Quantifying the Diets of Breeding Bald Eagles on the Channel Islands: A Multi-Proxy Approach

Bald eagles (Haliaeetus leucocephalus) were once a familiar apex predator and scavenger in ecosystems on and around California's Channel Islands. As a result of direct (e.g., shooting, egg collection, poisoning) and indirect (e.g., pesticides, resource competition) interactions with humans, bald eagles disappeared as a resident breeder on the islands by the late 1950s to early 1960s. Similar to other bald eagle populations in North America, the decline in breeding pairs on the Channel Islands coincided with the extensive production and application of DDT as an agricultural insecticide. Although DDT use was banned in the 1970s, until recently bald eagles have been unable to naturally reproduce on the Channel Islands due to high residual concentrations of DDE, a metabolite of DDT, in local marine food webs.Understanding the types of prey that bald eagles are currently consuming or have targeted during the centuries and millennia prior to extirpation on the Channel Islands can inform wildlife managers about: 1) the prey that eagles are likely to focus on and impact as they reestablish breeding populations on the Channel Islands; (2) the possible conflicts that a reestablished bald eagle population might have with other recovering wildlife populations (e.g., seabirds) on the islands; and (3) the impacts that contaminated prey (e.g., gulls and marine mammals) might have on the reproductive success of a recovering bald eagle population.