Bison ecology, ecological influence, behavior, and decline.


Bison in North Dakota. Photo by George Wuerthner

Due to gross similarities in size, food preference, and appearance, it is often asserted that bison and domestic cattle are ecological analogs. However, a review of their evolutionary history demonstrates that they have significant differences in evolutionary pressures that manifest themselves in strikingly different modes of resource exploitation.

Compared to domestic cattle, bison wander more, are less apt to regraze a site during a single growing season, will use steeper terrain, select and consume drier, rougher forage, and spend less time in riparian areas and wetlands (Kohl et al. 2013) Bison are considered “ecosystem engineers” by creating and responding to heterogeneity across the landscape (White el. al. 2015).

In addition, bison were unable to colonize vast portions of the West due to a variety of factors. Evidence suggests these major rangeland ecosystems evolved in the virtual absence of large herding animals. The introduction of domestic livestock into these areas has had particularly negative impacts upon these landscapes.

This paper will discuss the differences in habitat utilization, and behavior between cattle and bison, the decline of bison as an ecological influence, and the implications for management of western rangelands and preservation of native biodiversity.


Bison (Bison bison) and cattle (Bos Taurus) both evolved from a common ancestor in Asia. This animal, named Leptobos, appeared in the Pliocene, and became widely distributed throughout Eurasia. Both Bison and Bos branched from Leptobos prior to its extinction in the late Pleistocene. Early in its evolutionary history, bison resembled cattle in many features including horns that pointed forward, a straight back and few seasonal secondary sexual characteristics. Both cattle and the early bison forms inhabited woodlands and forested areas. During the Pleistocene, bison gradually evolved adaptations that enabled them to exploit the steppe tundra ecosystem, and eventually spread into the available habitat across Asia and Europe. This form became known as Bison priscus (McDonald, 1981).

Bison priscus colonized North America via the Bering land bridge during the early to middle Pleistocene (Guthrie, 1980). Bison evolutionary history in North America is complex and interpretation of the finer points has been controversial. Some authorities believe several successive waves of bison immigration from Asia are responsible for the great variation in bison archeological remains, while others maintain bison responded rapidly to changing climatic and habitat conditions, producing numerous variations on the same theme (McDonald, 1981). Bison latifrons , for example, had very large horns almost resembling Texas Longhorn cattle. This form became extinct in the late Pleistocene. Another form, Bison antiquus survived into the Holocene where it evolved into two recognized subspecies Bison bison bison, the common plains bison and Bison bison athabascae reached maximum range and density approximately 2,500 BP (Guthrie, 1980; McDonald, 1981).

Guthrie (1980) summarizes the basic characteristics expected of animals evolving under different habitats. Savanna-steppe adaptations include non-lethal fighting apparatus, large groups, class hierarchy, elaborate gaudy social organs, migratory-nomadic behavior, less selective feeding and the ability to digest coarse fiber, and marked seasonal adaptations. By contrast, species evolving in woodlands tend to display the following adaptations: lethal fighting apparatus, small groups, linear or modified linear hierarchy, conservative social organs, territorial fidelity, selective feeding strategies, and reduced seasonality. A comparison between cattle and bison clearly shows that American bison fit the savanna-steppe adaptations while cattle, despite centuries of domestication and breeding, are defined more by the woodland attributes.

Although bison became an inhabitant of open landscapes such as plains, or grassy savannas, most of the evolutionary precursors of domestic cattle are inhabitants of subtropical lowland regions where they reside in swampy humid forests. Bison are the only member of the entire Bovini line that does not have at least a partial tropical distribution (McDonald, 1981).

Today, several species of wild cattle are confined to the southeast and central Asia where they occupy open areas in rainforests and uplands, feeding by grazing and browsing (McDonald, 1981). Their niche somewhat similar to whitetail deer in North America, which favors the edges along forest borders and the lush cover of riparian and other shrubby vegetation.

Residual herds of bison are still found in Eurasia where they are restricted to forest and mountain areas. However, these animals are said to resemble “cattle” in appearance and behavior (Guthrie, 1980). In North America, bison occupy primarily grasslands or parklands and have evolved into an animal adapted to “open” landscapes exhibiting migratory behavior, and tolerance for arid environments and a shifting mosaic of resources (Renyolds et al. 1982).

During the Pleistocene, vegetation across wide swaths of North America changed substantially from broadleaf evergreen vegetation towards a greater abundance of coniferous species, resulting in a deterioration in herbivore forage opportunities. However, at the same time, there was an expansion of steppe areas with fibrous and abrasive foods (McDonald, 1981). The adaptive response of bison was to enlarge body size while expanding its ruminant digestive system to permit greater intake of low-quality forage (McDonald, 1981).

In woodlands where food resources are patchy, small, isolated groups of animals are all that can be supported within any parcel of the landscape. As a consequence, one would expect animals in these situations to take on certain characteristics. For instance, living in small groups or in isolation increases vulnerability to predation. Larger body size can discourage predators, and not surprisingly, early forms of bison that lived in forested landscapes tended to be larger overall. However, larger size results in a slower maturation process, with animals living longer, but producing fewer young. Social behavior is less highly developed (Geist, 1971) as well.

Evolution of Bison bison under a grassland regime favored an animal with small body size (compared to woodland and earlier glacial versions of bison-though bison are still the largest terrestrial mammal in North America), a high degree of social behavior that manifests itself in strong herding characteristics, high biotic potential, and rapid maturation rates. These are all considered adaptations to an open grassland living situation (McDonald, 1981). The modern-day bison evolved into its present form only 5,000 BP (Hudson and Frank 1987).

Bison tend to have decreased aggressive encounters that are ritualistic rather than lethal. During the rut, bull bison develop exaggerated hair tuffs on the head and front legs that are used as a social display of size and rank. They lose these features outside of the rut, taking on the gross features of females. This defuses antagonism between bulls outside of the rutting season and is an adaptation to herding that permits living together in open spaces. (Geist, 1971; Guthrie, 1980; McDonald, 1981).

Morphological adaptations of the bison to facilitate existence in a grassland environment include the downward rotation of the head relative to the vertebral column, along with the lateral placement of the eye orbits which permits maintenance of visual contact with the herd as well as predator detection while grazing. Short limbs also permit easier access to short grasses (McDonald, 1981).

Also, bison horns have rotated towards the side of the head where they are less effective as lethal weapons (Guthrie, 1980). This is an adaptation to the intense daily social encounters that characterize herd animals. Most aggressive encounters involve head shoving, with encounters typically decided by threats (Meagher, 1973). Again, this is considered an adaptation to mixed-sex herd conditions (Guthrie, 1980; McDonald, 1981).

Another adaption to the mobility and the requisite movement necessary in open prairie landscapes is the high shoulder hump and lower hindquarters of the plains bison. According to Guthrie (1980) this rotation of forequarters, with the shoulders functioning as a fulcrum permitted a cantering gait–a rolling, energy-efficient movement. Guthrie theorizes this was an adaptation to frequent long-distance movements, in which wild bison seek areas with adequate forage, attempt to capture phenological peaks in plant growth or obtain water. As we shall see later, behaviorists have all noted the mobility of bison compared to domestic cattle as well as many other ungulates.

Although this rocking gait is efficient, it is not particularly rapid. However, since the termination of the last Ice Age, most of the larger predators that posed a threat to bison went extinct, freeing bison of the need to outrun predators as a predator avoidance tactic. Wolves were the only predator other than humans that posed any threat to bison. The large size of bison is an effective defense against predation by other predator species. Recent predator-prey studies between wolves and bison have shown that calves and older adults make up the majority of prey for wolves, while healthy adults are relatively safe from attack (Carbyn, et. al. 1993). Furthermore, where wolves have a choice of alternative smaller prey such as elk or deer, bison are seldom preyed upon.

Bison Yellowstone NP, Wyoming Photo by George Wuerthner

Prior to the adoption of the horse by Native Americans, most human bison predation was opportunistic relying upon bison jumps or occasional vulnerability created by deep snow. This relationship changed upon the introduction of the horse, destroying the bison’s major predator avoidance strategy of size and herding. As a consequence, they were easily run down on horses (Guthrie, 1980; Urness, 1989). There is evidence that once Native Americans obtained the horse, they were able to exterminate small, marginal populations in some of the peripheral portions of their range, particularly in southeast Idaho and northern Utah (Urness, 1989). Others argue that Indian hunting had a greater impact and ultimately was the main driver of bison decline (Flores, 2015).

By contrast, cattle, which evolved in moister woodland environments more characteristic of early woodland forms of bison, lack the well-developed features of bison that are adaptations to short grass plains environments, including the downward rotation of the head relative to the vertebral column. Plus, cattle tend to have longer legs (this varies among breeds), and a straight back which may permit short term bursts of speed but are not useful for long-distance movement. Not only are cattle less mobile by nature, but domestic breeding programs also have resulted in animals that are even more obese and less fit for long-distance movement.


Bison (Bison bison) once ranged across much of North America from the eastern seaboard states to southeast Washington, eastern Oregon, and northeastern California. They also roamed the high parks of the Colorado Rockies and were known from higher elevations of the Northern Rockies in Glacier National Park, and the mountains surrounding Yellowstone (Meagher, 1973; McDonald, 1981; Reynolds et al. 1982). However, the greatest numbers were found on the shortgrass plains east of the Rocky Mountains that stretched from Alberta to Texas (Reynolds et al. 1982) –sometimes referred to as the “bison belt”.

Some authorities estimated that 75 million bison roamed North America in the pre-Columbian era, while a more conservative estimate by McHugh suggested the maximum number should be pegged at 30 million (Reynolds et al. 1982), and there are even suggestions bison may have been as low as 10-12 million (Hamalainen, Pekka, 2001). Shaw (1995) attempted to summarize the varied estimates. The important idea to keep in mind is that all of these estimates were no more than educated guesses.

Due to hide hunting, sport hunting, and perhaps also as a consequence of the introduction of the horse which increased Native American hunting efficiency (Reynolds et al. 1982, Urness, 1989, Flores 1991) bison numbers plummeted nearly to the point of extinction by the late 1800’s (Meagher, 1973, Isenberg A. 2000).

Flores (2016) also notes that a drying climate that reduced plant productivity may have played a role in the decline of the herds as well. Bailey gives a good succinct accounting of bison hunting and its possible contribution to the virtual extinction of the herds (Bailey 2013).

Whatever the exact number in pre-Columbian times, there is no doubt from historic accounts that bison were abundant within their preferred habitat on the plains. The following quote from John Kirk Townsend (1978) is representative of the kind of abundance that early sojourners recorded. Traveling along the Platte River of Wyoming in 1834, Townsend noted that the “whole plain, as far as the eye could discern, was covered by one enormous mass of buffalo. Our vision, at the very least computation, would certainly extend ten miles, and in the whole of this great space, including about eight miles in width from the bluffs to the river bank, there was apparently no vista in the incalculable multitude.”

However, by 1859, bison numbers were already in decline. W. F. Raynolds led a military expedition guided by mountain man Jim Bridger from Fort Pierre, South Dakota to Montana and Wyoming and back again.  From Fort Pierre in the heart of bison country, although the occasional sign of bison was seen including tracks and dung, the expedition did not encounter a live bison until they reached the Powder River in Wyoming. They then saw numerous herds on the lower Yellowstone River in Montana, but once they turned south and crossed the Big Horn Basin, they did not see any more live bison that year.

After wintering on the North Platte River in Wyoming, they proceeded towards the Wind River and saw one small group of bison. Then they traveled around the Wind River Range, into Jackson Hole, across the Tetons into Pierre’s Hole then north over what is now known as Raynold’s Pass into the Upper Madison River of Montana where they saw another small herd of bison. From there, they proceed down the Madison to the Missouri River and past Great Falls to Fort Benton. Again. they did not see any bison until they were on the lower Missouri in Montana (Raynolds 1859).

The significance of Raynold’s daily account is that bison while still abundant in some places, they were not found everywhere as often is implied. The herds were mobile and often moved in response to Indian hunting, drought, fire, and other influences.

Bailey (2016) has a detailed description of the bison sightings which quotes from numerous sources detailing how mobile bison were with different individuals observing large numbers in other others where previous or future travelers observed none.


That bison were a major ecological force that shaped western rangelands is seldom disputed. Many plants in the “bison belt” have adopted flexible growth strategies that enable them to tolerate bison herbivory pressures as well as other ungulates, rodents like prairie dogs, and even invertebrates (Delting and Painter 1983, Painter et. al 1989). This suggests a long-standing relationship with herbivory pressure.

However, Belsky (1986) suggests cautions that this should not be interpreted as suggesting plants “benefit” from herbivory since shoot and leaf production to replace lost photosynthetic area does not itself constitute greater production.

Because of their current limited distribution, bison no longer function as a major disturbance factor or ecosystem engineers, nor influence ecosystem function in most of their former habitat. Within the last hundred to hundred fifty years, bison were replaced across most of their natural range by domestic cattle. Due to gross similarities in shape, size, and foraging habits between bison and cattle, many have argued that cattle are merely filling the vacant niche left by the virtual extinction of bison.

For example, in an article (Thomas, 1991) which appeared in Rangelands published by the Society for Range Management, the author states, “Long before the American pioneers laid eyes on the mountains and plains of North America, there were ‘cattle’ on our western ranges. Bison roamed the hills, migrating from winter to summer grazing areas, making seasonal use of these lands much as our domestic livestock do today. The bison and the domestic cow belong to the same family (Bovidae) and are genetically similar. They are also very similar in their grazing habits and preferences”.

Not surprisingly, because of the assumed similarities between the two animals, it is claimed that cattle are nothing more than domestic bison. Since bison herbivory was an important ecological influence upon many grassland ecosystems, many people assume that properly managed cattle have no negative impacts upon western rangelands, in part because they are thought to mimic bison herbivory pressures (Savory, 1983, Lauenroth et al. 1994, Goetz, H. 1994, Thomas, 1991).

The manager for the Nature Conservancy’s Pine Butte Swamp in Montana uses these presumed similarities to explain the use of cattle grazing on the Conservancy’s preserve, stating “because bison historically graze in the area, native grasses actually thrive with limited grazing” (Cheater, 1993).

Bridgeport Valley, California. Domestic cattle are not ecological analogs for bison. Photo by George Wuerthner

A livestock promotional piece published by the U.S.F.S., BLM, and Public Lands Council (USDA, 1989) says “for range grasses to thrive, they must be cropped to promote vigor. Often, the lack of grazing results in unhealthy, less dense stands that overwhelm good grasses, wildflowers, and other plants.”

However, others argue that plant response to herbivory is merely a defensive mechanism that should not be interpreted as a benefit or promoting rangeland “health”, but rather as generalized plant responses to damage (Belsky et al. 1993).

Some even assert that western rangelands, particularly the most arid or “brittle” landscapes require disturbance impacts from domestic cattle to replace the impact it is claimed resulted from vast herds of bison, antelope, or other wildlife in these areas.

For example, Thomas (1991) concludes that extirpation of the bison “would have put thousands of acres of rangeland into a stagnant and very unnatural situation except for one saving grace: we substituted domestic livestock for the buffalo.” Others suggest that herding animals are necessary to break up soil crusts, trample seeds, remove “decadent” plant material, and are purported to increase rainwater penetration (Savory, 1983, 1989, USDA, 1989).

Unfortunately, there have been few attempts to verify whether bison or cattle are ecological analogs, and furthermore if rangelands “require” herbivory for ecosystem health, or merely tolerate grazing pressures (Kohl. 2013).

There are important implications for these arguments with regard to public lands management. The argument that cattle are ecological equivalents to bison is used as a “scientific” justification for continuing domestic livestock grazing on some public lands.

Furthermore, public agencies are supposed to manage lands for ecosystem stability and health. Those who oppose removal or reduction of livestock from public lands frequently argue that grazing and herd impacts are necessary to avoid ecosystem decay and that plants “benefit” from herbivory by removing “decadent” plant growth. Thus, removal of domestic animals is reasoned to be counter-productive to good resource management.

This argument has already been used by land managers in a number of instances (Tohill and Dollerschell, 1990). So ingrained is the idea that livestock and grazing are synonymous that some livestock supporters assume removal of domestic cattle and sheep equal “no grazing” (Laycock, 1994) and caution against the presumed deleterious effects upon rangeland “health”.

It must be pointed out that the absence of livestock is not the same as no grazing since most native rangelands experience a wide variety of herbivory pressures, from nematodes in the soil to invertebrates like grasshoppers, to larger mammals and birds like prairie dog, antelope, elk and bison where they are still found (Archer and Smeins,1991).

Furthermore, under natural conditions, the populations of these animals fluctuate seasonally as well as annually due to changing conditions, such as variation in predation pressure, competitive interactions between and within species, and availability of forage. Due to these factors, some have questioned whether the ecological effects upon rangelands of near-constant numbers of cattle can be equated with naturally fluctuating numbers of wildlife (Heitschmidt,1990).

Despite the strong advocacy for the idea that cattle are merely tame bison, few studies have attempted to quantify the ecological-evolutionary differences between these two animals and their interactions with native ecosystems.

However, there is evidence that taken together, can shed some light on the issue, and provide the way for further research and better management decisions. These include a review of bison, cattle, and plant community evolutionary histories along with studies of their effects upon habitat selection, nutrition and behavior.


Many studies have documented the more persistent movement of bison compared to cattle. Van Vuren (1979, 1983) studying bison in the Henry’s Mountains of Utah reported that an introduced herd of wild bison differed from cattle using the same ranges in several notable ways. Bison tended to stray further from water sources, used steeper terrain and higher elevations than cattle. Van Vuren also noted that bison seldom stayed in one location more than 3 days.

Even where habitat variation is low, bison seem to wander widely and Lott and Minta (1983) characterized bison as “highly mobile” animals. According to Lott (1991) who has studied free-roaming bison introduced to Catalina Island in California, bison had much larger home ranges than nearly all species of African ungulates, except for during migration periods. For example, water buffalo which are approximately the same size as American bison, have home ranges about 5% of the bison on Catalina Island, even in drought periods (Lott, 1991).

Carbyn and his colleagues (Carbyn et al. 1993) commented that wood bison in Canada often moved up to 32 km over a short period of time “for no apparent reason”.

Norland, (1984) studying bison in Theodore Roosevelt National Park, noted that animals seldom stayed in the same location for more than 48 hours and characterized them as being “highly mobile, moving to new localities and habitats almost daily.” Norland concluded that due to the constant movement and random nature of these movements that plants were “potentially grazed only once, if at all, in a 3-4 week period”.

Meagher (1989) noted that though bison may have strong fidelity to home territory, they do make sudden movements of considerable distance.

Such sudden movements were noted by many early travelers on the plains as well. Along Wyoming’s North Platte River in 1834 John Kirk Townsend (1978) commented that “buffalo still continue immensely numerous in every direction, and our men kill great numbers…”. But the next day he wrote, “When we rose this morning, not a single buffalo, of the many thousands that yesterday strewed the plain, was to be seen. It seemed like magic. Where could they have gone? I asked myself this question again and again, but in vain.”

Not only do bison move more frequently than cattle, but their selection of habitat within the landscape is also different (Kohl 2013). In northern Colorado, Peden (1974) found that bison spent less time near water and only watered once a day. Similarly, Norland (1984) reported that bison would go to water once a day. The length of stay at watering areas was “short duration–one hour or less for even the largest herds”. In both studies, it was noted that bison appeared to prefer drier forage, spent less time in swales and depressions where soil moisture was higher than might be expected.

Cattle, on the other hand, are less efficient water users and display a marked preference for moister forage. Pinchak and colleagues reported that 77% of the observations of cattle grazing foothill ranges in Wyoming were within 366 meters of water (Pinchak et al. 1991) and noted that the majority use was on wetlands or sub-irrigated, level sites. Similarly, Smith (Smith et. al. 1992) found that cattle selected a higher percentage of floodplain habitat and a lower percentage of upland habitat than these habitat types represented in their study area, as did Goodman (Goodman et. al. 1989).

The negative effects of domestic cattle on riparian ecosystems are well documented (GAO, 1988, Kauffman, and Krueger, 1984) as is the ecological value of riparian areas to wildlife (Chaney, et al. 1990; GAO, 1988; Beschta, et al. 1991). Riparian areas make up approximately 1% of the land area of the West, yet 60-80% of the native vertebrate species are associated or require this habitat for their continued survival (GAO, 1988; Chaney, et. al. 1990).

Cows trash riparian area, BLM lands, Ruby Mountains, Nevada Photo by George Wuerthner

Because of their natural propensity to linger in riparian areas or wetlands, domestic cattle pose a far greater threat to arid land biodiversity than native species like bison. Preventing damage by livestock to riparian areas requires capital investments in upland water development, fencing, salting, and riding–all of which increase the costs per unit of production, quickly exceeding the financial return upon investment in many arid western rangelands, unless costs are subsidized (Holechek, 1992).

Peden (Peden et al. 1974) also noted that bison selected rougher, less digestible forage. This gives them a competitive advantage on native grasslands where forage quality varies seasonally. Plus, the ability to utilize lower quality forage results in better distribution of herbivory pressure on rangelands grazed by bison than under livestock usage.

A comparison of digestion between domestic cattle, bison, and Tibetan yak (Schaefer, et al. 1978) found that bison retained forage in its digestive tract longer, hence had a greater ability to digest fibrous feed material and resulted in higher nitrogen intakes. This may be one reason that bison can survive and persist on ranges where cattle perish without supplemental feed.

Furthermore, bison are able to forage in deep snow (Meagher, 1973, Carbyn 1993) which at least in northern regions is a distinct advantage over domestic livestock which requires supplemental feed. Bison also have a hide of higher insulative value than cattle (Peters and Slen, 1964), another adaptation to harsh winters and seasonal food limitations.

Bison also generate more internal heat and can survive lower temperatures than cattle. White (2015) noted that six-month-old bison calves were more tolerant of cold than yearling cattle.

Finally, bison interact with other native species in ways not typically observed with domestic livestock, which may result in reciprocal ecological relationships between different native species. For example, it was noted that bison tended to graze areas around prairie dog towns, thus enjoying succulent new regrowth of plants previously cropped by prairie dogs while at the same time reducing the grass cover which benefited the rodents by making it easier to spot predators (Coppock et. al. 1983).

The factors listed above explain some of the differences between cattle and bison utilization of the landscape. Bison naturally wander widely, far more than cattle, even under essentially open range conditions (Pinchak et. al. 1991).


Although there are historical accounts documenting that bison occasionally heavily grazed an area, it would be incorrect to assume that bison carpeted the plains as one great mowing machine. Many early travelers on the plains noted both the abundance and the absence of bison and other large ungulates due to seasonal movements and other factors. For example, in 1806 while returning from the Pacific, Captain Clark (1964) of the Lewis and Clark Expedition traversed nearly 200 miles of Montana from the Continental Divide in the Big Hole Valley near the Idaho border, down to the Missouri headwaters confluence, across the Gallatin Valley and down the Upper Yellowstone to where the town of Big Timber, Montana now sits before they were successful in seeing and killing a single bison. Their Indian guide, Sacajawea informed Clark that the bison were once numerous in the Upper Missouri headwaters, but had been driven away by heavy Indian hunting. Nevertheless, further down the Yellowstone below what is now Billings, Montana, Clark (1964) noted “the entire country is enlivened by herds of buffalo, elk, and wolves.” And in 1834, John Kirk Townsend (1978) crossing the region near South Pass, Wyoming complained that his party was suffering from a what of food, commenting that “buffalo are rarely seen.” And as previously noted, Captain Raynolds on his 1859 traverse through the heart of the Great Plains bison range, had extensive periods of time without a single bison sighting (Raynolds 1868).

Thus, the shifting mosaic of grazing pressure resulting from the near-constant movement, along with periodic mass die-offs due to disease, harsh weather, or predation, almost ensured that heavily grazed areas would be rested, often for months or even years.

Finally, bison interact with other native species in ways not typically observed with domestic livestock, which may result in reciprocal ecological relationships between different native species. For example, it was noted that bison tended to graze areas around prairie dog towns, thus enjoying succulent new regrowth of plants previously cropped by prairie dogs while at the same time reducing the grass cover which benefited the rodents by making it easier to spot predators (Coppock et. al. 1983).


In addition to the above morphological and behavioral characteristics, a good portion of the West, particularly the majority of public rangelands that are located in the Intermountain West and Southwest consist of ecosystems that historically did not support large herds of bison, if at all. These include most of the sagebrush steppe of the Intermountain West, the Southwest desert regions, and the Palouse grasslands of Washington and eastern Idaho (Miller et al. 1994; Mack and Thompson, 1982).

A number of researchers have commented upon the historic absence or small numbers of bison in the sagebrush-steppe zone west of South Pass, Wyoming, and total absence from the Great Basin Sagebrush deserts. When the first Europeans entered the western United States during the fur trade era in the early 1800’s, bison were reported for southeast Idaho (Work, 1913, Russell, 1955), northern Utah, and eastern Oregon (Ogden, 1910, Bailey, 1936).

However, they were absent from many other portions of the Intermountain West such as the Great Basin Sagebrush deserts of Nevada, the desert grasslands of Arizona, and elsewhere west of the Rockies (Reynolds et. al. 1982). Other large ungulates such as elk, deer, antelope, and bighorn sheep were also patchily distributed or even absent from large areas of these semi-desert and desert regions according to early historic accounts, with bighorn sheep and antelope being the most numerous large animals (Davis, 1982; Ogden, 1910; Simpson, 1983).

There is evidence that suggests that even where bison were found, their numbers were small, and distribution was patchy. Periods of favorable climatic and forage conditions probably enabled intermittent recolonization of suitable habitat by herds moving in from the plains. However, deformities among the skulls and teeth of bison remains from eastern Oregon suggest such periodic recolonizations were infrequent occurrences and these populations were isolated, locally inbred populations (McDonald, 1981).

A number of people have addressed this issue. Daubenmire (1985) argued that protein deficiencies of native bunchgrass rangelands, along with occasional deep snowfalls limited bison populations along their western margins–although as seen earlier, bison are more efficient at extracting nutrients from forage than other ruminants (Peden et al. 1974)

Mack and Thompson (1982) suggested that grass phenology may have limited bison reproduction compared to the plains. While cool-season grasses provide plenty of protein early in the spring, early onset of dormancy in summer, with a consequent loss of nutritive value, may have stressed lactating female bison. On the plains, a mixture of cool-season and warm-season grasses extend the season of high nutrient food resources, permitting greater exploitation by bison.

Van Vuren (1987) has postulated that bison living on rangelands in the Intermountain West found forage inadequate to sustain large numbers of bison except for a few locations. Frequent local extinctions due to weather, human hunting, or the effects of inbreeding, with slow recolonization, rates may have kept bison numbers exceedingly low over this region and may account for the relative lack of historic sightings and limited distribution.

Further evidence to the absence or limited distribution of bison throughout the Intermountain West comes from the native vegetation itself. The native vegetation of these regions has no previous evolutionary experience or adaptation (Mack and Thompson, 1982) to persistent, heavy grazing and trampling.

Although Savory (1983, 1988) and others contend that arid landscapes suffer as a consequence of “under grazing” or from the absence of herd trampling effects, there is growing evidence that soil disturbance by exotic livestock has damaged microphytic crusts and lichen cover in many parts of the Intermountain West. These crusts are important for nitrogen fixation, reduced overland flow, and increased moisture infiltration and often enhance native vegetation establishment and growth (Harper and Pendleton, 1993). Most researchers agree that livestock destroys such crusts through trampling (Anderson, et. al 1982; Miller et al. 1994, Resiner et. al 2013, Roots et al. 2019).

Unlike the rhizomatous Great Plains grass species dominated by blue grama (Bueteloua gracilis) and buffalo grass (Buchloe dactyloides) that seem to tolerate grazing pressure, the native vegetation in this region including dominants like bluebunch wheatgrass (Pseudoroegneria spicata), Idaho fescue (Festuca idahoensis), and Indian ricegrass (Oryzopsis hymenodies), are caespitose or bunchgrasses, and thus less tolerant of both grazing and trampling (Mack and Thompson, 1982, Mack, 1986). Anderson (1991) suggests that it may take up to a decade for bluebunch wheatgass to recover from one grazing event.


Bison robes and meat were a major trade item among Indian tribes of the West. Branch (1962) recounts how by 1738 the Assiniboines were trading muskets, pots, and other items they obtained from the Hudson Bay Company in Canada for bison robes from the Mandans. And John Jacob Aster’s 1810 exploratory fur trading expedition found that the Snake Indians in Idaho were wearing bison robes they obtained by trading salmon to other bison hunting tribes.

One of the contributing factors to increased tribal warfare was the decline of bison due to Indian hunting. Not only did native people use the bison for their own food and shelter, but bison hides were a major trade item that enabled them to obtain blankets, rifles, ammunition, metal knives, metal arrowheads, pots, and other desired trade goods.

The number of bison killed annually by tribes on the plains may have numbered in the hundreds of thousands if not millions. (Since we don’t know how many bison actually resided on the plains, any estimates of bison kill are just guesses)  Much of this slaughter occurred long before there was any significant white settlement and the Euro American bison hunting era which occurred between 1870 and 1883.

In the past, bison were killed primarily by accidental encounters and occasional bison jumps where entire herds were stampeded off of cliffs.

After the adoption of the horse, bison hunting became more efficient with year-round hunting possible, and the area where bison could be encountered was greatly expanded. Plus, the horse permitted the transport of meat and hides great distances.

In Canada, the Indian fur trade of the Hudson Bay Company required canoe transport with numerous portages. This necessitated minimizing weight; therefore, beaver hides were the primary focus of trade. By contrast, the river access provided by plains rivers like Missouri created an opportunity to transport large bundles of bison hides to markets in the East by keelboat and later steamboats. Most plains tribes were not inclined to trap beaver, which is why the trapping brigade consisting of 50-100 white trappers and annual rendezvous became the standard means of obtaining beaver hides between the 1820-1840s.

Bison hides were a favorite trade item at Fort Union on the Missouri River in ND. Photo by George Wuerthner

However, many Indian tribes since they were killing bison for food anyway and could have their wives work preparing the hides for trade, preferred to engage in the bison hide trade.  As Larocque (1805) noted about the relationship of men to women in 1805 “Like all other Indian nations, the women do most of their work…while the men are proportionally idle.” Larocque goes on to say “…they kill the cattle (bison) and their wives who generally follow them skin the animal, and dress it while they sit looking by; they do not even saddle their own horses when their wives are present, not do they take off their shoes or leggings when come in to go to bed.”

All of this profoundly changed the relationship of tribes to the bison, and to each other. Tribes with superlative bison habitat like the Crow were almost in continuous warfare with neighboring tribes seeking to occupy and take over the best bison territories.

Despite the common myth that Indians did not waste animals, the actual situation as reported by many observers was quite different. Like everyone when bison were easily killed and abundant, Indians choose to take the best parts of meat and left the rest to the wolves and other scavengers. This is not unlike brown bears feeding on salmon streams in Alaska which initially eat only the heads of salmon they catch, but later in the run, when the fish are scarce, tend to consume the entire carcass.

Francis Antonie Larocque (1805), a French-Canadian trader, traveled to the Upper Missouri River in 1805 to initiate a trade with tribes located there. This was the same year that Lewis and Clark traveled up the Missouri River and spent the winter of 1805 at the Mandan villages in North Dakota. Larocque noted in his journal that: “They (the tribes) live upon buffalo and deer, very few of them eat bears or beavers flesh, but when compelled by hunger: they eat no fish. They are most improvident with regards of provisions. It is amazing what number of buffalos or other quadrupeds they destroy—yet 2-3 days after a very successful hunt the beef is gone. When hunting they take but the fattest and out part of an animal and leave the remainder; “

Shepard Krech (1999) quotes Trader Charles McKenzie who lived among the plains Indians in 1804 who noted that Gros Ventre Indians he traveled with killed “whole herds” only for their tongues.

Similarly, Alexander Henry in 1809 noted that the Blackfeet left most of the bulls they had killed intact and reported that took “only the best parts” of meat.”    And Paul Kane, another visitor to the Great Plains, remarked that the Indians “destroy innumerable buffaloes” and he speculated that only “one in twenty is used in any way by the Indians” while “thousands are left to rot where they fall.”

Bailey (2016) described Native Americans bison killings: “Stuart (Spaulding 1953:116 117) found immense numbers of bison bones in every direction of the upper Green River Valley, Wyoming, in 1812 and Bonneville observed similar conditions in the same place in 1833 (Irving 1837:95). Clyman (1984:25) observed Crows killing “upwards of a thousand” bison in a day of 1824. Russell (Haines 1965:36) describes one village of Shoshones killing, without using guns, “upwards of a thousand cows” in one day of 1835. On the Great Plains, 500 or more Sioux killed 1400 bison in less than a day of1832 (Catlin in Roe 1951:631) and 100 or more Minatarees and Mandans killed several hundred bison in 15 minutes (Catlin in Hornaday 1889:482). Native Americans often attempted to kill whole herds of bison. In the cited Minataree/Mandan slaughter, every Intermountain Journal of Sciences, Vol. X, No. X, 201X animal of the herd was slain. Using the same hunting technique, the “surround” or “running hunt”, Flatheads (Salish) “usually carried a hunt to the point of extermination.” (Point, nd:141). Literature cited here contains descriptions of pre-hunt ceremonies of Native Americans. Many appear to have believed that providence, more than prudence, determined the continued availability of bison.”

Given the natural mobility of bison herds, it was impossible for tribes to know that they might be slaughtering the bison. However, herds on the fringes on the edge of the bison natural distribution were the first to go.

For instance, Osborn Russell (1955) observed the slaughter of several thousand bison by the Bannock Indians in Idaho. Russell described the scene: “I walked out with the chief to a small hillock to watch the view of slaughter the cloud of dust had passed away in the prairie was covered with the slain several thousand cows were killed without burning a single grain of gunpowder.”

A few years later along the Portneuf River near present-day Pocatello, Idaho Russell noted: “In the year 1836 large herds of buffalo could be seen in almost every little valley on the small branches of this stream: at this time the only traces which could be seen of them were the scattered bones of former years, deeply indented in the earth, were overgrown with grass and weeds.”

Trader Edwin Denig who spent 23 years on the Upper Missouri remarked in 1855 in describing the territory of the Sioux tribe that area east of the Missouri River “used to be the great range for the buffalo, but of late years they are found in greater numbers west of the Missouri” (Ewers 1961).

In the late 1800s, bison had been nearly extirpated from the West (in part by Indian hide hunting).   For instance, by 1830 a decline of bison numbers was already noted at Fort Union on the North Dakota and Montana borders.  In 1834 Lucien Fontenelle told a visitor that the “diminution of the buffalo was very considerable.  A survey of the Upper Missouri in 1849 noted a lack of bison and by the 1850s bison were becoming scarce in Kansas and Nebraska (Isenberg 2000).

This is where paying attention to dates is critical. In the 1830s the only whites in the Great Plains and Rocky Mountain region were the fur trappers, whose numbers even at the height of the fur trade never exceeded 1000 across the entire West. Though they shot bison for food, their focus was on beaver.

The hunting of bison by whites did not become a significant factor until after the mid-1800s and intensified in the 1870s and 1880s when bison numbers were already in steep decline across the West (Flores 1991).

One of the factors that may have contributed to bison extirpation is that cow bison were the only hides traders wanted, hence Indians focused their hunting upon female bison, which may have led to over-harvest.

In a sense, the bison slaughter by whites was the coup de grace, and final nail in the coffin, not the original source of decline (Bailey 2013).

Climate may have also had a role as the early part of the 1800s was the tail end of the Little Ice Age which was among the wettest periods of recent times, and forage was abundant on the plains, helping to support large bison herds.  Towards the late 1800s, droughts began to limit forage productivity, further constricting bison herds, and making territorial conflicts over bison habitat even more intense. Some estimates suggest that perhaps as few as 12 million bison existed on the plains by the 1860s (Flores 2016).

A further complication may have been the numerous herds of horses that competed for forage with the bison. Among the plains tribes, horses were a source of wealth and each band had thousands of horses. In addition, in the southern Plains, there may have been several million wild horses (Flores 2016).

Just the Blackfeet alone were trading tens of thousands of bison robes annually at Fort Union and other trading posts on the Upper Missouri River.  In 1840 the American Fur Company shipped 67,000 bison robes to market in St. Louis. In 1850 fur companies shipped more than 100,000 robes out of present-day Colorado alone. In the early 1870s, some estimate that as many as 1.5 million bison per year were being slaughtered.

These bison robes were in addition to the tens of thousands of bison killed for food, teepees and other direct Indian consumption. As early as the 1830s, some trappers and traders were remarking that the bison slaughter could not be sustained.

I go through the bison slaughter in part because it explains the territorial conflict that existed among many Indian tribes over access to bison hunting territories. Bison were not only an indispensable food source for tribes, but they had also become an essential trade item. By the mid-1800s, most tribes were thoroughly dependent on white man’s trade goods. Blankets, rifles, ammunition, and other trade goods became crucial elements of Indian life. A single bison robe might “buy” a metal pot that could be banged around the plains for years without breaking or you could procure dozens of metal arrowheads for one hide. In fact, by the mid-1800s, many tribal members did not know how to make a stone arrowhead or a clay pot.

The control of bison habitat and thus bison as a source of trade became the driving force in tribal interactions. As bison numbers declined, it put more pressure on the remaining bison herds, and by extension the tribes that still occupied these lands. For instance, the intrusion of the Sioux into Crow territory in the 1850-1860s was in part driven by the Sioux’s desire for control of bison.


The net effect of livestock introduction into regions where bison numbers were restricted or absent is a significant loss of native biodiversity and major shifts in ecosystem function. For example, for the 10,000 years prior to European settlement, the flora of the sagebrush steppe remained essentially unchanged, although migrations up and down mountains due to shifting climatic conditions did occur (Miller, et. al. 1994).

Due to their respective evolutionary histories, a variety of behavioral, biological, and ecological differences exist between bison and cattle. Cattle are poorly adapted for a dry, arid landscape with rugged terrain, and the consequences of their evolutionary heritage may lead to degraded rangelands (Jacobs, 1990). Wild free-roaming bison, on the other hand, are more favorably adjusted to their environment and were sustained for thousands of years without contributing to the serious degradation of rangeland ecosystems.

Since substantial differences in behavior and habitat use and selection exist between bison and cattle, it may be erroneous to suggest that domestic livestock fill a vacant niche left by the extirpation of the bison. Rather cattle should more properly be viewed as a new ecological force that differs significantly from the native species.

Furthermore, some native ecosystems apparently did not support bison in any numbers, or they were completely absent. Much of the Great Basin, Palouse Prairie, Southwest deserts, and California annual grasslands evolved without the presence of bison. These native rangeland ecosystems display limited tolerance to grazing pressure of any kind (Jones et. al 1991; Miller et al, 1994). Indeed, in many of these areas’ large groups of any kind of herding animal were only of local abundance or completely absent (Holechek et al. 1989; Jacobs, 1990; Mack, 1982). Under grazing pressure from domestic animals, these arid landscapes have not adapted or thrived in the presence of domestic livestock as some suggest (Savory, 1988), rather they have shown substantial degradation.

Careful attention to the evolutionary histories of both native species and ecosystem development may prevent degradation of ecosystem function and loss of native biodiversity. The assertion that exotic animals are a replacement for native species should be scrutinized closely before it is assumed gross outward similarities really translate into similar use of the landscape.




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  1. Maggie Frazier Avatar
    Maggie Frazier

    Good truthful, researched information that tells the facts on the difference between wildlife (bison, etc) and domestic livestock that was brought to this country from Asia! I am surprised more readers of this article havent commented here.
    Certainly puts the lie to the livestock industry’s propaganda claim that livestock do the same job as our wild herbivores, doesnt it?
    Anyone who has had a tiny bit of common sense as to how & where cattle “hang out” should realize wild animals, whether bison, deer, wild horses (?) graze or drink & move on.


George Wuerthner is an ecologist and writer who has published 38 books on various topics related to environmental and natural history. He has visited over 400 designated wilderness areas and over 200 national park units.

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