Reindeer

The tundra traveller whose eyes change colour

The reindeer is the only deer whose females have antlers too! In winter its eyes change colour: gold in summer, blue in winter — to see better in the dark. Reindeer walk 5,000 km a year — the longest walk of any animal. Their hooves spread out on snow — like snowshoes.

The reindeer (Rangifer tarandus; 'caribou' in America) lives in the Arctic tundra and taiga. The tapetum (reflective layer) of its eye changes colour with the seasons — gold in summer, blue in winter, capturing more light in the polar night. It sees ultraviolet, picking out lichen and wolves against snow. It migrates 5,000 km a year in herds of up to 500,000. It is the only ruminant that lives mainly on lichen ('reindeer moss') in winter. The Sámi, Nenets and Chukchi have herded reindeer for thousands of years. Climate change has cut numbers by 40% in 20 years.

Fun facts

• A reindeer's eyes are blue in winter and gold in summer.
• Reindeer see ultraviolet — things invisible to us.
• A reindeer's knees click as it walks — in a blizzard the herd finds each other by the sound.