The common sea turtles, the famous ones Caretta carettacarry out, over the course of their lives, decades-long migrations that lead them to travel thousands of kilometers – an infinite journey that begins when the eggs hatch on a beach and the small turtles enter the water for the first time.
We have known for a few years that they can orient themselves over such immense distances thanks to their ability to perceive the Earth’s magnetic field, but until now we did not know the physiological mechanism behind this “superpower”. Now a study published on Journal of Experimental Biology sheds light on what is the main orientation method of sea turtles, but also suggests that the situation may be even more complex.
Earth’s magnetic field. Let’s go into details: there are two main methods used by animai to perceive the Earth’s magnetic field, as we had already told you here (also pointing out that “their ability to map individual areas, however, is governed by… something else, which we have not yet been able to identify”and which this study identifies).
One plans to “see” it indirectly, using particular light-sensitive molecules as sense organs in which the light itself activates chemical reactions that can be influenced by the Earth’s magnetic field. The other method, however, involves the presence of small crystals of magnetite in the animal, which move inside its body, allowing it not to see, but to “feel” the magnetic field.
The dance of food. To understand which of the two methods sea turtles use, the University of North Carolina team took advantage of their passion for food. In fact, since their birth, turtles have been trained to associate a particular magnetic field (specifically those around the islands of Turks and Caicos and Haiti) with the presence of food.
After two months of training, the turtles were first removed from the field, then brought back to the area; here they began to “dance”, pulling their body out of the water, opening their mouths and waving their front legs: a sign that they were anxiously awaiting the arrival of food, associated with that specific magnetic field.
The experiment. At this point, the team tried to deactivate their superpower, using a special metal cage that emits a magnetic pulse that temporarily “turns off” the effectiveness of the lodestone. The turtles subjected to the treatment did not dance when brought into their magnetic field: this suggests that their main method of sensing it is by hearing it, not seeing it.
Senses in synergy. However, this does not exclude that sea turtles can integrate the information from the magnetite with the other sense, that of “magnetic sight”, which we already know that these animals use to choose the direction in which to swim. It is very likely, therefore, that the two senses work in pairs, with one of the two “guiding” and the other completing the work.
