Not Out of the Woods, Yet—Genetic Extinction (Part 3)

We all have issues.  The strategies and means employed to preserve the wild bison genome and promote genetic diversity is no exception.  As discussed in the previous blog—Not Out of the Woods, Yet—Genetic Extinction (Part 2)—several issues are involved in working toward these objectives.

Inbreeding and Genetic Drift:

The common strategy to avoid inbreeding depression and genetic drift is to create large herds.  It is estimated that herd sizes of 2000 to 3000 minimum are required [1].  Wild, free-ranging bison need to forage over large swaths of land.  For a herd size of 1000 animals it is estimated a land parcel of 100,000 acres or approximately 156 square miles would be needed [2].  Achieving the minimum herd sizes, then, would require land areas from 300 to 500 square miles.   For 500 square miles, this would be a square with each side having a length of 22.4 miles.  The only large conservation herd that meets both requirements for minimum herd size and land is the Yellowstone herd.  The herd of approximately 3500 roams over 3500 square miles [3].  However, much of that is mountainous and so does not represent the actual land available for exploitation by the bison, raising another issue—habitat requirements.  It is not enough that sufficient amount of land is acquired.  It must be terrain that can be exploited by the bison. 

Relatedly, especially where private lands are acquired, restoration of the terrain may be necessary.  Typically, private lands have been plowed-over and fenced-in for farming and ranching practices.  Any fencing has to be removed to allow for movement of the bison.  Other fencing, suitable for bison, has to be established along the perimeter of the reserve or refuge.  Any dams built to retain water for livestock would also have to be removed [4]. 

Then there is the issue of money [2].  The cost to acquire the necessary land and place a herd of 1000 onto that land may run well over $ 1 million. Reaching the minimum requirements to preserve and promote the bison genome could then run $2 to $3 million per herd. Significant funding raising efforts will be needed.

So what land is possibly available?  Bailey concludes that land east of 98 degrees longitude—Minnesota, Iowa, Missouri, eastern Oklahoma, eastern Texas and all points east—is  too fully developed to allow for the necessary land areas.  Between farmland and cities is there is no land parcel large enough to support the minimum herd size.  This leaves the plains—lands west of 98 degrees west longitude to the Rocky Mountains—available.  Perhaps some parts of Nevada and Oregon could be utilized [5].  There are still large tracts available in this region to promote such herds.

Cattle-Gene Introgression:

A potential problem has been identified in regard to purifying bison herds of cattle-gene introgression.  Removing bison with cattle genes may inadvertently remove genes of common ancestry.  Authors Kathleen O’Neal Gear and Michael Gear [6] raise the question: Did bison interbred with any prehistoric species of the Bos side of the Bison-Bos family, and if so, is this the source of the cattle genes?  No one really knows. Removing bison having only genes from domesticated cattle requires the DNA testing to differentiate between those genes belonging to both cattle and bison ancestors from genes belonging only to domesticated cattle.  This would require a complete mapping, or sequencing, of the bison genome [Gears], which to date has not been performed.  Except for the Yellowstone and the Henry Mountains herds, and more recently the American Prairie Reserve herd, all bison most likely have at least some cattle genes.  Derr has found cattle genes in approximately 64% of US federally managed herds [7].

The Gear position, though, does not address the cross-breeding that did take place on private ranches in the US and performed by the Canadian government into the 1960s. There is no doubt the cross-breeding occurred and a few studies have suggested that introgression has been detrimental to bison [8].

Purifying the herds of cattle-gene introgression along with the movement to list wild bison under the Endangered Species Act presents another potential issue if such listing would succeed, according to the Gears.  Some are arguing that the scarcity bison without cattle ancestry qualifies wild bison as an endangered species.  Under the ESA the sale or transporting of bison free of cattle genes could be punishable by a $50,000 fine and one year in prison per charge.  Ranchers or farmers owning bison without cattle ancestry could find themselves being charged under the ESA if they would try to sell or move their bison.  The argument to list wild, pure, bison as endangered, then, could lead to conflicts with current legal definitions governing the status of bison. 

Yet, legal recognition of plains bison as wildlife is required if the wild genome is to be restored on federal lands.  But this seems unlikely at this time.  Most states do not recognize wild bison (see March 2019 post, Legal Status of the American Bison), and the federal government will not restore wild plains bison without support from the affected states.  This could change if the Fish and Wildlife Service would recognize the threat domestication represents to the wild genome, and lists the plains bison as a threatened or endangered species [9].

In any event, the greater goal is to restore wildness to the bison genome.  Reducing cattle-gene introgression to low levels and letting nature takes it course, may over time swamp the cattle genes.  Achieving absolute purity may not be needed if the other actions to promote the wild genome are taken [10].

Artificial Selection:

Purifying the conservation herds of cattle-introgression, though, is not enough to preserve the wild genome and promote genetic diversity.  Artificial selection, caused by human intervention, must be minimized as much as possible.  The complete elimination of human intervention may not be feasible.   No matter how large the land parcel may be, fencing will still be required to keep bison out of private lands.  Handling, needed for testing, culling and transporting of animals, will also be involved in implementing the other objectives. 


Various mechanisms threaten the existence of the wild bison genome, requiring various strategies to thwart the threat.  These strategies and their implementation, however, present conflicting objectives, which may require trade-offs, and issues, which demand solutions.  But the restoration of the wild genome and the promotion of genetic diversity cannot wait until all issues have been fully resolved to all interested parties’ satisfaction.  Fortunately, efforts are proceeding to realize the necessary objectives (e.g., The American Prairie Reserve, the Buffalo Field Campaign, etc.) while work continues to resolve the obstacles still in the way.

End Notes:

[1] Hedrick, Paul W. “Conservation of Genetics and North American Bison (Bison bison).” Journal of Heredity 2009: 100(4): 411-420.

[2] Heidebrink, Scott, Bison Restoration Manager, American Prairie Reserve.  Email to author 03-Oct-2019.

[3] Bailey, 180. Baily, James A. 2013. American Plains Bison: Rewilding an Icon. Sweetgrass Books. Helena, MT.

[4] American Prairie Reserve Bison Report 2016-2017.  Retrieved 10-Oct-2019 from  Also, Bailey, 207.

[5] Bailey, 207.

[6] The Gears are well-known authors of over 50 novels.  They may be best known for their People of the Earth series.  In addition to writing novels, they raise bison.

[7] O’Neal Gear, Kathleen and Gear, Michael W. August 2010.“Bison Genetics—The New War Against Bison.”

[8] Geist, Darrell, Habitat Coordinator.  Buffalo Field Campaign.  Email to author 19-Sep-2019.

[9] Bailey, 220.

[10] Bailey, 214.

Not Out of the Woods, Yet—Genetic Extinction (Part 2)

The mechanisms by which genetic extinction of the wild bison genome may occur were described in the September post.  If the prevention of loss of genetic information and the promotion of genetic diversity are to be achieved, how should we proceed?  What avenues are available or can be created? Broad objectives were laid out in the Vermejo Statement (see the Feb. 27, 2019 post From the Brink to the Foothills-Part 2).  More recently Paul Hedrick has laid out more specific objectives.  These include:

  • Keep cattle ancestry at a very low level,
  • Avoid inbreeding and artificial selection for livestock-related traits, and
  • Retain sufficient genetic variation for future adaptation.

Achieving these objectives requires a variety of strategies.

Cattle-Gene Introgression:

The greatest focus of conservation genetics has been identifying herds with cattle ancestry, since the efforts to restore the wild bison have been threatened by domestic cattle introgression.  Reduction of cattle-gene introgression involves several approaches because of various circumstances [1].

The popular tenet from the medical profession—Do No Harm—applies here as well.  The first and most logical strategy is to not introduce bison with known cattle ancestry into herds free of cattle  introgression.  Though this seems to be the easiest approach, there are only a few herds known to be free of cattle ancestry—e.g., the Yellowstone herd, the Henry Mountains herd, and more recently, the American Prairie Reserve herd.  This approach only protects these herds until other herds free of cattle ancestry can be established.  It should be noted the notion of cattle ancestry free is relative.  There may always be the presence of cattle genes.  Additionally, the complete eradication of cattle genes may not be desirable since the genetic testing has not matured enough to differentiate between genes unique to domesticated cattle and genes having common ancestry to bison and cattle (This issue will be explored in more depth in part 3).

A corollary to the above strategy is to introduce bison without cattle ancestry into herds with cattle-gene introgression.  The benefits could possibly include: a decrease in inbreeding depression, an increase in genetic variation, and genetic swamping of cattle ancestry. This would dilute the presence of cattle genes to the point at which natural selection would eventually take over and reduce the effects of cattle ancestry. A variation of the introduction of cattle-gene free bison strategy involves starting new herds.  

Another approach regarding cattle ancestry involves translocation of bison between herds with similar levels of cattle-gene introgression.  This, at least, would not raise the overall level of cattle ancestry, but would have the benefit of avoiding inbreeding depression.  But this requires more accurate tests to estimate the level of introgression and further examination of potential phenotypic effects [2].

Finally, culling may be used to reduce mitochondria DNA (mtDNA) and specific nuclear alleles (one of two or more alternative forms of a gene found at the same place on a chromosome) of cattle ancestry.  Culling involves separating out the undesirable animal with the objective of reducing or eliminating the traits, qualities or disease of that specific animal from the herd.  Undertaking this strategy to reduce the mtDNA, however, incorrectly assumes this also reduces nuclear DNA.  Care needs to be taken to retain variation at the nuclear level, requiring more extensive and accurate testing.  And culling to reduce specific nuclear alleles is also problematic. Unfortunately, this action will most likely have other alleles associated with the cattle ancestry remaining at other unidentified genetic regions [3].

Inbreeding and Genetic Drift:

Inbreeding and Genetic Drift are significant issues.  Most of the conservation herds are relatively small (i.e., less than 1000). Under these circumstances maintaining the genetic information and diversity required to promote the wild genome is difficult if not impossible.  To avoid these processes of genetic extinction, herd sizes of at least 2000 to 3000 are needed [4].  Out of the 44 conservation herds, only 10 herds have more than 400 animals, and out of these, only 4 have more than 1000 bison—Yellowstone National Park, Medano Ranch, Co., Tallgrass Preserve, OK, and Custer State Park, SD).  The herds smaller than 400, are most definitely, losing genetic diversity, and in danger of inbreeding.  Six of these herds are being managed as a meta-population with exchanges of animals.  This practice may alleviate some inbreeding but will not prevent loss of genetic diversity.  Only the Yellowstone herd is large enough (3000 to 4000) to limit that loss [5].  In addition to the four conservation herds mentioned above, the American Prairie Reserve [see link to the American Prairie Reserve’s website in the Favorite Links section of this blog] in Montana has a herd which is currently slightly less than 1000. 

The regular exchange of bison between herds is another method to avoid inbreeding and genetic drift. In moving bison to other herds, though, consideration must be given to disease control, handling practices, and state laws.  Animals would need to be tested prior to transfer to ensure diseases such as brucellosis and tuberculosis would not be transferred.  Handling of bison is difficult.  Care would be required to ensure the safety of the animal, not to mention the personnel involved.  Finally, laws defining the status of bison differ from state to state and would have to be taken into account.

Achieving genetic diversity requires ongoing assessment of genetic variation from which strategy decisions can be made.  In this regard, Hedrick offers several recommendations which are beyond the scope of this post [6].

Artificial Selection/Domestication:

A certain amount of human intervention in conservation herds cannot be avoided.  Even in Yellowstone the herd suffers from human management—the herd size is limited, the herd has been vaccinated, the average age of the herd has been artificially reduced, and  access to seasonal ranges has been restricted [7].  And this is the most “wild” bison we have!

Herd sizes are managed through random culling with the first animals coming through the chute being selected.  It has been observed, though, the largest animals are usually the first.  Bison traits, then, associated with large body size are being artificially selected out.  Thus, even random culling can have a negative effect on natural selection.  Culling along with vaccination is also used for disease control.  However, disease control treats low resistance bison equally with high-resistance bison, preventing natural selection from promoting bison with high-resistant immune systems. Intervention to control disease, then, tends to retain susceptible animals [8].  If the wild genome is to be encouraged, culling to limit herd size and efforts at disease control must be either eliminated or be rare and minimal.  Still, culling to reduce herd size may be necessary due to land and carrying capacity [9].

Keeping human intervention at a minimum is not enough.  As has been found with the re-introduction of wolves in Yellowstone bison have had to relearn their defensive traits. Avoidance of loss of defensive traits will require the introduction of the bison’s natural predators—the wolf and the grizzly. Predation is also a natural selective force. 


The various genetic extinction mechanisms and the circumstances in which bison find themselves—large herds, small herds, land issues, etc.—require several strategies to prevent genetic extinction and promote genetic diversity. The American Prairie Reserve’s bison management approach is a good example of the implementation of some of those strategies discussed above:

  • Their overall goal is to achieve a herd size of 2000 to 3000 within the next 5 to 7 years
  • Their approach is “hands-off” as much as possible. 
  • Manipulation of bison population is minimized to allow for the development of natural sex ratio and age structure
  • Mortality from bull competition, predation, and other natural events is permitted (However, no wolves or grizzlies are currently present on the Reserve)
  • Continue to secure more land and habitat to support the herd and allow for continuous grazing
  • Ensure new bison introduced into the herd are free of cattle-gene introgression [10]

Implementing these strategies involves answering many questions. For instance, land is perhaps the most significant issue.  The common strategy to address the extinction mechanisms is to create large, free-ranging herds, requiring large amounts of land.  But not just any terrain will do.  The habitat must support large swaths of grazing land. How much land is needed for a large herd of free-ranging bison?   What needs to be done to prepare the habitat? Are there state and/or federal regulations involved?

Another concern involves genetic testing.  Ridding herds of cattle genes may cause the loss of common ancestry genes.  How do we differentiate?

If predation is to be re-introduced, what is required to make that happen?

These issues need to be worked out, and will be pursued in part 3 of this discussion.

End Notes:

[1] Hedrick, Paul W. “Conservation of Genetics and North American Bison (Bison bison).” Journal of Heredity 2009:100(4): 411-420.

[2] Phenotypic Effects—Effects on an organism’s observable characteristics or traits and covers the organism’s physical form and structure, developmental processes, biochemical and physiological properties, behavior and products of behavior (Wikipedia).

[3] Hedrick.

[4] Bailey, James A. 2013. American Plains Bison: Rewilding an Icon. Sweetgrass Books. Helena, MT. 179. and Hedrick.

[5] Bailey, 179.

[6] Hedrick.

[7] Bailey, 140.

[8] Bailey, 142-145.

[9] Carrying Capacity—the ability of a habitat to sustain a population (Bailey, 87).

[10] Retrieved 02-Oct-2019 from Also, email to author from Scott Heidebrink, Bison Restoration Manager, American Prairie Reserve. 03-Oct-2019.

Not Out of the Woods, Yet–Bison Genetic Extinction

The topic of genetic extinction of the wild bison genotype is rather extensive.  So, the plan is to discuss this issue in several parts, beginning with the mechanisms contributing to the loss of genetic information. Then follow with an exploration of how to avoid those mechanisms and a review of particular issues involved.

Part I: Mechanisms

Imagine a river running endlessly in both directions (nevermind the logical inconsistency) with only one bridge crossing the river, the only means to the other side. Furthermore, coming up to that bridge is a 12-lane highway, but the bridge only permits one lane with no merging lanes allowing access to that one lane.  Instead the other 11 lanes all end with a wall at the river’s shore.  But this is unknown until the ends of those lanes are reached.  Only those traveling on the lane accessing the bridge are able to cross the river.  This situation presents a bottleneck.  By the 1900s the North American bison entered a genetic bottleneck.   From a population of many millions only less than a 1000 were able to cross over our imagined bridge.  A genetic bottleneck occurs when a population is reduced to a small subset of the original population.  The last remaining individuals, then, represent the remaining genetic heritage of the entire initial population. But they do not represent the overall genetic diversity of the population before the bottleneck.  Such circumstances are detrimental to the viability of a species because of the loss of genetic diversity [1].

                Other than out-right extermination of a species, Bailey has identified five processes contributing to the genetic extinction of the wild bison genotype [2]:

  • Founder Effects (Initiating herds with few individuals having limited genetic diversity)
  • Genetic Introgression (Crossbreeding with cattle genes–hybridization)
  • Inbreeding depression in small herds
  • Genetic drift in small populations
  • Artificial selection by human intervention (domestication)

Before going further the concept of wildness needs definition.  According to Bailey, wildness refers to the impact humans have on an animal population or an ecosystem.  A species or an ecosystem is considered wild if it exists and functions with no human intervention [3].  Of course, in the case of bison, Native Americans have interacted with the bison.  But perhaps it could be argued their intervention had no more impact than that of natural, random events; certainly not the impact our culture has had. 

Founder Effects:

Founder effects involve initiating herds with few individuals. Today’s herds have been initiated with the few bison left from the slaughter that took place in the latter half of the 19th century.  Because of this, and as illustrated in the thought experiment above, with the loss of genetic diversity the potential for effective natural selection has been reduced.  In addition, with few founders the stage is set for other resulting mechanisms contributing to genetic extinction—for instance, inbreeding depression and genetic drift experienced in small herds.

Genetic Introgression and Hybridization:

Bison were saved from extinction primarily by 5 ranchers and the small remnant in Yellowstone National Park.  The ranchers during the end of the 19th century and early 1900s experimented with crossbreeding bison with cattle in an effort to raise a hybrid for meat production.  This endeavor quickly ended since bison-cattle hybrids almost always resulted in female offspring and no viable male offspring.  Hybridization that results in one sex being absent, rare or sterile indicates evolutionary incompatibility between the two species [4].  Even though hybridization was a dead-end, the attempt introduced cattle genes into bison herds, known as genetic introgression. Many of the bison from these early hybridization efforts were used to initiate or grow other herds, injecting traits related to domestication into the bison herds and effecting physiology.  One study by Derr found bison with cattle-gene introgression tend to be smaller at an early age and never grow as large as more pure, wild bison [5].


Inbreeding involves the breeding of closely-related individuals and occurs in small herds or in herds maintained with few bulls [6], limiting the genetic diversity. Bison bulls will mate with as many cows as is possible, and dominant bulls will father more calves while less dominant bulls may not father any calves [7].  In small herds the genetic material of the dominant bulls will tend to be concentrated and passed on with genetic material of others bulls lost. The negative effects of inbreeding replace natural selection in determining the future genetic make-up.

Genetic Drift:

A change in the relative frequencies of alleles (one of two or more alternative forms of a gene found at the same place on a chromosome) is known as genetic drift. This process occurs in a population due to random events during survival and reproduction [8]. Random chance determines which genes or animals survive and reproduce, causing genetic change in a population.  For instance, a bison could break through the ice when crossing a river and drown. But the major source of changes in allele frequency lies in reproduction during the production of ova and sperm.  When ova and sperm are formed in cell division, chromosomes split leaving the reproductive cells with only half the chromosome set. Thus, during reproduction some alleles are discarded both from the bull and the cow. In large populations random events effects are relatively unimportant because opportunities are present for natural selection to work, mitigating any loss of genetic information. However, in small populations genetic drift may cause some genes to disappear, reducing the genetic diversity and evolutionary potential [9].

Artificial Selection—Domestication:

Domestication results from the replacement or weakening of natural selection by artificial, human-managed selection.  Thus domestication is eradication of wild bison by modification. For example, aurochs were continually domesticated eventually leading to modern domesticated cattle.  These efforts were so extensive aurochs no longer exist.  The essence of selective breeding involves humans deciding which individuals will produce the next generation which will better serve human goals [10].

One of the goals involves handling. Wild bison are difficult to handle, causing harm to the animal, causing potential damage to shoots and pens, and involving more time and effort on the part of the ranchers.  To mitigate handling issues, bison ranchers and farmers have found that by increasing the level of serotonin and lowering the levels of dopamine bison become more docile.  Over time selecting those animals with increased serotonin and lower dopamine for breeding will artificially select the more manageable bison, moving from wildness to domestication. 

Additionally, since ranching and farming are bottom-line businesses, each bison is seen as a productive unit.  Under this perspective management of bison will increase the number of cows altering the natural sex ratio. Bulls can breed many cows, whereas a cow will only have one, possibly two calves per year. Maximizing the commercial herd requires few bulls but many cows.  Besides, cows are also easier to handle than bulls. A biased sex ratio shifts the breeding behavior.  Cows that do not incite competition between bulls will more likely be bred.  Thus the traits associated with competition between bulls become artificially selected out.  Unfortunately, this management perspective not only occurs with private herds.  Public herds are seen as a revenue source, and consequently, subjected to the same practice [11].

               Given the above mechanisms pushing us toward the genetic extinction of wild bison, the question becomes:  how do we mitigate or prevent these processes?  Complete avoidance may not be possible. The means and objectives involved may be in conflict with each other and may require trade-offs.

Prevention and mitigation of the genetic extinction mechanisms contributing to the loss of wildness in bison will be explored in the next post.


[1] Bison Bellows. Retrieved 09-Sep-2019 from

[2] Bailey, James A. 47.  2013. American Plains Bison: Rewilding an Icon. Helena, MT. Sweetgrass Books.

[3] Bailey, 73.

[4] Hedrick, Paul W. “Conservation of Genetics and North American Bison (Bison bison)”. Journal of Heredity 2009: 100(4): 411-420.

[5] Bailey, 48.

[6] Bailey, 76.

[7] Lott, Dale F. 194. 2002. American Bison: A Natural History.  Berkeley. University of California Press.

[8] Bailey, 78.

[9] Bailey, 49-50.  Also for a full discussion of genetic drift see Bailey, 78-80.

[10] Lott, 196-198.

[11] Lott, 198-200.

Bison Romance

During North America’s early spring, a reddish-orange creature emerges.  Within minutes of its appearance, the newly-born bison calf rises and begins expending pent up energy.  Its movements constantly watched over by its mother, the largest animal on the North American continent.  Colloquially known as a “red dog,” this little beastie weighs in from 30 to 70 lbs [1] upon its debut, a far cry from its future weight (approx. 2000 lbs for males and 1000 lbs for females), easily attained within a couple of years.  Some may consider this newly arrived entity as “cute.”  They would be deceived.  For this “cute-ness” scampering around in the spring air will transform into potentially the greatest source of animal-induced injuries to humans in North America.  It will scoff at bears, coyotes and mountain lions.  Oh my!!  Of course, wolves are a different matter.  Hunting in packs, they can take down an adult bison. So what is the origin of this “cute” beastie?

Bison Calf – “The Cute Little Beastie”

                Its genesis begins slightly more than 9-1/2 months [2] prior to its emergence. During the summer months of July or August romance rumbles and shakes the earth.  The females of the species begin to gather with the up-until-now aloof males straggling in from their own groups to join the females.  Before now, the bulls do not communicate much with other bison.  Prior to the breeding season, they are usually off on their own or in small groups, being content to graze.  However, with the onset of the breeding season, the rut, the bulls become more communicative.  One may believe only courtship of the female occurs during the rut.  But the male has a tough job ahead.  He not only has to win the attention of a receptive female, but he also has to manage other bulls.  The bull will seek out a female and stay with her.  This behavior is called tending.  While doing so, he must also ward off other bulls by fighting and threatening.

                Males will vie for the females.  Even though a bull is tending a cow, it is not entirely a foregone conclusion this will be the mating pair.  Other bulls may threaten to replace the tending bull.  The one who dominates will take over the tending, but will then also have to ward off anxious bulls looking to mate. But fighting requires much energy which is also required for breeding.  So, the bull will generally threaten first in order to conserve energy.  Threatening may begin with bellowing, a sound the bull makes, which to the undiscriminating ear, may sound like thunder off in the distance.  The intruder may also bellow in return, and if the bellowing competition escalates, as typical of males, the sounds become louder and the bravado more expressive.  During the bellowing, the bulls may paw the ground or wallow [3] [4]. Bison often will lie down in a barren depression and role back-and-forth, throwing up dust.  Though there are other reasons as well for this behavior, it is often used in the bull’s threatening behavior.

                During challenges, wallowing may also engage a strange phenomenon. But males of other species sometimes exhibit bizarre behavior when attempting to win over the female as well — nothing really new here.  A threatening bull may urinate in a wallow and then roll in the moist ground.  The reason is not fully understood.  Dale Lott, a naturalist, speculates the testosterone level is being signaled to the challenging bull.  As the bull uses up physical resources, muscle begins to metabolize with the metabolites entering the urine, which can be detected by the conditioned nose of the challenger.  The opposing bull will know if fat is still being burned and if muscle is still intact [5] of the threatening bull, allowing the opposition to determine if he has the resources to continue the fight against the threatening bull.

Bison Wallowing

                If bellowing and wallowing do not work, then the males will begin to posture.  There are two types of posture: head-to-head and broadside.  Head-to-head posture precedes a charge in which the two bulls will run straight at each other.  As they approach one another, either one or the other may submit by turning  away or they will bang heads.  If they approach slowly, they will engage in a behavior called “nod-threatening”.  The two bulls will stand close enough to each other to reach the other with their horns by turning their heads aside.

                In the broadside posture the bull will keep himself broadside to his opponent and raise his head a little as well as arch his back and bellow.  The idea is to show he is not to be messed with.  However, this posture usually does not lead to a fight.  The broadside and the nod-threatening postures demonstrate the lengths bulls will go to forewarn each other.  The issue is efficiency.  Perhaps even more than offering protection to the herd, producing calves is the bull’s prime directive.  Breeding requires energy, and the bull, instinctually driven, attempts to mate as much as possible to produce  as many calves as possible.  Fighting seriously reduces the bull’s energy.  Further, fighting and breeding burn up fat and muscle mass, which have to be replaced between the end of the rut, which may last into September, and the onset of winter if the bull is to survive the winter [6].

Bulls Going Head-to-Head

                Before the tending of the female and the subsequent efforts to win his prize, the bull first selects a female.  Cows come into heat sometime during the rut, and will only be in that state for about two days.  Cows only release one egg at a time.  Achieving fertilization requires attracting a suitable mate and be willing to mate, which means changes for the cow.  When she comes into heat, the vulva becomes swollen and oozes mucus and lymph, signaling to the bull she is ready to mate.  The bull will wander through the herd inspecting each cow to determine which ones are ready to mate.  After inspecting, the bull may curl his lip.  Lip curling is a complex expression.  The bull stretches out his neck, holds his head level, distends his nostrils and curls back his lips.  This occurs after examining the cow’s vulva or sniffing her urine [7].  The cow’s urine will indicate how close she is to ovulation.  The bull detects this through the vomernasal organ, which has an opening in the roof of the bull’s mouth.  This organ seems specialized for analyzing the female’s urine [8].

Bison Lip Curling

                Often the cow rebuffs the bull by the swing of the head, a thrust of horns or sometimes just a good swift kick. After selecting a cow, and if the bull has not been dissuaded, the courting begins.  During courting, the bull stands parallel to her side, warning off intruders which may even include the cow’s previous calf or yearling.  The pairing may last only a few minutes if a more dominant bull intrudes and displaces the tending bull.  Or the pairing could last one or two days.  In either case, the tending bull will move on to another cow, being driven by the bull’s prime directive.

Even though the bull may seem dominant, but the cow rules the courtship. Typically the bull follows behind her.  If he tries to direct her in a particular direction, she can easily dodge him and wander off on her own.  He is resigned to follow her.  Eventually, the herd leaves the pairs behind.  The cow may try to rejoin the herd, but the bull will move to block her, which she can easily evade. Or she may also go for a higher ranking male.  She, too, has a prime directive to breed the best calf.  After all, she only has one shot each season.  So she must choose wisely, and is more receptive to older bulls who have survived winters, predators, disease and battles.  Older bulls have been tested and have been found worthy.  If, however, she stays, she has chosen him.

The bull utters brief panting sounds as he approaches the cow, warning her.  First advances are typically repelled but the bull will be insistent.  His intentions are made known by standing and swinging his head.  Eventually he will attempt to put his chin on her rump, which, in response, she will evade.  He may try to climb upon her, only to have her slip out from under him.  But once receptive, the cow will allow the bull to mount.  He uses his chin as leverage to lift himself onto her rump, leaning his head against her side and pressing his forelegs around her.  After insertion, the thrusts last only 4 to 10 seconds.  Then he either drops off or releases his forelegs so the cow can walk out from underneath him.  The copulation may harm the cow.  Her flanks may have bloody wounds from the bull’s front hoofs striking and rubbing her. The moment of copulation usually attracts the attention of younger males who will follow the couple afterwards.  But the tending bull will stay with the cow, warding off other suiters to prevent them from also mating with her.  This ensures the tending bull’s seed is successful fertilizing the egg and not replaced by the seed of another.  Eventually though, the tending bull will move on to attempt to mate with other cows [9][10]. 

Bison Mating

Nine and-a-half months later, the fruition of the bison romance occurs, as a reddish-orange little beastie emerges.  Upon birth the cow licks, pulls away and even eats the membranes entangling the calf.  After disposing of these membranes, she licks the slimy wet coat of the newborn.  Meanwhile oxytocin, a pituitary gland hormone, has flooded her brain stimulating her endearment of this new creature, which she will nurture and protect [11]. If the cow is only three years old, then this is most likely her first calf.  Females breed when 2 years old and have their first calf at 3 years old.  Cows can live 20-25 years, having a calf each year [12]. 

The cycle completed, the newborn “red-dog”, if male, will repeat the fine tradition of seeking and tending a female, threatening and fighting challenging bulls, and mating with as many females as possible.  If the little beastie is female, she will enter into the honored role of controlling the mating process and producing off-spring, and nurturing the next generation.  And so the cycle continues, sustaining the herd and ensuring the survival of the species.

End Notes:

[1] Retrieved from

[2] The average gestation period is 9-1/2 months.  Retrieved from 5-Jul-2019.

[3] McHugh, Tom. 1972. The Time of the Buffalo. University of Nebraska Press. 191-195.

[4] Lott, Dale.  2003. American Bison: A Natural History. University of California Press. Berkeley. 14-18.

[5] Lott. 9.

[6] McHugh. 192-193.

[7] Lott. 15.

[8] Lott. 20-21.

[9] McHugh. 192-195.

[10] Lott. 15-17.

[11] Lott. 29.


Brucellosis: Crying Wolf?

Just north and outside of Yellowstone National Park, deep snow covers the ground and bitter March winds blow through the pines. Because of the adverse winter conditions in the Park, the bison have had to seek better grazing. Following the easily traveled snowmobile trails, they have wandered out of the harsher conditions of the late winter park.  Using their heads to plow away snow to uncover the buried grass, a small group of bison graze.   Only the crunching of the snow under their hooves, the occasional snort of exhaled breath, and their rhythmic breathing along with the occasional bird song and the moaning of the pines swaying in the wind can be heard.  Suddenly, a shot rings out!  A bison cow goes down!  Then another shot and another!  Two more cows are hit.  One stumbles and then drops.  The other runs back toward the park bleeding profusely.  The rest have already bolted for the safety of Yellowstone.  The wounded one makes it back to within the confines of the park, but has stopped, exhausted, drained.  She tries to take another step in the deep snow, but cannot.  She lies down and slowly dies.  No one comes for her.  A few days later, her scavenged carcass will be found.  Back at the killing grounds, the hunters are celebrating.  They have thwarted another incursion of the feared bison onto the bison’s natural grazing habitat.

            So why fear the bison outside of Yellowstone Park?  They do not attack humans or other animals unless they feel threatened. They do not devastate the land as they graze. So why such hostility toward them as illustrated above, which is a fictionalized account of what has happened and continues to happen.  Bison roaming outside of the Park into Montana are either hazed back into the park or killed.  Hazing involves rounding up the bison and herding them back into the boundaries of Yellowstone or into a quarantine pen, which inherently causes trauma for them.  But herding of bison is difficult.  Killing is easier.  But why slaughter an animal carrying the last known wild bison genome?

            The Montana ranchers claim bison threaten the cattle herds with the disease brucellosis.  Brucellosis, a bacterial infection (B. abortus), causes abortions and still-births in cattle, bison, elk, bear, deer, etc.  If a brucellosis outbreak would occur and spread through a cattle herd, financial devastation could result for the rancher.  As a side note, any losses, ironically, would be covered by government subsidies. 

            Upon closer examination of the circumstances and history of brucellosis in bison, the claim of the ranchers and the Montana Livestock industry strike one as a smoke screen.  One would think that science should be driving the claim, but politics and profits seem to be the drivers.  The USDA has threatened the state of Montana with the loss of Montana’s brucellosis-free status, which permits shipment of untested cattle across state lines.  The loss of such status means the ranchers would have to pay to have the cattle tested prior to shipment, which incurs additional costs. To ensure no risk of cattle infection the eradication of brucellosis has taken on a zero tolerance approach, giving absolute priority to achieving a zero risk level for cattle infection [1].  In addition, since almost no brucellosis can be found in American cattle herds, the USDA has expanded its efforts to eradicate the disease. The US Dept. of Agriculture has turned its attention to eradication of brucellosis in wild animals.  Thus, agencies whose funding depends on the USDA are recruited into the cause [2].  The eradication of brucellosis has become politicized with agencies increasing their power and funding by joining the crusade to rid the wild animal population of brucellosis.  The crusade, of course, includes the method of slaughter as well as vaccination.  However, the slaughter only seems to be restricted to bison; other wild life are not included. The slaughter of the Yellowstone bison arose, then, out of fear and political expediency, not science.

            Brucellosis probably arrived with infected cattle imported by Spanish settlers into Mexico.  Sometime prior to 1917 infected cattle were introduced into the Greater Yellowstone Area [3][4] with the disease spreading to the bison.  But the transmission of brucellosis from bison to cattle has never been established.  The actual transmission path would have to be through the ingestion of infected birthing materials or from an aborted fetus.  Thus, bison bulls, calves, yearlings and non-pregnant bison cows would not pose a threat. Furthermore, infected pregnant bison females will only pass infected material in her first pregnancy since after the first pregnancy, the uterus develops protection, preventing infected material being shed in subsequent births [5]. 

In order for brucellosis to be passed on to cattle cows, the cattle cows would have to lick or eat the discharged reproductive debris.  But bison abortions or still-births are rare.  If they do happen, the most likely time is winter when cattle are not present.  Cattle are unable to withstand bitter winters and are not grazed near Yellowstone until June.  By this time, the bison would have returned to the park [6].  But even should there be aborted or birth materials in June or later, the brucellosis bacteria cannot survive warm weather or direct exposure to sunlight.  Besides, predators and scavengers would all but guarantee fetuses or infected reproductive material would not persist beyond mid-May [7]. Thus, the possibility of cattle cows contacting infected material is remote.

Recent studies have shown that bison are not the primary reservoir of the brucellosis bacteria.  The bison were once considered to be the primary source because of high levels of B. abortus.  But examining the extent and transmission characteristics in other wildlife has shown elk to be the primary source of B. abortus.  Even though elk have a lower level of B. abortus, they are more numerous and widespread than bison.  Bison rarely move outside of conservation areas and are subject to rigorous management practices that limit migration, making comingling with cattle almost impossible.  In contrast, elk are allowed to freely range, and make long-distance migrations between summer and winter grounds, increasing the probability of contact with livestock.  Genetic studies have confirmed this, demonstrating elk to be the likely source of infections, not bison [8].  This begs the question: Why are elk, the primary source of brucellosis infections, allowed to roam free and bison are not?  The revenue generated from elk hunting may have something to do with it.  Revenue from elk hunting activities amounts to approximately $11 million annually for the state of Montana alone [9].

            Hazing and killing of bison that have roamed outside of YNP are not the only methods employed to placate the fears of the ranchers. With the state of Montana and the USDA insisting, bison are periodically rounded-up and tested.  About 45% of the bison test positive for long-term antibodies.  Using a positive test as proof of infection, the bison is slaughtered.  But another test is performed after the bison has been killed to determine if actual bacteria are present.  Comparing these two tests reveals a drastic difference.  Very few slaughtered bison have the actual bacteria.  The bison, then, are being slaughtered simply because they have developed immunity to brucellosis [10]. The control of brucellosis is a “no holds barred” approach when it comes to bison. Of course, the slaughter includes both bulls and cows. But why slaughter the bulls who cannot transmit the disease, and are essential for breeding? The logic to the slaughter remains elusive unless it is understood as arising from an unjustifiable fear.

            In response to the brucellosis eradication efforts in bison a number of viable solutions have been offered.  The Buffalo Field Campaign ( has offered several. These include:

  • Develop herd management plans that adjust cattle grazing dates which would eliminate transmission potential;
  • The Greater Yellowstone Area could be exempted from the OIE certification process by keeping cattle out of the area.
  • The state of Montana could develop risk management strategies for domestic cattle that allow free roaming bison [11].

            In light of the evidence–genetic studies, the migration and grazing habits of bison, the elk herds as a primary brucellosis reservoir, the transmission dynamics, and the testing results—and the offered solutions, why does the slaughter of the bison continue? Based on the above, it appears to be a result of the efforts of the livestock industry in Montana to maintain political control, using the fear and the paranoia over brucellosis as the means to maintain that control.

[1] Lott, Dale F. 2002. American Bison: A Natural History. University of California Press. Berkely, CA. 111

[2] Callenbach, Ernest. 1996. Bring Back the Buffalo: A Sustainable Future for America’s Great Plains. Berkeley. University of California Press. 281-283. These actions of the USDA continue to this day.  Confirmed by Darrell Giest, Buffalo Field Campaign, in an email to the author dated 15-April-2019.

[3] Callenbach. 134-139

[4] Kamath, Pauline L., Foster, Jeffery T., et. al. Genomics reveals historic and contemporary transmission dynamics of a bacterial disease among wildlife and livestock. Nature Communications. 11-May-2016.

[5] Yellowstone Bison and Brucellosis: Persistent Mythology.  Retrieved from (3/30/19).

[6] Callenbach. 280.

[7] Yellowstone Bison and Brucellosis: Persistent Mythology.

[8] Kamath.

[9] Willcox, Louisa. 8 March 2017. The Last Stand for Yellowstone’s Bison.  Retrieved from

[10] Yellowstone Bison and Brucellosis: Persistent Mythology.

[11] Yellowstone Bison and Brucellosis: Persistent Mythology.

Bison Air Support

When we think of the Great Plains and the prairies, we most likely envision a landscape of grasses rolling on to the horizon.  But the skies above those grasses are as much a part of the ecosystem as the land itself.  Upon the air currents circulating over the land, birds, insects, and bats fly searching for food, nesting materials, and escape routes from predators.  These same air currents disperse seeds over the plains and prairies, increasing plant diversity.  Though the aerial species may be above it all, they, like any air force, are dependent upon ground support.  Key to that support is the bison.

                In tall-grass prairies, lupine, a flowering plant, has diminished along with the demise of the bison.  Lupine flourishes with a mix of shade and sun.  Without the bison, the trees and woody shrubs of the oak savannah [1] overshadow the other plants, depriving the lupine of much needed sunlight,  resulting in a decline of lupine across the northern prairies due to loss of habitat.  Much of that loss resulted from converting the prairies into farmland.  But in the remaining prairie, tree and other woody plant cover has suppressed lupine growth.  In the past, when bison were present, they maintained a reduction of woody plant cover.  They kept woody shrubs and trees out of the area by rubbing their horns and bodies against the shrubs and trees, and by causing minor soil disturbance, the bison had a significant impact [2].

Wild Blue Lupine
An Oak Savana

                Among the lupine, flitter approximately 50 rare species of butterflies.  One in particular is the Karner Blue Butterfly [3], listed as endangered in 1992.  The Karner relies on lupine as both a food source and a place to lay their eggs.  The bison create and restore the open habitats of the oak savannah prairie, which the lupine and the butterflies desperately need.

The Karner Butterfly

                Re-introducing the bison to one area, the Sandhill State Wildlife Area in Wood County, Wisconsin, [4] bore out this relationship among the butterflies, the lupine and the bison.   Since the return of the bison, a significant recovery of both lupine and the Karner has occurred [5].

                Birds of the Great Plains and the prairies benefit from the bison as well.  While bison graze the wealth of perennial grasses, they are often surrounded by a small flock of birds, including brown-headed cow birds (also known as buffalo bird), starlings, and magpies.   The grazing stirs up insects out of the grasses, providing an easy feast for the surrounding birds.  In addition, the birds get free rides, hitching on the backs of the bison, consuming the insects found in the bison’s hair.  The bison amenities, though, not only offer meals.  During inclement weather, the backs of bison also offer protection against the elements. 

The Brown-Headed Cow Bird
Birds and Bison

                While grazing renders insect-hunting easier, bison-grazing creates heterogeneity of grasses, resulting in a range of forage heights  from very low (heavy grazing) to high grass (no grazing).  These conditions promote a variety of bird species from those who nest only in low vegetation to those who nest only in high vegetation and those species whose nesting preference is somewhere in between. In contrast, cattle graze uniformly in regard to vegetation height, leaving forage at a mid-height which reduces habitat for those avian species that require either low or high vegetation [6].

                Amid the grasses where the bison roam, shallow soil depressions can be found.  For various reasons bison roll in the soil, creating wallows.  Filling with water during storms, wallows provide habitat for a variety of insects, frogs, and birds.  For the birds, the water-filled wallows provide drinking water and a staple of insects.  Dry, the wallows offer habitat for such birds as the sharp-tailed grouse and the burrowing owls [7].

                Aerial support though, also involves providing materials for ground cover.  Bison hair and wool, as well as dung, [8] are used in the construction of nests.  Hair and wool provide insulating and water-repellant materials and more.  Nests lined with bison wool suffer less predation because the hair, serving as olfactory camouflage, masks odors of the nest site [9], warding off predators.

                A significant example of the importance of the bison to bird species would be the burrowing owl, which has been declining for many years due to the loss of habitat and the control programs of prairie dogs and ground squirrels.  Prairie dogs are just as essential to the Great Plains and prairies as the bison are.  A full discussion of the significance of prairie dogs is beyond the scope of this article, but in respect to the borrowing owl, the prairie dog burrows provide ideal habitat for the burrowing owl.  The bison’s contribution, especially in tall-grass and mixed-grass prairies, comes through their grazing.  The bison make the prairie dog towns possible.  Prairie dogs will not live in tall-grass since it is less nutritious and hides predators.  But bison grazing keeps the tall-grass short enough to promote prairie dog towns [10].  

Once a burrow becomes available, the burrowing owl brings together the burrow and bison dung into a unique arrangement.  Using bison dung to line the burrow, the burrowing owl ambushes dung beetles.  Attracted by the feces, dung beetles are an important food source for adults and developing nestlings [11] (Perhaps this is why owls are considered wise, because they know their shit).

Burrowing Owl

Even in death the bison provide for the aerial life of the plains.  Scavenger birds such as crows, ravens, magpies and turkey vultures feed on the carcasses. Typically such scavenger birds as ravens and magpies along with turkey vultures will show up first.  Initially, these birds feed on carrion flies, since they cannot break through the hide.  Later, perhaps after spotting the ravens and magpies, bald and golden eagles may join the feast. But even the eagles may have difficulty tearing open the hide and generally depend on other predators such as wolves to perform that task. Once opened, the eagles are able to rip apart the innards of the carcass into smaller chunks, creating serving sizes for smaller mammals [12].  Indirectly, the carcasses, as they decay, nourish the plant life which in turn offers habitat and food for birds and butterflies.

From flittering butterflies to soaring and burrowing birds, bison support a variety of invertebrate and avian species which populate the skies above the plains and prairies.  The decline of the bison and the conversion of the Great Plains and prairies into farms, ranches and concrete has devastated the indigenous avian, riparian and lepidopteran species. The avian species of the Great Plains have seen significant population decline [13], while the many butterfly species of the surrounding prairies also appear on the threatened or endangered species lists.  Fortunately, such efforts as those of the American Prairie Reserve in Montana and the Sandhill State Wildlife Area in Wisconsin are making strides in recovering many of those species.  But the questions will be:  Will these efforts be expanded? How will we act upon what we have discovered?  How quickly will we act?  Some time ago Joni Mitchell wrote a song called Big Yellow Taxi, which starts out:

They paved paradise
And put up a parking lot
With a pink hotel, a boutique
And a swinging hot spot
Don’t it always seem to go
That you don’t know what you’ve got
‘Till it’s gone

It would seem these words are still apropos in regard to the ecosystem of the Great Plains and the surrounding prairies.


[1] An oak savannah is a plant community where the oak tree is a dominant component but the density of the oaks is so low it allows grasses and other vegetation to become the actual dominants of the community. Retrieved from

[2] Bison Bellows: Bison Bolster Endangered Blue Butterfly Recovery. https//

[3] Named by the novelist Vladimir Nabokov. 

[4] In 1962 12 bison were donated to the Sandhill State Wildlife Area.  The current herd consists of 15 bison on 260 acres.

[5] Bison Bellows: Bison Bolster Endangered Blue Butterfly Recovery

[6] Heidebrink, Scott. Bison Restoration Manager. American Prairie Reserve. Email to author dated 3/8/19.

[7] Retrieved from

[8] Coppedge, Bryan R. Patterns of Bison Hair Use in Nests of Tallgrass Prairie Birds.  The Prairie Naturalist. 41: December 2009. 110-115.

[9] Baily, James A. American Plains Bison: Rewilding an Icon. 2013. Sweetgrass Books. Helena, MT. 46. and Coppedge

[10] Lott, Dale F. American Bison: A Natural History. 2002. University of California Press. Berkley, CA. 128.

[11] Coppedge

[12] Lee, Barbara. Decomposition.  Montana Outdoors. 2014. 21-22. Retrieved from

[13] Brennan, L.  A., and  W.  P.  Kuvlesky. 2005. North American  grassland  birds:  an  unfolding  conservation

crisis?  Journal of Wildlife Management 69:1–13.

Dung Cake and Feces Pie: Yum!

In architecture there is a stone upon which the whole structure depends.  It is known as the keystone.  More precisely keystone is a masonry term, and is the stone without which the structure collapses. 

Bison are a keystone species for the Great Plains. But specifically for the bison and the Great Plains what does this keystone look like? How does it work?  Perhaps a good place to start is where the poop hits the trail.  Usually when we hear “the chips are down,” we understand life is not going so well; but that is not true for the grasslands of the Great Plains.  When the chips are down, a veritable feast ensues.  Life is great for a host of microbes, insects, fungi and plants, which themselves present a delicious offering to other species.  Who would think dung could be so sweet?

We on the so-called upper echelon of the food chain look down on the unassuming dung pie.  Casting a disdainful glance on the heap, holding our noses as we pass, we hurry by to avoid further sensibility damage.  Our minds formulate a four-letter word, which, if spoken is a “naughty word.”  In our passing, though, we fail to see a dung beetle working feverishly on its claim.  It, in turn, has ignored us, so intent on its business; perhaps it is thinking in Cheech and Chong style: “This is some good shit man.” 

So what does the world of a bison dung pile entail? To understand this unique world its origin story must be told. In this case, the genesis of bison dung begins in the hidden regions of the bison digestive tract and in particular in its rumen, the first chamber of the bison’s four-chambered digestive system. In the rumen microbes aid the digestion of plant matter. The microbes provide enzymes which facilitate the breakdown and metabolism of the plant matter. These microbes and undigested plant matter, then, pass through the bison’s digestive system and deposit as feces on the soil. This is the fundamental means of nutrient flow for the grasslands. The average bison produces 10-12 quarts of dung in a day, providing a valuable source of nitrogen, phosphorus, calcium, sulfur and magnesium for microbes, plants and critters [1].

 In our walk by, and side-step of, the odious heap, we probably perceive the pile of blended nutrients to be just that: a static plop of poop.  However, we would be so wrong.  A diverse population of parasites, hosts, predators, prey, flies, dung beetles, wasps, earwigs, springtails, mites, etc. inhabit this aroma-rich world.  Not a static world, the dung world bustles with activity varying as it ages. The drying pile attracts different residents at different times.  Flies which may have been hovering around the bison hoping not to be snatched by a cowbird are ready to swoop down on the freshly dropped excrement as soon as it hits the ground, swarming over it like…well…like flies on poop.  The flies close to the herds literally have the drop on flies further away. Flies and other insects not close to the herds will come later following a spoor of wind-blown odors [2].  The flies test the surface of dung-world until it is dry enough to lay eggs.  The fly-infested bison chip can produce up to 3000 flies in over two weeks, providing a banquet for box turtles, bats and birds.

Dung beetles, bussing in flies and mites, come later, searching out bison dung. In our passing we probably did not consider that dung piles also vary in nature.  Poop is diverse, and dung beetles are selective.  Indeed the dung beetle populations have declined since the introduction of livestock because they cannot find just the right plop of poop.  The decline of the bison brought the decline of the industrious dung beetle.  This has reduced the ability of natural systems to cycle nutrients and decompose fecal matter, impacting the function of the Great Plains ecosystem [3].  Perhaps we should be required to go to Dung Diversity classes to address our dung-bias. 

During our next walk past a bison pile, after our Dung Diversity course, we pause and now notice our little Cheech and Chong  friend (Well, at this point it’s probably not the same beetle, but for the sake of this discussion we are pretending that it is).  We see it is perhaps a tunneler or roller  beetle working feverishly, burying the fresh manure into the soil.  From what we learned in our course, we realize what a great service these beetles offer.  Our little friend, by burying the excrement, moves nitrogen and carbon directly into the soil and activates microbial activity.  Microbes convert the nitrogen into ammonia which is essential to plants [4].

But dung-world is not a quaint, peaceful world of maggot nurseries, nutrient farms, ammonia factories and waste management facilities.  A ruthless insect-eat-insect environment exists.  Beetle and wasp larvae eat or kill maggots.  One kind of beetle can take away so much of the dung pile nothing is left for other insects.  The tumble bug will take a large mass of dung, roll it into a ball, deposit its eggs inside and then roll the ball of dung to a nesting site [5].

Insects, microbes and plant material are not alone in composing the fecal cake.  Seeds consumed during grazing, pass through the bison digestive tract and find a home in dung-world.  Bison feces contain an abundance and diversity of plant seeds, making bison an important dispersal agent [6].  Without the bison, the range and diversity of the grasses of the Great Plains and prairies is greatly reduced.

By providing crucial residence for invertebrate life, nutrient transformation processes for plants, and transportation means facilitating grass diversity, bison dung sustains the life of the Great Plains.  When the bison roamed the Great Plains and surrounding prairies in the millions, those ecosystems had an efficient means of replenishment and sustenance.  Now, without wild free-ranging bison grazing over vast stretches, without a keystone species, what will become of the Great Plains?  Not to mention: where will our little dung beetle friend find a home?


[1] A Healthy Prairie Relies on Bison Poop. Bison Bellows.

[2] McHugh, T. 1972.  The Time of the Buffalo. 233.

[3] Bison Bellows

[4] McHugh, 234.

[5] McHugh 234.

[6] Rosas, Claudia A., Engle, David M., Shaw, James H. & Palmer, Michael W. See dispersal by bison bison in a tallgrass prairie. Journal of Vegetation Science 19: 769-778. 2008.