What happened to the yellow waist willow and warbler tail hair

The yellow waist willow and warbler tail hair falls.This kind of bird has changed from March each year, and some will be in July.When changing the hair, you must be calm, you must not interfere with it, and at the same time, avoid wind blowing, so as not to get cold.In addition, you can't take a bath at this time, which will also increase the possibility of getting sick. It is best to feed some green feed, which is very helpful to the growth of feathers.