The Bird Dawn Chorus Revisited

The bird dawn chorus has fascinated humans since ancient times, but still today numerous questions remain unclear. This chapter will explore this puzzling phenomenon, a communal display that likely involves the highest level of sound complexity found among animal signals. Covering from the first descriptive studies to recent multidisciplinary approaches, we review the physiological, behavioural and environmental factors affecting dawn chorus. In addition, we provide a critical assessment of the supporting evidence for the functional hypotheses proposed so far to disentangle its proximal and ultimate causes. We find that, despite the latest empirical and theoretical studies, there is still a good degree of confusion, and that four out of the nine hypotheses proposed so far in the literature have not been empirically tested. We show that most of these hypotheses are not incompatible with each other, and that their explanatory value changes depending on the species and the season. We argue that, at any rate, a single explanation may not be a reasonable expectation. The best-supported hypotheses for early singing provide three complementary lines of explanation: (1) singing at dawn has a relatively low energetic cost, most likely because it does not interfere with feeding; (2) is optimal to manipulate female mating or settle territory boundaries; and (3) may promote a handicap mechanism that prevents dishonest signalling. Thus, it follows that a combination of hypotheses based on both an optimality standpoint and costliness assumptions is needed to understand the phenomenon. We provide a series of specific suggestions for further research to refine our knowledge of this intriguing aspect of animal behaviour.