Every year millions of birds make heroic migratory journeys guided by the Earthâs magnetic field. How they detect magnetic fields has puzzled scientists for decades. A combined effort between the Keaysâ lab at the Institute of Molecular Pathology in Vienna and researchers at the Australian Microscopy & Microanalysis Research Facility (AMMRF) at the University of Western Australia has added some important pieces to this puzzle. Their work, published in Current Biology, reports the discovery of iron balls in sensory neurons. These cells, called hair cells, are found in the ear and are responsible for detecting sound and gravity. Remarkably each cell has a single iron ball, and itâs in the same place in every cell. They are found in every bird, whether itâs a pigeon or an ostrich but they are not in humans. Itâs an astonishing finding, despite decades of research these conspicuous balls of iron had never been observed previously.
AMMRF researchers Dr Jeremy Shaw and Prof. Martin Saunders, who specialise in the use of analytical electron microscopy, helped to describe these new iron structures. An example of a ball is seen in the TEM image on the left and an iron map on the right. âNature keeps surprising us with the various ways iron can be utilised by animalsâ?, states Dr Shaw, who has studied iron in a range of animals from molluscs to humans. This finding builds on previous work by the same team who last year showed that iron-rich cells in the beak of pigeons that were believed to be the magnetic sensors, were really just blood cells. âThese hair cells are much better candidates, because theyâre definitely neurons. But weâre a long way off understanding how magnetic sensing works â we still donât know what these mysterious iron balls are doing.â? said Dr Keays. âWho knowsâ¦perhaps they are the elusive magnetoreceptorsâ? muses Dr Keays âonly time will tellâ?.