One: use the position of the sun to identify the direction.
At first, it was assumed that pigeons used the position of the sun to identify their own position, and that pigeons had the ability to distinguish their nests according to the position of the sun. When a pigeon flies to a strange place, it can infer the height of the sun at noon by measuring a small part of the sun's orientation, and compare it with the height of the sun it last saw in the nest area to infer that it is in the south or north of the nest area, and determine its east-west direction by measuring the orientation of the nest area and the moving area. But there is no evidence that pigeons can determine the specific location by determining the longitude. At present, it is agreed that only the sun can guide the direction. But people who disagree with this assumption will ask: pigeons can fly on cloudy or rainy days or even at night. What does it rely on to orient itself?
Second: infrasound theory.
Someone put forward infrasound theory. They believe that pigeons are highly sensitive to infrasound and can distinguish sounds that are difficult for humans to hear from a distance. Experiments also prove that pigeons are particularly sensitive to infrasound, that is, extremely low-frequency sound waves, but people can't prove how they use this unique ability to navigate. If they can distinguish the cries of their companions in Qian Qian from a few meters away, their hearing ability seems out of reach. In this respect, the problem is not so simple.
Three: Identify the direction by smell.
Some people pay attention to the olfactory organs of pigeons, and think that each area has an olfactory map composed of volatile odor substances in a specific way. They think pigeons can pass through this area and leave a smell. This special smell can form an invisible network in the air and find out "landmarks".
After this hypothesis was put forward, German scholars did a lot of verification. In the experiment, they anesthetized the olfactory organs of pigeons and stuffed their noses with wax. However, after the experimental pigeon was released, it flew back to the nest smoothly, and the hypothesis of locating by smell was overthrown.
Four: magnetic theory.
Later, scientists tried to explain the pigeon's directional ability with magnetic theory. In a vast area, the earth's magnetic field changes with different places and directions. So as to provide position information for pigeons. Magnetic field strength, magnetic dip angle and magnetic declination angle can form a highly non-orthogonal network with each other. These components are almost constant in an area of several hundred kilometers. But it changes gradually all over the surface of the earth. The gradient network formed by these changing components is called navigation chart, which can be used for orientation. Experiments in recent years have confirmed the existence of magnetic navigation. When the artificial magnet with specific polarity is added to the head of the pigeon bomb, the pigeon's flight cannot be oriented correctly; Whenever the solar proton activity is intense, the earth's magnetic field is disturbed, and the homing rate of pigeons is greatly reduced. In addition, the preliminary research results show that there is a needle magnet with a length of about 0. 1 micron in the forebrain under the skull of pigeons. They think pigeons can use geomagnetism to determine their own direction. They have the ability to detect the four basic points of the earth and can receive the changing signals fed back by the magnetic field. However, some people think that these changes are extremely subtle, and whether pigeons can feel these subtle changes needs full proof.
But experiments have proved that magnetic induction can affect pigeons. William Keelen, an American scholar, tied a small magnet to the pigeon's head and found that if it was sunny, it didn't seem to have much impact. On cloudy days, homing pigeons become a little confused and can't find the right direction. Although this experimental result does not reveal the mystery of homing pigeon orientation, it opens up a new way for research from another angle.
The above assumptions can only explain the orientation of one aspect. In short, when pigeons spread their wings and fly to the blue sky and the sea of clouds, they look so confident and calm that no one will doubt their ability to tell the direction. Therefore, pigeons have been friends and faithful messengers of mankind for thousands of years.