Many bacteria are able to perceive magnetic fields and follow lines of strength of those fields when they move. Magneto-orientation may provide bacteria a way of achieving straight-line movements, which otherwise would be difficult or impossible. They also may combine magnetic field information with other environmental factors, such as oxygen concentration, to find favorable habitats (Frankel et al. 1997). Magneto-receptors, which are iron rich, membrane bound structures in bacterial cells, apparently evolved more than once in bacteria (Delong et al. 1993).
In multicellular animals, the first suggestion of magenetic field perception came from work on homing pigeons. Pigeons seemed to retain their navigation abilities under adverse conditions for compass orientation, such as cloudy skies. Keeton found that, at least in some experiments, equipping pigeons with magnets on their heads disrupted their orientation. He took this to implicate perception of the earth’s magnetic field in pigeon orientation. Magnetite crystals were later found at the base of pigeon skulls, suggesting a magnetic perception organ (Gould 1980).
The realization that fluctuations of the earth’s magnetic field are correlated with systematic errors in honey bee dances (missweisung) led investigators to explore whether honey bees, as well, might have the ability to perceive the earth’s magnetic field. This prompted the discovery of magnetite crystals in the abdomen of honey bees (Gould 1980).
We don’t know how widespread or important magnetoperception organs are in the animal kingdom. The typical experimental approach is to place magnets in or on an animal and monitor the it for changes in orientation. Recent experiments with salmon (Diebel et al. 2000) show that they have magnetite crystals in their olfactory organs, but implanting magnets in salmon did not affect their orientation (Yano et al. 1997). Similarly sea turtle migration was not disrupted by magnets placed on the animals (Papi et al. 2000). In field orientation experiments animals have access to many possible inputs, and may discard magnetic information in favor of other information when the magnetic field is disrupted.