What Do Reindeer Eat? Lichen, Grass and Winter Feeding

The reindeer’s year of food

Reindeer, known as caribou in North America, live in places where green food is available for only a few months a year. Their diet changes with the seasons:

In summer the diet is at its most varied and nutritious. This is when reindeer rebuild their fat and muscle, cows produce milk for their calves, and bulls grow their antlers. The Alaska Department of Fish and Game notes that caribou switch back to lichens, dried sedges and small shrubs around September.

Lichen: the winter staple

A lichen is not a plant but a partnership between a fungus and algae or cyanobacteria. Several ground-growing lichens form thick, pale carpets in northern forests and tundra. The best known is reindeer lichen (Cladonia rangiferina), often called reindeer moss. Other important winter foods include closely related Cladonia lichens and Iceland moss (Cetraria), also a lichen.

Lichens suit winter feeding because they stay available all year and are rich in carbohydrates that supply energy. They are, however, poor in protein and minerals, so reindeer usually lose weight and body condition over winter. In many herds lichens make up the majority of the winter diet, though the share varies and is lower where lichens are scarce.

Few animals can digest lichen. Many lichens contain bitter, toxic compounds such as usnic acid. Reindeer have a four-chambered stomach in which microbes ferment their food, and their rumen holds special bacteria that break down these compounds. They also have enzymes that turn lichenin, the main lichen carbohydrate, into sugar.

Cratering: digging for dinner

In winter, reindeer find food under the snow by smell. Once they detect lichens below, they dig a feeding hole, called a crater, with their large, sharp-edged front hooves. In winter the soft pads of the hooves shrink and the hard rim becomes exposed, which makes the hooves better tools for scraping through crusty snow.

Digging takes energy, so reindeer prefer areas where snow is soft and not too deep, such as open forests. Dominant animals often take over craters dug by others. Cows that still carry antlers in winter can defend their craters, one reason why female reindeer grow antlers, as explained in do female reindeer have antlers?

Summer foods

As snow melts, reindeer move onto the tundra and feed heavily on fresh growth. Willow leaves are a favorite and among the most nutritious foods available. Sedges and cotton grass are eaten in large amounts, along with grasses and many flowering plants.

In late summer and fall, after the worst of the insects have gone, reindeer spread out and eat as much as they can to build fat reserves. Mushrooms are a prized food at this time; reindeer seek them out eagerly. Herders in Siberia have long noted how strongly reindeer are drawn to mushrooms.

Surprising extras

Although they are plant eaters, reindeer sometimes eat other things, mostly to get protein and minerals that their diet lacks:

• Shed antlers and bones, gnawed for calcium and phosphorus.
• Lemmings and other small rodents, recorded especially in spring when food is scarce.
• Bird eggs and occasionally fish, eaten opportunistically.
• Salt, which draws reindeer to mineral licks and to places where people have spilled salt or urine.

These are rare additions. The basis of the diet is always plants and lichens.

How much does a reindeer eat?

Food intake varies with body size, season and food quality. Reindeer eat the most in summer, when food is abundant, and much less in winter, when they save energy by moving less and their metabolism slows. In the constant daylight of the Arctic summer they feed and rest in short cycles around the clock instead of following a day-night routine.

Because lichens grow very slowly, often only a few millimeters a year, heavy grazing can strip an area for decades. On St. Matthew Island in the Bering Sea, 29 reindeer released in 1944 multiplied to about 6,000 by 1963. They overgrazed the island’s lichen, and almost all of them starved during the severe winter of 1963–64; only 42 were left when biologists returned in 1966.

When winter food is locked in ice

The greatest danger to a reindeer’s food supply is ice. Warmer winters bring more rain-on-snow events, when rain falls on snow and then freezes into a hard crust. Reindeer cannot break through it to reach the lichens beneath.

In November 2013, a rain-on-snow event on the Yamal Peninsula in Arctic Russia led to the deaths of about 61,000 herded reindeer, more than a fifth of the animals there, as they starved over the following winter. Similar icing events have killed wild reindeer on Svalbard. Scientists expect these events to become more common as the Arctic warms, which is one reason the species is now listed as Vulnerable.