The caribou, a species of deer known as Rangifer tarandus, is a herbivore, classifying as an intermediate ruminant. While the answer is yes, this simple classification fails to capture the dynamic and complex nature of their feeding habits. The harsh, nutrient-poor Arctic and sub-Arctic environments force the caribou to adopt an exceptionally flexible diet. This foraging strategy is continuously adapted across the seasons to ensure the intake of sufficient energy and scarce minerals. Their survival depends on a specialized digestive system and the ability to locate various food sources in a challenging landscape.
Defining the Caribou Diet
The caribou is an ungulate possessing a four-chambered stomach, placing it in the category of ruminants. This specialized digestive anatomy processes large quantities of fibrous plant material. The rumen hosts symbiotic microbes that ferment the tough cellulose found in plant cell walls. The caribou regurgitates this partially digested plant matter, known as cud, to chew it again, mechanically breaking it down further. This process is vital for extracting maximum nutritional value from the low-quality forage available in their northern habitats, which during summer and autumn consists overwhelmingly of grasses, sedges, and the leaves of woody shrubs like willow and birch.
Seasonal Dietary Shifts
The caribou diet alters significantly with the onset of winter and the covering of ground vegetation by snow. They shift to a food source that requires specialized foraging: lichens. The caribou use their large, shovel-like hooves to dig through compacted snow, a behavior known as cratering, to access terrestrial lichens, particularly the variety often called “reindeer moss.” Lichens are an energy-dense food source, high in easily digestible carbohydrates, which helps fuel the caribou’s metabolism in the cold. However, this winter diet presents a physiological challenge: lichens are low in crude protein (often 2% to 6%), resulting in a negative nitrogen balance as the caribou slowly deplete their body’s protein reserves throughout the winter.
Essential Non-Plant Consumption
Despite the overwhelmingly plant-based nature of their diet, caribou regularly consume non-plant items to supplement minerals absent in their primary forage. The most common example is osteophagia, the gnawing on bone fragments and shed antlers. This behavior is driven by a need for vital macro-minerals, particularly calcium and phosphorus, which are necessary for bone maintenance, lactation, and the rapid growth of new antlers.
Studies show that caribou will intensively gnaw on nearly 90% of shed antlers, which are highly concentrated sources of these minerals. Lactating females have the highest demand, as their bodies are depleted of calcium and phosphorus to support milk production. Caribou also seek out mineral licks, consuming mineral-rich earth and saline deposits to replenish sodium stores. They also consume fungi and, very rarely, engage in opportunistic feeding on small animal matter, such as rodents or bird eggs, to acquire concentrated protein and trace elements scarce in tundra vegetation.