Why Do Birds Moult Every Year?

Birds rely on their feathers to fly. After a long time in wind and rains, the feathers are weak and easily broken. Birds can't fly with those broken feathers. Therefore, most birds lose their old feathers and grow new ones every year, but some birds moult twice a year.

Besides, feathers can keep a bird warm, just like clothing keeps people warm. With the change of seasons, some birds moult much like we change clothes, wearing lightweight clothes in the summer, and heavier clothes in the winter. Some birds even change their feather’s colors. in winter, the feathers are light, while in summer they become dark. The changes their colour can also prevent the birds from being attacked. However, birds, unlike people who their clothes consciously, moult instinctively.