Molecular Action May Help Keep Birds on Course

Scientists had theorized that a molecule with the right characteristics might change its behavior depending on the inclination of the magnetic field around it. It might react with another chemical more quickly, for example.

In the new work -- conducted in a chamber that blocks Earth's magnetic field and creates fresh ones of various strengths -- the team made a three-part molecule that, in response to light, gives up electrons at one end and passes them to the other end. There they linger for a millionth of a second or so before returning. Significantly, the precise amount of time each electron spends in its temporary home at the far end of the molecule varies with the angle of the surrounding magnetic field.

If cryptochromes or other chemicals in a bird's eye behave as the new molecule does, they could provide the foundation of a bird's magnetic sense. Their shape would probably vary slightly, depending on how much time electrons spent at the far end, or those lingering electrons might affect the shape of another, nearby molecule in the eye. And shape determines biological function.

So depending on how far north or south a bird is from the equator, these molecules could be expected to send different signals to its brain, telling the flier whether it is veering east or west and pinpointing its latitude.

No one knows how a bird would perceive this input. Light looks like light. Sound sounds like sound. What would magnetic information "feel" or "look" like?

"It could be a bright or dark spot that would move around" in the bird's field of vision, Hore said. As in a video game, the goal might be to keep that spot centered.

But maybe not.

"I think it would be annoying to have this dot moving around," said Thorsten Ritz, a biophysicist at the University of California at Irvine, who nonetheless called the new work "breathtaking." Perhaps as a bird veered off course it would feel the way airplane passengers do in a quick descent, he suggested.

Others doubt that birds have, or need, anything more than their magnetite mouths.

"Hore is a great chemist, and this is an impressive demonstration of a weak field effect. However, I'm not sure it has any biological relevance," said Sönke Johnsen, who studies bird navigation at Duke University.

Joe Kirschvink, an expert in magnetoreception at the California Institute of Technology, was even more dismissive, noting among other things that Hore's experiment worked only at very cold temperatures -- "a major stumbling block to the suggestion that optical effects in any organism can be used as the basis of a physiological compass," he said.

Hore and Ritz said similar molecules are expected to work at warmer temperatures.

And in the end, both camps may be right.

"Maybe there is a compass in the eye of birds," Ritz said, "and a map in their beaks."