Arctic caribou, the iconic migratory herds traversing the tundra and boreal forests of the far north, possess digestive systems finely tuned to an extreme environment. Understanding what do arctic caribou eat reveals a complex relationship with a landscape that shifts dramatically through the seasons. Their nutritional strategy is a cornerstone of survival, enabling them to endure brutal winters and fuel epic journeys across vast distances.
Seasonal Foraging Patterns and Dietary Shifts
The diet of an arctic caribou is not static; it is a dynamic response to the fleeting abundance of the subarctic world. During the brief but explosive summer months, caribou enter a phase of intense feeding, known as hyperphagia, to build fat reserves for the long winter ahead. Their primary focus shifts to nutrient-dense forbs, such as fireweed and Arctic aster, alongside the lush shoots of willow and birch. This seasonal abundance provides the protein and carbohydrates necessary for milk production in females and the replenishment of body mass depleted during winter.
Winter Survival and Lichen Utilization
When the Arctic winter sets in, burying the tundra under deep snow and ice, the caribou's menu undergoes a dramatic transformation. Their specialized hooves, which act as snowshoes in summer, become shovels to uncover vegetation. The most critical winter food source is lichen, particularly reindeer moss, which grows slowly but covers vast expanses of ground. Caribou can metabolize the carbohydrates found in these fruticose lichens, allowing them to subsist for weeks on this sparse, frozen forage when other options are completely inaccessible beneath the snowpack.
While lichen forms the starvation diet during the harshest conditions, caribou will also browse on woody shrubs, mature twigs, and evergreen needles. This shift to a high-fiber, low-nutrient diet is a calculated risk, relying on fat stores accumulated in the fall. Their unique gut microbiome, adapted over millennia, plays a vital role in breaking down these tough, fibrous materials, extracting whatever minimal nutrition the frozen landscape can offer.
Geographic Variation and Food Availability
The specific composition of an arctic caribou's diet varies significantly across its range, from the tundra of the Canadian Arctic Archipelago to the forested regions of Scandinavia and Siberia. Herds in areas with deeper snow may rely more heavily on wind-scoured ridge tops where lichen persists, while those in shallower snow zones can access a greater variety of buried vegetation. This geographic flexibility is a testament to their adaptability, allowing different populations to exploit the specific ecological niches available in their home territories.
Impact of Environmental Change
Climate change is altering the delicate balance of the Arctic ecosystem, directly impacting the caribou's food web. Warmer temperatures lead to increased shrub growth, which can provide more browse in some areas but also creates a thicker, less navigable landscape. More critically, unpredictable freeze-thaw cycles and rain-on-snow events create ice layers that physically block access to lichen and other buried forage. This growing mismatch between the caribou's migratory calendar and the peak nutritional availability of plants poses a significant long-term threat to herd stability.
