Foraging behaviors and prey depletion by wintering scoters in Baynes Sound, British Columbia: Inferring food availability and habitat quality

I quantified diet composition and foraging behaviors of Surf Scoters and Whitewinged Scoters wintering in Baynes Sound, British Columbia. Manila and varnish clams were the predominant prey of both scoter species. Manila clams decreased in density over the winter period, while pronounced declines were not detected for varnish clam density. Estimates of clam consumption by scoters accounted for most of observed declines in combined abundance of Manila and varnish clams. Clam capture success of both scoter species and foraging effort of Surf Scoters were unrelated to variation in clam density, while White-winged Scoter foraging effort was negatively related to clam density. Observed clam densities were apparently high enough to not elicit strong behavioral shifts in foraging scoters. Further, scoters rarely foraged at night, sufficiently meeting energetic requirements during diurnal hours. These combined results suggest that Baynes Sound constituted high-quality winter habitat in which scoters were not constrained by food availability.