How pigeons exploit magnetic fields for navigation

Iron-rich immune cells in the liver may act as sensors for magnetic fields, serving as an internal compass. Scientists have long known that migrating birds and homing pigeons navigate in part by sensing the Earth’s magnetic fields, especially at night or in overcast conditions when visual landmarks or sunshine are in short supply. But exactly where this magneto-sensing occurs in the body—and the mechanism that enables it—remains a matter of intense debate. A new paper published in the journal Science suggests that homing pigeons have iron-rich immune cells in their livers that help them detect magnetic fields and transmit that information to the brain. There are three primary hypotheses for how birds might sense Earth’s geomagnetic field. One is a compass-like mechanism, whereby the Earth exerts a pull on magnetic particles in a bird’s upper beak that relays directional information via a large nerve in the cranium. A second is that it happens biologically via cellular ion channels sensitive to voltage, enabling birds to sense changes in the magnetic field. And a third suggests that physical effects on retinal pigments enable birds to detect photons and send signals to the brain, al