Magnetoreception in animals

Different animals may detect magnetic fields in different ways, and behavioral experiments and microscopic examinations of possible magnetoreceptors have both yielded results that are consistent with all three mechanisms, namely electromagnetic induction, ferrimagnetism, and chemical reactions involving pairs of radicals. Nevertheless, a magnetoreceptive organ has not yet been identified with certainty in any animal. Here, Johnsen and Lohmann discuss the physics of the three main mechanisms that have been proposed and highlight some of the critical evidence in support of each.