Wolf numbers in Wyoming dropped to their lowest level in 20 years following a severe outbreak of canine distemper that killed an estimated two-thirds of wolf pups born in 2025.

State wildlife officials counted 253 wolves and 14 breeding pairs statewide at year’s end, down from 330 wolves and 24 breeding pairs in 2024. The 23% drop in overall population and 42% decline in breeding pairs marks the smallest wolf count since the species was still reestablishing following its 1995-96 reintroduction.

Ken Mills, a wolf biologist with the Wyoming Game and Fish Department, said canine distemper was detected in 64% of captured animals in the northwestern trophy game zone. While adult wolves can survive the virus, it proved deadly for young animals.

Only 31 to 34 of the 87 documented pups born last year survived to year’s end, a survival rate of just 37%, according to the department’s annual monitoring report.

The outbreak marks the first time Mills has documented widespread distemper when wolf populations were not particularly high. Previous flare-ups, including one in 2018, occurred when wolf numbers were elevated.

Mills is examining whether the disease might follow an eight-year cycle, though he cautioned that more data collection is needed to understand the pattern.

Of Wyoming’s wolves, 132 animals in 22 packs lived in the northwestern trophy game area, which includes 10 breeding pairs. Another 84 wolves in seven packs, including three breeding pairs, resided in Yellowstone National Park.

The Wind River Indian Reservation had nine wolves in three packs with no breeding detected. In areas where wolves are classified as predators and can be killed without limit, 28 wolves in five packs included one breeding pair.

Yellowstone also saw its lowest pup survival on record, with just 17 pups surviving to year’s end. The park’s overall wolf count has dipped into the 80s twice before, in 2012 and 2018, but the low pup survival was unprecedented since reintroduction.

Mills said the outbreak appeared to occur simultaneously across Wyoming and Yellowstone. Based on past patterns in the park, he expects the disease to subside this year as wolves develop antibodies and resistance.

The reduced population will factor into fall 2026 hunting season planning, though Mills anticipates the state will still set harvest limits that allow hunting outside the park and protected areas.

Wyoming’s wolf management objective calls for maintaining at least 160 wolves statewide. Even with the 2025 decline, the population remains above that threshold.