Every autumn, flocks of migratory birds rise into the sky, the air is filled with noisy hubbub. Sometimes, in order to rest, they sit on the nearest wires or trees, leaving no free space on them. After that, the flocks again rise into the air, and they fly, most likely, to the south.
When asked why the birds fly away, the first answer that comes to mind is because they are getting too cold. But this is not the case. The structure of a bird's feather is such that a layer of down is located near the body, which allows birds to stay warm even at very low temperatures. On the outside, the feathers are covered with a thin layer of sebum, which prevents them from scattering from the wind, and also does not get wet in water. For example, ducks can swim even in the coldest weather and stay warm. So, the reason is not the cold, then what is it? Most bird species leave their homes at the onset of autumn for a completely different reason. They have nothing to eat. Almost all birds feed on insects, which hide or die when cold weather sets in. The birds can no longer easily find food for themselves. This is the main reason, scientists believe, for birds such as swallows or wild geese. In southern countries it is warm, insects do not hide from the cold there, so you can safely spend the winter there. Storks and herons, which feed on frogs, also leave cold places when their water bodies freeze over. At the same time, the practice of flights is so ingrained in many species of birds that they do not wait until it gets colder and there is no food left at all. They begin to prepare for a long journey back in August, guided by the fact that the length of the day has already decreased. During migration, birds cover different distances, it depends on their species and on where the flock is heading. Different birds fly from 40 to 1000 km per day. In cities and near human settlements, some birds do not fly away anywhere, since they are used to eating what remains of humans. In winter, they have enough food remnants found among the garbage, so they may not leave their usual places. There are also just sedentary species of birds that do not fly anywhere in the fall at all. For example, these are sparrows. Some scientists believe that birds experience a special kind of anxiety in the fall. It is due to the fact that the Earth's magnetic field changes slightly, becomes stronger, and this puts pressure on the birds. Their metabolism is very fast, so they react very sharply to such changes. Experiencing anxiety, the birds want to quickly leave the unpleasant territory. By the way, in order not to get lost, during migration, bird flocks are guided by nothing more than the lines of the Earth's magnetic field.