Animals in Yellowstone National Park | Wildlife of Yellowstone

Yellowstone National Park Animals | Wildlife of Yellowstone

Yellowstone National Park is more than geysers, canyons, and hot springs—it’s a living, breathing wilderness teeming with some of North America’s most iconic animals. From powerful predators to elusive creatures, the wildlife of Yellowstone offers visitors unforgettable encounters and a glimpse into nature’s raw beauty.

If you’re dreaming of spotting wolves, grizzly bears, bison, or bald eagles, here’s everything you need to know about the animals that roam Yellowstone National Park’s 2.2 million acres of protected habitat.

Mammals

Yellowstone National Park is indeed renowned for having the largest concentration of mammals in the lower 48 states, boasting a rich predator-prey complex that is a key feature of its ecosystem. 

Yellowstone National Park's rich diversity of mammals includes 67 different species, ranging from small mammals to large predators. 

The park's vast and diverse habitats support a remarkable variety of species, including eight ungulate species (bison, elk, bighorn sheep, moose, mountain goats, mule deer, pronghorn, and white-tailed deer) and seven large predators (grizzly bears, black bears, Canada lynx, coyotes, mountain lions, wolverines, and wolves), making it an unparalleled sanctuary for wildlife.

Here are some of the iconic and notable Mammals species found in Yellowstone:

1. American Bison:

Yellowstone is home to one of the largest wild bison herds in North America. The park is the only place in the United States where bison have lived continuously since prehistoric times. The bison population is estimated to be around 5,000, making it one of the largest herds in North America. These iconic mammals can be seen throughout the park, especially in the Lamar Valley and Hayden Valley.

Bison are known for their massive size, with adult males (bulls) weighing up to 2,000 pounds and standing about 6 feet tall at the shoulder. Females (cows) are smaller, weighing around 1,000 pounds. Despite their size, bison are surprisingly agile and can run at speeds of up to 35 miles per hour. They are also excellent swimmers, capable of crossing rivers in search of food.

Bison hold great cultural significance for many Native American tribes, who have revered them as a source of food, clothing, and spiritual inspiration for thousands of years. The bison's survival and resurgence in Yellowstone are not only a conservation success but also a symbol of resilience and renewal.

Visitors to Yellowstone are often thrilled to see bison up close, particularly in areas like the Lamar Valley and Hayden Valley, where they are most commonly found. However, bison are wild animals and can be dangerous if approached too closely. Park guidelines advise keeping a safe distance of at least 25 yards (23 meters) from bison to avoid dangerous encounters.

Bison in Yellowstone National Park

Bison Herd in Yellowstone National Park

2. Elk:

Elk (Cervus canadensis) are among the most prominent and frequently seen large mammals in Yellowstone National Park. These majestic creatures, also known as wapiti, play a vital role in the park’s ecosystem and are a key species for both wildlife enthusiasts and researchers.

Yellowstone is home to several elk herds, with the largest being the Northern Range herd. During the summer, tens of thousands of elk can be found throughout the park, particularly in the Lamar Valley, Hayden Valley, and the meadows around Mammoth Hot Springs. In the winter, many elk migrate to lower elevations outside the park to find food, while others remain in Yellowstone’s lower valleys.

Adult elk are large animals, with bulls (males) weighing between 700 and 1,100 pounds and standing about 5 feet at the shoulder. Cows (females) are smaller, weighing around 500 to 600 pounds. Bulls are known for their impressive antlers, which can span up to 4 feet across and are shed and regrown each year.

Elk are a favorite among visitors to Yellowstone, and they are often seen grazing in meadows or resting in forests. During the rut, visitors can witness the dramatic behavior of bulls vying for dominance, which is one of the most exciting wildlife spectacles in the park. However, it’s important for visitors to maintain a safe distance (25 yards) from elk, as they can be unpredictable, especially during the rut or when they feel threatened.

Elk in Yellowstone National Park

3. Bighorn Sheep:

Bighorn sheep (Ovis canadensis) are one of the most iconic and recognizable species in Yellowstone National Park. Known for their impressive curved horns and agile climbing abilities, these animals are well-adapted to the rugged terrain of the park's mountainous regions.

Yellowstone's bighorn sheep are typically found in the steep, rocky areas of the park, particularly in the northern range near Mount Washburn, the Gardner River Canyon, and other high-elevation areas.

Bighorn sheep are medium-sized ungulates, with rams (males) weighing between 150 and 300 pounds and ewes (females) weighing between 75 and 200 pounds. The most distinctive feature of bighorn sheep is the large, curved horns of the rams, which can weigh up to 30 pounds. These horns are not shed and continue to grow throughout the ram's life. Ewes also have horns, but they are much smaller and less curved.

Bighorn sheep are highly social animals, typically forming small groups known as bands. These bands usually consist of females and their young, while males often form separate groups outside the breeding season. Bighorn sheep are known for their agility and sure-footedness, allowing them to navigate steep and rocky terrain that is inaccessible to many predators.

Bighorn Sheep in Yellowstone National Park

Bighorn Sheep in Yellowstone National Park

4. Moose:

Moose (Alces alces) are the largest members of the deer family and one of the most striking animals found in Yellowstone National Park. Known for their towering height, long legs, and distinctive broad antlers, moose are a symbol of the park's wild and remote areas.

Yellowstone's moose population is relatively small compared to other large mammals in the park, with estimates ranging from a few hundred individuals. Moose are primarily found in the park's wetter areas, including marshes, lakeshores, and river valleys, where their preferred food sources are abundant. Some of the best places to spot moose in Yellowstone are the Lamar Valley, Hayden Valley, and along the Soda Butte Creek, as well as in the southwestern parts of the park near Bechler River and the surrounding wetlands.

Moose are the largest of the deer species, with adult males (bulls) standing up to 7 feet tall at the shoulder and weighing between 1,200 and 1,500 pounds. Females (cows) are slightly smaller, weighing between 800 and 1,300 pounds. The most recognizable feature of a bull moose is its antlers, which can span up to 6 feet across. These broad, flat antlers are shed and regrown annually, with new growth starting in the spring and reaching full size by late summer.

Moose in Yellowstone National Park

5. Mountain Goats:

Mountain goats (Oreamnos americanus) are a fascinating species found in the northern portions of Yellowstone National Park. Despite their name, mountain goats are more closely related to antelopes and are not true goats. They are well-adapted to the park’s rugged, high-altitude terrain.

Mountain goats are not native to Yellowstone; they were introduced to the park in the 1960s to provide hunting opportunities and to enhance wildlife viewing. They have since established populations in the park's mountainous regions. They are most commonly found in the northern part of the park, particularly in areas such as the Absaroka Range and the steep cliffs around the Lamar Valley. Mountain goats prefer steep, rocky areas with high elevations, where they can find food and avoid predators.

Mountain goats are known for their impressive climbing abilities and distinctive appearance. They have thick, white fur that provides insulation against the cold and allows them to blend into snowy environments. Adults have sturdy, curved horns that can grow up to 12 inches long. Males (bills) are larger and heavier than females (nannies), with males weighing between 150 and 300 pounds and females weighing between 100 and 200 pounds. Both sexes have strong hooves with rough pads that help them grip and navigate rocky surfaces.

Mountain Goat in Yellowstone National Park

6. Mule Deer:

Mule deer (Odocoileus hemionus) are a common and widely recognized species in Yellowstone National Park. Known for their distinctive large ears and adaptability, mule deer are an integral part of the park's diverse wildlife community.

Mule deer are found throughout Yellowstone, with notable populations in the northern and eastern parts of the park, including the Lamar Valley and Hayden Valley. They prefer a variety of habitats, from forested areas and shrublands to open meadows and river valleys. Mule deer are especially common in areas with a mix of vegetation types, which provide both food and cover.

Mule deer are named for their large, mule-like ears, which help them detect predators and regulate body temperature. They have a reddish-brown coat in the summer that turns to a grayish-brown in the winter. Adult males (bucks) typically weigh between 150 and 300 pounds, while females (does) are smaller, weighing between 100 and 150 pounds. Bucks are known for their antlers, which are typically forked and branch out into two main tines, growing larger each year. Unlike white-tailed deer, mule deer have antlers that fork rather than forming a single beam.

Mule Deer in Yellowstone National Park

Mule Deer in Yellowstone National Park

7. Pronghorn Antelope:

Pronghorn antelope (Antilocapra americana) are one of the most unique and fastest animals in North America, and they are a notable presence in Yellowstone National Park. They are the only members of their family, Antilocapridae, making them a distinct part of the park’s wildlife.

Pronghorns are found primarily in the northern and northeastern parts of Yellowstone, particularly in the Lamar Valley and surrounding areas. They prefer open grasslands, sagebrush flats, and areas with sparse vegetation, where they can easily spot predators and use their incredible speed to escape. The park's vast, open landscapes provide an ideal environment for pronghorns.

Pronghorns are easily recognizable by their unique features. They have a slender, agile body built for speed, with long legs and a sleek, reddish-brown coat with white markings on their underbelly, rump, and throat. Adult males (bucks) typically weigh between 120 and 150 pounds, while females (does) are slightly lighter. One of the most distinctive features of pronghorns is their horns. Males have longer, more curved horns with a distinctive prong or fork near the tip, while females have shorter, less curved horns. Both sexes have horns, but males' are more prominent and branched.

Pronghorns are known for their exceptional speed and endurance, which they use to evade predators. They are capable of running at speeds up to 55 miles per hour, making them the fastest land mammals in North America. This incredible speed allows them to escape from predators such as coyotes and mountain lions, though they are also adapted to outrun threats over long distances.

Pronghorn Antelope in Yellowstone National Park

Pronghorn Antelope in Yellowstone National Park

8. White-tailed Deer:

White-tailed deer (Odocoileus virginianus) are the most widespread and commonly recognized deer species in North America, and they are present in Yellowstone National Park, though they are less common there compared to other regions of their range. Their adaptability and distinctive features make them an interesting species within the park.

In Yellowstone, white-tailed deer are found primarily in the park's lower elevations, such as the northern and northeastern areas, including parts of the Lamar Valley and along the northern boundary. They tend to prefer habitats with dense cover, such as riparian areas, brushy edges, and forested regions, which provide both food and protection from predators. While their numbers in Yellowstone are not as high as those of mule deer, they still inhabit suitable areas throughout the park.

White-tailed deer are named for the distinctive white underside of their tail, which they raise as a flag when alarmed. This characteristic helps them communicate with other deer and signal danger. They have a reddish-brown coat in the summer that turns to a grayish-brown in the winter. Adult males (bucks) typically weigh between 150 and 300 pounds, while females (does) are smaller, weighing between 100 and 200 pounds. Bucks are known for their antlers, which are usually branched with a single main beam. Unlike mule deer, the antlers of white-tailed deer do not fork but instead form a series of tines along a single beam.

White-tailed deer are known for their agility and can quickly run, jump, and change direction to evade predators. They are often more elusive and wary than other deer species, and their tendency to seek cover in dense vegetation can make them harder to spot.

White-tailed Deer in Yellowstone National Park

9. Grizzly Bears:

Grizzly bears (Ursus arctos horribilis) are one of the most iconic and powerful mammals in Yellowstone National Park. They are a key species in the park's ecosystem and have a significant impact on the environment and the wildlife community.

Grizzly bears are found throughout Yellowstone National Park, particularly in the forested and mountainous regions, including the northern and eastern parts of the park. They inhabit a range of environments from dense forests to open meadows and river valleys. The estimated grizzly bear population in the Greater Yellowstone Ecosystem is around 1,063 individuals. Their habitat encompasses a variety of terrain types, which provides the diverse resources they need for survival.

Grizzly bears are large and robust animals with distinctive features. They have a pronounced muscular hump over their shoulders, which is created by a large muscle mass that supports their powerful forelimbs. Their fur color can vary from light brown to dark brown, and they often have a grizzled appearance, with lighter tips on their fur. Adult males (boars) typically weigh between 400 and 600 pounds, though some individuals can exceed 800 pounds. Females (sows) are generally smaller, weighing between 250 and 400 pounds.

Grizzly bears have strong claws, measuring up to 4 inches long, which they use for digging and foraging. Their large, powerful jaws and sharp teeth are adapted for a varied diet that includes both plant material and meat.

Grizzly bears are omnivorous and have a diverse diet that changes with the seasons. They eat a variety of foods including berries, roots, nuts, insects, fish, and small mammals. In the spring and summer, their diet consists largely of plant material and insects, while in the fall, they focus on high-calorie foods like berries and salmon to build up fat reserves for hibernation. Grizzly bears are known for their ability to catch and eat fish, particularly during the spawning season when salmon are abundant.

Grizzly bears were listed as a threatened species under the Endangered Species Act in 1975, largely due to habitat loss and conflicts with humans. However, thanks to conservation efforts, their populations have recovered significantly. In 2007, grizzly bears in the Greater Yellowstone Ecosystem were delisted from the Endangered Species Act, though they remain under state management and monitoring.

Seeing a grizzly bear in Yellowstone is a memorable experience, but it’s important for visitors to follow safety guidelines to ensure both their safety and the bears’ well-being. Visitors should always keep a safe distance from bears (at least 100 yards), never approach or feed them, and be aware of their surroundings. Grizzly bears are often seen in areas with abundant food sources, such as along riverbanks or in berry-rich meadows.

Grizzly Bear in Yellowstone National Park

Grizzly Bear in Yellowstone National Park

10. Black Bears:

Black bears (Ursus americanus) are another prominent species in Yellowstone National Park, known for their adaptability and diverse diet. They are one of the park's most commonly seen large mammals.

Black bears are found throughout Yellowstone, occupying a wide range of habitats including forests, meadows, and riparian areas. They are more common in the park compared to grizzly bears and can be spotted in various elevations from the lower valleys to the higher mountain areas. Their ability to adapt to different environments helps them thrive in the park’s diverse landscape.

Black bears vary in color from black to brown, with some individuals displaying a cinnamon or even a blonde color. They are generally smaller and less robust than grizzly bears. Adult males typically weigh between 150 and 300 pounds, while females are usually smaller, ranging from 100 to 200 pounds. Black bears have a more uniform build compared to grizzlies, lacking the pronounced shoulder hump and having relatively smaller claws and less muscular forelimbs.

Black bears are omnivorous and have a highly varied diet that includes fruits, nuts, seeds, insects, small mammals, and carrion. Their diet changes with the seasons; in the spring, they consume new growth vegetation, insects, and small animals, while in the summer and fall, they focus on high-calorie foods such as berries, nuts, and honey to build fat reserves for hibernation. They are also known to forage for and eat fish, though this is less common than in grizzly bears.

Black Bears in Yellowstone National Park

Black Bears in Yellowstone National Park

11. Gray Wolves:

Gray wolves (Canis lupus) are a keystone species in Yellowstone National Park, playing a crucial role in the park's ecological balance. Their reintroduction and subsequent recovery have had significant impacts on the park’s ecosystems.

Gray wolves were reintroduced to Yellowstone in 1995 after being extirpated from the park in the 1920s. This reintroduction was part of a broader effort to restore the species to its historical range and to balance the park's predator-prey dynamics. As of January 2024, approximately 108 gray wolves were estimated to live primarily in Yellowstone National Park. The population has fluctuated over the years due to various factors, including prey availability, disease, and human activity.

Gray wolves are the largest members of the Canidae family in North America. Adults typically weigh between 70 and 110 pounds, with males generally being larger than females. They have a diverse coat color that can range from white and gray to brown and black. Their fur is dense and provides insulation against cold temperatures. Wolves have long legs, a bushy tail, and large, rounded ears, and they possess strong jaws and sharp teeth adapted for hunting and consuming meat.

Gray wolves are social animals that live and hunt in packs. A typical wolf pack consists of an alpha pair (the breeding pair) and their offspring, which may include several generations. Pack sizes can vary but usually range from 4 to 8 wolves. The pack structure helps them effectively hunt and defend their territory.

Wolves are apex predators and primarily prey on large ungulates such as elk, bison, and mule deer. They hunt in coordinated groups, using strategies to isolate and bring down their prey. In addition to hunting, wolves scavenge and may feed on smaller mammals and carrion when larger prey is not available. Their predation helps regulate ungulate populations and contributes to the health of the park’s ecosystems by preventing overgrazing and allowing vegetation to recover.

Observing gray wolves in Yellowstone can be a rare and exciting experience. They are often seen in the Lamar Valley and other areas with high concentrations of prey. Wolves are more active during early morning and late evening, making these times the best for spotting them. Visitors should use binoculars or spotting scopes to view wolves from a safe distance, as they are sensitive to human presence.

Gray Wolves in Yellowstone National Park

Pack of Wolves Attacking Bison in Yellowstone National Park

12. Wolverines:

Wolverines (Gulo gulo) are among the most elusive and robust predators in Yellowstone National Park, known for their strength, tenacity, and solitary behavior. They are a unique and intriguing part of the park's wildlife.

Wolverines are relatively rare in Yellowstone, and their populations are small compared to other large mammals. They inhabit the park's higher elevations, including the mountainous and remote regions, where they can find suitable habitat with abundant prey and cover. Their preference for rugged terrain and remote areas contributes to their elusive nature and makes them less frequently seen by visitors.

Wolverines are the largest members of the weasel family (Mustelidae). They have a stocky, muscular build with short legs, a broad head, and a thick, bushy tail. Their fur is dense and provides insulation against harsh winter conditions. Wolverines typically weigh between 20 and 40 pounds, with males being slightly larger than females. They have strong jaws and sharp claws adapted for digging and tearing apart carcasses.

Wolverines are solitary animals with large home ranges. They are known for their aggressive and opportunistic feeding habits. Wolverines have a varied diet that includes carrion, small mammals, birds, and occasionally the young of larger mammals. They are capable of taking down prey much larger than themselves and are known to scavenge from kills made by other predators, such as wolves and bears.

Wolverines are highly mobile and have large territories, which they defend from other wolverines. They are well-adapted to cold environments and often cache food to eat later, a behavior that helps them survive through the winter months when food is scarce.

Wolverine in Yellowstone National Park

13. Coyotes:

Coyotes (Canis latrans) are highly adaptable and widespread members of the canid family, and they are common inhabitants of Yellowstone National Park. Their presence adds to the park's dynamic predator-prey interactions.

Coyotes are versatile and can thrive in a variety of habitats, from deserts to forests and grasslands. In Yellowstone, they are found throughout the park, including in open meadows, forest edges, and along river valleys. They are often seen in lower elevations and are well adapted to the park's diverse environments.

Coyotes are medium-sized canids with a slender build, long legs, and a bushy tail. They have a varied coat color, typically ranging from gray to reddish-brown, with a lighter underbelly and distinctive facial markings. Adult coyotes generally weigh between 24 and 46 pounds, with males being slightly larger than females. They have a narrow snout, large ears, and a sharp, bushy tail.

Coyotes are opportunistic feeders and have a highly varied diet. They are omnivorous and eat a wide range of foods, including small mammals (like rodents and rabbits), birds, insects, fruits, and carrion. Their diet changes with the seasons and availability of food sources. Coyotes are known for their adaptability and ability to exploit different food sources based on what is available.

Coyotes are often seen throughout Yellowstone, particularly in the early morning and late evening when they are most active. They can be spotted in meadows, near water sources, or along the roadsides. Coyotes are relatively habituated to human presence, but it's important to observe them from a respectful distance. Visitors should use binoculars or spotting scopes to watch coyotes without disturbing them.

Coyote in Yellowstone National Park

14. Mountain Lions:

Mountain lions (Puma concolor), also known as cougars or pumas, are elusive and solitary predators in Yellowstone National Park. They play a crucial role in the park's ecosystem as apex predators.

Mountain lions are generally rare in Yellowstone but are present in the park, primarily in the more rugged and remote areas. They are found in various habitats within the park, including forested areas, mountainous terrain, and rugged canyons. Their preference for less accessible areas helps them avoid human contact and competition with other predators.

Mountain lions are large, powerful felines with a sleek, muscular build. They have a tawny or light brown coat, a white underbelly, and distinctive black markings on their tail tip and ears. Adult males typically weigh between 120 and 200 pounds, while females are smaller, weighing between 65 and 100 pounds. They have long, powerful legs and a strong tail that aids in balance and agility.

Mountain lions are solitary animals with large home ranges. They are highly adaptable and can prey on a variety of animals, including deer, elk, and smaller mammals. Their diet primarily consists of ungulates, particularly deer and elk, though they will also take smaller prey when available. Mountain lions use stealth and strength to ambush their prey, relying on their powerful muscles and sharp claws to bring down and subdue animals.

Mountain lions are primarily nocturnal and crepuscular, meaning they are most active during the dawn and dusk hours. They use their keen senses of sight and hearing to detect prey and navigate their territory. Their ability to climb and jump allows them to access different types of terrain and evade potential threats.

Observing mountain lions in Yellowstone is quite rare due to their elusive nature and preference for remote areas. They are typically seen only by those who venture into their less accessible habitats or who are fortunate enough to spot their tracks or signs. Visitors interested in seeing mountain lions should focus on areas with dense cover and be aware of the low likelihood of encountering them.

Mountain Lion in Yellowstone National Park

15. Canada lynx:

The Canada lynx (Lynx canadensis) is a rare and elusive predator found in Yellowstone National Park. Known for its distinctive features and specialized hunting skills, the lynx plays an important role in the park’s ecosystem.

Canada lynx are found in the higher elevations and forested areas of Yellowstone, particularly in the more remote and less disturbed parts of the park. They prefer dense coniferous forests with abundant snow, which provides them with the cover and hunting conditions they need. Their populations are generally low and can fluctuate based on prey availability and environmental conditions.

The Canada lynx is a medium-sized wildcat with several distinctive features. It has a short tail, tufted ears, and large, padded paws adapted for walking on snow. Its fur is thick and dense, ranging from gray to reddish-brown, with a light underbelly. Adult lynx typically weigh between 15 and 30 pounds, with males being larger than females. Their legs are relatively long, which helps them navigate snowy terrain.

Canada lynx are solitary and territorial animals. They primarily hunt at night and during the dawn and dusk hours. Their diet mainly consists of snowshoe hares, which are their primary prey. Lynx have specialized hunting adaptations that make them highly efficient at catching these hares. Their large, padded paws allow them to move easily through deep snow, and their keen senses help them locate and ambush prey.

Lynx are known for their stealth and patience when hunting. They rely on their excellent hearing and sight to detect the movements of hares. In times of prey scarcity, lynx may also hunt other small mammals, birds, and occasionally carrion.

Spotting Canada lynx in Yellowstone can be very challenging due to their elusive nature and the dense forest cover they prefer. Observations are rare and often require patience and luck. Signs of lynx activity, such as tracks or scat, may be more commonly found than the animals themselves.

Canada lynx in Yellowstone National Park

16. Red Foxes:

Red foxes (Vulpes vulpes) are adaptable and resourceful mammals found in various habitats across Yellowstone National Park. Known for their striking appearance and clever behavior, red foxes are a common sight in many areas of the park.

Red foxes are widely distributed throughout Yellowstone, inhabiting a range of environments including forests, meadows, and even the edges of human-developed areas. They are versatile animals that can adapt to different habitats, from dense woodlands to open grasslands and shrublands. In the park, they are often seen in areas with ample cover for hunting and denning, such as along the edges of forests and in areas with abundant prey.

Red foxes are medium-sized members of the canid family, with a body length of about 18 to 35 inches, excluding the tail, which adds an additional 12 to 22 inches. They weigh between 6 and 24 pounds, with males being larger than females. Their fur is typically reddish-orange with a white underbelly, a black-tipped tail, and black markings on their legs and ears. They have a slender body, long legs, and a bushy tail, which aids in balance and communication.

Red foxes are primarily nocturnal and crepuscular, being most active during the dawn and dusk hours. They are omnivorous and have a varied diet that includes small mammals (such as voles, mice, and rabbits), birds, insects, fruits, and carrion. They are skilled hunters and foragers, using their keen senses of sight and hearing to locate prey. Their ability to adapt their diet to available food sources helps them thrive in diverse environments.

Red foxes are known for their intelligence and problem-solving skills. They often cache food for later consumption, burying it in the ground to protect it from other animals. Their vocalizations include barks, screams, and howls, which they use to communicate with other foxes and to establish territory.

Red Fox in Yellowstone National Park

17. River Otters:

River otters (Lontra canadensis) are lively and playful mammals that inhabit the waterways of Yellowstone National Park. They are well-adapted to aquatic life and contribute to the park's biodiversity.

River otters are found throughout Yellowstone, including in rivers, streams, lakes, and wetlands. They prefer habitats with abundant water and a good supply of prey. In the park, they are often seen in areas like the Lamar Valley, the Yellowstone River, and various smaller streams and ponds.

River otters are medium-sized members of the weasel family (Mustelidae). They have a streamlined body, webbed feet, and a long, thick tail that helps with swimming. Their fur is dense and waterproof, typically brown or dark brown, which provides insulation in cold water. Adult river otters weigh between 10 and 30 pounds, with males being slightly larger than females. They have a rounded head, small ears, and keen eyes adapted for underwater vision.

River otters are highly social and often live in family groups or small social units. They are most active during the early morning and late afternoon, although they can be seen throughout the day. River otters are playful and engage in activities such as sliding down mud or snowbanks and wrestling with one another.

Their diet is primarily composed of fish, but they also eat amphibians, crustaceans, small mammals, and insects. River otters are skilled hunters and foragers, using their sharp senses and agility to catch prey in water. They are known for their ability to dive and swim underwater for extended periods.

River Otters in Yellowstone National Park

18. American Martens:

American martens (Martes americana) are elusive and agile members of the weasel family found in Yellowstone National Park. Known for their adaptability and elusive nature, martens are an integral part of the park’s forest ecosystems.

American martens are typically found in the mature, coniferous forests of Yellowstone. They prefer dense forests with abundant tree cover, which provides them with shelter and hunting opportunities. Martens are more commonly found in higher elevations, where they inhabit areas with plenty of dead trees, fallen logs, and thick undergrowth.

American martens are small, slender carnivores with a body length of 16 to 24 inches and a bushy tail that adds an additional 8 to 10 inches. They weigh between 1.5 and 3.5 pounds. Their fur is thick and soft, usually golden brown or dark brown, with a lighter-colored throat patch that is characteristic of the species. They have sharp claws and strong limbs adapted for climbing and maneuvering through trees.

American martens are solitary and territorial animals. They are highly agile and spend a lot of time climbing trees and exploring their arboreal habitat. They are primarily nocturnal and crepuscular, being most active during the dawn and dusk hours.

Martens are omnivorous but primarily carnivorous. Their diet consists of small mammals such as voles, squirrels, and birds. They also eat insects, fruits, and occasionally carrion. During winter, their diet may include snowshoe hares and other small prey that they can find under the snow.

American Marten in Yellowstone National Park

19. American Pikas:

American pikas (Ochotona princeps) are small, mountain-dwelling mammals that inhabit the rocky slopes and talus fields of Yellowstone National Park. They are known for their distinctive appearance and behavior, which make them a charming and interesting species to observe.

American pikas are typically found in high-altitude habitats, including boulder fields, talus slopes, and alpine meadows. In Yellowstone, they are commonly seen in the park’s mountainous areas, particularly in the northern and northeastern regions, such as the Lamar Valley and the Mammoth Hot Springs area. They prefer cooler temperatures and are often found in areas with ample rock cover that provides shelter and protection from predators.

Pikas are small, herbivorous mammals with a round body, short legs, and a short, stubby tail. They resemble a cross between a rabbit and a hamster, with rounded ears and a soft, dense coat that helps insulate them against cold temperatures. Pikas typically weigh between 6 and 9 ounces and have a body length of about 7 to 9 inches, including their tail. Their fur is usually a mix of gray, brown, and beige tones.

American pikas are diurnal, meaning they are active during the day, and they are known for their energetic and industrious nature. They are herbivores and primarily feed on a variety of grasses, herbs, and other plant material. Pikas are known for their behavior of collecting and storing food in "haypiles" during the summer months. They gather vegetation and store it in their caches to ensure they have enough food to last through the winter when snow covers the ground.

Pikas are highly territorial and often make vocal calls to communicate with other pikas and to defend their territory. They are well-adapted to their alpine environment, with strong climbing abilities and an ability to navigate rocky terrain with ease.

American Pika in Yellowstone National Park

20. North American Porcupines:

North American porcupines (Erethizon dorsatum) are fascinating and distinctive mammals found in Yellowstone National Park. Known for their unique appearance and defensive adaptations, porcupines are an integral part of the park's forest ecosystems.

Porcupines are found in various habitats throughout Yellowstone, including coniferous and mixed forests, shrublands, and occasionally near alpine meadows. They prefer habitats with abundant vegetation for food and shelter, as well as trees for climbing and denning. In the park, porcupines are often spotted in areas with dense tree cover where they can find both food and protection from predators.

North American porcupines are medium-sized rodents with a robust build. They typically weigh between 10 and 30 pounds and have a body length of about 25 to 36 inches, including their tail. Their most distinctive feature is their coat of sharp quills, which cover their back, sides, and tail. These quills are modified hairs that are barbed and can detach easily when they come into contact with a predator. The quills are typically yellowish to brownish, with some individuals having a more varied coloration.

Porcupines are primarily nocturnal, meaning they are most active during the night. They are herbivorous, feeding on a diet that includes leaves, twigs, bark, and fruits. In the winter, they often rely on tree bark and evergreen needles, which they can strip from trees using their strong teeth.

Porcupines are excellent climbers and spend a significant amount of time in trees, both foraging and seeking shelter. They are solitary animals and are typically found alone, except during the breeding season or when a mother is caring for her young.

The primary defense mechanism of porcupines is their quills. When threatened, a porcupine may raise its quills and make a hissing sound to warn potential predators. If a predator makes contact, the quills can become embedded in its skin, causing pain and discomfort. The quills are not poisonous but can cause infections if not properly removed.

Birds

Since its establishment in 1872, Yellowstone National Park has kept extensive records of bird sightings. These records have identified nearly 300 bird species, including raptors, songbirds, shorebirds, and waterfowl. Of these, around 150 species are known to nest within the park. The park’s diverse elevation and wide range of habitat types contribute to its rich avian diversity. 

Here's a list of notable bird species found in Yellowstone National Park:

Raptors:

• Bald Eagle
• Golden Eagle
• Osprey
• Peregrine Falcon
• Northern Harrier
• Red-tailed Hawk
• Swainson's Hawk

Bald Eagle in Yellowstone National Park

Owls:

• Great Horned Owl
• Barn Owl
• Northern Saw-whet Owl
• Long-eared Owl

Songbirds:

• Mountain Bluebird
• Yellow-rumped Warbler
• Western Tanager
• Song Sparrow
• Chipping Sparrow
• House Wren

Shorebirds:

• Killdeer
• Greater Yellowlegs
• Lesser Yellowlegs
• Spotted Sandpiper
• Wilson’s Snipe

Waterfowl:

• Mallard
• Northern Pintail
• American Black Duck
• Common Goldeneye
• Canada Goose
• Common Merganser
• Trumpeter Swan

Other Notable Birds:

• Common Loon
• Double-crested Cormorant
• American White Pelican
• American Dipper 
• Water Ouzel
• Raven
• Sandhill Crane
• Rock Wren
• Clark’s Nutcracker
• Black-capped Chickadee
• White-headed Woodpecker

Fish

Yellowstone’s rivers, lakes, and streams are home to several fish species, including native Yellowstone cutthroat trout, which are an important food source for many of the park’s predators, including bears, otters, and birds of prey. The park also has non-native fish species like brook trout and rainbow trout, introduced for sport fishing in the early 20th century.

Native Fish Species:

• Yellowstone Cutthroat Trout
• Westslope Cutthroat Trout
• Arctic Grayling
• Mountain Whitefish
• Rocky Mountain Sculpin
• Utah Chub
• Redside Shiner
• Longnose Dace
• Speckled Dace
• Mountain Sucker
• Longnose Sucker
• Utah Sucker

Nonnative Fish Species:

• Lake Trout
• Rainbow Trout
• Cutthroat x Rainbow Trout Hybrids
• Eastern Brook Trout
• Brown Trout
• Lake Chub

Reptiles

Yellowstone National Park supports a variety of reptile species adapted to its unique environments. These reptiles contribute to the park's ecological balance, thriving in habitats ranging from sagebrush flats to forested areas. Reptile species are few, with only six documented.

• Bullsnake
• Prairie Rattlesnake
• Rubber Boa
• Common Garter Snake
• Terrestrial Garter Snake
• Sagebrush Lizard

Amphibians

Yellowstone National Park is home to several amphibian species that thrive in its diverse habitats, from wetlands to forested areas. Amphibians in the park are crucial for maintaining ecological balance, serving as both predators and prey in their ecosystems. Key amphibians found in Yellowstone include:

• Western Tiger Salamander
• Boreal Chorus Frog
• Western Toad
• Columbia Spotted Frog
• Plains Spadefoot Toad

Invertebrates

Yellowstone is also home to countless invertebrates, such as butterflies, beetles, and bees, playing crucial roles in the park’s ecosystem. The park’s thermal areas, such as geysers and hot springs, are unique habitats for certain microorganisms and extremophiles that can survive in these harsh conditions.