List of animals of Yellowstone
in the northwest United States is home to a large variety of mammals, birds, fish, reptiles and amphibians, many of which migrate within the Greater Yellowstone Ecosystem. These animals are a major park attraction.
Large mammals
American bison
are the largest grazing mammals in Yellowstone National Park. They are obligate herbivores, a grazer of grasslands and sedges in the meadows, the foothills, and even the high-elevation, forested plateaus of Yellowstone. Bison males, called bulls, can weigh upwards of 1,800 pounds. Females average about 1,300 pounds. Both stand approximately six feet tall at the shoulder, and can move with surprising speed to defend their young or when approached too closely by people. Bison breed from mid-July to mid-August, and bear one calf in April and May. Some wolf predation of bison is documented in Canada and has recently been observed in Yellowstone. Bison live an average lifespan of 20–25 years in the wild.Yellowstone is the only place in the lower 48 states where a population of wild American bison has persisted since prehistoric times, although fewer than 50 native bison remained there in 1902. Fearing extinction, the park imported 21 bison from two privately owned herds, as foundation stock for a bison ranching project that spanned 50 years at the Lamar Buffalo Ranch in Yellowstone's Lamar Valley. Activities there included irrigation, hay-feeding, roundups, culling, and predator control, to artificially ensure herd survival. By the 1920s, some intermingling of the introduced and wild bison had begun. With protection from poaching, the native and transplanted populations increased. In 1936, bison were transplanted to historic habitats in the Firehole River and Hayden Valley. In 2003, the entire population numbered 1,477. Bison were trapped and herds periodically reduced until 1967, when only 397 bison were counted parkwide. All bison herd reduction activities were phased out after 1966, again allowing natural ecological processes to determine bison numbers and distribution. Presently, the park's bison population is estimated at 4,000.
Bison are nomadic grazers, wandering high on Yellowstone's grassy plateaus in summer. Despite their slow gait, bison are surprisingly fast for animals that weigh more than half a ton. In winter, they use their large heads like a plow to push aside snow and find winter food. In the park interior where snows are deep, they winter in thermally influenced areas and around the geyser basins. Bison also move to winter range in the northern part of Yellowstone.
Bears
, the grizzly bear population within the Greater Yellowstone Ecosystem was estimated at 718, with a minimum of 640 and a maximum of 796. The black bear population within the same ecosystem was estimated at 575, with a minimum of 500 and a maximum of 650.While in spawning streams, Yellowstone cutthroat trout are preyed upon by numerous predators including black bears and grizzly bears. Due to their high digestibility, and protein and lipid content, spawning cutthroat trout are one of the highest sources of net digestible energy for grizzly bears in the Yellowstone ecosystem. Cutthroat trout are an important late-spring and early-summer food source for bears, providing them the opportunity to regain body mass after den emergence, and assisting females with cubs meet the energetic demands of lactation. The average lifespan of a grizzly bear is about 22 years, and the average lifespan of a black bear is about 17 years.
With the reintroduction of gray wolves to Yellowstone National Park, much interest has been shown regarding the effects of a restored wolf population on both grizzly bears and black bears. Grizzly bears, black bears, and gray wolves have historically coexisted in much of the same range throughout a large portion of North America.
Bears were once commonly observed along roadsides and within developed areas of Yellowstone National Park. Bears were attracted to these areas by the availability of human foods in the form of handouts and unsecured camp groceries and garbage. Although having bears readily visible along roadsides and within developed areas was very popular with park visitors, an average of 48 bear-caused human injuries occurred each year from 1930 through 1969. Rocky Mountain grizzly bears have killed several people in the park since the 1970s.
Image:Bear approaching vehicle in Yellowstone National Park 1967.jpg|thumb|Black bear searching for food in a camper
Park authorities initiated an intensive bear management program in 1970. The objectives were restoring the grizzly bear and black bear populations to subsistence on natural forage, and reducing bear-caused injuries to humans. As part of the bear management program, regulations prohibiting the feeding of bears were strictly enforced. As the bears became more desperate for food and more aggressive, more of them were encountered in camping areas. Over a hundred grizzly bears had to be euthanized in the next several years, putting the park's bear population on the brink of extinction. On July 28, 1975, under the authority of the Endangered Species Act, the United States Fish and Wildlife Service listed the grizzly bear as a threatened species in the lower 48 states.
Over the next several decades, the bears learned to hunt and forage for themselves from non-human food sources, and their population slowly grew. On March 22, 2007, the grizzly bear was taken off the endangered species list. In the years since it was listed as a threatened species, the Yellowstone grizzly bear population has increased to at least 640 by 2017.
From 1980 to 2002, over 62 million people visited Yellowstone National Park. During the same period, 32 people were injured by bears. Grizzly bear-inflicted injuries to humans in developed areas averaged approximately one per year during the 1930s through the 1950s, and four per year during the 1960s. Human injuries from black bears have decreased from averages of 46 per year from 1931 to 1969, to four per year during the 1970s, and less than one per year from 1980 to 2002. The chance of being injured by a bear while in the park is approximately one in 1.9 million. Eight known bear-caused human fatalities have occurred within the park since 1872, including two in 2011 and one in 2015. Seven of the eight bears were grizzlies, while the other was undetermined.
Bobcats
In the early years of the 20th century, bobcats were reported as "somewhat common" in the park. There have been 9 to 14 reported sightings each decade since 1960. These sightings have occurred throughout the park; about 80 percent have occurred in the northern half. Bobcats have been reported in about equal numbers during all seasons. In 1960, a bobcat was killed by a car near Squaw Lake on the north shore of Yellowstone Lake; its skull was deposited in the Yellowstone Museum collection. Other roadkilled bobcats were reported in 1993 and 1996. In 1960, a young bobcat was reported on the porch of the administration building at Mammoth; other young bobcats have been reported at Pebble Creek bridge and at Canyon campground, where one accompanied an adult bobcat.No research has been conducted in Yellowstone to determine the numbers or distribution of this elusive animal that usually is solitary, nocturnal, and widely scattered over its range.
Unlike Canadian lynx, which they resemble, bobcats elsewhere have been highly adaptable to human-caused changes in environmental conditions; some biologists believe that there are more bobcats in the United States today than in colonial times. Yellowstone has many rock outcrops, canyons bordered by rock ledges, conifer forests, and semi-open areas that seem to offer conditions favorable for bobcats—adequate shelter, a variety of rodents, rabbits, hares, birds, and other small animals as well as seasonal carrion, for food. Carrion is seldom used if live prey is available. Studies elsewhere have shown that bobcats also may kill both young and adult antelope and deer; they stalk bedded adults and may be carried long distances while biting their prey in the neck. Bobcats live an average lifespan of about 7 years.
Visitors are advised to report any sightings of bobcats or bobcat tracks to a ranger or visitor center. For animals so seldom recorded, every observation is considered useful and important.
Canada lynx
The Canada lynx is listed as a threatened species under the Endangered Species Act. Biologists studying the lynx in Yellowstone believe it has persisted in the park in some number since the park's creation in 1872. A four-year study completed in 2005 concluded there is a small resident population of lynx in the park, but it is rarely seen directly or indirectly by either biologists or visitors.Coyotes
Yellowstone's coyotes are among the largest coyotes in the United States; adults average about 30 pounds. and some weigh around 40 pounds.Coyotes live an average of about six years, although one Yellowstone coyote lived to be more than 24 before she was killed and eaten by a cougar. The coyote is a common predator in the park, often seen alone or in packs, traveling through the park's wide open valleys hunting small mammals. But they are widely distributed and their sign can also be found in the forests and thermal areas throughout Yellowstone. They are capable of killing large prey, especially when they cooperatively hunt.
The reintroduction of wolves in 1995 has significantly decreased the coyote population, although those who remain often scavenge from wolf kills. Throughout the restoration project, coyote research has continued, with an eye toward identifying the interactions between coyotes and wolves and on assessing the effects of wolves on coyote populations. During planning and environmental assessment of the effects of wolf restoration, biologists anticipated that coyotes would compete with the larger canid, perhaps resulting in disruption of packs and numerical declines.
Coyotes occasionally lose their wariness of humans and frequent roadsides or developed areas, becoming conditioned to human food by receiving handouts or picking up food scraps. They can quickly learn bad habits like roadside begging behavior. This leads to potential danger for humans and coyotes. Several instances of coyote aggression toward humans have occurred in the park, including one that involved an actual attack. Habituation most likely played a role in this unusual coyote behavior.