Reindeer (Rangifer tarandus) inhabit the Arctic and sub-Arctic regions across North America, Europe, and Asia. They are large ungulates that are primarily herbivores, meaning their diet is overwhelmingly plant-based. Their survival relies on a specialized, seasonally shifting feeding strategy to extract nutrients from limited vegetation.
Defining the Primary Diet
The herbivorous nature of the reindeer is most evident during the warm summer and spring months when the tundra is rich with vegetation. This intense foraging period allows them to build fat reserves necessary for winter. Their diet consists of grasses, sedges, and tender green leaves, selected for high protein and energy. Reindeer also browse on the new growth of shrubs, favoring the nutrient-dense leaves of willow and birch. As summer transitions into autumn, they actively seek out mushrooms and other fungi to supplement their diet before snowfall.
Survival Through Lichen and Moss
The reindeer’s diet shifts dramatically in the winter, relying almost exclusively on lichens, particularly Cladonia rangiferina (reindeer moss). This lichen can constitute between 40% and 90% of their intake during the coldest months. To reach this food source, reindeer use their hooves to dig through thick layers of snow, a process requiring considerable energy. They are aided by a keen sense of smell that allows them to detect lichens even under a meter of snow.
Lichens are rich in soluble carbohydrates but contain usnic acid, which is toxic to many other ruminants. Reindeer host specialized bacteria in their rumen that effectively degrade this acid, making the energy-rich food source accessible. Despite the high carbohydrate content, lichens are extremely low in protein, defining the winter period as a phase of negative energy balance and body condition decline.
The Need for Opportunistic Feeding
The nutritional limitations of the winter diet, specifically the scarcity of minerals like calcium and phosphorus, lead to periods of highly opportunistic feeding. Reindeer will consume non-plant matter out of necessity, a behavior known as osteophagia. They are frequently observed gnawing on shed antlers or bones to replenish macro-minerals lost during antler growth and lactation cycles. Reindeer have also been documented consuming small animal matter, such as lemmings or small rodents, to obtain concentrated sources of protein and iron. The consumption of eggs or the droppings of other animals, like geese, is another documented behavior used to acquire scarce nutrients or energy. These non-herbivorous activities are adaptive strategies, confirming the reindeer’s status as a flexible herbivore that occasionally adopts omnivorous traits to ensure survival in the nutrient-poor Arctic environment.