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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.
如果你是一只鸟，你能长到多大呢？鸵鸟倒是能长到400磅，但是它不能飞离地面。那么，你如果想飞，你的体重该保持在什么水平上呢？华盛顿大学的科学家们说，这取决于你在换羽期间更换飞羽的速度。这项研究刊载在《生物科学公共图书馆》杂志上。
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.
鸟的羽毛不会永远光洁如新，鸟类必须周期性的进行换羽，长出新的羽毛。小型鸟类一年进行一到两次换羽，在换羽期间，它们一次会替换掉9到10根左右的飞羽，而这个过程将持续几周时间。
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.
但是较大体型的鸟类需要更大的羽毛，这就是我们讨论的问题所在了：鸟类的体型增长时了，但它们新羽毛生长的速度不足以使新生羽毛达到旧羽毛那样的长度。所以，如果大型鸟类要以小型鸟类那样的方式换羽的话，它们就不得不花上整年的时间来做这件事，也就没有什么时间来觅食或繁殖了。
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.
一些大型鸟类，像是大雁或是体重能够达到30磅的天鹅，是以放弃飞行能力来解决换羽的难题的。换句话说，这些鸟类是一次性褪光所有羽毛的。
