Obviously, the matter of finding breathing holes in ice is a matter of life and death for Weddell Seals. But how do they successfully do so? A team of researchers led by Randall Davis, Terrie Williams, and Lee Fullman hypothesize that the seals may be sensing earth's magnetic field to navigate.
The researchers carefully mapped the magnetic field in one specific area, and have outfitted seals with video and data recorders; by comparing seal behaviour with location in the magnetic field, the researchers should be able to determine whether or not their hypothesis is correct.
Past theories include "piloting," whereby the seals use visible features of the ice to navigate; however, in winter months, very little light illuminates the ice from above. It is also possible that seals pass on the location of breathing holes by acoustic cues-- messages to other seals. The research team plans to use a "directional hydrophone" to pinpoint the location of incoming calls; this will either exclude (or verify!) acoustic information as the method by which seals find breathing holes.
This is not the first instance of hypothesized magnetic sensing in animals. Birds and insects unquestionably use Earth's magnetic field to navigate; foxes use electromagnetic sensing to better catch mice (by jumping along a N-S axis); cattle and deer tend to graze facing in a N-S direction (and this behaviour breaks down near field-disrupting power lines); marine animals such as sharks and turtles are deterred by active magnets; and some have proposed that animals sense and flee from oncoming storms due to electromagnetic disruption.
Whether or not seals are members of these illustrious ranks remains to be seen. If they are using electromagnetic sensing, they are doing so with a precision and fine-tuning that is somewhat different than the examples described above!
Seals have an incredible ability to find the breathing holes for when they are swimming under ice, but until now how they navigated was a mystery. Now, researchers believe that the marine mammals are using the Earth's magnetic field as a natural GPS. If the theory is correct, it would represent the first evidence of such a trait in a marine mammal.