Magnetic Receptors Possibly Found in Dog and Monkey Eyes

A receptor called cryptochrome 1 is present in the eyes of dogs, bears and some monkeys, and may help them sense and navigate the Earth's magnetic field. Russell Cheyne/REUTERS

Dogs, various primates and other mammals have receptors in their eyes that may be sensitive to Earth's magnetic fields, new research shows.

A study published February 22 in the journal Scientific Reports revealed the presence of a receptor called cryptochrome 1 in the eyes of dogs, wolves and foxes; five members of the weasel family including ferrets and sea otters; orangutans and two types of macaques; and brown and polar bears. But the receptors were not found in humans.

This is the mammalian equivalent of a receptor that's present in birds and allows them to visually sense magnetic field lines. This ability helps explain the amazing ability that some bird species have to migrate long distances in a relatively precise manner. But while the structure of the bird and mammal receptors are basically the same, their functions may not be, so further work will have to determine if these species can sense magnetic fields with their eyes, the authors write in the study.

Many of the species do in fact appear to be able to sense and navigate using magnetic fields. Dogs, for example, have incredible homing systems that are likely informed by the Earth's magnetism, and research has shown that dog preferentially poop while facing north or south. (Although why they prefer this orientation is unknown or "enigmatic," according to a 2013 study on the topic.)

Mammals that don't have these receptors have other ways of sensing and navigating Earth's magnetic field. For example, some are able to use the orientation of an iron-containing element called magnetite in bodily cells as a kind of compass. Birds may have other magnetic senses besides their vision; the inner ears of pigeons, for instance, contain microscopic iron balls that may respond to magnetic fields.