SPRING 1991
SHORT COMMUNICATIONS
21
J. Raptor Res. 25(1):21-22
¸ 1991 The Raptor ResearchFoundation,Inc.
NOTESONA SUCCESSFUL
NESTINGBYA PAIROF YEARLINGPEREGRINE
FALCONS
(Falcoperegrinus)
ANNIE
M.
WENDT
Wisconsin
PeregrineSociety,P.O. Box 1148,Milwaukee, WI 53210-1148
GREG A. SEPTON
Milwaukee Public Museum, 800 W. Wells St., Milwaukee, WI 53233
It is rare for yearling male PeregrineFalcons(Falco
peregrinus)
to breed;occasionally
an immaturefemalewill
Becauseof precariousfootingin front of the hack box,
we feared for the safetyof the nestlingsso we barred the
pair with an adult male. When yearlingsattemptto breed, front of the box on 10 July. The parentscontinuedto feed
many fail to produceeggsor lay a smallerthan normal the young through the bars. We added two captive-proclutch;if eggsare produced,youngseldomfledge(Hagar ducedchickson 15 July. We bandedall four chicks,colormarked them with fluorescentspray paint, and released
1965,Hickey 1965, Cade1982,Mearns andNewton 1984, them from the box on 26 July, at an age of 38-42 days.
Ambrose and Riddle 1988, Newton and Mearns 1988).
All four youngfledged.The male was stronglyaggresIn Milwaukee, Wisconsin,in 1988, a pair of yearling sive toward the young, stoopingand striking oncethey
peregrinesproducedand fledgedyoung.This is the first were in the air or when they perchedon exposedledges.
known recordof successful
nestingby a pair of yearlings. His attack was particularly intensewhen the flight of the
young falconsappeared unsteady;at times he actually
STUDY SITE
knockedthem out of the air. Although stoopingbecame
The First WisconsinCenter, overlookingLake Michlessintensewith time, each fledglingwas driven to the
igan, is the tallestbuildingin Wisconsin.The top floor is groundat leastonce.While stooping,the male often gave
an observationdeck,with full lengthglasswindowson all creakingcallsas describedby Ratcliffe (1980).
sides. The nest was in a hack box (Sherrod et al. 1982)
One youngsterbroke a femur when it hit the ground
that had beeninstalledon a 2 m ledgeoutsidethe windows after an attack and later died of complications.Another
on the west side of this floor, 178 m above street level.
diedafter hitting a glasswindow.The third youngsterwas
Fourteenyoungperegrines
hadbeenreleasedfromthe site injured twice, but survivedand was relocatedto a hack
in 1987.
sitein Omaha, Nebraska.The fourth stayedin Milwaukee
and was last seenin early September.
HISTORY OF FALCONS
The male of the pair, a F. p. pealei x F. peregrinus,had
been released in 1987 in Ft. Sheridan, Illinois, with 10
other youngsters.He was describedas a dominantbird
(J. McCoy and M. Spreyer,in litt.). The female,a F. p.
anatum,was oneof 20 youngreleasedin Rochester,Minnesota, in 1987.
BREEDING ACT•'IT•
DISCUSSION
Most reportsof juvenile peregrinesattemptingto breed
comefromrelativelyrecentobservations
of an expanding,
reintroducedpopulation.As Hunt (1988:673) pointedout,
"There is little informationon the ecologicalage of first
breedingin stable,undisturbedpopulationsof peregrines."
Competition for nest siteshas been recognizedas a factor
limiting the number of breedingyearlings.From 1935A peregrinewas seenhuntingnear the First Wisconsin 1957, Hagar (1969) observedonly one mated juvenile
Center on 21 March 1988. Within 10 d a second falcon
female on a highly rated cliff; six otherswere found on
hadjoined it. Both birdswere in juvenile plumage,except low rated cliffs. None of these seven nests were successful.
for a spatteringof adult featherson their backsand a fair Today, tall buildingsin citiesare providingmore highamount of white on the crop area. Both falconsmolted quality nestsites,and without a stablepopulationof adult
quickly. By mid-June they lookedadult, especiallyfrom peregrines,
thesesitesare availableforjuvenilesto attempt
a distance.By July, their heads,backsand well over75% to nest.
of their undersideshad molted and they were replacing
NewtonandMearns (1988) suggest
that breedingmight
their flight feathers.
be delayedbecause
juvenilesthat are inefficientforagers
Both falconswere seenregularlythrough18 May. We or areconfined
toareaswherepreyisscarce
cannotdevelop
inspectedthe hack box on 13 May, but foundno evidence the bodyreservesnecessary
to breedand cannotafford to
of nesting.When sightingsstoppedabruptlyafter 18 May, spendtime defendinga territory.This is especiallytrue
we thoughtthe pair had left the area. But on 15 June we foryoungmales,for whomtheincreased
burdenof feeding
foundthe femalein the hackboxbroodingtwo new chicks, a mateand family requireswell developed
huntingskills.
one male and one female.These were the first peregrines The westernshoreof Lake Michigan is a well-documented
hatchedin the wild in Wisconsinin over 20 years.
migrationroute, and the availability of prey may have
22
SHORT COMMUNICATIONS
VOL. 25, NO. 1
played a role in the pair of falconsselectingMilwaukee LITERATURE CITED
as a nestsite and breedingsuccessfully
as yearlings.
AMBROSE,R.E. AND K.E. RIDDLE. 1988. Population
Accordingto Ratcliffe (1980:341),pairedjuveniles"are
dispersal,turnover, and migration of Alaska pereoften in transitional plumage, with a mixture of dark
grines. Pages677-684 in T.J. Cade, J.H. Enderson,
brown and slategrey." He alsonotedthat breedingadults
C.G. Thelander and C.M. White. [Eds.], Peregrine
"donot usuallybeginto moltuntil nestingis well advanced
Falcon populations:their managementand recovery.
or actually over." Our juvenile pair moltedvery quickly;
both looked adult by the time the eggshad hatched,esThe Peregrine Fund, Inc., Boise, ID.
pecially when viewed from a distance.We agree with CADE, T.J. 1982. The falconsof the world. Cornell
Ambroseand Riddle (1988:680),who feelthat "theremay
University Press,Ithaca, NY.
be other casesof one year old birds attemptingto breed HAGAR,J.A. 1969. History of the Massachusetts
Perwhich were not detectedbecauseof their nearly adult
egrine Falcon population, 1935-57. Pages123-131 zn
plumage."It is possiblethat the hormonelevelsnecessary
J.J. Hickey [Ed.], PeregrineFalconpopulations:
their
to initiate and maintain breeding behavior might affect
biology and decline. University of Wisconsin Press,
the rate at which matedjuvenilesattain their adult plumage.
Madison, WI.
Skutch (1976) suggeststhat when parent birds drive HICKEY, J.J. AND D.W. ANDERSON. 1965. The Perefledglingsfrom the air or from exposedperches,this may
grine Falcon: life history and populationliterature.
be a responsethat reducesdetectionby predators.Also,
Pages3-42 in J.J. Hickey [Ed.], Peregrine Falcon
"surviving subadultfalconswhich returned to hack sites
populations:their biologyand decline.University of
from the precedingyear appearedto reactsomewhatlike
Wisconsin Press, Madison, WI.
parentswith this respect.The aggressive
stoopsby which
HUNT, W.G. 1988. The natural regulationof Peregrine
the subadultsforcedthe youngdown, however,were of a
Falconpopulations.Pages667-676 in T.J. Cade,J.H.
more seriousnature, and they often hit the youngstersa
Enderson, C.G. Thelander and C.M. White [Eds.],
forceful blow. The stimulus in this case seems to be a 'new
PeregrineFalcon populations:their managementand
falcon'flying in the area, and aggression
is the response"
(Sherrod 1983:144).
recovery.The PeregrineFund, Inc., Boise,ID.
The youngageof the male in our studymay well have MEARNS, R. AND I. NEWTON. 1984. Turnover and discausedhis stronglyaggressive
behavior.We do not know
persalin a peregrineFalcoperegrinuspopulation.Ibzs
if addingthe bars to the hack box contributedto his ag126:347-355.
gressionby limiting his contactwith the chicks,but had NEWTON,I. ANDR. MEARNS. 1988. Populationecology
the youngleft the box prematurely,they might havebeen
of peregrinesin SouthScotland.Pages651-665 in T.J.
knockedoff the ledgeby the male's attacksbeforethey
Cade,J.H. Enderson,C.G. ThelanderandC.M. White
were old enoughto fly. As a breedingadult, the male also
[Eds.], PeregrineFalcon populations:their manageharassedhis fledged young when their flight appeared
ment and recovery.The PeregrineFund, Inc., Boise,
weak, but never with the same intensity and we never
ID.
again saw him strike them forcefully.
RATCLIFFE,D.A. 1980. The Peregrine Falcon. Buteo
RESUMEN.--En 1988, en Milwaukee, Wisconsin,una paBooks, Vetmillion, SD.
reja de HalconesPeregrinos(Falcoperegrinus)de aprox- SHERROD,S., W. HEINRICH, W. BUg•HAM, J. BARCLAY
imadamenteun afio de edad,incub6y cri6 hastaque las
ANDT. CADE. 1982. Hacking: a methodfor releasing
criaspudieranvolar;siendo•ste, el primer casoque conoPeregrineFalconsand other birds of prey. The Percemosdeunanidadaconlogrospositivos.
La parejacambi6
egrine Fund, Inc., Ithaca, NY.
de plumajerapidamente;a mediadosdejunio, y especial1983. Behavior of fledgling peregrines.The
mente a la distancia,los dosten'an la aparienciaadulta.
PeregrineFund, Inc., Ithaca, NY.
E1 macho se mostr6 agresivocon sus cr•as, lanzfindose
SKUTCH,A.F. 1976. Parent birds and their young.Unihacia ellosy golpe•ndolesfuertemente.
[Traducci6n de Eudoxio Paredes-Ruiz]
versityof Texas Press,Austin, TX.
ACKNOWLEDGMENTS
Wc thank ClaytonWhite, W. Kranz, and Fran Hamerstrom for reviewingthis manuscript.
Received30 November 1989; accepted5 December 1990