The Bald Head Island Conservancy (BHIC) has led the charge in protecting the nesting turtles, nests and hatchlings (along with all the flora and fauna on the island) for more than three decades.
“We’ve been keeping records [on sea turtles] since 1980,” said Emily Hardin, Coastal Specialist and Sea Turtle Program Coordinator for the BHIC. “Field data sheets for nesting, hatching and stranding events from 1983 to present take up 28 two inch binders in the Barrier Island Study Center’s library.”
BHIC naturalists and interns collect data including the date, time and tide of each nesting; nest location; measurements of the carapace (shell); PIT microchip and flipper tag numbers; and, now, DNA samples. With all the sea turtle data collected and analyzed by BHIC and similar research and conservation groups the world over, it may come as a surprise that we have no definitive answer on just how sea turtles know their birth beach, the place they lay their own nest.
One researcher and Ph.D. candidate from the University of North Carolina Chapel Hill has a theory. As a child, J. Rogers Brothers saw a sea turtle nest emergence on Holden Beach, N.C., and it started a lifelong fascination with the ocean and with how migratory animals navigate over long distances. Sea turtles became a particular focus.
“Successful nesting requires a combination of different environmental features that are rare: soft sand, the right temperature for egg incubation, few predators, and an easily accessible beach. These factors are impossible to assess from far away, so for a turtle in the open ocean, selecting a nesting beach is no trivial task,” Brothers said. “The only way a female turtle can be sure that she is nesting in a favorable place is to nest on the same beach where she hatched.”
In a paper published in Current Biology, “Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles,” which Brothers co-authored with his advisor, Dr. Kenneth Lohmann, Brothers posits that sea turtles essentially have an inborn GPS that allows them to mark their birth beach using the Earth’s magnetic field.
“While our work does not exclude the possibility that turtles use additional sensory information (olfactory or visual) during the final approach to the beach, no known cue, other than magnetism, provides the information necessary to locate a specific nesting beach over a long distance.”
Brothers goes on to say that once a turtle locates her beach, she may be deterred from nesting by bright lights or the scent of a predator. Once she finds her beach, sand grain size, moisture content, and other factors will determine whether that’s the place for her nest.