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。

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.

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鸟类、蝙蝠和其他会飞的生物是如何离开地面、保持飞行状态的呢？

How do birds and bats and other flying beasties manage to get off and stay off the ground?

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