Elk Bugles

An elk bugles outside of the town of Gardiner, Mont., near Yellowstone National Park, Wednesday Feb. 2, 2011.

Wolves reduce elk numbers by killing them, but it’s likely that they also decrease elk reproduction, according to a Montana State University study.

In a seminar at MSU on Thursday, ecology professor Scott Creel presented more evidence indicating that reintroducing wolves into the ecosystem has affected elk populations in some unforeseen ways. Creel and co-author David Christianson also presented the study to the Society of Conservation Biology last week.

“If we’re really going to have science-based management, we have to understand the causes of the changes we see,” Creel said. “Science has to get out in the lead.”

Creel’s research was based upon 12 elk management units in Montana, Wyoming and Yellowstone National Park that all had 30 years of data on elk populations, predators and climate characteristics.

Several factors act together to affect elk population swings, including the severity of the winter, elk population density, human hunters and animal predators — including wolves, lions and grizzly bears.

Six of the management units — those in or near the park — contained established wolf packs; the other six didn’t. Not surprisingly, data from the elk management units show that wolves can reduce elk numbers; but Creel saw some other trends.

For areas without wolves, scientists can predict what elk populations will do if there is a severe winter or if the herd density gets too high. In both cases, populations will drop because fewer calves are born or survive.

But for areas with wolves, winter severity and elk density no longer produce the same population responses. Calf survival still declines in a bad winter, but it doesn’t increase as much again in a mild winter.

“Due to climate change, winters are getting milder, which should improve calf recruitment, but calf recruitment is getting worse,” Creel said.

To explain why fewer calves are surviving even mild winters, Creel came up with a method that uses known yearly conditions to calculate the number of calves that should have been born in a certain area.

Creel then subtracted the number of calves that he calculated would have been eaten by predators. The result was a prediction of the number of calves that would have survived if predation was the only factor.

When Creel compared his predictions to the actual calf counts in management units with wolves, he found there were significantly fewer calves than predicted. So calf numbers weren’t low just because they were being eaten or killed by cold.

Creel said predation by grizzly bears could explain some of the difference but not much.

The likely explanation, he said, is that elk are more vigilant and feed less around predators. Diet and activity changes can cause females to have less energy to produce calves, a response that has been shown to occur in several animal species.

“I think the cost of anti-predator behavior explains a significant proportion of those missing calves,” Creel said. “When we did the EIS, we didn’t deal with the possibility that elk will start doing things differently to avoid predation, but those things that they do may carry physiological consequences.”

Creel supports the restoration of wolves to the Northern Rockies because some of the ways they have changed elk behavior are good. But he said it’s not up to him how wildlife managers use this information.

“If we can refine our ability to predict the outcome of things like this, that makes the contribution of science more valuable to management,” Creel said.

Laura Lundquist can be reached at 582-2638 or llundquist@dailychronicle.com.

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