Expert points finger at wolves for declining moose numbers, not climate change

• Article by: DENNIS ANDERSON , Star Tribune
• Updated: November 15, 2014

A wolf expert discussed why he thinks wolves are partly responsible for declining moose numbers in northeast Minnesota. Dave Mech is a senior research scientist with the U.S. Geological Survey and a University of Minnesota adjunct professor. He’s widely recognized as one of the world’s pre-eminent wolf experts. 

Early in his career, Mech researched wolves on Isle Royale, initiating what has become a 60-year study of wolves and moose on the Lake Superior island. In 1968, he began studying wolves in an area northeast of Ely. That study continues. Mech holds a bachelor’s degree from Cornell and a doctorate from Purdue. 

In the interview below, Mech expands on a recent study he co-published with John Fieberg of the University of Minnesota that challenges an earlier DNR study that said climate change is contributing to the decline of northeast Minnesota moose.

Mech and Fieberg instead believe wolves were a contributor to the decline.

Q Describe findings of the study you and professor Fieberg published recently in the Journal of Wildlife Management.

A Two major findings. The first is that studies by the Minnesota DNR in 2009-2010 suggesting that the decline of northeast Minnesota moose was related to some kind of climate change minimized indications that wolves were involved.

The study said wolves likely were not involved in the moose decline to a significant degree, because statewide surveys of wolves seemed to indicate a stable population. 

But our studies of wolves for more than 40 years differ from the state’s five-year statewide population estimate, because ours have been done annually in a single area, which overlaps in part the DNR’s moose study area.

Our data indicate that the wolf population in and near the moose study area had grown significantly. I also suspected that statistics from the DNR study were flawed, regarding the effect of climate change on wolves.

I’m not a statistician. So I teamed up with University of Minnesota statistician John Fieberg, and he demonstrated that statistics in the original DNR study did not support a climate effect.

There’s simply no evidence that climate change has contributed to the moose decline in the northeast. Instead, wolves likely were involved in some way.

Q Can your findings be extrapolated to other areas of the Minnesota wolf or moose ranges?

A They wouldn’t necessarily apply to the decline of moose in northwest Minnesota, which took place earlier. These systems are quite individual, with two separate moose populations, one in the northeast, one in the northwest, and the habitat in each being unique, as are the complement of predators, including bears and wolves.

Q Would the effect of wolves in your study area perhaps be more of an accelerant to the moose decline there, than the sole reason for it?

A Perhaps. And to the degree that wolves contributed to the moose decline in our study area, it probably relates more to the predation of moose calves, rather than adults, though they take both.

A stable moose population requires the survival of adults, as well as the recruitment of calves. So a moose decline could be the result of an accelerated decline of adults, an accelerated decline of calves or both.

What I think might be going on is this: As wolves increased, they took a higher percentage of the population of calves, which are a primary prey for them in summer, along with beavers.

Q Does climate change have any effect on the moose decline in Minnesota?

A Our study didn’t say anything about that. Only that the supposed effect of climate change on moose in the northeast is invalid. It doesn’t mean it’s not true. Just that there is no evidence of it.

Q Is it possible that various subtle effects of climate change, such as an increase in the number of ticks that attach themselves to moose, and perhaps weaken them, could contribute to their population falloff?

A It’s possible. But we don’t have evidence of it. I will say that four or five years ago, Isle Royale scientists were implicating climate change in the moose decline there. Now they’re not. Now they’re saying that because wolves have subsequently declined there, the moose population is in fact increasing.

Q Is there research confirming, or indicating, what might have happened to moose in the northwest?

A The data seem to indicate that most of what was going on there was parasites and disease.

Q Wolves have had documented detrimental effects on Yellowstone area elk and moose, and on Alaska moose, isn’t that correct?

A It is possible for wolves to have a strong effect on their prey, depending on circumstances. But remember: All of these ungulates (moose, elk, deer) are affected by things other than wolves, primarily winter weather, although out West it might also be drought. So you can have interplay between wolves and other conditions.

Deer in parts of the BWCA provide an example. In our study area in the late ’60s, there were deer all over those lakes in winter. Then we had a series of severe winters, and now, due to the combination of those winters and wolves in the area, you just don’t find any deer. They’re gone.

Q Could a similar situation occur across a broader area of northern Minnesota?

A It could.

Q In that situation, if a series of tough winters significantly depressed the deer population, would wolves also decline, as might be expected? Or would wolves simply expand their range, switch prey species or otherwise adapt?

A Typically, they decline. And as they do, deer come back. But it’s also very much related to the total proportion of years in which winters are bad. If tough winters just alternated, one good, one bad, that’s one thing. Deer populations can handle that. But if you get a series of severe winters, it will knock them down hard and take them longer to recover.

Simultaneously, of course, habitat is changing, and this also has an effect on the various species. Many factors constantly interact. It’s hard to predict outcomes. But for wolves, if the net food supply is reduced, whether it’s moose calves or deer, unless there is a significant supply of substitute prey, wolves likely will decline as well.

Q Given the mix of factors, including wolves, affecting northeast Minnesota moose, do these animals have a chance to sustain themselves in relatively constant numbers? Or are they doomed to disappear, as in the northwest?

A My guess — and it’s always hazardous to predict — is that the northeastern Minnesota moose will persist, although generally at a lower density than before the wolves increased. Already there is evidence that northeast wolves are starting to decrease, probably because of the moose decline.

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