How migratory birds read Earth's magnetic field has been one of sensory biology's most stubborn mysteries. In 1882 the French naturalist Camille Viguier proposed that the sense might reside in the inner ear and operate through small electric currents, an idea that was largely forgotten. Research published in Science by the group of David Keays at LMU's Faculty of Biology now puts that Victorian hypothesis back at centre stage.
Rather than hunting for a presumed sensor, the team took an unbiased approach, mapping neural activity across pigeon brains after exposure to magnetic fields. Advanced microscopy revealed strong activation in the vestibular nucleus, a region wired to the inner ear, pointing to a dedicated pathway for magnetic information. Genetic analysis of inner ear tissue then turned up cells carrying highly sensitive electrical sensors of the same type sharks use to detect prey.
The researchers propose that these cells detect magnetic fields through electromagnetic induction, the physical principle behind wireless phone charging, in which a changing magnetic field produces an electrical signal. Keays describes the system as a dark compass, operating independently of the light-dependent compass other studies place in birds' visual systems, and argues that magnetoreception probably evolved independently several times across the animal kingdom.