Birds navigate incredibly long distances using what the neuroscientist David Keays calls “a sixth sense”: the ability to detect how the earth’s magnetic field changes at different locations around the planet. The scientist, from the Institute of Molecular Pathology, in Vienna, has been hunting in vain for the cells responsible. But in what Mr. Keays calls “a stunning piece of work,” two other researchers have found cells in the pigeon brain that respond to specific changes in magnetism.

The cells, in the most primitive brain region, the stem, “encode the direction, intensity, and polarity of the Earth’s magnetic field,” one of those scientists, David Dickman, a neuroscientist at the Baylor College of Medicine, told me. “These cells have the key ingredients to form maps of spatial directional heading and location, similar to the GPS in your car or cellphone.” He and his colleague…

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