英语听力文摘761 蛋是如何成色的
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：为什么鸟蛋会有各种各样的颜色?有研究认为是因为蛋壳中胆绿素-IX、胆绿素的锌螯合物、原卟啉-IX这三种色素的比例不同导致。其中，原卟啉-IX色素形成黄色、粉红色、浅红色、淡黄或褐色，而胆绿素-IX以及胆绿素的锌螯合物形成蓝色和绿色，这三种色素按照不同比例，就形成从紫蓝色到橄榄绿等不同颜色。除此之外，鸟蛋的颜色还与其栖息的地方有关系，栖居在洞穴中的鸟，产的蛋大多为白色，其他鸟产的蛋，有着与环境颜色近似的保护色，比如水草丛中筑巢的鸭类的蛋为浅绿色。
