Life on the Brink: The Unsettling Numbers About How Grizzly Bears Die

Young grizzly crossing road
Vehicle collisions were a contributor to the record number of grizzly bear deaths documented in the Lower 48 in 2019, the majority of which carried human-related causes.

By Tatum McConnell, Communications Intern

There’s a hard truth about grizzly bears in the Lower 48. When adult bears die, it’s usually a human’s fault. In northwestern Montana from 2004-2014, a state-run study estimated 71 percent of independent grizzly mortalities had human causes.

I was floored when I read this number. It seemed unbelievable that these animals we associate with wilderness could have fatal encounters with humans so often. I wanted to know why and as I started to dig into the data, it became clear that grizzlies live in a minefield of deadly situations.

From estimates in the state’s 10-year study of the Northern Continental Divide Ecosystem (NCDE), poaching and malicious killing claim the most lives overall, nearly a third of human-related deaths at 32 percent. This is followed at 17 percent by agency removal, an event that occurs when a bear has had multiple negative encounters with humans. The sad truth is that some bears can’t lose these habits despite relocation and conflict mitigation efforts. In those cases, wildlife managers make the tough decision to kill them.

Fortunately, with proper steps taken other bears are able to avoid continued conflicts, and agency removal mortality numbers also include some live removals where bears are moved from the population in question. The rest of the human-caused grizzly mortalities are due to train and car collisions, self-defense, illegal defense of property, and illegal hunting due to misidentification. Just 12 percent of adult bears are estimated to die from natural causes, with 17 percent undetermined.

While a high rate of human-caused deaths is the reality for independent adult bears, it’s less common for cubs. I spoke with Cecily Costello, Montana Fish, Wildlife and Parks’ grizzly bear biologist for the NCDE and lead author of the 2004-2014 report. She explained that young grizzlies often won’t make it to adulthood due to natural causes, so for this age group, humans aren’t the biggest risk.

Time of year is also a factor. Grizzlies are at greater risk in fall, when bears enter hyperphagia and must eat an enormous amount each day to prepare for hibernation. This means more movement and more conflicts due to trash, livestock, run-ins with hunters, and other incidents as they search for food. In one grim week last October, six grizzly bears in Montana’s NCDE were killed, contributing to 51 overall deaths in the ecosystem in 2019, following an identical, record-setting 51 in 2018. Before then, yearly deaths in the NCDE had never surpassed 40. Meanwhile, farther south the number was even higher, with a record 69 recorded deaths in the Greater Yellowstone Ecosystem in 2019, 52 due to human causes.

Grizzly Mortality: A Shifting Picture

Okay, we just processed a lot of numbers, and a lot of thinking about dead bears, which nobody wants to do. So let’s think about some living bears: the good news here is that the grizzly population has grown considerably in the Lower 48 in recent decades. So, to an extent, we can expect to see mortalities rise simply because there are more bears.

Map with areas of priority for land easements in Montana and Idaho
Darker green areas indicate the grizzly’s federally-designated core recovery zones while lighter green shows the species’ current documented range. Vital Ground’s One Landscape priorities show our most urgent opportunities for habitat protection (blue dots) and conflict prevention (red dots).

This population growth also means that grizzlies are expanding out into more of their historical range, which often puts them into closer contact with people. Despite that risk, this geographic spread is crucial to reuniting currently-isolated grizzly bear populations. Having a large interconnected population south of Canada will promote genetic diversity and create resiliency within the species, meaning they have the space and safety they need to adapt to changes in their environment.

Costello explained that we’re now seeing bears venture out of core protected areas that are mostly made up of federal and state lands with greater protections for bears.

“In the long run we’re hopeful that in those core areas we’re not going to see a drastic change in human-caused mortality,” Costello said, but added that life for a bear is inevitably more dangerous in more human-populated areas. “It only really stands to reason that those survival rates may not be as high as they would be in highly protected areas.”

By supporting bear-aware communities and connecting core protected areas with conserved private lands, Vital Ground helps bears stay safer when they leave their wild strongholds. But the troubling statistics won’t go away overnight. Costello also pointed out that grizzly bears are in a unique position at the apex of an ecosystem’s food web, another reason human-caused mortality numbers are higher than we might expect.

“There’s not a lot that ends up killing them,” she said, “except for people.”

Protecting Grizzlies: Are We Doing Enough?

Grizzly bears were listed as threatened under the Endangered Species Act in 1975, with about 350-400 bears in the NCDE. Through recovery efforts that population has now climbed to over 1,000 bears. And there’s more good news: scientists are confident that mortality hasn’t reached a level that would be detrimental to the population’s survival.

Grizzly sow and cub in Glacier National Park
While this sow and cub in Glacier National Park are part of a stable grizzly sub-population, the species lacks the large-scale landscape connections biologists hold as the key to durable recovery in the Lower 48.

Costello told me that grizzly biologists and managers can use research to create a population estimate based on expected survival rates for adults and cubs and expected reproductive rates. With these numbers in place, they can project up to six years of future population figures. Once those six years have passed, they can see whether the model was correct and adjust it for future use. With this kind of adaptive management, she explained, they can use “real data to make management decisions and then use science and the data collected to refine that decision over time.”

In the end, the population estimates allow managers to create a threshold for the number of grizzly deaths that would be detrimental to population growth. Fortunately, the NCDE is currently under that threshold and the grizzly population will likely continue to grow in the coming years.

With larger populations in Canada and Alaska, grizzlies as an overall species are doing all right. But is all right good enough? Grizzlies are a pillar of their ecosystems, impacting animals from insects to elk, and plants from wildflowers to trees. For humans, they’ve become a symbol of American wildlife even as we’ve confined them to just a small fraction of their former range. They’re an integral part of our culture and the natural spaces many of us cherish. When we lose a grizzly we lose all of that, as well as the undefinable value of its own life.

Grizzlies deserve better. They deserve long, healthy lives and natural deaths, but at the moment barely one in 10 adult bears make it that far.

Costello added that there’s hope for grizzly populations connecting between core zones. “We have plenty of examples of bears that are able to navigate a human-dominated landscape,” she said. “So those bears that have learned how to live in harmony with the local community are the ones we have to lean on to make connectivity happen.”

Thanks to decades of conservation and those remarkable bears, we’re making progress toward a resilient grizzly population across the northwestern states, and toward communities that adapt to their presence. But there’s clearly more work to do.

Help Protect Habitat and Keep Bears Safe Today!

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