Yellowstone National Park, spanning over 2.2 million acres across Wyoming, Montana, and Idaho, is a vast and diverse ecosystem. Its landscape, characterized by lakes, canyons, rivers, and mountain ranges, serves as a haven for a wide array of wildlife. Yellowstone supports the largest concentration of mammals in the lower 48 states, and its varied habitats contribute to exceptional biodiversity, making it a premier destination for observing animals.
Iconic Mammals
Yellowstone National Park is home to several iconic mammal species, including American Bison, Grizzly Bears, Black Bears, Gray Wolves, and Elk. These animals are often considered the park’s “big five” and play interconnected roles within its dynamic ecosystem.
American Bison represent a significant conservation success story in Yellowstone, as the park is the only place in the United States where bison have lived continuously since prehistoric times. Their population, ranging from 3,500 to nearly 6,000 individuals, is the largest free-roaming herd on public land. Bison are primarily grazers, with over 90% of their diet consisting of grasses and sedges. Their grazing habits and wallowing behaviors help maintain grassland diversity and create microhabitats for other species.
Yellowstone is one of the few places in the lower 48 states where both Grizzly Bears and Black Bears coexist. Grizzly bear populations in the Greater Yellowstone Ecosystem have increased from 136 in 1975 to an estimated 1,030 in 2024. These large omnivores, weighing 400-700 pounds, can run up to 40 miles per hour and are adept swimmers. They adapt their diet seasonally, consuming grasses and sedges in summer and whitebark pine nuts in the fall. Black bears, while often black, can also be brown, cinnamon, or blonde, and are generally smaller than grizzlies, lacking the distinct shoulder hump. Their diet is omnivorous, including berries, nuts, insects, and small mammals, and they are more arboreal, often climbing trees.
The reintroduction of Gray Wolves to Yellowstone in 1995 and 1996 marked a significant ecological restoration effort. Wolves had been eradicated by the early 20th century, leading to an ecosystem imbalance. Their reintroduction triggered a “trophic cascade,” influencing the behavior and population of elk, their primary prey. As of January 2024, an estimated 124 wolves reside within the park, forming about 10 distinct packs.
Elk are the most abundant large mammal in Yellowstone, with summer populations ranging from 10,000 to 20,000 individuals across six to seven herds. They are essential to the park’s food web, comprising about 85% of wolves’ winter kills and serving as a food source for bears, mountain lions, and scavengers. Elk are sociable, forming large summer herds and migrating to lower elevations with shallower snow during winter. The reintroduction of wolves has led to a more sustainable elk population, which had previously surged and overgrazed young trees like aspen.
Diverse Terrestrial Mammals
Yellowstone’s diverse habitats support a wide array of other terrestrial mammals. Moose are found in wetland and riparian areas, browsing on willows and other woody vegetation. Bighorn Sheep inhabit rugged mountainous terrain, particularly in the northern section of the park, navigating steep, rocky slopes with agility.
Mule Deer and Pronghorn are common ungulates in Yellowstone. Mule deer are widespread, often seen in forested areas and open meadows, identifiable by their large ears and bifurcated antlers. Pronghorn, known for their speed, prefer open grasslands and sagebrush steppe, using their keen eyesight to detect predators from a distance.
Coyotes and Red Foxes are frequently observed throughout the park, acting as opportunistic hunters and scavengers. Coyotes are adaptable canids, while red foxes, with their distinctive reddish-orange fur, are often found in mixed forest and open country. More elusive carnivores include Bobcats and Mountain Lions. Bobcats are medium-sized felines that prefer rocky areas and forests, preying on small mammals and birds. Mountain lions, the largest cat species in the park, are powerful ambush predators that primarily hunt deer and elk, though they are rarely seen due to their secretive nature.
Badgers are burrowing predators that primarily hunt rodents in open, grassy areas. River Otters are semi-aquatic mammals found along the park’s waterways, known for their playful behavior and fish diet. Beavers, through their dam-building, create and modify wetland habitats, supporting numerous other species. Various species of squirrels and marmots are abundant, serving as a food source for many predators and contributing to seed dispersal.
Rich Avian Life
Yellowstone National Park’s varied landscapes, from dense forests to expansive wetlands and mountain ranges, create ideal conditions for a diverse array of avian life. Nearly 300 species of birds have been documented within the park, with approximately 150 species regularly nesting there. This includes a wide range of raptors.
Bald Eagles, with their distinctive white heads and tails, are often seen soaring above lakes and rivers, preying on fish. Ospreys, also skilled fish-eaters, build large stick nests near water bodies. Various species of hawks, such as Red-tailed Hawks, are common, hunting rodents and other small prey. Owls, including Great Horned Owls and Northern Hawk Owls, are present throughout the park, with many species being nocturnal hunters.
Waterfowl are abundant in Yellowstone’s lakes, rivers, and ponds. Trumpeter Swans, the largest wild waterfowl in North America, are notable for their impressive wingspan and unique calls. Various species of ducks, including Mallards and Green-winged Teal, and geese, such as Canada Geese, utilize the park’s aquatic habitats for breeding and foraging.
Songbirds inhabit forests, meadows, and riparian zones, including species like American Robins, Mountain Bluebirds, and various warblers. Scavengers, such as the Common Raven, are an integral part of the avian community, often seen near large mammal carcasses, playing a role in nutrient recycling.
Aquatic and Other Wildlife
Yellowstone’s extensive network of rivers, lakes, and wetlands supports a variety of aquatic wildlife. The park contains over 600 lakes and ponds and approximately 2,500 miles of running water.
Native fish species are a crucial component of these aquatic environments. The Yellowstone Cutthroat Trout is a primary food source for many animals, including grizzly bears, otters, and various bird species. Other native fish found in the park’s waters contribute to the overall aquatic biodiversity.
Amphibians are present in Yellowstone’s moist environments. Boreal Chorus Frogs, recognized by their distinctive “creaking” call, are found in wetlands and near ponds. Western Toads are another common amphibian, often seen near water or in damp areas during breeding season.
Reptiles are less diverse in Yellowstone due to the cooler climate, but several species of snakes and lizards inhabit the park. Garter Snakes are the most commonly encountered reptiles, often found near water sources where they hunt amphibians and small fish. These diverse groups of animals are integral to the park’s ecological balance, demonstrating the interconnectedness of all life within Yellowstone.