The beaver, a large semi-aquatic rodent, is widely recognized for its unique ability to construct dams and lodges, fundamentally altering its environment. These industrious mammals, including the North American beaver (Castor canadensis) and the Eurasian beaver (Castor fiber), are strict herbivores. Their entirely plant-based diet varies significantly depending on the season and the availability of local vegetation. Their consumption habits are tied to their engineering work, as the trees they fell and the ponds they create dictate what and how they eat.
The Staple Diet: Bark and Woody Plants
The core of a beaver’s diet, particularly during the colder months, centers on the inner bark and soft tissues of woody plants. Beavers do not eat the hard, structural wood of a tree but instead focus on the nutrient-rich layer directly beneath the bark called the cambium. This soft, living tissue provides the necessary carbohydrates and energy to sustain them when other food sources are scarce.
Beavers prefer certain deciduous trees and shrubs, including aspen, willow, poplar, and birch, because these species are soft and easily digestible. Willows and cottonwoods are favorites due to their high palatability and growth patterns that encourage re-sprouting after cutting. The bark and twigs of less-preferred species, like maple, alder, and sometimes conifers, may also be consumed when the choicest trees are unavailable.
Beavers use their powerful incisors to fell trees, consuming the nutritious cambium and smaller branches for food. The larger, debarked wood is then utilized for building and maintaining their dams and lodges. This efficient use of resources ensures that very little of the material they harvest goes to waste.
Seasonal Variety: Aquatic and Herbaceous Vegetation
During the spring, summer, and early fall, the beaver’s diet shifts to incorporate a wide variety of softer, nitrogen-rich plants. This change is driven by the abundance and easy accessibility of succulent, actively growing vegetation. In the warmer months, aquatic plants can make up a significant portion of their food intake, sometimes comprising up to 50% of the total diet.
Beavers consume water lilies, including the leaves and rhizomes, as well as cattails, pond weeds, rushes, and sedges that grow in and around their ponds. These herbaceous foods are easier to access and digest than woody material, providing essential nutrients that are particularly important for growing young. They often graze on grasses, ferns, clover, and other flowering plants found near the water’s edge.
The consumption of these softer plants minimizes the need to fell large trees, which is a more energy-intensive activity. As plants mature and become more fibrous in the late summer, beavers begin to transition back toward woody material in preparation for the coming cold season.
Foraging Behavior and Winter Caching
Beavers are primarily nocturnal foragers, often leaving the safety of their water-based homes under the cover of darkness to search for food. They typically forage within 60 meters of the water’s edge, using their sharp incisors to fell trees by gnawing around the trunk in an hourglass shape. Once a tree is down, they strip the edible bark and twigs, transporting the pieces back to the water using their mouths and forepaws.
Foraging becomes highly focused in the autumn as beavers prepare for the extended period of ice cover. They create a large underwater food cache, often called a “food raft,” placed near the submerged entrance of their lodge. This cache consists of small, palatable branches and saplings, primarily from preferred species like willow and aspen.
The beavers anchor the butt end of these branches into the mud at the bottom of the pond, creating a dense pile that remains accessible even when the surface water freezes solid. This cache of submerged woody material, sometimes weighing two or more tons, serves as the family’s sole food source throughout the winter. When the pond is iced over, the beavers simply swim out from the lodge, retrieve a branch from the cache, and bring it back inside to consume the preserved bark and cambium.