Alaska News

Lone, predatory black bears responsible for most human attacks

Most fatal attacks by North American black bears during the past century were conducted by lone, male animals that stalked and then killed their human victims as prey, according to a new study by the world’s top authority on what triggers bear attacks.

Though black bears rarely kill or seriously injure people, when they do, it's most often the result of predatory behavior by males inside their wilderness home ranges and not by females protecting cubs or animals defending a carcass, said Dr. Stephen Herrero, professor emeritus at the University of Calgary and author of the classic Bear Attacks: Their Causes and Avoidance.

"Most fatal black bear attacks were predatory and all fatal attacks were carried out by a single bear," Herrero said in a U-Cal story. "With training, people can learn to recognize the behavior of a bear that is considering them as prey and deter an attack by taking aggressive action such as fighting back."

The study examined 59 fatal encounters between black bears and humans in Alaska, Canada and the Lower 48 during the 110 years ending in 2009. Some 88 percent of the 63 deaths were caused by a bear that exhibited predatory behavior, and 92 percent of these predatory black bears were male.

Of the total fatalities, five occurred in Alaska and 44 in Canada, with only 14 spread among the Lower 48 states -- including several states with thousands of black bears and millions of residents.

"There were 3.5 times as many fatal attacks in Canada and Alaska, but there were only 1.75 times as many black bears and much less human contact (due to fewer people in black bear habitat) for black bears in Canada and Alaska," wrote Herrero and four other authors.

Still, the scientists cautioned, the risk of being attacked by non-captive, free-roaming black bears in the wild (or even the backyards of human settlements) of North America remains exceedingly small -- even in Alaska or Canada.


"Each year, millions of interactions between people and black bears occur without any injury to a person, although by 2 years of age most black bears have the physical capacity to kill a person," they wrote.

Reducing this risk even further might hinge on recognizing predatory behavior by the animals when it happens, and then taking other reasonable precautions when traveling or living in black bear territory, they said.

Examining 59 attacks across 110 years

The study — Fatal Attacks by American Black Bear on People: 1900–2009 — appeared this week in the prestigious peer-reviewed journal published by the Wildlife Society. Over the past 40 years, Herrero, the lead author, pioneered the practice of applying biological and forensic insight to investigate why black and brown bears attack, maul and sometimes kill people in North America. His current coauthors were Canadian scientist Andrew Higgins, James Cardoza and Laura Hajduk with the Massachusetts Division of Fisheries and Wildlife, and bear biologist Tom Smith of Brigham Young University. Smith is a former Alaskan biologist who conducted ground-breaking research into bear encounters in Katmai National Park.

"Our findings raise some important new insights that can be used to better understand the cause of attacks and how they can be avoided in both the front and backcountry," Herrero said.

The study results undercut several assumptions about what poses risks in black bear country.

"In particular, the common belief that surprising a mother bear with cubs is the most dangerous kind of black bear encounter is inaccurate," Herrero said. "Instead, lone male black bears hunting people as a potential source of food are a greater cause of deadly maulings and related predatory attempts."

The authors did find that the incremental increase in human population correlated with the increase in fatal attacks -- some 86 percent of the fatalities have occurred since 1960.

"We suspect it is because there are more people pursuing recreational and commercial activities in black bear habitat," Herrero said in the story. "Similarly, we don't know exactly why there have been more attacks in Canada and Alaska, but we speculate that it could be because bears in those areas are living in less productive habitat with periodic food stress, which may predispose some bears to consider people as prey."

Other insights:

  • No fatal attacks involved more than one bear, and almost all were adult males.
  • Bears that have previously killed are most likely to act aggressively again.
  • People traveling or camping alone were the mostly likely victims — almost 70 percent of the fatalities involved single person. Only 9 percent of attacks occurred with more than 2 people present.
  • Human food and garbage tended to attract aggressive black bears and might increase the likelihood of a serious bear attack.
  • The victims were ranged from small children to old people. No single activity or region correlated with the fatal attacks. “The widespread geographic distribution of fatal attacks suggests that they may occur in a variety of bear habitats and bear population conditions,” the authors wrote. “Fatal attacks do not appear to be associated only with a specific black bear population, geographic area, or habitat.”
  • Fatal attacks were most numerous in August — when black bears are shifting into overdrive to put on weight for the winter. Most attacks occurred during the day, with about 60 percent in the backcountry and 40 percent closer to communities.
  • None of the victims used bear spray. “Nor was bear spray available for other party members to deter the attacking bear,” the authors wrote, adding: “Two studies of the effectiveness of bear spray that had capsaicin as its active ingredient demonstrated its effectiveness but noted possible interference with wind.”

Beware the bear that stalks in silence

Recognizing the difference between a predatory attack and defensive, fearful activity -- and possibly wielding a fresh can of bear spray -- may be the crux of protecting oneself against a fatal attack by a determined blackie. The authors wrote:

Faced with this chilling, single-minded tableau, people should use "all possible deterrents such as bear spray, loud noises, fists, firearms, rocks, knives, or clubs," the authors wrote.

At the same time, if a black bear acts stressed or shows "defensive threat" behaviors -- swatting the ground, mounting short charges, clacking teeth, making huffing or growling noises -- it's much less likely to attack.

"A predatory attack is unlikely, which is counterintuitive to many people because the bear is acting aggressively," they said. "However, this aggression is defensive, and if the bear is given space it will likely leave."

The authors noted that brown bears behave much differently than black bears, and a significant proportion of fatal attacks or serious maulings that involved brown bears began with the bears acting defensively, including sows lashing out to protect cubs.

Still, the authors emphasized more than once that people face little risk from black bears, with uncounted millions of encounters ending with the bear fleeing or without the human ever knowing the bear was present. The vast majority of black bears want nothing to do with people. Given a North American population of 750,000 to 950,000 black bears, this lack of serious injuries is remarkable.

"Given the strength and opportunistic predation by black bears one can ask why bears do not prey on people more often," they wrote. "Part of the answer may be that bears that try to or do prey on people are usually killed and removed from a population's gene pool, decreasing the frequency of any genes the individual might have had that could contribute to predatory attacks on people."

Contact Doug O’Harra at doug(at)