The challenge
Wolves had been wiped out in Yellowstone, leaving elk without their main predator.
The case
Under the Endangered Species Act, the National Park Service and US Fish and Wildlife Service brought 14 wolves from Alberta in 1995 and 17 from British Columbia in 1996. They were held in acclimation pens, then released into the park. The wolves bred quickly and spread across the region. At the end of 2024 the park had 108 wolves in nine packs. Northern Yellowstone elk fell from about 23,000 to 12,000 between 1995 and 2004, though researchers dispute how much of that was due to wolves rather than hunting, drought and bears. Wolves leaving the park have caused conflict with ranchers over livestock.
Why it worked
A small, well-planned release can restore a missing predator for good. Its wider effects on the ecosystem are real but harder to measure than early reports claimed.
Sources
- National Park Service (2025). Yellowstone Wolf, Cougar and Elk Project Annual Report 2024.
- Eberhardt, L. L., White, P. J., Garrott, R. A. & Houston, D. B. (2007). A seventy-year history of trends in Yellowstone's northern elk herd. Journal of Wildlife Management, 71(2), 594–602.
- US Geological Survey. Yellowstone wolf restoration.
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