Once a bird fledges , therefore , it leaves its parasites behind .

因此，一旦鸟长出羽毛，鸡蚤就离开了。

But they do not ( as , for example , lice do ) live on their hosts continually . Once a bird fledges , therefore , it leaves its parasites behind .

但是它们不会一直寄生在它们的宿主身上（虱子才会），当鸟儿羽翼丰满时，鸡蚤就会离开。