A bioassay of isolate cowbird song.

Abstract

Captive female cowbirds [Molothrus ater], both isolation reared and wild caught, were exposed during the breeding season to experimentally manipulated versions of isolate male song. A single song element, a brief note between the song phrases, plays a pivotal role in eliciting the female''s copulatory response to song. Relative amplitude variation and the fine structure within the interphrase unit may affect the potency of a given song. The acoustic properties of this unit may account for the enhanced effectiveness of isolate song over normal cowbird song as a sexual releaser.