Roosters \'tell time\' to begin crowing

Roosters crowing at dawn aren\'t just reacting to the external stimulus of light, Japanese researchers say; they actually know what time of day it is. In a study reported in the journal Current Biology, scientists at Nagoya University say there is indeed a clock in \"cock-a-doodle-doo\" -- a biological one. \"\'Cock-a-doodle-doo\' symbolizes the break of dawn in many countries,\" researcher Takashi Yoshimura said. \"But it wasn\'t clear whether crowing is under the control of a biological clock or is simply a response to external stimuli.\" While external stimuli such as a car\'s headlights can cause a rooster to crow at any time of day, the researchers say the morning call is a matter of their responding to their internal clock. Yoshimura and his colleague Tsuyoshi Shimmura placed birds under constant light conditions and found when kept under round-the-clock dim lighting, the roosters were still crowing each morning just before dawn, proof that the behavior is linked to a circadian rhythm. So whether it\'s \"cock-a-doodle-doo\" or \"ko-ke-kok-koh\" as they say in the research team\'s native Japan, roosters are reliable alarm clocks because they\'ve got a clock of their own, the study found.