Countersinging as a signal of aggression in a territorial songbird

Neighbouring territorial songbirds often interact through countersinging, where birds sing in response to the singing of neighbours such that their song bouts are temporally related. Complex forms of countersinging such as song type matching or song overlapping appear to be correlated with aggressiveness and readiness to escalate confrontations. Less attention has been paid to the importance of simpler forms of countersinging, where matched song types are not used and where individual songs do not temporally overlap. I examined countersinging behaviour in male Carolina wrens, Thryothorus ludovicianus, which countersing regularly. Why they countersing and how countersinging is perceived by neighbours is unknown. By comparing singing behaviour before and after simulated intrusions, I determined that subjects countersing with their neighbours more readily when highly aroused. Comparing responses to countersinging and noncountersinging playbacks showed that countersinging elicited more aggressive responses than did noncountersinging. Carolina wrens appear to exchange aggressive signals regularly through countersinging. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.