Magnetic orientation by magnetoreception has been observed in insects, such as honey bees, some flies, and termites, in some fish, and in certain species of migratory birds.
As far as we know, there is no specialized organ for magnetoreception in mammals. However, there are observations that show that some animals, such as cows, tend to orient themselves in a certain direction while they are at rest—while grazing or resting. In order to know if these observations respond to real behavior, or if it is only due to a confirmation bias – scoring as success when an animal performs that behavior, ignoring the times that it does not do so – it was necessary to analyze it from a scientific perspective.
A trend that is not always fulfilled
Research led by Sabine Begall of the University of Duisburg-Essen, Germany, used Google Earth satellite imagery to conduct a massive, non-invasive field study of the orientation in which cattle around the world grazed or rested. . They analyzed 308 locations distributed across six continents, and a total of 8,510 head of cattle . Given the quality of the image, they could see the orientation of the animal, but they could not always discern where the head was and where the tail was, so they obtained direction data, but not sense.
In the study they were able to verify that there was a clear orientation trend in a north-south axis significantly deviated at 6.4º with respect to magnetic north. However, at rest—resting or grazing—this orientation close to the north-south axis was more of a general trend than an absolute law. That is to say, although most of the cows were oriented on that axis, there were quite a few specimens arranged in other directions, and covering practically the entire circumference of the compass.
In addition, they also checked whether this orientation trend on the north-south axis was more in line with the geographic pole or the magnetic pole , since both have a certain deviation. A geographical orientation would be a response to the position of the sun in the sky , while a magnetic orientation would respond to a process of magnetoreception, through some kind of internal compass.
To verify this phenomenon, they checked the orientation of those geographical places where the declination of the magnetic axis is high, such as in certain areas of North America, which can exceed 14º. They also checked the direction of the shadow — where it was visible — to see whether or not the direction of the animals was related to the position of the sun. After carrying out the analyses, everything seemed to indicate that this orientation was magnetic and not geographical.
Other animals that also orient
In that same study, in addition to analyzing the orientation of cows, they also analyzed that of other ruminants, specifically roe deer and deer . For their study, they made direct observations in populations of cervids in the Czech Republic, grazing or resting —avoiding the detection of the observer by the animals—, or they measured the beds of animals that had rested in the snow. The results showed that both roe deer and red deer oriented on a near north-south axis for grazing and resting. The deviations were about 10º from the north-south axis for roe deer, and about 8º for red deer , with slight deviations depending on whether they were resting (slightly higher) or grazing (somewhat lower).
But those results exceeded expectations; in the wild, the dispersion of the data was much lower. In these cases, the number of roe deer, and even more so the number of deer, that deviated more than 20º from that reference orientation, were practically anecdotal, and the vast majority remained within that narrow range.
Ruminants are not the only mammals capable of orienting in this way. Rodents such as the African mole frog, the Siberian hamster, the blind mole rat, or mice , as well as other groups such as bats , have also shown the capacity for magnetoreception . Even dogs, when it comes to defecating, seem to be oriented in a certain direction.
How do they orient themselves in this way?
Magnetic alignment is an expression of behavior observed as spontaneous, produced by magnetoreception, and that appears when the animal is at rest and, more especially, when body orientation is not conditioned by other factors, such as an excess of insolation, terrain irregularities or a wind-dependent orientation to avoid detection by potential predators or prey.
Both insects and birds that have magnetoreception capacity do so through certain organs that have tiny magnetite crystals, which are oriented according to the Earth’s magnetic field.
In the case of some fish, such as sharks, it is based on the ampullae of Lorenzini , electroreceptor organs capable of detecting small variations in electrical potential. This not only helps them to detect prey by their nervous activity, but also to detect the earth’s magnetic field, thanks to Faraday’s law of electromagnetic induction.
Mammals do not have such mechanisms. The answer to how certain species, such as cows, roe deer or bats, are able to orient themselves is still unknown. Some research points to certain pigments — cryptochromes — in the retina, or to specific receptors in the eye’s cornea. In the first case, magnetoreception would depend on light , and could explain the orientation of ruminants or dogs. The second case would allow magnetoreception in complete darkness, and could explain this ability in rodents and bats. In either case, these organs would be associated with a specific brain structure for magnetoreception.
The most fascinating thing is that the same type of cryptochromes that, in molecular terms, could fulfill this function have been found, as well as magnetite deposits in the sphenoid and ethmoid bones. There are also studies in humans that suggest the existence of certain brain activity in response to changes in magnetic orientation, but it is so subtle that it does not have a physiological response. If ever the human species had the capacity for magnetoreception, unfortunately today it is only an evolutionary vestige.
References:
Baker, R. R. et al. 1983. Magnetic bones in human sinuses. Nature, 301(5895), 79-80. DOI: 10.1038/301096b0
Begall, S. et al. 2008. Magnetic alignment in grazing and resting cattle and deer. Proceedings of the National Academy of Sciences, 105(36), 13451-13455. DOI: 10.1073/pnas.0803650105
Burda, H. et al. 1990. Magnetic compass orientation in the subterranean rodentCryptomys hottentotus (Bathyergidae). Experientia, 46(5), 528-530. DOI: 10.1007/BF01954256
Foley, L. E. et al. 2011. Human cryptochrome exhibits light-dependent magnetosensitivity. Nature Communications, 2, 356. DOI: 10.1038/ncomms1364
NĚMECJENS, P. et al. 2001. Neuroanatomy of Magnetoreception: The Superior Colliculus Involved in Magnetic Orientation in a Mammal. Science, 294(5541), 366-368. DOI: 10.1126/science.1063351
Wang, C. X. et al. 2019. Transduction of the Geomagnetic Field as Evidenced from alpha-Band Activity in the Human Brain. eNeuro, 6(2), ENEURO.0483-18.2019. DOI: 10.1523/ENEURO.0483-18.2019
