For example, summertime garden warblers were believed to transform into black caps every winter.

比如，一般相信，夏季的园林莺每年冬季时会转变成黑头莺。

The same is true of individual species such as the garden warbler, bullfinch and swallow.

相同的情况也适用于个别物种，如园林莺、红腹灰雀、燕子。