Chapter 3: Ungulate Migration

Two of the longest land migrations in the world start in the Jackson Hole area: the Path of the Pronghorn from Grand Teton National Park to the Green River Basin (up to 160 mi) and the Hoback mule deer migration from south Teton County to the Red Desert near Rock Springs (150 mi). Two new migration theories are currently being studied by ungulate researchers: green-wave surfing and stopover ecology. Green-wave surfing in the movement of ungulates from lower elevation winter habitat to higher elevation summer habitat in pace with the timing of spring greenup, allowing migrating ungulates to feed on the most nutritious, fresh plants available as they move. This helps ungulates regain body fat after winter and enables females to feed their young once born. The second concept, stopover ecology, occurs when ungulates stop at key forage locations for days or weeks. These stopovers are important habitat patches used only migration; deer spend approximately 95% of their migration at these locations.

Mule deer and elk face a dire threat from chronic wasting disease. Although it has not been detected in the Jackson Hole area yet, it is expected to impact these animals in the near future. Conserving migration routes and habitat connectivity can buffer these populations from the worst impacts of the disease by increasing the exchange of genes that may confer disease resistance.

Bighorn Sheep © iStockphoto

Anthropogenic changes to the landscape represent potential disruptors to migration corridors; as the levels of residential or commercial development increase, the risks to ungulates increase. Migrating ungulates either have to speed up their movement through developed areas or change their migration routes. Knowledge of migration routes are passed from mother to offspring and it is unclear if or when ungulates would rediscover their historical migration routes if routes are disrupted and then made available again.

Due to human settlement and agricultural development, bighorn sheep in the Tetons have become non-migratory, even though they migrated as recently as 70 years ago. Sheep are additionally impacted by humans through recreation, reducing their habitat by 30% as they avoid areas used by winter backcountry recreationalists.

Energy development in their winter range in the Pinedale Anticline region has substantially reduced the habitat available to pronghorn. Between 2005 and 2009, high-use pronghorn habitat in the Jonah and Pinedale Anticline Project Area gas fields south of Pinedale declined by 82%. Future energy development in this area could further threaten the Path of the Pronghorn migration.