“Magnetic signtures” help sea turtles find birthplace
Several species – salmon, birds, and sea turtles among them – use the magnetic field to navigate the earth during their migrations. Many of these same species also return to their birthplace to spawn or nest. Researchers believe that returning to their birthplace to lay their eggs (and, more rarely, raise their young) helps assure these species that the environment in which their offspring will be born is safe: if it was safe for the parents, it will likely be safe for the offspring too.
Precisely how the parents know exactly where to return, however, has long remained a mystery and is a difficult topic to research in the wild. A recent study of loggerhead sea turtles’ nesting data may have provided the answer for at least one species: researchers believe that the turtles use the ‘magnetic signature’ of their birthplace to find their way back again.
Loggerhead sea turtles spend many years migrating across thousands of miles of open ocean – using the magnetic field to find their way – before returning to the same stretch of coastline on which they were born to nest. Because the turtles are known to use the magnetic field to guide their navigations at sea, Dr. Kenneth Lohmann and graduate student J. Roger Brothers of the University of North Carolina at Chapel Hill decided to see if the magnetic field helped the turtles find their way to their birthplace too.
To test their hypothesis, the researchers looked at 19 years’ worth of loggerhead nesting data from nesting sites along the east coast of Florida. They found a strong association between the distribution of turtle nests along the beaches and naturally-occurring shifts in the magnetic field. As the field shifts, the magnetic “signatures” of certain locations can move closer together or farther apart. The researchers found that the nesting turtles clustered into smaller stretches of beach when locations for nesting sites moved closer together; when locations drifted apart, the nests were more spread out. The data indicates that the turtles return to very specific magnetic signatures to nest.
Magnetic signatures’ importance may not be limited to sea turtles. Years ago, Dr. Lohmann proposed that salmon may also use magnetic navigation to help them return to the waters in which they were born. These new insights into loggerhead turtles' nesting behavior may indicate that his hypothesis about salmon was correct.
Based on materials originally written for EurekAlert.
Journal reference: J. Roger Brothers, Kenneth J. Lohmann. Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles. Current Biology, 2015; DOI: 10.1016/j.cub.2014.12.035
Image: A loggerhead hatchling on a beach in Okinawa, Japan. (Credit: Okinawa Nature Photography on Flickr.)