Caribou, a species of deer also known as reindeer, are herbivores inhabiting circumpolar Arctic and boreal forest ecosystems. Their diet primarily consists of various plant materials, adapted to seasonal availability.
Their Primary Plant-Based Diet
Caribou sustain themselves predominantly on a plant-based diet, consuming a diverse array of vegetation. This includes graminoids (grasses and sedges), mosses, and various fungi. Lichens, particularly “reindeer moss,” form a substantial part of their diet and are available year-round. These organisms are highly digestible and provide a significant energy source. However, lichens are generally low in protein, which influences seasonal dietary shifts.
Seasonal Shifts in Food Sources
Caribou diet varies with changing seasons, reflecting plant availability and nutritional content. During warmer summer months (typically May to September), caribou shift to a diet rich in vascular plants. They consume leaves and shoots from willows and birch, sedges, flowering tundra plants, and various shrubs and forbs. Mushrooms also become part of their diet during late summer. This summer foraging helps them gain body reserves for colder periods.
As winter approaches, caribou rely heavily on lichens, including terrestrial and arboreal varieties. They use their large hooves to dig through snow and uncover these energy-rich food sources. Dried sedges and small shrubs, such as blueberries, also contribute to their winter sustenance. While lichens are a consistent winter food, their limited protein often leads caribou to lose weight despite consuming large quantities.
Digestive Adaptations for Foraging
Caribou possess specialized digestive systems that enable them to process their fibrous, plant-based diet efficiently. Like other ruminants, they have a four-chambered stomach, including the rumen, reticulum, omasum, and abomasum. This complex system allows them to break down tough plant materials and extract nutrients. Microbes within the rumen play a crucial role in fermenting and digesting plant cell wall components.
Caribou engage in rumination, a process where they regurgitate partially digested food, known as cud, to chew it further. This action reduces the particle size of the forage, improving its digestibility. Their dental structure also shows adaptations for their diet; they lack upper incisors, instead possessing a thick callous pad against which their lower incisors press to tear off vegetation. Molars in the back of their mouth are used for grinding the plant material.