Yellowstone is home to the largest concentration of mammals in the lower 48 states. In addition to having a diversity of small animals, Yellowstone is notable for its predator–prey complex of large mammals, including eight ungulate species (bighorn sheep, bison, elk, moose, mountain goats, mule deer, pronghorn, and white-tailed deer) and seven large predators (black bears, Canada lynx, coyotes, grizzly bears, mountain lions, wolverines, and wolves).
The National Park Service’s goal is to maintain the ecological processes that sustain these mammals and their habitats while monitoring the changes taking place in their populations. Seasonal or migratory movements take many species across the park boundary where they are subject to different management policies and uses of land by humans.
Understanding the links between climate change and these drivers will be critical to informing the ecology and management of Yellowstone’s wildlife in the years to come.
- 67 different mammals live here, including many small mammals.
- As of 2016, an estimated 690 grizzly bears live in the Greater Yellowstone Ecosystem.
- Black bears are common.
- Gray wolves were restored in 1995. As of January 2016, 99 live primarily in the park.
- Wolverine and lynx, which require large expanses of undisturbed habitat, live here.
- Seven native ungulate species—elk, mule deer, bison, moose, bighorn sheep, pronghorn, and white-tailed deer—live here.
- Nonnative mountain goats have colonized northern portions of the park.
Carnivores (Order Carnivora)
Carnivores all started out as meat-eaters, but many have evolved to be omnivores (consumers of plants and animals). Over a dozen carnivores can be found within the park.
- 22–28 inches long, 13–25 pounds.
- Short and stout; adapted to digging.
- Light body with dark stripe down back and darker feet. Broad head forms a wedge. Sides of face are white with black patches, white stripe from nose extends towards back.
- Prefers open areas like grasslands.
- Adapted to eat ground squirrels, pocket gophers, and other small rodents; will also eat ground-nesting birds and their eggs. Average badger needs to eat about two ground squirrels or pocket gophers a day to maintain its weight. Digs burrows in pursuit of prey.
- Adults preyed on by mountain lions, bears, and wolves. Coyotes and eagles will prey on young.
- Mostly solitary except in mating season (summer and early fall). Have delayed implantation; active gestation starts around February.
- Excavated dens are used for daytime resting sites, food storage, and giving birth. Typically have one entrance, marked by a mound of soil. May be inactive in their dens for up to a month in winter, but they are not true hibernators.
- Mostly active at night. May live up to 14 years.
The black bear (Ursus americanus) is the most common and widely distributed bear species in North America. However, the Greater Yellowstone Ecosystem is one of the few areas south of Canada where black bears coexist with the grizzly bears. From 1910 to the 1960s, park managers allowed visitors to feed black bears along park roads, although the National Park Service officially frowned on this activity. During this time, along with Old Faithful, black bears became the symbol of Yellowstone for many people, and are still what some people think of when Yellowstone bears are mentioned. Since 1960, park staff have sought to deter bears from becoming conditioned to human foods.
Number in Yellowstone
Where to See
Tower and Mammoth areas, most often.
Size and Behavior
- Males weigh 210–315 pounds, females weigh 135–200 pounds; adults stand about 3 feet at the shoulder.
- May live 15–30 years.
- Home range: male, 6–124 square miles, female, 2–45 square miles.
- Can climb trees; are adapted to life in forest and along forest edges.
- Food includes rodents, insects, elk calves, cutthroat trout, pine nuts, grasses, and other vegetation.
- Mates in spring; gives birth the following winter to 1–3 cubs.
- Considered true hibernators.
- Have fair eyesight and an exceptional sense of smell.
- Were fed by visitors from vehicles and, like grizzlies, used to be fed at dumps within the park.
- As a result, bears lost fear of humans and pursued human food, which resulted in visitor injuries, property damage, and the need to destroy “problem bears.”
Little is known about the black bear population in Yellowstone or whether it has been affected by the increase in grizzly bear numbers and distribution since the 1970s. Black bears are commonly observed in the park, especially on the northern range and in the Bechler area of the park. Black bears have few natural predators, although both cubs and adults are occasionally killed by their own kind or by the other large carnivores with which they compete for food—wolves, cougars, and grizzly bears. Vehicle collisions (average = 1 per year) and removals of nuisance bears (average = 1 every 5 years) are not common either. Most black bear mortality in the park is likely attributed to old age or other natural causes. Outside the park, some black bears are killed during state regulated hunting seasons. As their access to human foods has been reduced, human injuries from black bears in the park have decreased from an average of 45 per year during the 1930s–1960s to approximately one injury every five years since 1980. Black bears are occasionally radio-collared for management and scientific reasons, with the latter focusing on research on habitat selection and multi-carnivore interactions.
In Yellowstone, about 50% of black bears are black in color; others are brown, blond, and cinnamon. Black bears eat almost anything, including grass, fruits, tree cambium, eggs, insects, fish, elk calves, and carrion. Their short, curved claws enable them to climb trees but do not allow them to dig for roots or ants as well as a grizzly bear can.
The life cycle of black bears is similar to grizzly bears. Like grizzly bears, black bears spend most of their time during fall and early winter feeding during hyperphagia. In November, they locate or excavate a den on north-facing slopes between 5,800–8,600 feet (1,768–2,621 m), where they hibernate until late March.
Males and females without cubs are solitary, except during the mating season, May to early July. They may mate with a number of individuals, but occasionally a pair stays together for the entire period. Both genders usually begin breeding at age four. Like grizzly bears, black bears also experience delayed implantation. Total gestation time is 200 to 220 days, but only during the last half of this period does fetal development occur.
Birth occurs in mid-January to early February; the female becomes semiconscious during delivery. Usually two cubs are born. At birth, the cubs are blind, toothless, and almost hairless. After delivery the mother continues to sleep for another two months while the cubs nurse and sleep.
The Greater Yellowstone Ecosystem is one of the few areas south of Canada where black bears coexist with grizzly bears. Although grizzly bears in Yellowstone have been studied continuously for more than 50 years, very little research has been conducted on the park’s black bears since the 1960s. The last black bear study in YNP was completed during a period when black bear behavior was still influenced by the availability of human foods from garbage dumps, non-bear-proof garbage cans, and recreational hand feeding by park visitors along roadsides.
Thus, there is a scarcity of current information available for park managers to use in making decisions on black bear management. In a current study, a combination of GPS-tracking camera collars and non-invasive DNA samples from hair snares will help biologists learn more about the black bears’ population size and density, predatory rates on elk, home range sizes, movements, food habits, and habitat use.
Results from the data are still being analyzed, but some preliminary data have yielded insights. More black bear hair samples are being collected than was expected. GPS readings from tracking collars are showing male black bears to range farther than previously thought, and video from the collars has shown a new variety of food choices and behaviors.
Yellowstone is home to two species of bears: grizzly bears and black bears. Of the two species, grizzly bears have a much smaller range across the United States. The grizzly bear is typically larger than the black bear and has a large muscle mass above its shoulders; a concave, rather than straight or convex, facial profile; and much more aggressive behavior. The grizzly bear is a subspecies of brown bear that once roamed large swaths of the mountains and prairies of the American West. Today, the grizzly bear remains in a few isolated locations in the lower 48 states, including Yellowstone.In coastal Alaska and Eurasia, the grizzly bear is known as the brown bear.
Visitors should be aware that all bears are potentially dangerous. Park regulations require that people stay at least 100 yards (91 m) from bears (unless safely in your car as a bear moves by). Bears need your concern, not your food; it is against the law to feed any park wildlife, including bears.
The Greater Yellowstone Ecosystem and northwest Montana are the only areas south of Canada that still have large grizzly bear (Ursus arctos horribilis) populations. Grizzly bears were federally listed in the lower 48 states as a threatened species in 1975 due to unsustainable levels of human-caused mortality, habitat loss, and significant habitat alteration. Grizzly bears may range over hundreds of square miles, and the potential for conflicts with human activities, especially when human food is present, makes the presence of a viable grizzly population a continuing challenge for its human neighbors in the Greater Yellowstone Ecosystem.
Numbers in Yellowstone
Approximately 150 with home ranges wholly or partially in the park. As of 2018, 712 estimated in greater Yellowstone.
Where to See
Dawn and dusk in the Hayden and Lamar valleys, on the north slopes of Mt. Washburn, and from Fishing Bridge to the East Entrance.
Size and Behavior
- Males weigh 200–700 pounds, females weigh 200–400 pounds; adults stand about 31⁄2 feet at the shoulder.
- May live 15–30 years.
- Grizzly bears are generally 11⁄2 to 2 times larger than black bears of the same sex and age class within the same geographic region, and they have longer, more curved claws.
- Lifetime home range: male, 800–2,000 square miles, female, 300–550 square miles.
- Agile; can run up to 40 mph.
- Can climb trees, but curved claws and weight make this difficult. Can also swim and run up and downhill.
- Adapted to life in forest and meadows.
- Food includes rodents, insects, elk calves, cutthroat trout, roots, pine nuts, grasses, and large mammals.
- Mate in spring, but implantation of embryos is delayed until fall; gives birth in the winter; to 1–3 cubs.
- Considered super hibernators.
A behavioral note: Are grizzly bears overly attracted to menstrual odors?
The question whether menstruating women attract bears has not been completely answered. While there is no evidence that grizzly bears are overly attracted to menstrual odors more than any other odor and there is no statistical evidence that known bear attacks have been related to menstruation, certain precautions should be taken to reduce the risks of attack. The following precautions are recommended:
- Use pre-moistened, unscented cleaning towelettes.
- Use internal tampons instead of external pads. Do not bury tampons or pads (pack it in – pack it out). A bear may smell buried tampons or pads and dig them up. By providing bears a small food “reward,” this action may attract bears to other menstruating women.
- Place all used tampons, pads, and towelettes in double zip-loc baggies and store them unavailable to bears, just as you would store food. This means hung at least 10 feet above the ground and 4 feet from the tree trunk. Tampons can be burned in a campfire, but remember that it takes a very hot fire and considerable time to completely burn them. Any charred remains must be removed from the fire pit and stored with your other garbage.
- Many feminine products are heavily scented. Use only unscented or lightly scented items. Cosmetics, perfumes, and deodorants are unnecessary and may act as an attractant to bears.
- The U.S. Fish and Wildlife Service removed the grizzly bear population in the Greater Yellowstone Ecosystem from the federal threatened species list in June 2017. Read Grizzly Bears & the Endangered Species Act to learn more.
- Scientists and managers believe the grizzly population is doing well. Grizzlies are raising cubs in nearly all portions of the greater Yellowstone area and dispersing into new habitat. Currently, they occupy 20,522 square miles in the Greater Yellowstone Ecosystem.
The estimated Greater Yellowstone Ecosystem grizzly bear population increased from 136 in 1975 to a peak of 757 (estimated) in 2014. The 2018 population estimate is 712 bears. The bears have gradually expanded their occupied habitat by more than 50%. As monitored by the Interagency Grizzly Bear Study Team, the criteria used to determine whether the population within the Greater Yellowstone Ecosystem has recovered include estimated population size, distribution of females with cubs, and mortality rates. An estimated 150 grizzly bears occupy ranges that lie partly or entirely within Yellowstone. The number of females producing cubs in the park has remained relatively stable since 1996, suggesting that the park may be at or near ecological carrying capacity for grizzly bears.
There were 69 known or probable grizzly bear mortalities in the Greater Yellowstone Ecosystem in 2018 (51 in the Designated Management Area), including 10 adult females, 21 adult males, and 14 dependent young. There was one known grizzly bear death inside the park: an adult female of unknown age was found near the Lamar River. Cause of death is unknown, but was likely intra-specific conflict.
On August 23, 2018—for the first time in three years—a bear attack was reported in Yellowstone National Park. A family of four hikers from Washington state had a surprise encounter with an adult female grizzly bear on the Divide Trail. The sow charged out of the vegetation and knocked a 10-year-old boy to the ground. The child suffered an injured wrist, puncture wounds to the back and wounds around the buttocks. The parents successfully deployed bear spray and the bear left the scene. Further investigation determined that the female grizzly was defending at least one cub-of-the-year or yearling bear and no effort was made to search for them.
Where are the bears?
People who visited Yellowstone prior to the 1970s often remember seeing bears along roadsides and within developed areas of the park. Although observing these bears was very popular with park visitors, it was not good for people or bears. In 1970, the park initiated an intensive bear management program to return the grizzly and black bears to feeding on natural food sources and to reduce bear-caused human injuries and property damage. The measures included installing bear-proof garbage cans and closing garbage dumps in the park.
Bears are still seen near roads and they may be seen occasionally in the wild. Grizzly bears are active primarily at dawn, dusk, and night. In spring, they may be seen around Yellowstone Lake, Fishing Bridge, Hayden and Lamar valleys, Swan Lake Flats, and the East Entrance. In mid-summer, they are most commonly seen in the meadows between Tower–Roosevelt and Canyon, and in the Hayden and Lamar valleys. Black bears are most active at dawn and dusk, and sometimes during the middle of the day. Look for black bears in open spaces within or near forested areas. Black bears are most commonly observed between Mammoth, Tower, and the Northeast Entrance.
The grizzly bear’s color varies from blond to black, often with pale-tipped guard hairs. In the Greater Yellowstone Ecosystem, many grizzly bears have a light-brown girth band. However, the coloration of black and grizzly bears is so variable that it is not a reliable means of distinguishing the two species.
Bears are generally solitary, although they may tolerate other bears when food is plentiful. Grizzlies have a social hierarchy in which adult male bears dominate the best habitats and food sources, generally followed by mature females with cubs, then by other single adult bears. Subadult bears, who are just learning to live on their own away from mother’s protection, are most likely to be living in poor-quality habitat or in areas nearer roads and developments. Thus, young adult bears are most vulnerable to danger from humans and other bears, and to being conditioned to human foods. Food-conditioned bears are removed from the wild population.
Bears are generalist omnivores that can only poorly digest parts of plants. They typically forage for plants when they have the highest nutrient availability and digestibility. Although grizzly bears make substantial use of forested areas, they make more use of large, nonforested meadows and valleys than black bears. The longer, less curved claws and larger shoulder muscle mass of the grizzly bear makes it better suited to dig plants from the soil, and rodents from their caches.
Grizzly bear food consumption is influenced by annual and seasonal variations in available foods. Over the course of a year, army cutworm moths, whitebark pine nuts, ungulates, and cutthroat trout are the highest-quality food items available. In total, grizzly bears in the Greater Yellowstone Ecosystem are known to consume at least 266 species of plant (67%), invertebrate (15%), mammal (11%), fish, and fungi. They will eat human food and garbage where they can get it. This is why managers emphasize that keeping human foods secure from bears increases the likelihood that humans and bears can peacefully coexist in greater Yellowstone.
Bears spend most of their time feeding, especially during “hyperphagia,” the period in autumn when they may gain more than three pounds per day until they enter their dens to hibernate. In years and locations when whitebark pine nuts are available, they are the most important bear food from September through October. However, not all bears have access to whitebark pine nuts, and in the absence of this high-quality food, the bear’s omnivory lets them turn to different food sources. Fall foods also include pondweed root, sweet cicely root, grasses and sedges, bistort, yampa, strawberry, globe huckleberry, grouse whortleberry, buffaloberry, clover, horsetail, dandelion, ungulates (including carcasses), ants, false truffles, and army cutworm moths.
From late March to early May, when they come out of hibernation, until mid May, a grizzly bear’s diet primarily consists of elk, bison, and other ungulates. These ungulates are primarily winter-killed carrion (already dead and decaying animals), and elk calves killed by predation. Grizzly bears dig up caches made by pocket gophers. Other items consumed during spring include grasses and sedges, dandelion, clover, spring-beauty, horsetail, and ants. When there is an abundance of whitebark seeds left from the previous fall, grizzly bears will feed on seeds that red squirrels have stored in middens.
From June through August, grizzly bears consume thistle, biscuitroot, fireweed, and army cutworm moths in addition to grasses and sedges, dandelion, clover, spring-beauty, whitebark pine nuts, horsetail, and ants. Grizzly bears are rarely able to catch elk calves after mid-July. Starting around mid-summer, grizzly bears begin feeding on strawberry, globe huckleberry, grouse whortleberry, and buffaloberry. By late summer, false truffles, bistort, and yampa are included in the diet as grasses and others become less prominent.
Bears’ annual denning behavior probably evolved in response to seasonal food shortages and cold weather. Bears hibernate during the winter months in most of the world. The length of denning depends on latitude, and varies from a few days or weeks in Mexico to six months or more in Alaska. Pregnant females tend to den earlier and longer than other bears. Grizzly bear females without cubs in Greater Yellowstone den on average for about five months.
Grizzly bears will occasionally re-use a den in greater Yellowstone, especially those located in natural cavities like rock shelters. Dens created by digging, as opposed to natural cavities, usually cannot be reused because runoff causes them to collapse in the spring. Greater Yellowstone dens are typically dug in sandy soils and located on the mid to upper onethird of mildly steep slopes (30–60°) at 6,562–10,000 feet (2,000–3,048 m) in elevation. Grizzly bears often excavate dens at the base of a large tree on densely vegetated, north-facing slopes. This is desirable in greater Yellowstone because prevailing southwest winds accumulate snow on the northerly slopes and insulate dens from sub-zero temperatures.
The excavation of a den is typically completed in 3–7 days, during which a bear may move up to one ton of material. The den includes an entrance, a short tunnel, and a chamber. To minimize heat loss, the den entrance and chamber is usually just large enough for the bear to squeeze through and settle; a smaller opening will be covered with snow more quickly than a large opening. After excavation is complete, the bear covers the chamber floor with bedding material such as spruce boughs or duff, depending on what is available at the den site. The bedding material has many air pockets that trap body heat.
The body temperature of a hibernating bear, remains within 12°F (22°C) of their normal body temperature. This enables bears to react more quickly to danger than hibernators who have to warm up first. Because of their well-insulated pelts and their lower surface area-to-mass ratio compared to smaller hibernators, bears lose body heat more slowly, which enables them to cut their metabolic rate by 50–60%. Respiration in bears, normally 6–10 breaths per minute, decreases to 1 breath every 45 seconds during hibernation, and their heart rate drops from 40–50 beats per minute during the summer to 8–19 beats per minute during hibernation.
Bears sometimes awaken and leave their dens during the winter, but they generally do not eat, drink, defecate, or urinate during hibernation. They live off of a layer of fat built up prior to hibernation. The urea produced from fat metabolism (which is fatal at high levels) is broken down, and the resulting nitrogen is used by the bear to build protein that allows it to maintain muscle mass and organ tissues. Bears may lose 15–30% of their body weight but increase lean body mass during hibernation.
Bears emerge from their dens when temperatures warm up and food is available in the form of winter killed ungulates or early spring vegetation. Greater Yellowstone grizzly bears begin to emerge from their den in early February, and most bears have left their dens by early May. Males are likely to emerge before females. Most bears usually leave the vicinity of their dens within a week of emergence, while females with cubs typically remain within 1.86 miles (3 km) of their dens until late May.
Grizzly Bears, Black Bears, and Wolves
Grizzly bears are more aggressive than black bears, and more likely to rely on their size and aggressiveness to protect themselves and their cubs from predators and other perceived threats. Their evolution diverged from a common ancestor more than 3.5 million years ago, but their habitats only began to overlap about 13,000 years ago. Grizzly bears, black bears, and gray wolves have historically coexisted throughout a large portion of North America. The behavior of bears and wolves during interactions with each other are dependent upon many variables such as age, sex, reproductive status, prey availability, hunger, aggressiveness, numbers of animals, and previous experience in interacting with the other species. Most interactions between the species involve food, and they usually avoid each other. Few instances of bears and wolves killing each other have been documented. Wolves sometimes kill bears, but usually only cubs.
Wolves prey on ungulates year-round. Bears feed on ungulates primarily as winter-killed carcasses, ungulate calves in spring, wolf-killed carcasses in spring through fall, and weakened or injured male ungulates during the fall rut. Bears may benefit from the presence of wolves by taking carcasses that wolves have killed, making carcasses more available to bears throughout the year. If a bear wants a wolf-killed animal, the wolves will try to defend it; wolves usually fail to chase the bear away, although female grizzlies with cubs are seldom successful in taking a wolf-kill.
Number in Yellowstone
Unknown, but generally widespread.
Where to See
- Rarely seen; most reports from rocky areas and near rivers.
- Typical habitat: rocky areas, conifer forests.
Size and Behavior
- Adult: 15–30 pounds; 31–34 inches long.
- Color ranges from red-brown fur with indistinct markings to light buff with dark spotting; short tail; ear tufts.
- Distinguish from lynx: has several black rings that do not fully circle the tail; no black tip on tail, shorter ear tufts, smaller track (2 inches).
- Solitary, active between sunset and sunrise.
- Eats rabbits, hares, voles, mice, red squirrels, wrens, sparrows, grouse; may take deer and adult pronghorn.
Historical information suggests lynx were present, but uncommon, in Yellowstone National Park during 1880 to 1980. The presence and distribution of lynx in the park was documented during 2001 to 2004, when several individuals were detected in the vicinity of Yellowstone Lake and the Central Plateau. A lynx was photographed in 2007 along the Gibbon River, and another lynx was observed near Indian Creek Campground in the northwestern portion of Yellowstone during 2010. Tracks of an individual were verified near the Northeast Entrance in 2014. Reliable detections of lynx continue to occur in surrounding National Forest System lands. Evidence suggests lynx successfully reproduce in the GYE, though production is limited.
In 2000, the US Fish and Wildlife Service listed the lynx as “threatened” in the lower 48 states. Portions of the park and surrounding area is considered much of the critical habitat for the species in the Greater Yellowstone Ecosystem.
Lynx habitat in the Greater Yellowstone Ecosystem is often naturally patchy due to natural fire frequency and generally limited to conifer forests above 7,700 feet where the distribution of its primary prey, snowshoe hare, is often insufficient to support lynx residency and reproduction. The lower quality habitat means home ranges in this ecosystem are larger than those farther north, with lynx traveling long distances between foraging sites.
Number in Yellowstone
- Few; 112 known observations
Where to See
- Very rarely seen.
- Typical habitat: cold conifer forests.
Size and Behavior
- Adult: 16–35 pounds, 26–33 inches long.
- Gray brown fur with white, buff, brown on throat and ruff; tufted ears; short tail; hind legs longer than front.
- Distinguish from bobcat: black rings on tail are complete; tail tip solid black; longer ear tufts; larger track.
- Wide paws with fur in and around pads; allows lynx to run across snow.
- Track: 4–5 inches.
- Solitary, diurnal and nocturnal.
- Eats primarily snowshoe hares, especially in winter; also rodents, rabbits, birds, red squirrels, and other small mammals, particularly in summer.
The cougar (Puma concolor), also known as mountain lion, is the one of the largest cats in North America and a top predator native to Greater Yellowstone. (The jaguar, which occurs in New Mexico and Arizona, is larger.) As part of predator removal campaigns in the early 1900’s, cougars and wolves were killed throughout the lower 48 states, including national parks. Wolves (Canis lupus) were eradicated and, although cougars were probably eliminated from Yellowstone, the species survived in the West because of its cryptic nature and preference for rocky, rugged territory where the cats are difficult to track. Eventually the survivors re-established themselves in Yellowstone in the early 1980’s, possibly making their way from wilderness areas in central Idaho.
Number in Yellowstone
Estimated 25–35 (across all age classes) on the northern range; others in park seasonally.
Where to See
Behavior and Size
- Litters range from 2–3 kittens; 50% survive first year.
- Adult males weigh 145–170 pounds; females weigh 85–120 pounds; length, including tail, 6.5–7.5 feet.
- Average life span: males, 8–10 years; females, 12–14 years. Cougars living in areas where they are hunted have much shorter average life spans.
- Preferred terrain: rocky breaks and forested areas that provide cover for hunting prey and for escape from competitors such as wolves and bears.
- Prey primarily on elk and mule deer, plus smaller mammals, especially marmots.
- Bears and wolves frequently displace cougars from their kills.
- Male cougars may kill other male cougars within their territory.
- Adult cougars and kittens have been killed by wolves.
Interaction with Humans
Very few documented confrontations between cougars and humans have occurred in Yellowstone.
If a big cat is close by: Stay in a group; carry small children; make noise. Do not run, do not bend down to pick up sticks. Act dominant—stare in the cat’s eyes and show your teeth while making noise.
Though seldom seen by the public, biologists estimate that 20-31 adult cougars reside year-round in the northern range (an average of 12-18 females and 8-13 males). These estimates are based on field surveys and statistical analyses conducted from 2014–2017. Biologists found higher estimates in the later years of the study. The numbers do not include kitten and sub-adult cougars which accompany a portion of the adult females each year. Monitoring efforts since 2017 suggest a stable population consistent with these estimates for previous years.
While disease and starvation are occasional causes of cougar deaths, competition with other cougars or predators, and human hunting (during legal seasons outside protected areas) are the main causes of cougar mortality. Habitat fragmentation and loss are the main long-term threats to cougar populations across the western United States.
Cougars live throughout the park in summer, but few people ever see them. The northern range of Yellowstone is prime habitat for cougars because snowfall is light and prey always available. Cougars follow their main prey as they move to higher elevations in summer and lower elevations in the winter.
Adult male cougars are territorial and may kill other adult males in their home range. Male territories may overlap with several females. In non-hunted populations, such as in Yellowstone, the resident adult males living in an area the longest are the dominant males. These males sire most of the litters within a population; males not established in the same area have little opportunity for breeding.
Although cougars may breed and have kittens at any time of year, most populations have a peak breeding and birthing season. In Yellowstone, males and females breed primarily from February through May. Males and females without kittens search for one another by moving throughout their home ranges and communicating through visual and scent markers called scrapes. A female’s scrape conveys her reproductive status. A male’s scrape advertises his presence to females and warns other males that an area is occupied. After breeding, the males leave the female.
In Yellowstone, most kittens are born June through September. Female cougars den in a secure area with ample rock and/or vegetative cover. Kittens are about one pound at birth and gain about one pound per week for the first 8–10 weeks. During this time, they remain at the den while the mother makes short hunting trips and then returns to nurse her kittens. When the kittens are 8–10 weeks old, the female begins to hunt over a larger area. After making a kill, she moves the kittens to the kill. Before hunting again, she stashes the kittens. Kittens are rarely involved in killing until after their first year.
Most kittens leave their area of birth at 14 to 18 months of age. Approximately 99% of young males disperse 50 to 400 miles; about 70–80% of young females disperse 20 to 150 miles. The remaining proportion of males and females establish living areas near where they were born. Therefore, most resident adult males in Yellowstone are immigrants from other areas, thus maintaining genetic variability across a wide geographic area.
In Yellowstone, cougars prey upon elk (mostly calves) and deer. They stalk the animal then attack, aiming for the animal’s back and killing it with a bite to the base of the skull or the throat area.
A cougar eats until full, then caches the carcass for later meals. Cougars spend an average of 3–4 days consuming an elk or deer and 4–5 days hunting for the next meal. Cougars catch other animals—including red squirrels, porcupines, marmots, grouse, and moose—if the opportunity arises.
Cougars are solitary hunters who face competition for their kills from other large mammals. Even though a cached carcass is harder to detect, scavengers and competitors such as bears and wolves sometimes find it. In Yellowstone, black and grizzly bears will take over a cougar’s kill. Coyotes will try, but can be killed by the cougar instead. Wolves displace cougars from approximately 6% of their elk carcasses.
Although cougars and wolves once co-existed across much of their historical range, ecological research on each species has often had to be conducted in the absence of the other. By assessing pre- and post-wolf reintroduction data, biologists can learn about the ecological relationships between the two species. As social animals, wolves use different hunting techniques than the solitary cougar, but the two species prey on similar animals. While prey is abundant this competition is of little concern, but, a decrease in prey abundance could lead to an increase in competition between these carnivores.
In the early 1900s, cougars were killed as part of predator control in the park and likely eradicated along with wolves in the 1930s. However, cougars naturally recolonized by the early 1980s.
From 1987 to 1996, the first cougar ecology study was conducted in Yellowstone National Park. The research documented population dynamics of cougars in the northern Yellowstone ecosystem inside and outside the park boundary, determined home ranges and habitat requirements, and assessed the role of cougars as a predator. Of the 88 cougars that were captured, 80 were radio-collared.
From 1998 to 2006, the second phase of that research was conducted. Researchers monitored 83 radio-collared cougars, including 50 kittens in 24 litters. Between 1998 and 2005, researchers documented 473 known or probable cougar kills. Elk comprised 74%: 52% calves, 36% cows, 9% bulls, 3% unknown sex or age. Cougars killed about one elk or deer every 9.4 days and spent almost 4 days at each kill. The study also documented that wolves interfered with or scavenged more than 22% of the cougar-killed ungulates. The monitoring associated with this project has been completed and all of the radio-collars have been removed, but years of data are still being analyzed. New research is underway to evaluate population abundance, predation patterns, and competition with other carnivores.
Very few cougar–human confrontations have occurred in Yellowstone. However, observations of cougars, particularly those close to areas of human use or residence, should be reported.
Coyotes (Canis latrans) are intelligent and adaptable. They can be found throughout North and Central America, thriving in major urban areas as well as in remote wilderness. This adaptability helped coyotes resist widespread efforts early in the 1900s to exterminate them in the West, including Yellowstone National Park, where other mid-size and large carnivores such as cougars and wolves were eradicated. The coyote is a common predator in Greater Yellowstone, often seen traveling through open meadows and valleys.
Number in Yellowstone
Where to See
Meadows, fields, other grasslands, and foraging for small mammals along roadways.
Size and Behavior
- Weigh 25–35 pounds, 16–20 inches high at the shoulder.
- Average life span 6 years; up to 13 years in the park.
- Home range: 3–15 square miles.
- Primarily eat voles, mice, rabbits, other small animals, and carrion—and only the very young elk calves in the spring.
- 4–8 pups are born in April in dens; emerge in May.
- Like other predators, coyotes were often destroyed in the early part of the 1900s because they sometimes preyed on livestock.
- Coyotes continued to thrive because their adaptability enabled them to compensate for the destruction efforts.
- Elimination of wolves probably resulted in high coyote population densities; wolves’ absence opened a niche that coyotes could partially occupy in Yellowstone.
Often mistaken for a wolf, the coyote is about one- third the wolf’s size with a slighter build. Its coat colors range from tan to buff, sometimes gray, and with some orange on its tail and ears. Males are slightly larger than females.
During the 1900s, coyotes partially filled the niche left vacant after wolves were exterminated from the park. In Yellowstone, they lived in packs or family groups of up to seven animals. This social organization is characteristic of coyotes living in areas free from human hunting. With the reintroduction of wolves, Yellowstone coyotes have returned to a more typical social organization—pairs with pups.
Coyotes, also known as “song dogs,” communicate with each other by a variety of long-range vocalizations. You may hear groups or lone animals howling, especially during dawn and dusk periods. Coyotes also mark with their scent (urine and feces) to communicate their location, breeding status, and territorial boundaries.
Until 1995, coyotes faced few predators in Yellowstone other than cougars, who will kill coyotes feeding on cougar kills. After wolves were restored, however, dozens of coyote pups and adults were killed by wolves—primarily when feeding on other animals killed by wolves. On the northern range, the coyote population decreased as much as 50% after wolves were restored as a result of competition with wolves for food, attacks by wolves, and loss of territory to them. More recent trends in the Lamar Valley, however, indicate that the coyote population has increased.
Comparisons of coyote population and behavioral data from before and after wolf restoration provide evidence of how the presence of wolves is changing ecological relationships on the northern range. A reduced coyote population could mean that smaller predators such as the native red fox, whose numbers were previously kept low by coyotes, will have less competition for small prey and their populations may increase.
Coyotes and Humans
Coyotes also face threats from humans. They quickly learn habits like roadside feeding. This may lead to aggressive behavior toward humans and can increase the risk of the coyote being hit by a vehicle. Several instances of coyote aggression toward humans have occurred here, including a few attacks.
Park staff scare coyotes from visitor-use areas and becoming habituated to humans with cracker-shell rounds, bear pepper spray, or other negative stimuli. Animals that continue to pose a threat to them- selves or to humans are killed. Coyotes and other park wildlife are wild and potentially dangerous and should never be fed or approached.
- Typical weasel shape: a very long body, short legs, pointed face, long tail.
- 13–18 inches long, 4.8–11 ounces.
- Fur is light brown above and buff to rusty orange below in summer; all white in winter, except for tail, which is black-tipped all year.
- Males 40% larger than females.
- Compare to marten and short-tailed weasel.
- Found in forests, open grassy meadows and marshes, and near water.
- Eat voles, pocket gophers, mice, ground and tree squirrels, rabbits; to a lesser degree birds, eggs, snakes, frogs, and insects.
- Breed in early July and August; one litter of 6–9 young per year.
- Solitary animals except during breeding and rearing of young.
- 18–26 inches long, 1–3 pounds.
- Weasel family; short limbs and long bushy tail; fur varies from light to dark brown or black; irregular, buffy to bright orange throat patch.
- Smaller than a fisher; buffy or orange bib rather than white.
- Compare to long-tailed weasel and short-tailed weasel.
- Found in conifer forests with understory of fallen logs and stumps; will use riparian areas, meadows, forest edges and rocky alpine areas.
- Eat primarily small mammals such as red- backed voles, red squirrels, snowshoe hares, flying squirrels, chipmunks, mice and shrews; also to a lesser extent birds and eggs, amphibians and reptiles, earthworms, insects, fruit, berries, and carrion.
- Solitary except in breeding season (July and August); delayed implantation; 1–5 young born in mid-March to late April.
- Active throughout the year; hunts mostly on the ground.
- Rest or den in hollow trees or stumps, in ground burrows or rock piles, in excavations under tree roots.
The red fox (Vulpes vulpes) has been documented in Yellowstone since the 1880s. In relation to other canids in the park, red foxes are the smallest. Red foxes occur in several color phases, but they are usually distinguished from coyotes by their reddish yellow coat that is somewhat darker on the back and shoulders, with black “socks” on their lower legs. “Cross” phases of the red fox (a dark cross on their shoulders) have been reported a few times in recent years near Canyon and Lamar Valley. Also, a lighter-colored red fox has been seen at higher elevations.
Three native subspecies exist at high elevations in the United States: the Sierra (V. v. necatar), Cascade (V. v. cascadensis), and Rocky (V. v. macroura) mountains and are collectively called mountain foxes. (Yellowstone’s fox is V. v. macroura.) Little is known about any of these subspecies. Most foxes in the lower 48 states, especially in the eastern and plains states, are a subspecies of fox from Europe introduced in the 1700s and 1800s for fox hunts and fur farms. The foxes that survived the hunt or escaped the fur farms proliferated and headed westward.
Number in Yellowstone
Unknown, but not nearly as numerous as coyotes.
Where to See
- Hayden and Pelican valleys, Canyon Village area.
- Typical habitat: edges of sagebrush/ grassland and within forests.
Size and Behavior
- Adult males weigh 11–12 pounds; females weigh average 10 pounds.
- Average 43 inches long.
- Average life span: 3–7 years; up to 11 years in Yellowstone.
- In northern range, home range averages 3.75 square miles, with males having slightly larger range than females.
- Several color phases; usually red fur with white-tipped tail, dark legs; slender, long snout.
- Barks; rarely howls or sings.
- Distinguish from coyote by size, color, and bushier tail.
- Solitary, in mated pairs, or with female from previous litter.
- Prey: voles, mice, rabbits, birds, amphibians, other small animals.
- Other food: carrion and some plants.
- Killed by coyotes, wolves, mountain lions.
Red foxes are more abundant than were previously thought in Yellowstone. The many miles of forest edge and extensive semi-open and canyon areas of the park seem to offer suitable habitat and food for foxes. They are widespread throughout the northern part of the park with somewhat patchy distribution elsewhere in the park. During the past century, especially within the past few decades, the number of fox sightings has significantly increased. This could be related to better documentation beginning in 1986. Wolves and coyotes are more closely related both genetically and physically than wolves and foxes. Wolves successfully competed with coyotes, causing a decline in the coyote population when they were reintroduced. This may have caused an increase in the number of fox sightings in core wolf areas such as the Lamar Valley.
A research project conducted between 1994–1998 determined at least two subpopulations of foxes live in the Greater Yellowstone Ecosystem. At about 7,000 feet in elevation, there seemed to be a dividing line with no geographical barriers separating these foxes. The genetic difference between these foxes was similar to mainland and island populations of foxes in Australia and their habitat use was different as well. In addition, their actual dimensions, such as ear length and hind foot length, were adapted to some degree for colder environments with deep snow and long winters. A yellowish or cream color most often occurs above 7,000 feet in areas such as Cooke City and the Beartooth Plateau and is being studied by researchers.
Foxes are not often seen because they are nocturnal, usually forage alone, and travel along edges of meadows and forests. During winter, foxes may increase their activity around dawn and dusk, and even sometimes in broad daylight. In late April and May, when females are nursing kits at their dens, they are sometimes more visible during daylight hours, foraging busily to get enough food for their growing offspring.
Recent research shows that red fox are more nocturnal than coyotes, and strongly prefer forested habitats, while coyotes tend to use sagebrush and open meadow areas. In this way, potential competition between fox and coyotes is minimized. Foxes do not seem to actively avoid coyotes during an average day, they just stick with forested habitat, sleep when coyotes are most active, and then forage opportunistically. Foxes will visit carcasses (like wolf kills) for the occasional big meal, especially during winter, but this is more rare than the scavenging coyotes that park visitors can expect to see on many days, especially during winter.
Foxes can become habituated to humans usually due to being fed. In 1997, one fox was trapped and relocated three times from the Tower Fall parking area because visitors fed it human food. The fox was relocated between 10 and 60 miles away from Tower but it returned twice. Finally the fox came to Mammoth where it was fed again and as a result was killed by managers. While this story gives us interesting information about the homing instinct of fox, it also shows the importance of obeying rules to avoid inadvertently causing the death of one of Yellowstone’s animals.
- 40–54 inches long, 10–30 pounds.
- Sleek, cylindrical body; small head; tail nearly one third of the body and tapers to a point; feet webbed; claws short; fur is dark dense brown.
- Ears and nostrils close when underwater; whiskers aid in locating prey.
- Most aquatic member of weasel family; generally found near water.
- Eat crayfish and fish; also frogs, turtles, sometimes young muskrats or beavers.
- Active year-round. Mostly crepuscular but have been seen at all times of the day.
- Breed in late March through April; one litter of two young per year. Females and offspring remain together until next litter; may temporarily join other family groups.
- Can swim underwater up to 6 miles per hour and for 2–3 minutes at a time.
- Not agile or fast on land unless they find snow or ice, then can move rapidly by alternating hops and slides; can reach speeds of 15 miles per hour.
- May move long distances between water bodies.
Short-tailed Weasel (Ermine)
- 8–13 inches long, 2.1–7 ounces.
- Typical weasel shape: very long body, short legs, pointed face, long tail.
- Males about 40% larger than females.
- Fur is light brown above and white below in summer; all white in winter except for tail, which is black-tipped all year.
- Compare to long-tailed weasel and marten.
- Eat voles, shrews, deer mice, rabbits, rats, chipmunks, grasshoppers, and frogs.
- Found in willows and spruce forests.
- Breed in early to mid-summer; 1 litter of 6–7 young per year.
- Can leap repeatedly three times their length.
- Will often move through and hunt in rodent burrows.
A mid-size carnivore in the weasel family, the wolverine (Gulo gulo) is active throughout the year in cold, snowy environments to which it is well adapted. Its circumpolar distribution extends south to mountainous areas of the western United States, including the greater Yellowstone area where they use high-elevation islands of boreal (forest) and alpine (tundra) habitat. Wolverines have low reproductive rates, and their ability to disperse among these islands is critical to the population’s viability. Climate change models predict that by 2050, the spring snowpack needed for wolverine denning and hunting will be limited to portions of the southern Rocky Mountains, the Sierra Nevada range, and greater Yellowstone, of which only the latter currently has a population. Wolverines are so rarely seen and inhabit such remote terrain at low densities that assessing population trends is difficult and sudden declines could go unnoticed for years.
2006–2009: seven documented in eastern Yellowstone and adjoining national forests (two females, five males).
Size and Behavior
- 8–47 inches long, 13–31 pounds.
- Opportunistic eaters. Eat burrowing rodents, birds, eggs, beavers, squirrels, marmots, mice, and vegetation (including whitebark pine nuts); chiefly a scavenger in winter, but has also been known to take large prey such as deer, elk, and moose.
- Active year-round, intermittently throughout the day.
- Breed April to October; one litter of 2–4 young each year. Females give birth in dens excavated in snow.
- Den in deep snow, under log jams, and uprooted trees in avalanche chutes.
- Mostly solitary except when breeding.
- In August 2014, the US Fish and Wildlife Service withdrew a proposal to list wolverines living in the lower 48 states as a threatened species under the Endangered Species Act.
- Due to uncertainty of the effects of climate change on wolverines and their habitat in the foreseeable future, plans to list the species are on hold.
Commercial trapping and predator control efforts substantially reduced wolverine distribution in the lower 48 states by the 1930s. Some population recovery has occurred, but the species has not been documented recently in major portions of its historic range. In the Greater Yellowstone Area, wolverines have been studied using live traps, telemetry, and aerial surveys. A group sponsored by the Wildlife Conservation Society has documented ranges that extend into Yellowstone National Park along the northwest and southwest boundary. A second group, which included researchers from the National Park Service, the US Forest Service, and the Northern Rockies Conservation Cooperative, which surveyed the eastern part of the park and adjoin- ing national forest from 2006 to 2009, documented seven wolverines. The average annual range for the two monitored females was 172 mi2 (447 km2); for three males, 350 mi2 (908 km2). The other two males, both originally captured by the Wildlife Conservation Society, dispersed from west and south of the park: M557 established a home range north of the park in 2009; M556 became the first confirmed wolverine in Colorado in 90 years. But to create a breeding population there, he will need to find a female.
Wolverine populations in the US Rockies are likely to be genetically interdependent. Even at full capacity, wolverine habitat in the Yellowstone area would support too few females to maintain viability without genetic exchange with peripheral populations. The rugged terrain that comprises a single wolverine home range often overlaps several land management jurisdictions. Collaborative conservation strategies developed across multiple states and jurisdictions are therefore necessary for the persistence of wolverines in the continental United States.
In August 2014, the United States Fish and Wildlife Service withdrew a proposed rule to list the wolverine as a threatened species under the Endangered Species Act in the contiguous United States. In spring of 2016, a US District court reinstated the proposal ruled that it shall be conferenced on as necessary until a final proposed.
Climate change impacts on wolverine habitat, specifically the likelihood of declining habitat in high elevation snowpack for denning females, had been identified as a chief threat to this species. In Montana, which has the largest wolverine population of the lower 48 states, an annual quota of 5 wolverines were available for harvest by licensed trappers in recent years.
Although wolf packs once roamed from the Arctic tundra to Mexico, loss of habitat and extermination programs led to their demise throughout most of the United States by early in the 1900s. In 1973, the US Fish and Wildlife Service listed the northern Rocky Mountain wolf (Canis lupus) as an endangered species and designated Greater Yellowstone as one of three recovery areas. From 1995 to 1997, 41 wild wolves from Canada and northwest Montana were released in Yellowstone National Park. As expected, wolves from the growing population dispersed to establish territories outside the park where they are less protected from human-caused mortalities. The park helps ensure the species’ long-term viability in Greater Yellowstone and has provided a place for research on how wolves may affect many aspects of the ecosystem.
Wolves are highly social animals and live in packs. Worldwide, pack size will depend on the size and abundance of prey. In Yellowstone, average pack size is 10 individuals. The pack is a complex social family, with older members (often the alpha male and alpha female) and subordinates, each having individual personality traits and roles within the pack. Packs defend their territory from other, invading packs by howling and scent marking with urine.
Wolves consume a wide variety of prey, large and small. They efficiently hunt large prey that other predators cannot usually kill. In Yellowstone, 90% of their winter prey is elk; 10–15% of their summer prey is deer. They also kill bison.
Many other animals benefit from wolf kills. For example, when wolves kill an elk, ravens arrive almost immediately. Coyotes arrive soon after, waiting nearby until the wolves are sated. Bears will attempt to chase the wolves away, and are usually successful. Many other animals—from magpies to invertebrates—consume the remains.
Changes in Their Prey
From 1995 to 2000, in early winter, elk calves comprised 50% of wolf prey, and bull elk comprised 25%. That ratio reversed from 2001 to 2007, indicating changes in prey vulnerability and availability. The discovery of this change emphasizes the importance of long-term monitoring to understand predator-prey dynamics. Changes in wolf predation patterns and impacts on prey species like elk are inextricably linked to other factors, such as other predators, management of ungulates outside the park, and weather (e.g. drought, winter severity). Weather patterns influence forage quality and availability, ultimately impacting elk nutritional condition. Consequently, changes in prey selection and kill rates through time result from complex interactions among these factors. Current NPS research focusses on the relative factors driving wolf predation over the past two decades.
- An estimated 528 wolves resided in the Greater Yellowstone Ecosystem as of 2015.
- As of December 2018, there were 80 wolves in 9 packs. A biological count (April 1, 2019) was 61 wolves in 8 packs.
- In general, wolf numbers have fluctuated between 83 and 108 wolves since 2009.
Where to See
- They inhabit most of the park; peak activity is at dawn and dusk.
- The northern range of Yellowstone is one of the best places in the world to watch wolves.
Size and Behavior
- 26–36 inches tall at the shoulder, four to six feet long from nose to tail tip.
- Males weigh 100–130 pounds, females weigh 80–110 pounds.
- Home range within the park is 185–310 square miles (300– 500 km2); varies with pack size, food availability, and season.
- Average lifespan in the park is four to five years. Average lifespan outside is two to three years. The oldest known wolf to live here was 12.5 years old.
- Two main color variations exist in Yellowstone in approximately equal proportions: black and gray.
- Prey primarily on hoofed animals. In Yellowstone, 90% of winter diet is elk; summer prey consist of more deer and smaller mammals.
- Mate in February.
- Give birth to average of five pups in April after a gestation period of 63 days.
- Young emerge from den at 10–14 days; pack remains at the den for three to ten weeks unless disturbed.
- Leading cause of death for wolves within the park is death by other wolves.
- Leading cause of death for wolves outside the park is human-caused.
Interesting Wolf Behavior
Wolves kill each other and other carnivores, such as coyotes and cougars, usually because of territory disputes or competition for carcasses. In 2000, however, the subordinate female wolves of the Druid pack exhibited behavior never seen before: they killed their pack’s alpha female; then they carried her pups to a central den and raised them with their own litters.
In the first years following wolf restoration, the population grew rapidly as the newly formed packs spread out to establish territories with sufficient prey. The wolves have expanded their population and range, and now are found throughout the Greater Yellowstone Ecosystem.
Disease periodically kills a number of pups and old adults. Outbreaks of canine distemper have occurred in 2005, 2008, and 2009. In 2005, distemper killed two-thirds of the pups within the park. Infectious canine hepatitis, canine parvovirus, and bordetella have also have been confirmed among Yellowstone wolves, but their effects on mortality are unknown.
Sarcoptic mange, an infection caused by the mite Sarcoptes scabiei, reached epidemic proportions among wolves on the northern range in 2009. The mite is primarily transmitted through direct contact and burrows into the wolf’s skin. This process can initiate an extreme allergic reaction and cause the wolf to scratch the infected areas, which often results in hair loss and secondary infections. By the end of 2011, the epidemic had mostly subsided; however, the infection is still present at lower prevalences throughout the park.
Wolf packs are highly territorial and communicate with neighboring packs by scent-marking and howl- ing. Occasionally, packs encounter each other, and these interactions are typically aggressive. Larger packs often defeat smaller groups, unless the small group has more old adult or adult male members. Sixty-five percent of collared wolves are ultimately killed by rival packs.
The park’s wolf population has declined substantially since 2007, when the count was 171. Most of the decrease has been in packs on the northern range, where it has been attributed primarily to the decline in the elk population and available territory. Canine distemper and sarcoptic mange have also been factors in the population decline.
Each year, park researchers capture a small proportion of wolves and fit them with radio tracking collars. These collars enable researchers to gather data on an individual, and also monitor the population as a whole to see how wolves are affecting other animals and plants within the park. Typically, at the end of each year, only 20% of the population is collared.
Wolves in the Northern Rocky Mountains have met the US Fish and Wildlife Service’s criteria for a recovered wolf population since 2002. As of December 2015, the US Fish & Wildlife Service estimated about 1,704 wolves and 95 breeding pairs in the Northern Rocky Mountain Distinct Population Segment.
The gray wolf was removed from the endangered species list in 2011 in Idaho and Montana. They were delisted in Wyoming in 2016, and that decision was upheld on appeal in April 2017. Wolves are hunted in Idaho and Montana under state hunting regulations.
Your Safety in Wolf Country
Wolves are not normally a danger to humans, unless humans habituate them by providing them with food. No wolf has attacked a human in Yellowstone, but a few attacks have occurred in other places.
Like coyotes, wolves can quickly learn to associate campgrounds, picnic areas, and roads with food. This can lead to aggressive behavior toward humans.
What You Can Do
- Never feed a wolf or any other wildlife. Do not leave food or garbage outside unattended. Make sure the door is shut on a garbage can or dumpster after you deposit a bag of trash.
- Treat wolves with the same respect you give any other wild animal. If you see a wolf, do not approach it.
- Never leave small children unattended.
- If you have a dog, keep it leashed.
- If you are concerned about a wolf—it’s too close, not showing sufficient fear of humans, etc., do not run. Stop, stand tall, watch what the wolf is going to do. If it approaches, wave your arms, yell, flare your jacket, and if it continues, throw something at it or use bear pepper spray. Group up with other people, continue waving and yelling.
- Report the presence of wolves near developed areas or any wolf behaving strangely.
To date, eight wolves in Yellowstone National Park have become habituated to humans. Biologists successfully conducted aversive conditioning on some of them to discourage being close to humans, but two have had to be killed.
Yellowstone is the only place in the United States where bison (Bison bison) have lived continuously since prehistoric times. Yellowstone bison are exceptional because they comprise the nation’s largest bison population on public land and are among the few bison herds that have not been hybridized through interbreeding with cattle. Unlike most other herds, this population has thousands of individuals that are allowed to roam relatively freely over the expansive landscape of Yellowstone National Park and some nearby areas of Montana. They also exhibit wild behavior like their ancient ancestors, congregating during the breeding season to compete for mates, as well as migration and exploration that result in the use of new habitat areas. These behaviors have enabled the successful restoration of a population that was on the brink of extinction just over a century ago.
However, some Yellowstone bison are infected with brucellosis, a livestock disease that can be transmitted to wild bison and elk as well as cattle through contact with infected fetal tissue. To prevent conflicts with ranching and other activities outside the park, the National Park Service works with other federal, state, and tribal agencies to manage and develop policies for bison access to winter range outside the boundaries. Conservation of wild bison is one of the most heated and complex of Yellowstone’s resource issues. All of the interested parties bring their own wide-ranging values and objectives to the debate.
Numbers in Yellowstone
Estimated at 4,527 in August 2018. This includes two primary breeding herds: northern (3,337) and central (1,190).
Where to See
- Year-round: Hayden and Lamar valleys.
- Summer: grasslands.
- Winter: hydrothermal areas and along the Madison River. Blacktail Deer Plateau, Tower, and the Gardiner Basin.
Size and Behavior
- Male (bull) weighs up to 2,000 pounds, female (cow) weighs up to 1,000 pounds.
- May live 12–15 years, a few live as long as 20 years.
- Feed primarily on grasses and sedges.
- Mate in late July through August; give birth to one calf in late April or May.
- Can be aggressive, are agile, and can run up to 30 miles per hour.
- Yellowstone is the only place in the lower 48 states to have a continuously free-ranging bison population since prehistoric times.
- In the 1800s, market hunting and the US Army nearly caused the extinction of the bison.
- By 1902, poachers reduced Yellowstone’s herd to about two dozen animals.
- The US Army, who administered Yellowstone at the beginning of the 20th century, protected these bison from further poaching.
- Bison from private herds were used to establish a herd in northern Yellowstone.
- For decades, bison numbers were reduced due to belief that they, along with elk and pronghorn, were over-grazing the park.
- By 1968, herd reductions of bison ceased.
- Reductions began again in the 2000’s due to increasing numbers and litigation about migration into Montana.
Bison are the largest land-dwelling mammal in North America. Males (2,000 lbs/900 kg) are larger than females (1,100 lbs/500 kg) and both are generally dark chocolate-brown in color, with long hair on their forelegs, head, and shoulders, but short, dense hair (1 in/3 cm) on their flanks and hindquarters. Calves of the year are born after 9 to 9-½ months of gestation. They are reddish-tan at birth and begin turning brown after 2-½ months. Both sexes have relatively short horns that curve upward, with male’s averaging slightly longer than those of adult females.
All bison have a protruding shoulder hump. Large shoulder and neck muscles allow bison to swing their heads from side-to-side to clear snow from foraging patches, unlike other ungulates that scrape snow away with their front feet. Bison are agile, strong swimmers, and can run 35 miles per hour (55 kph). They can jump over objects about 5 feet (1.5 m) high and have excellent hearing, vision, and sense of smell.
Bison are mostly active during the day and at dusk, but may be active through the night. They are social animals that often form herds, which appear to be directed by older females. Group sizes average about 20 bison during winter, but increase in summer to an average of about 200, with a maximum of about 1,000 during the breeding season (known as the rut) in July and August. Bison are sexually mature at age two. Although female bison may breed at these younger ages, older males (>7 years) participate in most of the breeding.
During the rut mature males display their dominance by bellowing, wallowing, and engaging in fights with other bulls. The winners earn the right to mate with receptive females. Once a bull has found a female who is close to estrus, he will stay by her side until she is ready to mate. Then he moves on to another female. Following courtship, mature males separate and spend the rest of the year alone or in small groups. Group sizes decrease through autumn and into winter, reaching their lowest level of the year during March and April.
Yellowstone bison feed primarily on grasses, sedges, and other grass-like plants (more than 90% of their diets) in open grassland and meadow communities throughout the year. They also eat forbs (weeds and herbaceous, broad-leafed plants) and browse (the leaves, stems, and twigs of woody plants) through the year, but those usually comprise less than 5% of the diet. They typically forage for 9 to 11 hours daily. Bison are ruminants with a multiple-chambered stomach that includes microorganisms such as bacteria and protozoa to enable them to effectively digest plant material. Bison alternate between eating and ruminating, which is regurgitating partially digested food and chewing it again, to allow microorganisms to further break down plant material into volatile fatty acids and other compounds. Their large digestive tract allows them to digest lower quality foods with greater efficiency than other ungulates such as cattle, deer, or elk.
Interaction with Other Wildlife
Wolves and grizzly bears are the only large predators of adult bison. However, predation currently has little effect on bison population trends. Bison usually face their attackers and defend themselves as a group, making them more difficult to kill than animals like elk that run from predators. The size of bison also plays a role in persuading predators to look for an easier meal. When they die, bison provide an important source of food for scavengers and other carnivores. Bison will rub against trees, rocks, or in dirt wallows in an attempt to get rid of insect pests. Birds such as the magpie perch on a bison to feed on insects in its coat. The cowbird will also follow close behind a bison, feeding on insects disturbed by its steps.
Like most other ungulates of the Greater Yellowstone Ecosystem, bison will move from their summer ranges to lower elevation as snow accumulates and dense snowpack develops. Most bison alter their diets somewhat during winter, feeding in lowland meadows with concentrated sedges and grasses compared to a more diverse diet during the rest of the year. Bison appear to select foraging areas during winter based more on plant abundance than quality, and then consume the most nutritious plants available. High densities of bison can deplete forage in high quality patches, resulting in subsequent use of areas with plants of lower diet quality. Bison in central Yellowstone frequently use thermally influenced areas near geysers, hot springs, fumaroles, and rivers with less snow during winter. Forested areas are used occasionally for shade or shelter, escape from insects and other disturbances, or to travel between foraging areas or seasonal ranges.
Yellowstone bison historically occupied approximately 7,720 square miles (20,000 km2) in the headwaters of the Yellowstone and Madison rivers. Today, this range is restricted to primarily Yellowstone National Park and some adjacent areas of Montana. The bison population lives and breeds in the central and northern regions of the park. The northern breeding herd congregates in the Lamar Valley and on adjacent plateaus for the breeding season. During the remainder of the year, these bison use grasslands, wet meadows, and sage-steppe habitats in the Yellowstone River drainage, which extends 62 miles (100 km) between Cooke City and the Paradise Valley north of Gardiner, Montana. The northern range is drier and warmer than the rest of the park, and generally has shallower snow than in the interior of the park.
The central breeding herd occupies the central plateau of the park, from the Pelican and Hayden valleys with a maximum elevation of 7,875 feet (2,400 m) in the east to the lower elevation and thermally influenced Madison headwaters area in the west. Winters are often severe, with deep snows and temperatures reaching -44°F (-42°C). This area contains a high proportion of moist meadows comprised of grasses, sedges, and willows, with upland grasses in drier areas. Bison from the central herd congregate in the Hayden Valley for breeding. Most of these bison move between the Madison, Firehole, Hayden, and Pelican valleys during the rest of the year. However, some bison travel to the northern portion of the park and mix with the northern herd before most return to the Hayden Valley for the subsequent breeding season. In addition, some females switched breeding ranges and successfully bred and reared young on their new range.
Yellowstone has played a key role in the conservation of wild bison in North America. If fact, we’ve been so successful that we now face the challenge of helping to manage a rapidly growing population of migratory bison that frequently roam beyond our borders onto private land and land managed by other agencies. Read more about the history of bison management and the challenges of maintaining a wild, migratory population of bison in a modern landscape.
Although widely distributed across the Rocky Mountains, bighorn sheep (Ovis canadensis) persist chiefly in small, fragmented populations that are vulnerable to sudden declines as a result of disease, habitat loss, and disruption of their migratory routes due to roads and other human activities. About 10 to 13 interbreeding bands of bighorn sheep occupy steep terrain in the upper Yellowstone River drainage, including habitat that extends more than 20 miles north of the park. These sheep provide visitor enjoyment as well as revenue to local economies through tourism, guiding, and sport hunting. Mount Everts receives the most concentrated use by bighorn sheep year-round.
Number in Yellowstone
329 in the northern Yellowstone area in 2015 (163 counted inside the park).
Where to See
- Summer: slopes of Mount Washburn, along Dunraven Pass.
- Year-round: Gardner Canyon between Mammoth and the North Entrance.
- Also: On cliffs along the Yellowstone River opposite Calcite Springs; above Soda Butte; in backcountry of eastern Absarokas.
Behavior and Size
- Average life span: males, 9–12 years; females 10–14 years.
- Adult male (ram): 174–319 pounds, including horns that can weigh 40 pounds. The horns of an adult ram can make up 8–12% of his total body weight.
- Adult female (ewe): up to 130 pounds.
- Horn growth is greatest during the summer and early in life. Female horns grow very little after 4–5 years, likely due to reproductive costs.
- The horn size of bighorn sheep rams can influence dominance and rank, which affects social relationships within herds.
- Older ram horns may be “broomed” or broken at the tip, which can take off 1–2 years of growth.
- Mating season begins in November.
- Ram skulls have two layers of bone above the brain that function as a shock absorber, an adaptation for the collision of head-on fighting that is used to establish dominance between rams of equal horn size, especially during mating.
- One to two lambs born in May or June.
- Feed primarily on grasses; forage on shrubby plants in fall and winter.
- Rocky Mountain bighorn sheep, found in greater Yellowstone, differ from other currently recognized subspecies in the United States: Desert bighorn sheep, which is currently listed as an endangered species, Dall sheep found in Alaska and northwestern Canada, and Stone’s sheep, which are a subspecies of Dall sheep.
- Early reports of large numbers of bighorn sheep in Yellowstone have led to speculation they were more numerous before the park was established.
- A chlamydia (pinkeye) epidemic in 1981–1982 reduced the northern herd by 60%.
Yellowstone provides summer range for an estimated 10,000–20,000 elk (Cervus canadensis) from 6–7 herds, most of which winter at lower elevations outside the park. These herds provide visitor enjoyment as well as revenue to local economies through hunting outside the park. As Yellowstone’s most abundant ungulate, elk comprise approximately 90% of winter wolf kills and are an important food for bears, mountain lions, and at least 12 scavenger species, including bald eagles and coyotes. Competition with elk can influence the diet, habitat selection, and demography of bighorn sheep, bison, moose, mule deer, and pronghorn. Elk browsing and nitrogen deposition can affect vegetative production, soil fertility, and plant diversity. Thus, changes in elk abundance over space and time can alter plant and animal communities in Yellowstone.
Number in Yellowstone
- Summer: 10,000–20,000 elk in 6–7 different herds.
- Winter: <5,000
Where to See
- Summer: Gibbon Meadows, Elk Park, and Lamar Valley.
- Fall, during “rut” or mating season: northern range, including Mammoth Hot Springs; Madison River.
- Winter: migrate north to the northern range and around Gardiner, Montana; <100 year-round along the Firehole and Madison rivers; south to the Jackson Hole Elk Refuge in Jackson, Wyoming.
Size and Behavior
- Male (bull) weighs about 700 pounds and is about 5 feet high at the shoulder; female (cow) weighs about 500 pounds and is slightly shorter; calf is about 30 pounds at birth.
- Bulls have antlers, which begin growing in the spring and usually drop in March or April of the next year.
- Feed on grasses, sedges, other herbs and shrubs, bark of aspen trees, conifer needles, burned bark, aquatic plants.
- Mating season (rut) in September and October; single calves born in May to late June.
Elk are the most abundant large mammal found in Yellowstone. European American settlers used the word “elk” to describe the animal, which is the word used in Europe for moose (causing great confusion for European visitors). The Shawnee word “wapiti,” which means “white deer” or “white-rumped deer,” is another name for elk. The North American elk is considered the same species as the red deer of Europe.
Bull elk are one of the most photographed animals in Yellowstone, due to their huge antlers. Bull elk begin growing their first set of antlers when they are about one year old. Antler growth is triggered in spring by a combination of two factors: a depression of testosterone levels and lengthening daylight. The first result of this change is the casting or shedding of the previous year’s “rack.” Most bulls drop their antlers in March and April. New growth begins soon after.
Growing antlers are covered with a thick, fuzzy coating of skin commonly referred to as “velvet.” Blood flowing in the skin deposits calcium that makes the antler. Usually around early August, further hormonal changes signal the end of antler growth, and the bull begins scraping the velvet off, polishing and sharpening the antlers in the process.
The antler growing period is shortest for yearling bulls (about 90 days) and longest for healthy, mature bulls (about 140 days). Roughly 70% of the antler growth takes place in the last half of the period, when the antlers of a mature bull will grow two-thirds of an inch each day. The antlers of a typical, healthy bull are 55–60 inches long, just under six feet wide, and weigh about 30 pounds per pair.
Bulls retain their antlers through the winter. When antlered, bulls usually settle disputes by wrestling with their antlers. When antlerless, they use their front hooves (as cows do), which is more likely to result in injury to one of the combatants. Because bulls spend the winter with other bulls or with gender-mixed herds, retaining antlers means fewer injuries sustained overall. Also, bulls with large antlers that are retained longer are at the top of elk social structure, allowing them preferential access to feeding sites and mates.
Antlers are usually symmetrical and occur on males, or very occasionally females.
- The average, healthy, mature bull has 6 tines on each antler, and is known in some parts of the US as a “six point” or “six by six.”
- One-year-old bulls grow 10–20 inch spikes, sometimes forked.
- Two-year-old bulls usually have slender antlers with 4 to 5 points.
- Three-year-old bulls have thicker antlers.
- Four-year-old and older bulls typically have 6 points; antlers are thicker and longer each year.
- Eleven- or twelve-year old bulls often grow the heaviest antlers; after that age, the size of antlers generally diminishes.
Moose in Yellowstone are one of four subspecies of moose (Alces alces shirasi) in North America, and are found in forested areas and willow flats from southeastern British Columbia to northern Colorado. They are better adapted to survival in deep snow than other ungulates in Greater Yellowstone. Except during the rut, moose are usually found alone or in small family groups. This behavior, and their use of habitat where they are often well concealed, impedes accurate estimates of population size and distribution.
Number in Yellowstone
- Fewer than 200
- Population has declined in last 40 years due to loss of old growth forests surrounding the park, hunting outside the park, burning of habitat, and predators.
Where to See
- Marshy areas of meadows, lake shores, and along rivers.
Behavior and Size
- Adult male (bull) weighs close to 1,000 pounds; female (cow) weighs up to 900 pounds; 5½ to 7½ feet at the shoulder. Young weigh 25–35 pounds at birth.
- Usually alone or in small family groups.
- Mating season peaks in late September and early October; one or two calves born in late May or June.
- Lives up to 20 years.
Moose are the largest members of the deer family in Yellowstone. Both sexes have long legs that enable them to wade into rivers and through deep snow, to swim, and to run fast. Despite its size, a moose can slip through the woods without a sound. Moose, especially cows with calves, are unpredictable and have chased people in the park.
Both sexes are dark brown, often with tan legs and muzzle. Bulls can be distinguished from cows by their antlers. Adults of both sexes have “bells”—a pendulous dewlap of skin and hair that dangles from the throat and has no known function.
In summer, moose eat aquatic plants like water lilies, duckweed, and burweed. But the principle staples of the moose diet are the leaves and twigs of the willow, followed by other woody browse species such as gooseberry and buffaloberry. An adult moose consumes approximately 10–12 pounds of food per day in the winter and approximately 22–26 pounds of food per day in the summer.
Some moose that summer in the park migrate in winter to lower elevations west and south of Yellowstone where willow remains exposed above the snow. But many moose move to higher elevations (as high as 8,500 feet) to winter in mature stands of subalpine fir and Douglas-fir.
Moose are solitary creatures for most of the year, except during the mating season or rut. During the rut, both bulls and cows are vocal: the cows may be heard grunting in search of a mate, and bulls challenge one another with low croaks before clashing with their antlers. The weaker animal usually gives up before any serious damage is done; occasionally the opponent’s antlers inflict a mortal wound.
Bulls usually shed their antlers in late November or December, although young bulls may retain their antlers as late as March. Shedding their heavy antlers helps them conserve energy and promotes easier winter survival. In April or May, bulls begin to grow new antlers. Small bumps on each side of the forehead start to swell, then enlarge until they are knobs covered with a black fuzz (called velvet) and fed by blood that flows through a network of veins. Finally the knobs change into antlers and grow until August. The antlers are flat and palmate (shaped like a hand). Yearlings grow six to eight inch spikes; prime adult bulls usually grow the largest antlers—as wide as five feet from tip to tip. When the antler reach their full size, the bull rubs and polishes his antlers on small trees in preparation for the rut.
Cows are pregnant through the winter; gestation is approximately eight months. When ready to give birth, the cow drives off any previous year’s offspring that may have wintered with her and seeks out a thicket in which to give birth.
Descendants of mountain goats (Oreamnos americanus) introduced in southern Montana mountains during the 1940s and 1950s established a population in the park in the 1990s and have reached a relatively high abundance in the northeastern and northwestern portions via the Absaroka and Gallatin mountain ranges. Investigations of paleontological, archeological, and historical records have not found evidence that the mountain goat is native to Greater Yellowstone.
Many people consider the goats a charismatic component of the ecosystem, including those who value the challenge of hunting them outside the park. But the colonization has raised concerns about the goats’ effects on alpine habitats. Competition with high densities of mountain goats could also negatively affect bighorn sheep, whose range overlaps that of mountain goats.
Number in Yellowstone
208 in and adjacent to Yellowstone.
Where to See
- Infrequently seen; northeastern and northwestern portions of the park in alpine habitat.
- Winter: steep, south-facing slopes, windblown ridgetops; Spring: south- and west-facing cliffs; Summer: meadows, cliffs, ravines, and forests.
Behavior and Size
- Mature male (billy) weighs 300 or more pounds; female (nanny) weighs 150 pounds.
- Young (kids) born in late May–June.
- Females usually begin to breed at 2½ years.
- Live in precipitous terrain.
- Both sexes have horns; females curve less and are thinner and sometimes longer than males.
Mountain goats live in alpine habitats. Studies of alpine vegetation in the northeast portion of the park during 2002 and 2003 suggest that ridge top vegetation cover is lower, and barren areas along alpine ridges are more prevalent in areas that have received relatively high goat use. Studies by Idaho State University and the National Park Service during 2008–2010 suggest goats are affecting the soil chemistry of sites they inhabit by increasing the availability of soil nitrogen through deposition of urine and feces. Soil rockiness may be increasing slightly over time at sites with high goat presence, but no largescale effects have been detected so far with respect to vegetation (species, community structure).
Colonization of suitable habitats south of The Thunderer and along the eastern park boundary within the Absaroka Mountain Range appears to be occuring, with a larger number of groups with females and young observed on Saddle Mountain and on Castor and Pollux peaks during recent years. Mountain goats were not surveyed in 2016 due to poor flying conditions for survey aircraft.
The mule deer (Odocoileus hemionus), also called blacktail deer, is an exclusively western species commonly seen in open-brush country throughout the western states. Widely dispersed throughout Yellowstone National Park during the summer, mule deer migrate seasonally and most of the population winters outside of the park.
The Greater Yellowstone Ecosystem is home to both mule deer and white-tailed deer. The two deer species are differentiated by their antler shape, and tail size and appearance.
Number in Yellowstone
Summer: 1,850–1,900; winter: less than 400
Where to See
Summer: throughout the park; Winter: North Entrance area.
Size and Behavior
- Male (buck): 150–250 pounds; female (doe): 100–175 pounds; 31⁄2 feet at the shoulder.
- Summer coat: reddish; winter coat: gray-brown; white rump patch with black-tipped tail; brown patch on forehead; large ears.
- Males grow antlers from April or May until August or September; shed them in late winter and spring.
- Mating season (rut) in November and December; fawns born late May to early August.
- Lives in brushy areas, coniferous forests, grasslands.
- Bounding gait, when four feet leave the ground, enables it to move more quickly through shrubs and rock fields.
- Eats shrubs, forbs, grasses; conifers in spring.
- Predators include wolves, coyotes, cougars, and bears.
All species of deer use their hearing, smell, and sight to detect predators such as coyotes, cougars, or wolves. They probably smell or hear the approaching predator first; then may raise their heads high and stare hard, rotating ears forward to hear better. If a deer hears or sees movement, it flees.
The State of Montana Department of Fish, Wildlife, and Parks surveys the northern range population outside the park. In 2016 an aerial survey detected 1,1,757 mule deer in the Gardiner Basin area. No surveys are conducted within the park. Since surveys began in 1986 we have observed an average of 66 mule deer (or 3% of the total count) in northern Yellowstone each year. While the relative distribution of mule deer across their winter range has remained similar over the last two decades, the population appears to cyclical increases and decreases. Mule deer populations may decline during severe winters, when deep snow and extremely cold temperatures make foraging difficult.
Although researchers estimate that northern Yellowstone has a summer mule deer population of 1,850 to 1,900, fewer than several hundred stay in the park all winter. Unlike elk and bison, many of which remain in the park throughout the year, mule deer are preyed upon by wolves, coyotes, cougars, and bears in the park mostly in the summer. Because of the mule deer’s seasonal distribution, the relative scarcity of white-tailed deer, and the abundance of elk, which are the main prey of wolves, wolf recovery in Yellowstone is believed to have had little effect on deer populations and recruitment.
Although the primary causes of deer mortality are winter kill and predation, mule deer and white-tailed deer outside the park are subject to state-regulated harvesting in the fall. Because of their scarcity, little is known about the white-tailed deer that inhabit the northern range, and the population within the park is not monitored.
The North American pronghorn (Antilocapra americana) is the surviving member of a group of animals that evolved in North America during the past 20 million years. It is not a true antelope, which is found in Africa and southeast Asia. The use of the term “antelope” seems to have originated when the first written description of the animal was made during the 1804–1806 Lewis and Clark Expedition.
Number in Yellowstone
466 in in February, 2016 (highest count since 1992, which had 536)
Where to See
- Summer: Lamar Valley; some may be near the North Entrance near Gardiner, Montana.
- Winter: between the North Entrance and Reese Creek.
Behavior and Size
- Male (buck) weighs 100–125 pounds; female (doe) weighs 90–110 pounds; adult length is 45–55 inches and height is 35–40 inches at shoulder.
- Average life span: 7–10 years.
- Young (fawns) born in late May–June.
- Live in grasslands.
- Can run for sustained sprints of 45–50 mph.
- Eat sagebrush and other shrubs, forbs, some grasses.
- Both sexes have horns; males are pronged.
- Prior to European American settlement of the West, pronghorn population estimated to be 35 million.
- Early in the 1800s, pronghorn were abundant in river valleys radiating from Yellowstone; settlement and hunting reduced their range and numbers.
- Park management also culled pronghorn during the first half of the 1900s due to overgrazing concerns.
- Pronghorn are a species of special concern in the park.
- This small population could face extirpation from random catastrophic events such as a severe winter or disease outbreak.
The pronghorn has true horns, similar to bison and bighorn sheep. The horns are made of modified, fused hair that grows over permanent bony cores, but they differ from those of other horned animals in two major ways: the sheaths are shed and grown every year and they are pronged. (A number of other horned mammals occasionally shed their horns, but not annually.) Adult males typically have 10–16 inch horns that are curved at the tips. About 70% of the females also have horns, but they average 1–2 inches long and are not pronged. The males usually shed the horny sheaths in November or December and begin growing the next year’s set in February or March. The horns reach maximum development in August or September. Females shed and regrow their horns at various times.
Pronghorn are easy to distinguish from the park’s other ungulates. Their deer-like bodies are reddish- tan on the back and white underneath, with a large white rump patch. Their eyes are very large, which provides a large field of vision. Males also have a black cheek patch.
Females that bred the previous fall commonly deliver a set of twins in May or June. The newborn fawns are a uniform grayish-brown and weigh 6–9 pounds. They can walk within 30 minutes of birth and are capable of outrunning a human in a couple of days. The young normally stay hidden in the vegetation while the mother grazes close by. After the fawns turn three weeks old they begin to follow the females as they forage. Several females and their youngsters join together in nursery herds along with yearling females.
Pronghorn form groups most likely for increased protection against predators. When one individual detects danger, it flares its white rump patch, signaling the others to flee. The pronghorn is adapted well for outrunning its enemies—its oversized windpipe and heart allow large amounts of oxygen and blood to be carried to and from its unusually large lungs. Pronghorn can sustain sprints of 45–50 mph. Such speed, together with keen vision, make the adults difficult prey for any natural predator. Fawns, however, can be caught by coyotes, bobcats, wolves, bears, and golden eagles.
The pronghorn breeding season begins mid-September and extends through early October. During the rut the older males “defend” groups of females (called a harem). They warn any intruding males with loud snorts and wheezing coughs. If this behavior does not scare off the opponent, a fight may erupt. The contenders slowly approach one another until their horns meet, then they twist and shove each other. Eventually, the weaker individual will retreat. Although the fights may be bloody, fatalities are rare.
The most important winter foods are shrubs like sagebrush and rabbitbrush; they eat succulent forbs during spring and summer. They can eat lichens and plants like locoweed, lupine, and poisonvetch that are toxic to some ungulates. Their large liver (proportionately, almost twice the size of a domestic sheep’s liver) may be able to remove plant toxins from the blood stream. Grasses appear to be the least-used food item, but may be eaten during early spring when the young and tender shoots are especially nutritious.
During winter, pronghorn form mixed-sex and- age herds. In spring, they split into smaller bands of females, bachelor groups of males between 1–5 years old, and solitary older males. The small nursery and bachelor herds may forage within home ranges of 1,000 to 3,000 acres while solitary males roam smaller territories (60 to 1,000 acres in size). Pronghorn, including three-fourths of the individuals in Yellowstone, migrate between different winter and summer ranges to more fully utilize forage within broad geographic areas.
During the early part of the 1800s, pronghorns ranked second only to bison in numbers, with an estimated 35 million throughout the West. The herds were soon decimated by conversion of rangeland to cropland, professional hunters who sold the meat, and ranchers who believed that pronghorns were competing with livestock for forage. Today, due to transplant programs and careful management, pronghorns roam the sagebrush prairies in herds totaling nearly 500 thousand animals.
The pronghorn’s population fluctuations on the northern range show the effects of management interventions as well as natural shifts in forage availability, competition with elk, and predation. Efforts to keep pronghorn in the park with fences and winter feeding reduced their abundance and use of migratory routes by the 1920s, and about 1,200 pronghorn were removed from 1947 to 1967 to address perceived sagebrush degradation. Although hunting has not been allowed north of the park since the 1970s, complaints about crop depredation led to the removal of about 190 pronghorn on private land from 1985 to 2002. The reason for the sudden population decline in the early 1990s remains unclear, but fawn survival is low due to coyote predation, and development of private land north of the park has reduced available winter range. The pronghorn winter range in the park is former agricultural land infested with nonnative vegetation of low nutritional quality.
Recent evidence of migration and dispersal into Paradise Valley and mixing with pronghorn herds outside the park should improve the long-term viability of the Yellowstone population. Research continues to search for answers to the population decline. This small population is susceptible to extirpation from random catastrophic events such as a severe winter or disease outbreak.
Although the white-tailed deer (Odocoileus virginianus) is the most common deer species throughout North America, it has never been abundant in Yellowstone. This may be due to habitat and elevation constraints on the northern range or competition from other ungulates that are better suited to park habitat.
White-tailed deer and mule deer are differentiated by their antler shape, and tail size and appearance.
Number in Yellowstone
Scarce, not monitored.
Where to See
Along streams and rivers in the northern range.
Size and Behavior
- Adults 150–250 pounds; 31⁄2 feet at the shoulder.
- Summer coat: red-brown; winter coat: gray-brown; throat and inside ears with whitish patches; belly, inner thighs, and underside of tail white.
- Waves tail like a white flag when fleeing.
- Males grow antlers from May until August; shed them in early to late spring.
- Mating season (rut) peaks in November; fawns born usually in late May or June.
- Eats shrubs, forbs, grasses; conifers in spring.
- Predators include wolves, coyotes, cougars, and bears.
In addition to the big game mammals found in Yellowstone National Park there are many species of rodents, Hares, Rabbits, Pika and Bats.
Rodents are a vital part of the ecosystems in Yellowstone, serving as a major food source for many of the park’s predators. All rodents have a pair of incisors in their upper and lower jaws with a large gap between the incisors and the molars. The incisors continue to grow throughout their lives, so they continually wear them down through chewing. These include beavers, squirrels, chipmonk, montane vole, gopher and marmot.