Many scientists believe that some birds are guided by the earth’s magnetic field, and homing pigeon is a typical example.
In the age of underdeveloped transportation and communication, people often use pigeons to send messages. When people go on expeditions, even though they are crossing mountains and mountains and rolling for thousands of miles, as long as they tie the letter to the carrier pigeon’s feet and release it, it will quickly identify the direction of going home, fly straight back, and finish the task of delivering family letters excellently.
Carrier pigeon, as a special skill, has attracted people’s interest since the 1940s and has been systematically studied. It is found that homing pigeons are guided by the geomagnetic field.
We know that every point on the earth has its own geomagnetic field strength and Coriolis force generated by the earth’s rotation. Magnetic field for life, just like air and water for life, is indispensable. Air and water, everyone can feel, but no one can feel the magnetic field around. This is because of the long-term evolution of organisms. Has adapted to this physical environment factor. However, carrier pigeons can not only know the intensity of magnetic field and the magnitude of Coriolis force, but also recognize the subtle differences between the intensity of geomagnetic field and Coriolis force at any time. They fly home accurately with this special ability.
In the mid-1970s, Professor Charles Walcott, an American biophysicist, began to find the position of the magnetic compass in pigeons. He first measured the magnetic properties of pigeon tissues, then selected those with magnetic properties, divided them into smaller pieces, and then measured the magnetic properties of each piece in turn. The scope of research gradually narrowed down, and finally found natural magnetic substances in every pigeon’s body.
The researchers put the pigeon’s magnetic tissue under an electron microscope and found that it was made of nerve fibers. There are a lot of dense particles in the tissue that can block the electron beam. The particles are 0.1 μ m long and 0.025 μ m wide. These particles contain a lot of iron, which is the basic element of various magnets. The particles also contain a small amount of nickel, copper, zinc and lead. The composition and proportion of these elements prove that the magnetic substance of carrier pigeon is a kind of magnet. The researchers measured the Curie point of the pigeon’s magnetic material, the temperature at which the magnetic properties of the material disappeared, and found that its Curie point was equal to that of magnetite. At last, the pigeon crystal is observed by optical microscope. The color of the crystal is exactly the black that magnetite should have.
Whether the birds can really identify the direction by the earth’s magnetic force has been a controversial issue for a long time. Now researchers believe that not only birds, fish, insects and even viruses can feel the magnetic field. But how animals perceive magnetic fields remains a mystery.
Two recent studies in the 1990s have shown that light may be an important factor in bird’s perception of magnetic fields. Scientists at the State University of New York found that the sparrow uses aurora to set its magnetic compass and determine its direction. Researchers at the University of Frankfurt in Germany found that some birds, such as silver finches, use light to sense magnetic fields. These views need to be confirmed by further research.