Confusion Over the Yellowstone Grizzly

Grizzly cruising the edge of a lodgepole pine forest in Yellowstone. Photo: NPS/Jim Peaco.

It would be hard for anyone reading regional news to miss recent pronouncements by agency scientists that the previously rapid expansion of Yellowstone’s grizzly bear distribution had stalled – and even retracted in parts of Montana. Nor would a reader likely miss speculation by government spokespeople that this recent stasis was attributable to hard limits imposed by conflicts with humans.

Most people interested in Yellowstone’s grizzly bears are probably confused by this news or, at the very least, not sure what it means. How does this pronouncement reconcile with previous government statements that connectivity between the Greater Yellowstone and Northern Continental Divide grizzly bear populations is only a few years away? What does it mean for grizzly bear management? How does it fit with other seemingly contradictory statements regarding size and growth of Yellowstone’s population?

One year we hear that the population’s distribution is expanding at a breathtaking pace, the next year that it is not. One year we hear that the grizzly bear population numbers roughly 700+ bears, the next year 1000+, and most recently, 900+. One year we hear that Yellowstone’s grizzly bear population has plateaued, and the next we hear that it has continued to grow.

Researchers from the Interagency Grizzly Bear Study Team have rightly acknowledged that annual additions or subtractions of literally hundreds of grizzlies from estimated size of Yellowstone’s grizzly bear population are largely an artifact of changing methods, not anything real. But this all-important proviso usually gets buried in the flurry of resulting news coverage, along with any references to statistical uncertainy. Artifacts imposed by changing methods should not only be the headline of media articles, but also placed front and center in reports by researchers to agency managers.

On a related note, it is unclear the extent to which limitations built into methods for calculating distribution of Yellowstone’s grizzly bears might have biased biannual estimates. As with any statistical method, there are guaranteed to be problems, especially given that data sources become increasingly unreliable the further one goes towards the population periphery. Agency researchers almost certainly cannot reliably estimate a change in distribution as small as 0.5% – as was claimed in the most recent report by researchers to grizzly bear managers assembled in Cody, Wyoming.

Perhaps more problematic, the implied claim – or at best speculation – that the stalled increase in distribution is somehow attributable to intractable conflicts rooted in immutable human behaviors is specious. People’s attitudes and behaviors can change, and have changed, largely in ways that foster coexistence with grizzly bears. Numerous endeavors are afoot to promote continued positive change, most notably in the High Divide region of southwestern Montana.

If anything, mounting grizzly bear mortality on the population periphery is more plausibly ascribed to the unlimited license being provided by the U.S. Fish and Wildlife Service for managers to kill grizzlies, largely based on the assumption that we are awash in expendable bears. This is about policy, not uncompromising people. More certainly, researchers with the Interagency Study Team are not social or political scientists, and thus not in a position to make authoritative claims about anything other than biological data and statistical methods.

People have a right to be confused. Agency researchers owe the public and grizzly bear managers a well-publicized and accessible explanation for how vagarous but weighty pieces of information about Yellowstone’s grizzly bear population can be reconciled – without lapsing into bald assertions about human motivations and behaviors that are well outside their expertise.

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