moult

Finches start to moult at around twelve weeks of age.

燕雀大约在12个星期大小的时候开始换羽毛。

When do young swallows have their first moult?

雏燕在什么时候第一次换毛？

After they have begun to breed they may continue to moult.

它们在开始产仔之后可能会继续脱毛。