This ended up being a topic of interest on two of my favourite blogs: both Krulwich Wonders (by Robert Krulwich of NPR) and Not Exactly Rocket Science (by Ed Yong previously of Discover Magazine, now of Nat Geo). So, naturally, I have to talk about it here too!
Both of the aforementioned articles focus on the ability of foxes to detect small prey items underneath the snow when they can’t see them. The fox is believed to use a “magnetic sense” to hunt these prey items. It orients itself in a northeasterly direction, then leaps into the air and dives into the snow, snapping up its food.
As both writers point out, there are many animals with documented magnetic senses. Foxes are surely cool in their capacity to hunt by magnets, but there are other astounding stories.
Even cows and deer line up along north-south lines!
So what other kinds of animal magnetism are there? Let’s look at some cool examples.
Sharks: Dr. Yong leaves this tantalizing clue in his article that all animals use one of two methods of detecting magnetic fields except sharks! What about sharks, Dr. Yong?!?!?! Well, I did a little of my own research to find out.
Sharks, rays, chimaeras (and a few primitive bony fish) have a special electroreceptive organ known as the Ampullae of Lorenzini. This organ is extremely sensitive to small amounts of electricity (the better for detecting the tiny electrical impulses in the muscles of prey items) and, according to Wikipedia: “The electric fields produced by oceanic currents moved by the Earth’s magnetic field are of the same order of magnitude as the electric fields that sharks and rays are capable of sensing.”
Magnetotactic Bacteria: Yes, even these humble single-celled organisms can align themselves to the earth’s magnetic field. Bacteria that are responsive to magnetic fields are called magnetotactic and they have special organelles which are full of magnetic crystals (usually magnetite, which is also found in other animals). Probably the coolest aspect of these magnetotactic bacteria (in my humble opinion) is that their magnets will align the cells…even if they are dead.
Birds: Birds are thought to navigate using the Earth’s magnetic fields as well. There is good support for the hypothesis that birds detect the magnetic field via cryptochromes, or light receptive proteins in the eye which when activated form two radicals, the spin of which is determined by the surrounding magnetic fields. However, they also might use magnetite, as it has been found in their beaks.
Most of the research on the magnetoreception of birds has been done on homing pigeons, which have a remarkable capacity to orient themselves and find their way home! (PS Relevant RadioLab episode! Listen to it!!!)
But pigeons are not the only birds to use these methods, and in fact it seems to be quite common; it is even found in our friendly backyard birds, like robins.
Flies and honeybees: For fruit flies, which have been studied extensively, we have strong evidence to suggest that cryptochromes are also the primary method of detecting magnetic fields. On the other hand, honeybees seem to use magnetite (Hsu et al. 2007).
Mammals: Obviously our fox friend seems to use magnetic cues, but there is also some evidence to suggest that other mammals do as well.
For example, the Zambian Mole Rat, with its long subterranean tunnels:
Bats are also thought to use magnetic fields as a way of orienting at night: