Relying on more than wings and prayers.

Relying on more than wings and prayers

For centuries, people have marveled at the pigeon's ability to find its way home over hundreds of miles of unfamiliar terrain. And for almost as long, they have sought to understand how this otherwise mundane bird accomplishes the feat.

Despite significant attention to the mystery, however, ornithologists remain largely stumped. They know homing pigeons can use the sun as a navigational instrument, but they have yet to agree on the backup systems that come into play on cloudy days. One of the more prominent theories suggested in the past two decades -- that pigeons can use the Earth's magnetic field as a navigational reference--fell from grace with a 1988 research report that appeared to refute the notion (SN: 7/23/88, p.55). However, a new assessment of a large body of work from around the world suggests the birds are indeed capable of using magnetic fields--if they've learned to do so and if the magnetic forces vary enough over the flight zone.

Charles Walcott, executive director of the Cornell Laboratory of Ornithology in Ithaca, N.Y., says the reams of conflicting data about the usefulness of various sensory inputs for pigeon navigation become meaningful if one accepts that the birds may be capable of many different orientation modes. Just which mode an individual pigeon uses seems to depend upon what kind of information is available, perhaps especially during a critical imprinting period in the bird's yout.

For example, Walcott says, experiments performed with homing pigeons at a magnetized site in Rhode Island and at another nea Ithaca, called Jersey Hill (whose reputation for confusing homing pigeons has led ornithologists to dub it "a Bermuda Triangle for Ithaca pigeons"), suggest the birds can indeed glean useful information from magnetic forces.

Research in Europe suggests that smell, too, can show the way home--if a pigeon has grown up in an environment that provides useful olfactory cues. Experiments in which scientists numbed some pigeons' nostrils with topical anesthetics--and others in which they either allowed or withheld olfactory stimulation during the birds' first few weeks of life--suggest pigeons can construct an "olfactory map," Walcott says. In pigeons unexposed to olfactory cues, he speculates, other means of orientation may supplant that ability.

While it's clear that pigeons prefer to orient themselves by the sun, they may also be "born with a Chinse laundry list" of second-string environmental cues they can learn to use, he concludes. "The real difficulty has been that we all assumed we were using the same beasts" in the hundreds of experiments performed over the decades. "We all argued with each other, but maybe we were all right."

As for how pigeons make use of magnetic information, previous research has hinted that two systems may come into play, Walcott says. A pigeon's optic nerves may respond to differences in the angles of magnetic fields, and magnetic crystals bound to nerves in the brain may detect field strength.

The incentive to understand a pigeon's sense of direction goes beyond mere curiosity, Walcott notes. More than 14,000 pigeon-racing clubs in the United States sponsor homing competitions featuring high-priced birds, upon whose wings rest the fates of substantial wagers.