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List of animals of Yellowstone

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List of animals of Yellowstone

Yellowstone National Park 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.

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 (cows) 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.

As of 2017, the grizzly bear (Ursus arctos horribilis) population within the Greater Yellowstone Ecosystem (Yellowstone and surrounding areas) was estimated at 718, with a minimum of 640 and a maximum of 796. The black bear (Ursus americanus) 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 (Canis lupus) 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.

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