The Economist: For decades scientists have known that birds’ ability to navigate with great accuracy over long distances, in some cases migrating from one side of the world to the other, relies on a magnetic sense that humans lack. Experiments with homing pigeons performed in the early 1970s found that attaching a magnet disrupted their ability to orientate themselves. Since then, research has intensified into the precise mechanism of birds’ magnetic sense. So how does it work?
Scientists have focused their attention in three areas: the beak, the inner ear and the eyes. Birds’ beaks contain tiny grains of magnetite, a form of iron oxide which is easily magnetised, and is known to be involved in magnetic sensing in bacteria. But when David Keays of the Institute of Molecular Pathology in Vienna examined the beaks of 200 pigeons, the results were surprising. He found that the magnetite grains were mostly located in macrophages, which are sort of biological garbage collectors that wander around the body, rather than in specialised sense cells. This strengthened the case that birds’ magnetic sense resides not in their beaks, but in their inner ears. Dr Keays and his colleagues changed tack, and earlier this year they reported that they had found tiny concentrations of iron in the neurons of a pigeon’s inner ear.