The issue of bird flights can be divided into two:
1. Why birds annually migrate to foreign lands?
2. Why they come back, do not stay where they were quite good?
The questions are as interesting as difficult to answer!
Long flights of birds explained only one: in the winter they are cold and need to change the climate. However, oddly enough, the temperature itself is not the cause of flights. Feathers may well protect the bird from the cold. For example, a Canary can survive a frost of up to -45°C, if it will have enough food.
It is now believed that in winter, birds migrate to warmer climes in winter, barren. Birds very quickly expend the energy they get from food, and this means that they need a lot. Therefore, when the ground freezes and food is hard to find, especially insectivorous birds, many of them heading South.
Proof that birds "drives" to the South of the lack of food, is this fact: if food is in abundance, some birds even in the cold don't leave places where he was born.
However, this response should not be considered exhaustive. Migratory birds, their behavior is asked of us many mysteries that we cannot fathom.
For example, the swallow leaves cold edge to pass the winter in Africa or Asia, under a cloudless summer sky. But why did she flies over the whole of Africa, then how can find warmer climes and closer?
Sometimes shearwaters fly from Antarctica to the North pole. What here for warmth!
And many tropical birds that are not threatened nor cold, nor hunger, vicrmin Chicks, go on a long journey. Grey valiant men, for example, (he looks like a little on our Shrike) each year visit the Amazon valley and back to the West Indies, when it comes time to reproduce.
If scientists are still not clear about the reasons why birds fall from their homes in warmer climes, the question of why they return back to the North with the fertile South, it is even more difficult.
It is believed that when the autumn pores in the South for birds and their offspring experiencing adverse conditions. For example, in the tropics and the equator such frequent storms, just don't know which country's temperate climate. Moreover, the number of stormy days there's much more than we have, dozens of times. Birds that fly in India and subtropics, have in the summer to escape from the dry season.
White owl breeds in the tundra, where cold summer, the climate is humid and a lot of lemmings, which the owl eats. Winter she spends in the forest-steppe of the middle band. Could this owl to stay for the summer in a hot dry desert, where few usual for her food? Of course, no. It flies in the native tundra.
Partly cravings to return home can be explained by internal changes in the body of the bird. When the breeding period, the glands under the influence of external stimuli produce in the body bird special substances - hormones. Under the influence of hormones starts and runs seasonal development of the sex glands. This, apparently, and encourages birds to flight.
Another reason for returning birds home is that birds in the summer profitable breed offspring in the middle latitudes, because here in the summer the days are longer than in the South. And migratory birds are diurnal lifestyle, and a long day gives them more opportunities to feed offspring.