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Yosemite National Park:


American black bears (Ursus americanus) are an integral part of the Sierra Nevada ecosystem and are only one of the many animal species protected in Yosemite National Park. Black bears forage on a wide variety of natural foods, including grasses, insects, berries, and acorns. The bears, however, are intelligent and adaptable, and will readily accept human foods when they are available. Bears that are exposed to human food often change their behavior and begin seeking it in campgrounds, parking lots, and from backpackers. This results in property damage and dangerous confrontations between humans and bears. The ecological role of such bears is also changed - their use of natural foods diminishes, they become more nocturnal, and the elevation range of habitat use changes. When a bear's search for human food makes them aggressive toward humans, it poses an unacceptably high threat and must be killed. As a result, black bears have been the subject of intense management efforts in Yosemite for many years, to protect both people and the bears.

Bear Biology

A majority of animal matter in a black bear's diet is insects, such as ants, termites, and grubs ripped from rotting logs. Photo by S. Epperly/NPS.

Black bears (Ursus americanus) in Yosemite have long been of intense interest to both park visitors and park managers. For visitors, the sight of a bear can evoke a mixture of excitement, awe, and fear; all of which can mark the highlight of a vacation. For park managers, black bears offer the challenge of preserving an ecologically-important species that, by its nature, can easily be "corrupted" by human influences in Yosemite.

When Euro-Americans arrived in California, grizzly bears (Ursus arctos) inhabited most of the state, including the area that is now Yosemite National Park. The grizzlies, however, were seen by the settlers as a dire threat to life and property and were killed in large numbers. By the early 1900s, few grizzlies and little of their prime habitat in the Central Valley remained. The last known grizzly bear in California was killed in the Sierra foothills south of Yosemite in the early 1920's.

Many years ago, the National Park Service maintained bear feeding pits to entertain visitors and draw bears out of developed areas. This practice, however, led to many human injuries and many killed bears, and ended in the 1950s. NPS photo.

In contrast, black bears have fared much better. Much of their preferred habitat in the foothills and mountains remains suitable, and their more timid behavior has limited persecution by humans. Black bears have proven to be adaptable to many human-caused changes to their habitat in the Sierra Nevada and eagerly take advantage of food sources these changes sometimes provide - such as garbage cans and dumps, orchards, and domestic beehives. These food sources, however, often bring the bears into conflict with humans, for which the bears can pay with their lives. Nonetheless, there are an estimated 20,000 to 24,000 black bears in California, despite a fall hunting season that annually removes up to 1,500 bears from the population. No scientific census of bears has occurred in Yosemite, but it is estimated that there are roughly 300 to 500 black bears in the park.

Despite their name, most black bears in Yosemite are not black in color. Most are some shade of brown, ranging from almost blond, to reddish brown, to a dark chocolate color. Truly black black bears are relatively rare here. In other areas of the country, such as the eastern United States, and the Pacific Northwest, black bears with black fur are the most common.

A large Yosemite black bear "sizes up" the photographer. Photo by Amber Bethe/NPS.

One common question is how big are Yosemite's bears? This is a difficult question to answer because bears, like people, can vary greatly in size. Also, an individual bear's weight can change greatly throughout the year. Before entering winter hibernation, a bear's weight can be double what it was when it emerged from its den the previous spring, if food sources are rich enough. In general, however, the weight of an average, adult male Yosemite black bear in summer is 300 to 350 pounds (136 to 159 kg). Females are smaller, with typical weights ranging from 200 to 250 pounds (91 to 113 kg). Much bigger bears, however, do occur. The largest black bear ever captured in Yosemite weighed 690 pounds (375 kg)!

Bears are classified as carnivores, in the same taxonomic order as dogs and cats, but a majority of a black bear's diet is made up of vegetable matter. In the spring, after emerging from winter dens, the bears feed largely on meadow grasses, which are relatively low in nutrition, but sustain the bears until more nutritious foods become available. As berries of various plant species ripen in the summer, the bears shift to these higher-calorie foods. Animal matter that is eaten consists primarily of ants, termites, and insect larvae ripped out of logs or dug from the ground. Black bears also sometimes kill young deer or scavenge the kills of other predators, such as mountain lions and coyotes. In the fall, black bears gorge on acorns, which are especially important to the bears as they fatten before going into winter dens for hibernation.

The capture and handling of bears requires a complex array of equipment. Photo by S. Thompson/NPS.

Winter dens are typically established in hollow trees or logs, under the root mass of a tree, or in caves formed by the jumble of large rocks on a talus slope. Here, the bears enter a state of reduced body temperature, pulse rate, and respiration that enables them to conserve energy. They neither defecate nor urinate while hibernating, and even have unique metabolic pathways that enable them to extract energy from body wastes. Their "sleep," however, is not a deep one, and bears may leave the den periodically. Cubs are born in the winter den, weighing less than 1/2 pound (0.23 kg) at birth, and typically number from one to three cubs in a litter. The fast-growing cubs will remain with its mother through another winter, before leaving her in the spring at about 16 to 17 months of age. By spring, a hibernating bear can lose as much as half of its body weight. This is especially true of females nursing cubs.

Human-Bear Management Program

Black bears in Yosemite have caused hundreds of thousands of dollars in property damage as they seek food improperly stored in vehicles. Photo by S. Thompson/NPS.

The history of interactions between humans and black bears in Yosemite is a long one, marked by some periods that we now look upon as shameful. Early in the park's history, little was done to keep bears from becoming conditioned to human food. Garbage was readily available in developed areas, and little was done to discourage visitors from feeding bears. Indeed, the National Park Service maintained several "bear pits" in the park where bears were fed garbage in an attempt to keep them out of park campgrounds and lodging areas, and to provide visitor entertainment. Human injuries were common, and many bears were killed in the name of public safety.

Thankfully, times have changed, and the emphasis is now on managing the behavior of humans rather than the behavior of bears. All outdoor garbage cans and dumpsters are bear-resistant. All campsites, parking lots, and major trailheads are equipped with bear-proof food storage lockers that allow visitors to remove food from their cars and store it safely away from bears. In recent years, increased staffing has allowed more patrols to detect and correct food storage problems and to provide visitor education. Also, all park employees - of the National Park Service, the concessioner, and other park partners - have accepted larger roles in protecting the bears, whether it is diligence in emptying trashcans or dispensing information to visitors. As a result, human-bear incidents and property damage have declined by nearly 90% over the last three years. To continue this success and protect Yosemite's bears, strict compliance with the park's food storage regulations is necessary.

Use of bear-resistant food canisters is required in some areas of Yosemite's wilderness, but all backpackers are strongly encouraged to use canisters to protect themselves and the bears. Photo by M. Floyd/NPS.

The bear management program still involves some actions that deal directly with the bears. Bears are hazed out of developed areas, while others are captured, tagged, and released . Some of these bears are relocated to other areas within the park, although most of them just return. Despite all the improvements in facilities and education, some bears become dangerously aggressive and must be killed, usually two to three per year. These sad events indicate that further progress must be made in making human food unavailable to bears in Yosemite. To learn more about how to avoid dangerous encounters with bears, see our bear safety page.

The Hornocker Wildlife Institute, a program of the Wildlife Conservation Society, recently examined and evaluated factors influencing human-bear interactions in order to accurately identify methods to improve bear management, reduce the number of human-bear incidents, and provide for the continued, long-term existence of bears in Yosemite National Park.

Specific recommendations included maintaining personal contacts by park staff to remind visitors of food storage regulations, increasing the level of human interest in the messaging used to educate visitors about bears and bear-related regulations, stronger law enforcement efforts, more effective waste management, more aggressive aversive conditioning techniques on bears visiting developed areas, and research into the transmission of the damage behavior throughout the bear population. Additional information regarding the 2000-2003 research effort and copies of the final report and scientific publications can be found here.

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