Piracy as an Important Foraging Method of Aplomado Falcons in Southern Texas and Northern Mexico

3 Pages·2003·1.8 MB·English

by  Jessi L Brown

THE WILSON BULLETIN
A QUARTERLY JOURNAL OL ORNITHOLOGY
Published by the Wilson Ornithological Society
VOL. 115, NO. 4 December 2003 PAGES 357-524
Wilson Bull., 115(4), 2003, pp. 357-359
PIRACY AS AN IMPORTANT LORAGING METHOD OL
APLOMADO LALCONS IN SOUTHERN TEXAS AND
NORTHERN MEXICO
JESSI L. BROWN,i2 ANGEL B. MONTOYA,' ERIN J. GOTT,' AND
MARTA CURTE
—
ABSTRACT. Piracy (kleptoparasitism) accounted for 14% of observed foraging attempts on vertebrates (n
= 125) by Aplomado Falcons {Falcofemoralis) in southern Texas and northern Mexico, and was over twice as
successful as hunting (82% versus 37%). Aplomado Falcons pirated prey cooperatively as well as individually.
Eight bird species were targeted for piracy, six ofwhich were as large or larger than the falcons. The majority
ofprey items stolen were mammals. Received 10 December 2002, accepted 12 March 2003.
Piracy (kleptoparasitism) has been docu- mado Falcons in southern Texas: one near the
mented for many birds, particularly those liv- Laguna Atascosa National Wildlife Refuge in
ing in open landscapes (Paulson 1985) andhas Cameron County (26° 05' N, 97° 21' W) and
been reported for 12 of 39 species of falcons the other at Matagorda Island National Wild-
(Cade 1982, Brockmann and Barnard 1979, life Refuge (28° 14' N, 96° 37' W). We also
Clark et al. 1990, Clark and Schmitt 1993). observed Aplomado Falcons in the Mexican
Hector (1985) observed Aplomado Falcons state of Tamaulipas near the city of Matamo-
{Falcofemoralis) taking small mammals from ros (25°49' N, 97° 26' W). Most or all indi-
American Kestrels {F. sparverius) and White- viduals were derived from captive stock as
tailed Kites (Elanus leucurus), and Clark et al. part of a long term release program of The
(1990) described piracy by this species on a Peregrine Fund (Mutch et al. 2000). We ob-
Little Blue Heron (Egretta caerulea). The ob- served the activities of breeding pairs during
jective ofthis study was to determine ifpiracy February to June, 1999 to 2002. These pairs
is an important foraging mode for both indi- occurred in open coastal plains, characterized
viduals and pairs of Aplomado Falcons in by low herbaceous cover and few, widely
southern Texas and northern Mexico. scattered trees and shrubs (Perez et al. 1996).
We monitored two populations of Aplo- Here we report only piracy and hunting at-
tempts upon vertebrates with known out-
comes.
Boi'sTeh,eIDPer8e3g7r0i9n,eUFSuAnd., 5668 West Flying Hawk Ln., Of 125 foraging forays for vertebrates, 17
^Corresponding author; (14%) were attempts at piracy, 14 (82%) of
e-mail: [email protected] which were successful. The hunting success
FRONTISPIECE. Aplomado Ealcon {Falcofemoralis) in southern Texas. Watercolor on paper, by Barry
Kent MacKay.
357
358 THE WILSON BULLETIN • Vol. 115, No. 4, December2003
rate was 38% (41 of 108 attempts). This is a coordinated attack, with the falcons alter-
similar to 37% {n = 100) reported by Hector nately stooping at the target bird, the latter
(1986) for eastern Mexico. Piracy thus was visibly disoriented, vocalizing, and often
more than twice as successful as hunting. dropping its prey. In two piracies on Chihu-
Although mammals have been included in ahuan Ravens, the ravens dropped their prey
qualitative accounts ofthe Aplomado Falcon’s at the first sign of attack, suggesting routine
diet (Bendire 1892, Cherrie 1916, Bent 1938, harassment and habituation to surrender. JLB
Wetmore 1965), recent detailed studies ofcap- watched a pairofAplomado Falcons approach
tured prey and prey remains show no evidence a flying White-tailed Kite 5 m above the
that mammals normally are an important food ground and perform a series of alternating
(only 1 of 341 vertebrate prey items; Hector stoops and horizontal attacks. The falcon pair
1985, Jimenez 1993). Only 2 ofthe 108 hunts effectively stopped the kite’s forward move-
we observed were for mammals, even though ment, and within 5 s the kite flipped upside
we saw Aplomado Falcons consuming mam- down in response to a stoop from the male
malian prey of unknown acquisition. Howev- falcon. The male seized the rodent prey still
er, the majority of identified pirated items clutched in the kite’s talons, then immediately
were mammals (9 of 13 items ofknown class; dropped the prey, which the female falcon
see Hector 1985), suggesting that piracy may caught in mid-air.
account for this incongruity. Pairs of Aplomado Falcons defending a
Eight (73%) of 1 1 observed piracy attempts breeding territory also dominated larger spe-
by single falcons were successful, whereas all cies. Aplomado Falcons attacked and success-
six attempts by pairs succeeded. These obser- fully expelled much larger raptors, including
vations parallel the findings of Hector (1986) Turkey Vultures (Cathartes aura), Harris’
that pairs were more successful at hunting Hawks (Parabuteo uincinctus). White-tailed
birds than individuals hunting alone. Our ob- Hawks (Buteo albicaudatus). Red-tailed
servations imply that piracy by pairs is a co- Hawks {B. jamaicensis). Crested Caracaras
operative act, involving mutual monitoring of (Caracara plancus). Peregrine Falcons, and
movements and food sharing (Hector 1981, Great Horned Owls {Bubo virginia?ius; The
1986). Four successful piracies by single fal- Peregrine Fund unpubl. data). In contrast,
cons were in the presence of a nearby mate, nonbreeding Aplomado Falcons tended to tol-
whose visibility may have increased the de- erate heterospecific intruders. Temeles (1990)
gree of intimidation of the target. suggested that such behavior by Northern
Aplomado Falcons targeted eight species Harriers increased opportunity for kleptopar-
for piracy: the American Kestrel {n = 1), Mer- asitism by not excluding potential future tar-
lin (F. columharius\ n = 1), Peregrine Falcon gets. Our observations indicate that Aplomado
(F. peregrinus; u = 1), White-tailed Kite (/? Falcons, particularly when paired, may im-
= 6), Northern Harrier {Circus cyaneus; n = prove their foraging efficiency and broaden
3), Chihuahuan Raven {Corx’us cryptoleucus; their diet by pirating.
n = 2), a gull (most likely Laughing Gull,
La?us at?icilla\ n = 1), and other Aplomado ACKNOWLEDGMENTS
Falcons {?? = 2). We commonly observed tar-
giteatt,sapencdieWshiitne-AtpaliolemdadKioteFsa,lctohen mboresetdifnrgeqhuaebn-t WD.eThMtiuhstacnshkt,uWd.aynAdw.aAsB.usrNuniphcpahomor,ltaeBsd.bfHoyeriTnhrheielcphP,etJrh.ergoP.ruigJnheeonunFtyu,ntdBh..e
target for piracy, often nested within sight of study. CommentsbyT.J. Cade,G. Hunt,J. E.Jimenez,
Aplomado Falcon nests. Only two of these and an anonymous reviewer significantly improved
species, American Kestrels and Merlins, are earlier versions ofthis manuscript.
smaller than Aplomado Falcons (approximate-
ly 250-400 g), whereas the others are similar LITERATURE CITED
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Brown et al. • PIRACY IN APLOMADO FALCONS 359
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