Birds are likely to judge the direction by looking at the earth's magnetic field with "eyes"

byRichard Hurd

Migratory birds traveling long distances at constant intervals have been considered to be able to "fly the earth's magnetic field" because they can continue flying towards the target direction with no marks on the sea It was. Based on this hypothesis, many researchers continued their research, and it seems that they have reached the conclusion that "birds may be able to see the magnetic field with eyes".

Cryptochrome and Magnetic Sensing
http://www.ks.uiuc.edu/Research/cryptochrome/

Birds can see Earth's magnetic fields, and we finally know how that's possible
https://www.sciencealert.com/birds-see-magnetic-fields-cryptochrome-cry4-photoreceptor

The ability to sense a magnetic field is not unique to birds, but we know that several living creatures, such as salmon and sea turtle, sense and use the magnetic field. Birds traveling over long distances are also thought to be able to sense magnetic fields and research has been ongoing for years but it has not been known what kind of mechanism can sense the magnetic field.

Researchers at Lund University in Sweden and researchers at the Oldenburg University in Germany pointed out that the mechanism by which birds detect the magnetic field is a protein that sensitively accepts blue lightCryptochromeI thought that it was involved. Cryptochrome is a protein originally thought to be related to regulation of the circadian rhythm of plants, and it is known that some animals also have cryptochrome.

Researchers at Lund UniversityZebra halo, Researchers at Oldenburg UniversityComodriAs a result of investigation, it turned out that the genes of the brains, muscles and eyeballs of Zebra-finch and Communderhi have the property of expressing proteins called Cry1, Cry2 and Cry4 which belong to cryptochrome. Although the amounts of Cry 1 and Cry 2 fluctuate daily due to circadian rhythm, Cry 4 is kept constant every day, and it is highly likely that Cry 4 is involved in bird magnetic field sensing system.

byLinda Rogan

In addition, researchers are thinking that birds may perceive magnetism from images actually seen by eyes, as Cry 4 is often seen around the retina receiving light. Studies show that the amount of Cry 4 increases as migratory birds in Europe move at the season when they move, making it a material to reinforce the expectation that Cry 4 is related to the bird's magnetic sensing mechanism It is.

However, there is still a possibility that Cry 1 and Cry 2 are involved in magnetic field sensing, so researchers say that it is necessary to continue research in the future.

If the bird is looking at the magnetic field, the figure that the researchers at the University of Illinois expressed on how the field of view of the bird is shown is as follows. Birds may perceive by visually observing the world that applied the "magnetic field filter" to the actual field of view.