英語聽力文摘761 蛋是如何成色的

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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.

PS：為什么鳥蛋會有各種各樣的顏色?有研究認(rèn)為是因為蛋殼中膽綠素-IX、膽綠素的鋅螯合物、原卟啉-IX這三種色素的比例不同導(dǎo)致。其中，原卟啉-IX色素形成黃色、粉紅色、淺紅色、淡黃或褐色，而膽綠素-IX以及膽綠素的鋅螯合物形成藍(lán)色和綠色，這三種色素按照不同比例，就形成從紫藍(lán)色到橄欖綠等不同顏色。除此之外，鳥蛋的顏色還與其棲息的地方有關(guān)系，棲居在洞穴中的鳥，產(chǎn)的蛋大多為白色，其他鳥產(chǎn)的蛋，有著與環(huán)境顏色近似的保護(hù)色，比如水草叢中筑巢的鴨類的蛋為淺綠色。