In their experiment, Shimmura and Yoshimura took roosters and enclosed them in a room where no sunlight could penetrate. Then they subjected the birds to two sets of light. At first, they got 12 hours of bright light and 12 hours of dim light. In the second, the roosters got a steady dose of dim light. In both experiments, the crowing began just a few hours before the supposed dawn.
The research indicates that the timing of roosters’ crowing is set off by the bird’s internal clocks and not by any external factor. To confirm the findings, the researchers subjected the birds to various other stimuli, such as spotlights and subjecting them to various sounds. Still, the birds began crowing in the early morning.