CLAM DROPPING BEHAVIOR OF THE GLAUCOUS-WINGED GULL (LARUS GLAUCESCENS)

hard-shelled molluscs in order to break them open, but that their selection of substrate appears to be random, with the birds as likely to drop potential food objects on soft surfaces (sand) as on hard (rocks). The European Gull (Larus canus) also shows this same apparently non-adaptive behavior with regard to cockles (Cardium edule, Oldham 1930). This curious failure of such adaptive food generalists to make maximal use of a foraging technique is surprising. Our own observations of Glaucous-winged Gulls (Larus glaucescens) in northwestern Washington suggested that this species also commonly feeds on marine shellfish, which it opens by dropping. We therefore attempted to investigate substrate selection and other behaviors related to this clam dropping habit.