60秒科学:Molting Molds Flying Bird Size Limit

Molting² Molds Flying Bird Size Limit

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. Karen Hopkin reports.

[The following is an exact transcript³ of this podcast.]

If you were a bird, how big could you be? Well, an ostrich⁴ 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 molt¹. The report is in the journal Public Library of Science Biology.

Feathers don’t last forever. So birds periodically shed their plumage and then sprout⁵ replacements⁶. 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. [“Hey, whaddya doing?” “Still molting.”]

Some large birds, like honking⁷ big geese and 30-pound swans, get around the problem by forgoing⁸ flight while they get all their molting over with in one fell swoop⁹. In other words, these birds of a feather defrock together.

—Karen Hopkin

1 molt   

n.换毛，脱皮，换毛期

参考例句：

• The fourth time they molt,they change into pupae.换第四次皮时，它们蜕变成蛹。
• This veterinary product is very effective in preventing animal molt.这种兽药对于防治兽类掉毛很有效。

2 molting   

n.蜕皮v.换羽，脱毛( molt的现在分词 )

参考例句：

• The old cuticle is digested by molting fluid. 旧表皮被蜕皮液消化。 来自辞典例句
• Molting in insects is triggered by rising levels of a hormone called ecdysone. 昆虫的脱皮是由于称为脱皮素激素的含量升高而引起的。 来自辞典例句

3 transcript   

n.抄本，誊本，副本，肄业证书

参考例句：

• A transcript of the tapes was presented as evidence in court.一份录音带的文字本作为证据被呈交法庭。
• They wouldn't let me have a transcript of the interview.他们拒绝给我一份采访的文字整理稿。

4 ostrich   

n.鸵鸟

参考例句：

• Ostrich is the fastest animal on two legs.驼鸟是双腿跑得最快的动物。
• The ostrich indeed inhabits continents.鸵鸟确实是生活在大陆上的。

5 sprout   

n.芽，萌芽；vt.使发芽，摘去芽；vi.长芽，抽条

参考例句：

• When do deer first sprout horns?鹿在多大的时候开始长出角？
• It takes about a week for the seeds to sprout.这些种子大约要一周后才会发芽。

6 replacements   

n.代替( replacement的名词复数 )；替换的人[物]；替代品；归还

参考例句：

• They infiltrated behind the lines so as to annoy the emery replacements. 他们渗透敌后以便骚扰敌军的调度。 来自辞典例句
• For oil replacements, cheap suddenly looks less of a problem. 对于石油的替代品来说，价格变得无足轻重了。 来自互联网

7 honking   

v.（使）发出雁叫似的声音，鸣（喇叭），按（喇叭）( honk的现在分词 )

参考例句：

• Cars zoomed helter-skelter, honking belligerently. 大街上来往车辆穿梭不停，喇叭声刺耳。 来自《简明英汉词典》
• Flocks of honking geese flew past. 雁群嗷嗷地飞过。 来自《现代汉英综合大词典》

8 forgoing   

v.没有也行，放弃( forgo的现在分词 )

参考例句：

• Everything, in short, is produced at the expense of forgoing something else. 总之，每一种东西的生产，都得以牺牲放弃某些其他东西为代价。 来自互联网
• These aren't the only ones forgoing the morning repast, of course. 当然，他们并不是放弃早餐的唯一几个。 来自互联网

9 swoop   

n.俯冲，攫取；v.抓取，突然袭击

参考例句：

• The plane made a swoop over the city.那架飞机突然向这座城市猛降下来。
• We decided to swoop down upon the enemy there.我们决定突袭驻在那里的敌人。