Identifying Impediments to Wyoming Mule Deer Seasonal Movements and Long Distance Migration
Photo of mule deer moving across sagebrush landscape.

Migration corridors are key habitats for migratory mule deer. But land managers need to understand how migrating animals respond to habitat alterations and conservation measures in order to appropriately plan development and human activity.

Project Partners

Wyoming Game and Fish Department

Wyoming Cooperative Fish and Wildlife Research Unit

Wyoming Migration Initiative

University of Wyoming

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Contact Matt Kauffman

307-766-6404

Wyoming is home to some of the largest mule deer (Odocoileus hemionus) herds in North America. Migratory ungulates, such as mule deer, are susceptible to development along their migration corridors. Increasingly we are understanding that migration corridors are key habitats for migratory mule deer, where they spend time foraging to regain energy stores along the route. As migration routes become constrained by development and human disturbance, a common response is for migrating animals to increase rate of movement, reduce stopover use, and occasionally detour around established routes. Thus, alterations to the behavior of animals during migration has the potential to modify their ability to track changing plant green-up - and thus the pulse of high-quality forage -  across the landscape.

 

Key Findings

  • During their 3-week-long migrations between winter and summer ranges, mule deer were faithful to traditional migration routes. 
  • Mule deer used a series of feeding stopover sites along their migration routes. When selecting stopover sites, they shifted away from development.
  • Along undisturbed migration routes, mule deer spent 95% of their time feeding at stopover sites. When they encountered development, however, they moved faster and spent 35% less time at stopover sites. 
  • During spring migration, the timing of mule deer arrival at migration stopover sites was closely tied to the timing of plant green-up or flowering at those sites.

Study Objectives

  • Identify and map mule deer migration routes and stopover sites in southwestern Wyoming.
  • Conduct a long-term study of the Red Desert to Hoback mule deer migration.
  • Distinguish between low-use and high-use migration corridors to help land-use planners avoid development along high-use routes and prioritize them for protection.
  • Assess the rates at which mule deer migrate and how long they spend at stopover sites.
  • Evaluate the role of stopovers in providing prolonged access to high-quality forage and summer ranges.
  • Evaluate whether development reduces the typically high degree of mule deer faithfulness to their migration routes.
  • Identify the level of development or disturbance that causes mule deer to alter their migration patterns.
  • Evaluate the effect of drought on green-wave surfing.
  • Assess the effect of fencing and other barriers on mule deer movement and migrations.

As mule deer migrate from their low-elevation winter ranges to high-elevation summer ranges, they track the nutritious “green wave” of spring plant growth that steadily progresses upslope. (Left click to enlarge)

Spring green-up is when the nutritional value of mule deer food plants is highest. As they migrate from their low-elevation winter ranges to high-elevation summer ranges, they track the nutritious “green wave” of spring plant growth that steadily progresses upslope. By tracking the “green wave” from lower to higher elevations, mule deer prolong the period during which they can access the most nutritious foods of the year. They may spend days or even weeks at preferred stopover sites to feed before moving on. Protecting and ensuring access to these stopover sites allows mule deer to regain fat lost overwinter and delay their arrival to poor-quality winter ranges in late autumn. USGS biologists and students from the University of Wyoming are using data collected from mule deer radio-marked with global positioning system (GPS) collars to evaluate the influence of development on the migratory behavior of individual deer in western Wyoming. By fitting many mule deer with GPS units, researchers can track their movements to better understand their migration patterns and needs, including main routes traveled, speed of travel between stopover sites and around development, which stopover sites they prefer, and how long they remain at stopovers.

We fitted 107 adult female mule deer (including 52 long distance migrants) with GPS radiocollars and we deployed trail cameras along the migration corridor, including areas where migration routes cross fences and highways. We now have more than 4 years of capture and migration data, and we have begun to evaluate the fitness benefits of migration (fat dynamics, fawn survival, forage availability), fidelity to migration routes and summer range, and timing of spring and fall migration.We found that mule deer surf spring green-up closely and that alterations to green-up patterns strongly influenced surfing. Ongoing analyses indicate that drought makes it more difficult for mule deer to surf during spring movement patterns.

Photo of radiocollared mule deer.
Graphic showing how deer movements hypothetically track peak forage production when deer surf the green wave.
Two photos of mule deer captured on trail cameras crossing over and under a barbed wire fence.

Mule deer were fitted with GPS radiocollars to track their movements and time spent in stopover sites during migration.

Hypothetical illustration of annual change in forage biomass (dashed line) and forage quality (solid line). Deer surf the green wave when they synchronize their movements with the timing of peak biomass across the landscape. Click to enlarge.

Photographs of mule deer crossing fences will help us determine behavioral responses associated with encountering different types of migration barriers.