Male chickadees match neighbors interactively at dawn: support for the social dynamics hypothesis

Males of many songbird species participate in a distinct chorus beginning before sunrise. Despite its ubiquity, the function of dawn chorusing remains poorly understood. We tested the social dynamics hypothesis, which states that males sing at dawn to mediate their social relationships with neighbors through interactive communication. Using a 16-microphone acoustic location system, we recorded 29 entire dawn choruses in 10 neighborhoods of 6-10 territorial male black-capped chickadees (Poecile atricapillus) of known dominance rank. We analyzed song frequency matching and overlapping between neighboring males in 10 choruses and compared the intensity of these behaviors with social factors. Chickadees matched the frequency of their neighbor's songs more often than expected by chance. The level of matching was higher between neighbors who belonged to different flocks during the previous winter than between neighbors who had been flockmates. Males of the same dominance rank matched each other more than males of disparate ranks. There was no relationship between matching and pairing status or distance between opponents. Overlapping was used less than expected by chance. No measures of song overlapping were related to measured social factors. Our results show that neighboring male chickadees interact vocally at dawn by frequency matching. This is the first study to show that the intensity of songbird vocal interactions at dawn varies with social factors, supporting the social dynamics hypothesis.