"We can now say that the pigeon's magnetic sense is located in the nasal region and is most likely magnetite-based," Mora said.
Martin Wikelski, a professor of ecology and evolutionary biology at New Jersey's Princeton University, who was not involved with the study, said it "reveals very interesting data on the capacity of homing pigeons to detect magnetic anomalies in a cage. As such, it is a significant step forward in our understanding of magneto-reception in pigeons." Mora, the study author, said migrating birds are guided by the sun, moon, stars, and other visual clues, such as memorized landmarks. But she noted that Earth's magnetic field also provides birds spatial information that is ideal for accurate navigation.
"The Earth's magnetic field is very stable on a geological timescale," Mora explained. "The Earth's field is also highly predictable on a spatial scale, with intensity being weakest at the Equator and gradually increasing with latitude toward each Pole."
Other animals are also thought to navigate using magnetite. Scientists believe the mineral may explain the strong directional sense found in aquatic migrants such as whales, sharks, tuna, trout, and sea turtles.
Studies indicate that even marine mollusks have a magnetic compass sense.
Compass and Map
While birds have long been known to have a magnetic compass, some researchers suspect birds use this in conjunction with the type of magnetic map mentioned in the study.
Mora noted: "Other recent research indicates that some migratory birds may have a magnetic compass based on photopigments in the eye. If this is found to be true also in pigeons, then it may be the case that the compass is in the eye and the map is in the nose."
So do animals such as homing pigeons use the Earth's magnetic field as a map as well as a compass?
"Until now nobody had been able to demonstrate behaviorally in the lab that pigeons can detect magnetic field stimuli that mainly consist of changes in magnetic field intensity, and thus could form the basis of a magnetic map," Mora said.
She noted that proponents of the idea that birds chart flight routes principally by smell have used previous inconclusive experiments to back up the "scent map" theory. Birds are generally considered to have a poorly developed sense of smell. But seabirds such as albatrosses and petrels, which have large, tubular nostrils, are known to use scent clues to locate nesting sites and prey out at sea.
"It is not clear what the hierarchy of cues is the birds use in the wild," said Wikelski, the Princeton ecologist and evolutionary biologist. "They could still use olfaction first and foremost, not that I favor one hypothesis over the other. But the current experiments simply cannot distinguish between them."
Now that scientists know that homing pigeons' magnetic-map sense is located in their beaks, Mora says new studies are needed to find out for certain whether birds really can plot a homeward course by following their noses.
Don't Miss a Discovery
Sign up for the free Inside National Geographic newsletter. Every two weeks we'll send you our top news stories by e-mail.
SOURCES AND RELATED WEB SITES