Animal Senses #12: Magnetism

Magnetoreception refers to the ability to navigate using the earth’s magnetic field for context. A very interesting thought experiment on this topic was to change the magnetic field around such species and see if they changed direction. In practice, that’s easy to do with small animals, but how could one try that with something as big as a whale? Sounds impossible, except nature itself creates such situations, says Ed Yong in Immense World:

“The sun periodically throws cosmic tantrums and produces solar storms – streams of radiation and charged particles that affect the Earth’s magnetic field.”

Scientists collated 33 years of data on healthy whales that inexplicably stranded themselves onto beaches. They then compared that with the data on solar activity. And bingo! On days with the most intense solar storms, gray whales were four times more likely to beach themselves.

 

The magnetic field has two components. The first one is inclination, the angle at which the geomagnetic field lines meet the surface of the earth. At the equator, the lines run parallel to the ground; at the poles, they run perpendicular. The second one is intensity, the strength of the field. Both components vary across the earth, and thus the combo can be considered as similar to latitude-longitude system of coordinates.

 

Such magnetic “maps” have a serious limitation. While they can be sensed in the immediate vicinity, they can’t be used to predict what it will at a different place. The only way to find out is to move, and move quite a lot before there is any perceptible change. This is why species that use magnetoreception are the ones that travel very long distances. It simply can’t work over short distances.

 

We know that the earth’s magnetic field has reversed at least 183 times in the last 83 million years. While these flips are gradual and won’t affect individuals, does it mean species have had to evolve to adjust for such reversals, wonders Yong.

 

Magnetoreception is the only sense for which we haven’t yet identified the associated sensor in animals. There are 3 mains theories. The first one considers the material magnetite to be the key. But nobody has found such magnetite heavy cells in any species. The second one considers electromagnetic induction as the key – species produce electric currents, which would interact with the magnetic field, and the animal could then decipher meaning via this interaction of the fields. This theory isn’t very popular for obvious reasons – it can’t work for aerial species since they are immersed in air, an insulator. Which is why the third theory, though the most complicated, is the one most widely accepted. It involves two molecules called a radical pair and quantum mechanics. In theory, it can explain how a weak magnetic signal could be converted into a chemical signal that is easier to process.

 

There are multiple challenges in studying magnetoreception. The three theories have led to very vicious fights among scientists. That has led to outright fraud in some cases, but more often, it reduces objectivity and increases bias. Another challenge with studies in this field is that the magnetic field is imperceptible to us humans and it is very weak in any case, so we can easily miss if there is any setup error or background activity that is interfering with the study. Additionally, the signal in question is very weak, so it is not clear how clearly it can/is interpreted by animals that use it. It surely cannot be as precise as light or sound, but how imprecise is it exactly? In addition, as mentioned earlier, it works over long distances, but how long? And over how much time does course correction happen? Without knowing any of these details, it is hard to study, interpret or reproduce any studies. Or is it the case that for exactly all these reasons, animals use other senses in combination with magnetoreception, or put differently, perhaps magnetoreception is never used in isolation?

“The boundaries of our own Umwelt corral our ability to understand the Umwelten of others.”