Feeding Behavior of the Glaucous-Winged Gull on an Alaskan Salmon Stream

TitleFeeding Behavior of the Glaucous-Winged Gull on an Alaskan Salmon Stream
Publication TypeJournal Article
Year of Publication1966
AuthorsMoyle, P. B.
JournalThe Wilson Bulletin
Date Published06/1966
AbstractThe feeding behavior of the Glaucous-winged Gull was studied on Olsen Creek, a salmon stream flowing into Prince William Sound, Alaska. It was found that feeding took place in two distinct situations: (1) on the banks of the stream on salmon carcasses pulled up by gulls or bears and (2) in the stream itself, on salmon eggs drifting with the current. The behavior patterns centering around the defense of salmon carcasses appeared to be very similar to the territorial displays of the breeding season with these exceptions: actual territories did not exist, the carcasses were defended only by hungry birds, and the attacking gull won more often than the defender in disputes over a carcass. Upright Displays, Oblique-cum-Long-Call Displays, and Mew Call Displays were all observed frequently during carcass defense. The effectiveness of such behavior, however, tended to break down in the presence of bears feeding on freshly caught salmon, particularly when the salmon were females. The gulls also seemed to exhibit preference for female over male carcasses of spawned out salmon. Birds in immature plumage usually could not defend a salmon carcass against adult gulls, although first-year juveniles had a certain immunity to attack by their unresponsiveness to adult threat displays. Apparently, even adults cannot defend themselves against other adult gulls while diving for drift eggs in the stream. At the approach of a low-flying attacker, the swimming gull must either fly up or be bowled over. If drift egg feeding occurs in a riffle, however, the riffle can be defended like a salmon carcass. Paddling, probably to stir up salmon eggs caught in the surface gravel, also occurred in the riffles.