Habitat characteristics of black oystercatcher breeding territories

Abstract

Habitat use in birds is often related to forage resources and predation avoidance. The large, long-lived black oystercatcher is a shorebird that defends a composite breeding territory for foraging in the intertidal zone and nesting in the immediate upland. Predation on young is a major source of mortality for many bird species, including black oystercatcher. As these are long-lived birds with many reproductive opportunities, adult survival, associated with forage resources, is expected to be more important in habitat use than less-predictable breeding success. To identify which factors most influence black oystercatcher breeding territory use, logistic regression models were developed and tested in south-central Alaska and tested in southeast Alaska. Intertidal community composition was sampled at a subset of sites. All known breeding sites in Kenai Fjords National Park and western Prince William Sound, plus sites in southeast Alaska, were matched with available breeding sites based on substrate and exposure classifications. Two factors available breeding related to predation avoidance, greater distance to vegetation and isolation from the mainland, were the most important variables in habitat models. Intertidal community composition did not vary between known breeding and available breeding sites. This suggests black oystercatchers choose breeding territories that reduce predation risk, contrary to expectations.