REEVALUATING MARINE DIETS OF SURF AND WHITE-WINGED SCOTERS: INTERSPECIFIC DIFFERENCES AND THE IMPORTANCE OF SOFT-BODIED PREY

Abstract

Abstract Past studies of the marine diets of Surf Scoters (Melanitta perspicillata) and White-winged Scoters (M. fusca) have reported that they eat mostly bivalves, but deviations from well-established methods by most studies suggest that the importance of soft-bodied prey has been underestimated for both species. Methods needed to reduce bias in diet estimates include collecting birds that are feeding, immediately preserving gut contents, excluding gizzard contents, averaging food-item percentages across birds versus pooling gut contents for all birds, and using energy or ash-free dry mass versus wet mass values of foods. For Surf Scoters collected in northern Puget Sound, Washington during 2005–2006, adherence to the latter three methods alone resulted in the assessed bivalve component of diet declining by over half and a near doubling of soft-bodied prey (i.e., crustaceans, polychaetes). Diets of Surf Scoters differed among three heavily used bays with distinct benthic habitats, yet 67%–86% of the ash-...