Clocks rule cocks, crows this study:
“Circadian clock determines the timing of rooster crowing,” Tsuyoshi Shimmura and Takashi Yoshimura, Current Biology, Volume 23, Issue 6, March 18, 2013, pp. R231-R233. The authors, at Nagoya University, Japan, report:
“Crowing of roosters is described by onomatopoetic terms such as ‘cock-a-doodle-doo’ (English), ‘ki-ke-ri-ki’ (German), and ‘ko-ke-kok-koh’ (Japanese). Rooster crowing is a symbol of the break of dawn in many countries. Indeed, crowing is frequently observed in the morning. However, people also notice that crowing is sometimes observed at other times of day. Therefore, it is yet unclear whether crowing is under the control of an internal biological clock, or is simply caused by external stimuli. Here we show that predawn crowing is under the control of a circadian clock. Although external stimuli such as light and crowing by other individuals also induce roosters’ crowing, the magnitude of this induction is also regulated by a circadian clock.”
BONUS: Video of a rooster crowing: