O. G. Dely szerk.: Vertebrata Hungarica 21. (Budapest, 1982)

Adler, Kr.: Sensory aspects of Amphibian navigation and compass orientation 7-18. o.

In about half of the tests the salamanders were oriented along the expected. - that is, trained - magnetic compass axis, whether they were exposed to the natural earth field or the 90° altered field, implying that magnetic cues can, under some circumstances, be used as a compass for orientation. In the other half of these tests animals oriented randomly (In no tests were they oriented along the corridor axis perpendicular to the trained magnetic axis). Further analysis revealed that there was a significant inverse correlation between the degree of orientation and small daily fluctuations in the earth's magnetic field caused by solar storms (Fig. 7). The earth's field is approximately 0.5 gauss (or 50,000 gamma) and normal daily variations due to changes in the ionosphere are typically in the range of 30-60 gamma with very large magnetic storms rarely resulting in fluctuations as great as 1000 gamma. A possible explanation is suggested by some recent preliminary experiments with newts (Salamandridae: Notophthalmus vlridescen

s) tested in circular arenas. The newts are oriented along a homeward axis but the axis rotates with increases in geomagnetic disturbance. Thus, in the case of the cave salamanders what appears to be random, unoriented movement may, instead, be oriented movement along an axis midway between the axes of the two corridors; but since movement can coly be into the four arms of the assembly this results in apparent randomness. Recently it has been suggested that magnetic information might be used in two quite separate ways: in both determination of compass direction as well as in position-findig (the so-called "map" step; GOULD 1980). This may explain why orientation of salamanders, as well as that of birds, is affected by tiny magnetic fluctuations. Whereas the magnetic compass apparently responds only RELEASE DEVICE (Einsetz-Schacht) TESTING ASSEMBLY (Prüf apparat) EARTH'S FIELD (Erdfald) RESULTANT FIELD (Resultierend«« Feld) ARTIFICIAL FIELD (Synthetisches Magnetfeld) Fig. 6. Testing procedure for magnetic orientation in salamanders. The teat assembly consists of two light-tight corridors with a release chamber in the center. When the release device Is raised (by means of a string; not shown), animals can move in any of the four directions, although when orienting non-randomly they preferentially choose the magnetic axis to which they previously had been trained. The testing assembly Is situated inside a magnetic cube-coil which, when activated, produces an artificial horizontal field that sums with the earth'

s field to yield a resultant field rotated 90° to the earth's natural N-S axis. Thus, animals can be tested in two orthogonal magnetic field conditions relative to the corridors. Adapted from PHILLIPS (1977)