FORAGING ECOLOGY OF BALD EAGLES IN A FRESHWATER TIDAL SYSTEM

Abstract

We studied the summer foraging ecology of resident and migrant bald eagles (Haliaeetus leucocephalus) along the lower Hudson River, New York, from 1998 to 2001. In this area the Hudson is a freshwater tidal river with 1- to 2-m tidal ranges. Eagles foraged most often in the open channel (35%), where success was lowest (68% capture rate). When compared to landscape availability, eagles foraged in tidal mudflats devoid of aquatic vegetation more often than expected, and they avoided areas of deep water (>3 m). Eagles foraged more often during ebb tides with foraging activity peaking just before low tide. Eagles avoided areas of high human activity but also preferentially selected areas of low to moderate activity. Fish were the most important source of food and comprised 91% of prey identified. Over 50% of the observed prey captures consisted of 3 species: American eel (Anguilla rostrata), gizzard shad (Dorosoma cepedianum), and white catfish (Ictalurus catus). Our data indicate that unvegetated tidal mudflats that were isolated from intensive human activity provided the highest quality foraging habitat. Future loss of tidal mudflats through exotic plant invasions or shoreline development may limit eagle foraging opportunities and population growth.