The fact that it’s time to fly away, the birds determine by their biological clock. What is a “biological clock”? Inside every living organism, be it a bird or a person, there are rhythms set by nature. They have developed over millions of years of life on Earth and depend on the daily cycles. For example, all day animals sleep at night. And they want to sleep at this time, even if at night it will be light, and in the afternoon they have already slept. Their body “believes” the time of the onset of this night and it can not bring down that the light is turned on. This applies to everything: not only sleep, but also the time when food is better digested, the time of the greatest mental activity, etc. etc.
In birds, a biological clock is much more sensitive than a human. And when the sunny day is shortened, the birds know that it’s time to fly away for the winter. Experiments were carried out – they caught wild birds, kept them warm, fed well. It would seem, why should they fly somewhere for the winter? But as soon as the time of flight came, birds in captivity began to restlessly behave, they had “flight” behavior. Conduct an experiment with the baby to monitor the increase in daylight hours. Every day, record the time of sunrise and sunset (for this I made this table, at the click it can be enlarged and copied for printing). And in a week or two you will notice a difference in the measurements. By the way, it is not necessary to “catch” the moment of sunrise-sunset. It is possible, for example, as we did – to record the time when the first sun rays appear on the loggia and when the sun leaves it. Every day this time begins all earlier and lasts longer.
There are several other versions:
1. The simplest assumption: birds know where to fly, as older individuals have studied the topography of the route during past trips . However, such an explanation is doubtful, since the migratory routes of most species lie above the monotonous landscapes of land or water without any features that could serve as direction indicators for the pack. Moreover, this unlikely version arose from the assumption that the conscious and cognitive processes in the head of birds are similar to human ones.
2. The second explanation is related to the magnetic fields of the earth, which birds are able to determine. Scientists have discovered tiny crystallites of magnetite in the organs of the sense of smell of certain species of birds.
3. The following hypothesis suggests that birds can distinguish between the polarization of sunlight. Some light waves are scattered in the atmosphere, and some pass through it. The result is a picture of the polarization in the form of a butterfly hovering in the blue sky. . The wings of the “butterfly” are oriented to the north and south and are visible at sunset. Although birds may not see the shape of polarized light, they can distinguish the gradation of polarization, which, like a compass, indicates the direction they need.