While many of Colorado’s Rocky Mountain bighorn sheep herds continue to struggle with disease, 2024 was a better year for the state animal. 

Andy Holland, a big game manager at Colorado Parks and Wildlife, gave what he referred to as his annual “state of the herds” report at the Jan. 9 Parks and Wildlife Commission meeting. The report examined the health of Colorado’s Rocky Mountain bighorn sheep and its desert bighorn sheep and mountain goat populations and how herd health impacts available hunting licenses for the three species. 

How are Colorado’s Rocky Mountain bighorn sheep faring? 

In last year’s report, Holland referred to 2023 as the worst year for Rocky Mountain bighorn sheep herd health in over a decade in Colorado. 

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From a high-level perspective, 2024 brought good news about the statewide population numbers, Holland said last week.  

In 2024, 23 of Colorado’s Rocky Mountain 71 herds saw population increases in 2024. Still, 15 of the herds faced declines while the rest remained stable. This “balance” meant the sheep’s statewide populations stayed relatively stable, Holland reported.

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“Our current (population) estimate is about 7,000,” Holland said. “Our Rocky Mountain bighorn sheep population estimate has hovered around 7,000 for about 30 years. We’ve hit a ceiling at 7,500 twice, but if you take a step back and squint, it’s been about 7,000 for 30 years.” 

Over half of the state’s current bighorn sheep herds are here due to translocation efforts by Parks and Wildlife. After Colorado’s bighorn sheep declined to near extinction in the early 1900s by disease and unregulated hunting, the state began transplanting the native species in the 1940s. In the 1970s and 1980s, Parks and Wildlife did around 150 transplants of over 2,500 sheep.

The state still transplants animals but at a much lower rate. Holland reported the state now does one or two a year because “there’s very few areas remaining that have both suitable habitat, and there’s no domestic sheep or goats nearby.”

Domestic sheep and goats pose one of the biggest threats to wild bighorn sheep health, he added. 

“Contact between domestic sheep and bighorn sheep increases the probability of respiratory disease outbreaks in bighorn sheep,” Holland said. 

In 2024, despite steady populations, disease concerns continued to be prevalent in many of the herds, including several “Northern Front Range herds” located north of Interstate 70. This includes bighorn sheep herds in Georgetown as well as the St. Vrain, Big Thompson Canyon and the Lower Poudre Canyon herds just west of Fort Collins. 

All of these herds have suffered from all-age mortality events related to a “triple whammy” of three respiratory pathogens impacting the herds, Holland reported. 

“That means that lambs, ewes and rams are dying and with no lambs surviving to 1 year of age the last couple of years,” Holland said. “So, of course, that’s a pretty dire situation.”

The population estimate for the Georgetown unit — historically one of the largest in the state — has fallen from 350 to 225 in the past three years. 

This year, Parks and Wildlife biologists also confirmed the presence of a respiratory disease causing death among the lambs in the Rocky Mountain bighorn sheep herd in Snowmass. This is an “emerging concern,” Holland said. 

While the source of the disease remains unknown, Parks and Wildlife officials are currently collecting data and monitoring lamb survival, he added.

It was not all bad news, however, with Holland noting two particularly “bright spots” for bighorn sheep. 

Last year, the wildlife agency had significant concerns about the Gore Range herd near Vail after it saw an all-age death event and the loss of 50% of its collared females. 

“The good news is that it wasn’t that disease event was not as bad as we expected based on that sample of collar(ed bighorn sheep),” Holland said. “We did have lambs that survived last winter and were recruited to adulthood in the summer.” 

Additionally, the Mount Blue Sky — formerly Mt. Evans — herd “is doing great,” even though located just across I-70 from the Georgetown herd. Over the past three years, the population estimates have grown from 187 to 270. 

Of the 15 bighorn sheep units without public hunting seasons, only one saw a population estimate decline in 2024. The Yampa River herd in Dinosaur National Monument dropped 50% from the previous two years when it had been estimated at 40 sheep. The rest of the management units without hunting either increased or remained stable. 

Monitoring disease in the state animal 

In addition to maintaining separation between domestic and wild sheep, the agency has several programs to improve health. This includes research on pathogens and habitat projects to maintain migration corridors and improve winter ranges for the animals. 

Part of the challenge is that there are “literally hundreds of strains of multiple different pathogens that we’re dealing with,” Holland said.

These all-age mortality events are new to Colorado in the last 20 years, Holland reported, adding that previous diseases primarily impacted lambs. 

As for developing immunity — or even vaccines — to some of the pathogens, Holland likened it to the COVID-19 pandemic. 

“There’s so many different pathogens and so many new strains that actually we’re learning each strain … affects herds totally differently,” Holland said. “And the previous exposure of that herd to different strains either predisposes them for a crash or protects them from (it), so it’s very complicated. We’re still trying to sort out how this is really changing on the landscape.”

Additionally, Holland said that managing the number of hunting licenses helps “reduce density to help keep disease from spreading between the wild herds.”

What does this mean for bighorn sheep hunting licenses? 

On Thursday, Parks and Wildlife recommended that the number of hunting licenses for Rocky Mountain bighorn sheep drop from 327 to 307 in 2025. The reduction is the greatest in the Georgetown unit, dropping from 27 licenses to 14. 

In 2023, of the 351 licenses issued across the state, 230 sheep were killed.  

At the start of his presentation, Holland emphasized the importance of hunting in the agency’s management of the sheep. 

“Big-game hunting is highly regulated in Colorado and especially for these species, bighorn sheep and mountain goat,” Holland said. “Hunting is critical for managing these species within the capability of their habitat … A significant amount of funding and the horsepower for conservation comes from hunters themselves and conservation organizations that are made up of hunters.”

He added that the mandatory inspections and checks of hunted animals provide information — including genetic samples, disease samples and geographic intel  — utilized in Parks and Wildlife’s herd management plans. 

Desert bighorn sheep and mountain goats

Holland’s state of the herds address also addressed populations of desert bighorn sheep — slightly smaller than the Rocky Mountain bighorns and located in southwest Colorado — and mountain goats. 

Overall, the desert sheep are “doing well,” with population estimates totaling around 500 across the state, Holland said. As such, the agency will offer the same number of hunting licenses in 2025 that it did in 2024: 15 ram licenses.

Colorado Parks and Wildlife estimates that its mountain goat population — deliberately introduced to the state in 1948 — is around 1,500. This is relatively stable following a 10- to 15-year period where the agency intentionally reduced the mountain goat numbers to “reduce competition with high-priority bighorn sheep and to minimize damage to sensitive Alpine plants.” 

The state agency increased the number of hunting licenses by two for 2025, increasing to 246 statewide. 

This overall increase included reductions in licenses for a few herds. This included the Maroon Bells herd, which the state has intentionally reduced the population over the past three years from 320 to 160, dropping the licenses from 80 to 30 in the last two years. It also includes a reduction for the Mount Guyot herd in Summit County where the herd has dropped from 170 to 70 in the past three years and the agency wants to see its population increase. 

It also increased the number of licenses for herds in the Gore Range, Tenmile and Holy Cross units where populations are increasing and population density needs to be lower in defense of the Rocky Mountain bighorn sheep herds in those areas.

“When bighorn sheep and mountain goats overlap, occupying the same range, we manage in deference to native bighorn sheep,” Holland said. “Mountain goats compete for forage and can transmit pathogens to bighorn sheep, so we keep mountain goat populations lower in some places to benefit sympatric bighorn sheep.”