Colorado is defined by dramatic contrasts, where the flat expanse of the Great Plains meets the jagged peaks of the Rocky Mountains. This incredible geographic variation, including a vertical climb of over 10,000 feet, creates a mosaic of ecological zones. The resulting landscape supports extraordinary biological diversity, hosting hundreds of vertebrate species adapted to everything from arid scrublands to alpine tundra. This overview explores the major animal groups—mammals, reptiles, amphibians, birds, and aquatic life—that thrive across the state’s varied terrain.
Colorado’s Mammalian Diversity
Colorado is home to approximately 128 native species of mammals. The state’s large herbivores are highly visible and include the Rocky Mountain elk, which represents one of the largest herds in North America. Mule deer are common, distinguishable by their large, mule-like ears and bounding gait. The smaller white-tailed deer is found predominantly in riparian areas and on the eastern plains.
Other large ungulates include the American bison, which roam in protected herds, and the bighorn sheep, the state’s mammal, known for its climbing ability on steep, rocky slopes. Moose, a more recently established population, are found in the state’s wetter, subalpine environments, especially those with willow thickets.
The predator guild includes the mountain lion, an apex hunter that is solitary and highly elusive, preying mainly on deer and elk. Black bears are widespread and omnivorous, their diet consisting mainly of berries, nuts, and insects, though they often seek out human food sources. In a significant conservation effort, the gray wolf has been reintroduced via a voter-mandated program, with initial releases occurring in December 2023 on the Western Slope.
Small mammals and rodents comprise the largest portion of the state’s diversity, with over 50 species of rodents alone. The American pika, a small relative of the rabbit, is adapted to high-altitude living, collecting and storing vegetation in haypiles for winter survival. Black-tailed prairie dogs are a keystone species whose extensive burrow systems provide habitat for numerous other animals, including the endangered black-footed ferret. Eighteen species of bats, such as the migratory Mexican free-tailed bat, also contribute to the state’s fauna.
Reptiles and Amphibians of the State
Reptiles and amphibians (herpetofauna) are present throughout Colorado, though their distribution is limited by their dependence on external heat sources. The state is home to a variety of snakes, lizards, and turtles, with snakes being the most numerous group. Non-venomous species like the bullsnake are widespread and often attain lengths exceeding six feet.
The bullsnake is beneficial to agriculture due to its diet of rodents and is often mistaken for a rattlesnake when it defensively hisses and vibrates its tail. Other common non-venomous snakes include the striped plains garter snake, found near water sources, and the yellow-bellied racer. Colorado is home to three species of venomous rattlesnakes: the prairie rattlesnake, the midget faded rattlesnake, and the western massasauga.
Lizards are restricted to the warmer, drier areas of the state, particularly the western canyons and eastern plains. Species such as the six-lined racerunner and the western whiptail are fast-moving, diurnal hunters. The greater short-horned lizard utilizes camouflage to blend into rocky and sandy environments.
Amphibians include frogs, toads, and salamanders, all requiring moist habitats for reproduction. The tiger salamander is the state’s largest terrestrial amphibian, often found in aquatic environments from temporary ponds to irrigation ditches. Common toads, like the Woodhouse’s toad, possess parotoid glands that secrete a toxin for defense.
Chorus frogs are abundant near wetlands, often signaling spring with their distinctive, loud calls. The presence of amphibians like the northern leopard frog is used as an indicator of water quality, highlighting their sensitivity to environmental changes.
Avian and Aquatic Life
Colorado’s location along major migratory flyways and its varied elevations support a vast number of bird species. Raptors are prominent; bald eagles are often seen during winter near open water, and the peregrine falcon nests on high cliffs. Red-tailed hawks and golden eagles are common across the plains and mountains, utilizing updrafts to scan for prey.
Upland game birds include the wild turkey, found in foothills and montane forests, and the white-tailed ptarmigan, a resident of the alpine tundra whose plumage changes seasonally for camouflage. Waterfowl, such as ducks and geese, rely on the numerous lakes, reservoirs, and riparian corridors for breeding and resting during migration. Smaller songbirds like the mountain bluebird and American robin inhabit every ecological zone below the treeline.
The aquatic life of Colorado is influenced by its headwater status, with cold, clear streams supporting numerous fish species. Trout are the most iconic aquatic species, attracting anglers. The non-native rainbow trout is widely stocked, but native cutthroat trout subspecies are the focus of conservation efforts.
The state is home to three native subspecies of cutthroat trout: the Greenback, the Rio Grande, and the Colorado River cutthroat, each historically occupying different drainages. These fish require cold, oxygenated water, limiting their distribution primarily to high-elevation streams and lakes. Warm-water fish, such as walleye and bass, are found in lower-elevation reservoirs and ponds.
Ecological Zones and Wildlife Distribution
Wildlife distribution is directly tied to Colorado’s distinct ecological zones, which change dramatically with elevation and moisture. The Eastern Plains, characterized by shortgrass and mixed-grass prairie, support species adapted to open, semi-arid environments. Animals like the pronghorn, the fastest land mammal in North America, graze alongside prairie dogs.
Moving westward, the Foothills and Montane Zones (5,500 to 9,000 feet) are transitional areas dominated by Ponderosa pine and Gambel oak. This zone is a primary habitat for mule deer and black bears, offering a mix of cover and foraging opportunities. The mixed conifer forests provide diverse vertical structure utilized by many species of raptors and songbirds.
The Subalpine and Alpine Tundra Zones represent the highest elevations, with the treeline marking the transition to the tundra above 11,000 feet. The specialized conditions, including short growing seasons and high winds, support hardy mammals like the mountain goat and the yellow-bellied marmot. The American pika is restricted to the rocky talus slopes, relying on the insulating snowpack for winter survival.
The Western Slope and Canyonlands feature arid environments and Pinyon-Juniper woodlands, which are important for reptiles and certain mammals. These warmer, drier conditions allow for greater concentrations of lizards, such as whiptails, and snakes, including the midget faded rattlesnake. Large elk herds inhabit the sagebrush steppe and forested areas, where the newly reintroduced gray wolves are expected to establish themselves.