The Wood Bison (Bison bison athabascae) is North America’s largest terrestrial mammal, a distinct northern subspecies that faced a dramatic population collapse and was nearly extinct by the turn of the 20th century. Its survival and recovery represent a significant conservation achievement. Determining the current population status requires examining the specific herds and the geographic areas where they have been successfully reestablished.
Defining the Species and Historical Range
The Wood Bison is a northern ecotype, physically distinct from its close relative, the Plains Bison (Bison bison bison). Wood Bison are larger and heavier, with adult males weighing up to 2,000 pounds or more, making them the continent’s most massive land animal. A key identifying feature is the shape and placement of the hump, which is taller and located forward of the front legs, an adaptation believed to help them sweep snow for foraging.
Historically, their vast range spanned the boreal forests and parklands of North America, extending from Alaska and the Yukon through the Northwest Territories, and into northern British Columbia, Alberta, and Saskatchewan. This population, once estimated at 168,000 animals, was decimated by overhunting and disease in the 19th and early 20th centuries. By the late 19th century, the subspecies was nearly extirpated from its range, with only a few hundred individuals remaining in isolated pockets of northern Canada.
Current Population Status and Geographic Distribution
The total population of free-ranging Wood Bison is estimated to be between 7,000 and 10,000 animals, a significant increase from its near-extinction low. This total figure is a composite of numerous herds located primarily across Canada, along with a single reintroduced herd in the United States. Population data reveals a division between disease-free herds and those infected with bovine diseases.
The largest portion of the population resides in Canada, where herds are categorized by health status. Approximately 4,700 to 5,000 wood bison are part of free-ranging, healthy herds, which are valuable for long-term recovery. The Mackenzie Bison Sanctuary in the Northwest Territories holds one of the largest and most successful disease-free populations. Elk Island National Park in Alberta also maintains a captive, disease-free herd that serves as a source of stock for reintroduction projects.
A separate portion of the population, estimated at around 6,000 animals, inhabits the area around Wood Buffalo National Park (WBNP). This population is co-infected with bovine brucellosis and tuberculosis, diseases introduced earlier in the 20th century. This infection complicates management and limits their use as a source for conservation. The presence of these diseases in the WBNP region remains the primary barrier to the overall recovery of the subspecies.
The only wild Wood Bison population in the United States is the Lower Yukon/Innoko Rivers Herd in Alaska, established through a reintroduction effort in 2015. This herd is smaller than the Canadian populations, with a minimum count of 72 wild bison recorded in the summer of 2023. This Alaskan herd represents an expansion back into the subspecies’ historical range, with the goal of growing the population to several hundred animals.
Key Conservation Milestones
The recovery of the Wood Bison began with the establishment of Wood Buffalo National Park (WBNP) in 1922, a reserve intended to protect the last remaining herds. However, initial conservation efforts were undermined by the translocation of thousands of Plains Bison into the park in the late 1920s. This action led to hybridization and the introduction of cattle diseases. For decades afterward, the pure Wood Bison was thought to be extinct in the wild.
A pivotal moment occurred in 1957, when a small, isolated herd of approximately 200 genetically pure Wood Bison was discovered in a remote section of WBNP. This discovery provided the genetic foundation for modern disease-free recovery efforts. Conservation managers used this remnant to begin a successful program of translocation and captive breeding.
In the 1960s, a founding group was moved to the Mackenzie Bison Sanctuary, which became the first healthy, free-ranging herd to be reestablished. Subsequent translocations to Elk Island National Park ensured the survival of a clean, captive breeding population. These efforts led the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) to downlist the Wood Bison from Endangered in 1978 to Threatened in 1988, acknowledging the progress made toward recovery. The successful reintroduction to Alaska in 2015 cemented the species’ return to its historic homeland, demonstrating the effectiveness of decades of collaborative conservation work.