Canada geese, monarch butterflies, bonnethead sharks, and sockeye salmon are a few of the many animal species that navigate the globe by sensing small changes in Earth’s magnetic field. Previous studies of these organisms have identified several types of sensors, such as magnetically sensitive chemical reactions and compass-like cellular structures, but it’s been unclear how sensitive these so-called biological magnetoreceptors are. Now Iannis Kominis and Efthmis Ghoudinakis of the University of Crete, Greece, have calculated bounds on the sensing ability of three main types of biological magnetoreceptor, showing that two of them can likely sense magnetic fields with magnitudes close to the quantum limit for magnetic-field detection [1].
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