The Obama administration's proposal to bump the gray wolf off the federal endangered species list could lead to the endangerment of other species, according to researchers who warn that, if passed the way it is currently written, the rule would set a dangerous precedent. (Photo : Reuters)

The greater Yellowstone ecosystem is full of predators and prey, but a new study on the behavior of Yellowstone's elk shows that the presence of wolves in the ecosystem does not reduce the reproductive rates or body condition of female elk.

Prior research on the Yellowstone ecosystem offered no consensus on whether wolves reintroduced into the region would affect elk populations indirectly, such as by creating an environment of fear wherein the elk are less able to forage or reproduce.

"Elk respond to wolves, but less strongly and less frequently than we thought," Arthur Middleton, a researcher at University of Wyoming, said in a statement.

Middleton spent three years tracking an elk herd west of Cody, Wyo., and the wolf packs that prey on it.

"We found that wolves influence elk behavior, but the responses were subtle and -- over the course of winter -- did not reduce body fat or pregnancy. Our work indicates that the effect of wolves on elk populations is limited to direct predation and doesn't include so-called harassment, stress and fear," he said, adding that the find differs from some previous studies indicating wolves influence elk behavior strongly enough to contribute to regionwide declines in calf production.

When wolves approached within 1.6 miles, the elk became more active and vigilant. But such encounters only occurred an average of once every nine days, even in high-risk areas. The frequency of encounters and high risk of predation, the study concluded, was not associated with the nutrition elk were getting or the frequency of pregnancy in female elk.

Middleton said the study was unique because the research team tracked wolves while also monitoring the movements, foraging behavior, body fat and pregnancy of the elk they hunted.

"This approach, essentially connecting the dots from wolf movements all the way to elk behavior and nutrition, revealed that elk respond to wolves too weakly and too infrequently for those behaviors to carry nutritional costs."

Gray wolves, which roam throughout much of the American west, have made headlines recently because of a move to delist the animals as an endangered species, a protected status they have enjoyed for 40 years.

Middleton and his colleagues' study was published in the journal Ecology Letters.

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