Birds' homing instincts still baffle

UCI physicist says it may be all about light, chemicals.

By Gary Robbins

May 13, 2004

A popular belief about the way migrating birds find their way from place to place may be fundamentally wrong, a UCI physicist says today in a journal article that's likely to surprise devotees in the exacting world of bird watching.

Thorsten Ritz is challenging the idea that magnetic particles in the brain and, possibly, beak of a bird allow it to read Earth's magnetic field, sharpening its sense of direction.

It's more likely that a bird's "magnetic compass" is controlled by little chemical changes in the brain, says Ritz, a University of California, Irvine researcher who lays out his ideas in the journal Nature.

"Light is probably behind the change in chemistry. I'm not sure," says Ritz, whose findings are based on the study of 12 European robins, the cute but somewhat high-strung national bird of England.

Ritz placed the robins in a cage and exposed them to a harmless artificial magnetic field that fluctuated greatly.

"We found that the birds faced in the usual direction for their migration when the artificial field was paralled to the Earth's natural magnetic field, " Ritz says. "But (the birds) were confused when the artificial field was applied in a different direction."

He concluded from this and other queues that chemistry - not the magnetic particles - were responsible for the magnetic compass.

"In a way, birds might chemically "see" the magnetic field," says Ritz, 33. "This will surprise people who assumed the compass was controlled by magnets."

Lots of "birders" believe in the magnet theory. But no one is certain how migratory birds navigate. In fact, researchers say there's evidence that such birds guide themselves in three ways - by reading sunlight, starlight and the magnetic field.

All three factors have been debated among birders, a group that prides itself on specificity.

One of the most infuential voices in the debate is the British Broadcasting Corporation, or BBC, which can get snarky in these matters. Ritz recalls an earlier BBC report that basically ridiculed a scientific study that said that some carrier pigeons followed roads while flying the friendly skies. The BBC reporter sniffed that, if that were true, the birds might pause at stop signs.

Ritz was scheduled to be interviewed by the BBC late Wednesday night.

"I'm going to tell them that there's a lots of unanswered questions and that scientists are going to be picking bird brains for years to come."