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. The same as the uh brothers in the wild.
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.
Ways of migration
The migration route of birds is the area that birds pass through between the wintering ground and the breeding ground. The factors that determine the migration route of birds include the topography of the ground, the vegetation type, the weather, and the biological characteristics of the birds themselves. The traditional view that migration must be the way south north -west, but banding studies have shown that a large number of migratory birds is way east west trending.
According to the area covered by the migration route of birds, the migratory route of birds can be divided into two types : wide surface migration and narrow surface migration . The so-called wide-faced migration is a group of birds that are widely distributed in their own right. In the process of migration, they migrate toward the destination in a basically consistent direction. The pathways for migration between different individuals are far apart and the entire migration route covers a large area. Narrow-faced migration means that birds that live in a wide range of areas migrate along the same route during the migration process. The entire migration route covers a very small area. Most of the narrow-faced migratory birds have certain requirements on their habitats. For example, the Erhai wading bird can only migrate along the coastline , so as to obtain the recharge sites on the way. Wide-faced migratory birds, due to changes in the characteristics of the surface, will turn into narrow-faced migrations at certain locations. Such sites are often referred to as bird paths . The bird path has important significance in the protection of birds

There are several versions:

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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.

4. Some scientists believe that birds are guided by the position of stars: at least one species of bird knows how to do it. In one scientific study, the birds in the cage were placed in a planetarium, where they reproduced a picture of the starry sky of the Northern Hemisphere. Then they were released, and the star projections began to rotate around the North Star. It was assumed that this movement is informing the birds how to choose the right direction of flight. However, subsequent experiments led to another conclusion: perhaps the reference point for birds is not the immovable polar star, but the location of the constellations. The fewer stars were seen on the improvised planetarium sky, the more birds lost their sense of orientation.