The elk, or Cervus canadensis, is the most abundant large mammal in Yellowstone National Park. Their sheer numbers and wide distribution mean their foraging habits profoundly influence the park’s plant communities. As a large herbivore, the elk’s diet is highly variable, shifting dramatically with the availability of forage across Yellowstone’s distinct seasons. Understanding their diet is key to understanding the health and dynamics of the entire Greater Yellowstone Ecosystem.
The Core Summer and Fall Diet
During summer and early fall, when resources are plentiful, the elk’s diet focuses on maximizing nutrition to build fat reserves for the coming winter. Elk are primarily grazers; grasses and grass-like plants constitute the bulk of their food intake when high-quality forage is available. They seek out the lush, green growth in meadows and open grasslands, which provides a low-fiber, high-protein diet essential for body maintenance and reproduction.
A significant portion of the summer diet is composed of forbs, which are broad-leaved herbaceous plants like wildflowers, clover, and legumes. These forbs are nutrient-dense, supplying the energy and protein necessary for antler growth in males and lactation in females. Specific species consumed include asters, geraniums, and dandelion. As fall progresses, the protein content in this vegetation decreases, but it remains a good source of energy before the onset of deep snow.
Survival Strategies: The Winter Diet
Yellowstone’s long, severe winters necessitate a dramatic shift in foraging strategy, moving the elk from a high-quality diet to one focused purely on survival. When deep snow covers the grassy meadows, elk transition from grazing to browsing, consuming less nutritious, woody vegetation. This winter diet consists of the twigs, buds, and bark of shrubs and trees, as well as the needles of evergreen plants.
During this period, elk must dig through the snow, or “crater,” to access cured grasses and sedges buried underneath, which still make up a substantial part of their diet. The energy required for cratering and moving through deep snow is considerable, leading to a focus on energy conservation. Some elk herds utilize geothermally warmed areas, such as those along the Firehole River, where heat from thermal features melts the snow and exposes small patches of vegetation for year-round grazing.
Survival depends on utilizing these low-quality food sources while minimizing energy expenditure until spring green-up. Shrubs, such as willow and sagebrush, become components of the diet when herbaceous plants are buried or depleted. This switch to woody browse is a necessary adaptation, but it results in nutritional stress and weight loss over the winter months.
How Elk Foraging Shapes the Yellowstone Landscape
The volume of plant material consumed by the park’s elk population results in intense pressure that sculpts the Yellowstone landscape. When elk congregate on the winter range, their concentrated browsing profoundly affects specific plant communities, especially willows and aspens. Continuous browsing removes the young shoots and saplings, preventing them from growing tall enough to escape the elk’s reach.
This sustained herbivory limits the regeneration of trees like quaking aspen, which have historically declined in the northern range due to elk consumption. The loss of woody species is an ecological consequence, as willows and aspens provide shade, bank stabilization, and habitat for beavers and songbirds. The intensity of browsing damage is also influenced by the movement and distribution of elk, which can be affected by the presence of predators such as wolves.
Migration patterns and the risk of predation dictate where elk spend their time, resulting in patchy browsing pressure across the ecosystem. Where elk density is high, the transfer of nitrogen from plant tissue to elk bodies causes a net loss of nutrients from the soil, reducing the productivity and growth rate of the impacted plants. The elk’s role as an ecosystem engineer is visible in the stunted and suppressed growth of woody vegetation throughout the wintering areas.