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, cantraverse 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.
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.
1.magnetic field 磁场
例句:The article studies a simple method for any energy level of three dimensional harmonic oscillator in uniform magnetic field.
2.rely on 依靠
例句:It would be rash to rely on such evidence.
3.allow to 允许
例句:Add a little of the warmed milk and allow to froth a little.
4.keep in mind 记住
例句:We must keep this lesson in mind.