Roosters greet the rising sun with crowing sound.…

Roosters greet the rising sun with crowing sound. But they also crow at other times. So are they 1 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 2 the light levels in rooster habitats. For two weeks, the birds experienced 12 hours of light followed by 12 hours of dim light. 3 with the pre-dawn noises observed in wild fowl, the roosters began to crow about two hours before their rooms lit up. Then, for two weeks, the roosters lived in 4 dim light. Yet they continued to crow about once a day—at intervals of 23.7 hours to be precise. Even without morning light, their circadian rhythms told them when dawn should be breaking. The birds also 5 in response to sudden light, and to the sounds of other roosters. But they were more likely to react when those stimuli 6 near dawn. Showing that you can't really keep a rooster in the dark about the time.