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). In Swedish it is ku-ke-li-ku.
In many countries rooster crowing is a symbol of the break of dawn and crowing is frequently observed in the morning. Sometimes crowing is observed at other times of day and it is yet unclear whether crowing is under the control of an internal biological clock, or is simply caused by external stimuli.
The roosters were put into an environment where light did not change and the experiment shows that the roosters, independent of light, crow just before the break of dawn.
It is now concluded that predawn crowing is under the control of a circadian clock.
The study is presented in Current Biology, Volume 23, Issue 6 by Tsuyoshi Shimmura and Takashi Yoshimura