Roosters' Crowing

Roosters greet the rising sun with crowing sound. But they also crow at other times. So are they responding to the light? Or do they simply know that it's morning? New research says the latter: roosters crow because of internal time cues. The finding is in the journal Current Biology. Scientists controlled the light levels in rooster habitats. For two weeks, the birds experienced 12 hours of light followed by 12 hours of dim light. Consistent with the pre-dawn noises observed in wildfowl, the roosters began to crow about two hours before their rooms lit up. Then, for two weeks, the roosters lived in constant dim light.