Sunsets help songbirds fly home
Sunsets could recalibrate the internal compasses of migrating songbirds, U.S. and German researchers say.
The researchers said their findings help explain how birds fly across the equator at night without getting lost.
The results were published in the current issue of journal Science.
Scientists know birds that migrate at twilight can use the stars, the Sun, the Earth's geomagnetic field and polarised light to find their way, at least in captivity.
But Assistant Professor Martin Wikelski of Princeton University and colleagues' experiment was one of the first to use free-flying birds instead of captive birds in a laboratory.
The researchers first caught several dozen thrushes and attached tiny radio transmitters to them.
Knowing that birds use magnetic fields to orientate themselves, they put some birds in an artificial magnetic field to confuse them, and then let them go.
The researchers then followed the birds by car at night, for up to 1100 kilometres.
The birds that had not been tricked flew north, as they usually did. But the birds exposed to the artificial field flew west.
The next evening, all the birds were free to see the Sun. Subsequently, all flew north again.
"We suggest that birds orient with a magnetic compass calibrated daily from twilight cues," the researchers wrote.
They also suggested that other species of birds that migrate at night may also re-set their magnetic compass this way.