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Greater Yellowstone Ecosystem Report

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Many ungulate populations have lost access to their traditional migration routes and seasonal ranges, resulting in rapid and severe population declines. Some ungulate populations have been able to adapt to living year-round on one seasonal range and persist despite loss of migration. However, our understanding of how ungulates adapt their habitat selection and foraging strategies in order to compensate for migration loss is poor. This study investigates how a formerly migratory, now sedentary and isolated, bighorn sheep (Ovis canadensis) population persists year-round on high-elevation summer range in the Teton Range in northwest Wyoming. We captured and GPS-collared 20 bighorn ewes throughout the Teton Range in February 2008 and an additional 8 ewes in March 2009. In 2008, ninety percent of captured ewes were pregnant, and 100% were pregnant in 2009. During summers 2008 and 2009, we located and observed GPS-collared ewes, determined lamb survival, collected fecal samples for diet composition analysis, conducted vegetation surveys, and observed time-budgets. We found that 50% of lambs survived until at least mid-summer in 2008 and 60% survived in 2009. We observed differences in movement patterns between GPS-collared ewes during the summer seasons, ranging from 5 km to a maximum of 15 km. At this time, eight GPS-collared ewes have died (4 in avalanches, 1 from predation, and 3 unknown). This study is ongoing and will be completed in 2011. Results will directly contribute to management of this non-migratory and isolated bighorn sheep population, and will shed light on how a formerly migratory ungulate population has been able to persist on high-elevation range year-round