Turtles Can Sense Earth’s Magnetic Field — And Some Even Dance When They Feel It
Loggerhead turtles are always on the move. Traveling thousands of kilometers over the course of their lives, these sea turtles navigate based on the Earth’s magnetic field, which they detect via two distinct approaches. In fact, loggerheads see the terrain, and they feel it too, having both a compass and a map for their travels. But for years, scientists have struggled to explain how exactly the latter sense works.
Researchers finally found an answer, exploring how these turtles track the magnetic field in a study conducted in the United States. Journal of Experimental Biology. By testing these turtles’ ability to sense the field after teaching them to signal this sensation through an adorable dance, the researchers revealed that the loggerhead turtles’ “magnetic sense” could work thanks to the existence of pieces of magnetite embedded throughout their bodies.
The research is as engaging as it is scientifically significant. According to the researchers, the results represent a major step in understanding these turtles and understanding how they navigate using the Earth’s magnetic field.
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Turtle migration and the Earth’s magnetic field
Loggerhead turtle migrations are epic, spanning thousands of miles across the open ocean. Although the journey is difficult, the turtles are well equipped, having been born with a built-in navigation system based on the Earth’s magnetic field.
Surprisingly, there are two distinct sensations that allow these turtles to orient themselves using magnetism: in one, the turtles see the magnetic field, thanks to the photosensitive molecules which activate around it. In another, turtles feel the field, although the exact explanation of how this has long eluded scientists.
In an effort to learn more, the team trained eight loggerhead hatchlings to signal, through a delightful twirling dance, when they felt the magnetic field at a particular location around the Turks and Caicos Islands. (They also trained eight additional hatchlings to do the same when they felt the magnetic field around Haiti.) Then, after exposing the turtles to strong magnetic pulses, the researchers observed their behavior, waiting to see if they signaled the presence of the field through their rotations.
If the turtles weren’t dancing, the researchers said, that could suggest they felt the magnetic field through embedded pieces of magnetite, which would be disrupted by the strong magnetic pulses. Alternatively, if the turtles were dancing, this could suggest that they sensed the magnetic field through another mechanism. Putting the turtles to the test, the team found that the hatchlings danced less after their exposure to the pulses, indicating that their magnetic map may depend on the presence of these bits.
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Dancing magnetism
Of course, the trick to the discovery was the turtles’ signaling, triggered by the hatchlings’ love of food. “They are very motivated by food and eager to dance when they think there is a possibility of being fed,” said Alayna Mackiewicz, study author and graduate student at the University of North Carolina at Chapel Hill, according to a press release.
Indeed, loggerhead turtle hatchlings toss and turn in anticipation of food, circling in an excited dance. Thus, by teaching the turtles, over two months, to associate their sensation of the magnetic field with food, the researchers effectively encouraged them to communicate when they felt the magnetism.
“It’s really fun, but it takes quite a bit of time,” Mackiewicz said.
According to the team, turtles use both of their magnetic senses to make sense of their surroundings, by seeing and feeling the magnetic field. While one functions as a compass, informing them of the direction of their travel, the other functions as a map, tracking their location. The results show that the latter is a particularly essential component of turtle navigation, now better understood thanks to the turtles’ twirling dance.
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