Some Animals Can Sense Earth's Magnetic Field

A compass that reads angles, not "north"

In 1972, Wolfgang and Roswitha Wiltschko published a short paper in Science about European robins. When they tested migratory robins in controlled magnetic fields, the birds oriented themselves using the field. But not the way your hiking compass does.

Instead of sensing which end of the field is "north", the robins read the inclination of the field lines. That's the angle at which the lines dip toward the ground. Scientists call it an inclination compass. It tells a bird "toward the pole" versus "toward the equator", rather than north versus south.

Turtles that read a magnetic map

Loggerhead sea turtles that hatch in Florida swim a huge loop around the North Atlantic before coming back to the North American coast. So how do tiny hatchlings stay on course in open ocean?

In a 2001 study in Science, Kenneth Lohmann and his colleagues exposed hatchlings to magnetic fields copied from three far-apart points along that route. Each time, the turtles swam in the direction that would keep them inside the circling currents of their migration path. Regional magnetic fields seem to work like road signs.

Salmon that remember home

Pacific salmon use smell to find their home river at the very end of their trip. But how do they get to the right stretch of coast from the open ocean?

A 2013 study in Current Biology looked at 56 years of fisheries data on Fraser River sockeye salmon. To get home, these fish have to swim around Vancouver Island by a northern or a southern route. The route they picked tracked slow shifts in Earth's magnetic field. That fits the idea that salmon remember the magnetic "signature" of the place where they first swam into the sea. The authors called it the first real evidence of geomagnetic imprinting in any species.

How does it work? Maybe quantum physics

Here's where things get strange, and honestly unsettled.

One leading idea for birds involves proteins called cryptochromes in the eye. When light hits them, they can form pairs of molecules with unpaired electrons, called "radical pairs". A magnetic field could nudge how those pairs behave. In a 2021 Nature study, researchers showed that cryptochrome 4 from the European robin reacts to magnetic fields in the lab. It reacted more strongly than the same protein from chickens and pigeons, which don't migrate at night.

Your gadgets can jam it

A 2014 Nature study turned up something unexpected on a university campus in Oldenburg, Germany. European robins couldn't use their magnetic compass inside ordinary wooden huts. When the researchers grounded the huts and lined them with aluminum, background electromagnetic noise dropped by roughly a hundredfold. The birds' sense of direction came back.

The noise came from everyday electronics, at levels well below safety limits for people. That doesn't mean it harms you. It means a bird's magnetic sense is incredibly delicate.

What's still unknown

This sense has been tested in experiments for more than fifty years, so it's not folklore. Robins read field angles, turtles react to regional signatures and salmon seem to remember a magnetic "address". What scientists still can't fully explain is exactly how it works, and how many other species have it.

Want to test your own science instincts? Our science quiz has a question about robins.