California towhee vocal duets are multi-functional signals for multiple receivers
Avian vocal duets provide a model system for studying the evolution and production of complex signals which require input from multiple individuals. Duets serve a variety of communication functions in diverse species. To explore the function of duetting in California towhees (Pipilo crissalis) I collected behavioural data from a marked population, conducted sound playback experiments, and removed males from established pairs to observe the behaviour of new partners. Results indicate that
... ndicate that California towhees use duets during extra-pair communication with conspecifics and during intra-pair communication between duetting partners. During the breeding season duetting frequency peaked during the chick-rearing period and was low during periods of high female fertility. Playbacks provoked similar levels of aggressive response from male and female territory holders. Mated pairs duetted in response to simulated intrusion by conspecific males, females and pairs. California towhee duets briefly increased in frequency after pairing, and showed no evidence of change due to learning. Duets facilitate spatial and behavioural coordination by mates, which should allow them to more effectively perform behaviours related to mutual reproductive success. No single existing hypothesis adequately explains vocal duetting among California towhees. Instead, duets function in multiple contexts and provide multiple potential benefits.