Not long ago, researchers with the Department of Natural Resources issued what was clearly meant to be the final word on the decline in the northeastern Minnesota moose population. Their finding? …
Not long ago, researchers with the Department of Natural Resources issued what was clearly meant to be the final word on the decline in the northeastern Minnesota moose population. Their finding? Blame it on the deer. That’s the short version, anyway.
But the DNR’s take is facing a bit more kickback from Dr. David Mech and fellow researchers John Fieberg and Shannon Barber-Meyer in their latest research paper, just published in the Wildlife Society Bulletin. The latest study, “An Historical Overview and Update of Wolf-Moose Interactions in Northeastern Minnesota,” reads similarly to some of Mech’s other recent work, which has portrayed a greater link between the ups and downs of both the moose and wolf populations than DNR researchers have been willing to acknowledge. But Mech also makes the intriguing suggestion (perhaps merely an implication) that there may be a lot less drama going on in the moose population than perhaps we’ve been led to believe.
From the first sentence of the study’s abstract, Mech notes that the populations of both wolves and moose have fluctuated for decades, trends with which Mech is very well acquainted. Mech, of course, has been studying the relationships between wolves and their prey in a 2,060 sq. kilometer study area just east of Ely, since the 1960s. Mech and company write: “Published historical data indicate that estimated moose numbers in northeastern Minnesota have fluctuated between approximately 2,760 and 8,800 for the past few decades, and that from 1935 to 1955 estimates were below 1,000.”
While we’ve been led to think of the latest moose population estimates as at or near a low ebb, it’s worth noting that the DNR’s moose population estimates in the region averaged about 4,000 from 1997-2003, and not much higher than that in the early 1990s. Over the past four years, the DNR’s moose population estimate averaged 3,882. Statistically, that’s indistinguishable from those earlier numbers. The DNR has changed its sampling methods (using helicopters rather than fixed-wing aircraft) but it’s not clear why that would invalidate the earlier numbers, since the DNR corrects for these types of differences in their analysis. And even if they aren’t directly comparable, the earlier data shows the same kind of population fluctuations in the past that we’ve seen more recently.
We know that wildlife populations rise and fall all the time based on a wide range of factors. And it’s clear that both wolves and deer do affect moose. The impact of deer is more indirect, which is why you can’t very readily correlate changes in the moose population with fluctuations in the deer herd. Higher deer numbers do impact moose, however, by increasing the incidence of parasites and by helping to sustain a greater wolf density on the landscape.
The impact of wolves is more direct, which is why Mech, et al., have been able to clearly correlate declining moose calf survival, and an overall population decline as a result, with rising wolf numbers, and vice-versa. Mech has made this connection before, as I’ve written in the past, and this latest study simply adds more data to the argument. The connection between wolf numbers and moose calf survival is especially plain, and there’s a strong argument to be made that this is the connection that is behind most of the moose population decline in northeastern Minnesota. Too many deer are undoubtedly increasing the incidence of parasites and related disease in moose, but wolves are limiting their reproductive potential more than anything. The DNR appears institutionally-resistant to this idea, preferring to discount their own data that shows wolves are the overwhelming source of mortality for moose calves, and keep the focus on deer as the primary factor behind the moose decline.
From a political standpoint, that’s probably understandable. At this point, the agency has little ability to manage wolves, so identifying them as a primary factor behind the decline of an iconic species like the moose is just asking for an unhappy public. Still, politics isn’t supposed to factor into science.
And while DNR officials have portrayed the moose decline as the harbinger of a greater systemic breakdown— probably fueled by climate change— Mech clearly doesn’t find the data convincing at this point.
He notes that moose bounced back after previous, similar population declines (1990-1993 and 1997-2001). Those declines correlated with spikes in wolf numbers in Mech’s study area and in each instance, the moose recovered after wolf populations eventually declined. That’s exactly what one would expect from a functional predator-prey system. It’s worth noting, too, that the worst of the most recent moose decline coincided with, by far, the highest wolf densities Mech had ever seen in his study area. Those wolf numbers have since fallen dramatically in the past five years, and that corresponds with a stabilization of the moose population over the past few years.
Could other factors, like climate change, slowly begin to overwhelm this longstanding predator-prey relationship? It’s probably inevitable over the next several decades if the world doesn’t seriously address its emissions of heat-trapping gases.
But it’s not yet clear whether the latest moose decline represents a system change or simply the natural fluctuation inherent in wildlife populations. In other words, it may not be a crisis, but simply another downturn from which the moose will likely recover given time and adequate habitat.