Why do migratory birds migrate?

Posted on Mar 9, 2022      279

The question of bird migrations can be divided into two:

1. Why do birds fly away to foreign lands every year?

2. Why do they fly back, not stay where they were well?

The questions are as interesting as they are difficult to answer!

For a long time there was only one explanation for the migrations of birds: they feel cold in winter and need a change of climate. However, strange as it may seem, temperature alone is not the reason for migrations. Feathers can protect birds from the cold well. For example, a canary can survive the cold to -45 degrees Celsius if it has enough food.

Now it is believed that birds fly away to warmer lands in winter from winter starvation. Birds use up the energy they get from food very quickly, which means they need to eat often and a lot. So when the ground freezes and food is hard to find, especially for insectivorous birds, many of them head south.

The proof that birds are driven south by the lack of food is this: if food is plentiful, some migratory birds do not leave the place where they were born, even in frosty weather.

This answer cannot be exhaustive. Migratory birds with their behavior ask us a lot of mysteries, which we can’t solve yet.

For example, the swallow leaves the cold to spend the winter in Africa or Asia, under a cloudless summer sky. But why does it fly over all of Africa, then how can it find warmer climes even closer?

Petrels fly from the Antarctic to the North Pole. What a search for warmth!

And many tropical birds, which are not threatened by either cold or hunger, having nursed their chicks, set off on their long journeys. The gray tyrant, for example, (it looks a bit like our shrike) visits the Amazon jungle every year and returns to the West Indies when it is time to breed.

If scientists are still unclear about the reasons birds leave their homes for warmer climes, the question of why they return north from the bountiful south is even more difficult.

It is believed that when the autumn season arrives in the south, conditions are unfavorable for birds and their offspring. For example, thunderstorms are frequent in the tropics and at the equator, which countries with temperate climates simply do not know. Besides, the number of thunderstorm days there are dozens of times greater than here. Birds that migrate to India and the subtropics are forced to flee the dry season in the summer.

The Snowy Owl nests in the tundra, where summers are cold, climates are humid, and there are plenty of lemmings for the owl to feed on. It spends the winter in the middle forest-steppe. Can this owl stay for the summer in the hot, dry steppe, where its usual food is scarce? Of course not. It flies away to its native tundra.

The urge to return home can be partly explained by internal changes in the bird’s body. When the breeding season comes, the endocrine glands secrete special substances - hormones under the influence of external stimuli. Under the influence of hormones begins and passes seasonal development of sex glands. This, apparently, is what drives the birds to migrate.

Another reason birds come back home is that it is more profitable for them to breed in the middle latitudes in summer because the days here are longer than in the south. And migratory birds have a daytime lifestyle, and a long day gives them more opportunity to feed their offspring.