The effects of episodic predation by migratory shorebirds in Grays Harbor, Washington

Abstract

Exclusion experiments were performed in Grays Harbor, Washington, in the springs of 1989 and 1990 to test the effect of predation by migratory Western Sandpipers [ Calidris mauri (Cabanis)] on invertebrate abundance. Although over a million shorebirds pass through Grays Harbor each spring, experimental data showed no significant depression of prey abundance for any of the sandflat invertebrates. Unlike better studied stop-over areas, Grays Harbor is not characterized by rich prey densities. The surprising lack of effects on prey abundance likely arises because these sandpipers do not need to deposit large fat stores to fuel their migration to their next stop-over area, the Fraser River delta in British Columbia, or the Copper River Delta in south-central Alaska. The effects of episodic predation by shorebirds appears to differ at different stop-over areas.