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Follow your beak
Natural History, June, 2007 by Graciela Flores
Homing pigeons and other birds can sense the Earth's magnetic field, an ability that helps them find their way home, even when home is hundreds of miles away. But how this magnetic sense works remains one of the most puzzling questions in sensory biology.
To learn the birds' secret, Gerta Fleissner, a neurobiologist at the University of Frankfurt in Germany, teamed up with physicists and other biologists. Their investigation focused on the skin of the upper beak--where the mysterious magnetic sense is thought to reside. With powerful microscopes they identified three clusters of nerve endings on each side of the homing pigeon's beak, each cluster oriented along one of the bird's three perpendicular axes (beak-tail, wing-wing, and back-belly). Inside the nerve cells they discovered something even more intriguing: two kinds of magnetic iron oxide--square platelets of maghemite and bullet-shaped particles of magnetite. The investigators propose that an extremely delicate arrangement of those intracellular minerals constitutes the long-sought receptor for birds' magnetic sense.
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Here's how they think it works: Each pair of clusters (one on each side of the beak) is tuned to detect one of the three perpendicular spatial components of the Earth's magnetic field (north-south, east-west, and up-down). Depending on how closely a pair of clusters aligns with its magnetic-field component, the maghemite platelets in the clusters line up and magnetically attract the magnetite bullets. The rearrangement of maghemite and magnetite in all three pairs of clusters triggers nerve impulses to the bird's brain, enabling the bird to sense the angle and intensity of the local magnetic field--and fly home. Fleissner located similar iron-bearing nerves in several other bird species, and she suspects all birds possess them. (Naturwissenschaften)
COPYRIGHT 2007 Natural History Magazine, Inc.
COPYRIGHT 2008 Gale, Cengage Learning
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