Colorado's bighorn sheep had the 'worst year for herd health in over a decade' in 2023. Has it improved?

DENVER — After a poor year for herd health among Colorado's Rocky Mountain bighorn sheep in 2023, how have the animals fared so far this year?

In January, Andy Holland, big game manager with Colorado Parks and Wildlife (CPW), sat in front of a CPW Commission meeting and delivered "the worst report I've had the misfortune of giving in the decade-plus that I've been doing this."

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Herd health of Colorado's bighorn sheep is at its lowest in a decade, CPW says

Stephanie Butzer

He had documentation of bighorn sheep deaths across all ages in three herds, and an infectious respiratory disease that led to lamb pneumonia in four other herds. The S32 herd, better known to the public as the Georgetown bighorn sheep herd, had little to no lamb survival due to respiratory pathogens causing lamb mortality since 2021, he added.

"This is our worst year for herd health in over a decade for bighorns in Colorado," he said in January.

About 10 months later, Denver7 wanted to follow up with Holland to see if the situation had changed for the iconic state animal of Colorado.

"I got accused of being doom and gloom last year," Holland joked during an interview on Monday. "I was like, 'No, I wasn't doom and gloom. I was trying to make sure everybody knows that things are not rosy. Get ready. This could get worse,' is essentially what I was trying to say."

So, did it?

Watch our follow-up story in the video below to learn more about the status of Colorado's bighorn sheep herds.

We touched base with him to look over what happened to the Rocky Mountain bighorn sheep in 2023 and if CPW biologists could glean any information about the animals' current status ahead of a December population report.

Holland said he will get to look over those new population estimates in a couple months, but "whatever was happening last year looks to be ongoing" and there appears to have been no improvement in the overall health of bighorn sheep. However, it's still too early to say that with complete certainty, he added.

Respiratory pathogens, particularly pneumonia, are the biggest challenge CPW faces with bighorn sheep management. Pneumonia is often deadly for bighorns and there is no vaccination or treatment for it. The National Park Service said the primary cause of bighorn sheep pneumonia complex has been heavily debated for years, but transmission often occurs from domestic sheep or goats passing the disease to wild sheep populations.

Jerry Neal/CPW

"Domestic species do not show clinical signs of disease; however, commingling and transmission of bacteria to susceptible bighorn sheep herds can result in significant illness and death in the wild sheep," the NPS said. "Following outbreaks, bighorn sheep survivors often carry the bacteria and transmit disease to lambs in subsequent years causing lamb death and poor lamb survival for years."

A recent study by Christopher A. MacGlover, an expert in respiratory diseases in wild ungulates, dives into respiratory pathogens associated with bighorn sheep pneumonia in more depth. You can explore the study in the PDF below or here.

Because there are no federal domestic sheep grazing allotments east of the Continental Divide in Colorado, the biggest concern to bighorns are interactions with small private flocks. West of the Continental Divide, the worry lies with domestic sheep on large federal grazing allotments that are close to, or overlap with, bighorn sheep, Holland explained.

Once a sickness gets into the herd, it can circulate for years or decades.

"Maintaining separation between wild and domestic sheep is important to maintaining healthy wild sheep," Holland said. "And then once these bacteria — generally bacteria — get into the wild sheep, then they can circulate within and between herds for years... There's a place for domestic grazing and obviously that we feel like there's definitely a place for wild sheep — it's just not together."

Jerry Neal/CPW

This year, CPW biologists continued to pick up sick and dead sheep in many of the same herds as they did in 2023, with new sickly herds now on the radar. CPW is still waiting for the results from a polymerase chain reaction (PCR) test to determine the pathogen and strain impacting these herds.

"There's reason for concern, but this disease in bighorns is one of our primary challenges with managing bighorns. But it's nothing new. It's not a new situation," he explained to Denver7 on Monday morning. "And that's why I'm trying not to be alarmist. This is, to some degree, par for the course. We'd had a good run for the last 10 (to) eight years or so."

In 2024, the herd in Georgetown saw continued lamb and adult sheep mortality, illness and pneumonia, and the Big Thompson herd and North Poudre herd also saw lamb pneumonia like last year. This year, two additional herds showed troubling levels of illnesses.

"That's Pikes Peak — that's unfortunate, we're not happy about that one — and the Aspen Snowmass herd also now has a disease event going on with lamb mortality, lamb pneumonia," Holland said. "And that one's new and that one's concerning because that herd has been doing pretty well. And the adjacent herd to the west was recovering from an all-age die-off event 10 or 15 years ago. So, that herd was finally coming back, and we finally were seeing lambs survive. So, it's unfortunate to start seeing it in that Aspen Snowmass herd, S13, to the east."

A lot of the herds on the western slope are in remote areas, and CPW often misses disease outbreaks because it cannot fly those locations each year to keep tabs on them. So, there may be bighorn illnesses in those areas too, but CPW has not obtained fresh carcasses to test and therefore cannot confirm if they have been affected negatively.

But looking at the big picture, Colorado's Rocky Mountain bighorn sheep population in 2023 hovered around 7,000, which is the state's 25-year average. Despite disease in some herds, the overall population is not dramatically declining, Holland said. In 2022, the statewide population reached 7,500, which has been the historic peak number. The state has hit that peak twice in the past 25 years.

"It's kind of a ceiling for us, it looks like," Holland said. "We've hit 7,500 and then a number of these disease issues happen, and then it drops down."

Behind that 7,000 number is "a lot of noise in the background," he explained. Some herds are increasing in numbers, while others decline or stay stable.

Hunting license recommendations, which are awarded by herd, may go up and down depending on the animals' health. Having a ewe harvest every year — where hunters go after adult female sheep — can help keep diseases from circulating, he said.

Holland will present new findings on the bighorn sheep population at the CPW Commission's meeting in January.

"Hopefully I have better news in January. We'll see," he said. "So far, it doesn't look like I'm going to have better news. But you know, it's hard to say... We'll know a lot more in January. I'll be able to say things are good or things are worse. I just can't quite say that yet."

While the public can't always lend a helping hand in wildlife matters, this is one where they have that chance.

If you're out on the trails and see domestic sheep and wild sheep together, let CPW know as soon as possible by calling the regional office. A list of those contacts is available on CPW's website here.

"There are instances where there's a stray domestic sheep, for example, that wandered somewhere where it's not known to be, and then there's also instances where the bighorn rams will wander many, many miles and show up in places we don't expect them, in a private flock of domestics," he explained. "In both cases, people can and should absolutely let us know, and then we can address that. The local biologists and district wildlife managers can address that quickly."

He believes there are likely a lot of outdoor enthusiasts and private flock owners who are unaware of this issue with bighorn sheep.

"Information and education on this can go a long way to raising awareness on this," he said. "And I would just encourage people that do care about whatever part of the state they're interested in, to be involved in the federal land management planning process, where they're establishing the multiple use mandate on public lands."

Colorado is home to two species of bighorn — the Rocky Mountain bighorn, which is native to the state and which we focused on for this story, and the desert bighorn, which was introduced in 1979 near the Colorado National Monument.

The last time the desert bighorn were translocated from out of state was 2001.

Rocky Mountain bighorn sheep call Colorado's steep, high mountain terrain home. When it comes time for some shut eye and rest, they prefer cliffs that are often inaccessible for predators. They breed in November and December, with lambs dropping in April through July. Typically, a sheep will give birth to just one lamb. The greatest threat to the species is pathogens, energy development and land use, and poaching, CPW reported. Coyotes, mountain lions and eagles prey on them. Gray wolf predation on bighorns "is not anticipated to be significant," per the 2023 wolf management plan.

Its population was decimated in the early 1900s when European livestock transmitted diseases to the animals and hunting was unregulated. Collaborative work between Colorado and the North American Model of Wildlife Conservation helped the population rebound over the past few decades, starting with sheep transplants in the 1940s. Since then, CPW said it has completed more than 100 bighorn sheep transplants, mostly in the 1970s and 1980s.

While no new bighorn sheep from out of state have been brought in since then, CPW does transplant within the state. This happens once or twice a year, and involves moving between 10 and 40 animals to suitable habitats away from domestic sheep and goats. It's less risky than bringing in sheep from outside Colorado, which may carry diseases, Holland said.

CPW released the below video in February 2018 showing the capture of sheep in Colorado Springs and their relocation to the San Isabel National Forest near Salida.

To learn more about Colorado's bighorn sheep, click here. For information on their conservation and management, click here.

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