A conservation success story
By the early 1900s, the wood bison (Bison bison athabascae), the larger, darker cousin of the plains bison, had been driven to the edge of extinction. Their population, once estimated at over 160,000 animals across the boreal forests of North America, had crashed to just a few hundred due to overhunting. For decades, the subspecies was believed to be entirely gone, lost to hybridization after plains bison were moved into their last refuge, Wood Buffalo National Park, in the 1920s.
The story changed in 1957. An aircraft patrol spotted a small, isolated herd of about 200 bison in a remote corner of the park. Genetic testing confirmed they were pure-bred wood bison and, importantly, free of the cattle diseases that plagued the main hybrid herd. This discovery created an opportunity. In a complex operation during the winter of 1963, wildlife officials captured 18 of these bison and transported them north to a newly established 10,000-square-kilometer protected area: the Mackenzie Bison Sanctuary.
Rewilding an ecosystem
The 16 surviving bison that founded the Mackenzie herd thrived in their new home. From that small starting number, the population grew rapidly, reaching a peak of about 2,400 animals by 1989. This success became an example of large mammal reintroduction. Following an anthrax outbreak in 2012 that killed at least 450 animals, the population has since stabilized and is showing signs of recovery. The most recent estimates place the herd's size at around 850 individuals.
The return of the bison has had effects that ripple through the entire food web. As the bison population grew and expanded its range, it created a substantial new food source. In response, wolves (Canis lupus) have naturally recolonized the area, re-establishing a predator-prey relationship that had been absent for nearly a century. The first observations of wolf-killed bison were recorded in the winter of 1983. Studies show the wolves selectively prey on calves and older, weaker individuals, a natural process that helps regulate the bison population and improve the overall health of the herd. This restored dynamic, where a large herbivore and its primary predator interact, is an outcome of successful rewilding projects.