Keeping Track of Wolf Deaths

Illegal killing seems to be rising, says wildlife ecology professor Tim Van Deelen

Tim Van Deelen, a CALS professor of wildlife ecology, specializes in the management of large mammals, including population estimation and dynamics, hunting, interaction of deer life history and chronic wasting disease—and, not least, the growth of Wisconsin’s wolf population and its effects on white-tailed deer.

As this year’s wolf hunt season opens in Wisconsin, we talked with him about a hidden and disturbing topic: illegal killing, which Van Deelen says may have increased in recent years. Much of the data on this subject, he says, comes from work by his former doctoral student Jennifer Stenglein MS’13 PhD’14, who is now a wildlife researcher with the Wisconsin Department of Natural Resources.

Can you give us an idea of how wolves die?
As we know from radio collaring data, wolves die for a variety of reasons. Wolves in Wisconsin have relatively high mortality rates, and that probably has to do with the fact that they’re living on a landscape that’s much more highly impacted by humans than, say, northern Canada or Alaska. We have higher levels of wolves getting hit by cars, especially as they begin encroaching parts of central and southern Wisconsin where we have higher road densities.

Wolves are also territorial, so on the margins of their pack territories or where there are territorial disputes between packs, wolves will kill each other.

Wolves die of disease. We’ve had deaths due to parvovirus and mange. Wolves sometimes starve to death if they can’t get enough prey or if they’re old or injured and otherwise inefficient as hunters.

There’s also a fair amount of unexplained mortalities that we have from radio tracking data.

Can you elaborate on that?
We have radio-collared wolves that outlive the radio collars—that is, they outlive the battery that powers the collar—so you have a record that starts when the animal is radio-collared and ends when you stop getting signals. Understanding mortality rates at the population level requires you to make some decisions about how you’re going to treat those animals once the record stops.

Research that my graduate student has been doing suggests that a fair number of those animals are dying.

Do you suspect illegal killing?
Well, the problem with illegal killing is you don’t observe it. You can’t point to something and say, “That wolf died from illegal killing,” but you need extra mortality in the system once you explain everything else in order to reconcile the mortality rates that we’re seeing with the reproductive rates that we get from the pup counts and the growth rate that we see from the annual population counts.

So there’s a missing gap in the data of why some animals disappear.
Right. The basic population dynamics equation is very simple. It says that the number of animals born minus the number of animals dying is the net addition or subtraction from the population. If we have a population that we can count every year like we do with wolves—we count them every winter—then we can mathematically fit an equation to that growth using things like observed deaths and estimated reproduction.

When we can’t get that to reconcile, then we need some additional deaths that are unobserved to make the growth rate that we see agree with the mortality and the reproductive rates that we’re measuring.

The suspicion is that many or some of those unobserved deaths are due to illegal killing. Because from our radio tracking data we do have good estimates on the relative amounts of deaths that are due to other things, like being killed by other wolves or dying of disease or being hit on the road.

What would prompt illegal killing?
Human dimensions research done at the Nelson Institute suggests that people living in wolf range have a sense of frustration that many people think traces back to this on-again, off-again listing of wolves under the Endangered Species Act.

We went through a period where the wolves would be de-listed, or there would be movement toward de-listing, and then somebody would step in, the courts would intervene, and the wolves would become listed again.

There’s good human dimensions research in wildlife that says that attitudes toward wildlife tend to degrade when people feel like they have no options for dealing with the problems that those wild animals are causing.

When wolves are put “off limits” because of the Endangered Species Act, then people who are experiencing problems with wolves, real or imagined— their attitudes toward wolf conservation begin to degrade.

That aligns with some of the research that’s been done on this campus suggesting, among other things, that people who are interviewed in the
north say they’d be more willing to illegally kill a wolf if the opportunity presented itself. More people are saying that now than in the early 2000s. That time period aligns with the growing frustration people have experienced over de-listing.

How many unexplained wolf deaths are there?
About 20 to 30 per year, in our best estimate. That’s been from the period 1980 to 2013, where we fit the models. There’s evidence that it’s been increasing recently. By “recently,” I mean within the past five or 10 years.

Can you please elaborate?
During the early part of the growth phase of wolves in Wisconsin (1996– 2002) the wolf population averaged about 200 wolves during midwinter counts. We estimated that about 43 of these would die during the year, and unobserved deaths were likely not needed to reconcile observed popula- tion growth. During the latter part of the growth phase (2003–2012), Wisconsin’s wolves averaged about 600 wolves, and about 138 of these would be expected to die during the year. However, you would also need another 24 dead wolves to reconcile the rate of population growth observed. These 24 would include a mix of natural and human-caused subtractions, including an unknown level of illegal killing. The change from 1996–2002 to 2003–2012 suggest that illegal killing may have increased.

What kinds of conflicts do people have with wolves in Wisconsin?
Probably the most important right now are conflicts with livestock producers. We have a handful of areas in Wisconsin that are hot spots where there’s been sort of long-term chronic depredation by wolves on livestock.

That’s a real problem—and fortunately in Wisconsin, the Department of Natural Resources has a partnership with USDA Wildlife Services. They have professional USDA trappers who can go in, verify whether a calf or a cow was killed by wolves, and then help the landowners either by excluding the wolves from the territory or by trapping and euthanizing the wolves that are causing problems. They’re very professional, they’re very good at what they do, and they’re very successful.

Another problem in Wisconsin is wolves depredating hounds. These are mostly hounds used for hunting bears and smaller carnivores. If you’re running hounds late in the summer, that’s when the wolves are provisioning their pups at rendezvous sites.

The wolves probably interpret that incursion as an invading pack, so they would attack and kill those hounds. That happens, that’s an issue to deal with. DNR has been proactive with trying to identify those areas where depredations have occurred and might be more likely, and warn people to avoid those areas with their hounds if at all possible.

There’s a lot of talk about wolves having impacts on deer in the north. In some places, that’s probably a reality. In some places it might be more perception than reality. At a statewide scale using the harvest statistics, we just haven’t seen a real impact of wolves, but that’s sort of a coarse-filter approach.

We have two deer research projects going, one in eastern farmland and one in the northwest. We actually don’t find a whole lot of wolf predation on adult deer, which would be the mechanism by which wolves would have the most impact on the deer herd. Still, if you’re the unlucky individual whose hunting spot happens to be sitting right on top of a wolf rendezvous zone, you might not be seeing very many deer.

What would you like to see done with wolf management going forward?
One of the unique things about wolf management in Wisconsin is that we’re managing this population now at a pretty high exploitation rate—meaning that we’ve got heavy harvest seasons. Those are designed explicitly to reduce the wolf population.

Harvest management theory would suggest that there’s some danger of long-term instability. I think the most important thing that managers of Wisconsin’s wolf population need to do is keep putting efforts into monitoring the wolf population—tracking population trends, tracking the extent to which wolves live on the landscape. Those are the measurements you can use to identify some sort of instability and then be able to deal with it.

To be fair to the managers, they know that, they’re working on that. We’re collaborating with them to come up with more cost-effective ways to get the sort of information they need to track population trends.