Le-Qing Wu and David Dickman from the Baylor College of Medicine have found neurons in a pigeon's brain that encode the properties of a magnetic field. They buzz in different ways depending on how strong the field is, and which direction it's pointing in.

We show that the artificial field through an attached magnet will quickly disrupt the birds' ability to distinguish pole-ward from equator-ward headings, but that much stronger fields are necessary to disrupt their ability to detect the magnetic axis.