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Hunting tactics of Peregrines and other falcons - Section: 13 Page: 92 - Peregrine prey selection and eagle interference

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92

Huntin tactics of Pere ines

CHAPTER 9

Dekker. D. 2003. Peregrine Falcon predation on Dunlins and ducks and kleptoarasitic interference from Bald Eagles wintering at Boundary Bay, British Columbia. Journal of Raptor Research 37:91-97.

Abstract — At Boundary Bay, British Columbia, wintering Peregrine Falcons (Falco peregrinus) captured 94 Dunlins (Calidris alpina) in 652 hunts. The major hunting techniques were open attacks on flying flocks (62'/o) and stealth attacks on feeding or roosting flocks (35'/o). Success rates for these techniques were 9.1'/o and 23.6'/o. Sixty-five Dunlins were taken directly from the edge of flocks; 29 Dunlins were seized after they had split off from flocks or were flying alone. Adult Peregrines were significantly more successful than immatures (26.8'/o vs. 9.0'/o). Peregrines captured one Green-winged Teal (manas crecca) and three larger ducks. The teal was carried away, but the larger ducks were pirated by Bald Eagles (Haliaeetus leucocephalus). Eagles often joined Peregrines that were chasing Dunlins; six eagles succeeded in either capturing the Dunlin or forcing a Peregrine to drop its just-caught prey. I postulate that Peregrines wintering at Boundary Bay abstain from capturing prey species such as ducks that are too heavy to be carried out of reach of klepto-parasitic eagles. Female Peregrines aggressively chased off other females, but tolerated males. Female Peregrines often joined males that were chasing Dunlins; 14 males were forced to surrender their prey to females. Four Peregrines pirated Dunlins from Merlins (Falco columbari us).

INTRODUCTION

In their nearly worldwide range, Peregrine Falcons (Falco peregrinus) prey on a wide variety of birds, although they may locally specialize on very few species (Brown and Amadon 1968; Palmer 1988). The size of the prey taken is partly determined by the sex of the Peregrine since females are about one-third heavier than males. This sexual size-dimorphism has spawned several hypotheses, including that it widens the range of prey that can be taken by paired falcons (Selander 1966; Cade 1982). In human altered habitats or over the ocean, both sexes of Peregrines may hunt the same prey species, namely Rock Doves (Columba livia) or small alcids (Beebe 1960; Ratcliffe 1993; Frank 1994;

OCR
Tag: beebe ducks eagle eagles falcon falcons flocks peregrine peregrines peregrinus sizedimorphism

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