Desert Bighorn Sheep in Arizona

A Comprehensive Overview of Decline, Recovery, Distribution, Transplants, and Current Population Status

Historical Decline of the Desert Bighorn Sheep in Arizona

The desert bighorn sheep (Ovis canadensis nelsoni and O. c. mexicana) has long been emblematic of Arizona’s rugged landscapes, representing both natural resilience and the consequences of environmental pressures. Historically, bighorn sheep thrived across nearly every major mountain range of Arizona, and population estimates prior to significant European-American settlement suggest that tens of thousands inhabited the Southwest1. However, sweeping changes in land use, human expansion, and management policy would catalyze one of the most dramatic large-mammal declines in the American West.

From approximately 1860 to 1920, bighorn populations experienced precipitous declines. The primary factors cited include habitat loss and fragmentation due to settlement, expansion of mining and agriculture, the introduction of roads, canals, and other infrastructure, and unregulated hunting. The widespread presence of domestic livestock also brought direct competition for forage and critical water sources, pushing bighorn sheep into smaller, more isolated patches of suitable habitat1. More insidious, and ultimately more devastating, was disease transmission from domestic sheep and goats. Pneumonia and other illnesses often swept through herds, resulting in rapid die-offs and pushing many historically robust populations to the brink of extirpation23.

By the mid-20th century, research and agency accounts suggest that only about 1,000 bighorn sheep remained in Arizona, occupying fewer than a third of their historical ranges43. Notably, many of the state’s iconic ranges—such as the Santa Catalina, Bill Williams, and San Francisco Peaks—had lost their herds altogether, and only the most remote or inaccessible deserts, such as the Kofa and Cabeza Prieta regions, harbored viable populations. The Arizona Game and Fish Department (AZGFD) and various conservation stakeholders would later recognize this as an existential crisis, demanding a more coordinated and aggressive response3.

Early Recovery Efforts and Legislative Response

Arizona’s recognition of the bighorn’s plight came at a time when wildlife management nationwide was evolving. In 1893, the territorial legislature provided the first total protection for bighorn sheep, making it illegal to hunt them, decades ahead of modern wildlife management efforts5. However, gaps in enforcement and a lack of active, science-driven management limited the effectiveness of this protection during the most critical years of decline.

With shifting perspectives in the 20th century, new frameworks emerged. The establishment of the Kofa and Cabeza Prieta National Wildlife Refuges in 1939 was a watershed moment for Arizona conservation, creating protected reserves specifically structured to conserve the remnant bighorn populations and their habitat. These refuges, spanning over a million acres combined, offered both sanctuary for the remaining animals and a launching pad for future recovery efforts.

After widespread scientific and hunting community input, limited regulated hunting of mature desert bighorn rams resumed in 1953, under a tightly controlled permit system. The guiding belief was that the visibility and economic value generated by limited hunts would help galvanize public and political support for the species’ broader conservation—a model later echoed by the North American conservation community3.

Early recovery was further aided by the founding of the Arizona Desert Bighorn Sheep Society (ADBSS) in 1967, a citizen-led group specifically dedicated to funding, advocating for, and implementing on-the-ground conservation. Their focus on habitat improvement—especially water development in arid ranges—ushered in a new era of collaborative restoration between state agencies, non-profits, federal land managers, and conservation-minded hunters4.

Modern Conservation and Recovery Programs: AZGFD and Partners Lead the Way

The trajectory of the desert bighorn sheep in Arizona since the mid-20th century is one of hard-won, science-based recovery, underpinned by intensive management strategies and broad-based partnerships. The Arizona Game and Fish Department (AZGFD), working with organizations like the ADBSS and national groups such as the Wild Sheep Foundation (WSF) and the Western Association of Fish & Wildlife Agencies (WAFWA), has propelled the state from near extirpation to a legitimate conservation success story6.

Translocation and Augmentation:

Translocating bighorn sheep has been a cornerstone strategy. Since 1955, the AZGFD has captured and moved approximately 1,400 desert bighorn sheep within Arizona and beyond, establishing new herds in suitable but unoccupied habitat and supplementing struggling existing herds37. Shelter records and genetic studies show these efforts have maintained, and in some cases enhanced, genetic diversity without leading to the erosion of distinct lineages—debunking fears of genetic “bottlenecking” or outbreeding depression7.

Water Development and Habitat Restoration:

Because water availability is a limiting factor across the Sonoran and Mojave deserts, agencies and ADBSS have constructed and maintained hundreds of water catchments (“guzzlers”), often in inaccessible areas through helicopter-supported logistics89. These projects now dot the landscape in dozens of mountain ranges, securing year-round water access and enabling sheep to recolonize these habitats8. Additional efforts in prescribed burning, vegetation management, and restrictions on human disturbance in lambing areas have all been deployed to ensure range suitability and minimize undue stress on vulnerable herds3.

Adaptive Management and Partnerships:

AZGFD’s data-driven approach incorporates intensive monitoring, with periodic helicopter surveys, remote camera networks at water sources, and extensive disease testing for each management unit. When necessary, test-and-remove strategies for disease management and targeted mountain lion control to protect small, vulnerable sheep populations are implemented, reflecting an adaptive, science-based management style32.

Stakeholder Collaboration:

The rise of public-private conservation partnerships is particularly notable. From the ADBSS’s all-volunteer waterhole construction teams to the WSF’s direct conservation funding and continuing role in transplants and disease research, this collaboration integrates hunters, NGOs, agencies, and the general public in a shared mission108.

Outreach and Education:

ADBSS and AZGFD regularly host hunter clinics, public informational events, and community habitat projects, fostering a supportive conservation culture and keeping the broader Arizona community invested in the bighorn’s recovery4.

Current Distribution of the Desert Bighorn Sheep in Arizona

After decades of focused management and restoration, the desert bighorn sheep’s presence in Arizona is more robust and geographically expansive than at any point in the last century. As of 2025, the statewide desert bighorn sheep population is estimated to be over 5,600, with the Rocky Mountain bighorn sheep population at about 1,300 individuals, for a combined total approaching 7,000 animals.

Regional Distribution

Desert bighorn sheep in Arizona are divided into two primary subspecies: the Nelson’s (O. c. nelsoni) inhabiting the northern and western regions (such as the Black Mountains and Grand Canyon), and the Mexican (O. c. mexicana) found in the central and southern mountain ranges (including the Kofa, Cabeza Prieta, Catalina, and Harcuvar Mountains). The dividing line between the two is generally approximated at the Bill Williams River.

Northern Arizona: The Nelson’s desert bighorn are concentrated in the Black Mountains region, the Grand Canyon, and adjacent areas.
Central and Southern Arizona: The Mexican desert bighorn occur in the Kofa, Harcuvar, Eagletail, Sierra Estrella, Catalina, Galiuro, and other mountain ranges. Kofa and Cabeza Prieta remain the two most significant refuges, both for population size and as source herds for translocation.
Translocated/Restored Ranges: Thanks to decades of augmentation, bighorns now also inhabit restored habitats such as the Catalina, Harcuvar, Sierra Estrella, New Water, Galiuro, and desert ranges along the lower Colorado River9.

Rocky Mountain bighorn sheep, while less numerous, have been established in the rugged eastern Arizona ranges, including the Eagle Creek–Blue River region, West Clear Creek, Black River, and Mazatzal areas. Transplants from Arizona have helped restore or supplement populations in other states as well3.

Notable Transplants: Successes, Innovations, and Lessons

Translocation has defined Arizona’s bighorn sheep recovery narrative and offers key case studies in restoration ecology.

Kofa Mountains

Once the heart of Arizona’s largest bighorn population, the Kofa Mountains have seen cycles of boom and decline. The dramatic fall from over 800 sheep in 2000 to fewer than 400 in 2006, attributed to severe drought, disease, and predation, prompted aggressive restoration strategies11. Management responses included more cautious hunting quotas, predator management (particularly using “adaptive mountain lion management” protocols), disease monitoring, and intensive water development. By 2021, the estimated Kofa population had rebounded to 941 sheep, becoming a statewide anchor for both population recovery and as a translocation source12.

Cabeza Prieta National Wildlife Refuge

Established in 1939 primarily to protect the desert bighorn sheep, Cabeza Prieta shelter’s population depends on both natural adaptation and modern management. The construction of artificial and improved natural water catchments, and technological innovations in remote hydrological monitoring, now enable refuge managers to target water supplementation with minimal disturbance, vastly reducing mortality risk during severe droughts13. Population targets at Cabeza Prieta are maintained at 500-700 animals, with the refuge providing a genetic and demographic reservoir for other Arizona herds and neighboring Sonoran Desert ecosystems.

Catalina Mountains Project

Arguably the most high-profile contemporary transplant, the Catalina Bighorn Sheep Project began in 2013, seeking to re-establish a once-thriving population in these “sky island” mountains north of Tucson. The multi-agency effort involved several transplants of bighorn sheep from the Kofa and Plomosa Mountains, with all adults collared for post-release monitoring14. Predator management (targeted mountain lion control), habitat improvements, and restrictions on recreational activity in lambing areas—sometimes controversial—were all implemented to support herd reestablishment. By 2024, the herd had become visible across the Catalinas, with natural reproduction occurring and documented lamb recruitment, providing a hopeful model for future complex restoration projects.

Harcuvar Mountains

One of Arizona’s most recent, large-scale transplants, the Harcuvar Mountains project in 2022 involved moving 30 desert bighorn sheep into suitable, previously unoccupied habitat, with a goal of ultimately supporting 400+ sheep in the range. The project integrated innovative technology (GPS collaring for adaptive management), robust funding ($50,000 from WSF and partners), and a multi-year planning horizon for additional water catchment improvements and future transplants108. Water developments—like the Rinehart-Newlon Water Catchment—provided critical support infrastructure to extend population viability through periods of drought.

Population Estimates: Statewide and Regional Data

Arizona has invested heavily in systematic population monitoring. Helicopter and ground surveys, genetic studies, hunter check-ins, and capture data all contribute to regular estimates at both the statewide and management unit levels. Below, the most up-to-date regional and historical estimates are compiled:

Region	Historical Low (Post-1950s)	Notable High Point	2000 Estimate	2012 Estimate	2021-2024 Estimate
Arizona Statewide (Total Bighorn)	~1,000	—	~6,000	—	6,900–7,000
Desert Bighorn Sheep (O. c. nelsoni & mexicana)	<700	—	—	—	~5,600 (2024–2025)
Kofa Mountains	390 (2006)11	812 (2000)	812	404 (2012)	941 (2021)
Cabeza Prieta NWR	—	—	—	—	500–700 (2024 target)
Catalina Mountains	<20 (1990s)14	200 (1920s)	—	—	~90–120 (2024 est.)
Harcuvar Mountains	0 (pre-2022)	—	—	—	100–120 (2024–2025 est.)
Rocky Mountain Bighorn (RMBS)	<100	—	—	—	~1,300 (2024–2025)

Discussion of Population Trends:

The Kofa Mountains, long serving both as a conservation stronghold and source population for transplants, suffered dramatic declines in the early 2000s, but thanks to targeted management, its numbers have rebounded, though not to historic highs.
Cabeza Prieta NWR has maintained a relatively stable population, with sustained management efforts focusing on water provision and minimal human disturbance.
The Catalina Mountains demonstrate both the risks and potential of translocation, with the current population still relatively small but increasing, and with lambing and dispersal observed since the project’s inception.

Over the last two decades, Arizona’s statewide bighorn sheep population has shown a net increase, bucking the regional trend of stagnation or decline in many neighboring states. This success is largely attributed to the aggressive, data-driven management strategies implemented by AZGFD and partners.

Key Stakeholders and Partnerships

The rise of Arizona’s bighorn sheep is a testament to the power of collective conservation.

Arizona Desert Bighorn Sheep Society (ADBSS)

Founded in 1967 in response to the crisis facing bighorn populations, ADBSS has been central to nearly every major restoration and habitat improvement effort in the state. It boasts over 1,100 members, and its contributions exceed $9.5 million since inception—funds raised through auctions, raffles, and direct donations, all reinvested into sheep conservation and habitat projects4. ADBSS remains instrumental in waterhole development, population surveys, public education, and mobilizing volunteers for on-the-ground projects.

Wild Sheep Foundation (WSF) and WAFWA

On the national and continental scale, the Wild Sheep Foundation and the Western Association of Fish and Wildlife Agencies (WAFWA) have provided crucial technical, financial, and policy support. Arizona both receives from and contributes to their multi-state initiatives, ranging from disease research to joint restoration projects and inter-state translocations6.

Government Agencies

The Arizona Game and Fish Department orchestrates all management activities and coordinates logistics, research, and regulatory compliance. The U.S. Fish and Wildlife Service, overseeing the Kofa and Cabeza Prieta refuges, works in tandem with state and non-profit partners. The U.S. Forest Service and Bureau of Land Management similarly play a role in habitat management, especially in wilderness and National Forest lands intersecting historic and current sheep ranges.

Local and National Volunteers

A defining feature of Arizona’s success has been the mobilization of thousands of volunteers, from high school students to seasoned conservationists, providing the labor and logistical support for water development, monitoring, and habitat improvement8.

Disease and Herd Health Management

Disease—particularly pneumonia caused by Mycoplasma ovipneumoniae—remains the most serious existential threat to bighorn sheep, capable of causing catastrophic herd-level mortality events and stunting population recovery for decades23. AZGFD’s approach involves:

Routine disease monitoring and surveillance in both translocated and native herds
Mandatory disease testing for all hunter-harvested sheep and all relocated individuals
The use of “test and remove” pilot projects in some units, particularly when a chronic carrier (usually an adult ewe) is identified as central to lamb mortality cycles2
Rigorous separation of domestic sheep and goats from wild sheep habitat, in partnership with land management agencies and private landowners3
Partnering with veterinary and academic institutions for diagnostic and epidemiological studies

Die-offs remain an ever-present threat, as isolated incidents in the Black Mountains (2015) and other regions have shown. However, Arizona’s management now represents one of the most advanced and proactive disease surveillance frameworks in the western United States.

Habitat Restoration and Water Development Projects

Arizona’s arid climate means that water is often the limiting factor for bighorn sheep. The ADBSS, AZGFD, and partners have responded with an extensive program to develop, restore, and maintain water sources across the landscape:

Over 150 waterholes and guzzlers constructed, many in remote, helicopter-access-only terrain98
Examples like the Rinehart-Newlon Water Catchment in the Harcuvar Mountains demonstrate the scale and collaborative spirit of these efforts, with multi-thousand-gallon capacity catchments serving both sheep and a suite of desert wildlife8
Restoration of natural tinajas and coordinated water hauling during drought years, now informed by advanced lidar remote-sensing to optimize timing and minimize human impact13

Habitat restoration additionally includes prescribed fire, invasive species control, closure or restriction of sensitive lambing or movement areas during critical periods, and systematic range assessments to prioritize future interventions3.

Public Outreach and Education Initiatives

Regular public outreach, hunter education, and citizen science projects keep the bighorn story alive in Arizona’s cultural imagination. Efforts include:

Annual clinics for permitted sheep hunters, run by ADBSS and AZGFD, which educate participants on proper sheep identification, field aging, ethics, and data collection for herd health
School and community programming highlighting conservation achievements and the role of hunting and citizen science in wildlife restoration
Ongoing media campaigns, sustainability reports, and participatory research projects linking the public to real-world conservation

Hunting Regulations and Their Impact on Population Recovery

Regulated hunting is both an economic and management lever in Arizona’s bighorn sheep program. The hunting model is characterized by:

Extremely limited “Any-Ram” permit allocations—about 135 for desert bighorn sheep and 20 for Rocky Mountain bighorn sheep annually, amounting to roughly 2% of eligible rams
Permit draw odds among the most competitive of any North American big game (with a success rate of less than 1% for most applicants)15
All hunting proceeds, through tag auctions and raffles, are reinvested directly into conservation, funding everything from water development to disease research4
Hunt quotas are continually adjusted based on population survey data, ensuring no population segment is over-harvested and that hunting remains sustainable
AZGFD’s model is cited nationally as an example of the successful integration of hunter-conservationist interests with robust scientific oversight

Population Estimates by Region: Summary Table

Below, a tabulated summary incorporates major herd units, highlighting both the historical and current bighorn sheep population estimates in Arizona (all recent as of 2024–2025).

Region/Mountain Range	Historical Estimate (Pre-decline)	Post-decline (1950s–1970s)	2000 Estimate	2012 Estimate	2021–2025 Current Estimate
Statewide (All Bighorn)	20,000 (pre-settlement, est.)	~1,000–1,500	~6,000	—	6,900–7,000
Desert Bighorn Sheep	—	~700 (by 1967)	—	—	~5,600
Kofa Mountains	—	800 (1960s)	812	404	941 (2021 survey)
Cabeza Prieta NWR	—	—	—	—	500–700
Catalina Mountains	200 (1920s)	<20 (1990s)	—	—	90–120
Harcuvar Mountains	—	0 (until 2022)	—	—	100–120
Rocky Mtn. Bighorn Sheep	—	—	—	—	1,300

Note: Some regional counts are based on single-season or triennial helicopter surveys and may under- or overestimate transient individuals.

Sources: AZGFD, ADBSS, WAFWA, FWS reports (2023–2025); historic data synthesized from field literature across referenced sources.

Conclusion and Looking Ahead

The story of the desert bighorn sheep in Arizona is one of resilience, science-driven management, and the remarkable power of partnerships. While challenges such as disease, drought, climate change, and habitat fragmentation persist, the framework developed by AZGFD, ADBSS, WSF, and their myriad collaborators has decisively reversed the spiral of decline for this iconic species. Arizona’s model now guides recovery efforts across the West, providing a wellspring of best practices in adaptive management, community engagement, and habitat engineering.

Continued vigilance, funding, research innovation, and robust stakeholder support will be essential. With public interest and robust partnerships intact, Arizona can maintain and even continue expanding its desert bighorn sheep populations, ensuring that these icons of the Sonoran landscape remain a living part of the state’s wild heritage for generations to come.