Wyoming and Yellowstone National Park faced a steep wolf-population dip in 2025 after a disease outbreak that hit pups particularly hard, according to Wyoming Game and Fish Department wolf biologist Ken Mills. Mills said the combined counts fell to the lowest level since wolves were still reestablishing after their historic 1995-96 reintroduction.
Mills told WyoFile that 2025 brought “the lowest number of wolves in 20 years,” and he said that timing corresponded to a “population creep stage” when the animals were still establishing in Wyoming. He said all signs pointed to canine distemper as the primary reason wolves plunged statewide to a minimum of 253 wolves and 14 breeding pairs at the end of 2025.
In the northwestern Wyoming zone, Wyoming Game and Fish found distemper in 64% of animals. Mills said adults can survive the contagious virus, which he described as “a measles-like affliction in canines,” but he said it proved “quite lethal” for pups. Based on the state’s 2025 wolf monitoring report, the department estimated that only “31 to 34” of 87 documented born pups lived to the end of the year, for a pup survival rate of 37%.
Mills said the pattern of past distemper outbreaks offered context for why the 2025 flare up was unusual. He said distemper had been density-dependent in the past—surging when wolf populations were higher—and that it last flared up in 2018, shortly after a two-year period when wolves were protected from hunting under the Endangered Species Act and wolf numbers, and conflict, were higher.
He said the 2025 outbreak differed because biologists saw “lots of distemper” while wolf numbers were not particularly high. Mills said, “Could it be cyclical? Yeah,” adding that he suspected any cycle might be “potentially eight-year cycles,” but he said it takes time to collect data and determine what is happening.
Mills also said there was reason to expect distemper would ease this year. He said when Yellowstone wolves have experienced outbreaks in the past, the episode typically lasts a year and then ends with recovery. He added that Wyoming’s wolves now have more antibodies and built-up resistance, leaving the population in “good shape to recover itself,” though he said distemper had still damaged Wyoming’s numbers in 2025 in a way that was new.
For comparison, Mills said that in 2024, Wyoming Game and Fish detected 330 wolves and 24 breeding pairs statewide. He said the estimated 253 wolves and 14 breeding pairs at the end of 2025 represented a 23% drop in the raw wolf count and a 42% decline in the reproductive segment. He said 132 wolves in 22 packs with 10 breeding pairs lived in the mountainous portion of northwest Wyoming in the “trophy game” area, while there were nine wolves in three packs and no breeding detected on the Wind River Indian Reservation.
In the zone where Wyoming manages wolves as predators—where they can be killed by any means without limit—Mills said there were 28 wolves in five packs, including one breeding pair. He said the rest of the statewide wolf population was concentrated in Yellowstone National Park, where the monitoring report estimated 84 wolves in seven packs with three breeding pairs.
Mills said the distemper outbreak appeared “synchronous” across Wyoming and Yellowstone, and that pup production and survival were also poor in the national park. He said “Seventeen pups survived in Yellowstone,” and he described that as the lowest number he had recorded. The story also noted that park public affairs officers, whose office had been inundated with questions about a recent grizzly bear attack, did not respond to WyoFile’s request for an interview before publication.
Outside Yellowstone, Wyoming is likely to adjust wolf hunting plans for 2026 based on the lower counts. The story said Wyoming Game and Fish and its wardens would consider the reduced wolf population when setting fall 2026 hunting seasons, noting that hunting is not allowed inside the park though wolves can leave the park area.
Mills said Wyoming’s relatively small wolf population has allowed the state to manage the animals with “a degree of predictability,” but he said the distemper surge interrupted a long run of stability. Still, he said he felt good about Wyoming’s management plan because it already had accounted for disease-related disruptions, including a population objective of 160 wolves designed to accommodate an event like what the state experienced and still meet the minimum recovery criteria.
He said the recovery criteria includes 10 breeding pairs outside Yellowstone in Wyoming’s trophy game area. Mills said the 2025 surveys detected exactly 10 packs with pups in that zone, adding: “We met the minimum.” “It actually worked exactly as we intended.”