Why do migratory birds fly south before winter comes?

For migratory birds, they can resist the cold of winter, but migratory birds don't have this ability. So whenever winter comes, when they move, they will come back when the snow and ice melt and spring comes.

Among migratory birds, there are summer migratory birds and winter migratory birds because of the different migration time. The former usually flies to the north in spring and summer to nest, hatch and raise young.

When autumn and winter come, they will fly back to the south, such as the most common swallows, azaleas and orioles in China. The latter usually flies from high latitude to low latitude in autumn to spend a long winter, such as geese and ducks.

For the "owners" of the latter, they live in places where they were born and raised all the year round, and will not move at will because of the changes of seasons. This kind of bird is a resident.

Extended data

1. Migratory birds fly very fast and can fly 69 ~ 90 kilometers per hour. Their journey is long and they often need to fly for a month or two. In order to save their strength, they often use updraft to glide in long-distance flights, except flapping their wings.

2. The migratory birds in front encourage their wingtips to generate a weak updraft, and the ones behind use the momentum of this airflow to glide in the air. So one by one, naturally formed a neat herringbone or zigzag team.

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