In the Arctic regions, where reindeer live, their staple food is a white lichen, Cladonia rangiferina.

It is generally known as reindeer moss although it isn’t really moss.

To humans, the white lichen would not be visible from afar in the snowy Arctic.

Reindeer’s eyes have evolved in a manner that enables them to spot their food even in the dark, a new study has found.

The study comes at a time when reindeer are the flavour of the season, with children all over the world waiting for Santa Claus.

A membrane called the tapetum turns blue in the reindeer’s eye during winter.

This helps amplify light and enable the reindeer to see better.

As a result, the reindeer see the white lichen as dark patches where humans and most other mammals would have not seen them at all.

The researchers suggest that the reindeer’s eyes are primed to enable them to locate Cladonia rangiferina during the winter

One effect of the blue tapetum is that in winter, reindeer see the Arctic surroundings in purple.