美国科学60秒 SSS 2013-03-25

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　　Roosters greet the rising sun with Ohh, but they also crowed at other times, so are they responding to the light or do they simply know that it's morning. New research sets the lantern.

　　Roosters crowed because of internal time cues. The finding is in the journal Current Biology. Scientists controled the light levels and roosters have a tants. For two weeks the birds experienced 12 hours of light, followed by 12 hours of dim light, consisting with the predawn noises observed in wildfowl. The roosters began to crowed about two hours untill their room is lit up. Then for two weeks the roosters lived in constantly dim light. Yet they continued to crowed about twice a day, and intervals¹ are 23.7 hours, to be precise. Even without morning light, their circadian rhythmstold them when dawn should be breaking. The birds also crowed in respond to sudden light and to the sounds of other roosters. But they were more likely to react to those ... dawn, showing that you can't really keep a rooster in the dark about the time.

　　Thanks for the minute for SSS. I'm Sofie Bushway.

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