Yellowstone elk study points to effects of a hotter, longer summer

March 09, 2011

A new article in the online publication New West focuses on the habitat component of Absaroka Elk Ecology Project’s findings. For more discussion of the role of calf predation by bears and wolves, you can visit the Absaroka Elk Ecology Project page on this site.

In this study, we have been comparing the performance of migratory elk that spend their summers at high elevations inside Yellowstone National Park, with resident elk that stay year-round in the Absaroka foothills near Cody. Migratory elk productivity has been very low for the past decade. This appears to be a result of two factors: low pregnancy, probably driven by a severe drought during part of the past decade (as discussed in detail in this article), as well as high levels of predation by bears and wolves on migratory elk calves. In Yellowstone, grizzly bears, black bears, and wolves – particularly grizzly bears – preferentially hunt elk calves in summer, when the calves are especially vulnerable in comparison with other prey animals. Bear and wolf numbers are 3-4 times higher on the summer range of migratory elk (inside the park), partly because these predators are managed and/or averse to human presence on the year-round range of the nonmigratory elk (outside the park). Over the past decade, these differences have led to large differences in the number of calves in the two subpopulations.

Click here to read the full New West article.

Though our results to date implicate summer drought in explaining lower pregnancy rates of migratory elk, ongoing study of the same elk (pending retrieval of a number of wolf GPS collars) will explore whether predator-induced nutritional stress may be influencing elk reproduction.