Black-Capped Chickadee Dawn Chorus Singing Behaviour: Evidence for Communication Networks
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There has been a recent paradigm shift in the study of animal communication from examining interactions as dyads to considering interactions as occurring in a communication network. The dawn chorus of songbirds, a striking acoustic phenomenon, provides an ideal opportunity to study network communication because multiple singers are within range of each other, permitting eavesdropping by both males and females. I used a 16-microphone Acoustic Location System (ALS) to simultaneously record and analyse the dawn chorus in a population of black-capped chickadees (Poecile atricapillus) breeding in eastern Ontario. Males frequency-match neighbours 24% of the time at dawn, more often than expected by chance or during daytime singing interactions. The amount of matching between males from different over-wintering flocks is significantly greater than between flockmates. Males of the same winter dominance rank match significantly more than do males of disparate ranks. Male black-capped chickadees are interacting vocally with neighbours at dawn, using the dawn chorus to mediate social relationships in ways that suggest useful information is available to the network of male and female receivers. Matching levels are not related to distance between opponents. However, males with non-fertile mates move over larger areas while chorusing and are further from their nest than males with fertile mates, suggesting dawn mate guarding. Males with non-fertile mates spend more of their chorus near boundaries with fertile neighbours than non-fertile neighbours possibly positioning themselves to facilitate eavesdropping by fertile females. Male chickadees of high and low winter social rank do not differ in either the size of their communication network, or the way they use their songs when interacting with neighbours. Males match multiple neighbours both sequentially and simultaneously. Simultaneous matching is most often the result of a former flockmate joining an interaction between two males who had been in different winter flocks. High-ranked males join the interactions of their lower-ranked flockmates, preferentially when those males are matching other high-ranked males. The dawn chorus is an interactive communication network in which all males participate and is characterized by interactions between multiple senders and receivers with males eavesdropping on interactions in which they are not involved.