An international group of researchers, which included Nikita Chernetsov, Professor of St Petersburg University, has found out that for orientation on the magnetic map migratory birds use the ophthalmic branch of the trigeminal nerve. It is thanks to it that the animal receives information about its location, and can therefore understand in which direction to move to its breeding or wintering site.

 The study, published in the journal Scientific Reports, will help to learn more about the magnetoreceptors of birds that have not yet been found.

The Professor of St Petersburg University Nikita Chernetsov and his colleagues conducted an experiment involving 49 reed warblers - birds that nest in the Baltic, and for wintering fly to West Africa. Since the experiment took place in the spring, the animals endeavoured to reach ​​Northern Europe.

The study was supported by a grant from the Russian Science Foundation No. 17-14-01147.

Birds were divided into two groups: the first were warblers with crossed ophthalmic branches of the trigeminal nerve, and the second were ordinary birds. All birds were placed almost in the "magnetic virtual reality": although they were in the village of Rybachiy on the Curonian Spit (Kaliningrad region), special instruments changed the magnetic field so much, as if the birds were 1,000 km to the east - in Zvenigorod (Moscow region). What is important, the remaining landmarks that the warbler uses or can use remained unchanged such as sun, stars, landscapes and smells.

As a result, birds with broken nerves were not able to "notice" the magnetic displacement. As before, they jumped in the cage in the direction of the northeast. But ordinary birds behave as if they really moved to the suburbs, and turned to the north-west. The fact is that during migration, while in captivity, the bird still jumps in the direction to which it would fly if it was  free. Because of these active movements on the floor of special circular cells there are scratches from the claws of warblers - it is from them that scientists understand the preferences of animals.

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Our data proves that the information is transmitted through the ophthalmic branch of the trigeminal nerve, and it is needed for the bird to understand the magnetic direction. We solved the question of the function of the magnetoreceptor innervated by the ophthalmic branch of the trigeminal nerve which have never been described before. Now specialists in sensory physiology of birds should find and describe this receptor. "There is a nerve, there is a function, the receptor itself has not yet been found," said Nikita Chernetsov.

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Scientists have long known that migratory birds know how to navigate with the help of stars, the sun, smells and the magnetic field of the earth. Interestingly, the last point is also used by turtles, newts, fish from the salmon family and eels. However, for ornithologists, it remains a mystery what kind of sensory system birds are using to determine their position on a magnetic map. Earlier, researchers from the University of Oldenburg in Germany showed that it is through the ophthalmic branch of the trigeminal nerve that the brain receives information from an as yet unselected magnetoreceptor. Therefore, the international research team, which included Nikita Chernetsov, decided to check how this nerve is related to the ability of birds to navigate the magnetic map.

Such studies help to study the ways and means of migration of various animals, which means they are able to protect them throughout the habitat, because species living in several regions at once are often vulnerable. In addition, if scientists manage to study the bird's "magnetic compass" in detail, it may be possible to reproduce this system in the future and obtain a magnetic navigator that does not require connection with satellites.