Increased predator numbers in Yellowstone changing elk migration patterns

Migration no longer best strategy for Yellowstone elk herd

June 2013. Migratory elk are returning from Yellowstone National Park with fewer calves due to drought and increased numbers of big predators - two landscape-level changes that are reducing the benefits of migration with broader implications for conservation of migratory animals, according to a new study published in the journal Ecology.

Long-term decline in the number of calves in migratory elk

The new study by the Wyoming Cooperative Fish and Wildlife Research Unit - a joint program involving U.S. Geological Survey, the University of Wyoming, and the Wyoming Game and Fish Department, describes a long-term decline in the number of calves produced annually by the Clarks Fork herd, a population of about 4000 elk whose migrants travel annually between winter ranges near Cody, Wyoming and summer ranges within Yellowstone National Park. Migratory elk experienced a 19 percent depression in rates of pregnancy over the four years of the study and a 70 percent decline in calf production over 21 years of monitoring by the WGFD, while the elk that did not migrate, known as resident elk, in the same herd experienced high pregnancy and calf production and are expanding their numbers and range into private lands outside of the park.

Ungulates still retain their long-distance seasonal migrations

"This is one of North America's wildest and best-protected landscapes, where elk and other ungulates still retain their long-distance seasonal migrations - and yet it is the migratory elk that are struggling while their resident counterparts thrive in the foothills," said Arthur Middleton, who led this work as a University of Wyoming doctoral student and is now a postdoctoral fellow at the Yale School of Forestry and Environmental Studies.

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