One theory says that animals use magnetite minerals to somehow sense magnetic field direction. The other theory holds that birds might ‘see’ a magnetic field using their eyes. For this to be perceived, there would have to be some sort of chemical reaction of molecules in the eye (perhaps involving free radicals) that could be influenced by the direction of magnetic field lines.[image from/read more at Nature.com]
But until now, there has been no evidence that such a reaction could be influenced by a field as weak as that produced by the Earth. Now, an international team lead by Christiane Timmel and Peter Hore at the University of Oxford has demonstrated that this is possible.
"We’ve established a proof-of-principle that this kind of chemistry can be used to detect fields as weak or weaker than that of the Earth, and that we can detect the direction of that field, which is crucial for a compass," says Hore.
OK, you got me there, I just find it fitting to post an article with the word compass like an article with the word brain. This is after all brain compass.