ananyo writes "Individual neurons in birds' brains can relay crucial information about Earth's magnetic field, possibly providing the animals with an 'internal GPS.' Pigeons' remarkable navigational feats have long been pegged to the birds' ability to sense magnetic fields, but pinning down how they do so has frustrated scientists for years. Work published in Science (abstract) shows that individual cells seem to encode information on a magnetic field's direction, intensity and polarity. The work also suggests that these signals come from a part of the inner ear called the lagena, further complicating matters for researchers in the field. The Science paper comes just days after a report in Nature (abstract) revealed that cells in pigeons' upper beaks, previously thought to be magnetoreceptors, are actually immune cells called macrophages."