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.
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?
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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