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Grizzly Bears are Dying and That’s a Fact

Photo by  Roger Hayden.

More grizzly bears are dying, being seen, and in conflicts with humans in and around the Northern Continental Divide Ecosystem (NCDE). These are irrefutable facts.

According to Montana Fish, Wildlife and Parks (FWP) these trends are a straight-forward consequence of more bears. As a corollary, environmental change doesn’t matter to bears in this population because, as omnivores, they can freely substitute one food for another. End of story.

Unfortunately, simple explanations such as this one offered by FWP are little more than “just so” stories. Anyone who has studied wildlife populations and the environments they occupy knows that things are invariably more complicated. Data for estimating population size are always flawed and the models these data are fed into are fraught with assumptions; and no amount of statistical gimcrackery can fix it. Even more important, any student having taken Wildlife Management 101 could tell you that habitat affects numbers, behaviors, and distributions of animals — including grizzly bears. This was Chuck Jonkel’s mantra during the years he taught at University of Montana.

In other words, there is almost never a 1:1 correlation between the numbers of bears we see and numbers of bears in the population. Moreover, changes in habitat will lead to changes in where bears live and what they eat, with consequences for the rates at which they reproduce and die.

You wouldn’t know this based on what you hear from FWP. They steadfastly refuse to monitor any aspect of grizzly bear habitat or diet. And they claim that recent record numbers of deaths in the NCDE are not a problem.

Yet the approach used by FWP for managing mortality is tantamount to driving with your eyes fixed on an out-of-focus rearview mirror. The data FWP uses are on average nine years old; the models they employ rest on unsubstantiated assumptions; and they disregard much of the uncertainty in their population estimates. (You can see more in a report entitled “Heart of the Grizzly Bear Nation”).

So, what’s an alternative explanation for what we’re seeing, one that attends to the limitations of models and data, the configurations of habitats, and what we know about environmental change?

For one, the NCDE grizzly bear population has probably grown during the last 10 years, but not by as much as advertised. We have perhaps 100 more bears, not 250 more. If so, then FWP managers are wrong when they say current levels of mortality are sustainable. If you inflate the divisor in a division problem, you axiomatically under-estimate the result (i.e., death rate, or dead bears divided by live bears).

But more importantly, increases in distribution have outstripped even the most optimistic estimates of population growth, which begs the question Why? There is good reason to think that habitat productivity has declined in portions of the population’s core, partly because of escalating wildfires and the transient unproductive conditions that follow. We also lost whitebark pine to white pine blister rust. Seeds from this tree were once an important food of grizzlies along the Front.

Bears have plausibly spread out in search of alternative foods, especially east from the Rocky Mountain Front. And the spread of bears onto the plains has predictably been accelerated by the attenuation of habitats along riparian corridors. Changes in foods and habitats are almost certainly driving increased conflicts and sightings every bit as much as are increasing bear numbers.

Given the stakes of grizzly bear management, it’s time for FWP to offer us something more than convenient “just so” stories.

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David Mattson worked for the grizzly study team for 2 decades. He retired from the US Geological Survey two years ago. 

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