Bighorn Sheep Monitoring

Contribute to mountain science while you recreate in the alpine!

Public Bighorn Photo 1.jpg

To help the Forest Service (FS) and Colorado Parks and Wildlife (CPW) record observations of bighorns in the San Juan Mountains near the Weminuche Wilderness, especially in or near active domestic sheep grazing allotments.

Rocky Mountain Bighorn Sheep, the highly valued and iconic state animal of Colorado, are at risk of developing respiratory disease contracted from domestic sheep grazing on public land. Effective separation of domestic sheep and goats from wild sheep is the only currently available management solution for preventing or minimizing disease transmission. Our volunteer efforts will help the FS and CPW gain more information about the presence of bighorns near active grazing allotments. For more background on Weminuche Bighorns and additional resources, scroll to the bottom of the page.


Observation Instructions - MUST READ! Please print, share, and spread the word!
iNaturalist - Upload observations!

In the News
Backcountry Hunters & Anglers Article - 2018
High Country News Article - Nov 2018

Maps - Scroll down for overviews
Weminuche Grazing Allotments - low resolution with active allotments hilighted in red.
Weminuche Grazing Allotments - high resolution, large scale map with grazing allotments outlined.

-- Main Focus Area Grazing Maps and Schedules --
Endlich Mesa Map - Grazing Schedule Tank Creek Map - Grazing Schedule Virginia Gulch Map - Grazing Area
-- North Weminuche Grazing Maps -- Red Mountain Map
Engine Creeek/ Deer Creek Map
Elk Creek
Deer Park

Paper Datasheets - Can be used instead of or in addition to phone app or computer submissions.
Paper Datasheet
Paper Datasheet Instructions

Learn More
VIDEO 1 - by CPW on Bighorn populations (4 minutes)
VIDEO 2 - Award winning film (7 minutes) hilighting bighorn lambs.
WAFWA - Sheep management document by Wester Association of Fish and Wildlife Agencies Backcountry Hunters and Anglers - Partner website with more info
Tips for interacting with sheep dogs

This project is open to all members of the public.

Any time, but mainly during domestic sheep grazing season (Mid-June through Mid-October) and shortly after to detect stray domestic sheep (October - November).
Best times to observe are dawn and dusk with the sun to your back.

The bighorn observation program includes all of the San Juan Mountains, but researchers are particularly interested in looking for bighorns in and near the three active grazing allotments in the Weminuche Wilderness. These allotments are in the area between the Animas River and Vallecito Creek and South of Needle Creek/ Chicago Basin. See the map below or additioanl maps in the "Resources" box for more detailed information.

Trails of High Interest

  • Upper Endlich Mesa Trail
  • City Reservoir Trail
  • Needle Creek Trail
  • Johnson Creek Trail
  • Upper Lime Mesa Trail
  • Upper Burnt Timber Trail
  • Elk Creek Trail
  • Vallecito Creek Trail

Tips for spotting and photographing bighorns

If you can't submit to iNaturalist (preferred), please report your sighting here:

Good optics are essential! A good pair of binoculars for surveying a large area for sheep and a good spotting scope for close up viewing and photography can greatly increase the odds of seeing bighorns and enhance your overall experience. Your smartphone can be attached to either your binoculars or spotting scope with a special adapter to allow you to take some important and beautiful close-up shots. BHA and Glassitup have arranged for a 40% discount on adapters used by volunteers on this project. Go to select the model you need for your phone and optics and enter bha40 to get the discount!

Background on Weminuche Bighorns:

At almost 500,000 acres, the Weminuche wilderness located northeast of Durango is Colorado’s largest wilderness. Renowned for its rugged high peaks, pristine alpine lakes and wide-open expanses of tundra and mountain meadows it is home to headwaters of the Florida and Pine Rivers as well as Vallecito Creek. This wild public landscape is also home to iconic Rocky Mountain Bighorn Sheep. Weminuche bighorns are highly valued by sportsmen, wildlife watchers and scientists. The Weminuche population, including the Vallecito Creek Herd is classified as Tier 1 by Colorado Parks and Wildlife (CPW) because it is a true native population – a genetically distinct remnant of the once large, wide-spread herds of bighorns that lived in southwest Colorado. This population is made up of three herds that are believed to be interconnected and now number, in total, only about 425 animals.

Historically, bighorn sheep were once among the most abundant wild ungulates in the American West. Population estimates range from 1.5 to 2 million at the onset of the 19th century. Bighorn populations declined with westward expansion of human populations because of market hunting, introduction of domestic sheep and overgrazing of rangelands.

Aggressive restoration and protection efforts have allowed populations to grow in the West from an estimated 25,000 in 1955 to 70,000 now. Yet in recent years, bighorn population growth has stagnated across the West despite continued restoration efforts. Bighorn populations in Colorado reflect this trend, increasing from an estimated 2000 in 1955 to a peak of nearly 7500 in 2002 to approximately 6800 now.

Current scientific consensus is that bighorn populations fail to thrive in large measure because of recurrent herd-level respiratory disease outbreaks associated with exposure to domestic sheep. According to a joint issue statement of The Wildlife Society and the American Association of Wildlife Veterinarians released in March 2015, “... it is now apparent that disease transmission from domestic sheep to wild sheep is a significant risk factor for the conservation and restoration of wild sheep populations,” and “effective separation of domestic sheep from wild sheep is the only currently available management solution for preventing or minimizing disease transmission.”

Weminuche bighorns are listed by the Forest Service as a sensitive species, meaning there is concern for their long-term viability on the forest landscape. Whether due to disease from domestic sheep or other factors, the Vallecito Creek herd, which summers nearest the current active grazing allotments, has declined in number from 125 animals in 2000 to approximately 70 now. Hunting opportunities have been reduced from three ram tags to one annually.

Because the Vallecito Creek herd (S-28) is interconnected with the Cimaronna herd (S-16) and Sheep Mountain herds (S-15), an outbreak of respiratory disease in the Vallecito Creek herd could potentially spread to this greater meta-population resulting in the potential loss of all of the highly valued Tier 1 bighorns on the Weminuche landscape.

Young bighorn rams and ewes often wander in historic home ranges in search of new grazing or breeding opportunities. Foray distances of a few miles to 20 plus miles have been recorded. Bighorns are naturally attracted to domestic sheep and may mingle with them resulting in a transfer of pathogens (spillover) that often causes acute respiratory disease in the affected bighorns. Once infected, the foraying bighorns may die before they return to their home herd or they may bring disease to the herd. Once the pathogens are introduced into the herd, the herd may suffer anything from a non-lethal pneumonia outbreak to a catastrophic all-age die-off. Even subclinical infections of adults can cause respiratory disease in lambs that may negatively impact lamb survival for decades. As such, bighorns known to be exposed to domestic sheep are killed by CPW staff in a desperate effort to prevent further disease spread. Durango Herald article (Nov. 30, 2016)

In addition to foray activity by bighorns, separation is influenced by grazing practices that may result in some domestic sheep straying out of allotments and/or being left behind after the grazing season and potentially coming in contact with nearby bighorns. In the Weminuche Wilderness and in many other public lands in the West there is a lack of current data documenting distribution of bighorns and foray activity in or near active domestic sheep grazing allotments. There have been a few reported sightings (none verified and recorded by agencies) of bighorns in the active allotments in the Weminuche Wilderness. CO BHA hopes to help the Forest Service and CPW obtain more information about foraying bighorns, overall bighorn distribution and the presence of stray domestic sheep on the landscape by putting some BHA “boots on the ground” as bighorn observers.

The Forest Service is responsible for managing bighorn habitat and livestock grazing on the Weminuche Landscape. Currently the Forest Service has delayed its final decision on the Weminuche Grazing Analysis pending further review of data being collected now. Six bighorns from the Vallecito Creek Herd (S-28) were captured in early 2017, fitted with GPS collars and released. Blood samples were also collected for disease screening. More bighorns will be captured, collared and tested in 2018/2019. GPS data will help researchers note the movements of collared bighorns across the landscape. A final decision will likely be made based in part on this new information and possibly from verifiable citizen science observations like this bighorn monitoring project.

Verified sightings of foraying bighorns in or near active allotments, although perhaps unlikely because of the size of the landscape and the small number of bighorns in the area, will trigger necessary and required actions by the Forest Service, CPW and the permittee. MSI thanks all volunteers in this endeavor and thanks the Forest Service and CPW for the opportunity to be of service.

To immediately report bighorn sheep in proximity to domestic sheep, please contact in this order:

Brad Weinmeister (Terrestrial Biologist, CPW, 970-375-6714) or
Chris Schultz (District Wildlife Biologist, FS, 970-799-2425) or in this order Jared Whitmer (District Range Program Leader, FS, 970-799-1221) or
Matt Janowiak (District Ranger, Columbine Ranger District, FS, 970-884-1403)

For more information or with questions, email

Bighorn Summer Ranges.png

THE BIG PICTURE MAP - Bighorn Sheep Summer Ranges and Domestic Grazing Allotments in the Weminuche Wilderness. The areas outlined in red are active grazing allotments. The area outlined in green is of particular interest.

Weminuche with focus area.png

Project Area of Highest Interest The green circle shows the study area of most interest within the Weminuche Wilderness.

PROJECT AREA OF HIGH INTEREST:    Active Domestic Sheep Allotments in Relation to Bighorn Core Home Range in Weminuche Wilderness. Note Vallecito Reservoir at the bottom center for reference.


Active Domestic Sheep Allotments in Relation to Bighorn Core Home Range in Weminuche Wilderness. Note Vallecito Reservoir at the bottom center for reference.

Additional Resources: 
Weminuche Wilderness information 

Bighorn biology and viewing tips

Current References for Bighorn Sheep Pneumonia

The Wildlife Society and American Association of Wildlife Veterinarians Joint Issue Statement, Domestic Sheep and Goats Disease Transmission Risk to Wild Sheep.  March, 2106  

The Wildlife Society Fact Sheet, Impacts of Disease on Bighorn Sheep Management.  February, 2014. 

The following very current and important articles and related articles can be found at 

Cassirer, F., Manlove, K., Almberg E., Kamath P., Cox M., Wolff P., Roug, A., Shannon J.; Robinson R., Harris R., Plowright R.K., Hudson P., Cross P., Dobson A., Besser T. 2017. Management of pneumonia in bighorn sheep: risk, reservoirs, and resilience. Journal of Wildlife Management. doi:10.1002/jwmg.21309

Plowright, R. K., Manlove, K. R., Besser, T. E., Páez, D. J., Andrews, K. R., Matthews, P. E., Waits, L. P., Hudson, P. J. and Cassirer, E. F. (2017), Age-specific infectious period shapes dynamics of pneumonia in bighorn sheep. Ecology Letters. doi:10.1111/ele.12829

Frances Cassirer, Kezia R. Manlove, Raina K. Plowright, Thomas E. Besser. Evidence for strain-specific immunity to pneumonia in bighorn sheep. 2016. Journal of Wildlife Management. doi:10.1002/jwmg.21172.