Washington: Roosters crow at the break of dawn, not in response to the morning light, but because they are genetically programmed to do so, a new study has found.
Until now, it has not been known that when roosters crow with the dawn, are they simply reacting to the environment, or do they really know what time of day it is?
The study published in journal Current Biology, found that a rooster`s crow is controlled by its own internal body clock and does not depend on lighting conditions.
"`Cock-a-doodle-doo` symbolises the break of dawn in many countries. But it wasn`t clear whether crowing is under the control of a biological clock or is simply a response to external stimuli," said Takashi Yoshimura of Nagoya University.
To find out whether the roosters` crowing is driven by an internal biological clock, Yoshimura and his colleague Tsuyoshi Shimmura placed birds under constant light conditions and turned on recorders to listen and watch.
Under round-the-clock dim lighting, the roosters kept right on crowing each morning just before dawn, proof that the behaviour is entrained to a circadian rhythm. The roosters` reactions to external events also varied over the course of the day.
In other words, predawn crowing and the crowing that roosters do in response to other cues both depend on a circadian clock.
The findings are just the start of the team`s efforts to unravel the roosters` innate vocalisations, which aren`t learned like songbird songs or human speech, the researchers said.
"We still do not know why a dog says `bow-wow` and a cat says `meow`. We are interested in the mechanism of this genetically controlled behaviour and believe that chickens provide an excellent model," Yoshimura said.