Working with Bighorn Sheep: A Q and A with NMDGF biologists

Working with Bighorn Sheep: A Q and A with NMDGF biologists

New Mexico has a rich wildlife heritage that can be experienced either through hunting, wildlife viewing, photography or by people seeking to connect with the outdoors. Here, you’ll find an array of habitats, from alpine tundra, forested mountains, grasslands, rivers and lakes, to sandstone canyons and the Chihuahuan desert, which is why New Mexico is aptly referred to as the Land of Enchantment. These diverse habitats are home to a species that draws people to New Mexico every year: bighorn sheep.

The New Mexico Department of Game and Fish manages bighorn sheep and their habitats on behalf of all New Mexicans to conserve and protect bighorn for their beneficial use and enjoyment across a diversity of interests and activities. The management of both Rocky Mountain and desert bighorn relies on several key elements that contribute to NMDGF’s Bighorn Program, including annual inventory and monitoring of bighorn populations, disease surveillance, captures and translocations, habitat conservation and enhancement, and many more programs that contribute to the conservation and management of bighorn sheep in New Mexico.

We sat down with Katie Piecora and Tom Batter, Ph.D., two NMDGF bighorn sheep biologists, to discuss the important work being done to conserve and protect this unique species.  

What are the different bighorn sheep subspecies found in New Mexico?

Tom Batter: New Mexico is home to two subspecies of bighorn sheep: Rocky Mountain and desert. There are two lineages of desert bighorn sheep: Nelson’s desert bighorn (Ovis canadensis nelsoni) and Mexican desert bighorn (Ovis canadensis mexicana). The lineage native to New Mexico is the Mexican desert bighorn. NMDGF is committed to maintaining the mexicana lineage within the state. The mexicana lineage is currently limited to New Mexico, Arizona and Mexico. Limited numbers of desert bighorn highlight the importance of interagency collaboration and capture and translocation efforts, which can be used to restore populations in vacant range or increase demographics of existing populations, both of which help maintain genetic diversity within the state’s populations.

Key differences between Rocky Mountain bighorn sheep and Mexican desert bighorn sheep include habitat, physical appearance, behavior, and reproduction. Rocky Mountain bighorn typically occupy mountain regions at elevations between 5,000-13,000 feet in alpine, subalpine, and rugged terrain, usually near areas with water and meadows. Desert bighorn occupy arid country in the southwest, often at elevations below 6,000 feet. Desert bighorn are adapted to dry climates with limited water sources and sparse vegetation.

Can you talk about the programs the Department is working on with desert bighorn sheep in the Red Rock Wildlife Management Area and why it’s critical for a healthy sheep population?

Katie Piecora: Like many large mammal species in North America, bighorn sheep experienced rapid population declines following European settlement due primarily to unregulated harvest, disease exposure from livestock, competition with livestock, and habitat loss/degradation. By the early 20^th century, desert bighorn sheep were on the brink of extinction. The state game commission added the desert bighorn to the state list of endangered species in 1980.

Red Rock Wildlife Management Area is home to our desert bighorn sheep conservation breeding population. This population was established in 1972 in response to the significant challenge of successfully reintroducing desert bighorn sheep into New Mexico. The 1,500 acre facility is home to a breeding population of Mexican desert bighorn sheep and serves as a source population for reintroduction into free-ranging populations across the state. This program has been tremendously successful and was critical to achieving the restoration of free-ranging desert bighorn populations to the point of de-listing in 2011 and the initiation of annual desert bighorn hunts that continue today.

Substantial suitable vacant habitat remains in New Mexico, and Red Rock continues to serve as our primary source herd for reintroducing new populations and increasing existing populations to bolster herd demographics and genetics.

The Department conducts an annual population survey of sheep in the Red Rock area, identifying, counting, and analyzing the presence, abundance, and condition of desert bighorn sheep. Can you elaborate on why these evaluations are critical for species management?

Katie Piecora: Each year, we survey the population to determine herd size and demographics. Depending on annual lamb production and overall survival from the previous year, we determine if there are sufficient numbers to support a translocation of bighorn into a free-ranging population and how many individuals of each sex and age class are eligible for translocation. On average, we have sufficient population growth to translocate around 30 bighorn every two years.

Close monitoring of the herd is imperative to understand herd health and productivity, so that we can anticipate and plan for reintroduction efforts. These translocation efforts also maintain the Red Rock herd’s abundance at an appropriate level that can be supported by the natural vegetation and water resources within the facility and avoid habitat degradation.

Can you talk about additional projects supporting sheep conservation? 

Katie Piecora: We’re in the developmental phase of a few new projects, but the one that we are currently embarking on is an evaluation of desert bighorn sheep diet and nutritional availability on the landscape. With ongoing drought in our desert ranges and the presence of invasive plant species, we can’t be sure that bighorn are getting the best bang for their buck when it comes to nutrition. We need to determine if nutrition/vegetation availability is a limiting factor on population growth. We plan to collect bighorn sheep fecal pellets to identify what plant species bighorn are consuming in specific ranges and compare that to the plant species that are available on the landscape. We’ll also determine the nutritional composition of those plants to see if bighorn are maximizing the nutrition available to them. We are initially focusing this study on the Peloncillos range, but are looking to expand it into other desert bighorn ranges in the future.

Jemez is another important area in New Mexico for bighorn sheep management. Can you discuss the important programs in place in the area?

 Tom Batter: We are working to get new GPS collars deployed on bighorn sheep in our Jemez Rocky Mountain bighorn sheep population (Game Management Units 6A and 6C).

Maintaining sufficient GPS collars within each population allows us to closely monitor long-term population abundance, as well as seasonal and annual space use and annual survival rates. Current GPS collar batteries last 2-4 years, depending on the model and how many data points they are programmed to collect; meaning that every few years, we need to be prepared to deploy new collars on newly captured bighorn or replace old collars on previously collared animals. Collar points are collected daily, transmitted via satellite, and stored in an online database. The collar data can be downloaded and used in various data models at any given time. The longer data is collected, the more certain we can be in monitoring and describing populations. The collars are also programmed to send an alert when they don’t detect movement for eight hours. This alert is also sent via satellite, and we are alerted via text and email, so we can have the most immediate knowledge of a potential mortality event. This expedites getting boots on the ground while there are sufficient remains left to determine the cause of mortality. Understanding and tracking trends in causes of mortality provides insight into the challenges bighorn are facing in a particular range, which can guide potential management actions to mitigate these factors. Factors can include predators, vehicle or train strikes, habitat fragmentation (i.e., fencing), and disease, among others. These limiting factors fluctuate over time and because of this, staying on top of the collaring effort allows us to maintain an up-to-date knowledge of what may be impacting bighorn population performance at an individual and herd level.

Can you discuss the introduction of sheep into the area following the Las Conchas fire? 

Tom Batter: The Jemez herd was reintroduced to Cochiti Canyon in 2014 following the Las Conchas fire, which subsequently thinned out vegetation. This fire essentially restored the area to prime bighorn habitat. It opened up the landscape, providing visibility for bighorn to better detect predators. New vegetation growth as a result of the fire provided highly nutritious vegetation to support the annual life cycle of bighorn, resulting in high lamb-ewe ratios and high recruitment, leading to remarkable population growth. The 2024-2025 hunting season marked the inaugural ram hunt in the Jemez. Two of the three harvested rams are now the first and second largest Rocky Mountain bighorn ever harvested in New Mexico. The larger of the two is now in the top three largest Rocky Mountain rams harvested in North America. The success of this herd is a testament to the conservation successes that can be achieved when state, federal, tribal, and other entities collaborate from a mutual appreciation of the intrinsic and ecological value of native wildlife. It also exemplifies how leveraging a natural wildfire event can benefit native species.

For a more comprehensive overview of bighorn sheep management in New Mexico, visit the following link: wildlife.dgf.nm.gov/download/new-mexico-bighorn-sheep-management/?wpdmdl=51880&refresh=685aeecbaff3d1750789835