Image Image Image Image Image

Bighorn Sheep Project Raffle

Support a great cause and be entered in for a chance to win a 2019 Wyoming Commissioner’s License. * See below for project details.

Click here to purchase

Overview of Dr. Monteith’s Study:

Summer nutrition, disease, or predation? Quantifying causes of poor lamb survival in northwest Wyoming

Kevin L Monteith & Doug McWhirter, along with multiple other collaborators (University of Wyoming and Wyoming Game and Fish Department)

Our aim is to take a multi-pronged approach to address multiple causal factors contributing to population dynamics of bighorn sheep in northwest Wyoming, and how that broadly will aid in future management of chronically infected sheep herds. Specifically, we will quantify the relative contributions of nutrition, disease, and predation on population performance, and assess the current state of forage on summer ranges. Our approach is to continue our longitudinal monitoring of adult females from each of the three herds, which will yield valuable information on nutritional status and reproduction as females transition from one season to the next. We will link data on nutrition and reproduction to patterns of pathogen presence over time. With this next phase of the work however, we apply increased efforts to understand contributions of summer nutrition and disease to lamb survival by monitoring summer diet, forage quality, and survival, and cause-specific mortality of lambs in the Dubois and Jackson herds.

Given current observations, our aim is to continue to unravel the processes underpinning the dynamics of the Cody, Jackson, and Dubois herds by maintaining our longitudinal study design and increasing our efforts to understand contributions of summer ranges, and role of pathogens and predation especially in Dubois and Jackson. Importantly, our current objectives are completely driven and informed by what we have learned in the past three years of research, and are explicitly aimed at better understanding the contributions of summer nutrition, predation, and disease on survival of young sheep.

Project objectives include:

1) Estimate nutritional carrying capacity (NCC) of bighorn sheep populations in Wyoming to assess the capacity of habitats to support sheep.

  1. Over the long term, a key goal of this effort is to calibrate nutritional models for bighorn sheep, by coupling data on nutritional condition, pregnancy, recruitment, adult survival, and ultimately, population growth to develop models of animal-indicated NCC for Wyoming sheep. This will provide managers with tools to assess the proximity of populations to NCC.

2) Assess survival and cause-specific mortality of adult female sheep in Jackson, Dubois, and Cody herds.

  1. We will assess factors that contribute to probability of survival (e.g., nutritional condition, body mass, age, reproductive status), and causes of mortality when it occurs (e.g., disease, predation, accident). To date, leading cause of mortality for adult females has been predation by mountain lions.

3) Assess survival and cause-specific mortality of newborn sheep in Whiskey and Jackson herds to provide a comparison of the relative roles of nutrition, habitat, predation, and disease on recruitment of young.

  1. We will determine survival and cause-specific mortality of neonatal sheep.
  2. We will assess factors that contribute to probability of survival of neonatal sheep, including but not limited to: birth mass, sex, birth date, litter size, habitat conditions, maternal nutritional condition, presence of respiratory pathogens, and maternal age.
  3. We will evaluate factors that contribute to the cause of mortality (e.g., disease, predators, malnutrition, accident), including but not limited to: birth mass, sex, birth date, litter size, habitat conditions, maternal nutritional condition, presence of respiratory pathogens, and maternal age.

Respiratory disease has afflicted populations of bighorn sheep for the past century and, despite substantial research on the topic, pneumonia continues to be one of the most poorly understood diseases that afflict wildlife in North America. Although we have learned much in recent years, most research has been myopically focused on identifying the primary infectious agent associated with pneumonia. Nevertheless, evidence continues to support multiple primary and perhaps secondary infectious agents, and in most instances, we now manage herds that are chronically infected as opposed to those subject to new exposure. Moreover, fundamental components underlying any large ungulate population including, habitat quality and quantity, and predation remain operational and yet, are often neglected when considering disease dynamics. Indeed, performance of bighorn sheep in northwest WY is mostly asynchronous, despite three herds possessing a similar suite of pathogens. Of great concern in particular, is the abysmal lamb recruitment in what historically was one of the largest and most robust population of bighorn sheep in the West: the Whiskey Mountain bighorn sheep herd. Following an all-age pneumonia die off in 1991, the herd has exhibited consistently low lamb recruitment, and more recently in the past 3 years has been near or below 10 lambs per 100 ewes. Finally, in the past year the presence of wolves on their winter range and the apparent redistribution of some animals has highlighted the question associated with the potential interactive role of predation on this highly cherished bighorn sheep herd.


For a link to the full lamb mortality study proposal, visit:


Raffle partnered with:

Thank you Wyoming Game Commissioner Patrick Crank.

mule deer mule deer conservation muley fanatic