Bird Compasses..

Many birds navigate with pinpoint accuracy over long distances
and in all types of weather. How ?

Researchers have discovered that birds can sense the earths magnetic field.
However, the earth's " magnetic field lines vary from place to place and don't allways point toward true north,
" states the journel Science.

What prevents migrating birds from veering off course ?

Birds apparently calibrate their compass to the settling sun each evening.
Since the postion of the sunset changes with latitude and season,
researchers think that theses birds must be able to compensate for the changes by means of " a biological clock ,
that tells them the time of year," says Science.