No one doubts that songbirds migrating during the night are remarkably adept navigators. For example a boreal songbird's are migrating 20,000 km from Alaska to Venezuela. When flying alone, often over long distances, they use a variety of directional signals, including the all-important light-dependent magnetic compass.
Its principle has so far remained hidden to science. New research is revealing its function, and showing the intriguing world we are slowly peering into.
It's long been widely believed that birds navigate by an internal magnetic compass during migration.
There may even be several of these compasses, and they're being combined. In addition to the magnetized particles in the cells, there is a so-called quantum compass in the body of animals.
Its principle lies in the existence of protein molecules called cryptochromes, which are often found in the retina of the eye. In vertebrates, we know Cryptochome 1A, 1B and 2. These are molecules that respond to changes in daylight.
But then there is cryptochrome 4 (CRY4), which is just part of the quantum compass. This exists in fish, amphibians and reptiles. It has not yet been detected in mammals.
How does the quantum compass work?
Cryptochrome 4 combines with another molecule to form a radical free electron pair. It is then the relative position of the electrons (spin) that changes the nature of the molecule and its reactions.
This has been demonstrated in the European red migratory robin (Erithacus rubecula). By studying its DNA, it was found to have a gene disposition that then produces protein molecules in the body that are sensitive to even relatively small changes in magnetic field. So far, this has been demonstrated under laboratory conditions.
It seems that, like sharks, birds can create and remember entire "magnetic maps" by which they orient themselves and correct their direction of flight.
After all, note what direction is comfortable for animals in nature. For many animals, it is the north-south direction. That's the direction that cows, for example, like to rest.
Humans, for the most part, do not perceive magnetism, although there are individuals who are sensitive to it. They are said to have a so-called sixth sense. The question is whether this disposition is in all people or only in some individuals who have it written in their genes.
Xu J. et al.: Magnetic sensitivity of cryptochrome 4 from a migratory songbird. Nature, 2021, DOI: