Bison Management Notes

Guiding Question: The United States named bison the national mammal, but we still haven't decided if we're ready to restore them as wild animals on the American landscape. Could we ever live with wild, free-roaming bison again? Should we try? Why, or why not?

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Written Summary of Bison Management

An Introduction to Bison

Before the Europeans arrived, there were 50 million bison living on the continent. To put those numbers in perspective, bison represented the largest single-species concentration of terrestrial biomass ever…including the dinosaurs.

But in the span of about 80 years (1820 - 1902), we brought the number of wild bison down to just 23 animals. This small herd was living in Yellowstone and needed to be protected from poachers by the U.S. cavalry.

Today, bison continue to face persecution and are managed differently from all other forms of wildlife over concerns of disease, public safety and competition with cattle for grass.

The near extermination of the bison…

Symbol of the American Spirit

“These animals go into the storm. Most animals’ll turn, cattle and horses’ll turn and hump up and let the snow come to their backs. But they just, I don’t what it is, it’s just their nature, they just turn into the storm and face it, you know?” (7, 6:21)

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• Ervin Carlson, buffalo program director for Montana’s Blackfeet Nation

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Bison Introductory Videos

To better get acquainted with this iconic species, let’s review the following resources:

• Nat Geo: Yellowstone’s Iconic Animals
• NPS: Finding Space for an American Icon (2015)
• NPS: Why Yellowstone Bison Are Managed (2024)

Please Respect the Wildlife…

Tragedy of the Commons: Bison

• When Europeans arrived in North America, they saw wildlife as a commodity to be exploited and implemented an unregulated market for the trade of wildlife. Bison were used for food, belts and furs, skulls were ground up as fertilizer, but most left to rot.
• We over harvested wild bison to the point of near extinction; 30-60 million in 1820 → 325 in 1884 → 23 in 1902 (genetic bottleneck).
• Along with bison, pronghorn antelope, bighorn sheep, mule deer, elk, beavers, wolves and grizzlies were nearly wiped out.

What issues of environmental externalities and equity does this example of overharvest pose?

Efforts to save the remaining bison by William Hornaday and even Teddy Roosevelt were rooted in racism as efforts to preserve “the survival of white masculinity”.

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Inclusion and Natural Resources

In addition to the obvious moral imperative to have an inclusive society, if we truly value natural spaces and wildlife we need EVERYONE to have equal and unrestricted access to our environment:

• Our environment provides numerous ecosystem services that keep our society alive and functioning, all without charging a dime, but these positive externalities are often overlooked and underappreciated.
• If we want to preserve our environment and achieve sustainability with our natural resources, we need to engage as many people as possible in understanding the true value of nature or we risk losing the things we love most.

Historically, the conservation movement has been dominated by white people with minorities, especially African Americans and Native Americans, pushed aside by racist rhetoric. A strong environmental movement will require input from all stakeholders.

Foundation of Stewardship

• The North American Model of Wildlife Conservation is a set of principles that has guided wildlife management and conservation decisions and has become the global standard for success.
• The Model has 7 basic tenets that support the notion that wildlife is a public trust, an American birthright, and that wildlife species need to be sustained forever.

Bison as a Species

• Mate in late July through August and give birth to one calf in late April or May. Timed with the emergence of fresh plant growth.
• Can be aggressive, are agile and can run up to 30 miles per hour.
• Wolves and grizzly bears are the only large predators of adult bison.
• Read more about bison here.

• Males (bulls) weighs up to 2,000 pounds, females (cows) weighs up to 1,000 pounds.
• May live 12–15 years; a few live as long as 20 years (generally females live longer).
• Feed primarily on grasses and sedges.

Bison as a Keystone Species

Bison Ecosystem Engineering:

• When more bison grazed an area more intensely, the area “greened up” earlier and faster and the grass stayed greener and had a higher nutritional quality for a much longer time.
• Grasses heavily grazed by bison were more productive compared to exclosures where bison were not allowed to graze.
• Bison wallowing also contributes to ecosystem engineering.

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• Like wolves, bison are a keystone species that have a disproportionate impact on their environment. Rather than apex predators, bison act as ecosystem engineers.
• Bison are able to use their dung and urine to constantly fertilize the landscape.

2024 Bison Management Plan

• In 2023, the National Park Service (NPS) began developing a new Yellowstone Bison Management Environmental Impact Statement (EIS) for public comment.
• Based on feedback, the NPS opted for Alternative 2, which would prioritize the NPS’s trust responsibilities to tribes by using the Bison Conservation Transfer Program (BCTP) to restore bison to tribal lands and treaty hunting outside the park to provide tribes with access to traditional resources.
• Alternative 2 is largely an updated and moderately improved version of the original Interagency Bison Management Plan (IBMP).
• The new plan calls for a (slightly) larger population size of about 3,500 to 6,000 animals after calving with an average of 5,000 animals compared to the original 3,500 to 5,000 animals.
• And of course, this plan prioritizes the transfer of Yellowstone bison to Tribal lands over capture/slaughter by the NPS and tribal/public hunting events outside the park to maintain the Yellowstone bison population size.

Avian Species Richness and Bison Grazing

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• The relationship between bison grazing (measured as mean patty count) and predicted plot species richness at the National Bison Range and Yellowstone National Park study sites.
• The solid line represents the mean predicted response, and dashed lines show the 95% credible interval.
• Moderate levels of grazing → maximum species richness (in-line with IDH).

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Avian Species Richness and Bison Grazing

• The relationship between bison grazing intensity (measured by patty count) and occupancy probability in Yellowstone National Park.
• The solid line represents the mean predicted response, and dashed lines represent the 95% credible interval.
• Moderate levels of grazing → maximum species richness (again in-line with IDH).

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Avian Species Richness and Bison Grazing

• Predicted density per 250 m2 for vesper sparrow and western meadowlark across the spectrum of bison grazing intensity measured by patty counts in the National Bison Range and Yellowstone National Park.
• The solid lines represent the mean response, and dashed lines represent 95% credible intervals.
• Moderate levels of grazing → maximum species richness (again, in-line with IDH).

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Bison Wallowing

• As bison roll and lay about in wallows, they disturb and compact the soil.
• The disturbed soil in the wallows can provide habitat for pioneer plant species. Wallows can even serve as water reservoirs.
• These small ponds can enhance the growth of specific prairie vegetation that requires moist habitats. While the plant diversity in one wallow is often lower than the surrounding prairie, many wallows across the landscape create a mosaic of different vegetation.
• With bison wallows, the prairie is more biologically diverse.

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Bison Historic Range

• Herds of bison originally stretched from Virginia to California, Canada to Mexico.
• Exploitation driven primarily by European settlers quickly fractured the herds until they nearly disappeared.

Traditional Views of Nature

Nature as a Commodity

• Often associated with the traditional European view of nature.
• Nature is seen as a commodity, a raw material product that can be bought and sold.
• Nature exists to serve man and development (e.g. agriculture) is seen as progress and improvement → foundation of public land disposal system.

Nature as a System

• Often associated with the traditional Native American view of nature.
• Humans are a part of nature, not an entity separate from it.
• Emphasis on balance and cultural knowledge of the landscape.
• The concept of land ownership does not exist, which becomes the foundation of numerous early conflicts with settlers.

These are generalized models of each culture and do not necessarily represent ALL individuals in that culture.

Why Yellowstone Bison are Special

• The Yellowstone bison herd is special because they represent the largest bison population on public land and are among the only bison to have not hybridized through interbreeding with cattle.
• Bison are a migratory species, resulting in seasonal movement that makes management challenging as they try to migrate out of the park in winter.
• A major challenge with bison management in Yellowstone is that some are infected with brucellosis, a livestock disease that can be transmitted between ungulates including elk, bison and cattle through contact with infected fetal tissues.
• Although the risk of brucellosis transmission from bison to cattle remains nebulous, it has become a major component of the Interagency Bison Management Plan (IBMP), a legal document meant to provide a voice to all stakeholders on the issue of bison management.

Bison and Brucellosis

• Brucellosis, caused by the bacterium Brucella abortus, can cause pregnant cattle, elk, and bison to abort their calves.
• The bacteria can be transmitted between individual bison and also among elk and cattle via contact with infected birth tissues.
• While no cure exists for wild animals, it should be noted that male bison do not transmit the disease.
• Cattle brought this nonnative disease to the region when pioneers settled the West. The disease was subsequently transmitted to local wildlife populations including bison and elk in the Greater Yellowstone Ecosystem.

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Because brucellosis is transmitted by infected birth tissues, predators and scavengers (e.g. wolves and ravens) can help prevent the spread of the disease by quickly consuming infected tissue before it can infect another bovine animal (regulating service).

NPS Assessment of Brucellosis Risk

• “...the risk of brucellosis transmission from bison to cattle is negligible because: (1) management successfully limits bison movements and mingling with cattle, (2) bison calving mostly occurs in April and May before cattle are released on summer ranges, and (3) bison naturally move to higher elevation summer ranges in national parks following snow melt and vegetation green-up” (Yellowstone Bison: Conserving an American Icon, page 24).
• “The estimated risk of brucellosis exposure to cattle from Yellowstone bison is insignificant (less than 1 percent) compared to elk (more than 99 percent of total risk) because elk have a larger overlap with cattle and are more tolerated by managers and livestock producers” (Yellowstone Bison: Conserving an American Icon, page 24).

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Bison Management

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• Today, the National Park Service manages Yellowstone bison near the boundary of the park through a combination of hazing, capture, culling and vaccination.
• The goal is to mitigate the risk of bison leaving the formal park and entering the GYE where they could spread brucellosis to cattle, damage private property (e.g. fencing) and compete with cattle for grass.
• Annual culling of about 900 animals helps to keep the bison population at around 3,500 animals, the estimated carrying capacity of the park.
• While bison are not the only wildlife to carry brucellosis, they are the only one managed through these intensive strategies and remains a central issue preventing the return of bison to the larger landscape.

“Total eradication of brucellosis as a goal is more a statement of principle than a workable program at present; neither sufficient information nor technical capability is available to implement a brucellosis-eradication program in the Greater Yellowstone Area.”

The Interagency Bison Management Plan (IBMP)

• The Interagency Bison Management Plan (IBMP) was first developed in 1992 between the State of Montana and the federal government. Progress on the plan was slower than anticipated, and in 1995, the State sued the National Park Service and the Animal and Plant Health Inspection Service over the delay.
• By the year 2000 an agreement was reached and the IBMP has been updated numerous times since and created the designated surveillance zone to monitor brucellosis and protect the state of Montana’s disease free status required for free trade agreements.
• The adjusted Interagency Bison Management Plan has three categories of objectives: (1) conserve a viable population of wild bison, (2) prevent brucellosis transmission from bison to cattle, and (3) reduce the prevalence of brucellosis in bison.

Eight groups, including state and federal agencies and American Indian tribes, play a role in making decisions about Yellowstone bison.

Questions for Future Management

• Abundance—How many is too many (or too few)?
• Brucellosis—What should be done and what can be done to suppress the disease and/or lessen transmission risk to cattle?
• Distribution—Where and when will bison be tolerated outside the park?
• Elk—Should management of brucellosis in elk be considered as well?
• Genetic Integrity—What should be done to preserve existing genetic diversity and population substructure?

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Questions for Future Management

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• Habitat—Should humans intervene to control ungulate numbers and grazing effects?
• Property Damage and Human Safety—How intensive should management be to minimize risk?
• Wildness—What intensity and types of management are appropriate for migratory wild bison whose core range occurs within a national park?
• Cultural/Economic—What is the optimal abundance and distribution of bison for people that value them, and how much are they willing to invest to realize that value?
• Hunting—How, when, and where should hunting occur, while respecting tribal treaty rights and the concerns of other stakeholders?

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Bison as a Cultural Resource

• Many Native American cultures regard wildlife including wolves, beavers and sage grouse as sacred and perhaps no species was more revered than the bison (George Horse Capture Jr, Former VP of Fort Belknap).
• Tribes hunted bison for food for thousands of years while maintaining a careful balance.
• “Buffalo Jumps” were used to help harvest bison (push method).
• Prescribed fires allowed Native Americans to alter the landscape to attract bison toward fresh, green plant growth (pull method).

Cultural Connections of Native Americans to Bison

• The economies of many tribes (particularly those of the Great Plains such as the Crow, Comanche and Blackfoot nations) were centered around the bison.
• There is some speculation that European-Americans specifically exterminated bison to cripple the American Indians, but this was never an official policy of the federal government.

Indigenous Voices

“These animals go into the storm. Most animals’ll turn, cattle and horses’ll turn and hump up and let the snow come to their backs. But they just, I don’t what it is, it’s just their nature, they just turn into the storm and face it, you know?” (7, 6:21)

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• Ervin Carlson, buffalo program director for Montana’s Blackfeet Nation

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Indigenous Voices

“Our Indian’s name’s tatanka oyate. Buffalo people...Tatanka oyate. And we follow the ways of the buffalo, we’re the buffalo people. And again, we learned our structure of our life...is based on the same what the buffalo do….Buffalo has taken care of Native Americans since the beginning of time. And now the buffalo need help. So as a Native American, I feel it is our responsibility that we put a hand to help them. To pay back the favor.”

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• Robbie Magnon, Director of the Fort Peck Tribes Fish and Wildlife Department (4, 2:00)

American Prairie Reserve

• The American Prairie Reserve (APR) seeks to protect one of the 4 remaining examples of an intact grassland ecosystem (Northern Great Plains, Patagonia, Mongolian and Kazakh Steppes).
• The APR is backed by very wealthy donors which has allowed it to make a great deal of progress, but also generated resentment from local, small ranching families.
• APR seeks to create a park of 3.2 million acres (compared to YNP’s 2.2 million acres) and home to a wild bison herd 10,000 strong (compared to YNP’s herd of ~5,000).

The great conservation debate (SLOSS): which is the more effective conservation approach: single large or several small reserves?

Environmental Themes and Bison

Positive Externalities

• Ecosystem Services: Bison provide numerous ecosystem services (especially ecotourism) that benefit the local ecosystem, society and the economy.
• Environmental Equity: Improving bison populations helps to return a culturally significant species to many indigenous cultures.
• All species have intrinsic value.

Negative Externalities

• Tragedy of the Commons: The near extinction of bison from wreckless overhunting represents a tragedy of the commons.
• Bison compete for grass with livestock and can damage property and injure people who harass them.
• Bison can carry brucellosis and while it has never happened in the field, bison can transmit the disease to cattle under laboratory conditions.
• Environmental Inequity: Bison were slaughtered in part to undermine indigenous cultures, especially the Native American tribes of the Great Plains who’s societies were built around bison.

Ecosystem Services and Bison

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Supporting Services

• As a species bison contribute to biodiversity and therefore the supporting services of ecosystems.
• Bison act as ecosystem engineers, creating habitat for other species through wallowing and other behaviors.

Regulating Services

• Bison are a keystone species, helping to provide balance to ecosystems by grazing and “greening up” the landscape thereby storing carbon through plant growth.

Provisioning Services

• Bison serve as a food source for many individuals including indigenous tribes.

Cultural Services

• Bison hold archaeological, scientific and cultural significance especially for Native American groups like Blackfeet tribes.
• Just as with wolves in Yellowstone, ecotourism is generated from visitors who travel to view the bison every year.