FOUR decades after scientists showed that migratory birds use Earth’s magnetic field to orient themselves during their seasonal journeys, researchers have at last found a molecular mechanism that may explain how they do it. If the hypothesis is true, the planet’s magnetic field lines—which arch around Earth from north to south—may be plainly visible to birds, like the dashed line in the middle of a road.

The work, described online in the journal Nature, was conducted in a test tube and does not prove that birds actually use the mechanism. And researchers aligned with a competing model say they are not convinced. But by identifying for the first time a molecule that reacts to very weak magnetic fields, the experiments prove the plausibility of a long-hypothesised method of avian navigation that has had a credibility problem because no one had ever found a molecule with the required sensitivity.

“This is a proof of principle that a chemical reaction can act as a magnetic compass,” said Peter Hore of the University of Oxford, who with fellow chemist Christiane Timmel led the research. Hore is testing similar molecules, called cryptochromes, isolated from the eyes of migratory birds.

The seasonal comings and goings of birds have mystified people for millennia. Recent scientific findings have seemed almost as incredible. By reversing the magnetic fields around captive birds as they prepared to migrate, scientists could induce them to take off in the wrong direction. The conclusion was that birds have a “sixth sense” that can detect magnetic energy the way eyes detect light and ears detect sound.

... contd.