Agonistic asymmetries and the foraging ecology of Bald Eagles

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We investigated the effects of both asymmetries and differing food levels on contest outcomes of wintering Bald Eagles (Haliaeetus leucocephalus) feeding on chum salmon (Oncorhynchus keta) carcasses. Large eagles, regardless of age, were more successful in pirating than smaller eagles. Small pirating eagles were usually unsuccessful unless they were adults attempting to supplant other small eagles. Feeding eagles were more successful in defeating pirating eagles according to (1) whether their heads were up to prior to a pirating attempt, (2) how long their heads had been up, and (3) whether they displayed. During periods of food scarcity pirating eagles were less successful, a fact attributed in a proximate sense to the increase incidence of retaliation by feeding birds. When food was scarce and eagles had a choice between scavenging the pirating, they chose to scavenge more often. Body size appears to be an important factor in determining social dominance and influencing differences in foraging modes of wintering Bald Eagles.

Publication type Article
Publication Subtype Journal Article
Title Agonistic asymmetries and the foraging ecology of Bald Eagles
Series title Ecology
DOI 10.2307/1941273
Volume 69
Issue 4
Year Published 1988
Language English
Publisher Ecological Society of America
Description 7 p.
First page 1188
Last page 1194
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