Roosters crow at dawn due to their internal clock and not the rising sun, researchers have found.
"'Cock-a-doodle-doo' symbolizes the break of dawn in many countries," scientist Takashi Yoshimura of Nagoya University said in a statement, according to LiveScience. "But it wasn't clear whether crowing is under the control of a biological clock or is simply a response to external stimuli."
In a study published today in the journal Current Biology, Yoshimura explained how he and his fellow researchers solved the mystery.
The researchers placed several groups of four roosters in a room with no light and observed that they crowed roughly every 24 hours, Smithsonian Magazine reported. That indicates that crowing is triggered by an internal circadian clock, rather than external conditions, according to LiveScience.
After about two weeks, the roosters' crowing diminished and occurred at irregular times, suggesting that roosters need to see the sun for their circadian rhythms to function normally, Smithsonian Magazine reported.
In another part of the experiment, the researchers studied how the roosters responded to flashes of light or the crows of their fellow chickens, Smithsonian Magazine reported. They found that the stimuli often had no effect unless it occurred around daybreak.