Magnetic maps in animals: a theory comes of age?

The magnetic map hypothesis proposes that animals can use spatial gradients in the Earth's magnetic field to help determine geographic location. This ability would permit true navigation--reaching a goal from an entirely unfamiliar site with no goal-emanating cues to assist. It is a highly contentious hypothesis since the geomagnetic field fluctuates in time and spatial gradients may be disturbed by geological anomalies.