Reindeer

In summer, reindeer eat leaves, grass and mushrooms.

In winter, they dig in the snow with their hooves. Under the snow is reindeer moss, a kind of lichen they love.

In summer, reindeer feast on willow leaves, sedges, tundra flowers and even mushrooms. In winter, when snow covers everything, they eat lichens, especially one called reindeer moss. A lichen is a living partnership between a fungus and tiny algae.

Reindeer dig holes, called craters, in the snow with their wide hooves to reach the lichen. A calf follows its mother and shares her crater. Female reindeer keep their antlers in winter, which helps them protect their feeding holes.

Summer diets are high in protein: willow and birch leaves, sedges, forbs and, in late summer, mushrooms. From about September, reindeer switch to lichens such as 'reindeer moss', dried sedges and small shrubs. Lichens are rich in carbohydrate but poor in protein.

Reindeer cope with this by slowing their metabolism in winter and recycling urea, normally a waste product, inside the digestive system to reuse its nitrogen. They reach food by digging feeding craters in the snow. Cows keep their antlers through winter and use them to defend craters (pregnant cows usually until their calves are born), while large bulls shed theirs soon after the autumn rut.

Some families in the north take care of reindeer herds.

The reindeer give them milk, meat and warm skins. Some reindeer even carry bags or pull sleds.

People have herded reindeer for thousands of years. In northern Europe, about 3 million reindeer live in herds looked after by people, including many Sámi families in Norway, Sweden, Finland and Russia. Herders use them for meat, milk and skins, and as pack and sled animals.

In Alaska, wild caribou are an important food for many people living in Arctic villages, and some call themselves 'caribou people'.

Reindeer have been herded for thousands of years, and Britannica notes nearly 3 million domestic reindeer in northern Europe, important to traditional herders such as the Sámi of Scandinavia and Russia, who use them for meat, milk and hides and as pack and draft animals. In northeastern China, Evenk herders use reindeer as pack animals and mounts, and small numbers of Tsaatan (Dukha) herders keep reindeer in northern Mongolia.

In North America, wild caribou remain a central subsistence resource. The National Park Service notes that caribou are a main food source for Native residents of Arctic Alaska, many of whom describe themselves as 'caribou people'. Herds such as the Western Arctic Herd are monitored as a vital sign of Arctic change.

There are fewer wild reindeer than before.

Scientists follow the herds to learn how to help them. People protect the places where calves are born.

The IUCN lists the reindeer as Vulnerable because the number of wild reindeer has fallen in many places. Their tundra home is changing as the Arctic warms, and mines and other development can change the routes herds use every year.

Scientists track herds to learn where and when they travel. Protecting calving grounds and migration routes helps reindeer keep making their long journeys.

The IUCN's 2015 global assessment lists Rangifer tarandus as Vulnerable, with about 2.9 million mature individuals. It is listed under criterion A2a, which means a large population decline over the past three generations, measured by direct observation of herds. Climate change, natural disruptions and industrial development are among the pressures scientists watch.

In Alaska, the National Park Service tracks the Western Arctic Herd's migrations, because where caribou go each season is one of the simplest ways to measure the effects of climate change, development and other pressures. Conserving calving grounds and keeping migration routes open are key.