听力文摘：鸟儿如何睡觉？

How do birds sleep?

鸟儿如何睡觉？

How do birds hang onto trees when they're asleep? Why don't they fall off?

鸟儿睡觉时是如何挂在树上的呢？它们为什么掉不下来？

That's easy. It's because of the hallux toe. Hallux toe? Is that the toe on some birds that points backwards¹ instead of forwards? That's the one. We already mentioned the hallux toe once on the show, when talking about how well-adapted some bird feet are for perching on branches.

很简单！那是因为它们有大趾。大趾？就是某些鸟儿身上指向后方而不是前方的趾头吗？对，就是那个。我们曾在节目中谈论适应性强的鸟儿的脚是如何帮助其栖息于树枝上时，提到过“大趾”。

But you say it holds the bird in place even when it's sleeping. Absolutely! It's because of the way the tendons work in a perching bird's leg. When the bird hunkers down for sleep, it bends its leg at the knee and the heel. Two thin wires, called flexor tendons, run down the leg around the knee and heel, and attach to the toes.

但是你刚刚说大趾能在鸟儿睡觉时助其保持平衡。正是！这与栖息的鸟儿腿里鸟腱运作的方式有关。当鸟儿蹲下睡觉时，鸟腱使鸟腿在膝盖和脚踝弯曲。两根纤细的屈肌腱使腿在膝盖和脚踝处弯曲，然后就与脚趾连接在一起。

The bending of the bird's legs when it perches² tightens³ up these tendons, and, like a puppet's strings⁴, curls the toes. The neat thing is the bird doesn't even have to think about it to make it happen.

鸟儿栖息时，鸟腿的弯曲拉紧了这些屈肌腱，就像是拉动木偶的绳子一样，使得脚趾卷曲起来。有趣的是，鸟儿根本不用去想怎么让其发生。

1 backwards   

adv.往回地，向原处，倒，相反，前后倒置地

参考例句：

• He turned on the light and began to pace backwards and forwards.他打开电灯并开始走来走去。
• All the girls fell over backwards to get the party ready.姑娘们迫不及待地为聚会做准备。

2 perches   

栖息处( perch的名词复数 )； 栖枝； 高处； 鲈鱼

参考例句：

• Other protection can be obtained by providing wooden perches througout the orchards. 其它保护措施是可在种子园中到处设置木制的栖木。
• The birds were hopping about on their perches and twittering. 鸟儿在栖木上跳来跳去，吱吱地叫着。

3 tightens   

收紧( tighten的第三人称单数 )； （使）变紧； （使）绷紧； 加紧

参考例句：

• One set of provisions tightens emission standards. 一套使排放标准更加严格的规定。 来自英汉非文学 - 环境法 - 环境法
• Requires no special tools or fittings; hand tightens to relief valve outlet. 不需要专用工具或管件；用手将其紧固到安全阀上即可。

4 strings   

n.弦

参考例句：

• He sat on the bed,idly plucking the strings of his guitar.他坐在床上，随意地拨着吉他的弦。
• She swept her fingers over the strings of the harp.她用手指划过竖琴的琴弦。