A Keystone Species on Open Ground
The plains bison (Bison bison bison) once roamed the Canadian prairies in numbers that stagger the modern imagination. At their historical peak, herds grazed across what is now Saskatchewan, Alberta, and Manitoba, their movement shaping the character of the entire ecosystem. Today, remnant populations managed within national parks and conservation ranches carry forward a lineage that nearly vanished within a single generation.
Few animals have had as direct an influence on their habitat as the plains bison. A herd moving across a grassland does not simply consume vegetation — it actively restructures the landscape. The animals' heavy hooves break up compacted soil, creating depressions that collect water and support distinct plant communities. Wallowing behaviour — repeated rolling in dry earth — carves shallow basins used by other species for generations after the bison have moved on. Nutrient-rich droppings introduce concentrated fertiliser into the soil column, accelerating decomposition and supporting invertebrate communities that feed other grassland residents.
This combination of disturbance and enrichment has led ecologists to classify the plains bison as a keystone species — an animal whose presence maintains biodiversity well beyond what its population size alone would predict.
Historical Range and the Collapse
Before European settlement, bison occupied a continuous range stretching from the northern parkland edge of the boreal forest south to the semi-arid shortgrass prairie of the Great Plains. Canadian populations grazed from the Rocky Mountain foothills in the west to the aspen parkland of central Manitoba in the east. Seasonal migrations followed the greening of grasses northward in spring and retreated south ahead of winter.
Commercial hunting, the settlement of the plains, and deliberate eradication campaigns reduced the total North American population to fewer than 1,000 animals by the 1880s. Canadian herds fared no better. By the close of the 19th century, bison had effectively disappeared from their historical grassland range.
The speed of this collapse is difficult to overstate. Within the span of two or three decades, a population that had defined the ecology of the entire interior plain was reduced to small, scattered remnants.
Recovery Through Protected Areas
Canada's recovery story for the plains bison began in earnest in 1907, when the federal government purchased a herd of 716 bison from rancher Michel Pablo in Montana. These animals were transported north and established at what would become Buffalo National Park in Wainwright, Alberta. Subsequent transfers and breeding programmes created the foundation for several modern herds.
Today, significant plains bison populations exist at Riding Mountain National Park in Manitoba, Prince Albert National Park in Saskatchewan, and Banff National Park in Alberta — where a small reintroduced herd was established in 2017 after a century-long absence. Parks Canada manages these herds with goals that include genetic diversity assessment, herd health monitoring, and ecosystem observation.
The Wood Buffalo National Park herd, located in northern Alberta and the Northwest Territories, is primarily composed of wood bison (Bison bison athabascae), the northern subspecies, and represents the largest free-roaming bison herd in the world. While a distinct subspecies, its presence in Canada's protected landscape demonstrates the conservation gains that dedicated management can achieve.
Behaviour and Grassland Ecology
Plains bison are grazers rather than browsers, feeding predominantly on grasses and sedges throughout the growing season. Daily feeding patterns vary with temperature and daylight. During summer, feeding peaks in the early morning and late afternoon, with midday devoted to resting and rumination in sheltered draws or near water sources.
Bulls and cows typically live in separate groups for most of the year, coming together only during the late-July to September rutting season. During rut, bulls engage in dramatic displays — head-to-head pushing, rolling in wallows, and sustained bellowing — to establish dominance and access to cows. Calves, born in spring with reddish-brown coats, gain their adult colouring within a few months and remain close to their mothers through their first winter.
Plant Communities That Follow Bison
Repeated grazing by bison maintains short and mixed-grass structure across large areas of prairie, preventing the encroachment of shrubby species. This maintained grassland supports populations of insects, ground-nesting birds, and small mammals that depend on open sightlines and exposed soil patches. Species including the ferruginous hawk, the burrowing owl, and the swift fox are among those that benefit from the open character that bison grazing maintains.
Experimental plots from which bison have been excluded consistently show a shift toward taller, denser vegetation and a corresponding reduction in small mammal activity. This effect, documented across prairie systems in both Canada and the United States, underlines the ecological function that large grazers perform — a function that has been largely absent from most of the Canadian prairie landscape for well over a century.
Current Conservation Status
The plains bison in Canada is listed as a species of special concern under the federal Species at Risk Act. This designation recognises the animal's dependence on active management for its continued survival in Canada. Breeding populations outside national parks and a handful of private conservation ranches remain limited.
Genetic analysis has confirmed that most surviving herds carry some introgression from domestic cattle, a legacy of 19th-century crossbreeding experiments. Work to maintain and prioritise genetically pure lineages continues, with Parks Canada publishing updated monitoring reports through its Species at Risk public registry. The ecological restoration that bison enable remains one of Canada's most tangible opportunities to recover grassland biodiversity lost over the past century.