爲什麼鳥類的蛋的顏色各異?
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.
根據種類的不同，鳥類的蛋的顏色也各異，從白色的雞蛋，到藍色的知更鳥蛋，還有有條紋的、斑點的、鮮亮的、淺色的，以及其它介於這些顏色的蛋。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.
當蛋順着雌性鳥類的輸卵管向外移動時，連接卵巢和外界的管道會擠壓腺體產生色素，這些共同作用下，蛋殼就染上了各種各樣的顏色。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.
如果蛋在接觸顏色腺體時是靜止的，它就會染上斑點。如果蛋是運動的，則會染上條紋。
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.
爲何要如此大費周章的給蛋上色呢？對許多露天築巢的鳥類來說，蛋的顏色有隱身的作用，可以藉着顏色與外界融爲一體。
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.
有顏色的蛋還有另一個作用，那就是對諸如海鷗之類的鳥來說，它們能夠識別蛋上的獨特印記，以丟棄那些不屬於自己的蛋。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.
相反的，在洞裏築巢的鳥，或是一生下蛋就開始孵化的鳥，它們不需要把蛋藏起來，因此更容易生下沒有顏色的白色的蛋。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.
既然這樣，科學家又怎麼解釋有着顯眼純藍色的知更鳥蛋呢？或許是因爲當寄生鳥把蛋下在知更鳥的巢裏時，這會幫助知更鳥區分出它們。
