蛋是如何成色的【阅读听力】

困得不行

How Eggs Get Their Color 

Egg Dye

Depending on the species, bird eggs can be any color ranging from chicken’s plain white to a robin’s blue, streaked, spotted, bright, pale, and anything in between.

As the egg moves down the female’s oviduct, the tube that connects the ovary to the outside, it squeezes against glands that produce colored pigments that combine to form every color in the egg shell spectrum. If the egg is stationary at the time that it comes in contact with these glands, it’ll be spotted. If the egg is in motion, it will be streaked.

With Flying Colors

So why go through all the trouble of producing colored eggs? For many species of birds that nest out in the open, the eggs’ colors help to conceal them by enabling them to blend into the background. Another way that colored eggs come in handy, is that in some species, like murres, individual birds learn to recognize their own particular markings and reject eggs that don’t match. In contrast, birds that nest in cavities, or that start incubating as soon as the egg is laid and consequently don’t need to hide their eggs, tend to lay unmarked white ones.

Given all this, how do scientists explain the fact that robin’s eggs are an eye-catching, unmarked blue? Perhaps this enables robins to spot when a parasitic bird tries to add its own eggs to the nest. For some species, this may pose a greater threat than that of nest robbers.

译文：

蛋是如何成色的

根据种类的不同，鸟类的蛋颜色各异，从白色的鸡蛋，到蓝色的知更鸟蛋，还有条纹的、斑点的、鲜亮的、浅色的，以及其它介于这些颜色的蛋。

当蛋顺着雌性鸟类的输卵管向外移动时，连接卵巢和外界的管道会挤压腺体产生色素，这些共同作用下，蛋壳就染上了各种各样的颜色。如果蛋在接触颜色腺体时是静止的，它就会染上斑点。如果蛋是运动的，则会染上条纹。

大获全胜

为何要如此大费周章的给蛋上色呢？对许多露天筑巢的鸟类来说，蛋的颜色有隐身的作用，可以借着颜色与外界溶为一体。有颜色的蛋还有另一个作用，那就是对诸如海鸥之类的鸟，它们能够识别蛋上的独特印记，以丢弃那些不属于自己的蛋。相反的，在洞里筑巢的鸟，或是一生下蛋就开始孵化的鸟，它们不需要把蛋藏起来，因此更容易生下没有颜色的白色的蛋。

既然这样，科学家又怎么解释有着显眼纯蓝色的知更鸟蛋呢？或许是因为当寄生鸟把蛋下在知更鸟的巢里时，这会帮助知更鸟区分出它们。对于一些鸟类来说，鸠占鹊巢比被抢了老窝更危险。

【本译文由普特网友阿福歪歪提供】