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Cockerel’s internal clock

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The timing of a cockerel’s crow is largely controlled by its own circadian rhythm, and influenced only to a lesser extent by external stimuli such as light and sound.

Japanese researchers, writing in Current Biology, showed that predawn crowing is under the control of a circadian clock, and while light and crowing by other birds also influence crowing, the magnitude of this induction is regulated by a circadian clock.

The researchers kept cockerels under constant conditions of 12 hours light and 12 hours dark. The roosters crowed about two hours before the onset of light. Under conditions of constant dim lighting they crowed according to a free-running rhythm of around 23.7 hours. Since crowing is an androgen-dependent behaviour, implanting the cockerels with testosterone made this rhythm more prominent.

The researchers also found that higher intensity light increased the amount of crowing immediately after light onset, and if the sound of other roosters crowing was played more loudly it also increased crowing in a dose-dependent manner. Light and sound given together had an additive effect.

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From: Beyond pharmacy blog

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