Beavers are large, semi-aquatic rodents renowned for constructing dams and lodges. As herbivores, their diet is entirely plant-based, but their lifestyle near waterways raises questions about what they consume from their aquatic environment. This exploration will clarify the specific roles that woody material, larger aquatic vegetation, and microscopic life like algae play in the overall diet of this industrious animal.
The Main Diet of Beavers
The primary source of sustenance for beavers comes from terrestrial and woody plants, particularly the inner bark and cambium layer of deciduous trees. The cambium is the soft, nutrient-rich tissue found just beneath the rough outer bark, providing a high-calorie winter food source. Beavers prefer fast-growing, easily accessible species such as willow, aspen, cottonwood, and birch.
They strip the bark and cambium off felled branches and logs, rather than eating the hard wood. This woody material, including twigs and leaves, is stored in a large underwater food cache near the lodge for access during cold winter months when ice covers the water surface. Their digestive system is uniquely equipped with specialized microorganisms that help them break down the high amount of cellulose found in these woody plants.
Gnawing on these trees also serves the dual purpose of providing building materials for their dams and lodges, which are constructed using the larger, uneaten sections of the timber.
Consumption of Aquatic Vegetation
While woody plants are their winter staple, beavers switch to a diet dominated by soft, herbaceous aquatic vegetation during the spring and summer months. These aquatic plants are collectively known as macrophytes and are a highly palatable and easily digestible food source when actively growing. Studies have found that aquatic vegetation can constitute a significant portion, sometimes over half, of a beaver’s annual diet.
Beavers target the entire structure of many aquatic species, including the leaves, stems, and especially the carbohydrate-rich underground parts like roots and rhizomes. They frequently consume the tubers and rhizomes of water lilies, which are often stored in their winter food piles alongside woody branches. Other favored non-woody plants include cattails, rushes, pondweed, and various grasses and sedges found along the water’s edge.
The consumption of these aquatic materials is so extensive that beaver herbivory can noticeably reduce the overall biomass of plant life in their ponds. Their foraging can even shift the local plant community composition, as they preferentially graze on certain species over others.
Do Beavers Target Algae?
Beavers are not classified as primary algivores like some other aquatic species, but they do consume algae as part of their diverse herbivorous diet. Algae is not a preferred staple food, as their digestive system is optimized for the cellulose found in larger plant structures. They will readily ingest it when available.
The algae they consume often consists of filamentous types or periphyton—the attached algae that grows on the surfaces of other aquatic plants and submerged objects. When a beaver consumes the leaves or stems of a larger plant like a cattail or water lily, it will inevitably ingest the attached microscopic life as well. Some observations have noted beavers actively consuming large masses of algae.
The presence of beavers often creates sun-drenched, nutrient-rich ponds, which are ideal environments for algae and other aquatic plants to flourish. While their main caloric intake comes from woody cambium in winter and larger aquatic plants in summer, algae provides a supplementary source of nutrients.