Research: Mule Deer

Wyoming Range Mule Deer Project

Wyoming Range Mule Deer Project


The Wyoming Range Mule Deer project is focused on understanding various aspects of mule deer ecology to inform on-the-ground management and policy regarding Wyoming Range mule deer, as well as answer foundational questions in wildlife ecology. Our work primarily centers on tracking mule deer throughout their lives, while assessing their nutritional condition, movement, habitat use, and survival, among other elements. Through these efforts, we are uncovering previously unknown aspects of mule deer behavior, life history, and population dynamics that have direct implications for the conservation of mule deer in the Wyoming Range and beyond.

Our hypothesis:

Everything matters in nutritional ecology...

WRMD_ConcFig

What's the issue?

Winters in the Wyoming Range can be extremely harsh, which can cause dramatic dips in over-winter survival. Climate change has resulted in increasingly variable weather around the world with extreme conditions occurring more frequently, and animals must find a way to survive that change. Understanding how animals respond to changing environments and how they cope with increasingly severe weather conditions has important implications for population persistence.

How're we tackling it?

Through long-term monitoring of individual mule deer in the Wyoming Range since 2013, we are assessing what factors influence survival of GPS-collared mule deer in harsh conditions, how fat levels during different seasons affect survival and reproduction, and the long-term effects of winter on animals. To get these data, we recapture the same GPS-collared individuals every autumn and spring and use ultrasonography to monitor changes in fat levels and pregnancy rates relative to habitat conditions. Evert animal that dies in the winter is retrieved and necropsied (i.e., biopsied) to determine the cause of death.

What are our findings?

From 2013 to 2019, the Wyoming Range mule deer herd experienced two incredibly severe winters, with adult survival dropping to around 65%. Our ongoing research is working to better identify how animals survive harsh conditions, and identify the potential long-term consequences that harsh winters might have for both individuals and populations.

What's the issue?

Energy development has increased in Wyoming over the last two decades, and much of this development has occurred on winter ranges for migratory mule deer. Although population declines often follow development of winter ranges, the pathways by which human disturbance prompts population declines is rarely revealed. Quantifying the losses in habitat and food associated with energy development can give managers and planners a better understanding of what can be expected for mule deer populations where future development is being proposed.

How're we tackling it?

We connected animal behavior with use of available food relative to it’s proximity to energy development by:

  1. Using GPS-collar data from mule deer to evaluate avoidance of energy development.
  2. Collecting on-the-ground data on how much of available food (i.e., sagebrush) deer were eating near and away from energy development.

What are our findings?

We found that deer avoided energy development at multiple scales and this left untapped food near development. This avoidance resulted in an additional loss of viable habitat that was 4.6 times greater then habitat lost directly to development.

What's the issue?

Successfully recruiting young animals into the population is needed to grow populations, but young animals are the most sensitive component of a population. Mule deer fawns that are still growing and learning can be more vulnerable to predation, disease, and malnutrition. Often, the factors that influence fawn survival can work interactively; thus identifying what is most important in promoting fawn survival is challenging but not impossible.

How're we tackling it?

To disentangle the factors that most influence fawn survival, we will pair information maternal condition, behavior, weather, and habitat conditions with fawn survival.

Cause-specific mortality of fawns: Each spring, we catch our adult female deer and ultrasound for pregnancy, each pregnant deer is fit with a Vaginal Implant Transmitter (VIT) that notifies us of a birth event, and each summer we locate and collar fawns belonging to our collared deer. We follow each of these animals throughout the summer to identify survival, and where necessary, identify cause of mortality (e.g., disease, predation, malnutrition, etc.).

Maternal nutritional condition: We evaluate nutritional condition of pregnant deer using ultrasonography to measure fat before giving birth in spring.

Fall recruitment: We determine recruitment of fawns that survived until autumn, by relocating GPS-collared fawns and observing uncollared fawns.

Behavior: We evaluate behaviors of both mother and fawn(s) using GPS locations collected from their collars.

What are our findings?

Cause-specific mortality of fawns:

Across the years, the leading causes of mortality from fawns has changed, in 2015 disease was the leading cause of death for fawns in the Wyoming Range. Stillbirths were the leading cause in 2017 (following a particularly harsh winter), and predation in other years.

What's the issue?

Summer is supposed to be a time of plenty for migratory mule deer because they can access higher-quality forage at their higher-elevation summer ranges. Yet, not all summer ranges are created equal and some deer may have access to better food opportunities than other; thus, gaining more fat that they can use towards financing reproduction (i.e., raising fawns). Although this all seems somewhat obvious, knowing the food and habitat conditions that are most conducive for raising young is still widely unknown. Identifying the foods that are most nutritious for mule deer can help guide wildlife and land managers in efforts to conserve or bolster plant communities that are beneficial to mule deer.

How're we tackling it?

Mule deer diet quality: During summers of 2013 and 2014, we collected and analyzed fecal samples from areas used by GPS-collared mule deer to determine diet composition. With this information, we then revisited those areas to collect and analyze the quality of the top plants in mule deer diets.

Summer food and habitat conditions: Throughout the summer, we visit sites used by GPS-collared does and measure the vegetation and food available to her at those locations.

Nutritional condition: We use ultrasonography to measure fat each spring and autumn to track how much fat is gained or lost over the summer.

Reproduction: Each spring we measure pregnancy rates using ultrasonography and each autumn we determine recruitment of young back to their winter ranges.

What are our findings?

Mule deer diet quality:

Mule deer diets varied widely across individuals, but the most common species included geranium, lupine, and sagebrush. Quality also varied, with lupine (Lupinus), milkvetch (Astragalus), and dandelions (Taraxacum) being some of the most nutritious food available to mule deer.

What's the issue?

When migrating in the spring, ungulates can encounter vegetation that is fresh, nutritious, and abundant—if they time their migration right. Called “surfing the green wave,” ungulates can prolong access to high-quality forage if they time their migratory movements such that they move with the growth of fresh, nutritious vegetation. Knowing the ways animals depend on vegetation during migration highlights the importance of maintaining intact migration corridors.

How're we tackling it?

To understand whether ungulates match their migration with the growth of spring vegetation, we compared the movements of mule deer with the emergence of vegetation. We used locations of deer from GPS collars and characterized patterns of vegetation using data that were remotely sensed from satellites.

What are our findings?

We found that animals matched their movements closely with fresh, nutritious vegetation while migrating, which may allow them to gain the most energy on their way to summer range.

What's the issue?

Each year, millions of ungulates migrate across seasonally changing landscapes to access food that is only available during certain times of the year, to reduce risk of predation and disease, or to escape harsh climactic conditions. Some ungulates, such as mule deer, tend to be incredibly faithful to their migratory patterns and behaviors. Scientists do not yet understand how these patterns and behaviors are established in the first place, though many assume that offspring learn from their mothers.

How're we tackling it?

To understand whether ungulate migration is learned from an animal’s mother, we are tracking GPS-collared mule deer fawns from the day they are born for the remainder of their life and comparing their movements with those of their mother.

What are our findings?

After years of tracking adult females and their offspring, the offspring have just now reached adulthood, and some are having offspring of their own. In general, offspring are mostly following the migration path of their mother, but there is much more deviation from mom’s  path than expected.

This research is ongoing, with preliminary results expected in winter 2020.

What's the issue?

The production of high-quality males is often a primary goal of management agencies, and is valued among hunters and the public. Surprisingly, we know relatively little about the ecology of males, including their migratory behaviors, dispersal, and vulnerability to harvest.

We aim to address questions related to migration, habitat selection, and harvest. Males and females differ dramatically in the stressors they face: females expend the most energy in rearing offspring, whereas males focus on obtaining mating opportunities. To date, however, most research concerning the management of mule deer has focused primarily on females because of their role in driving population dynamics; yet, this singular focus renders a weaker understanding of the ecology of the male segment of our deer populations.

How're we tackling it?

By GPS-collaring male mule deer…duh!

What are our findings?

We are still in the preliminary stages of this project and are excited to uncover answers to many of these questions over the next few years.

What's the issue?

Effective wildlife management hinges on decisions grounded in science, as well as public support of issues related to wildlife. In an effort to increase public support, many wildlife scientists have increasingly shared their findings and the importance of their work with members of the public. Scientists have little information, however, about the people they are communicating with, which could hinder their ability to effectively communicate.

How're we tackling it?

To improve communication with members of the public, we are examining how multiple stakeholder groups think about the issues affecting mule deer populations in Wyoming. Using a social science approach, we are interviewing individuals from multiple stakeholder groups across the state.

What are our findings?

We are still working through these data, but currently, there appear to be three big themes that emerged from the interviews:

  1. habitat (e.g., habitat fragmentation, winter ranges, and migratory corridors)
  2. humans (hunting pressures, shed hunting, and public and political interests)
  3. interactions (predators, elk, forest management).

People working on the project:

Tayler LaSharr, Rhiannon Jakopak, Ellen Aikens, Samantha Dwinnell, Gary Fralick, Jill Randall, Rusty Kaiser, Mark Thonhoff, Jeff Short, and Kevin Monteith

Funders

Muley Fanatic Foundation, Wyoming Wildlife and Natural Resource Trust, Knobloch Family Foundation, Bureau of Land Management, Wyoming Animal Damage Management Board, Wyoming State Veterinary Laboratory, US Geological Survey, National Science Foundation, Wyoming Governor’s Big Game License Coalition, University of Wyoming Biodiversity Institute, Wyoming Outfitters and Guides Association, Bowhunters of Wyoming, Inc., Pope & Young

Publications

Jakopak, R. P., T. N. LaSharr, S. P. H. Dwinnell, G. L. Fralick, and K. L. Monteith 2019. Rapid acquisition of memory in a complex landscape by a mule deerEcology.

Dwinnell, S. P. H., H. Sawyer, J. E. Randall, J. L. Beck, J. S. Forbey, G. L. Fralick, and K. L. Monteith. 2019. Where to forage when afraid: Does perceived risk impair use of the foodscape? Ecological Applications.

Merkle, J. A., H. Sawyer, K. L. Monteith, S. P. H. Dwinnell, G. L. Fralick, and M. J. Kauffman. 2019. Spatial memory shapes migration and its benefits: Evidence from a large herbivoreEcology Letters.

Sawyer, H. J. A. Merkle, A. D. Middleton, S. P. H. Dwinnell, and K. L. Monteith. 2018. Migratory plasticity is not ubiquitous among large herbivoresJournal of Animal Ecology.

Aikens, E. O., M. J. Kauffman, J. A. Merkle, S. P. H. Dwinnell, G. L. Fralick, and K. M. Monteith. 2017. The greenscape shapes surfing of resource waves in a large migratory herbivoreEcology Letters.

Find our other publications on mule deer Mule Deer

Project updates

  • Project PDF download here