Despite chickens being domesticated for 10,000 years, the function of their characteristic crowing calls is not fully understood
The ‘cock-a-doodle-doo’ sound made by a rooster is unmistakeable, but so far there are only theories as to why they do it. Screeching out booming calls first thing in the morning might help a cockerel mark his territory or attract females.
The trigger for these early morning shouting matches is rather interesting. Although a cockerel can crow at any time, they are famously noisy at daybreak. Scientists tested to see whether the trigger was the appearance of the sun or something in the bird’a brain by housing a group of roosters in the dark.
For two weeks the birds crowed every morning at the same time, and at regular 24 hour intervals every day. After the first 14 days, their crowing became less regular. By the end of the four-week experiment the roosters stopped crowing full stop. This suggests that cockerels have an internal clock, but need regular access to light to keep it in time.
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Image from commons.wikimedia.org/wiki/rooster