Wyoming and Yellowstone Wolf Populations Hit 20-Year Low Due to Deadly Disease Outbreak

A recent outbreak of canine distemper, a highly contagious and often lethal disease, has significantly impacted wolf populations in Wyoming and Yellowstone National Park. According to data from the Wyoming Game and Fish Department, the state's wolf population has declined to its lowest level in 20 years, with only 253 wolves and 14 breeding pairs recorded at the end of 2025.

The decline is attributed to the distemper outbreak, which was particularly devastating for wolf pups. The disease, which is similar to measles in humans, has a high mortality rate among young wolves, with only 31-34 of the 87 documented pups surviving to the end of the year. This represents a survival rate of just 37%, according to the department's 2025 wolf monitoring report.

Canine distemper is not a new threat to wolf populations, but its impact has been felt more significantly in recent years. In the past, the disease has been density-dependent, meaning that it tends to surge when wolf populations are high. However, the 2025 outbreak occurred when wolf numbers were not particularly high, leaving biologists searching for alternative explanations.

Wyoming Game and Fish Department wolf biologist Ken Mills notes that the occurrence of distemper in wolf populations can be cyclical, with outbreaks potentially occurring in eight-year cycles. However, it takes a significant amount of time to collect data and understand the underlying factors driving these cycles.

Despite the challenges posed by the distemper outbreak, there is cause for optimism. Historically, wolf populations in Yellowstone have experienced outbreaks of the disease, only to recover the following year. With the Wyoming population now having built up antibodies and resistance, the state's wolves are well-positioned to recover from the decline.

The decline in wolf populations has significant implications for the ecosystem and for wildlife management in the region. In 2024, there were 330 wolves and 24 breeding pairs recorded statewide, but the estimated 253 wolves and 14 breeding pairs in 2025 represent a decline of 23% and 42%, respectively. The impact of the distemper outbreak has been felt across the state, with wolf numbers declining in both the 'trophy game' area and in Yellowstone National Park.

The park's wolf population, which is typically one of the most stable and well-studied in the country, has been particularly hard hit. With only 84 wolves in seven packs, including three breeding pairs, the park's wolf population has declined to its lowest level since the reintroduction era. The distemper outbreak has also had a significant impact on pup production and survival, with only 17 pups surviving in the park in 2025.

As the Wyoming Game and Fish Department considers the impact of the distemper outbreak on wolf populations, it will also be taking into account the need to balance the state's wolf population with the needs of other wildlife species and human stakeholders. The department will be setting fall 2026 hunting seasons with the lower wolf population in mind, and will continue to monitor the state's wolf population to ensure that it remains healthy and sustainable.

The decline of wolf populations in Wyoming and Yellowstone National Park serves as a reminder of the complex and often unpredictable nature of wildlife management. As biologists and wildlife managers work to understand the factors driving the decline, they must also balance the needs of multiple stakeholders and ensure that the state's wolf population remains healthy and sustainable for generations to come.