Migration Routes of Pronghorn in Sublette Herd in Wyoming

Pronghorn (Antilocapra americana) within the Sublette herd comprise one of the largest pronghorn populations in North America. Sublette pronghorn winter in the more southern areas of the upper Green River Basin. Depending upon winter severity, individual pronghorn winter between Pinedale in the north to Rock Springs in the south, and in the western portions of the Red Desert. Winter ranges include a mix of grassland and sagebrush dominated mesas and rolling hills. During migration, animals that have been tracked with GPS collars (n = 362 females) travel an average one-way distance of nearly 60 miles (96 km), with some animals migrating over 200 miles (320 km). This herd is home to the longest distance migrating pronghorn and the ‘Path of the Pronghorn’, the first federally-designated migration corridor. The herd, which currently numbers around 35,000 individuals, has a variety of summer range destinations. Some individuals migrate north to Grand Teton National Park following the ‘Path of the Pronghorn’. Others migrate to summer ranges in the Bondurant Valley, the Gros Ventre Mountains, and along the base of the Wyoming Range. Animals in the southeastern portion of the herd migrate in a more convoluted manner, crisscrossing the Red Desert with their migration routes. Summer ranges generally consist of higher elevation grasslands and open sagebrush habitats inter-mixed with mesic meadows. Sublette pronghorn have a mix of movement strategies, with 55% of individuals displaying migratory behavior with distinct summer and winter ranges, 32% are nomadic with no distinct patterns between seasonal ranges, and 12% are resident residing all year in more local areas. This herd’s population objective is 48,000 individuals, and over the last 15 years modeled population size has oscillated between 31,000 and 62,000. Many individuals within this herd migrate or winter near energy development, mainly oil and gas developments in the Pinedale Anticline, Jonah, and Calpet fields. Previous research has shown that pronghorn spend less time in areas after they have been developed, and in some cases, pronghorn abandon traditional winter ranges altogether. Additional gas wells are permitted in the Normally Pressurized Lance field in the center of the Sublette herd, and pressures are increasing from renewable energy sources such as wind and solar developments along the I-80 corridor in the southern reaches of the herd. However, migrations of Sublette pronghorn have benefitted from wildlife overpasses recently built over HW 191 at Trapper’s Point and Boroff Hill in high-use portions of the migration corridor, and new crossing structures are planned to be built along highway 189 south of Big Piney. These data provide the location of migration routes for pronghorn (Antilocapra americana) in the Sublette population in Wyoming. They were developed from 688 migration sequences collected from a sample size of 362 animals comprising GPS locations collected every 2-5 hours.

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