Bats in the group exposed to the clockwise magnetic fields flew east, for example, while those in the opposite group flew west.
But some of the errant bats eventually realized their mistake and made it home that night, suggesting either a recalibration of the compass or use of other navigational cues, Holland says.
A Sense of Where You Are
A magnetic sense has been described in a wide array of animals, not just ones that fly. Lobsters have it. So do salamanders. (Related: "Rat Radar: Rodent Uses Natural 'GPS'" [January 29, 2004].)
"It's not just associated with long-distance movements or migration," said John Phillips, a biologist at Virginia Tech university in Blacksburg. "We find even short-distance movements by simple animals are patterned by use of directional compass cues."
Scientists know of two kinds of magnetic orientation. In one, a simple compass sense is based on particles of a mineral found in many organisms known as magnetite.
Some birds can also "see" changes in light intensity in different locations within Earth's magnetic field. (Related story: "Magnetic Beaks Help Birds Navigate, Study Says" [November 24, 2004].)
This more sophisticated sensory apparatus provides an internal "map sense" of where the birds are on the globe.
"We don't know if bats have a light-dependent compass," Holland said. "But they do have magnetite in their bodies."
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