- ANAHEIM, Calif. - Researchers are homing in on the details of the magnetic
sense that seems to guide animals ranging from honeybees and homing pigeons
to trout and whales across vast distances. Though the navigational abilities
of birds and other migrating animals have been noted for centuries, scientists
are using new imaging techniques along with other tools to trace how the
internal compasses of animals work.
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- "Pigeons have proved to be unsatisfactory
test subjects because they're so difficult to keep in a controlled lab
setting, and they so far have been able to overcome every attempt that
scientists have made to thwart their finding their way," Michael Walker,
a biologist at the University of Auckland in New Zealand told the annual
meeting of the American Association for the Advancement of Science.
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- Walker and Carol Diebel, a researcher
at Auckland Medical School, have turned to the trout, first showing in
lab tests that the fish respond to magnetic fields in experimental tanks,
then finding the tiny organ within the trout's nose that actually senses
the Earth's magnetic field and sends information to the brain.
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- Diebel described the effort as akin to
"finding the magnetic needle in a haystack," and probably understated
the complexity of her quest. It took four years and involved using a series
of ever more powerful microscopes to find the cells containing magnetite
crystals near the end of a nerve network called the trigeminal nerve.
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- Magnetite, an oxide of iron, is also
known as lodestone, the mineral first used by humans to make magnetic compasses
more than 2,000 years ago.
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- Joseph Kirchvink, a professor of geobiology
at California Institute of Technology, said the material has been found
in animals ranging from bacteria to humans, though people have shown no
innate ability to navigate without visual cues.
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- Walker said the only thing his research
team hasn't been able to observe is how rainbow trout (actually American
imports) use navigation skills in their life cycle, "since our trout
seem to have given up ocean spawning in favor of our lakes."
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- Scientists suspect many animals have
several built-in navigation systems, including electrical currents in some
fish and signals from sunlight in birds, which appear to fall back on the
magnetic field mainly when sunlight is blocked by clouds.
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- Although researchers haven't been able
to confuse pigeons with magnets or wire coils attached to them, nature
does sometimes throw them off, with flocks of homing birds occasionally
becoming irretrievably lost.
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- "There has been some speculation
and some confirmation that magnetic storms have been going on when the
pigeons were lost," said Robert Beason, a professor at the State University
of New York at Geneseo.
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- Beason, who has been studying navigation
in the bobolink and other birds for more than 25 years, reported that the
magnetic sense in birds appears to be tied to optical nerves.
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- "Light is important in their magnetic
representation: it has to be present for their navigation system to be
activated. We've tried to get the bobolinks to move in darkness, but they
just slept," Beason said.
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- Walker said the new information about
the location of magnetic field detectors has prompted new experiments on
pigeons fitted with magnets on the front of their heads.
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- "Early indications are that the
birds find it hard, but not impossible to work out where home is after
this treatment. We suspect this may mean they have more than one built-in
compass, yet another needle to be found."
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- Lee Bowman covers health and science
for Scripps Howard News Service. Bowman can be reached at bowmanl#@shns.com.
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