Stable isotope-determined diets of black oystercatchers haematopus bachmani in the northern gulf of alaska

Black Oystercatchers Haematopus bachmani (BLOY) feed on intertidal invertebrates along coasts of the northern Gulf of Alaska and elsewhere. Details of their feeding ecology have only been marginally delineated, however, and as population sizes are small and limited geographically, rapid ecological changes may alter their prey base, placing BLOY resiliency in jeopardy. We examined the diets of BLOYs occupying the coast at three sites in Southeast Alaska using stable isotope analysis of carbon (delta C-13) and nitrogen (delta N-15) to answer the following three questions: (1) what are the diet proportions of prey groups consumed at different locations along the northern Gulf of Alaska; (2) how do individual diets vary; and (3) how do current diets compare to those of the past? Results indicate that: (a) the diet of individual BLOYs was approximately similar to 52% mussels Mytilus trossulus or other filter feeders, similar to 41% limpets Lottia spp. or other kelp and algal grazers, and similar to 5% dogwinkles Nucella spp. or other secondary consumers; (b) little variation in diet existed between seasons or locality; and (c) diets of adults during summer have varied little over the last 100 years. These findings indicate that BLOYs have a very specialized feeding niche that has not changed substantially over time. We discuss the possibility that changing ocean processes may alter the abundance of filter feeders and ultimately have effects on BLOY success in the study region.