Birds Use Light, Not Magnetic Field, to Migrate

In European robins, a visual center in the brain and light-sensing cells in the eye — not magnetic sensing cells in the beak — allow the songbirds to sense which direction is north and migrate correctly, according to a new study in Nature. The study may improve conservation efforts for migratory birds.

Researchers have known that built-in biological compasses tell migrating birds which way to fly, but the details of how birds detect magnetic fields has been unclear.

Some researchers had proposed that iron-based receptors in cells found in the upper beaks of some migratory birds sense the magnetic field and send that information along a nerve to the brain. Other scientists favor the hypothesis that light-sensing cells in birds’ eyes sense the magnetic field and send the information along a different route to a light-processing part of the brain called cluster N.

To find the location that houses the magnetic compass, scientists caught 36 migratory European robins and made sure that the birds could all orient correctly under natural and induced magnetic fields. Next, the researchers performed surgeries on the birds to deactivate one of the two systems. The team either severed the nerve that connects the beak cells to the brain, or damaged the brain cells in cluster N that receive light signals from cells in the eye.

Birds with the severed beak-to-brain nerve — called the trigeminal nerve — still oriented perfectly, suggesting that the beak cells are not important for orientation. On the other hand, birds with damaged cluster N regions could no longer sense and orient to magnetic fields. These robins failed to pick up both the Earth’s natural magnetic field and the artificial fields created by the researchers.

Understanding more about how birds navigate and sense the environment may have important conservation implications. Migratory birds that humans have relocated often fly back to the original migratory grounds. But if researchers can figure out how the birds navigate, conservationists may be able to trick the birds into staying where it’s safe.

Original article here.