Who would think you could train hatchling sea turtles to dance on cue? Monkeys and circus elephants, maybe, but turtles with their more modestly sized brains? However, that’s what a study published today in the Journal of Experimental Biology did to learn more about sea turtle navigation.
Researchers at the University of North Carolina, Chapel Hill, used food rewards to condition hatchling loggerheads (Caretta caretta) to “dance” when they encountered a familiar magnetic field, and then monitored the turtles’ responses to an interruption in the field.
Turtle “dancing” isn’t just for kicks. The behavioral term refers to the excited wiggle they do when expecting food, pushing higher out of the water with flippers flapping and mouths agape. The researchers knew from their earlier studies that hatchling loggerheads could learn to associate food rewards with magnetic fields, evidenced by dancing in response to a particular magnetism. They hypothesized that, during their annual long-distance journeys to feeding sites, turtles memorized food-rich areas based on their magnetic field signatures.
But they wondered which innate navigational tool the turtle hatchlings were relying on to traverse Earth’s magnetic fields. Animals, such as some fish and bird species, that migrate long distances typically use either light-sensitive molecules in their eyes to see magnetic fields or crystals of the mineral magnetite in their bodies to feel magnetic fields. Sea turtles could use either—or both.
Read more: “How Sea Turtles Find Their Way”
Over two months, eight hatchlings were trained to associate food rewards with two specific magnetic fields that mimicked areas within their natural range (one in Turks and Caicos, and one just off Haiti), which was “really fun but takes up quite a bit of time,” said grad student and lead study author Alayna Mackiewicz in a statement.
Once the turtles learned to expect food in those specific fields, each hatchling’s ability to feel the magnetic fields was interrupted using a strong magnetic pulse from an electromagnetic coil. While the hatchlings’ magnetic sense was temporarily disabled in this way, the scientists returned them to the magnetic field they had learned to associate with food. Their dancing abated, demonstrating that the turtles had mainly relied on feeling the magnetism as a way to map their position as the one that yielded food.
The researchers concluded that “magnetite-based magnetoreceptors underlie the map sense of turtles, inasmuch as a magnetic pulse can potentially disrupt such receptors.” But because the turtles’ dancing did not stop completely when their magnetic sense was disabled, the study authors leave open the question of whether other senses—besides magnetoreception—supplement sea turtle mapping of food resources.
No matter how they pull it off, it’s pretty remarkable how these little animals somehow find the best feeding spots across thousands of miles of ocean, to return to them again and again as they grow up. 
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Lead image: Hila Shaked / Wikimedia Commons
