AsianScientist (Mar. 25, 2013) – When roosters crow at the crack of dawn, do they really know what time it is, or are they simply responding to environmental cues? Writing in the journal Current Biology, a pair of researchers report evidence that a rooster’s crowing is in fact controlled by its circadian clock.
“‘Cock-a-doodle-doo’ symbolizes the break of dawn in many countries,” says Takashi Yoshimura of Nagoya University in Japan. “But it wasn’t clear whether crowing is under the control of a biological clock or is simply a response to external stimuli.” For example, the flash of a car’s headlights can trigger off crowing regardless of the time of day.
When Yoshimura and his colleague Tsuyoshi Shimmura kept roosters on a two-week schedule of twelve hours in the light and twelve in the dark, most “cock-a-doodle-doos” (or “ko-ke-kok-kohs,” if you’re in Japan) were uttered in a two-hour window just before the start of the artificial day.
The researchers then exposed the roosters to round-the-clock dim lighting for another fortnight. Undeterred, the birds stuck to their predawn crowing ritual, following a schedule dictated by their internal biological clocks. This pattern gradually disappeared as their circadian rhythms desynchronized under two weeks of perpetual dim light.
In other experiments, the researchers found that external stimuli – such as light or the sound of other roosters crowing – can set the roosters off throughout the day. However, crowing was most intense when the stimuli were applied in the early morning.
They concluded that the roosters’ circadian clock not only drives predawn crowing, but also controls crowing in response to external stimuli.
Unlike songbird songs or human speech, which are learned, rooster crowing is an example of an innate vocalization. This study is just part of the team’s larger efforts to understand such behavior.
“We still do not know why a dog says ‘bow-wow’ and a cat says ‘meow,'” Yoshimura says. “We are interested in the mechanism of this genetically controlled behavior and believe that chickens provide an excellent model.”
The article can be found at: Shimmura et al. (2013) Circadian clock determines the timing of rooster crowing.
Source: Cell Press; Photo: lincolndisplayimages.com/Flickr/CC.
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