Black bear density in Yellowstone's Northern Range is highest in Northern Rockies
In the Northern Range of Yellowstone National Park, researchers estimated there are twice as many black bears when compared to any other area in the northern Rocky Mountains.
Bordered to the south by the Yellowstone and Lamar river basins, the Northern Range contains about 20 black bears for every 62 square miles (100 square kilometers) of terrain. In comparison, most other areas in the northern Rockies have six to 12 black bears per 62 square miles.
Given the region is about 600 square miles, running along the border between Montana and Wyoming, there could be more than 150 black bears in the area.
In a similar study conducted in 2004 in Glacier National Park researchers identified 600 black bears or about 11.4 bears every 62 square miles.
Hair snares
The estimates are contained in a study published last September in "The Journal of Wildlife Management."
"Given these high densities, black bears could influence other wildlife populations more than previously thought, such as through displacement of sympatric predators from kills," the authors wrote. These researchers included Nathaniel Bowersock, Andrea Litt, Michael Sawaya, Kerry Gunther and Frank van Manen.
The study, which extended from mid-May to mid-July from 2017 through 2018, used hair snares and rub sites to conduct genetic sampling to arrive at the conclusions. During the study, 2,600 hair samples were collected from 26 snares and 270 rub objects.
"In both years, density estimates were higher in forested vegetation communities, which provide food resources and thermal and security cover preferred by black bears, compared with non-forested areas," the scientists wrote. "In 2017, density also varied by sex, with female densities being higher than males."
In all, 119 unique black bears were identified, 62 females and 57 males.
Also collected during the study were hair samples from 14 female and 21 male grizzly bears. Across the entire Greater Yellowstone Ecosystem, a much larger area, it is estimated there are roughly 1,000 grizzlies.
"On an individual level, grizzly bears generally outcompete black bears where resources are high quality or when the two bear species occur at similar densities," the study said. "Yet black bears can occur at higher densities than grizzly bears when resources are lower quality (e.g., lower availability of terrestrial meat resources), and grizzly bears may avoid areas with high densities of black bears to decrease the probability of (antagonistic) interactions."
Wildlife-rich
The Northern Range is recognized as one of the most productive and diverse wildlife regions in North America, sometimes referred to as "America's Serengeti," comparing it to Africa's vibrant wildlife region.
In addition to black bears, the Northern Range is home to other large predators including grizzly bears, wolves and mountain lions. Yellowstone is also one of the few areas where black bears coexist with grizzlies.
Large populations of migratory elk and bison also inhabit the Northern Range, along with lesser numbers of deer, bighorn sheep, pronghorn, moose, coyotes and foxes.
"When high-quality resources and habitat ... are readily available, wildlife populations can occur at higher densities," the researchers noted.
In Yellowstone, that higher density can come at the expense of other predators. For example, one study showed bears visited almost half of all mountain lion kills, displacing the big lions from about 10% of their prey in the spring.
Park visitors often see black bears near Tower Junction and on the road to Dunraven Pass. In 2015, a mother bear and three cubs were crossing a bridge near Gardiner and drew national attention when a video showed several tourists walking, then running away as the bears attempted to cross the bridge.
"When resources are limited, black bears are sometimes more tolerant of people, roads, and human developments, potentially increasing human–bear interactions," the researchers wrote.
Male black bears in Yellowstone average between 200 and 300 pounds with females ranging from around 135 to 200 pounds. They stand about 3 feet tall at the shoulder and can live 15 to 30 years.
Male bears have a home range of up to 124 square miles compared to females which range around 45 square miles. Their food sources include everything from rodents and elk calves to pine nuts, grasses and other vegetation.
As of 2019, Yellowstone estimated only one black bear was removed every five years for becoming a nuisance while vehicle collisions with bears averaged about one a year.
On the East Coast where food is readily available, some black bear densities can reach 37 bears every 62 square miles.
Great habitat
Although hunting seasons exist for black bears in Montana and Wyoming, no hunting is allowed in Yellowstone, which helps explain their abundance. Another is the habitat.
"The northern range is located at lower elevations of Yellowstone National Park and experiences longer green-up periods, supplying black bears with more abundant vegetative resources compared with other regions of the park," the study noted.
Although the researchers thought there would be a higher density of black bears near roads, as a way to avoid encounters with grizzly bears, that didn't pan out.
"Instead, frequent use of roadsides by black bears observed on the northern range may simply be related to resource selection without reflecting a density effect, but further research is needed to explore this result," the study found.
The research is intended to provide baseline information for park managers, enabling them to "better assess how bears are distributed across the landscape and develop focused management objectives and strategies."
In 2014, Bowersock attached a camera to one male black bear to assess its movements. It traveled from Mammoth Hot Springs to West Yellowstone. While scavenging on an elk carcass, the bear killed and ate an old female black bear.
Prior to this research, black bear studies had largely been limited to the 1960s when park managers began making it harder for bears to feed at garbage dumps and were even being hand-fed by tourists.
"Understanding the spatial distribution of black bears can also help with efforts to address human–bear conflicts, such as deploying more food storage boxes in forested backcountry areas where black bear densities are highest," the researchers said.
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