Scientists Uncover How Baby Turtles Navigate Thousands of Miles with a Hidden Magnetic Sense
Loggerhead turtles possess two distinct abilities to sense the Earth's magnetic field, yet scientists were uncertain about which one they rely on to interpret the magnetic map they inherit at birth. New research from the University of North Carolina at Chapel Hill, published in the Journal of Experimental Biology, reveals that hatchlings utilize their magnetic force perception to determine their position along their long migration routes.
As soon as they leave the beach where they hatch, young loggerheads embark on journeys spanning thousands of kilometers and can continue for decades. Even at this early stage of life, they are not traveling blindly. Hatchlings come equipped with a magnetic compass that helps them maintain direction and a magnetic map that provides essential location information for successful navigation.
Two Methods of Magnetic Field Detection in Animals
Scientists understand that animals can sense magnetic fields through two primary methods. One involves light-sensitive molecules that respond to magnetic conditions, potentially allowing the animal to 'see' magnetic patterns. The other method involves small magnetite crystals within the body that shift in response to magnetic forces, enabling the animal to feel the field. Until recently, it was unclear which of these systems loggerhead hatchlings use to determine their location in the vast ocean, and the research team set out to investigate.
Previous work by Kayla Goforth, Catherine Lohmann, Ken Lohmann, and their colleagues demonstrated that hatchling loggerheads can learn to associate a specific magnetic field with the arrival of food. Instead of producing a reflex like Pavlov's dogs, the turtles respond with an energetic 'dance.' They raise part of their bodies above the water, open their mouths, and move their front flippers in an excited pattern.
By feeding the hatchlings while placing them in a particular magnetic field, the researchers trained them to perform this dance whenever they later encountered that same magnetic signature.
Using Magnetic Pulses to Test Turtle Senses
Alayna Mackiewicz of the University of North Carolina at Chapel Hill explains, 'They are very food-motivated and eager to dance when they think there is a possibility of being fed.'
The research team realized that this trained behavior could help determine which magnetic sense the turtles were using. They exposed the hatchlings to a strong magnetic pulse, which temporarily interfered with the turtles' ability to feel magnetic forces. If the turtles stopped dancing afterward, it would indicate that they normally use a touch-based magnetic sense. If they continued dancing, it would suggest they rely on a different type of magnetic detection.
Training the turtles required patience. Mackiewicz and Dana Lim (University of North Carolina at Chapel Hill) spent 2 months feeding 8 newly hatched loggerheads while exposing them to the magnetic field found around the Turks and Caicos islands. This ensured the turtles would learn to dance when they later encountered that same field. They also trained another group of hatchlings to recognize the magnetic field near Haiti.
Each turtle was then placed in a large metal coil that emitted a strong magnetic pulse designed to temporarily disrupt its ability to feel magnetic forces. Afterward, the researchers moved the hatchlings into the magnetic field they had been trained to recognize to see whether they would dance.
Evidence That Hatchlings Rely on Magnetic Touch
After exposure to the pulse, the hatchlings danced less often, providing evidence that they use a feel-based magnetic sense to determine their location on their inherited map rather than relying on vision.
The researchers note that hatchlings may use additional cues to understand where they are in the ocean, but the ability to feel the Earth's magnetic field clearly plays a central role.
The young turtles are also known to use another magnetic sense that may allow them to 'see' magnetic fields, which helps them determine direction. Taken together, the two abilities complement each other and help hatchlings understand both where they are and which way they should travel during their remarkable migration.
