"Many animals possess abilities that let them know where in the world they are. They can orient, act appropriately, and navigate to a target thousands of miles distant. There is evidence that various animals are able to align themselves with the magnetic field of the earth. The sensory structures involved are not well known but the Earths magnetic field "inclination" varies with latitude, meaning that magnetic-field lines intersect the planet's surface at reliable, consistent angles, ranging from zero degrees at the equator to ninety degrees at the magnetic poles. Magnetic field intensity also varies in a consistent way over the surface of the planet so the information is there for the turtles to use to find their way back home."