Magnetism May Be Visible in Migrating Bird's-Eye View

Article excerpt

HERE'S an intriguing notion for bird watchers. Birds may actually see Earth's magnetic field when they use it for navigation.

This possibility goes to the heart of the mystery of how some animals sense Earth's magnetism. And, remarkable as it may seem, it has begun to receive some indirect experimental support.

Some biologists, such as Klaus Schulten of the University of Illinois at Urbana-Champaign, think the visual sense of some animals may be involved in their ability to sense magnetic fields. Dr. Schulten theorizes that pigment molecules in the eyes of migratory birds combine magnetic information with certain light colors to give visual clues. He speculates that the birds may actually see a visual distortion due to Earth's magnetic field when they fly.

Biologist John B. Phillips at Indiana University at Bloomington says he thinks such theorizing is "on the right track." Work in his laboratory using male Eastern red spotted newts has produced the "first clear demonstration that the {animal} magnetic compass is light dependent," he says.

Reporting this research in the Sept. 10 issue of Nature, Dr. Phillips and his colleague S. Chris Borland explain how certain wavelengths of light directly affect the compass sense of these semiaquatic salamanders. For example, long-wavelength light rotates the animal's magnetically derived directional sense 90 degrees anticlockwise from what it is under full spectrum light.

Commenting on this finding in a telephone interview, Phillips says that establishing the light-dependence of the animal "compass" is the "first step" in the long process of demonstrating the Schulten thesis. He added that his laboratory is getting the same kind of light-dependent response in the magnetic sense of certain species of flies. He believes there is little doubt that the magnetic field is affecting the flies' photoreceptors. …