Animals Use "Chemical Compasses," Study Says

John Roach
for National Geographic News
April 30, 2008
The idea that some animals navigate by "seeing" Earth's magnetic field has been shown to be feasible in laboratory tests, a new study says.

First proposed about 30 years ago, the theory suggests that sunlight absorbed by molecules in the eyes of animals such as birds and bats triggers a chemical reaction.

This reaction makes the molecules sensitive to the local magnetic field, according to study co-author Peter Hore, a chemist at the University of Oxford in England.

But Earth's magnetic field is so weak that scientists were skeptical that it could have a detectable effect on the molecules.

(Related: "Bats Use Magnetic 'Compasses' to Navigate, Study Says" [December 6, 2006].)

Big Step Forward

The Oxford team, led by Hore and Christiane Timmel, demonstrated as a proof-of-principle that a photochemical
reaction can act as a magnetic compass.

The scientists set up an artificial photochemical-reaction system in the lab and monitored its response to a magnetic field weaker than Earth's.

When exposed to light, this simulated model became sensitive to the magnitude and direction of the weak magnetic field.

The team thus proved that this occurrence, known as chemical magnetoreception, is possible in nature.

Thorsten Ritz is a physicist at the University of California, Irvine, whose field experiments with migratory birds support the idea of a photochemical compass.

He said the new study adds credence to his experiments and represents a "big step forward" in explaining how animals use the magnetic field to find their way in the world.

"The effects [Hore and colleages] see are matching exactly what you would expect from theory," Ritz said.

The scientists report the finding in tomorrow's issue of the journal Nature.

Future Experiments

Hore's team is now trying the same lab experiment on molecules called cryptochromes—photoreceptors that scientists suspect are responsible for birds' chemical compasses.

A similar result, Hore said, would be another step closer to validating the theory.

"Beyond that, you would want to show that cryptochomes are sensitive to magnetic fields in birds," he said.

According to UC Irvine's Ritz, these new experiments will help guide scientists who work with birds as to where and how to look for a chemical compass.

Some scientists believe a second theory: that a magnetic mineral called magnetite in their bodies helps animals orient themselves in Earth's magnetic field.

(Related: "Magnetic Beaks Help Birds Navigate, Study Says" [November 24, 2004].)

Other experts, such as Hore, think both mechanisms may be at play.

"This will all be resolved in the next five to ten years," Ritz said.

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