Research shows wolf population changes follow trends in deer, not the other way around

HOST: Firearm season for deer hunters has pretty much wrapped up in Minnesota. And data from the DNR shows hunters were more successful than they had been for the past few years. The number of harvests has climbed back from a low point in 2023. In low years, some hunters point to wolves as the cause.

A recent survey from far Northern Minnesota tells a different story. The Voyageurs Wolf Project studies wolves in Voyageurs National Park and the surrounding area, and biologist Tom Gable leads the project and joins me now. Welcome.

TOM GABLE: Thank you very much for having me.

HOST: OK. So what have you observed about wolf and deer populations in the past few years in this area that you study?

TOM GABLE: Sure. Well, so we've had some really important events recently. Particularly, we had two really severe winters in 2021-'22, and then '22-'23. And that had a really substantial impact on deer populations. Per our estimates, the deer population in our area declined almost about 60% during that time.

And so that led to a really substantial reduction in the deer population. And obviously, wolves, which are largely reliant on deer populations, have now started to decrease as well. And so we've seen over the past couple of years, the wolf population essentially adjusting to these changes in deer abundance, and the wolf population now has declined about 31% over the past two years as they're just exhibiting natural fluctuations based on changes in their prey abundance.

HOST: OK. So how do you figure this out? I mean, how do you figure out that the deer population has declined by 60% and the wolf population, what, by 30, 31%? I mean, it's not like you can be out there with a checklist and saying, OK, there you go, Harry. There's Sue.

TOM GABLE: Yeah. Yeah. We just have the wolves check in, you know? Tell us what's going on. So for the wolf population, I'll start there. So the way we understand changing the wolf population as we fit wolves with GPS collars, and we generally have about 50% of the packs in our area have a wolf with GPS collar. And that tells us how big their territories are.

And then we have over 350 remote cameras deployed across our study area. So we have about 15 to 20 cameras in each pack territory. And that gives us a really good estimate on the number of wolves in each pack. Really what we're trying to do is get as many observations of all the wolves in each pack as many times as we can each winter.

And so we not only want to how many wolves are in that pack, but we actually want to which individuals are in that pack. What do they look like? How many pups are there? How many subadults there are? So we're trying to gain a lot of really fine scale information on the different wolf pack territories in our area.

And by having that combination of territory size from GPS collars and pack sizes from the GP or from the trail cameras, we can get a really good estimate of how many wolves are in the area, and then we can track that change through time.

So that's how we understand changes in the wolf population. And then in the deer population, we do what are called pellet counts, which is a very common way to understand changes in the abundance of hooved animals like deer and moose and things like that. So we do pellet count surveys every spring in our area, and we've been doing that for the past 11 years. And that is a really good way to measure changes in deer populations through time.

HOST: So why are harsh winters so hard on deers? I mean, I can make some assumptions, but what are the reasons behind that?

TOM GABLE: So the main reasons are basically how long deer have to persist during a time when they don't have a lot of food and where they're expending a lot of energy. So when deer go into winter, obviously, a lot of the high quality food that they rely on in the summer is gone. There's not leafy vegetation. All they have are really woody browse. They can nibble on shrubs and things like that.

And so as deer get into the winter, they're also, they have reduced amount of food. And then they're also having to expend a lot of energy when they're moving through deep snow. And that deep snow is anyone who's snowshoed around in 2/3 feet of snow can attest to, it's very taxing.

And so deer, the more they have to trudge through that stuff and the longer they have to do it, the more it zaps their energy and reduces their fat reserves, which makes them more susceptible to predation or things such as starvation.

And in particular, what's really critical is when we think about severe winters, and if you're a deer, it's not so much does it get super cold, though that can play a factor. It's how much snow is on the ground, and how long does that snow last? And so for these long winters that we had a couple of years ago, there was snow on the ground into mid to late April, early May, and that is really challenging for white tailed deer.

HOST: OK. So Your research is largely the Voyageurs National Park and the surrounding area. But these insights, are they applicable elsewhere?

TOM GABLE: It's really hard to say. We would suspect that probably, it may be applicable regionally. Our area isn't unique, so to speak, in Northern Minnesota. It's very similar to much of the other areas in terms of the habitat, and the weather, and things like that.

But we really would caution against people extrapolating on a state level or anything like that because Minnesota's obviously a diverse state. Wolves occupy a good portion of the state. And so there could be different patterns occurring in different areas. And so really, I know the Minnesota Department of Natural Resources usually releases their annual report on wolf population. I don't believe this year's is out yet, but that's really what people should be looking at when they're trying to understand state level changes. And if ours match up similarly with what they see on the state, then maybe there's a good indication that what we're seeing is representative of what's going on in the state.

HOST: So in recent years, this low deer population, I mean, that's led to calls for wolves to be delisted or removed from protections in the Endangered Species Act. And the state could authorize a wolf hunt as a check on that population. So with your research, what have you learned about whether wolf hunt would reduce wolf numbers, increase deer numbers? Talk a little bit about that relationship.

TOM GABLE: Sure. Well, I think the first thing that's important to note is that our research really has no bearing on whether or not we should or shouldn't hunt wolves. Really, whether or not we should or shouldn't hunt wolves depends on what society's values are and how society wants to manage wildlife populations.

So for instance, we could provide evidence that says wolves don't really have much of an impact, it seems, on changes in deer populations. But that doesn't mean we can't hunt wolves. You still could have a hunting season if the majority of the public wants that or if the DNR decides to do that.

So our research can pinpoint, is a hunting season on wolves going to really change much as it pertains to deer populations? And all of our evidence doesn't seem to suggest it's not going to do very much if there is one, but that doesn't preclude the fact that we could do it.

So we really think it's important to separate out what the science can tell us versus what are the values because wolf hunting is obviously a loaded topic that a lot of people feel very strongly about. And we think it's important to separate science and values there.

HOST: So I'm curious. Minnesota Star Tribune has reported that people in Ely, that they're having more regular encounters with wolves this year. Are there factors that are contributing to wolves having more interactions with humans?

TOM GABLE: It's hard to say, especially when you only have a handful of observations like this. I'm not familiar with all of the data. But often, what happens, and this is not an uncommon pattern where wolves do something that seems a bit abnormal for a wolf, even though they didn't hurt anybody or try to harm anybody. And it's often calls is there some problem and if we need to start killing some of them to prevent those problems from occurring.

Certainly, if Wolves are doing things that they shouldn't be doing and are posing threats to people, then we certainly think then they should probably be removed because it's not going to be beneficial for anyone. But there are times where wolves do curious things that are not threatening or really of concern, even though it might be abnormal to see them doing things like they're doing.

So we've not seen anything in our area. Our part of Minnesota, where we're at, has one of the densest wolf populations, not only in Minnesota but almost all of North America. So we have a lot of wolves where we're doing our work. And we don't see any substantial conflicts with people where wolves are coming into human communities and being a threat or a menace or things like that.

That doesn't mean that there's not challenges of living with wolves, where wolves go after livestock or sometimes go after a pet. But in terms of posing a threat for human safety, we've seen no evidence of that here.

HOST: Well, thank you very much for your time. I really appreciate it.

TOM GABLE: Absolutely. Thanks for having me.

HOST: Tom Gable leads the Voyageurs Wolf Project in Northern Minnesota.