Bird navigation – great balls of iron

Every year millions of birds make heroic migratory journeys guided by the Earth’s magnetic field. How they detect magnetic fields has puzzled scientists for decades. A combined effort between the Keays’ 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 it’s in the same place in every cell. They are found in every bird, whether it’s a pigeon or an ostrich but they are not in humans. It’s 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. “Nature keeps surprising us with the various ways iron can be utilised by animals?, 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. “These hair cells are much better candidates, because they’re definitely neurons. But we’re a long way off understanding how magnetic sensing works – we still don’t know what these mysterious iron balls are doing.? said Dr Keays. “Who knows…perhaps they are the elusive magnetoreceptors? muses Dr Keays “only time will tell?.

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