Mammals

Amongst mammals, rodents (e.g. mole rat (Heterocephalus glaber) ^[1] and zokors (Myospalax) ^[2]) and bats ^{[3, 4]} have the ability to orient themselves according to the Earth’s magnetic field. A possible disturbance of this orientation by artificial static or low-frequency fields has not been investigated so far. In other mammals, magnetoreception has not yet been clearly demonstrated; however, this is being researched by some working groups. In animals that orientate themselves in darkness like the aforementioned species, it is assumed that magnetoreception is based on the mineral magnetite. A corresponding sense organ has not yet been discovered.

Magnetoreception has also been described in some rodents that live above ground and have good vision (e.g. wood mice (Apodemus sylvaticus) ^[5] and house mice (Mus musculus) ^[6]). As a possible mechanism of perception, it is suggested that the blue light receptor cryptochrome, which is located in the mammalian retina, is activated by magnetic fields ^[7]. A similar pathway is already well described in birds but has not yet been scientifically proven in mammals. However, recent experiments on rodents suggest that mammals also perceive static magnetic fields in their eyes ^[8]. Similar to birds, this mechanism is disturbed by high-frequency electromagnetic fields with frequencies below 100 MHz ^[9].

There is also evidence of magnetoreception in other mammals. Based on satellite images, it has been observed that ruminants such as cattle and deer prefer to orient themselves in a north–south direction when outdoors ^[10]. The preferred orientation was disturbed in cattle near power lines ^[11]. Based on field observations, similar behaviour has been described in wild boars and African warthogs ^[12]. From the above observations, the authors conclude that all hoofed animals can perceive magnetic fields. As a result, their behaviour could be influenced by the magnetic fields of high-voltage power lines. However, all these studies are observational and do not specify a possible sense organ or mechanism for perceiving magnetic fields.

It has been possible to train dogs to find a magnet ^[13]. The experiment was conducted in a blinded manner, and the use of other sensory organs was largely excluded. Field experiments with automated tracking systems on dogs have shown that dogs use the magnetic field to find their way back to the starting point from unknown locations ^[14].

Intensive research is being carried out in all the areas described. However, the exact biophysical mechanism and the corresponding neuronal signalling pathways are unknown; however, there are some plausible hypotheses.

References

[1] Kimchi T, Terkel J (2001) Magnetic compass orientation in the blind mole rat Spalax ehrenbergi. J Exp Biol. 204(Pt4):751 – 758.

[2] Burda H, Marhold S, Westenberger T, Wiltschko R, Wiltschko W (1990) Magnetic compass orientation in the subterranean rodent Cryptomys hottentotus (Bathyergidae). Experientia. 46(5): 528 - 30.

[3] Holland RA, Thorup K, Vonhof MJ, Cochran WW, Wikelski M (2006) Navigation: bat orientation using Earth's magnetic field. Nature 444(7120): 7002.

[4] Holland RA, Kirschvink JL, Doak TG, Wikelski M (2008) Bats use magnetite to detect the earth's magnetic field. PLoS One 3(2): e1676.

[5] Malkemper EP, Eder SH, Begall S, Phillips JB, Winklhofer M, Hart V, Burda H. Magnetoreception in the wood mouse (Apodemus sylvaticus): Influence of weak frequency-modulated radio frequency fields. Sci Rep 4:9917; 2015.

[6] Muheim R, Edgar NM, Sloan KA, Phillips JB. Magnetic compass orientation in c57bl/6j mice. Learn Behav 34:366-373; 2006.

[7] Nießner C, Denzau S, Malkemper EP, Gross JC, Burda H, Winklhofer M, Peichl (2016) L.Cryptochrome 1 in Retinal Cone Photoreceptors Suggests a Novel Functional Role in Mammals. Sci Rep. DOI: 10.1038/srep21848.

[8] Caspar, KR, Moldenhauer, K, Moritz, RE, Němec, P, Malkemper, EP, Begall, S (2020). Eyes are essential for magnetoreception in a mammal. J R Soc Interface 17(170): 20200513.

[9] Phillips J, Muheim R, Painter M, Raines J, Anderson C, Landler L, Dommer D, Raines A, Deutschlander M, Whitehead J, Fitzpatrick NE, Youmans P, Borland C, Sloan K, McKenna K. Why is it so difficult to study magnetic compass orientation in murine rodents? J Comp Physiol A; 2022.

[10] Begall S, Červený J, Neef J, Vojtech O, Burda H (2008) Magnetic alignment in grazing and resting cattle and deer. Proc Natl. Acad. Sci. USA 105(36): 13451 - 13455.

[11] Burda H, Begall S, Červený J, Neef J, Němec P (2009) Extremely low-frequency electromagnetic fields disrupt magnetic alignment of ruminants. Proc. Natl. Acad. Sci. USA 106(14): 5708 - 5713.

[12] Červený J, Burda H, Ježek M, Kušta T, Husinec V, Novákova P, Hart V, Hartová V, Begall S, Malkemper EP (2016) Magnetic alignment in warthogs Phacochoerus africanus and wild boars Sus scrofa. Mammal Review 46(3): 5.

[13] Martini S, Begall S, Findeklee T, Schmitt M, Malkemper EP, Burda H (2018). Dogs can be trained to find a bar magnet. PeerJ 6: e6117.

[14] Benediktova, K, Adamkova, J, Svoboda, J, Painter, MS, Bartos, L, Novakova, P, Vynikalova, L, Hart, V, Phillips, J, Burda, H (2020). Magnetic alignment enhances homing efficiency of hunting dogs. Elife 9.