Twice a year, residents of northern latitudes witness such a natural phenomenon as the arrival and departure of migratory birds. At the beginning of the year, this event is a symbol of the onset of spring, and in autumn - the approach of cold and frosty weather. In fact, even bird watchers do not have a definite answer to the question of why birds fly south every year. There are several versions explaining the reasons for this phenomenon.
For example, O. Bondarenko, a scientist working in the fields of natural science and non-academic philosophy, associates the constant migration of birds with the earth's magnetic field. He explains this by the fact that biological processes occur in the body of birds at an increased rate. This is what ensures their high muscle mass and allows them to fly. The processes that occur annually - incubation and feeding of chicks, loss of fat mass and a change in the balance between fat and muscles, make them fly to the equator, where the influence of the earth's magnetic field is less noticeable. Having gained weight in winter, they begin to feel discomfort in the low magnetic field and are forced to fly north again.
But the more reliable theory seems to be that most birds simply have nothing to eat in winter and, in addition, not all of them can survive the cold. Therefore, wild waterfowl, swallows, thrushes, starlings that feed on insects are simply deprived of the food they need so much in winter. An indirect confirmation of this is that those species that can provide themselves with food do not fly away.
Those forest birds that feed on insect larvae hidden in the bark of trees, or berries growing wild on bushes, may well feed in the winter months. Some species have adapted to life in cities, and their food does not depend on the season at all. These are pigeons, crows, sparrows and tits. They have adapted to life next to humans and now do not lack food either in winter or in summer.
Some bird watchers believe that the factor that influenced the adaptability of birds to living conditions in cold weather is the risk of survival. Those species of birds in which the number of individuals surviving during the flight will be greater than during frosty wintering have chosen this way of preserving the species. Others, those for whom the flight threatens a large loss of individuals, chose to winter at home.