The birds are sensitive even to rapidly fluctuating artificial magnetic fields. These fields had no effect on magnetic materials such as magnetite, indicating that the birds do not rely on simple chunks of magnetic material in their beaks or brains to determine direction, as experts had previously suggested.

The results are reported in the May 13 issue of Nature. The study is the first to reveal the mechanism underlying magnetoreception the ability to detect fluctuations in magnetic fields in migratory birds.

In the study, Thorsten Ritz, assistant professor of physics and astronomy, and colleagues exposed 12 European robins to artificial, oscillating magnetic fields and monitored the orientation chosen by these birds. The stimuli were specially designed to allow for responses that could differ depending on whether birds used small magnetic particles on their bodies or a magnetically sensitive photochemical reaction to detect the magnetic field.

We found that the birds faced in the usual direction for their migration when the artificial field was parallel to the Earths natural magnetic field, but were confused when the artificial field was applied in a different direction, said Ritz, the lead author of the paper. Since the artificial fields oscillations were too rapid to influence magnetic materials like magnetite, it suggests that the most likely mechanism for magnetic orientation in these birds involves tiny changes to magnetically sensitive chemical reactions, possibly occurring in the eyes of the birds we are not sure.

In the experiments, the robins could walk and flutter in their cages but could not fly. The birds oriented well in the Earths magnetic field alone, but were disoriented in the presence of a broad-band (
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Contact: Iqbal Pittalwala
iqbal@uci.edu
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University of California - Irvine
12-May-2004