She comes home by the magnetic field, and the field drifts

A loggerhead turtle swims back to nest near the beach where she hatched. She finds it by its magnetic signature: every stretch of coast has its own mix of the field's strength and angle. The glowing line marks where her remembered signature meets the shore. Over the years it slides up the coast (drawn much faster than real), and so does she.

Researchers compared 19 years of Florida nest counts with the field's slow drift. Nests crowded where these lines squeezed together along the coast and thinned where they spread apart, as the idea predicts (Brothers and Lohmann, 2015).