Social influences on barn swallow foraging in the Adirondacks: a test of competing hypotheses

Abstract

Three important predictions of the information-centre hypothesis were tested using a colony of barn swallows, Hirundo rustica, breeding in the Adironacks of central New York. Departures of foraging swallows were clumped in time as would be predicted if information about feeding sites was being obtained by foragers at the colony. Departure synchrony was probably increased by the tendency for foraging birds to follow their mates away from the colony. Two of the predictions of information transfer were not supported by the study: (1) birds leaving close together in time did not travel to the same foraging areas, and (2) previously unsuccessful foragers were not more likely to follow others away from the colony on subsequent feeding trips than were previously successful foragers. Foraging swallows were approached more often by conspecifics than non-foraging swallows were, suggesting that barn swallows may cue in on successfully feeding conspecifics when searching for foraging areas. Swallows do not appear to benefit by increasing their prey capture rates in groups, suggesting that foraging groups of barn swallows may simply be aggregations of birds using insect patches in an ‘ideal-free’ or opportunistic manner.