East and west coast female brown-headed cowbirds agree: both categories of male song are sexy

Abstract

Some prior studies of brown-headed cowbirds, Molothrus ater, suggest geographical variation in female copulatory responsiveness to the two categories of male courtship songs, flight whistles (FWs) and perched songs (PSs). Females from the eastern M. ater ater subspecies and midwestern populations of the M. a. artemisiae and M. a. obscurus subspecies were reported to give copulation solicitation responses only to playback of PSs. But females from far western populations of M. a. artemisiae and M. a. obscurus responded to both PSs and FWs. An east–west difference in the social salience of FWs could have an ecological basis. FWs are used mostly for long-distance signalling and because western birds have larger home ranges they may use FWs more often. However, the disparate FW findings may result from different procedures used to assess female responsiveness to playbacks. Determining whether the disparate findings are due to geographical variation or to methodological differences is important because many potentially significant insights into song development and female preferences in oscines are based on cowbirds. Furthermore, either explanation would elucidate important links between female choice and male sexual displays. To resolve this issue, we tested M. a. ater females from New York using identical procedures to those we used in the far west and found that they were highly responsive to both FWs and PSs. This does not support the hypothesis that there is pronounced geographical variation in the courtship salience of FWs. Rather, it suggests that different procedures used by researchers in different areas of the cowbird’s range are responsible for the disparate findings. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.