The song system and mating system of black-capped chickadees: Eavesdropping and female choice

The performance of male songbirds in countersinging interactions may be sexually selected through female choice and male-male competition. In my dissertation, I explored the communication behaviour and mating behaviour of black-capped chickadees (Poecile atricapilla), North American songbirds whose social interactions follow flock-specific dominance hierarchies. I evaluated the significance of overlapping and frequency-matching during the countersinging contests of breeding males. Interactive playback trials showed that overlapping and matching were more threatening signals than non-overlapping and non-matching, and that male behaviour during playback varied with male dominance status. I also tested whether territorial males eavesdrop on the countersinging interactions between other males to assess the quality of competitors. Multi-speaker playback trials showed that males discriminated between overlapping versus overlapped opponents, responding more aggressively to overlapping opponents.; I described the extra-pair mating system of black-capped chickadees using microsatellite paternity analysis and GIS spatial analysis. Low-ranking males were cuckolded frequently whereas high-ranking males were cuckolded rarely. Promiscuous females preferred high-ranking neighbours as extra-pair partners. Consequently, high-ranking males benefited from increased reproductive success. Although females constructed nests close to territory edges, they did not preferentially choose the neighbour nearest their nest as an extra-pair partner. I tested whether breeding females eavesdrop on the countersinging contests between males to inform mate-choice decisions. Interactive playback trials followed by paternity analysis demonstrated that females paired to high-ranking males, although normally monogamous, engaged in a mixed reproductive strategy after hearing their partner lose a song contest to an aggressive opponent. Females paired to playback-manipulated males generally preferred high-ranking males as extra-pair partners, although some females chose low-ranking males who had won song contests against a submissive playback opponent.; In summary, I show that song contests play an important role in male competitive behaviour and that the mating system of black-capped chickadees is driven by promiscuous females who discriminate between high and low-ranking males and modify their mate choice decisions based on male performance in countersinging interactions. My results support the idea that songbird communities may be viewed as communication networks, involving males and females who assess the quality of the individuals around them by eavesdropping on their vocal interactions.