Why do pigeons go home?

As early as the Babylonian period, humans began to use homing pigeons to deliver letters over long distances. Pigeons can find their way home from thousands of miles away, which is a bizarre ability. This instinct of pigeons aroused people's interest in studying this ability, but how this bird found its way home has always been an unsolved mystery.

The authoritative explanations are acute sense of smell and detecting magnetic field. Now, after decades of investigation and research, scientists have confirmed that the pigeon's upper beak does have a unit cell that can induce magnetic field, and it is this organ that guides the pigeon's flight.

. The report of this study was published in Nature on1October 25th, 165438.

keep a secret

Recently, after a series of detailed behavioral experiments in the laboratory, scientists announced that they had clearly proved for the first time that pigeons have magnetic sensing ability, just like a simple magnetic compass, which uses the earth's magnetic field to navigate pigeons and perhaps other birds and turtles. Dr. Kaddoura Nora, a biologist at the University of North Carolina in the United States, said at the Chapel Hill Academy of Arts: "There are two main theories about pigeons' ability to find their way home: one is that pigeons find their way home by smell; The other is that they have a magnetic map in their brains. Our work strongly supports the latter theory. Of course, this theory needs further proof. "

This research on pigeons is a doctoral research project in Nora, New Zealand. The report of this study was published in Nature on1October 25th, 165438. The other authors of the research report are Dr. Michael Walker, Dr. Michael Davidson and Dr. Martin Weil from the University of Auckland, New Zealand.

Dr Kenneth Roman, a famous professor of biology at the University of North Carolina, said: "This is a fascinating study. In this study, Nora trained some homing pigeons that can respond to magnetic fields. This is an important news in biology, because some people have done many experiments on 10 in the past few years, but they all failed. Nora was the first person to find an effective method. "

The experiment was carried out like this.

Nora said that in the experiment, if pigeons accurately find two platforms in a room similar to a tunnel, they will get food rewards. Under normal circumstances, they will climb to either platform to find food. But when horseshoe magnets are placed above and below the food platform to induce them, these pigeons will find food accurately. The accuracy rate reached 75%. This is much more accurate than their random search for food.

Knowing that pigeons can respond to magnetic field stimulation, Nora's next step is to find out where the magnetic field receptors are in pigeons.

They first tied a small strong magnet to the pigeons' beaks, and as a result, these pigeons found the wrong platform more than half the time. When they tied a piece of brass with the same weight but no magnetic force to the pigeon's mouth, the result had no effect. Then, they locally anesthetized the pigeon's upper beak and cut off the trigeminal nerve of the eye, and found that these would weaken the pigeon's ability to detect magnetic fields. But when the olfactory nerve that transmits olfactory information is cut off, it will not weaken the pigeon's ability to perceive magnetic field. Through these experiments, Nora thinks that the pigeon's magnetic field perception ability lies in the nose area. Nora said: "In the experiment, we know that pigeons have the ability to recognize magnetic fields. However, this ability can also be weakened in various ways. Now we can say that the pigeon's magnetic field perception ability is in the nose area. "

Scientists have realized that birds use the earth's magnetic field to navigate.

Maybe there is more than one answer.

Nora's research results are very convincing, that is, pigeons find their way by the earth's magnetic field. Other research results also show that pigeons may know their way in many ways, because other scientists have made other discoveries. For example, British researchers published a research report in February this year, claiming to have solved the mystery of pigeons identifying their way home. They think that the secret of pigeons finding their way home is actually very simple and direct. Like other birds, they often fly along artificial shipping and aviation signs such as roads, railways and canals, and finally reach their destinations.

The study was conducted by a zoologist at Oxford University. They studied the homing of pigeons in 65,438+00 years. In the last year and a half, they tracked the flight path of birds with the most advanced global positioning technology, with an error of 1 ~ 4 meters. Researchers in the Department of Zoology of Oxford University said that after more than 65,438+00 years of international research, it was really surprising to find that pigeons did not seem to rely on their innate instinct to tell directions, but flew according to the road system. If it is a long-distance flight or the first flight, pigeons will use their directional nature to identify their orientation according to the sun and stars. But as long as it flies once, the pigeon will fly back according to the familiar route, much like people driving or walking home after work. The researchers said: "Some people may think that this matter is trivial, but it is very important for us, because it will involve the memory structure of birds and what the map looks like in the eyes of birds."

However, this research result has caused controversy among some bird research experts, who insist that pigeons use the sun or geomagnetic induction to determine their direction and fly to their destination. Wilzko, a flying pigeon expert at Frankfurt University, expressed doubts about this study at Oxford University. His research shows that pigeons use various abilities such as the sun, geomagnetic field and even sense of smell to find their way. Wilzko said that pigeons have tiny magnetic particles in their beaks, through which they can be induced by geomagnetic fields. Obviously, Wilzko's point of view is consistent with the latest research results of scientists such as Nora.

Knowing the way is the result of comprehensive factors.

Now scientists agree that birds, including pigeons, can determine their absolute and relative positions through the local geomagnetic field. The magnetic lines of force emanating from the two magnetic poles of the earth are vertical at the polar regions and parallel within the tropic of cancer. At high latitudes, the earth's magnetic force is very strong; In equatorial regions, it will be weaker. Geomagnetic signposts are formed due to the different magnitude and direction of magnetic force.

There is a lot of evidence that birds can use this geomagnetic signpost as their own navigation system. Birds may perceive the strength and direction of the earth's magnetic field through pigments in the retina of their eyes. In addition, in the upper beak, crystalline magnetite-like tissues can also sense the earth's magnetic field. But scientists say this is not all birds can do. Since 1950s, ornithologists have realized that birds use the sun as a compass to determine their directions. The sun rises in the east every day, generally speaking, it runs about 15 degrees every hour, and finally sets in the west. Birds are definitely experts on this issue.

Further research found that birds determine their direction by combining various clues and senses. More interestingly, with the change of environment, birds can adjust their direction decision-making system very appropriately. For example, pigeons use the sun as a compass on sunny days, but when the sun is invisible, they mainly refer to the sensed geomagnetic signals. Those migratory birds that migrate at dawn and dusk, such as robins, are likely to determine their direction by polarized light at sunrise and sunset.