英语听力文摘 English Digest 404、自然界的闹钟（在线收听）

Cock-a-Doodle-Do

It’s four A.M. You’re tucked safely into a warm bed, savoring the last few hours of sleep before daybreak. And  then, suddenly… (a rooster crows).

It must be time to wake up, roll out of bed, and tend to the farm. Except it’s four A.M., it’s still dark out, and you’re not a farmer.

It’s that neighbor of yours, the one that for some unimaginable reason keeps a rooster as a pet. A rooster that flaunts the most basic rules of neighborhood etiquette by crowing every morning before sunrise. What gives?

Most people assume that roosters are programmed to crow at the first sign of sunlight to announce the dawning of a new day, or some such romantic notion.

Like all birds, roosters call in a daily cycle determined by circadian rhythms. That is, a rooster’s internal clock allows it to anticipate the sunrise and prepare for another exciting day of looking for food.

But why must roosters crow as they prepare to start their day, and why do some roosters sound off before dawn? Roosters are territorial creatures and don’t much like other roosters trespassing on their land.

They crow in order to establish their domain and warn other roosters to stay away or prepare to brawl. And because their internal clocks are sometimes set a bit early, some roosters begin crowing well before sunrise.

早上四点，你还在温暖的被窝里蜷着，享受着天亮前为数不多的睡眠时间。此刻却听到雄鸡打鸣……

闻鸡起“床”，爬出被窝，开始农作。但是，现在才四点！外面黑咕隆咚的，而且，你又不是农民。

公鸡是隔壁家的，因为什么难以理解的缘由把公鸡当做宠物。每天的黎明前，公鸡都会打鸣，仿佛问候邻居早安。这是为什么呢？

大多数人认为公鸡每当第一缕阳光照耀大地，就按规律打鸣，提示崭新一天的开始。另外，还有很多浪漫的解说。

和其他鸟类一样，生理节律决定了公鸡每天都要打鸣。也就是，公鸡的生理钟让它期待日出，积极地为新的一天觅食。

但是，为什么公鸡会打鸣呢？而且偏偏是在黎明前呢？公鸡有领地意识，自己的领地“决不许其它公鸡侵犯”。

公鸡以此来维护自己的领地，警告其它公鸡远离，否则一场争斗难以避免。又因为公鸡的生理钟有时候设置得早一些，所以，一些公鸡打鸣在日出前。