1 Tahrcountry Musings: Light as an Aid for Bird Migration

Thursday, October 29, 2009

Light as an Aid for Bird Migration

Latest research on European Robins is making established facts about migration of birds on its head. Scientists have discovered that In European Robins, a visual center in the brain and light-sensing cells in the eye and not magnetic sensing cells in the beak allow the songbirds to sense which direction is north and migrate correctly.

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.

Special proteins called cryptochromes in the birds’ eyes may mediate this light-dependent magnetic sensing according to the scientists. Light hitting the proteins produces a pair of free radicals, highly reactive molecules with unpaired electrons. These electrons have a property called spin which may be sensitive to Earth’s magnetic field. Signals from the free radicals may then move to nerve cells in cluster N, ultimately telling the birds where north is.

To find the location that houses the magnetic compass the 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. 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.

Details of the study appear in Nature dated October 29th.

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