Magnetic Beaks Help Birds Navigate

By: James Owen
Date: November 24, 2004
Category: General

"Magnetic Beaks Help Birds Navigate" Study Says for National Geographic News

The findings add to the debate over whether pigeons and other birds chart
their flight paths by using a magnetic sense or by following scent clues in
the atmosphere.

"The question of how [pigeons] might find their way home has fascinated
laymen and academics for several decades," said Cordula Mora, a biologist at
the University of North Carolina at Chapel Hill.

Descended from wild rock doves, homing pigeons can locate their lofts, or
roosts, even when released several thousand miles away. Because of this
ability, people have used the birds to carry messages since the days of
ancient Egypt.

"We know that pigeons have a magnetic 'compass' and a sun compass. But there
has been a long debate over the nature of the 'map' that pigeons use in
conjunction with these compasses," said Mora, the lead author of the study.

"The two main theories are that pigeons smell their way home using an
olfactory map, or that they have a magnetic map."

Seeking to test the magnetic-map theory, Mora and her colleagues placed the
birds in a wooden tunnel outfitted with feeding platforms at opposite ends
and magnetic coils on the exterior.

The researchers then trained the pigeons to fly to one feeder if the
magnetic field inside the tunnel was undisturbed and to the second feeder if
the coils were switched on.

Small Magnets

The researchers found that the birds' ability to select the correct feeder
was significantly impaired if the birds had small magnets attached to their
beaks. The scientists suggest this is because magnetite, an iron-rich
crystal with magnetic properties, is found inside the homing pigeons' beaks.

"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 photo pigments 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.
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