Song behaviour and reproductive strategies in a duetting wren, Thryothorus nigricapillus .1. Removal experiments

Mate removal experiments were conducted to test the hypotheses that vocal duetting functions in pair bond maintenance and/or territory defence in the bay wren, Thryothorus nigricapillus, in the Republic of Panama. Males and females were observed while in established pairs, while alone after mate removal and following the arrival of a new mate. Duet repertoires and precision of duet performance were then compared in birds singing with old and new mates. Another experiment in which males were exchanged between two territories was similarly analysed. These experiments demonstrated that (1) individual repertoires and duet precision do not change following a change in mates, refuting the pair bond maintenance hypothesis, and (2) unpaired birds do not lose their territories, failing to support the hypothesis that duets are necessary for territory defence. Analysis of vocalization rates suggested that male and female songs serve different functions. Male vocal behaviour was sensitive to male mating status: when males were alone, their vocalization rates dramatically increased. However, males answered the songs of a new mate less frequently than they did those of their original mate. These results suggest that unpaired males sing to attract females and that males might use participation in duets to assess new mates. The function of duetting by males in established pairs remains unclear. Female song rates were unaffected by female mating status, suggesting that female songs may be directed to conspecific females. Results also indicated that territory residency may play a more important role in mate acquisition for males than it does for females. (C) 1996 The Association for the Study of Animal Behaviour