Caribou eat a mix of lichens, sedges, grasses, willow and birch leaves, mushrooms, and other tundra plants. In winter, their diet shifts heavily toward lichens — especially the pale, branching “reindeer moss” they dig out from beneath the snow. Caribou are among the very few large mammals able to digest lichen, thanks to specialized microbes in their stomachs, and this unusual ability is what allows them to survive in places where most deer would starve.
Because caribou and reindeer are the same species (Rangifer tarandus), everything in this article applies to both animals. Whether you call them caribou or reindeer mostly depends on which side of the Atlantic you’re standing on — but the menu is essentially the same.
Let’s take a closer look at what these Arctic deer eat through the seasons, why lichen matters so much, and how their diet compares to that of other deer.
The Caribou Diet at a Glance
Caribou are herbivores, and like other deer, they are ruminants — animals with a multi-chambered stomach that ferments plant material before it is fully digested. That digestive system is what lets them pull nutrition out of some very tough foods.
Across the year, a caribou’s diet typically includes:
- Lichens — especially ground-growing Cladonia species, often called reindeer moss or reindeer lichen
- Sedges and grasses — a summer staple on the tundra
- Leaves of willow and dwarf birch — browsed heavily during the short growing season
- Forbs — flowering tundra plants and herbs
- Mushrooms — eagerly sought out in late summer and fall
- Mosses and horsetails — eaten in smaller amounts, often incidentally
The exact balance shifts dramatically with the seasons, and that seasonal rhythm is really the key to understanding how caribou survive in the Arctic.
Why Lichen Is the Caribou’s Superfood
Lichens are strange organisms — part fungus, part algae — that grow slowly on rocks, soil, and trees in cold climates. They are rich in carbohydrates but low in protein, and most mammals simply cannot digest them.
Caribou can. Their rumen hosts communities of bacteria and other microbes that break down the complex compounds in lichen and turn them into usable energy. This is one of the caribou’s defining adaptations, and it opens up a food supply that almost no other large animal is competing for.
In winter, when the tundra’s grasses and shrubs are buried or dormant, lichen can make up the majority of what a caribou eats. It works like a carbohydrate-heavy survival ration: not a perfect diet, but enough energy to keep a large animal alive through months of cold and darkness.
There’s a trade-off, though. Because lichen is low in protein, caribou tend to lose weight over the winter and rebuild their reserves during the brief, productive Arctic summer. Their whole year is a cycle of feasting and coasting.
What Caribou Eat Season by Season
Spring
As the snow melts, caribou seek out the first green shoots of sedges, grasses, and willows. This fresh growth is high in protein at exactly the moment the animals need it most — cows are in the late stages of pregnancy, and everyone is recovering from a lean winter. Many herds time their famous spring migrations to follow this wave of new plant growth north toward their calving grounds.
Summer
Summer is the season of plenty. Caribou graze almost constantly on sedges, grasses, forbs, and the leaves of willow and dwarf birch, packing on fat for the year ahead. An adult caribou can eat a substantial amount of vegetation each day during this period — they are, in effect, eating for the winter to come.
Fall
In late summer and fall, mushrooms appear across the tundra and forest floor, and caribou seem to relish them. Fungi are relatively rich in protein and minerals, making them a valuable supplement as the green plants begin to die back. As fall deepens, the diet gradually shifts toward lichens once again.
Winter
Winter is lichen season. Caribou use their broad, shovel-like hooves to dig feeding craters through the snow to reach the lichen mat below — a behavior so characteristic that the word “caribou” is often traced to a Mi’kmaq term meaning “snow shoveler.” Their keen sense of smell helps them locate lichen buried well beneath the surface. Where available, they’ll also nibble dried sedges and twigs, and forest-dwelling herds browse the wispy lichens that hang from trees.
How Caribou Diets Differ Between Tundra and Forest
Not all caribou live in the same landscape, and their menus reflect that. Barren-ground caribou of the open tundra rely heavily on ground lichens, sedges, and low shrubs. Woodland caribou living in the boreal forest have access to tree-dwelling (arboreal) lichens, which become especially important in winters when deep or crusted snow makes cratering difficult.
Domesticated and semi-domesticated reindeer in Scandinavia and Siberia eat much the same natural diet, though herders sometimes provide supplemental feed in hard winters when ice locks the lichen away beneath a frozen crust.
The Surprising Side of the Caribou Diet
Caribou are herbivores, but the Arctic is a hungry place, and these deer are opportunists. Caribou have been observed nibbling on shed antlers and bones to recover calcium and other minerals, and there are credible reports of them eating the occasional lemming or bird egg they stumble across. These moments are rare exceptions rather than the rule — but they’re a good reminder that “herbivore” is a guideline in nature, not a law.
Caribou also drink surprisingly little free water in winter, getting much of their moisture from snow and from the plants they eat.
Frequently Asked Questions
Do caribou really eat reindeer moss?
Yes — though “reindeer moss” is actually a lichen, not a true moss. The name refers mainly to pale, branching Cladonia lichens that carpet the ground across the Arctic and boreal zones. These lichens are a cornerstone of the caribou’s winter diet, and their slow growth is one reason caribou herds must keep moving to fresh feeding grounds rather than grazing one spot bare.
Do reindeer eat carrots?
The Christmas Eve tradition is charming, but carrots aren’t a natural part of a reindeer’s diet, and reindeer lack upper front teeth, which makes a whole raw carrot awkward for them to handle. A reindeer might nibble one, but they’re far better suited to lichen, leaves, and grasses. If you’re leaving a snack out for Santa’s team, a handful of oats is closer to what a real herder might offer.
How is the caribou diet different from other deer?
Most deer species are browsers or mixed feeders, eating leaves, twigs, grasses, and mast like acorns. Caribou eat many of those same foods in summer, but no other deer leans so heavily on lichen, and few can digest it at all. That single adaptation is what lets caribou live farther north than any other deer on Earth.
