Back in 2013, Digiat Journal reported on research which examined why male and female Loggerhead turtles adopt different strategies for mating. The females always return to their island of birth. This is not so with the males who mate at various locations. This behavior with the females was attributed to an immune response and was related to behavior designed to avoid the turtle contracting a parasitic infection. Now, an alternative theory has been proposed.
The loggerhead sea turtle is found in most parts of the major oceans. The turtle spends most of its life in saltwater habitats, with females coming ashore for short periods of time to lay eggs.
The magnetic signatures of Florida’s beaches appear to lead loggerhead sea turtles back to their birthplace to hatch the next generation. The turtles can carry out this feat even though the Earth’s magnetic field is in constant flux. Moreover, the turtles achieve this over great distances, using magnetic signatures to navigate in the open ocean.
Until recently the turtle’s magnetic senses were not explored as a possible explanation for the adult females’ incredible homing ability. A few years ago, J. Roger Brothers and Kenneth Lohmann of the University of North Carolina, hypothesized that if the turtles also followed the magnetic field back to their birthing beaches, shifts in the field should impact where on the beach loggerhead mothers-to-be landed. In particular, a change in the distances between the magnetic addresses (termed isolines) on the beach would lead to a change in the density of turtle nests.
To test out this theory, the researchers compared voluminous volunteer-collected nesting data and the positions of the isolines along the Florida coast over a 19-year period. By analysing this, the researchers found that when the distances between the magnetic signatures shrank, so did the distance between the nests. When the field shifted to create greater distances between isolines, the turtles were more spread out.
In their research, the two authors state: “These results provide strong evidence that nesting sea turtles use Earth’s magnetic field to locate their natal beaches.”
The research also has wider interest. Because many other species also follow the Earth’s magnetic fields to reach their destinations, the suggestion that turtles might be storing magnetic information from birth to maturity could impact the understanding of other animals’ journeys as well.
The findings have been reported to the journal Current Biology. The paper is titled “Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles.”
