Cooperative Fish and Wildlife Research Units Program: Wyoming
Education, Research and Technical Assistance for Managing Our Natural Resources

We are working to understand the changing demography and distribution of the Clarks Fork elk herd, which ranges widely in the Absaroka Mountains between Cody, WY and the headwaters of the Lamar River inside Yellowstone National Park (YNP). Each summer, while resident Clarks Fork elk remain in the foothills of the Absaroka Front, their migratory counterparts travel 40-60 kilometers across the Absaroka Divide to summer in high-elevation alpine and subalpine habitats of YNP. There, the migratory elk bear and nurse their calves, breed, and forage until the first substantial snows of winter, when they return to winter ranges neighboring and overlapping with those of resident elk. These two distinct strategies expose migrant and resident Clarks Fork elk to different densities of grizzly bears and wolves and different patterns of summer climate and plant growth – including access to irrigated fields for the resident elk. Long-term monitoring by the Wyoming Game and Fish Department (WGFD) and emerging results from our research suggest that these large-scale environmental differences are causing dramatic changes in the demography, movements, and distribution of the Clarks Fork herd. Over the past decade, WGFD has documented declining calf recruitment among migratory elk versus stable or increasing recruitment among resident elk. Concurrently, the overall distribution of the herd has shifted about 20 kilometers eastward into the Absaroka foothills, favoring the resident subpopulation. These trends have generated local attention and regional management concern because growing numbers of resident elk cause damage to agricultural crops, compete with domestic livestock for native grasses, and may threaten cattle with brucellosis. Meanwhile, shifting patterns of elk productivity have brought changes to hunter opportunity, including curtailed hunting of migratory elk and limited hunter access to large numbers of resident elk that frequent private land refuges.