It's well known birds can use Earth's magnetic field as their compass, but they may also use magnetism as their map. Christopher Intagliata reports
If you're lost, you need a map and a compass. The map pinpoints where you are, and the compass orients you in the right direction. Migratory birds, on the other hand, can traverse entire hemispheres and end up just a couple miles from where they bred last year, using their senses alone. Their compass is the sun, the stars and the Earth's magnetic field. But their map is a little more mysterious. One theory goes that they use olfactory cues—how a place smells. Another is that they rely on their sense of magnetism.
Researchers in Russia investigated the map issue in a past study by capturing Eurasian reed warblers on the Baltic Sea as they flew northeast towards their breeding grounds near Saint Petersburg. They moved the birds 600 miles east, near Moscow. And the birds just reoriented themselves to the northwest—correctly determining their new position.
Now the same scientists have repeated that experiment—only this time, they didn't move the birds at all. They just put them in cages that simulated the magnetic field of Moscow, while still allowing the birds to experience the sun, stars and smells of the Baltic. Once again, the birds re-oriented themselves to the northwest—suggesting that the magnetic field alone—regardless of smells or other cues, is enough to alter the birds' mental map. The study is in the journal Current Biology. [Dmitry Kishkinev et al, Eurasian reed warblers compensate for virtual magnetic displacement]
And if you're envious of that sixth sense—keep in mind that since the Earth's magnetic field fluctuates, the researchers say magnetic route-finding is best for crude navigation. Meaning for door-to-door directions—you’re still better off with your GPS.
[The above text is a transcript of this podcast.]