Clock-a-doodle-doo

Scientists in Japan have discovered that the dawn crowing of a rooster is controlled by their internal body clocks, not just by the rising of the sun.

A crowing cock signals the imminent sunrise and the start to a new day. But why does the rooster crow and how does he know when to do it? Nagoya University's Tsuyoshi Shimmura and Takashi Yoshimura wondered whether it's down to the animals' body clocks - circadian rhythms - or simply a response to seeing the sunrise?

The Japanese duo used video cameras and sound equipement to monitor groups of cockerels placed under either a 12-hour light and dim-light cycle, or a constant dim-light condition.

In the 12-hour situation, the birds began to crow about 2 hours before the light was switched on, just as they do in the wild. And when kept under only dim-light they also still crowed most at the pre-dawn period, indicating that they instinctively knew when to crow, even in the absence of any light cue.

Shimmura and Yoshimura also found in these low-light exposed birds that, with each successive day, the cocks crowed a little bit earlier each day. This is a characteristic sign that a process is under internal clock control.

Taking their ideas one step further, the researchers then decided to test whether other external stimuli like light or sound could also make the roosters crow. They found that both light stimulation and the sound of other familiar rooster crows could make the roosters crow if they were given at the onset of the daytime.

Delivered later in the day, however, these stimuli elicited far fewer responses. Moreover, if the stimuli were given during the night-time, the roosters didn't crow at all. This suggests that not only the pre-dawn crow, but also, light and sound-induced crowing, is under the control of the rooster's own body clock.

So, more accurately, we should be talking about clock-a-doodle-doo from these birds...