They undertake some of the most audacious journeys in the animal kingdom, navigating across thousands of miles to arrive at a precise location. Now scientists have unraveled exactly how migrating birds, butterflies and other animals are able to use the Earth’s magnetic field to help them find their way. They have discovered proteins that ‘act like a compass’ are produced in the retina and nerve cells running from the eye to the brain. These molecules form a rod-like complex with light sensitive proteins and orientate themselves in a north to south direction in a magnetic field. Perhaps most astonishingly, the researchers discovered that humans also express these same proteins, albeit in far smaller amounts, raising the prospect that we too have some ability to sense the magnetic field. Dr Can Xie, a molecular biologist at Peking University in China who led the research, said the proteins appear to act just like a compass needle and send information to the nervous system. Writing in the journal Nature Materials, Dr Xie and his colleagues said: ‘The notion that animals can detect the Earth’s magnetic field was once ridiculed, but is now well established. ‘The biocompass model we present here may serve as a step towards fully uncovering the molecular mechanism of animal navigation and magnetoreception. ‘The existence of a human magnetic sense remains controversial but geomagnetic fields are thought to affect the light sensitivity of the human visual system.’

Many animals are thought to use the Earth’s magnetic fields to help them navigate including sharks, sea turtles, birds, insects, wolves, whales and even worms. However, exactly how they do this has remained a mystery.

Some researchers previously identified specific cells in the eyes and beaks of birds like pigeons that seem to respond to a magnetic field. The exact source was unknown, and some researchers identified clumps of iron bound by molecules as being responsible, while others attributed it to light-sensitive proteins called cyrptochromes.

The research by Dr Xie and his team, however, has found that these two systems in fact work together to form a navigational complex inside the cells of these animals. In particular, they discovered a gene called MagR that produces a protein that combines with cryptochrome to form a cylinder shaped complex.

Ten cryptochrome molecules encase 20 MagR proteins to form this rod that then aligns itself with a magnetic field. They were so magnetic that the researchers had to develop special plastic tools to conduct their research.

The scientist found these molecules are particularly highly expressed in the retinal neurons running from the eye to the brain. Fruit flies, monarch butterflies, pigeons and humans all produce these molecules while other creatures including minke whales and naked mole rats also have these magnetic proteins.

The researchers say their findings may also now lead to a new area of research that could have numerous biological and industrial applications. It could lead to new types of genetic treatments that respond to magnetic fields or ways of increasing magnetic sensitivity.