- US scientists believe they have made an important breakthrough
in the mystery of how migrating birds manage to navigate thousands of kilometres
and arrive at exactly the same spot each year.
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- Laboratory experiments in the past have suggested the
birds may use a number of cues, including sunlight, stars and the Earth's
magnetic field, which they can detect inside their bodies.
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- But this new study, reported in the journal Science,
involved tracking a group of thrushes across hundreds of miles in the American
Midwest and finding out what happened when they were deliberately confused
by a man-made magnet and knocked off course.
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- The birds were captured during their northward migration
and released at nightfall when they would normally continue their journey
- having been fitted with tiny radio transmitters.
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- Remote chase
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- But just before setting off, the birds were exposed to
the artificial magnetic field pointing east.
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- Their flight path was then tracked by researchers chasing
animals for six days in a 1982 Oldsmobile with an antenna mounted on top.
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- On some nights, the scientists were held up by traffic
police who were suspicious of the battered car zooming along remote roads
laden with electronic equipment.
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- But the experiment yielded intriguing results. On the
first night, the songbirds headed west, apparently knocked off course by
the magnet.
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- On subsequent nights, they managed to correct this mistake
and continued northwards towards their destination.
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- The researchers concluded that each night the thrushes
must have "recalibrated" their inbuilt compass from the position
of the setting Sun.
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- Reliable navigation
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- This helps to explain two enigmas surrounding the "flying
by compass" theory.
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- First, the position of the magnetic North Pole shifts
significantly each year, so magnetic signals alone would not be reliable,
especially in higher latitudes.
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- Also, bird compasses cannot distinguish between north
and south, so you would expect them to be confused when crossing the equator.
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- Amazingly then, this study does seem to confirm that
birds can "reset" their navigation systems daily by comparing
the direction of the sunset with the magnetic signals they detect.
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- The research was conducted by William Cochran, at the
Illinois Natural History Survey in Champaign, and colleagues.
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- © BBC MMIV http://news.bbc.co.uk/2/hi/science/nature/3629775.stm
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