Migratory birds rely on internal world map, say scientists
Migratory birds successfully navigate thousands of kilometres because they are able to sense the difference between true and magnetic north, scientists have discovered.
For centuries, humans were stymied by the problem of accurately locating longitudinal position until the challenge was solved through maths. Now, research reveals that birds naturally develop an east- west understanding, enabling them to build a mental “world map” that they never forget. Experiments using the common reed warbler showed they were sensitive to the difference between true north, the geographic North Pole, and magnetic north, a separate location in the Arctic Circle.
In Europe, the difference increases from east to west and the study indicates warblers can sense this variation to determine where they are.
“It seems that a bird as unassuming as the reed warbler may have a geographic map or memory that enables it to identify its longitudinal position, only by detecting the magnetic north pole and its variance from true north,” said Dr Richard Holland, of Bangor University. “This, combined with other external cues, including the strength of the magnetic field, star positions or smells, enables it to locate its current position and orient itself during a long migration,” he said in the journal Current Biology.