A web of magnetic force enfolds us - Earth’s magnetic field. It’s different at every location - different strength, different angles. And it’s affected by tiny variations in the magnetism of the rocks themselves.
Humans need a compass or some other instrument to detect this magnetic web. Yet many species of life can not only detect it, they use it to help them navigate - sometimes across great distances.
The arctic tern, for example, can cover more than 40,000 miles a year as it migrates from the Arctic to the Antarctic. It uses a variety of navigational aids along the way, including the Sun and the magnetic field. Tiny grains of a magnetic mineral in its beak appear to serve as an internal compass.
Many sea creatures have a similar way of detecting the magnetic field. Recent research has shown that salmon use magnetic navigation to return each year to a river in Canada. And sharks have receptors that detect tiny fluctuations in electric and magnetic fields, which may help their navigation as well.
Lobsters and sea turtles seem especially attuned to the magnetic field. A loggerhead turtle, for example, may spend a decade or more looping around the Atlantic Ocean, all the way to Africa or Europe and back. When it’s time to reproduce, it returns to the same nesting area where it hatched, thanks to a magnetic “map” that may have been imprinted when it hatched.
Some species find their way with the help of the stars. More about that tomorrow.
Script by Damond Benningfield, Copyright 2013
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