Marine biologists at the University of North Carolina at Chapel Hill believe that salmon and sea turtles read the magnetic field of their home area and "imprint" it, allowing the animals to distinguish that location from all others when they're ready to return years later to reproduce.

Previous studies showed young salmon and sea turtles can detect the Earth's magnetic field and use it to sense direction during their first migration. The new study seeks to explain the more difficult navigational task accomplished by adult animals that return to reproduce in the same area where they themselves began life -- a process scientists refer to as natal homing.

"What we are proposing is that natal homing can be explained in terms of animals learning the unique magnetic signature of their home area early in life and then retaining that information," said Professor Kenneth Lohmann, first author of the study. "We hope (the hypothesis) will inspire discussion among scientists and eventually lead to a way of testing the idea."

The research is reported in the Proceedings of the National Academy of Science.