to structure and avian migration. Current Ornitholo-
interpret the data. We also wish to thank two anony- gy 6:109-142.
mous reviewers fortheircomments and ideas. In New Kladny, M. 2001. Slechtvalkjaagt ’s nachts op kok-
York City, S. Critelli, C. R. Howard, M. W. Kola- meeuwen. [Peregrine Falcon hunts Black-headed
kowski, W. J. Paulson, B. J. Saunders, E. Shapiro, S. Gulls at night.] Werkgroep Slechtvalk Nederland
Jw.itWhiluesy.,WaendthCa.nkA.thWeosotdaffoobfsetrhveeEdmPpeirreegrSitnaeteFaBluciolnds- Marc7o(n2)o:t1,1.B[.In2D0u0t3c.h]Comportement de chasse noc-
ing, including L. A. Ruth and all security personnel, turne du Faucon Pelerin Falco peregrinus a Bel-
for facilitating our research and making our evenings
at the building much more pleasant. We dedicate this fort. [Nocturnal hunting behaviorofthe Peregrine
paperto Rev. M. A. Hegyi who encouraged the senior Falcon Falcoperegrinus at Belfort.] Ornithos 10:
aivsuattHihaoonrwkstociMseotnuucndetyanNiunembwSearYnoctr12uk4a.rCyi’tys’scofnaturinbautainodnftloorca.onTsheirs- McLan2uo0gt7ha-tl2ui1sn1,.acJ[t.Iinv1eF98ra9et.ncnBhigl]hatc.k-AsuhsoturladleiraendBKiirtdesWaEtlcahnuesr
13:133.
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