Birds have a built in satnav — tiny magnets in their beaks that act as a compass, according to research.

The birds' 'beaknav' allows them to carry out the incredible long inter-continental migrations but exactly how it works remains a mystery.

As well as being able to detect the strength of magnetic fields, they have proteins in their eyes that allow them to see magnetic fields.

The proteins pick up lines of magnetism in the environment, and turn them into a visual compass.

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Writing in the Royal Society journal Interface, husband and wife research team Roswitha and Wolfgang Wiltschko, say a great deal of mystery still remains as to how the information received by the bird's beak and eyes is combined to create a navigational map

The two processes working together to transmit information to the bird's brains.

Writing in the Royal Society journal Interface, husband and wife research team Roswitha and Wolfgang Wiltschko, say a great deal of mystery still remains as to how the information received by the bird's beak and eyes is combined to create a navigational map.

Incredibly, the pieces of magnetic iron, or magnetite, are so small that attempts to find them in the beak have so far failed.

Incredibly, the pieces of magnetic iron, or magnetite, are so small that attempts to find them in the beak have so far failed (stock)

But scientists deduce that magnetic particles in the beak must have a role.

When a bird's upper beak is exposed to a strong enough to reverse the polarity of the magnets, the birds become confused as the information they are receiving no longer tallies with other cues in their environment.

And when the nerve connecting the homing pigeon's beak to its brain is anaesthetised, the confusing signals from the 'reversed' magnets in the beak no longer confuse the bird.

The researchers from Goethe University, Frankfurt, Germany say that it is still unknown how the bird's brain integrates the magnetic information with other sensory input such as vision and smell.

The hippocampus, where short term memories are formed, is one candidate.

But homing pigeons who have had their hippocampuses damaged were still able to navigate like birds without any brain damage.

Birds are not the only animals to use magnetic perception, but the authors say that current research suggests birds use magnetism quite differently from other animals, such as fish, mammals and reptiles.