A recent outbreak of canine distemper has had a significant impact on the wolf population in Wyoming and the Yellowstone National Park. Data from 2025 indicates that only 253 wolves and 14 breeding pairs remained, figures not seen since the species was reintroduced two decades ago.
While it does not imply an imminent extinction of wolves in Yellowstone, this situation serves as a reminder of how a disease can alter an ecosystem in a short time, especially when it affects pups, which are crucial for the future of the packs.
The cause of this decline is canine distemper, a highly contagious virus that attacks canids and other carnivores. In northwestern Wyoming, where wolves are considered big game animals, 64% of the specimens showed signs of this disease.
Biologist Ken Mills, from the Wyoming Department of Fish and Game, highlighted that this is the lowest number of wolves in 20 years, similar to when wolves were still establishing themselves in the state. Adults can withstand the disease, but for pups, it can be deadly.
In 2025, 87 pups were documented in Wyoming, of which only 31 to 34 survived, representing a survival rate of just 37%. This situation not only decreases the number of young but also affects the packs’ ability to grow and maintain their social structure.
Wolves in Yellowstone
The National Park Service had recorded other outbreaks in the past, affecting the survival of pups up to 23% in affected areas, compared to 77% in years without outbreaks. In 2024, there were 330 wolves and 24 breeding pairs in Wyoming, figures that fell by 23% and 42% respectively in 2025.
The breakdown by regions shows that in the mountainous northwest of Wyoming, there were 132 wolves in 22 packs, with 10 breeding pairs. In the Wind River Indian Reservation, nine wolves were found in three packs. In areas managed as predators, there were 28 wolves in five packs, with one breeding pair.
Yellowstone is an iconic place for wolves, with 41 specimens released between 1995 and 1997. Since 2009, their number has fluctuated between 83 and 123, and in 2025, 84 wolves were reported, near the lower limit of this range. Notably, only 17 pups survived in the park, the lowest number recorded.
The wolf plays a crucial role in Yellowstone, not only regulating prey populations such as deer and elk, but also providing food for other species. Therefore, a decrease in their number affects the entire food chain.
The National Park Service notes that diseases, along with prey availability and competition, affect population dynamics. In Wyoming, where wolf hunting is regulated, this situation demands a review of hunting policies for 2026.
Wyoming has a target of 160 wolves to manage episodes like this, and although they have been maintained, experts hope the population will recover if the outbreak diminishes. Precedents indicate that recovery is possible, but scientists continue to investigate, especially because this outbreak emerged when the population was already low.
In summary, the reduction of wolves in Wyoming and Yellowstone due to distemper highlights the importance of monitoring diseases, not just counting individuals, in the conservation of wildlife.
