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Serving Northern St. Louis County, Minnesota

WILDLIFE

Cause and effect in the mystery of the moose

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My April 10 column on Dr. L. David Mech’s 2014 study that links declining wolf numbers in his study area east of Ely with rising wolf numbers has generated a number of valuable letters from readers which I think have advanced the ongoing debate on this subject. It’s in the hope of furthering that debate that I respond to a couple of points raised by readers.

Roger Powell, of Ely, notes that moose and wolves have co-existed in the region for thousands of years and legitimately wonders what has changed now that has thrown the predator-prey balance between these two species out of whack. He says there’s evidence that changes in the climate are fueling a decline in the health of the moose herd overall, leaving them more susceptible to wolf predation— and that the end result is an increase in wolves (which may be temporary) and more predation on moose.

As such, Mr. Powell suggests that the link postulated by Dr. Mech between rising wolf numbers and declining moose survival is misplaced. The rising number of wolves is not the ultimate cause of the moose decline, he says, but merely a symptom of the larger overall problem.

Mike Ruzich, of Morse Township, offered another hypothesis, and it’s one that largely answers the question posed by Mr. Powell. Mr. Ruzich notes, accurately, that huge swaths of mature forest in the Boundary Waters Canoe Area have been converted to very young woods in recent years as a result of the 1999 blowdown and fuel reduction efforts undertaken in its wake. While he didn’t mention it, I would add the Cavity Lake, Ham Lake, and Pagami Creek fires to the list of recent large disturbances. As a result of these combined events, at least half of the million-plus-acre BWCAW has been converted from old to young forest. This has been most apparent along the Gunflint Trail, where the decline of moose has been so noticeable to residents and visitors there.

This conversion significantly improved the habitat for whitetail deer and Mr. Ruzich cites reports that whitetails have, in fact, re-colonized large areas of the wilderness where they were once rare or non-existent. I think this is a valid observation.

In his letter Mr. Powell asked: “After the long period of co-existence, why are wolves now killing enough moose possibly to cause extinction of the population?”

I think Mr. Ruzich has the likely answer. As whitetail deer spread into areas once dominated by moose, they have provided a substantial additional food source that has shifted the balance between wolf and moose, allowing the wolf population to expand—and that inevitably puts more predator pressure on the moose population in the area. The impact is felt most strongly on the most vulnerable moose, i.e. calves, and we’ve seen calf survival drop in half within a period of just a few years. The correlation between rising wolf numbers and declining calf survival demonstrated by Dr. Mech is a powerful one. Ignoring it is scientifically suspect.

So, what is the ultimate cause of the moose decline in this scenario? Climate change? Whitetail deer? Or an increase in the wolf population? And is there anything we can do about any of it?

Certainly one could argue that there is a connection to climate change, although I tend to dismiss the suggestion that temperature increases (though real in the long-term) have had much to do with it. That’s mostly because as recently as nine years ago, the moose population appeared to be doing just fine, with a DNR estimate of 8,800 animals in the northeast moose zone. And one could hardly argue that we’ve seen a string of mild winters (or hot summers) since then. Indeed, in the past ten years, we’ve seen four mild winters (one being historically mild) five severe winters (two being historically severe), and one moderate winter (2014-15) as determined by the DNR’s winter severity index. That’s hardly a trend that could account for such a dramatic change in the moose population.

The stronger link to climate change in this case correlates with the increased incidence of extreme weather events. It is extreme weather, such as devastating windstorms and persistent long-term drought (leading to fire), that have combined to completely remake the habitat within the heart of the region’s primary moose zone over the past ten years. Unlike rising temperatures, which are easier to link more directly to climate change, the 1999 blowdown and the series of major fires that have struck the BWCA in recent years could also be considered to be a cluster of freak events, the kind that have periodically altered the landscape for eons.

No doubt wildlife populations ebb and flow as these changes give some species temporary advantage over others. In this case, it appears that the change has advantaged whitetail deer and the appearance of a new food source has allowed for at least a temporary increase in the wolf population— which is currently impacting moose calf survival in these same areas. There’s real science that points to wolves impacting moose calf survival and it stands to reason that more wolves on the landscape will mean fewer moose calves live to adulthood. I don’t think that’s even debatable with what we know today.

We can argue whether wolves, or the events that allowed their population to increase, are ultimately responsible, but it’s hardly a worthwhile argument, since we can’t do anything to change past events. Through regulated hunting, however, it would be possible to trim wolf numbers, at least somewhat.

But, as Mr. Ruzich argues, perhaps it’s the deer that are to blame. Yet the fact is whitetail deer and moose have also co-existed in our region for at least a century, although their relative numbers have changed over time. In the wake of logging of the region’s primary forest 100 years ago, whitetail numbers exploded, and moose numbers declined to even lower levels than today.

As the forests grew up, whitetail habitat diminished and severe winters in the 1970s took a huge toll. Moose numbers rebounded as a result, and we came to see the moose population we experienced in the 1980s and 1990s as the norm, when we very well may have been experiencing an unusual peak. It’s worth noting, however, that the moose recovery came at a time when the wolf population was much lower in our region that it is today.

Beginning around 1990, we witnessed a significant expansion in the timber industry, which reset the clock on millions of acres of forest in our area. Whitetail numbers boomed as a result, and moose began a decline, particularly on the western end of the moose range where timber management was most intensive. While the BWCAW was seen as a refuge from that kind of forest conversion, Mother Nature had other ideas, as already noted, and whitetails gained there as well, at the expense of the moose.

There is no doubt that whitetail deer pose problems for moose, but it’s primarily a matter of density. While the reappearance of whitetails in the heart of the BWCAW has likely been a factor, what we don’t know is whether deer are present there in sufficient numbers per square mile to really impact the health of moose, by spreading parasites like brainworm and liver flukes to a significant percentage of the population, or if their presence impacts moose primarily by allowing wolf numbers to grow, limiting reproductive potential for the moose. I tend to think it’s the latter.

While the moose health issue is a real one, that likely impacts adult survival, its effect on calf survival should be less significant, since calves aren’t born with the parasites they may encounter later in life. Some have suggested that it could weaken the moose cows enough that they can’t defend their calves against a pack of wolves. That’s pretty speculative. Frankly, I suspect if a hungry wolf pack locates a moose calf in the woods, it’s a rare mother that can fight them off.

As for controlling whitetail deer numbers in the BWCAW, that is simply a matter of habitat and winters. Realistically, you’re never going to get the hunting pressure necessary to make a dent. In other words, there’s not much that can be done from a management perspective to address the return of whitetails to the heart of moose country.

On the other hand, hunters don’t need to take many wolves to provide a little temporary relief to moose.

And temporary relief may be all that’s needed. While the habitat changes in the BWCAW have been a windfall for whitetails, forests grow back and in other 10-15 years the advantage could well tip back in favor of the moose. That’s if we don’t lose a viable moose population in the meantime.

Ultimately, I still believe that forest management is the primary factor when it comes to our declining moose numbers. While moose like young browse, we know as a verified fact that they can also be very successful in habitat (i.e. mature boreal forests) that won’t support significant numbers of deer. That’s why they’ve been able to maintain a healthy population in the interior of the BWCAW, at least until extreme weather altered the landscape there, allowing whitetails to return and the wolf population to expand. I believe we can maintain a moose population in our region for at least several more decades (in the long-term climate change will probably wipe them out) if we provide habitat in which they can exist in relative isolation from whitetail deer. At present, we’re not able to do that very well. Over time, with proper management— of forests and predators— and a little help from Mother Nature, I’m optimistic that we can.