BIRDS that navigate using the Earth’s magnetic field rely more on their eyes than on the magnetic particles in their nostrils, an experiment on robins suggests.
Rival theories of bird navigation have suggested both mechanisms. Now Henrik Mouritsen at the University of Oldenburg, Germany, and his team have show that eyes could be key. In one group of robins, the team removed cluster N, a brain region involved in processing signals from the “pair-forming photopigments” in the eyes thought to relay magnetic compass information. In another group, the team cut the trigeminal nerve, which sends signals to the brain from the magnetic particles in the nostrils.
The researchers then exposed the surgically treated and untreated robins to the Earth’s natural magnetic field, and also to a field which artificially rotated magnetic north 120 degrees anticlockwise. The robins lacking their nostril-to-brain connection weren’t tricked, locating the true and artificial magnetic norths just as well as the controls. But the robins without cluster N were unable to navigate. “The results raise the distinct possibility that this part of the visual system enables birds to ‘see’ magnetic compass information,” conclude the researchers (Nature, DOI: 10.1038/nature08528).
“It goes a long way to demonstrating that the magnetic compass response is mediated by the eye,” says Verner Bingman of Bowling Green State University in Ohio.