MOLECULES ON A WING

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.

In birds, magnetite is often concentrated in the beak. Studies have shown that when the beaks of these birds are exposed to powerful magnetic fields—or are numbed with an anesthetic—the birds lose their ability to navigate properly.

But many scientists have suspected that another mechanism is also crucial—one that can tell a bird not only which way is north but also how far it is from the equator by detecting the angle of magnetic field lines. Those lines emerge from Earth’s magnetic poles perpendicular to the planet’s surface, then arch overhead to meet over the equator, at which point they run parallel to the surface. If a...