Differential response to interspecific and intraspecific signals amongst chickadees

Abstract

Black-capped chickadees (Poecile atricapillus) and mountain chickadees (P. gambeli) have a similar vocal repertoire and share many other life history traits; yet, black-capped chickadees are socially dominant to mountain chickadees where populations overlap. Previous research suggested that in contact zones, both species respond weakly to heterospecific songs during the breeding season, and have suggested minimal interspecific competition. However, both black-capped and mountain chickadees discriminate between conspecific and heterospecific chick-a-dee calls, suggesting attention is paid to interspecific signals. We compared the responses of both black-capped and mountain chickadees to conspecific and heterospecific chick-a-dee calls during the winter, when both species compete for the same food resources. We conducted an aviary playback experiment exposing both species to playback composed of heterospecific and conspecific chick-a-dee calls, which had been recorded in the context of finding food sources. Responses from the tested birds were measured by recording vocalizations and behaviour. Black-capped chickadees responded significantly more to conspecific than to heterospecific stimuli, whereas the subordinate mountain chickadees responded to both mountain and black-capped chickadee calls. Based upon the reactions to playbacks, our results suggest these two closely related species may differ in their perception of the relative threat associated with intra- versus interspecific competitors. © 2012 Blackwell Verlag GmbH.