Evidence for the use of magnetic map information by an amphibian

The question of whether animals navigate using 'map' information derived fr om one or more spatial gradients in the Earth's magnetic field has been deb ated for half a century. Although there is evidence that certain animals po ssess the sensory abilities necessary to perceive at least two magnetic com ponents that vary spatially, there previously has been no direct test of th e use of magnetic map information by experienced adult migrants. Magnetic i nformation could provide information about an animal's geographic position along a single axis ('unicoordinate map') or could be part of a position-fi xing system that provides positional information along two nonparallel axes ('bicoordinate map') with the second axis being derived from either magnet ic or nonmagnetic cues. Here we report that adult eastern red-spotted newts , Notophthalmus viridescens, displaced approximately 45 km NNE of their hom e ponds oriented in the home direction when exposed either to the ambient m agnetic field of the testing site, or to a 2 degrees increase in magnetic i nclination (normally found further from the home ponds in the same general direction as the testing site). When exposed to a 2 degrees decrease in inc lination resulting in a value that would normally be found on the other sid e of the home ponds from the testing site, however, newts reversed their di rection of orientation. The same changes in magnetic inclination had no eff ect on shoreward magnetic compass orientation, which does not rely on map i nformation. These findings provide support for two critical predictions of the magnetic map hypothesis, and suggest that information about geographic position along at least one axis relative to home may be derived from the m agnetic field. (C) 2001 The Association for the Study of Animal Behaviour.