Wyoming is home to some of the largest mule deer (Odocoileus hemionus) herds in North America. These animals play a crucial role in Wyoming’s biodiversity and the State’s hunting and tourism economies. Since the 1990s, however, mule deer populations have been declining. The Wyoming Range herd is of particular concern because its numbers continue to decline despite actions to stabilize the population. Migratory ungulates are susceptible to development along their migration corridors. It has been proposed that impermeable barriers (like tall fences) have apparent and detrimental effects to migratory ungulates; however, the effect of semipermeable barriers (like an energy field)—where connectivity is maintained but the benefits of migration routes are compromised—remains unclear. 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. Understanding the influence of current development on migratory routes, including stopover sites used for foraging, can provide insights on the effects of future landscape changes.
Identifying Threshold Levels of Energy Development that Impede Wyoming Mule Deer Migrations
Wyoming Game and Fish Department
Wyoming Cooperative Fish and Wildlife Research Unit
Wyoming Migration Initiative
University of Wyoming
- During their 3-week-long migrations between winter and summer ranges, mule deer were faithful to traditional migration routes. Except where development was rapid, deer did not alter their migration routes in response to development.
- Mule deer used a series of feeding stopover sites along their migration routes. When selecting stopover sites, they shifted away from development.
- Deer increased their rate of movement, reduced time at stopover sites, and shifted stopovers in areas of intense 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% time at stopover sites. This indicates that high levels of development can reduce the crucial benefits of migration.
- In the rapidly developing Atlantic Rim project area, we observed the most dramatic alterations to deer migratory behavior.
- Identify and map mule deer migration routes and stopover sites in southwestern Wyoming, including those within oil and gas fields.
- 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 whether rapid energy development alters the ability of mule deer to track spring green-up of plants during their spring migrations.