Conspecifics influence the settlement decisions of male Brewer's Sparrows at the northern edge of their range

Abstract

At the northern periphery of its range Brewer's Sparrow (Spizella breweri breweri) is in decline and breeds in small clusters within larger areas of suitable habitat. Clustered breeding that is unrelated to the distribution of resources may be explained by social attraction (conspecific cueing). We used a song-playback experiment to test the conspecific-cueing hypothesis in this species. The experiment was conducted during the spring settlement period in habitat that appeared physically suitable for breeding but had not been occupied during the previous two breeding seasons. Treatments were split between two periods that reflected peak settlement of experienced and firsttime breeders. In both periods, more Brewer's Sparrows visited and established territories in treatment plots than in untreated control plots. There were not, however, more treatment than control plots containing breeding pairs. This difference could mean that males attracted to playbacks are of lower quality than males in established breeding clusters and thus less attractive to females, that females settle only in groups of males larger than some threshold, or that females' site fidelity is higher than that of males. These results lend support to the conspecific-cueing hypothesis in this species, indicating that social attraction may play a role in Brewer's Sparrow's habitat selection. They also suggest that traditional habitat models, which consider only resource distributions and not social factors, may be inadequate tools for the conservation of this and other species. © The Cooper Ornithological Society 2009.