"Foxes seem to use the Earth's magnetic field to track down their prey, apparently the only animal to use the field to judge distance as well as direction. A pair of researchers in the U.S. and Germany believe foxes have an innate augmented reality system allowing them to accomplish this.
Foxes have what's called radical pair-forming photopigments located in their eyes which means they may see the magnetic field as a pattern on top of what they're already seeing."
No wonder Zoro gets lost so easily, the magnetic fields aren't magneting as they should.