The American Bison, often called the American Buffalo, is one of North America’s most iconic large mammals. To understand how this massive animal thrives, one must examine its diet of entirely plant matter. This article confirms that bison are indeed vegetarian and explores the specific mechanisms and foods that support their massive frames.
Classification as a Herbivore
The straightforward answer to whether bison are vegetarian is yes; they are formally classified as herbivores. This means their diet consists exclusively of plants, distinguishing them from omnivores and carnivores. Bison are further categorized as grazers, indicating a strong preference for grasses and grass-like plants over other types of vegetation. Bison must consume a large volume of vegetation to meet their energy needs, typically ingesting about 1.6% of their body mass in dry forage daily.
Primary Food Sources
The vast majority of a bison’s diet is comprised of two plant types: grasses and sedges. Studies of wild herds often show that these graminoids make up 90% to 100% of their total food intake, depending on the season and location. Specific grass species consumed include Blue gramma, little bluestem, and sand dropseed, which are abundant across the mixed-grass prairies.
Bison shift their selection based on the nutritional quality of the forage. They prefer areas where grasses are actively growing and contain the highest protein concentrations, which is often highest in the spring. During periods of scarcity or when grasses are less nutritious, they will incorporate forbs—broadleaf flowering plants—and occasionally browse on woody vegetation, such as twigs and leaves.
Specialized Digestive System
The ability of a bison to survive solely on tough, fibrous vegetation is due to its highly specialized anatomy; they are classified as ruminants. Like cattle and deer, bison possess a multi-chambered stomach, an adaptation necessary for breaking down the cellulose found in plant cell walls. This stomach is divided into four compartments: the rumen, reticulum, omasum, and abomasum.
The first and largest chamber, the rumen, acts as a massive fermentation vat, housing billions of specialized microbes, including bacteria and protozoa. These microorganisms produce the cellulase enzyme, which the bison cannot produce itself, to digest the plant fiber. The process is aided by rumination, where the bison regurgitates partially digested food, called cud, for further chewing before swallowing it again. This slow and thorough digestive process allows the bison to extract maximum nutrients from low-quality forage, with food taking approximately 80 hours to pass through their system.