The nose knows—smells point many an animal in the right direction. But for birds, the roles that smells may or may not play in navigation has long been up in the air.
Now, flocks of GPS-wearing seabirds add to growing evidence that birds not only follow their noses, but also remember smells like directions. (Read "Secrets of Animal Navigation" in National Geographic magazine.)
New data suggest these outfitted birds, called shearwaters, seem to know where they're going based on their memories of smells that waft in from different directions, according to a study published June 30 in Proceedings of the Royal Society B.
Rather than blindly flying around the ocean, the birds may associate smells with specific wind patterns. For instance, if they get a whiff of blossoming plankton that's typically carried on winds from a northern region, for example, they might know to turn south.
"They may be able to tell what their island smells like, possibly even their colony," says Geoff Le Baron of the National Audubon Society, who wasn't involved in the study.
The controversial idea that birds follow a map of odors to navigate dates back 50 years—it goes against the idea that birds get around purely by sensing the magnetic field.
Part of the problem for scientists studying birds' sense of smell is that it's hard to tell when and if they're actually using it, for instance in finding their way home.
But by essentially taping iPod-size GPS devices to the backs of seabirds—like a backpack of sorts—researchers can get daily data about where and when the birds travel. (See more seabird pictures.)
That's what study co-author Andy Reynolds, a mathematical modeler at Rothamsted Research in the U.K., and colleagues did with 210 birds from three species: Cory's shearwater (Calonectris borealis), Scopoli's shearwater (C. diomedea), and the Cape Verde shearwater (C. edwardsii).
The team tracked the birds back and forth on foraging trips and back to their breeding grounds in the Mediterranean Sea and the North Atlantic Ocean. (Also see "New Theory on How Homing Pigeons Find Home.")
Most birds followed a similar path: a few short flights, then a long flight. These paths follow Lévy flight patterns, mathematical patterns of movement in nature, and best matched how birds would respond to odors carried on the wind and disrupted by turbulence.
"The remarkable ability of shearwaters to pinpoint their breeding colony after crossing vast expanses of featureless open ocean can be attributed to their assembling cognitive maps of wind-borne odors," says Reynolds.
This strategy in studying bird smell and navigation was an "interesting approach," notes Richard Holland, an ecologist at Queens University in Belfast.
He cautions that the new study "can point us towards possible navigational explanations, but they're just correlations."
Dan Costa, an ecologist at the University of California, Santa Cruz, adds that odors may be more important to birds flying over the open ocean, which has fewer smells than on land.
Seabirds probably need as many directional clues as they can get, whether from sight, magnetic fields, or odor, Costa says. (See National Geographic's pictures of animals on the move.)
"For animals like this that cover great distances, it makes sense that they would have some 'trick' to get around."
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