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Chapter 6 Grizzly Bears and Other Animals

Grizzlies and Other Predators

Grizzly bears are often referred to as “top-of-the-food-chain predators.” Such a characterization is correct. I’ve found Internet chats debating the outcome of a fight between a grizzly bear and a lion or male gorilla. But under wild, natural conditions, precious few rival predators will challenge the supremacy of a grizzly bear. In eastern Russia, Siberian tigers are known to kill members of the Ursus arctos species (and vice versa). Conflicts between grizzly bears and polar bears may find the great white hunters of the north gaining the upper hand. Wolverines are believed capable of usurping or defending a carcass from a grizzly bear, primarily through a frightful display of snarling and intimidation. But with very rare exceptions, no single wild animal that shares its habitat deliberately challenges an adult grizzly bear.

Nonetheless, grizzly bears in many habitats maintain complex and important relationships with other predators. The relationship between wolves and grizzly bears is particularly intriguing. In Alaska and Canada interactions between grizzly bears and wolves have continued their natural course for centuries. In the lower forty-eight states, however, wolves were exterminated a century ago. The reintroduction of wolves to Yellowstone National Park and the natural colonization of wolves in Glacier National Park and other portions of the northern Rocky Mountains in the contiguous United States have necessitated that indigenous grizzly bear populations once again accommodate wolves in their world.

In Yellowstone researchers have had ample opportunity to observe interactions between grizzly bears and the recently returned wolves. From the standpoint of grizzlies, wolves represent both opportunity and opposition. Prior to wolf reintroduction management biologists theorized that winter wolf predation would leave fewer carcasses of winter-killed ungulates (primarily elk and bison) available for scavenging by grizzly bears in the early spring. However, they also postulated that this diminished presence of a potentially important food source might be offset by grizzly bears taking over carcasses of animals killed by wolves. Some concern was expressed regarding the possibility of wolf packs killing young grizzly bear cubs.

In general, biologists’ predictions regarding wolf and grizzly bear interactions in Yellowstone were accurate and reflect the relationship between the two species in Alaska, Canada, and other places where wolves and grizzlies share the same range. Adult grizzly bears in Yellowstone are usually successful in usurping carcasses from wolves, but not always. Female bears with cubs are frequently repelled by wolves, possibly for the cubs’ protection. Wolves and grizzly bears have also been observed peaceably feeding on the same carcass.

Do the two species kill one another? The short answer is yes. In 2001, 6 years after wolves were reintroduced to Yellowstone, researchers discovered the carcasses of two grizzly bear cubs in separate locations. Both were killed near animal carcasses (one an elk, the other a bison) that had been fed upon by both grizzly bears and wolves. Laboratory analysis of the dead cubs indicated both had been killed by wolves.

The status of interactions between wolves and grizzly bears in Yellowstone is essentially similar to those observed elsewhere. Grizzly cubs are in the greatest danger from wolves. Wolves take their greatest risk when attempting to defend a carcass from an adult grizzly bear. Den sites of wolves are vigorously protected by the pack. Wolf packs are highly successful repelling grizzlies from their denning areas. However, black bears are known to have killed single female wolves defending a den, so a similar outcome from an aggressive grizzly bear is also possible. Biologists seem to agree that where prey animals are abundant, competition between wolves and grizzly bears is negligible. Where prey is less plentiful, the presence of the two species may exert some influence on the populations of each other, but such a relationship is difficult to establish. For wildlife watchers the rare opportunity to view wolves and grizzly bears in the same setting or observe their infrequent interactions with each other is a thrill not soon to be forgotten.

Interactions between wolves and grizzly bears are not commonplace. But due to the fact that both of these predators frequent open country, these interactions are more easily observed by humans than interactions between grizzlies and more seldom seen predators, such as mountain lions (cougars). Mountain lions are rarely viewed by humans in the wild. As they prefer habitats with timber or shrub cover and are highly nocturnal creatures with incredible eyesight, the odds of a person sighting a mountain lion in uncontrolled outdoor settings is very low. Thus, directly observing behavioral exchanges between grizzly bears and mountain lions is like uncovering a needle in the proverbial haystack.

Nonetheless, researchers have discovered a potentially very important relationship between mountain lions and grizzly bears. Researchers in the northern Rocky Mountains of the United States have documented grizzly bears displacing cougars from their kills with a surprising frequency. In one study researchers found that of fifteen cougar-killed elk in the Kintla Lake region of Glacier National Park, grizzly bears visited 33 percent, or five of the kills. Mountain lions in several study areas routinely lost carcasses to grizzly bears. Grizzlies usurping cougar kills happens most frequently in the fall and early spring, when the two animals both tend to live in proximity to elk and deer, two of the most common prey species of mountain lions.

At least in some locations, it appears that stealing carcasses from cougars may be a significant way for grizzlies to access high-protein, nutritious forage at times when they most need it. Prior to denning and just after emergence are two times of the year when discovering abundant food sources is very beneficial to bears, and these are the times when they’re most likely to obtain carcasses from mountain lions. However, the situation isn’t so advantageous for the cats. When a grizzly bear moves in on a mountain lion’s kill, the cat is forced to attempt a defense of its prey or make another kill. Predation is a high-risk endeavor for cougars. A study in Alberta, Canada, indicated that almost 30 percent of the natural deaths to cougars were a result of wounds sustained while attempting to kill prey. Researchers once observed an exceptionally skilled team of mountain lion hunters consisting of a female and her two large cubs. In 23 days this hunting team killed four elk, two cows, and two large calves. Grizzly bears displaced the cougars from one of the kills and fed on two others. Biologists estimated that the bears gleaned nearly 350 pounds of food from these carcasses. Where grizzly bears and cougars share the same range, the bears may receive substantial benefit from the mountain lions. The cougars, by contrast, may experience more risk and adversity from the bears.

Grizzlies also share their world with other bears, polar and black. Interactions between grizzly and polar bears were discussed in Chapter 1, but what about black bears? In general, black bears give grizzly bears a wide berth. Large male black bears may effectively compete with subadult grizzly bears, but otherwise the dominance of grizzlies over their smaller, black cousins is obvious and rarely challenged. Grizzly bears may attempt to kill black bears, but in these infrequent instances the black bears’ climbing ability gives them an advantage. An adult grizzly bear is unlikely to expend the effort to try to dislodge a black bear from a tree it has climbed for protection. However, researchers have documented black bear deaths at the jaws of grizzlies.