飞行鸟类的大小取决于羽毛更换速度

A study in the journal Public Library of Science Biology finds that it's the rate at which flying birds can replace their flight feathers that determines how big they can grow and still get off the ground.
发表在《科学公共图书馆；生物》（Public Library of Science Biology）杂志上的一项研究发现，决定飞行鸟类到底能长到多大而且还能够飞起来的因素是它们更换飞行羽毛的速度。

Molting Molds Flying Bird Size Limit

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.

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.

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.

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.

羽毛更换速度决定了飞行鸟类的大小

如果你是一只鸟，你能长到多大呢？一只鸵鸟能长到400磅——但是它飞不起来。因此如果你想飞起来的话，可以长到多大呢？来自华盛顿大学（University of Washington）的科学家们说，这取决于在换羽的时候，你更换飞行羽毛的速度。该项研究发表在《科学公共图书馆；生物》（Public Library of Science Biology）杂志上。

羽毛不可能永远使用下去。因此鸟儿们定期地脱落羽毛，然后更换为新的羽毛。形体小的鸟儿一年脱羽一到两次。它们有9到10只主要用于飞行的羽毛，鸟儿们一次更换几只，在几周的时间内它们就可以完成更换。

但是个头大一些的鸟儿需要更大的羽毛。这就是问题的来源。随着鸟儿个头的增大，它们更换羽毛的速度跟不上羽毛生长的速度。因此如果个头大的鸟儿想和小的鸟儿一样更换羽毛的话，它们就会把整个时间用于换羽---这就没有时间用于寻找食物和交配了。

有一些大的鸟儿，比如爱叫唤的大鹅和体重达30磅的天鹅，它们解决这个问题的方法是一次性换掉它们的羽毛的时候放弃飞行。换句话说，这类鸟儿们一起被“免去”了飞行的能力。了。

Vocabulary:

Molt：换羽
Ostrich：鸵鸟
Periodically：周期性地
Shed：蜕；落
Plumage：羽毛
Sprout：发芽
Replacement：替代
Honk：按喇叭；鹅叫
Goose: 鹅；复数形式为geese
Forgo: 放弃
Swoop: 俯冲
Defrock：免去
此文章由小虹提供，佳禾外语进行整理。　

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