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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.
公雞總是以報曉聲來迎接朝陽。但在其它時刻它們也會鳴叫。那么它們是在響應光嗎？還是它們知道天什么時候亮？新的研究應證了后一說法：公雞打鳴是因為“內時鐘”。這項研究發表在《當代生物學》期刊上。
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 wild fowl, the roosters began to crow about two hours before their rooms lit up.
科學家們控制了公雞住所的光照強度。連續兩個星期，先讓公雞們經歷了12個小時的光照，接著是12個小時的微弱光線。公雞在房間被照亮前2個小時就開始鳴叫了，這與在野外觀察到的、公雞黎明前報曉的時間一致。
Then, for two weeks, the roosters lived in constant 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.
然后，讓公雞持續在微弱的光線中度過兩個星期。然而，它們仍然堅持每隔一天，確切來講是23.7個小時報曉一次。即使沒有晨光，它們的生物鐘也會告訴它們什么時候天亮。
The birds also crowed in response to sudden light, and to the sounds of other roosters. But they were more likely to react when those stimuli occurred near dawn. Showing that you can't really keep a rooster in the dark about the time.
為了響應突然亮起來的光線和其它公雞的叫聲，公雞也會鳴叫。然而，當這些刺激發生在黎明，公雞響應的可能性會更大。這說明人們不可能向公雞隱瞞時間。
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