Wolf density aids pronghorn fawn survival

Wednesday, January 24, 2007

By Melanie Stein

Pronghorn survival may be closely related to wolf population density, according to Wildlife Conservation Society Research Ecologist Kim Murray Berger, but not in the way you might think.

Last week, Berger presented results from a critical study, “Conservation Implications of Food Webs Involving Wolves, Coyotes and Pronghorn,” part of her Ph.D. research at Utah State University, at the Jackson Hole Conservation Alliance’s Info Lunch series.
Carnivore reintroduction is controversial because of the possible effects carnivores can have on human, pet and livestock safety. But Berger was more interested in looking at the effects carnivores have on other carnivores and the impact this may have on the larger food web.

“The idea that restoring top predators can influence species at lower trophic levels [i.e., positions on the food chain] is called ‘trophic cascades’ and it’s an active area of research,” Berger explained.

Her study shows why: Overall pronghorn populations in Grand Teton National Park have dropped by about 50 percent since the early ’90s, while coyote populations – the chief predators of pronghorn fawns in this region – have been on the rise over the past 200 years.

“Coyotes used to be concentrated in the midwestern and western regions of the United States,” she said. “Now we pretty much see them from Maine to Florida, Alaska to Canada, and down into Mexico.”  This population boom and diaspora can largely be attributed to the elimination of wolves from most of the continent and adaptation to new habitats, she said.

Since the reintroduction of wolves to Wyoming in the mid ’90s, coyotes are more likely to be killed (but not eaten) by wolves because wolves see coyotes as potential competitors for food.

Berger selected three areas in northwestern Wyoming to study, two of which were inside Grand Teton National Park. One area had a high wolf density, one had a low wolf density, and one did not have a wolf population. Using radio collaring and ground and aerial telemetry, Berger observed coyote mortality in these areas and determined that 83 percent of coyote mortality was due to wolf depredation.

Berger found that wolves were largely responsible for transient coyote mortality (i.e. coyotes that roam between territories), and that coyote density was 30 percent lower in areas used by wolves. Berger then began to examine pronghorn fawn survival rates in those same areas and discovered  that the pronghorn fawn survival rate is five times higher in areas used by wolves.

Berger will be submitting her findings to journals in the coming weeks, which will summarize “how wolves are impacting coyotes, how interactions among wolves, coyotes and pronghorn are impacting pronghorn survival, and how changes in fawn survival rates will likely impact the overall pronghorn population in Grand Teton National Park,” she states.
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Wolf density aids pronghorn fawn survival | Planet JH News Article: General Environment

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