ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Thursday, September 12, 1996 TAG: 9609130111
SECTION: NATIONAL/INTERNATIONAL PAGE: A8 EDITION: METRO
DATELINE: NEW YORK
SOURCE: ASSOCIATED PRESS
A small warbler has made scientists change their tune about how migrating birds know which way to fly.
Scientists have long thought birds navigate by the stars. Although birds can sense the Earth's magnetic field, scientists have thought this was a backup used on cloudy nights.
But an experiment showed that a young garden warbler needs information from both the magnetic field and the stars to choose the right heading on its first migration. The stars alone are only good enough to send the bird generally south.
It's a surprise that warblers need to combine both navigation systems rather than using one or the other at various times, said Charles Walcott, a professor of neurobiology and behavior at Cornell University in Ithaca, N.Y.
``It's both belt and suspenders,'' he said. ``For reasons we don't understand, birds seem to want to use both of these things.''
The garden warbler is a plump bird with a round head and stubby bill that breeds in central and northern Europe and spends its winters in Africa.
The work was reported in today's issue of the journal Nature by the husband-and-wife team of Wolfgang and Roswitha Wiltschko and graduate student Peter Weindler of the University of Frankfurt in Germany.
Wolfgang Wiltschko, a professor of zoology, said he suspects other migrating birds probably have the same system garden warblers do.
James Gould, a professor of ecology and evolutionary behavior at Princeton University, said Wiltschko may be right.
He also said the research implies that young birds store their flight plans as magnetic field cues and then translate that to a mental star map. That's the opposite of what scientists had believed, he said.
The researchers did their experiment with warblers that had been taken from their nests four to six days after birth and kept in laboratory cages. Until the birds were old enough to migrate, they lived beneath an artificial sky that had small lights as stars, set up to indicate north as it rotated through the day.
One group of warblers experienced the bogus sky along with the local magnetic field. But for the other group, the local magnetic field was wiped out with electromagnetic coils. So they had only the stars to chart their course.
When the time for migration came, the birds were put in octagonal cages under a bogus stationary sky and an obliterated magnetic field. Now scientists could see what they had learned.
Warblers that grew up with the stars plus the magnetic field tried to escape toward what the sky said was southwest. That was the right direction for migrating. But the birds that had grown up with only the stars erroneously headed almost due south, on average.
Gould said due south works fine for most migratory birds, which don't fly a dogleg route like the warblers. So the interplay between the two navigation systems is probably not crucial for them, he said.
``Most species of birds would continue to survive'' if that interplay didn't exist, he said. ``But garden warblers would be in trouble.''
LENGTH: Medium: 63 linesby CNB