Birds have “X-ray” vision

I SEE EVERYTHING: Scientists have discovered that some species of birds, like the carrier pigeon, can actually 'see' the Earth's magnetic field. Photo: PTI

Forget Superman with his red cape. The red-breasted robins in your own backyard have a kind of "X-ray" vision which allows them to navigate in bad weather or even at night, according to a team of German researchers.

For decades, scientists have known that robins and many other migratory birds somehow sense the Earth's magnetic fields, which they use as a compass to find their way to nesting grounds. Carrier pigeons are the prime examples. But no-one knew precisely how birds registered those magnetic fields. Now, for the first time, scientists say they have discovered that the tiny robin can "see" the Earth's magnetic field at night – like Superman with his X-ray vision.

It used to be thought that a special organ in birds' beaks was the centre of magnetic field detection. But the scientists say it is in fact a specialised part of the brain called "Cluster N," a part of the brain involved in processing light - in other words a vision region of the brain.

Hitherto, many experts believed that tiny magnets in the beak wired to the nervous system detect lines of magnetic force. But the new study suggests that birds "see" magnetic fields via their eyes using a complex light-sensitive mechanism.

The German scientists studied 36 European robins and found birds with damage to "Cluster N" were unable to orientate themselves using the Earth's magnetic field. But damage to another nerve channel necessary for a beak-sensing system had no effect.

The researchers, led by Dr Henrik Mouritsen from the University of Oldenburg, wrote in the journal Nature: “The results of the present study specifically suggest that Cluster N of European robins is an essential part of a circuit processing light-dependent magnetic compass information for night-time orientation.

“The exact role of cluster N within this circuit has not been determined, but the present results raise the distinct possibility that this part of the visual system enables birds to 'see' magnetic compass information.”

Other types of magnetic sensor may also exist in birds, said the scientists. There was strong evidence that upper beak magneto-sensors were used by carrier pigeons, they suggested.