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That’s just a hypothesis, though, and it’s hard to test because, despite decades of research, no one knows for sure what animals actually use to sense magnetic fields. Eyes see. Noses smell. Ears hear. But what’s the organ that senses magnetic fields?
It’s been fiendishly hard to identify partly because magnetic fields suffuse the entire body, which means a magnetic receptor doesn’t have to be in an exposed body part, like an eye or ear. It could be anywhere. It could be an inconspicuous bundle of tissue that looks identical to everything around it. As Granger’s colleague Sonke Johnsen once wrote, finding the magnetoreceptor is like searching for a “needle in a needle stack.”
There are two strong possibilities, though. One involves a mineral called magnetite, whose crystals act as small, rotating magnets. The other involves a chemical reaction that likely occurs in the eye, and that’s influenced by the direction of the magnetic field. Theoretically, radio-frequency noise could also influence that reaction, which might explain how it could send a migrating whale off-course. (It’s unclear whether human-made sources of radio waves could have the same effect, but such sources are likely to be much weaker than a solar storm.)
Other researchers have found similar evidence. One study found that whales are more likely to strand at places along the U.S. Eastern Seaboard where local magnetic fields are weak. Another found correlations between whale strandings and disturbances in the Earth’s magnetic field. A third found that migrating robins can be sent off-course by artificial magnetic fields that simulate the effects of a solar storm. And a couple of studies found that racing pigeons were slower to find their way home on days with lots of sunspots.
Neither these studies nor Granger’s can provide conclusive evidence that whales have a magnetic sense; they only reveal correlations. Still, such correlations exist, and are strong. They’re also hard to explain away. It’s not as if stranding whales are affecting the sun, and if there’s some other independent factor that’s tied to both solar activity and whale strandings, it’s hard to imagine what that might be.
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Granger’s study also has an important strength that’s missing from much of the research into magnetic senses—a large sample size. Many researchers run experiments with just a small number of animals, which might explain why the study of magnetoreception is so full of retracted and disputed findings. Granger couldn’t work with any animals, but she could amass decades’ worth of data on whale movements, solar activity, and more.
“This study has been done in a particularly rigorous way,” says Kenneth Lohmann from the University of North Carolina, Chapel Hill. It might imply that whales might have a magnetic sense, but there are also (equally controversial) reports that solar storms could affect animal health. “It is conceivable that the effect on the whales involves something that does not directly tie into navigation,” Lohmann adds.