Perhaps the most mysterious and not fully understood to date is the question: how do birds, overcoming such huge distances, arrive precisely at a certain place in which they or their older relatives have already been?
There are several 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. There is evidence that the domestic pigeons really fly following the lines of the Earth’s magnetic field .
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 image has blurry ends and is called the “Haidinger brush” in honor of the inventor who discovered this phenomenon. 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.
In the scientific world, it is generally accepted that all the phenomena and causes described influence the migration routes of birds. And different kinds of birds are guided in one way or another when flying for long distances, or maybe all at once.