The first clear evidence that some animals have a magnetic sense came from a simple-enough experiment—put an animal in a box, change the magnetic fields around it, and see where it heads.
German scientists first tried this in the 1960s, with captive robins. When it came time to migrate, the birds would hop in a particular direction, as if they innately knew the way to fly. But when the team altered the magnetic fields around the robins’ cages, the birds hopped along a different bearing. In later decades, researchers showed that other songbirds, sea turtles, spiny lobsters, bogong moths, and many other species can also be magnetoreceptive, using variations on this same experiment.
“But you can’t really do that with a whale,” says Jesse Granger, a biophysicist at Duke University.
Granger has good reason to think that whales should have a magnetic sense. “They have some of the most insane migrations of any animals on the planet,” she says. “Some of them almost go from the equator to the poles, and with astounding precision, traveling to the exact same area year after year.” But how? Smells will diffuse too broadly over such long distances. Visual landmarks like the sun or stars are useful, but whales also migrate on cloudy days.
The Earth’s magnetic field is omnipresent, providing a reliable navigational guide even when other cues fail. It’s no coincidence that many of the species known to be magnetically sensitive are also those that undertake long migrations. So it’s easy to think that whales have a compass. It’s just hard to prove it.
Granger used a clever approach: She looked for data about whales that had gone off-course. Now and then, whales and dolphins will beach themselves, sometimes in large groups, and often with tragic results. These events have many possible causes—loud human noises, collisions with ships, disease. But in cases where stranded whales weren’t ill or injured, they might simply have made a navigational error. “If it’s near to shore, a small miscalculation could have led to a stranding,” Granger says. Perhaps, she reasoned, some whales run aground because their internal compasses temporarily go haywire. And while there aren’t many things that could conceivably disturb such compasses, the sun is one of them.
Periodically, the sun throws a cosmic fit and unleashes a solar storm—streams of radiation and charged particles that affect the Earth’s magnetic field. Such storms could conceivably affect any animal that was magnetically sensitive. To see whether that might be true, Granger collected 31 years of data on gray-whale strandings from the National Oceanic and Atmospheric Administration. She looked at only events where the whales seemed healthy and unharmed. Then, she recruited an astronomer. Lucianne Walkowicz of the Adler Planetarium, in Chicago, was the perfect candidate: She’d originally wanted to be a marine biologist before she became an astronomer who specializes in solar storms. She worked with Granger to wrangle decades of data on solar activity.
Together, the team found that strandings where whales were otherwise healthy and uninjured—186 events in total—were twice as likely to happen on days with a high count of sunspots, or black patches that are signs of solar storms. “We found a huge correlation,” Granger says. (For the stats geeks among you, the P value was less than 0.0001.)
Initially, Granger thought that the whales might be thrown off by shifts to the Earth’s magnetic field, induced by the solar storms. But she found that such shifts don’t affect a gray whale’s risk of stranding. She then realized that the storms might be directly influencing the whales’ magnetic sensors, by releasing huge bursts of radio-frequency radiation. Indeed, Granger found that on days when radio waves from the sun are at their strongest, gray whales are four times more likely to strand. It’s not that the whales are sensing these waves directly—to our knowledge, no animal can do that, and they’d need eyes the size of a building to do so. It’s more that the radio waves might be screwing up the whales’ magnetic sensors, disrupting their biological compass.
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.
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.
Granger is now analyzing another set of data that tracked the movements of a pod of humpback whales over 12 years. She wants to see whether the animals deviated from a straight line on days with solar storms. Meanwhile, a team of NASA scientists is also looking at whether solar storms are connected to whale strandings.
This link might seem far-fetched at first, but perhaps it shouldn’t. We have no problem accepting that animals behave differently during the day and night, and that’s essentially the same idea—electromagnetic energy released by the sun, traveling across astronomical distances, affecting the lives of animals on Earth. We can’t see radio-frequency radiation the way we can visible light, so its effects seem more mysterious; perhaps they shouldn’t be. Still, Granger admits that the idea of solar storms sending confused whales onto beaches does have the air of a fringe theory. “I’m probably going to get a lot of weird people emailing me,” she says.
“Whales certainly use geomagnetism to navigate, but many factors contribute to whether they are successful over long distances, including both natural factors and human-caused ones, like sonar use or ship strikes,” Walkowicz says. “This project has driven home for me that biology—and particular animal behavior—is extremely complicated. Thank heavens I just do astronomy.”