Why early birds sing early: rebound singing from nighttime suppression can explain dawn chorus

Many birds sing intensively at dawn, a phenomenon known as the "dawn chorus," yet its cause remains unclear. This is largely due to prior research being limited primarily to ecological studies of wild birds. We investigated the dawn chorus under controlled laboratory conditions using an animal model, the zebra finch. We found that birds became hormonally aroused in the dark long before initiating dawn singing, and that suppression of spontaneous singing by darkness enhanced their intrinsic motivation to sing. This elevated motivation subsequently triggered a rebound of intensive singing at dawn. Moreover, dawn singing accelerated refinement of song structure, supporting its role as intensive vocal exercise to optimize song performance after overnight silence. These findings provide mechanistic and functional explanations for the dawn chorus.