Human disturbance of an avian scavenging guild

Abstract

Examined intraguild dynamics of bald eagles Haliaeetus leucocephalus, American crows Corvus brachyrhynchos and glaucous-winged gulls Larus glaucescens scavenging on spawned salmon Oncorhynchus in the Pacific Northwest. Spatial and temporal patterns of resource use by the three primary guild members varied with the presence and absence of human activity at experimental feeding stations. At control stations, eagles preferred to feed >100 m from vegetative cover, whereas gulls fed <50 m from cover. At disturbed stations, eagles rarely fed, and feeding activity by gulls increased at both near and far stations. Crows often fed on alternate food sources in fields adjacent to the river, especially when salmon carcasses were scarce; eagles and gulls rarely did so. In the absence of eagles, gulls and crows preferred stations far from cover, numbers of both increased at feeding stations, birds were distributed nearer to carcasses, and they fed more. -from Authors