WASHINGTON: Four decades after scientists showed that migratory
birds use Earth's magnetic field to orient themselves during their seasonal
journeys, researchers have at last found a molecular mechanism that may explain
how they do it.
If the hypothesis is true, the planet's magnetic field lines -
which arch around Earth from north to south - may be plainly visible to birds,
like the dashed line in the middle of a road.
The work, described in the online edition of Nature,
identifies for the first time a molecule that reacts to very weak magnetic
fields. The experiments prove the plausibility of a long-hypothesised method of
avian navigation that has had a credibility problem because no one had ever
found a molecule with the required sensitivity.
"This is a proof of [the] principle that a chemical reaction can
act as a magnetic compass," said Peter Hore, of the University of Oxford, who
with his fellow chemist Dr Christiane Timmel led the research. Professor Hore is
testing similar molecules, called cryptochromes, isolated from the eyes of
migratory birds.
Professor Devens Gust, a chemist at Arizona State University who
worked with Mr Hore and Ms Timmel, said the molecules "seem to have the right
structural and chemical features to allow them to show this effect".
If cryptochromes or other chemicals in a bird's eye behave as
the new molecule does, they could provide the foundation of a bird's magnetic
sense. Depending on how far north or south a bird is from the equator, these
molecules could be expected to send different signals to its brain, telling the
bird whether it is veering east or west and pinpointing its latitude.
No one knows how a bird would perceive this input. Light looks
like light; sound sounds like sound. What would magnetic information "feel" or
"look" like?
"It could be a bright or dark spot that would move around" in
the bird's field of vision, Professor Hore said. "As in a video game, the goal
might be to keep that spot centred. But maybe not."
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