Several species of marine turtle accurately migrate thousands of kilometers for nesting. Some species return to the exact beach where they were hatched. There are various proposed explanations for the behaviour, including magnetic navigation. But a year 2000 experiment by Papi et. al showed that (at least for Green Turtles) this is not the case. The experimenters attached powerful magnets to 7 turtles to mask any possible perception of the Earth's magnetic field. Satellite tracking revealed that they all performed their 2000 km migration without significant error.
“The navigational mechanisms used by these turtles remain enigmatic.”
source:Open-sea migration of magnetically disturbed sea turtles (J. Exp. Biol 203, 3435-3443.)