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If you were a bird, how big could you be? Well, an ostrich can weigh 400 pounds—but it can't get off the ground. So what if you want to fly? University of Washington scientists say it depends on how fast you can replace your flight feathers when you molt. The report is in the journal Public Library of Science Biology.
如果你是一只鳥，你能長到多大呢？鴕鳥倒是能長到400磅，但是它不能飛離地面。那么，你如果想飛，你的體重該保持在什么水平上呢？華盛頓大學的科學家們說，這取決于你在換羽期間更換飛羽的速度。這項研究刊載在《生物科學公共圖書館》雜志上。
Feathers don't last forever. So birds periodically shed their plumage and then sprout replacements. Small birds molt once or twice a year, and they replace their 9 or 10 primary flight feathers a few at a time over the course of a few weeks.
鳥的羽毛不會永遠光潔如新，鳥類必須周期性的進行換羽，長出新的羽毛。小型鳥類一年進行一到兩次換羽，在換羽期間，它們一次會替換掉9到10根左右的飛羽，而這個過程將持續幾周時間。
But bigger birds need bigger feathers. And that's where the problem comes in. As birds increase in size, the rate at which they grow their feathers doesn't keep up with their longer feather length. So if big birds tried to do like little birds, they'd spend the whole year molting—leaving little time for finding food or mates.
但是較大體型的鳥類需要更大的羽毛，這就是我們討論的問題所在了：鳥類的體型增長時了，但它們新羽毛生長的速度不足以使新生羽毛達到舊羽毛那樣的長度。所以，如果大型鳥類要以小型鳥類那樣的方式換羽的話，它們就不得不花上整年的時間來做這件事，也就沒有什么時間來覓食或繁殖了。
Some large birds, like honking big geese and 30-pound swans, get around the problem by forgoing flight while they get all their molting over with in one fell swoop. In other words, these birds of a feather defrock together.
一些大型鳥類，像是大雁或是體重能夠達到30磅的天鵝，是以放棄飛行能力來解決換羽的難題的。換句話說，這些鳥類是一次性褪光所有羽毛的。
