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A loggerhead sea turtle nests at the Archie Carr
National Wildlife Refuge in Melbourne Beach, Florida.
Credit: J. Roger Brothers |
Female sea turtles, known to swim thousands of miles before returning to their birthplace to lay eggs, find their way home by relying on unique magnetic signatures along the coast, a new study finds.
For more than 50 years, scientists have been mystified by how
sea turtles do this, said the study's lead researcher, J. Roger Brothers, a graduate
student of biology at the University of North Carolina at Chapel Hill.
"Our results provide evidence that turtles imprint on the unique
magnetic field of their natal beach as hatchlings, and then use this
information to return as adults," Brothers said in a statement.
Previous studies have shown that sea turtles use Earth's magnetic field to
help guide them at sea, but it was unclear whether magnetic features also help
steer them toward the nesting sites chosen by their mothers, the researchers said.
To investigate, the scientists examined a database
of records covering 19 years of loggerhead sea turtle (
Caretta caretta)
nesting along the eastern coast of Florida, the largest sea turtle
rookery in North America. Earth's magnetic field, which acts as a giant
invisible shield that protects the planet from dangerous solar
radiation, changes over time. Earth's iron core is surrounded by a layer
of molten metal, and as this molten metal sloshes around, it causes
fluctuations in the magnetic field, with some areas strengthening and
others weakening.
The researchers wondered whether
turtles had changed their nesting locations as magnetic signatures drifted across the coast
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A loggerhead sea turtle heads toward
the water in Melbourne Beach, Florida.
Credit: J. Roger Brothers |
"We reasoned that if turtles use the magnetic field to find their natal
beaches, then naturally occurring changes in the Earth's field might
influence where turtles nest," Brothers said.
A look at the data
,
from 1993 to 2011, confirmed this idea. At certain times in some
places, Earth's magnetic field shifted so that magnetic signals from
nearby beaches moved closer together. During these times,
turtle nests densely covered these areas, they found.
Similarly, there were fewer turtle nests, and the nests were farther
apart, in places where magnetic signatures diverged, just as the
researchers predicted.
"Our results provide the strongest evidence to date that sea turtles
find their nesting areas at least in part by navigating to unique
magnetic signatures along the coast," the researchers wrote in the
study.
Scientists are unsure how turtles detect the geomagnetic field, but
it's possible that tiny magnetic particles in their brains help the
turtles process unique signatures, Brothers said.
Whatever the mechanism, it clearly helps sea turtles find their birthplace so they can reproduce, usually on accessible
beaches that have soft sand, the right temperature and few predators.
"The only way a female turtle can be sure that she is nesting in a
place favorable for egg development is to nest on the same beach where
she hatched," Brothers said. "The logic of sea turtles seems to be that
'If it worked for me, it should work for my offspring.'"
The study was published today (Jan. 15) in the
journal Current Biology.
Follow Laura Geggel on Twitter @LauraGeggel. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.
