Recently, oscillating magnetic fields in the MHz-range were introduced as a useful diagnostic tool to identify the mechanism underlying magnetoreception. The effect of very weak high-frequency fields on the orientation of migratory birds indicates that the avian magnetic compass is based on a radical pair mechanism. To analyse the nature of the magnetic compass of mammals, we tested rodents, Ansell's mole-rats, using their tendency to build their nests in the southern part of the arena as a criterion whether or not they could orient. In contrast to birds, their orientation was not disrupted when a broad-band field of 0.1–10 MHz of 85 nT or a 1.315 MHz field of 480 nT was added to the static geomagnetic field of 46 000 nT. Even increasing the intensity of the 1.315 MHz field (Zeeman frequency in the local geomagnetic field) to 4800 nT, more than a tenth of the static field, the mole-rats remained unaffected and continued to build their nests in the south. These results indicate that in contrast to that of birds, their magnetic compass does not involve radical pair processes; it seems to be based on a fundamentally different principle, which probably involves magnetite.
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