Birds of Indian Subcontinent

Prey-Size Selection in Nesting Male and Female Cooper's Hawks

Publication Type:Journal Article
Year of Publication:1986
Authors:Kennedy, PL, Johnson, DR
Journal:The Wilson Bulletin
Date Published:1986
ISBN Number:00435643
Keywords:Accipiter, Accipiter cooperii, Accipitridae, Astur, Astur cooperii, bias, Callipepla, Callipepla californica, Columba, Columba palumbus, Columbidae, Coturnix, Coturnix coturnix, Erithacus, Erithacus rubecula, Lophortyx, Lophortyx californica, Muscicapidae, Odontophoridae, Turdidae, Turdus, Turdus migratorius
Abstract:The size and frequency of prey delivered by nesting Cooper's Hawks (Accipiter cooperii) were monitored throughout the nestling period at five nests on Lopez Island, Washington. Based on vocalizations during food exchange, we estimate that males captured 63% of the prey delivered to nests. Birds, primarily American Robins (Turdus migratorius) and California Quail (Callipepla californica), represented 85% of the prey captured by both males and females. The food niches of both sexes were similar as measured by maximum likelihood estimators of niche breadth and overlap. When the counts of prey delivered by males and females were adjusted for bias due to unequal observation time between years and differential hunting effort by the sexes, there were no significant differences between the sexes, nesting pairs, or prey size classes in the number of prey delivered to nests. These results and those of several other studies call into question the food-niche hypothesis as a comprehensive explanation for sexual size dimorphism found in many raptorial birds.
Short Title:The Wilson Bulletin
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