Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles

Compared nesting densities along the east Florida coast with the natural year-to-year drift of the geomagnetic field, testing whether nesting shifted with the field.

Studied in

Caretta caretta

Sample size

nineteen years of loggerhead nesting records along the Florida coast

Where magnetic signatures of adjacent coastal areas converged over time, nesting density increased; where they diverged, it decreased.

• Correlational, at population level: no individual turtle was followed from hatching to nesting.
• One species on one coast, where the field drifts unusually informatively.
• Field drift and other coastal changes are not fully separable over nineteen years.

• Nineteen years of turtle nests, against a field that will not stay still

  If turtles imprint on the magnetic signature of their birthplace, what happens when that signature drifts along the coast?

• Sea turtles

  Nesting turtles follow the magnetic signature of their natal coast, and that signature drifts. Where neighbouring stretches drifted together, turtles crowded in; where they drifted apart, nesting thinned.

• Salmon

  A river’s smell does not reach the open Pacific. Something else brings a salmon back to the right coast, and the best current candidate is the magnetic signature of the place it left.