Obtaining Magnetic Information
Traditionally, the question of how animals obtain the required information is an important issue in all considerations on magnetic orientation. Yet the search for receptors is handicapped in many ways. In contrast to the classical senses, it is not even clear in what part of the body magnetic information is perceived. The magnetic field, unlike light, sound and odors, penetrates living tissue with little modification. Hence, the sensory organs need not be on the surface of the body, but may lie within any structure inside. Sensory modalities like gravity and motion share this characteristic; the receptors for these stimuli are located in the head in the vicinity of the central nervous system. Thus one might spontaneously expect a similar arrangement for magnetic receptors, at least in vertebrates. This view is supported by the finding that coils around pigeons’ heads could cause a reversal of orientation (C. Walcott and Green 1974; Visalberghi and Alleva 1979; cf. Fig. 4.7); the observation that magnets are most effective when placed at the temple or at the forehead just above the nose (Baker 1989a,b) suggests that receptors are located in the frontal region of the head. The precise location is not yet known with certainty, however.
KeywordsMigration Anisotropy Cage Transportation Retina
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