Salmon hatch in rivers, where they spend a year or so before migrating to the sea – returning as adults to their riverbed of birth to spawn. This migration can extend over thousands of kilometres and studies in which young salmon were exposed to magnetic fields suggest that the fish use an internal compass to navigate.

Some other animals also respond to magnetic fields and scientists believe that this could be related to magnetite, which is a magnetic material present in some organisms. However, a specific magnetite receptor has not been found in animals – and how animals sense Earth’s magnetic field remains a mystery.