An intentional mistake
In 1922, Canada established Wood Buffalo National Park to protect the last remaining herds of wood bison (Bison bison athabascae), the largest land mammal in North America. At the time, their population had dwindled to between 1,500 and 2,000 individuals. A few years later, a well-intentioned but disastrous decision forever altered the genetics of this herd. Between 1925 and 1928, the Canadian government moved 6,673 plains bison (Bison bison bison) from an overpopulated park in central Alberta into Wood Buffalo National Park.
This transfer was vigorously opposed by zoologists, who feared the two subspecies would interbreed and that the plains bison would introduce diseases. The government proceeded, and the consequences were exactly as predicted. The smaller, more numerous plains bison hybridized with the resident wood bison, creating a massive population of hybrids. The plains bison also carried bovine tuberculosis and brucellosis, which spread to the wood bison herd and remain endemic in the park's population to this day. These diseases can cause weight loss, infertility, and abortions in the animals.
A subspecies debate
The physical differences between the two subspecies are distinct. Wood bison are up to 15% larger than plains bison, with some males weighing over 2,000 pounds. The highest point of a wood bison's hump is forward of its front legs, an adaptation thought to help it sweep away deep snow, while a plains bison's hump is located directly over the front legs. Plains bison have a shaggy "cape," a thick beard, and heavy hair "chaps" on their front legs, all features that are less pronounced in their northern relatives.
The genetic distinction is less clear-cut. While studies show consistent morphological and some genetic differences, some scientists argue the two are ecotypes adapted to different environments—forests versus grasslands, rather than true subspecies. All existing wood bison herds now contain some genetic material from plains bison due to the 1920s introduction. The herd within Wood Buffalo National Park is a genetic artifact of this historical management decision.
The search for purity
For decades, pure wood bison were thought to be extinct. Then, in 1957, a remote, isolated herd of about 200 genetically pure wood bison was discovered within Wood Buffalo National Park near the Nyarling River. Animals from this discovery became the founders for new, disease-free populations now located in places like Canada's Elk Island National Park and the Mackenzie Bison Sanctuary. These herds are central to wood bison conservation and have even been used for reintroduction efforts in Alaska.
This leaves conservationists with a difficult question. Should the massive, ecologically functioning, but hybridized and diseased—herd in Wood Buffalo be managed as a unique entity? Or should the focus be solely on protecting the "pure" but much smaller herds? This debate is at the core of modern conservation genetics for the species, weighing the value of genetic purity against the reality of a vast, wild hybrid population.