YELLOWSTONEBISON
conserving an american icon
in modern society

edited by

P.J. White, Rick L. Wallen,
and David E. Hallac

YELLOWSTONE BISON

Yellowstone Bison:
Conserving an American
Icon in Modern Society
Editors
P.J. White, Rick L. Wallen, and David E. Hallac

Contributing Authors
Katrina L. Auttelet, Douglas W. Blanton, Amanda M. Bramblett,
Chris Geremia, Tim C. Reid, Jessica M. Richards, Tobin W. Roop,
Dylan R. Schneider, Angela J. Stewart, John J. Treanor, and Jesse R. White

Contributing Editor
Jennifer A. Jerrett

Yellowstone Association

Yellowstone National Park, USA, 2015

P.J. White is the Chief of Wildlife and Aquatic Resources at Yellowstone National Park.
Rick L. Wallen is the Bison Project Leader at Yellowstone National Park. David E.
Hallac was the Division Chief of the Yellowstone Center for Resources at Yellowstone
National Park between 2011-2014.
The Yellowstone Association, Yellowstone National Park 82190
Published 2015
Printed in the United States of America
All chapters are prepared solely by officers or employees of the United States
government as part of their official duties and are not subject to copyright protectionin the United States. Foreign copyrights may apply. National Park Service (NPS)
photographs are not subject to copyright protection in the United States. Foreign
copyrights may apply. However, because this work may contain other copyrighted
images or other incorporated material, permission from the copyright holder may benecessary. Cover image: NPS/Neal Herbert. Half title image: NPS/Jacob W. Frank.
Library of Congress Cataloging-in-Publication Data
Yellowstone bison : conserving an American icon in modern society / edited by P.J.
White, Rick L. Wallen, and David E. Hallac ; contributing authors, Katrina L. Auttelet[and 10 others] ; contributing editor, Jennifer A. Jerrett.
pages cm
Includes bibliographical references and index.
ISBN 978-0-934948-30-2 (pbk. : alk. paper)
1. American bison--Conservation--Yellowstone National Park. 2. American bison-Conservation--United States. 3. Wildlife conservation--Yellowstone National Park.
4. Wildlife conservation--United States. 5. Wildlife management--Yellowstone
National Park. I. White, P. J. (Patrick James) II. Wallen, Rick L. III. Hallac, David E.
IV. Auttelet, Katrina L. V. Jerrett, Jennifer A.
QL737.U53Y45 2015
599.64’30978752--dc23
2015004628
The authors gratefully acknowledge the generous contribution of the Yellowstone
Association, whose publication grant enabled the production of this book.

Contents
Prefaceix
Daniel N. Wenk, Superintendent, Yellowstone National Park

Introductionxiii
P.J. White, Rick L. Wallen, and David E. Hallac

Chapter 1: The Population1
Douglas W. Blanton, P.J. White, Rick L. Wallen,
Katrina L. Auttelet, Angela J. Stewart, and Amanda M. Bramblett

Chapter 2: Brucellosis19
P.J. White, David E. Hallac, Rick L. Wallen, and Jesse R. White

Chapter 3: Historical Perspective45
Rick L. Wallen, P.J. White, and Chris Geremia

Chapter 4: Seasonal Distributions and Movements67
Chris Geremia, P.J. White, Rick L. Wallen, and Douglas W. Blanton

Chapter 5: Reproduction and Survival83
Chris Geremia, P.J. White, Rick L. Wallen, and Douglas W. Blanton

Chapter 6: Nutritional Ecology97
John J. Treanor, Jessica M. Richards, and Dylan R. Schneider

Chapter 7: Ecological Role107
Rick L. Wallen, P.J. White, and Chris Geremia

Chapter 8: Adaptive Capabilities and Genetics119
Rick L. Wallen and P.J. White

Chapter 9: Cultural Importance131
Rick L. Wallen, P.J. White, and Tobin W. Roop

Chapter 10: Current Management141
P.J. White, Rick L. Wallen, David E. Hallac, Chris Geremia,
John J. Treanor, Douglas W. Blanton, and Tim C. Reid

Chapter 11: The Future159
P.J. White, Rick L. Wallen, Chris Geremia, John J. Treanor,and David E. Hallac

Acknowledgments179
Glossary of Terms 181
References197
Index243

Abbreviations used in citations:
APHIS		

Animal and Plant Health Inspection Service

MDOL		

Montana Department of Livestock

MFWP		

Montana Fish, Wildlife & Parks

NPS		National Park Service

USDA		

United States [U.S.] Department of Agriculture

USDI		

U.S. Department of the Interior

USFS		

U.S. Forest Service

YNP		

Yellowstone National Park

Recommended citation format:
Entire book.—White, P. J., R. L. Wallen, D. E. Hallac, and J. A. Jerrett,editors. 2015. Yellowstone bison—Conserving an American icon inmodern society. Yellowstone Association, Yellowstone National Park,
Wyoming.
Individual chapter.—Wallen, R. L., P. J. White, and C. Geremia. 2015.
Historical perspective. Pages 45-65 in P. J. White, R. L. Wallen, D. E.
Hallac, and J. A. Jerrett, editors. Yellowstone bison—Conserving an
American icon in modern society. Yellowstone Association, Yellowstone
National Park, Wyoming.

Photograph courtesy of National Geographic by Michael Nichols

Bison in winter, Yellowstone
National Park.

Preface
Daniel N. Wenk, Superintendent, Yellowstone National ParkMy association with bison management in Yellowstone National
Park began in the early 1980s when I worked for Superintendents
John Townsley and Bob Barbee. Back then, there were fewer than
2,500 bison and the central herd was the largest herd in the park. Also,bison were not yet making seasonal migrations past the north and west
boundaries of the national park. Because bison were not leaving thepark, brucellosis within the population was less of a concern. Bison
contributed greatly to the enjoyment of the park by visitors as part ofthe incredible wildlife display.
Much has changed. About three decades later, when I was preparing to return to the park as Superintendent beginning February of
2011, I was made aware of a court-mediated settlement regarding themanagement of bison signed by the Secretaries of Agriculture andthe Interior and the Governor of Montana. But my knowledge camefrom a distance, and I did not yet fully understand or appreciate thecomplexity of management or the intensity of emotion and conflictthat was occurring on the boundaries of Yellowstone National Park.

x

Yellowstone Bison: Conserving an American Icon in Modern Society

My education came quick. The winter of 2010-2011 was harsh andbison were moving into the Gardiner basin of Montana in large numbers. Within two weeks of my arrival in the park, I was in Montana
Governor Brian Schweitzer’s office in the state capital to discuss bison
management. The Governor suggested methods to control population
numbers and brucellosis, including a proposal to hunt bison within thenational park. I rejected this proposal because it was contrary to law,regulation, and policy of the National Park Service and Yellowstone.
It was also unnecessary; the park could ecologically support the bison
population and we were successfully managing the population without
hunting in the park.
In an unexpected turn of events, and what would become my first
lesson in the politics of bison management, Governor Schweitzer issued
an Executive Order prohibiting the shipment of bison on state highways. The hands of the National Park Service were tied. That winter,approximately 850 bison were held in capture facilities until early May
when they migrated back into the park.
What I learned in my first weeks as Superintendent is that the science,so well-highlighted in this book, must be joined with the strength andcommitment of people to successfully manage a wide-roaming bison
population and prevent brucellosis transmission to cattle. Many ofthese individuals are the authors of this book: wildlife biologists, lawenforcement officers, and others who are the experts in the field ofbison management. Herein, they clearly articulate not only the science,but also, the cultural and political significance of bison management.
During my time in Yellowstone, I have watched with great interest — and some amazement— that bison are vilified as the primary threator vector for brucellosis transmission in the ecosystem. There is an
illusory belief that if brucellosis were eliminated in bison it would be
eliminated from the ecosystem. The authors show clearly that this scenario is unlikely, and that bison make up a small portion of the overallrisk for brucellosis transmission to cattle.
Bison are a wildlife icon in America, and Yellowstone bison represent
one of the greatest wildlife conservation stories in our nation’s history.

Preface

The authors provide a compelling history of the conservation of bisonfrom the early 1900s to the management of bison in modern society.
This book is based on the best available science, understanding theimportance of bison in the American Indian culture, understanding
brucellosis and the role bison play in the ecology of the Greater Yellowstone Area, and an understanding of the stakeholders and local
community issues. It informs our collective management and commitment to wild bison on the landscape.
The iconic bison deserves our best efforts to assure its place on theAmerican landscape. I am grateful to the authors for clearly articulating the issues we face as we collectively determine the future of theseanimals. The authors have given us a chance to advance our discussions
based on a common understanding of the science, culture, and politics
surrounding bison.

xiNPS/Neal Herbert

Clouds and bison acrossHayden Valley, Yellowstone
National Park.

Introduction
P.J. White, Rick L. Wallen, and David E. Hallac

The plains bison (Bison bison or Bos bison), also commonly known asbuffalo, once numbered in the tens of millions and ranged across muchof North America, from arid grasslands in northern Mexico, throughthe Great Plains and Rocky Mountains into southern Canada, andeastward to the western Appalachian Mountains (Lott 2002; Gates
et al. 2010; Bailey 2013). Plains bison are symbolic of the American
experience because they are an inherent part of the cultural heritageof many American Indian tribes and were central to national expansion and development (Plumb and Sucec 2006). Only a few hundred
plains bison survived commercial hunting and slaughter during the
middle to late 1800s, with the newly established (1872) Yellowstone
National Park providing refuge to a relict, wild, and free-ranging herdof less than 25 animals (Meagher 1973). This predicament led to one of
the first movements to save a species in peril and develop a national
conservation ethic by a few visionary individuals, American Indian
tribes, the American Bison Society, the Bronx Zoo, and federal andstate governments (Plumb and Sucec 2006). Bison numbers increased
rapidly after protection from poaching, reintroduction to various

xiv

Yellowstone Bison: Conserving an American Icon in Modern Society

locations, and husbandry (see Glossary of Terms). Today, more than
400,000 plains bison live in conservation and commercial herds acrossNorth America (Coder 1975; Boyd 2003; Plumb and Sucec 2006; Freese
et al. 2007; Hedrick 2009).
Despite this success, several scientists recently concluded that plainsbison are ecologically extinct because less than 4 percent (20,000)
are in herds managed for conservation and less than 2 percent (7,500)
have no evidence of genes from inter-breeding with cattle (Freese etal. 2007). Most bison are raised for meat production, mixed with cattle
genes, protected from predators, and fenced in pastures (McDonald
2001; Lott 2002; Freese et al. 2007; Sanderson et al. 2008; Gates etal. 2010; Bailey 2013). As a result, wild bison no longer influence thelandscape on the vast scale of historical times by enhancing nutrient
cycling, competing with other ungulates, creating wallows and small
wetlands, converting grass to animal matter, and providing sustenancefor predators, scavengers, and decomposers (Knapp et al. 1999; Lott2002; Freese et al. 2007; Sanderson et al. 2008; Bailey 2013).
The restoration of wild bison has advanced more slowly, and withmuch greater debate, than nearly all other wildlife species over the
past 150 years (Lott 2002; Bailey 2013). Bison are massive animals thatcompete directly with humans and livestock for use of the landscape(Boyd 2003). Their preferred habitats include nutrient-rich valley bottoms where agricultural and residential developments occupy most of
the land, while public lands are more likely to encompass mountainous
areas (Scott et al. 2001; Becker et al. 2013). Given existing habitat loss
and the constraints modern society has placed on the distribution ofwild bison, it is unlikely many additional populations will be established and allowed to roam widely across the landscape (Lott 2002;
Boyd 2003). Thus, the few remaining wild and wide-ranging populations of plains bison in the Greater Yellowstone Area (Jackson andYellowstone populations), Canada (Pink Mountain, British Columbia
and Prince Albert National Park), and Utah (Book Cliffs and Henry
Mountains) are very important (Keiter and Boyce 1991; Franke 2005;
Plumb et al. 2009; White and Wallen 2012; Bailey 2013).

Introduction

In 1973, Dr. Mary Meagher, a research biologist working in Yellowstone National Park, released a scientific monograph that provided
insightful information on the life history, behaviors, and ecology of
Yellowstone bison. This work was invaluable to biologists that managed bison during subsequent decades, and much of it is still pertinentand has been referenced in this book. During the past 40 years, however, there have been significant advances in understanding bison
ecology, and also, substantial changes in the abundance, distribution,
movements, and management of Yellowstone bison (Plumb et al. 2009;
Gates and Broberg 2011; White et al. 2011, 2013b; White and Gunther2013). In addition, there are biological, political, and social threats toYellowstone bison that hinder their conservation and the recoveryof the species elsewhere (Franke 2005; Plumb et al. 2009; Bailey 2013;
Treanor et al. 2013; White et al. 2013a).
This book provides updated information on Yellowstone bison.
We compiled information from numerous published and unpublished sources (e.g., articles, environmental compliance documents,
newspapers, reports, websites) not readily available to many stakeholders. We reorganized this information into a more concise andreadable format, without detailed data collection methods and statistical analyses. However, the original sources of information arecited and the wording is often similar to preserve original intent andavoid misrepresentation.
In the book, we discuss opportunities for bison conservation in the
Yellowstone area, misconceptions and competing social values thatprevent an easy path forward for bison conservation, and the potential for Yellowstone bison to contribute to the conservation of plainsbison across their historic range. Our objectives are to communicate
this information to natural resource managers, wildlife ecologists, andanyone interested in plains bison so they can work together to enhance
the conservation of this species in modern society. Also, we hope thisinformation will benefit the millions of people that visit Yellowstone
National Park each year or monitor the condition and managementof the park’s resources via the Internet or other outreach avenues.

xv

Photograph courtesy of Daniel Stahler

Bull bison in the Pelican Valleyof Yellowstone National Park.

Chapter 1
THE POPULATION — ATTRIBUTES,BEHAVIOR, DISTRIBUTION,RESOURCE USE, AND TRENDS
Douglas W. Blanton, P.J. White, Rick L. Wallen, Katrina L.
Auttelet, Angela J. Stewart, and Amanda M. Bramblett

Yellowstone bison are noteworthy in modern times because, unlike mostother conservation herds, this population has thousands of individuals
that roam relatively freely over an expansive landscape (Franke 2005;
Freese et al. 2007; Bailey 2013). They also exhibit wild behaviors reminiscent of prehistoric populations, with large congregations of individuals
during the breeding season to compete for mates, as well as migrationand pioneering movements to explore new areas (Plumb et al. 2009;
Gates and Broberg 2011; Geremia et al. 2011, 2014b). These behaviors
contributed to the successful restoration of a population that was on
the brink of extinction just over a century ago (Plumb and Sucec 2006;
Plumb et al. 2009).

2

Yellowstone Bison: Conserving an American Icon in Modern Society

Attributes
Plains bison are massive animals, with males (900 kilograms or 1,985
pounds) having larger maximum weights than females (500 kilograms
or 1,100 pounds; Meagher 1986). Males are full-grown by 5 to 6 yearsof age, while females mature near 3 years of age (Meagher 1986). Yearlings weigh 225 to 320 kilograms (500 to 700 pounds), while calves 8 to
9 months old weigh 135 to 180 kilograms (300 to 400 pounds; Meagher
1973; Gogan et al. 2010). Adult bison are dark chocolate-brown in color,
with long hair (15 centimeters or 6 inches) on their forelegs, head, andshoulders, but short dense hair (3 centimeters or 1 inch) on their flanks
and hindquarters (Meagher 1986). The fur of newborn calves is reddish
tan in color, but begins turning brown at about 2.5 months (Meagher1986). Both sexes have two horns that curve upward from their head
and are retained for their lifespan. Horns of adult males in Yellowstone
average about 36 centimeters (14 inches) in length, while those of adultfemales average about 31 centimeters (12 inches).1
All plains bison have a shoulder hump that extends to about 1.8 meters(6 feet) above-ground in adult males and 1.5 meters (5 feet) above-groundin adult females (Meagher 1986). Bison use their large shoulder and neckmuscles to swing their heads from side-to-side to clear snow from foraging patches (Picton 2005). Bison get their first permanent incisor during
their third year of life and gain teeth every year thereafter until they have afull set of permanent teeth at age five (Fuller 1959). Bison are agile, strong
swimmers, and can run 55 kilometers (35 miles) per hour (Meagher 1973,1986). They can jump over objects about 1.8 meters (6 feet) tall and haveexcellent hearing, vision, and sense of smell (Meagher 1973; Lott 2002).

Social Behavior
Yellowstone bison are gregarious and often form female-led groups consisting of females of all ages and young males less than 4 years old. Group
formation and dispersion is flexible, with the exception of a mother andher calf (Lott and Minta 1983; Lott 2002). Group sizes in Yellowstone
1
Portions of this chapter and other portions of the book have been included
in and/or adapted from briefs, letters, websites, the Yellowstone Resources and Issues
Handbook, and other National Park Service documents.

The Population

3

NPS/Jacob W. Frank

Bison near Wraith Falls
in the northern region of
Yellowstone National Park.

4

Yellowstone Bison: Conserving an American Icon in Modern Society

National Park average about 20 bison during winter (maximum = 175) and200 bison (maximum = 1,000) during the summer breeding season from
mid-July to mid-August. Group sizes decrease through autumn (average =50 to 100 bison; maximum = 250 to 450) and reach their lowest level during
winter in March and April (U.S. Department of the Interior [USDI2],
National Park Service [NPS] 2010). The gregarious nature of bison tends
to hold groups together, but their movements result in groups frequently
encountering each other and intermixing to some extent (Lott 2002).

Yellowstone bison
are noteworthy
in modern times
because, unlike mostother conservation
herds, this population
has thousands ofindividuals that roam
relatively freely over an
expansive landscape.

The strongest relationships in plains bison society are between adultfemales and their calves, which are dependent on their mothers for foodand security during their first three months of life (Lott 2002). Thereafter,
calves suckle less and begin to procure food by grazing (Green 1992).
When breeding begins, calves spend more time away from their mothers interacting with other bison approximately their own age (Greenet al. 1989; Green 1992). However, most calves stay near their mothers
for about one year (Lott 2002). Older and larger female bison often use
threatening postures and pushing to establish dominance over unrelated
younger or smaller animals, but actual fights are rare. Dominant females
often displace other bison from feeding craters dug into the snow packwhen food is limited during winter.
Adult bison form courtship groups in the Hayden and Lamar valleys of
Yellowstone National Park during July and August (Meagher 1973). Plainsbison reach sexual maturity at 2 to 4 years of age, but males usually do
not successfully breed until about 6 years due to the presence of larger,
older males (Meagher 1986; Berger and Cunningham 1994). Mature males
fight to determine dominance, with competitive interactions including threatening postures, growling-type vocalizations, and sometimes,
violent head-to-head clashes with opponents pushing to displace eachother (McHugh 1958; Berger and Cunningham 1994). Winners have an
opportunity to copulate with receptive females, and as few as 10 percentof the males in the population may complete 50 percent of the breeding during a given year (McHugh 1958, 1972; Berger and Cunningham
2
Abbreviations for government agencies frequently referenced in citations areprovided after the Table of Contents

The Population

1994; Halbert et al. 2004). Following breeding, mature males segregate
and spend the rest of the year alone or in small groups (McHugh 1972;
Meagher 1973; Lott 2002). More information on bison reproduction canbe found in Chapter 5.
Yellowstone bison employ a predator defense strategy whereby bisonin a group cooperate to defend themselves and their young (Smith et al.
2000; MacNulty et al. 2007; Becker et al. 2009a). When threatened by
predators such as wolves (Canis lupus), bison often gather together aroundyoung animals. Older males and females may challenge the predator(s),with their heads down and horns ready to hook their opponents. If
one bison becomes vulnerable or is attacked, other bison may engage
the predator(s) from a different direction. Bison usually prevail against
one or a few predators when they employ this group defense strategy(MacNulty et al. 2007). More information on predation and mortalityof bison can be found in Chapter 5.

Habitats and Distribution
Historically, bison occupied about 20,000 square kilometers (7,720 square
miles) near the sources of the Yellowstone and Madison rivers (Schullery and Whittlesey 2006). Today, this range is restricted primarily to thenorthern and central regions of Yellowstone National Park and adjacentareas in Montana (Figure 1.1). Few bison currently migrate from the park
into adjacent areas of Idaho and Wyoming. Within this range, Yellowstonebison use a variety of habitats, including sedge meadow, upland, burned
and unburned forest, sub-alpine, creek/river riparian areas, willow, andagricultural land outside the park (Meagher 1973; Jerde et al. 2001; Gross etal. 2010). Also, much of central Yellowstone is influenced by heat flowing
to the surface from the interior of the Earth (Watson et al. 2009). This heatproduces hydrothermal features such as geysers, hot springs, fumaroles,
and mud pots in some areas, but also warms more extensive portionsof the landscape where snow pack is reduced or eliminated (Watson etal. 2009). These geothermally influenced areas are often used by bison
during winter (Meagher 1973; Bruggeman et al. 2009c).

5

6

Yellowstone Bison: Conserving an American Icon in Modern Society

Figure 1.1. Map depicting Yellowstone National Park and the pre-settlement, mid-20th century,and 2014 distribution of Yellowstone bison (adapted from Plumb et al. 2009). This figure does
not depict the historic or current distribution of plains bison in and near Grand Teton National
Park, the National Elk Refuge, or Jackson Hole, Wyoming.

The Population

Bison in central Yellowstone occupy the central plateau, extending
from the Pelican and Hayden valley areas (Figure 1.2) with a maximum
elevation of 2,500 meters (8,200 feet) in the east to the lower-elevation(2,000 meters [6,570 feet]) and geothermally influenced Madison headwaters area in the west (Meagher 1973; Bruggeman 2006). Winters areoften severe, with temperatures reaching -42 degrees Celsius (-44 degrees
Fahrenheit) and snow pack exceeding 1.8 meters (6 feet) in some areas.
Bison in central Yellowstone congregate in the Hayden Valley for breeding (Meagher 1973; Geremia et al. 2011, 2014b). Afterwards, most bison
move between the Madison, Firehole, Hayden, and Pelican valleys, butsome travel to the northern region of the park before returning to the
Hayden Valley for the subsequent breeding season (Geremia et al. 2011,2014b; White and Wallen 2012).
Bison in northern Yellowstone primarily occupy the Yellowstone Riverdrainage and surrounding mountains between the Lamar Valley and
Mirror Plateau in the east (maximum elevation = 2,740 meters [9,000
feet]) and the lower-elevation Gardiner basin in the west (1,615 meters[5,300 feet]) (Meagher 1973; Houston 1982; Barmore 2003; Geremia etal. 2011, 2014b). The northern region of Yellowstone is drier and warmer
than the rest of the park, with average snow depths ranging from about 1
meter (3.5 feet) at higher elevations to less than 0.3 meter (1 foot) at lower
elevations. Bison in northern Yellowstone congregate in the Lamar Valley
and on adjacent plateaus during the breeding season (Meagher 1973;
Geremia et al. 2011, 2014b). More information and maps of the distribution and movements of Yellowstone bison are provided in Chapter 4.

Feeding
Bison are ruminants with a large, multiple-chambered stomach containing
microorganisms such as bacteria and protozoa that facilitate the breakdown of plant material (Van Soest 1994; Feist 2000). Grasses, sedges, andother grass-like plants comprise more than 90 percent of the diets of
Yellowstone bison through the year (Meagher 1973; Singer and Norland
1994; Barmore 2003). Forbs and the leaves of woody plants comprise lessthan 5 percent of their diets (Meagher 1973).

7

8

Yellowstone Bison: Conserving an American Icon in Modern Society

Figure 1.2. Names of various places and areas used by bison in and near Yellowstone National
Park. Darker shading indicates areas used more frequently by 66 adult female bison fit withradio collars during 2004 through 2012 (Geremia et al. 2014b).

The Population

Yellowstone bison make foraging decisions at multiple spatial scales,
including the selection of foraging areas across the landscape, foraging patches within an area, and plant species and individual plants
within a foraging patch (Bruggeman 2006). The length of time bison
spend foraging in an area before moving is affected by the perceived
value of the area compared to other recently visited areas — including
the quantity and quality of forage, amount of snow, previous foraging
experiences (learning), and competition with other bison and/or otherungulates (Bruggeman 2006).
During winter, forage for bison in the Yellowstone area is mostly
dead and of low quality. Thus, vegetation quality has little influence on
the selection of foraging patches, and factors such as snow pack andcompetition that influence the availability of forage are more important(Wallace et al. 1995; Fortin et al. 2003; Bruggeman 2006). Bison tend
to select foraging patches in areas with less snow because displacingsnow reduces efficiency and contributes to increased energetic costs(Bjornlie and Garrott 2001). As an area becomes covered by deeper
snow or occupied by numerous animals competing for forage, bison
will eventually search for another area with less snow or fewer animals(Bruggeman 2006). As a result, large shifts in bison distribution may
occur to lower-elevation meadows with more energy efficient foraging
during severe winters (Bruggeman 2006). Furthermore, bison in central Yellowstone may choose to feed in geothermally influenced areas
where the time and energetic costs of displacing snow are minimal,
but the quantity of forage is relatively low and there are other costs tofeeding (e.g., faster wear of teeth due to silica in the soil; high arsenic
and fluoride concentrations in water and plants; Garrott et al. 2009b;
Geremia et al. 2009).
During summer, bison tend to repeatedly graze productive areas,
selecting grasses from dry uplands and sedges from moist sites (Wallace et al. 1995; Olenicki and Irby 2003). High densities of bison candeplete high-quality forage patches, resulting in frequent movements
and substantial variation in grazing intensity across the landscape (Gates
and Broberg 2011; Kohl et al. 2013). A study during summer and autumn

910

Yellowstone Bison: Conserving an American Icon in Modern Societyof 1998 through 2000 found bison in the Hayden Valley foraged inupland grasslands until they had eaten 50 to 60 percent of the grasses
and foraging efficiency decreased (Olenicki and Irby 2003). Bison thenbegan moving across the valley in search of ungrazed patches or grazed
patches with regrowth (Olenicki and Irby 2003). They also used moist
communities adjacent to grasslands, and ate sedges and other grass-likeplants after they had depleted preferred grasses in upland communities(Olenicki and Irby 2003).
Scientists in Yellowstone National Park are currently studying theeffects of predators such as wolves on bison distribution, habitat selection, and foraging patterns. In Prince Albert National Park, Canada, theselection of foraging meadows by bison was primarily influenced byforage availability and quality, and secondarily by the risk of encountering wolves (Fortin and Fortin 2009; Fortin et al. 2009; Harvey andFortin 2013). Bison were more vulnerable to predation during winter,and as a result, groups avoided areas with deep snow and ate less ateach site when risk was greater (Fortin and Fortin 2009; Harvey andFortin 2013). More information on feeding by Yellowstone bison andtheir ecological role can be found in Chapters 6 and 7.

Energetics and Nutritional Condition
Metabolic rates for plains bison are about 0.12 to 0.16 megajoules per
kilogram of body mass per day in winter and about 0.21 to 0.24 megajoules per kilogram per day in summer (Christopherson et al. 1979; Feist
2000). Bison reduce their metabolic rates during winter via hormonalchanges in response to shorter daylight periods and colder temperatures(Christopherson et al. 1979; Feist 2000). Thus, there is a reduction inenergy costs and forage intake during the time of year when prolonged
under-nutrition lowers body condition (Feist 2000). Digestible energy
intake for adult female bison in Yellowstone during winter ranged from
115 to 155 kilocalories per kilogram0.75 of body mass per day, and was
greater in northern than central Yellowstone (DelGiudice et al. 2001).
Within central Yellowstone, intake of metabolizable energy by bison
during winter was lower for bison in the Hayden Valley with deep snows

The Population

11

NPS/Jim Peaco

Bison in a thermally influenced
area near Obsidian Creek in thenorthern region of Yellowstone
National Park during winter.

12

Yellowstone Bison: Conserving an American Icon in Modern Society

than for bison in the Madison headwaters area where geothermallywarmed basins reduced snow accumulation and afforded easier accessto vegetation (Bruggeman et al. 2009c).
Bison gain weight during the spring and summer and lose weight
during autumn and winter (Feist 2000). Yellowstone bison experience
progressive nutritional deprivation, low dietary intake of minerals (e.g.,
sodium, phosphorus), and increased break-down of muscle mass forenergy during winter (DelGiudice et al. 1994). Bison calves typically have
40 to 50 percent lower fat reserves and higher winter mortality rates
than adults, especially during severe winters (DelGiudice et al. 2001).
Under-nutrition and protein metabolism are usually higher in bison
spending winter in central Yellowstone than for bison in northern Yellowstone (DelGiudice et al. 1994). Fat contents for adult female bison in
March during the moderate winter of 1988 were 3 to 4 percent in central
Yellowstone and 5 to 7 percent in northern Yellowstone (DelGiudice
et al. 2001). The milder nutritional restriction of bison in northern
Yellowstone is likely due to shallower snow cover and greater accessto forage compared to the more severe winter conditions in central
Yellowstone that limit access to forage, increase the energetic costs offoraging and movements, and in turn, lead to increased depletion ofbody fat and protein (Parker et al. 1984; Torbit et al. 1985; DelGiudice etal. 2001). More information on the nutritional ecology of Yellowstonebison can be found in Chapter 6.
During winter, bison in Yellowstone can either travel through unbroken snow, through broken snow on trails created by bison or otherungulates, or on roads that are either plowed for wheeled vehicles ormechanically groomed (i.e., packed snow) for over-snow vehicles suchas snowmobiles and snow coaches. Coughenour (2005) estimatedthat 6 percent of winter travel by bison was through unbroken snow,
74 percent was through broken snow, and 20 percent was on plowed
or groomed roads. Travel costs were 11 to 14 percent of total energy
costs for bison in the central and northern regions of the park. Thoughbison readily travel through unbroken snow, they learn to sometimes
move along paths of least resistance like plowed or groomed roads

The Population

13(Coughenour 2005). However, 80 percent of their travel occurs offroad (Bjornlie and Garrott 2001; Bruggeman et al. 2009a,b).

Diseases
Several diseases and parasites have been detected in Yellowstonebison, including lungworms (Dictyocaulus sp.), tapeworms (Moniezia
benedeni), biting flies, and several outbreaks of hemorrhagic septicemia
between 1911 and 1922 that killed 9 to 15 percent of the bison in northern Yellowstone (Meagher 1973; Franke 2005; Plumb and Sucec 2006).
Also, outbreaks of the deadly disease anthrax, which is caused by thebacterium Bacillus anthracis and transmitted by inhalation or ingestionof endospores that are found in the soil or carcasses, have occurred indomestic bison herds in the Greater Yellowstone Area (Aune et al. 2010;
Adams and Dood 2011). However, these diseases and parasites have
had little effect on the abundance, demography, or distribution of Yellowstone bison. Conversely, the chronic exposure of Yellowstone bison
to the nonnative disease brucellosis, which is caused by the bacterium
Brucella abortus, and can be transmitted to cattle and humans, has
become a primary factor influencing bison survival (due to the cullingof exposed animals) and reproduction (due to decreased birthing rates;
Geremia et al. 2009; Rhyan et al. 2009). When cattle are infected, thereis economic loss to producers from killing infected animals, increased
disease testing requirements, and possibly, decreased marketability of
their cattle. Thus, brucellosis hinders the recovery of Yellowstone bisonoutside the park (Lott 2002; Franke 2005; Plumb et al. 2009; Bailey 2013).
More information on brucellosis and its management implications for
Yellowstone bison is provided in Chapter 2.

Population Dynamics
Historically, Yellowstone bison spent summer in the Absaroka Range
north of Yellowstone National Park; in the Lamar Valley-Mirror Plateau area of northeastern Yellowstone; in the Hayden Valley of central
Yellowstone; and in the Madison-Pitchstone plateaus of southwestern
Yellowstone (Meagher 1973). Bison in northern Yellowstone spent

NPS/Jim Peaco

14

Yellowstone Bison: Conserving an American Icon in Modern Society

winter in the Lamar Valley and nearby areas; bison in central Yellowstone spent winter in the Hayden and Pelican valleys; and bison insouthwest Yellowstone spent winter on the Snake River plains (Meagher
1973). However, bison were almost extirpated before 1900, leaving a
remnant, indigenous herd of approximately 23 bison in the Pelican
Valley of central Yellowstone (Meagher 1973). In 1902, managers createdanother herd in northern Yellowstone from 18 female bison that wererelocated from a ranch in northern Montana and 3 males from Texas(Cahalane 1944; Meagher 1973). Protection and supplemental feeding enabled the bison in northern Yellowstone to proliferate to about
1,000 animals by 1928 (Meagher 1973; Fuller et al. 2007a). Likewise,
the relocation of 71 animals from northern Yellowstone to central Yellowstone during 1936, combined with protection from poaching, led
to an increase in the number of bison in central Yellowstone to about
1,300 by 1954 (Meagher 1973; Fuller et al. 2007a).
Frequent culling by park managers reduced bison numbers through1966, but abundance increased rapidly after a moratorium on culling
was instituted (Meagher 1973; Figure 1.3). Bison numbers increased
from about 500 in 1970 to 2,000 in 1980, and 3,000 in 1990. At the sametime, elk (Cervus elaphus) numbers in northern Yellowstone increased
from about 4,000 in 1968 to 12,000 by the mid-1970s and 19,000 by 1988
(Eberhardt et al. 2007). As herbivore numbers increase in an area, theamount of forage available for each individual decreases, which caneventually reduce foraging efficiency, lead to a decrease in nutrition
and body condition, and in turn, lower pregnancy and survival rates(Caughley 1976; Eberhardt 2002). As bison and elk numbers increased,
however, they began to change their movement patterns and expand
their winter ranges to access more food resources and avoid lower foraging efficiency (Meagher 1989b; Lemke et al. 1998; Fuller et al. 2007a;
White et al. 2013b). Only a few bull bison left Yellowstone National
Park before 1975, but thereafter, larger groups with female bison beganmigrating into Montana during winter (Meagher 1989b; Geremia et al.
2011). Also, in the 1980s bison from central Yellowstone began moving
to northern Yellowstone during winter, where some of them stayed

The Population

15

Figure 1.3. Counts and removals of bison in Yellowstone National Park and nearby areas of Montana
during 1901 through 2014. IBMP refers to the Interagency Bison Management Plan.

and remained year-round (Fuller et al. 2007a; Bruggeman et al. 2009c).
These movements were induced by high bison densities combined withdeep snow packs that limited food availability during some wintersin the central region of the park (Fuller et al. 2007a; Bruggeman et al.
2009c; Gates and Broberg 2011; Geremia et al. 2011).
Between 1984 and 2000, more than 3,000 bison that migrated outside Yellowstone National Park and into Montana were harvested byhunters or culled from the population to prevent the possible transmission of brucellosis from bison to cattle (White et al. 2011). In 2000, theState of Montana and the federal government agreed to an Interagency
Bison Management Plan that prescribed collaborative actions to reduce
the risk of brucellosis transmission from Yellowstone bison to cattle,
including the culling of some bison near the park boundary, whileconserving a wild population of bison with some migration to winterranges on public lands in the state (USDI, NPS and U.S. Department ofAgriculture [USDA], Forest Service [USFS], Animal and Plant HealthInspection Service [APHIS] 2000a,b).

16

Yellowstone Bison: Conserving an American Icon in Modern Society

Photograph courtesy of National Geographic by Michael Nichols

Bison moving along the roadnear Corwin Springs, Montana.

The Population

Under this plan, counts of bison in central Yellowstone increased
from 1,900 in 2000 to 3,500 in 2005 due to high reproduction, survival,
and recruitment rates. Counts then decreased to 1,400 bison by 2013,
primarily due to large culls of about 1,000 bison at the park boundary
during winter 2005-2006 and 1,560 bison during winter 2007-2008(Geremia et al. 2014a). Conversely, counts of bison in northern Yellowstone increased from about 500 in 2000 to 3,400 in 2014 (Geremia
et al. 2014a). This rapid increase was enhanced by immigration of bisonfrom central Yellowstone, and possibly, reduced competition as counts
of northern Yellowstone elk decreased from about 19,000 in 1994 to
4,000 in 2013 following the recovery of grizzly bears (Ursus arctos),
mountain lions (Puma concolor), and wolves (Smith et al. 2003; Ruth
2004; White et al. 2012; Frank et al. 2013; White and Gunther 2013).
More information on the population dynamics and management of
Yellowstone bison can be found in Chapter 3.

Conclusions
The lack of tolerance for wild bison in most areas outside Yellowstone
National Park is the primary factor limiting their restoration in the
Greater Yellowstone Area. Large portions of the historical winter ranges
used by these bison are no longer available due to agricultural, residential, and recreational development (Gude et al. 2006, 2007; Schwartz etal. 2012; White et al. 2013b). Also, there are political and social concerns
about allowing bison outside the park, including human safety andproperty damage, competition with livestock and other ungulates forgrass, diseases such as brucellosis that can be transmitted between bisonand cattle, depredation of agricultural crops, and a shortage of funds
for state management (Lott 2002; Boyd 2003; Franke 2005; Bailey 2013).
Fortunately, many of these constraints can be remedied through thecollaborative actions of federal and state agencies across jurisdictionalboundaries, and the future choices of people in Montana and elsewhere(Franke 2005; Plumb et al. 2009; Bailey 2013; Becker et al. 2013). The
current management of Yellowstone bison, and recommendations forthe future, are discussed in Chapters 10 and 11.

17

NPS/Jim Peaco

Preparing blood samples forbrucellosis testing procedures.

Chapter 2
BRUCELLOSIS — A NONNATIVE DISEASEHINDERING THE RESTORATIONOF YELLOWSTONE BISON
P.J. White, David E. Hallac, Rick L. Wallen, and Jesse R. White

Wild bison and elk in the Greater Yellowstone Area were infected with
Brucella abortus bacteria by domestic European cattle before the 1930s(Meagher and Meyer 1994). This disease decreases the birthing ratesof Yellowstone bison and has indirectly influenced survival rates dueto the culling of exposed animals by humans (Geremia et al. 2009;
Rhyan et al. 2009). Moreover, this disease has been an overriding
factor influencing the distribution and management of Yellowstonebison due to concerns about transmission of the bacteria back to
cattle and economic losses to producers (USDA, APHIS 2010). Thus,
brucellosis directly limits the potential for further recovery of bisonin the Greater Yellowstone Area (Lott 2002; Franke 2005; Plumb et al.
2009; Bailey 2013). In contrast, elk in the Greater Yellowstone Area aremanaged and treated much differently, even though brucellosis is also

20

Yellowstone Bison: Conserving an American Icon in Modern Society

endemic in their populations and has been repeatedly transmitted tocattle over the last decade. Because brucellosis is mentioned throughout
this book, and elk are an important factor when discussing feasible
brucellosis containment and suppression strategies, in this chapter weprovide information about the disease, discuss attempts to suppress it
in wildlife, outline the challenges of reducing transmission risk fromwildlife, and recommend a pathway forward.3

Bovine Brucellosis
Brucellosis is primarily transmitted within and among bison, elk, andcattle during parturition when susceptible animals ingest Brucella bacteria from birthing materials (amniotic fluids, fetus, placenta) or the
newborn calf (Thorne et al. 1978; Williams et al. 1997; Cheville et al.
1998; Rhyan et al. 2001; Thorne 2001). A secondary mode of transmission is through milk when actively infected females nurse their calves(Rhyan et al. 2009). Females are often infected with Brucella bacteria
at a young age, but do not shed the bacteria until they become reproductively active at approximately 3 years (Roffe et al. 1999; Rhyan etal. 2009; Treanor et al. 2011). Male bison can shed Brucella bacteria insemen, but do not infect females during breeding due to low numbersof bacteria present and death of those bacteria in the vagina (Robison
1994; Frey et al. 2013; Uhrig et al. 2013).
Brucella bacteria establish persistent infections by remaining inactive in the lymphoid system tissues of females until conditions becomefavorable for bacteria to multiply and spread in the reproductive tract
during the latter part of gestation (Nicoletti and Gilsdorf 1997; Groveland Moreno 2002). At that time, the bacteria can rapidly increase incells of the placenta and induce abortions, still births, and premature
live births in some animals (Rhyan et al. 1994; Nicoletti and Gilsdorf
1997; Grovel and Moreno 2002). Some females appear to recover andclear the bacteria from their bodies after this infective phase, but others
retain Brucella bacteria and can become infective during subsequentpregnancies (Rhyan et al. 2009; Treanor et al. 2011). Also, some females
3

Portions of this chapter were included in and/or adapted from USDI, NPS (2014).

Brucellosis

Figure 2.1. The bovine brucellosis transmission cycle (USDI, NPS 2014).

could be re-infected at a later time by ingesting Brucella bacteria frombirthing materials shed by highly infected animals. However, theprobability of aborting their fetus should be reduced because theirimmune systems should be able to recognize Brucella bacteria due tothe previous infection (Treanor et al. 2011; Figure 2.1).
The spread of brucellosis is influenced by a variety of factors,
including the proportions of females in various populations thatare infectious, the amounts of bacteria encountered by susceptible
individuals, and the susceptibility of animals to infection (Dobson
and Meagher 1996; Williams et al. 1997; Cheville et al. 1998; Thorne
2001; Hobbs et al. 2014). Persistent, intracellular pathogens such as
Brucella abortus are difficult for animals to clear from their immune
systems, and as a result, infections may recur during periods when
immune defenses are weakened (Treanor 2013). Wild bison and elk in
the Greater Yellowstone Area experience chronic undernutrition and

21

22

Yellowstone Bison: Conserving an American Icon in Modern Society

poorer body condition during winter, which reduces their immune
defenses and increases their vulnerability to Brucella bacteria (Treanor2013). Also, females are more susceptible to infection during pregnancies because cell-mediated immune responses against Brucellaabortus are suppressed to safeguard developing fetuses (Treanor 2013).
For bison or elk to transmit brucellosis to cattle, they must be in thesame locale and undergo an abortion or birthing event that deposits
bacteria-laden tissues that are then contacted by cattle (Cross et al.
2007; Kilpatrick et al. 2009; Schumaker et al. 2010; Kauffman et al.
2013). Therefore, the risk of brucellosis transmission from wildlife
to cattle also depends on: (1) forage availability and winter severity
that influence the magnitude and extent of wildlife movements tolow-elevation areas occupied by cattle during winter and spring, (2)the number of interactions between cattle and wildlife living in close
proximity, and (3) the persistence of infectious material deposited on
the landscape (Kilpatrick et al. 2009; Schumaker et al. 2010; Schumaker
2013; Hobbs et al. 2014).

Diagnostics
To diagnose brucellosis infection with a high level of certainty, it isnecessary to kill animals and attempt to culture Brucella bacteria frommilk, lymphatic tissues, uterine discharges, and fetal tissues (Chevilleet al. 1998; Thorne 2001; Roberto and Newby 2007). Culturing thebacteria depends on sampling tissues where bacteria are residing in
the animal, which is not uniform and varies over time (Treanor et al.
2011). As a result, a positive culture of Brucella bacteria from tissue or
blood definitely indicates infection, but a negative culture test does
not prove the animal is not infected (Rhyan et al. 2009).
Serology is often used instead of killing animals to detect antibodies
circulating in the blood that indicate past exposure to Brucella abortus
bacteria. A positive serology test (i.e., seropositive) does not necessarily mean that the animal is still infected or capable of transmitting
the bacteria, but levels of antibodies tend to be higher in animals withactive infections (Rhyan et al. 2009; Treanor et al. 2011). Thus, assays

Brucellosis

such as fluorescent polarization can be used to estimate antibody
levels and identify animals that are likely infectious (Treanor et al.
2011). This assay is most reliable at identifying actively infected bisonolder than 5 years of age, but most bison less than 3 years old thattest positive for Brucella antibodies are actively infected with live
bacteria in their tissues (Treanor et al. 2011).

Brucellosis Prevalence, Transmission
Risk, and Regulation
More than $3.5 billion have been spent since 1934 to eradicate brucellosis from cattle in the United States, with the disease being detectedin less than 0.0001 percent of herds nation-wide (Cheville et al. 1998;
USDA, APHIS 2009; U.S. Animal Health Association 2012; Rhyan et al.
2013b). In North America, bovine brucellosis currently persists only
in bison and elk populations in the Greater Yellowstone Area andWood Buffalo National Park in Alberta and the northwest Territories
of Canada; though it is widespread world-wide and endemic in many
areas of the Russian Federation and nearby countries (Cross et al.
2007; Ivanov et al. 2011; Godfroid et al. 2013; Rhyan 2013). Also, several
other species of Brucella bacteria are endemic in certain areas of theworld, including Brucella melitensis and Brucella ovis in sheep andgoats, Brucella canis in dogs, and Brucella suis in swine—including
feral pigs in the United States (Godfroid et al. 2013; Rhyan 2013). Cattlein Wyoming, Montana, and Idaho were declared free of brucellosis
during 1983, 1985, and 1991, respectively, but bovine brucellosis was
detected in more than 20 cattle or domestic bison herds in thesethree states during 2002 to 2013 (U.S. Animal Health Association
2012; Rhyan et al. 2013b). These transmissions were traced to wild
elk using epidemiology or genetic tests, and apparently occurred due
to increases in brucellosis prevalence in elk and contacts between
elk and cattle on shared winter ranges (Beja-Pereira et al. 2009; U.S.
Animal Health Association 2012; Cross et al. 2013). To date, no cases ofbrucellosis transmission from wild bison to cattle have been detected,
though such transmission is possible and risk increases as winter

23

24

Yellowstone Bison: Conserving an American Icon in Modern Society

severity and the number of bison migrating into areas with cattle
increase (Kilpatrick et al. 2009; Schumaker et al. 2010; Rhyan et al.
2013b; Schumaker 2013).
Approximately 5,700 wild bison occur in two populations (Jackson,
Yellowstone) in the Greater Yellowstone Area, and these bison moveacross about 1.2 million acres (485,620 hectares) of mostly public
lands. The prevalence of brucellosis in Yellowstone bison is relatively
high with about 60 percent of adult females testing seropositive for
antibodies in their blood indicating previous exposure to Brucellabacteria (Hobbs et al. 2014). However, only about 10 to 15 percent of
all adult female bison, and 20 to 30 percent of seropositive femalebison, are infectious and could potentially shed live bacteria (Roffeet al. 1999; Rhyan et al. 2009; Hobbs et al. 2014). Also, the risk ofbrucellosis 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 moveto higher elevation summer ranges in national parks following snow
melt and vegetation green-up (Kilpatrick et al. 2009; Schumaker et al.
2010; White et al. 2011; Rhyan et al. 2013b; Schumaker 2013).
Approximately 30,000 to 40,000 elk live in the Greater Yellowstone Area in numerous populations (Schumaker et al. 2012). As manyas 18,000 of these elk may be supplementally fed during winter at
the National Elk Refuge and 22 state-operated feeding grounds innorthwestern Wyoming (Scurlock et al. 2010a; Schumaker 2013). Elkaggregate at these feeding grounds in the southern portion of theGreater Yellowstone Area because there is insufficient low-elevation
habitat to support current numbers due to human encroachment on
their historic winter range (Smith et al. 2004). Late winter coincides
with late gestation and the time when elk are likely to transmit Brucella bacteria via abortion events (Cross et al. 2007, 2010). Thus, theprevalence of brucellosis in elk at these feeding grounds was historically quite high (10 to 35 percent) compared to other elk populations(0 to 6 percent) in the Greater Yellowstone Area (Barber-Meyer et al.

Brucellosis

25

NPS/Jim Peaco

Bison and elk in the Lamar Valleyof Yellowstone National Park.

26

Yellowstone Bison: Conserving an American Icon in Modern Society

2007; Cross et al. 2007, 2010; Maichak et al. 2009; Proffitt et al. 2010a;
Scurlock and Edwards 2010).
Many disease regulators believed brucellosis would not persist
in elk throughout the Greater Yellowstone Area without frequenttransmission from wild bison or elk dispersing from winter feeding
grounds (Rhyan et al. 2013b; Schumaker 2013). However, surveillance
during the past decade indicates brucellosis prevalence has increased
from less than 5 percent to 8 to 25 percent in several elk populations

Total eradication ofbrucellosis as a goalis more a statementof principle than aworkable programat present; neither
sufficient information
nor technicalcapability is available
to implement a
brucellosis-eradication
program in the Greater
Yellowstone Area.

in the northern portion of the Greater Yellowstone Area (Cross et al.
2010). These increases coincided with increasing elk numbers and/or aggregations of elk on lower-elevation winter ranges, including agreater proportion of private land than 20 years ago (Cross et al. 2010;
Proffitt et al. 2010b, 2013). Many of these elk populations appear to
support the disease independently of wild bison or feed-ground elk(Cross et al. 2010; U.S. Animal Health Association 2012; Rhyan et al.
2013b). Also, in recent years the distribution of elk testing positive
for brucellosis exposure has expanded beyond the periphery of theGreater Yellowstone Area and now encompasses more than 20 million
acres (8 million hectares).
The estimated risk of brucellosis exposure to cattle from Yellowstone bison is insignificant (less than 1 percent) compared to elk (morethan 99 percent of total risk) because elk have a larger overlap withcattle and are more tolerated by managers and livestock producers(Schumaker et al. 2010). Many of the approximately 450,000 cattle in
the Greater Yellowstone Area are fed on private land holdings during
winter and released on public grazing allotments during summer — but
throughout the year they are allowed to mingle with wild elk (Schumaker et al. 2012; Schumaker 2013). Thus, the risks of brucellosis
transmission to cattle are primarily from wild elk, and management
to suppress brucellosis in bison will not substantially reduce the far
greater transmission risk from elk (Kilpatrick et al. 2009; Schumaker
et al. 2010; Rhyan et al. 2013b; Schumaker 2013). Therefore, numerous independent evaluations have recommended that management
actions for brucellosis focus on maintaining separation between bison

Brucellosis

and cattle, while attempting to decrease elk density and group sizes
in areas where mingling with cattle occurs (Keiter 1997; Cheville etal. 1998; Schumaker et al. 2010; Cross et al. 2013; Godfroid et al. 2013;
Treanor et al. 2013).
To reduce the economic loss to producers when cattle are sporadically infected with brucellosis, the Animal and Plant Health Inspection
Service changed their regulations in 2010 to allow livestock producers
to eliminate outbreaks of brucellosis in cattle on a case-by-case basis,
without imposing corrective regulations on the rest of the producers inthe state. Historically, the Animal and Plant Health Inspection Service
reclassified an entire state or area if two or more herds were foundto have brucellosis within a 2-year period or if a single brucellosisaffected herd was not depopulated within 60 days (USDA, APHIS2010). This reclassification often had adverse economic consequenceson producers state-wide because a “brucellosis-free” classification
allowed them to export cattle to other states or nations without testing (Bidwell 2010). Today, the entire state is not reclassified or subject
to corrective actions provided that outbreaks are investigated andcontained by removing all cattle testing positive for brucellosis exposure (USDA, APHIS 2010). In fact, brucellosis was detected in several
domestic bison and cattle herds in Idaho, Montana, and Wyoming
during 2009 through 2014, without any state-wide corrective actions
being implemented (U.S. Animal Health Association 2012; Brown 2013).
These regulatory changes by the Animal and Plant Health Inspection
Service focused increased attention on the Greater Yellowstone Area
where brucellosis is chronic in bison and elk. As a result, livestock regulatory agencies in Idaho, Montana, and Wyoming defined designatedsurveillance areas where elk testing positive for brucellosis exposure
are known or thought to exist and could mingle with livestock andexpose them to tissues containing Brucella bacteria (Barton 2013;
Logan and Correll 2013; Zaluski 2013). The combined designated surveillance areas cover approximately 71,290 square kilometers (27,525
square miles) in eastern Idaho, southwest Montana, and western
Wyoming (Figure 2.2). Within these areas there are requirements for

27

28

Yellowstone Bison: Conserving an American Icon in Modern Society

Figure 2.2. The Designated Surveillance Area (gold color) for brucellosis in eastern Idaho,
southwest Montana, and western Wyoming. Abbreviations: DSA = Designated Surveillance
Area; GYA = Greater Yellowstone Area.

Brucellosis

calfhood vaccination for brucellosis and individual identification for
all cattle to enable traceability. Also, all sexually intact cattle must be
tested for brucellosis exposure prior to sale or movement out of thedesignated surveillance areas. This testing provides assurance to trading partners and other state veterinarians that brucellosis-infected
livestock will not be moved into their states (Barton 2013; Logan andCorrell 2013; Zaluski 2013). These designations also benefit producers
by eliminating unnecessary testing elsewhere and providing for the
reimbursement of testing costs. The Montana Department of Livestock (MDOL 2013) estimated that the designated surveillance area
provided a net annual benefit of at least $5.5 million to producers.

Attempts to Suppress Brucellosis
Population Reduction — There have been several attempts to suppress
the prevalence of brucellosis in wild bison and elk in the Greater Yellowstone Area. Managers at Yellowstone National Park periodicallyremoved some bison and elk during 1908 to 1967 to reduce numbers
and the prevalence of brucellosis (Barmore 1968). About 810 bison
were relocated to other areas and 4,200 bison were shipped to meat
processing facilities (Skinner and Alcorn 1942; Meagher 1973). Also,
about 13,500 elk were relocated, 13,000 elk were shot or trapped in
the park, and 45,000 elk were harvested by hunters north of the park
(Houston 1982). Fewer than 500 bison and 4,000 elk were counted
by 1968, and at that point, park managers concluded they would only
eradicate brucellosis by eliminating bison and elk — which was counterto their mission of conserving these resources unharmed for the benefit and enjoyment of people (Barmore 1968; Meagher 1973; Houston
1982). Thus, culling ceased and wildlife numbers were allowed tofluctuate in response to predators, resource limitations, weather, andhunting outside the park (Houston 1982; National Research Council
2002; White and Gunther 2013).
Test-and-Slaughter  —  The Wyoming Game and Fish Department
spent $1.3 million on a 5-year effort at several feeding grounds to capture 2,624 elk, test 1,286 female elk, and cull 197 animals testing positive

29

30

Yellowstone Bison: Conserving an American Icon in Modern Society

for brucellosis exposure (Scurlock et al. 2010; Schumaker et al. 2012).
Brucellosis prevalence was reduced from approximately 37 to 5 percent,but the extent to which this reduced the risk of transmission to cattle
was unknown (Schumaker et al. 2012). Prevalence will likely increase
after the cessation of suppression efforts, and economic costs make it
infeasible to use this approach across the entire Greater Yellowstone
Area (Schumaker et al. 2012). Test-and-slaughter programs that only
remove modest numbers of elk (10 to 25 percent) are unlikely to control
brucellosis across the Greater Yellowstone Area, and could facilitatetransmission somewhat by removing animals that have recovered fromprevious infection and may have some resistance to future exposure(Bienen and Tabor 2006).
In addition, about 3,580 Yellowstone bison have been captured andshipped to meat processing or research facilities since 2000 to reduce
numbers and brucellosis prevalence (White et al. 2011). These culls were
extremely controversial and did not decrease brucellosis prevalence(White et al. 2011). As a result, bison managers decided to minimize
the future shipment of large numbers of bison to meat processing
facilities and use other tools such as conservation easements, hunting, and increased tolerance on public lands to limit bison numbers
and lessen conflicts with cattle and humans (USDI, NPS et al. 2008).
Dispersed Feeding — Brucellosis transmission is strongly influenced
by the density of bison or elk in close proximity during February
through June when most brucellosis-induced abortions occur (Crosset al. 2013). As a result, management actions that prevent large aggregations of wildlife on winter ranges could decrease transmission. The
Wyoming Game and Fish Department is trying to reduce large aggregations of elk on several feeding grounds by distributing food acrossa broader area and stopping feeding earlier in the year (Cross et al.
2013). However, early movements of elk away from feeding grounds
could actually increase contacts between elk and nearby cattle (Crosset al. 2013).
Hunting — Targeted hunts during late winter could be used to disperse large groups of bison or elk, move them away from cattle, and/

Brucellosis

or reduce population sizes (Cross et al. 2013). Targeted hunts for elk
have been implemented in some areas of southwestern Montana andwestern Wyoming in recent winters, but it is too soon to evaluate theireffects on brucellosis transmission (Cross et al. 2013). Also, there aremany landowners in the Greater Yellowstone Area that do not allow
hunters access to their lands. Elk have learned to use these areas, which
can result in large aggregations during winter that could facilitate
brucellosis transmission (White et al. 2012; Proffitt et al. 2013).
Bison hunting in Montana occurs outside the northern and westernboundary areas of Yellowstone National Park, with harvests varying
from year-to-year depending on how many bison move outside thepark in response to snow depths in the higher mountains (Geremia etal. 2011, 2014b; White et al. 2011). To date, hunting has not reduced theprevalence of brucellosis in the population because infectious animals
are not selectively shot. Also, many hunters select bulls, which do nottransmit the disease. In addition, bison reactions to hunting pressure
include moving back into the park and/or remaining inside the park
where hunting is prohibited.
Predators and Scavengers — The transmission of brucellosis could
be reduced by protecting predators and scavengers that reduce densities of bison and elk and quickly remove infectious birthing materials
from the environment (Cross et al. 2013). Numbers of elk that spend
winter and spring in Yellowstone National Park and nearby areas havedecreased by about 70 percent due, in part, to predation by wolves
and other large carnivores (Barber-Meyer et al. 2008; Hamlin et al.
2009; White and Garrott 2013). This reduction may have decreased
the risk of brucellosis transmission to cattle due to fewer infectious
elk, fewer elk aggregations, and smaller group sizes in some areas(Barber-Meyer et al. 2007; Cross et al. 2010; White et al. 2012). Also,
the recovery of wolves and grizzly bears in the Greater Yellowstone
Area has increased the amount of carrion, and in turn, the abundanceof scavengers that could remove Brucella-infected tissues before they
are discovered by susceptible bison, cattle, or elk (Garrott et al. 2013).
The Wyoming Game and Fish Department protects scavengers such

31

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Yellowstone Bison: Conserving an American Icon in Modern Society

Photograph courtesy of National Geographic by Michael Nichols

Infrared image of a grizzly
bear on an elk carcass inYellowstone National Park.

Brucellosis

as coyotes (Canis latrans) and red foxes (Vulpes vulpes) on some elk
feedgrounds to reduce the time infectious tissues remain on the landscape (Cross et al. 2013).
Vaccination — Three vaccines that consist of live, weakened strainsof Brucella abortus bacteria are used world-wide to provide bison,cattle, elk, and other domestic and wild ungulates with some resistanceto brucellosis infection and abortions (Olsen 2013). Elk on feeding
grounds in Wyoming have been vaccinated with strain 19 vaccine
since 1985. However, the Brucella infection rate in vaccinated andunvaccinated elk is similar, and 75 percent of vaccinated elk aborted
their fetus when they were subsequently exposed to Brucella bacteria(Cross et al. 2013). Likewise, several experimental studies with elk
detected little protection against brucellosis infection or abortion
after vaccination with strain 19 (Kreeger et al. 2000, 2002; Olsen 2013).
Some elk developed antibody responses after vaccination, but they
did not develop the cellular immune responses needed to suppress
Brucella bacteria inside cells (Olsen and Johnson 2012; Olsen 2013).
Similarly, vaccination with strain 19 did not protect bison calves from
subsequent infection and abortions (Davis et al. 1990, 1991; Olsen 2013).
Two-thirds of vaccinated bison aborted their pregnancies, thoughvaccinated animals did have fewer abortions and lower infection rates
thereafter (Davis et al. 1991).
Serological tests for Brucella antibodies cannot distinguish between
an animal that has been infected with field strains of the bacteria andthose which have been vaccinated with strain 19 (Cheville et al. 1998).
Consequently, many infections identified in livestock populations
were thought to be vaccine related. Strain 19 vaccine was replacedwith strain RB51 vaccine, which causes animals to produce antibodies that do not react on standard brucellosis serological tests. Cattle
operations in the designated surveillance areas of Idaho, Montana,and Wyoming vaccinate all calves and most adults with strain RB51
vaccine, which reduces abortions and further transmissions fromcattle that subsequently become exposed to, and infected with, Brucella bacteria (Olsen et al. 1998, 2009). However, the vaccine does not

33

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Yellowstone Bison: Conserving an American Icon in Modern Society

prevent cattle from becoming infected after exposure to infectious
amounts of Brucella (Olsen and Tatum 2010). Thus, vaccinating cattlewith strain RB51 will not eliminate the potential for brucellosis infection from wildlife (Olsen 2013).
Similarly, strain RB51 vaccine does not prevent bison or elk frombecoming infected following exposure to sufficient doses of Brucellabacteria (Treanor et al. 2010; Olsen 2013). In experiments, less than 15
percent of bison vaccinated with strain RB51 were protected against
infection following exposure to Brucella bacteria (Elzer et al. 1998;
Davis and Elzer 1999, 2002; Olsen et al. 2003). Also, vaccinated elk had
little protection against brucellosis infection or abortion (Kreeger et al.
2000, 2002; Olsen 2013). In captive settings, strain RB51 vaccine reduces
abortions and further transmissions of brucellosis in about 50 to 60
percent of bison, especially when they receive a subsequent booster
vaccination (Olsen et al. 1998, 2009; Plumb and Barton 2008; Treanor
2012; Olsen 2013). However, Treanor (2012) found the magnitude of
immune responses from single RB51 vaccinations in wild bison weremore variable and often substantially lower, likely due to the poorer
nutritional status of wild bison during winter. During 2004 to 2011,non-pregnant Yellowstone bison were sporadically vaccinated withstrain RB51 at boundary capture facilities. However, only 299 animals
were vaccinated and this low level of effort had no effect on brucellosis prevalence in the population (White et al. 2011; USDI, NPS 2014).
Strain 82 vaccine has been used to reduce outbreaks of brucellosis
in cattle in some regions of the Russian Federation (Olsen et al. 2010;
Ivanov et al. 2011; Denisov et al. 2013). In 1974, more than 5,300 cattle
herds were infected with Brucella abortus across the Soviet Union.
However, only 68 herds remained infected after widespread use ofstrain 82 vaccine for 34 years (Olsen et al. 2010; Ivanov et al. 2011). These
results appear promising, but the vaccine is not approved for use in
the United States and it will likely take many years to adequately test
the vaccine and possibly gain approval.
Fertility Control — Model simulations suggest that inhibiting fertility in bison testing positive for brucellosis exposure could decrease

Brucellosis

future transmission (Ebinger et al. 2011). Female bison 3 to 5 years oldhave a higher probability than older bison of being infectious andtransmitting Brucella bacteria during parturition (Treanor et al. 2011).
Therefore, preventing young female bison and elk from breeding forseveral years could decrease the risk of brucellosis transmission if
they were no longer infectious after returning to reproductive status(Miller et al. 2004; Rhyan et al. 2013a; USDI, NPS and Montana Fish,
Wildlife & Parks [MFWP] 2013). Immunocontraceptive vaccines are
currently being investigated for possible use in bison and other wildlife,
including porcine zona pellucida (PZP) and gonadotropin releasing
hormone (GnRH). The PZP vaccines induce the formation of antibodies that block sperm from fertilizing eggs, while GnRH vaccines
prevent follicle growth and ovulation (Kirkpatrick et al. 1996; Miller
et al. 2004; USDA, APHIS 2012; National Research Council 2013). In
2012, the Animal and Plant Health Inspection Service initiated a 6-year
study using GnRH vaccine (GonaCon™) on captive Yellowstone bison.
The objectives of the study are to determine if the vaccine prevents
the shedding of Brucella bacteria and whether bacteria that remain
dormant or latent will proliferate during pregnancies after the effectsof contraception wane (USDA, APHIS 2012).
No fertility control methods that are affordable, easily delivered,highly effective, and reversible are currently available for delivery towild bison and elk that are spread across a vast landscape. There isno contraceptive product for oral delivery that is species- and genderspecific, and remote delivery via bio-absorbable projectile or dart is
not feasible for most wide-ranging wildlife populations (Garrott andOli 2013; National Research Council 2013; USDI, NPS 2014). Also, allcontraceptive methods would alter the behavior and/or physiologyof wild bison or elk to some extent because, by design, they affectthe animal’s reproductive system (National Research Council 2013).
Infertility may last longer than expected and even become permanent,
especially after repeated vaccinations (National Research Council2013). In addition, preventing births in enough females could change
the age structure of a population by reducing the number of young

35

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Yellowstone Bison: Conserving an American Icon in Modern Society

NPS/Neal Herbert

Female bison and calf
near the Lamar Valley inthe northern region of
Yellowstone National Park.

Brucellosis

and enhancing the survival of infertile females that no longer haveenergetic costs from pregnancy and lactation (National ResearchCouncil 2013). Furthermore, fertility control can contribute to artificial
selection pressures that lead to unintended genetic consequences(Ransom et al. 2013). As a result, the implementation of fertility control
using current knowledge and techniques could lead to long-term,
unintended consequences to bison and elk populations in the Greater
Yellowstone Area (White et al. 2013c; USDI, NPS 2014).

Economic Assessments of Preventative Actions
Economists, biologists, and veterinarians in Wyoming evaluatedfeasible management strategies to reduce the risk of cattle herds
contracting brucellosis from wild elk (Roberts et al. 2012; Kauffman
et al. 2013). Cattle producers could take several actions to reduce
this risk, including: (1) fencing haystacks, (2) hazing elk from theirproperty, (3) booster vaccinating adult cattle, (4) spaying heifers, (5)modifying winter feeding schedules, (6) delaying cattle release on
summer grazing allotments, and (7) preventing the mingling of cattle
and wildlife (Roberts et al. 2012). However, these preventative actions
are not cost-effective for most cattle producers due to the apparent
randomness of brucellosis outbreaks, the high cost of prevention
measures compared to their effectiveness, and the comparatively
low cost of dealing with an occasional brucellosis outbreak in cattle(Roberts et al. 2012).
Researchers also compared the costs and benefits of implementing
management strategies with wild elk to increase the number of years
until a brucellosis outbreak occurred in cattle (Kauffman et al. 2013).
The evaluated management strategies were: (1) capturing elk andremoving animals testing positive for brucellosis exposure, (2) vaccinating calf elk, and (3) lower-density feeding of elk on feedgrounds
to avoid large aggregations (Kauffman et al. 2013). These management
strategies could increase the time between brucellosis outbreaks incattle, but the costs would be extremely high relative to the benefits

37

38

Yellowstone Bison: Conserving an American Icon in Modern Society(Kauffman et al. 2013). As a result, these preventative actions are notcost-effective to implement (Kauffman et al. 2013).

Challenges of Reducing Brucellosis Transmission Risk
Disease regulators have recommended the use of vaccines to reduce
brucellosis infection in wildlife in the Greater Yellowstone Area.
However, their use is limited due to financial, logistic, scientific, andsocial constraints (Cross et al. 2013; Godfroid et al. 2013; Olsen 2013;
White et al. 2013c). A successful vaccination program to reduce brucellosis transmission in bison and elk would require the consistentdelivery of known doses of vaccine to most females in autumn. Thistiming would facilitate the generation of sufficient protective immune
responses before potential exposure to Brucella bacteria during February through June (Plumb and Barton 2008; Treanor 2012). However,bison and elk inhabit millions of acres across the ecosystem and it
would be difficult to capture a majority of their populations in facilities for vaccination (Cross et al. 2013; White et al. 2013c). Also, remotedelivery of vaccine using darts or bio-absorbable bullets is challenging because approach and delivery of any projectile disturbs wild
animals, which could preclude the delivery of vaccine to many of theindividuals in larger groups (USDI, NPS 2014). In addition, it would be
difficult to deliver an oral vaccine to bison and elk by attracting themto bait because they are herbivores (USDI, NPS 2010). Moreover, avaccination program for bison and elk would need to be maintainedin perpetuity to prevent resurgences in prevalence (White et al. 2013c).
Capture and remote vaccination are likely unpleasant experiences forbison and elk, and therefore, they may begin to avoid humans. As aresult, it will probably become more difficult to vaccinate large portions of bison and elk populations in the Greater Yellowstone Area
over time (USDI, NPS and MFWP 2013; White et al. 2013c; USDI, NPS
2014). In turn, behavioral effects on bison and elk such as reduced
tolerance of people and vehicles could lead to shifts in their spatial
distribution across the landscape and reduce opportunities for visitors
and hunters to observe bison and elk (USDI, NPS and MFWP 2013).

Brucellosis

It may be possible to capture and/or remotely vaccinate more bisonand elk when they aggregate on their winter ranges. However, vaccination often stimulates less of a protective immune response inundernourished animals (Treanor 2012, 2013). Bison and elk in the
Greater Yellowstone Area are undernourished through winter due
to the limited availability of relatively low quality forage (grasses andgrass-like plants), most of which is senescent and covered by snow
(DelGuidice et al. 1994, 2001). This seasonally poor nutrition andbody condition increases the vulnerability of animals to bacterial
infections and coincides with increasing energy and protein demands
during late pregnancy; which in turn, limit the resources available
for immune defense (Clemens et al. 1979; Weinberg 1987; Jolly andFernandes 2000). Treanor (2012, 2013) found that brucellosis infection
was higher in Yellowstone bison in below-average condition, whichsuggests that fewer bison successfully avoid infection with Brucellabacteria during severe or prolonged winters. Also, fat and protein
metabolism strongly influenced the intensity of Brucella infections
and immune responses in yearling female bison (Treanor 2012, 2013).
As a result, the vaccination of wild bison or elk during winter may
be less effective against brucellosis than suggested by the results ofcaptive, experimental studies (Treanor 2012, 2013).
Given these challenges, we conclude that the eradication or substantial suppression of brucellosis in bison and elk in the Greater
Yellowstone Area is not feasible at this time without attempting depopulation or capture, test-and-slaughter, and vaccination on a regional
scale; which most stakeholders deem unacceptable and impossible(Bienen and Tabor 2006; MFWP 2013; Treanor et al. 2013). This infeasibility is due to:•

The absence of easily distributed and highly effective vaccines;•

Limitations of current diagnostic and vaccine delivery
technologies;•

Effects of bison and elk nutrition, condition, and pregnancy/
lactation that lessen protective immune responses;

39

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Yellowstone Bison: Conserving an American Icon in Modern Society•

Potential adverse consequences (e.g., injuries, changes inbehavior) to wildlife and visitor and hunter experiences from
intrusive brucellosis suppression activities; and•Our limited understanding of bison and elk immune responses
to brucellosis suppression actions such as vaccination (Crosset al. 2013; Godfroid et al. 2013; Olsen 2013; Treanor 2013; USDI,
NPS and MFWP 2013; White et al. 2013c).

This conclusion has been reached by several diverse and independent groups of citizens, regulators, and scientists that agree thevaccination of wild bison and elk with existing technologies and undercurrent conditions will not solve the problem of occasional brucellosis
transmission to cattle in the Greater Yellowstone Area. For example,
the National Academy of Sciences concluded that “total eradicationof brucellosis as a goal is more a statement of principle than a workable program at present; neither sufficient information nor technicalcapability is available to implement a brucellosis-eradication program in the Greater Yellowstone Area” (Cheville et al. 1998). Also,
the Citizens Working Group on Yellowstone Bison (2011) indicatedthat “remote vaccination of wild bison using the current vaccine anddelivery method as a means of reducing a risk of transmission should
not be a priority at this time.” Likewise, an expert bison/brucellosis
science panel indicated that “the best available data do not support
that vaccination of wild bison with currently available vaccines will
be effective at suppressing brucellosis to a level that changes bison
management strategies under the Interagency Bison Management
Plan” (USDI, NPS and MFWP 2013). Similarly, the Elk Management
Guidelines in Areas with Brucellosis Working Group for the State ofMontana did not recommend vaccination of wildlife but indicatedthat “eradication of brucellosis in elk is ultimately desirable, but it is
not currently feasible, and current methods to achieve this goal, suchas test-and-slaughter, are unacceptable” (MFWP 2013). Moreover, theState Veterinarian of Montana was quoted as saying “the reason why
the wildlife brucellosis issue hasn’t been addressed is because there’s
no easy solution. We don’t have a vaccine that’s effective enough, andBrucellosis

don’t have a delivery mechanism that works for wildlife” (Chaney2014).
Some modeling efforts have suggested that substantial reductions inbrucellosis transmission are feasible within a few decades using vaccination and/or other activities (Treanor et al. 2010; Ebinger et al. 2011).
However, these authors acknowledged their analyses were based onsome simplifying assumptions (e.g., 100 percent efficacy and lifetime
treatment effects) that were necessary to reduce model complexityand enable direct comparisons of differences among treatments. Also,these models were unable to make accurate, precise estimates of suppression amounts and timelines due to uncertainty in the parameters
used to inform the models (e.g., weather, abundance of bison, andshifts in behavior in response to management actions). Hobbs et al.
(2014) found including uncertainty in the number of bison that could
be removed, hunted, or vaccinated substantially reduced the chancesof meeting brucellosis suppression goals to less than 5 percent (USDI,
NPS and MFWP 2013).

Conclusions
Elk and bison in the Greater Yellowstone Area have been affected by
the disease brucellosis (Brucella abortus) for almost a century. The
disease has not had substantial deleterious effects on wildlife populations, but it presents an economic risk to cattle producers. As a result,
livestock managers want more permanent solutions, including brucellosis eradication and complete elimination of risk to cattle (Bidwell2010). The risk of brucellosis transmission from bison to cattle also
devalues bison as wildlife outside national park units, limits tolerance for their migration to essential low-elevation winter ranges insurrounding states, and prevents relocations elsewhere to enhanceconservation of the species (Franke 2005; White et al. 2011; Bailey2013). Therefore, many wildlife managers would likely support thesubstantial suppression of brucellosis if and when it was biologicallyfeasible, economically practicable, socially acceptable, and could beaccomplished without harming the integrity of wildlife populations.

41

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Yellowstone Bison: Conserving an American Icon in Modern Society

As discussed previously, however, the reality is that eradication oreven a substantial reduction of brucellosis in bison and elk is not
attainable at this time given available technologies (Cross et al. 2013;
White et al. 2013c).
An effective brucellosis control program for wildlife in the Greater
Yellowstone Area would require the de novo development of highly
effective vaccines for both elk and bison, a delivery system that can
cost-effectively provide the vaccine to thousands of female bison andtens of thousands of female elk across tens of millions of acres in thestates of Idaho, Montana, and Wyoming. Biologists would also need
new diagnostics that allow them to discriminate between previously
infected and infectious animals to gauge vaccination efficacy (Bienen
and Tabor 2006; Treanor et al. 2010; MFWP 2013). The development of
separate vaccines for bison and elk would likely be necessary due totheir different physiologies and protective immune responses (Cross etal. 2013; Godfroid et al. 2013; Olsen 2013). However, there has been little
progress in vaccine development, delivery systems, and diagnostics
due to a lack of market incentives and restrictions on research dueto the classification of Brucella abortus as a select agent that could bepackaged as a biological weapon by terrorists and used to threaten
public health or national security (www.selectagents.gov). Thus, thecurrent best alternative for wildlife and livestock managers is to suppress the probability of Brucella abortus transmission by maintaining
separation between bison, elk, and cattle during the transmission
period from February through June (Keiter 1997; Bienen and Tabor2006; Nishi 2010; Cross et al. 2013; Godfroid et al. 2013; Treanor et al.
2013; White et al. 2013c).
Given the myriad problems to overcome to substantially reduce
brucellosis infection in wild bison and elk distributed across a vast
region, we suggest an alternate approach to protect domestic livestock:
developing an infection-blocking vaccine for cattle. This alternative
would have a much higher likelihood of effectively reducing brucellosis transmission risk in a shorter period of time because of thebetter understanding of cattle as a model in the veterinary sciences,

Brucellosis

the substantially larger number of facilities available for research on
cattle, the better nutritional condition of cattle that may increase vaccination success, and the ability to efficiently capture and vaccinate
all cattle. Current cattle vaccines are only 65 to 70 percent effective against abortion and 10 to 15 percent effective against infection(Olsen et al. 1998; Olsen and Tatum 2010). Thus, there is substantial
room for improvement. Although significant resources have been
expended to develop and test vaccines in the past, there have been
several advances in recent years (e.g., DNA vaccines, nanoparticles)that suggest breakthroughs may still be possible (Olsen 2013; Yang etal. 2013). We realize the development of a perfect vaccine that prevents brucellosis infection in cattle will be challenging, but it seems
logical to fully explore this prospect before embarking on the much
more complex and difficult task of developing and delivering multiple
vaccines for wildlife across a vast geographic scale. Brucellosis waseliminated in cattle historically due to the captive and controlled
nature of managing livestock, and all of the factors that made it possible still exist. Moreover, if a highly effective vaccine was developed
for cattle, it would likely be somewhat effective in bison and perhaps
elk, so that wildlife practitioners could then focus on effective delivery
to contain and suppress brucellosis.

43

NPS/Photographer unknown

Park Ranger Ray Frazierwith bison calf “Buff” at the
Buffalo Corral in Mammoth
Hot Springs, Yellowstone
National Park, circa 1926.

Chapter 3
HISTORICAL PERSPECTIVE — FROM NEARERADICATION TO LIVESTOCK TO WILDLIFE
Rick L. Wallen, P.J. White, and Chris Geremia

Though bison were nearly eradicated across the Great Plains by thelate 1800s, there were at least hundreds and perhaps thousands ofbison in the Greater Yellowstone Area during the 1870s and 1880s(McHugh 1972; Isenberg 2000). Around the time the park was established in 1872, an observer noted the lower Gardiner basin near thenorthern boundary “would be covered with bison” (Potter 1962).
Also, Superintendent Philetus Norris reported in 1880 approximately
200 bison spent the summer near Crevice, Hellroaring, and Slough
creeks and winter in the Lamar Valley in northern Yellowstone (Schullery and Whittlesey 1992). A second herd of about 100 bison spentsummer in the high-elevation country between the Lamar Valley and
the Grand Canyon of the Yellowstone River and winter in either the
Pelican Valley or the Lamar Valley (Schullery and Whittlesey 1992). A
third herd of about 300 bison spent summer on the Madison Plateau

46

Yellowstone Bison: Conserving an American Icon in Modern Society

in west-central Yellowstone and winter outside the park to the west
(Schullery and Whittlesey 1992).4
Yellowstone National Park was established, in part, to protect
against the wanton destruction of fish and game found within thepark (U.S. Code, Title 16, § 22, 17 Statute 32). A detachment of the First
U.S. Cavalry was sent to the park in 1886, but poachers continued tokill bison and other wildlife because few remained elsewhere (Franke
2005; Whittlesey and Schullery 2011). It was not until Congress passed
the Lacey Act in 1894 that soldiers had the authority to prosecuteindividuals for killing or transporting wildlife from the park (Haines
1977; Whittlesey and Schullery 2011). By then, bison in and adjacentto the northern region of Yellowstone had been extirpated, and only
about 23 bison were left in the Pelican Valley of central Yellowstone
by 1901 (Meagher 1973). This remnant, indigenous herd was the largest
remaining wild population of plains bison south of Canada and wascompletely isolated from other populations (Meagher 1973; Bartlett
1985).

Protection, Husbandry, and Ranch Management
Restoration of bison to the northern region of Yellowstone National
Park began in 1902 with the reintroduction of 18 females from the
Pablo-Allard herd in northwestern Montana and 3 bulls from theGoodnight herd in Texas (Cahalane 1944; Meagher 1973). Also, during
1903 to 1909 a few calves were taken from the indigenous bison remaining in central Yellowstone and released into northern Yellowstone(Cahalane 1944; Meagher 1973). The bison in northern Yellowstone
were initially held in a fenced pasture near Mammoth Hot Springs,
and then moved to the “Buffalo Ranch” in the Lamar Valley during
1907 (Meagher 1973). These bison were herded during the day andput in a fenced pasture at night, with little effort to recreate a wild
population (Meagher 1973). Sometime between 1915 and 1920, thebison were allowed to roam more freely and at higher elevations during
summer, while the National Park Service produced hay in the valley
4

Portions of this chapter were adapted from White et al. (2011).

Historical Perspective

47

NPS/Photographer unknown

Bison at the Buffalo Ranch in
the Lamar Valley of Yellowstone
National Park, circa 1930.

48

Yellowstone Bison: Conserving an American Icon in Modern Society

bottom (Meagher 1973). During this time, the reintroduced bison from
northern Yellowstone probably began to mingle with the remaining
indigenous bison from central Yellowstone on the Mirror Plateau andin the upper Lamar Valley towards the eastern boundary of the park
(Meagher 1973, 1989b; Meagher et al. 2002; Plumb and Sucec 2006).
After 1921, a deliberate effort was made to keep bison from northern
Yellowstone on these higher elevation summer ranges by fencing the
hay fields in the valley (Meagher 1973). Mingling with the wild bisonfrom central Yellowstone likely increased during summer, but bisonfrom northern Yellowstone were still rounded up in late autumn, corralled, and fed hay at the Buffalo Ranch during winter (Cahalane 1944;
Meagher 1973). Bison numbers in northern Yellowstone increased
rapidly under this protection and husbandry, reaching about 1,100
by 1930 (Haines 1977; Sellars 1997).
Roundups and confinement of bison in northern Yellowstoneceased in 1938, and during the 1940s, managers decided these bisonshould live in a more natural state like other wildlife (Cahalane 1944;
Sellars 1997; Knudten 2011). However, managers continued to feedbison during winter until 1952, when ranching operations in the Lamar
Valley were discontinued and bison were allowed to move freely within
the park (Meagher 1973). Managers recognized that without supplemental feeding the bison in northern Yellowstone would disperse
more widely and eventually be subject to hunting outside the park
(Cahalane 1944; Meagher 1973). However, this shift in management
philosophy was deemed necessary to restore wild bison, as opposedto perpetuating “a semi-domesticated cattle herd” like on a ranch orgame farm (Cahalane 1944).
The indigenous, remnant bison in the Pelican Valley of central
Yellowstone gradually increased in numbers once protected frompoaching (Meagher 1973). To stimulate population growth and disperse bison more widely across existing habitat, park managers
relocated 71 bison from northern Yellowstone to the Firehole Riverdrainage and Hayden Valley in the central region of the park during
1936 (Cahalane 1944). Bison numbers increased during the 1940s

Historical Perspective

and there were more than 700 bison in central Yellowstone by 1949.
Bison soon began to move back-and-forth between the Firehole Riverdrainage and Hayden Valley areas (Meagher 1973). Most of these bison
spent summer in the Hayden Valley, with some use of the Madison
Plateau, through the mid-1950s (Meagher 1973). Many bison from the
Hayden Valley moved westward across the Mary Mountain divide tospend winter in the “Firehole geyser basin,” where snow depths werelower due to geothermal influences (Meagher 1998; Taper et al. 2000
provides maps and descriptions of the spatial distribution of bisonover time). However, there was little mixing between these relocatedbison and the indigenous bison in the Pelican Valley until the 1950s(Meagher 1998; Gates and Broberg 2011).
As early as the 1920s, park managers became concerned about brucellosis and overgrazing by bison and other ungulates, especially elk.
The Secretary of the Interior is authorized to dispose of “surplus”
bison (16 USC § 36) and destroy animals that may be detrimental toparks (16 USC § 3). Brucellosis can be considered detrimental to Yellowstone bison because it induces abortions and limits tolerance for
their migration to low-elevation winter ranges in Montana (Franke
2005; Plumb et al. 2009). Park managers used these authorities toimplement periodic removals of bison from northern Yellowstoneduring 1925 to 1966 and central Yellowstone during 1954 to 1966 to
reduce numbers and remove individuals exposed to brucellosis (Barmore 1968; Meagher 1973). Many hundreds of live bison were shipped
to zoos, parks, tribal reservations, and other places (Cahalane 1944).
Thousands of bison were killed and provided to American Indian
tribes, relief agencies, and contract sales (Skinner and Alcorn 1942;
Meagher 1973). By 1967, there were less than 100 bison in northern
Yellowstone and 400 bison in central Yellowstone (Fuller et al. 2007a).

Bison as Wildlife, Contributing to Ecological Processes
In 1968, managers ceased the culling of bison in Yellowstone National
Park, and allowed numbers to fluctuate in response to predators,
resource limitations, and weather (Cole 1971; Houston 1982; National

49

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Yellowstone Bison: Conserving an American Icon in Modern Society

NPS/Neal Herbert

Lone bison in the northern
region of Yellowstone
National Park.

Historical Perspective

Research Council 2002). Bison numbers increased under this new
management paradigm and hundreds of animals from the central
and northern regions of the park began to migrate and expand theirranges towards the boundary (Meagher 1989b, 1998; Cannon 2001;
Meagher et al. 2002; Bruggeman et al. 2009c). During the 1970s, bisonfrom northern Yellowstone expanded their range westward from theLamar Valley and down the elevation gradient formed by the Yellowstone River (Meagher 1989b). Subsequently, some bison began tospend portions of the summer in the Lamar Valley and along lower
Slough Creek and Soda Butte Creek, rather than migrating to higher
elevations (Meagher et al. 2002). Beginning in the 1980s, bison incentral Yellowstone began moving west from the Pelican Valley tothe northern shore of Yellowstone Lake and into the Hayden Valley
during winter (Meagher 1998). Subsequently, more bison began
moving earlier from the Hayden Valley west to the “Firehole geyser
basin,” and eventually, into the Madison Valley where some bisonremained during summer (Meagher 1998; Meagher et al. 2002; Bruggeman et al. 2009c). During a few winters in the 1980s and 1990s, bison
began moving from the Madison Valley in west-central Yellowstone
toward the northern boundary of the park (Meagher et al. 2002). Thesemovements increased during the 2000s (Clarke et al. 2005; Fuller et
al. 2007a). Concurrent with these westward and northern shifts, thesummer distribution of bison from Pelican Valley changed, with bison
no longer migrating across the Mirror Plateau to the upper Lamar
Valley after the mid-1980s (Meagher et al. 2002). Instead, more bison
stayed in the Hayden Valley and mingled with bison from the Mary
Mountain area (previously relocated from northern Yellowstone in1936) during summer and autumn (Meagher 1998; Taper et al. 2000).
Over time, intermixing between these bison increased (Meagher 1998).
Attempts to deter movements by bison outside Yellowstone National
Park and into Montana during winter failed (Meagher 1989a,b). As
a result, the occasional bison that left the park during 1967 to 1984
were killed by Montana game wardens or National Park Service
personnel to prevent the possible transmission of brucellosis from

51

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Yellowstone Bison: Conserving an American Icon in Modern Society

bison to cattle (MFWP and MDOL 2004). Montana Fish, Wildlife& Parks subsequently managed a state-licensed hunt for bison until
1991 (MFWP and MDOL 2004). As the number of bison migrating
outside the boundary of Yellowstone National Park increased, theNational Park Service agreed to control bison near the boundary of
the park and a series of management plans were developed to define
specific boundaries and lethal control measures (USDI, NPS and
USDA, USFS, APHIS 2000a,b). About 3,100 bison were culled fromthe population during 1985 through 2000 when they attempted tomigrate outside the park (White et al. 2011). This total included 2,339
bison that were captured and shipped to meat processing facilities
and 778 bison that were shot by hunters or state livestock or wildlife
personnel (White et al. 2011). These migrations and culls generated
intense controversy among environmentalists, stock growers, andmanagement agencies regarding issues of bison conservation anddisease containment (Cheville et al. 1998).

Interagency Bison Management Plan
The management of bison outside Yellowstone National Park is theprerogative of surrounding states and the U.S. Forest Service on
National Forest System lands. Differences in legal classifications andmanagement authorities among these governments and various agencies can lead to jurisdictional challenges in bison management (Plumbet al. 2009; Becker et al. 2013). Even though bison are the state mammalof Wyoming, they are considered livestock everywhere except in specific hunting areas adjacent to Grand Teton and Yellowstone nationalparks. In fact, the Wyoming Game and Fish Department does notsupport the establishment of wild bison populations outside nationalparks and refuges (Talbott 2014). The wildlife conservation strategy for
Idaho mentions bison as a species of concern, but state agricultural
regulations do not recognize wild bison and consider them livestock(Idaho Department of Fish and Game 2005). The Montana Legislature
has designated Yellowstone bison as a species requiring disease control because the population is chronically infected with brucellosis.

Historical Perspective

Figure 3.1. Conservation areas for bison in and near Yellowstone National Park
under the 2000 Interagency Bison Management Plan, as adjusted. Zone 2 depicts
areas where there is tolerance for some bison in Montana during winter.

As a result, the Department of Livestock is the lead agency for managing wild bison that migrate into Montana, and can remove animals
that jeopardize compliance with livestock disease control programs(81-2-120 [1-4] Montana Code Annotated; Administrative Rules ofMontana 32.3.224). The Montana Legislature also decided that Yellowstone bison pose a threat of brucellosis transmission to people orcattle, and for damage to persons or property (87-1-216 [1] Montana
Code Annotated). As a result, Montana Fish, Wildlife & Parks isrequired to cooperate with the Department of Livestock in managing bison, including administering public hunts on lands adjacentto Yellowstone National Park (87-1-216 Montana Code Annotated).
Elsewhere in the state, Montana Fish, Wildlife & Parks does not support free-ranging bison that are not contained by fencing or someother barrier (Brown 2014; French 2014). Similar biases, designations,and regulations do not exist for elk that are also chronically infectedwith brucellosis.

53

54

Yellowstone Bison: Conserving an American Icon in Modern Society

In 2000, the federal government and the State of Montana agreed
to guidelines for cooperatively managing the risk of brucellosis transmission from bison to cattle (Plumb et al. 2009). This Interagency
Bison Management Plan also emphasized conserving the wild bison
population and allowing some bison to occupy winter ranges on public
lands in Montana (USDI, NPS and USDA, USFS, APHIS 2000a,b;
Figure 3.1). Five agencies were originally responsible for implementing the plan — the National Park Service, Animal and Plant HealthInspection Service, U.S. Forest Service, Montana Fish, Wildlife &Parks, and the Montana Department of Livestock. The Confederated
Salish and Kootenai Tribes of the Flathead Nation, Nez Perce Tribe,and the InterTribal Buffalo Council were added as partners in 2009
due to their treaty hunting rights on open and unclaimed federal lands
in Montana and their commitment to reestablishing bison herds on
tribal lands.
The Interagency Bison Management Plan was designed to progress
through a series of management steps that initially tolerated only
bison testing negative for exposure to Brucella bacteria on winterranges outside Yellowstone National Park, but eventually tolerated
untested bison when cattle were not present (USDI, NPS and USDA,
USFS, APHIS 2000a,b). During step 1, the agencies agreed to (Whiteet al. 2011):•

Enforce spatial and temporal separation between bison andcattle;•Use hazing by humans on horseback, all-terrain vehicles, orin helicopters to prevent bison movements from Yellowstone
National Park;•

If hazing was unsuccessful, capture bison attempting to leave
the park and test them for brucellosis exposure;•

Send bison testing positive to meat processing facilities;•

Vaccinate non-pregnant bison testing negative;•

Hold bison testing negative at the north boundary for releaseback into the park in spring;Historical Perspective

55

NPS/Jim Peaco

Staff on horseback hazing
bison in the Gardiner basinnear the northern boundary of
Yellowstone National Park.

56

Yellowstone Bison: Conserving an American Icon in Modern Society

NPS/Neal Herbert

Bison feeding at Swan Lake Flat
in Yellowstone National Park.

Historical Perspective•

Release up to 100 bison testing negative at the west boundary
and allow them to use habitat adjacent to the park until May 15;•

Conduct research on Brucella persistence in the environment
to determine an adequate temporal separation period between
bison and cattle;•

Conduct research on the safety and efficacy of strain RB51
vaccine;•Develop and evaluate a remote vaccine delivery system; and•Encourage and, if necessary, mandate the vaccination of female
cattle greater than 4 months of age that might graze on winterranges used by bison.

Step 2 was to begin when cattle no longer grazed during winter on
the Royal Teton Ranch, just north of the park boundary in the Gardiner basin. Management actions initiated in step 1 were continued,
except up to 100 bison testing negative for brucellosis exposure would
be released at the north boundary and allowed to use habitat adjacentto the park until April 15. Also, any calf and yearling bison that could
not be captured at the west boundary would be vaccinated using a
remote delivery system.
Step 3 was to begin once the agencies determined an adequate
temporal separation period between bison and cattle, gained experience in managing bison outside the park, and initiated a vaccination
program for all female bison in the population. The agencies would
tolerate up to 100 untested bison in both the north and west boundary
areas, use capture and culling in these areas to maintain the populationnear 3,000 bison, and ensure no bison were outside the park after thespring cut-off dates. The agencies also agreed to develop a quarantine
protocol for certifying test-negative bison as brucellosis free.

Adaptive Management Adjustments
The Interagency Bison Management Plan was adjusted in 2005 and2006 to include bison hunting as a management action outside Yellowstone National Park and increase tolerance for bull bison because there
is virtually no risk of them transmitting brucellosis to cattle (Clarke

57

58

Yellowstone Bison: Conserving an American Icon in Modern Society

et al. 2005; Interagency Bison Management Plan Partner Agencies
2006). These adjustments allowed bison not tested for brucellosis
exposure to migrate to winter ranges outside the park and provide
hunting opportunities. Since 2005, Montana Fish, Wildlife & Parks has
administered a bison hunt between November 15 and February 15 onlands adjacent to the park. The intent is to hunt wild bison under fairchase conditions and reduce damage to private property by alteringbison behavior and distribution (MFWP and MDOL 2004). In 2006,

By 1894, bison in
and adjacent to thenorthern region of
Yellowstone had been
extirpated, and only
about 23 bison wereleft in the Pelican
Valley of central
Yellowstone by 1901.

Montana recognized the treaty rights of the Confederated Salish andKootenai Tribes of the Flathead Nation and the Nez Perce Tribe for
harvesting bison on open and unclaimed federal lands adjacent to thepark (MFWP 2006a,b). In 2009 and 2010, Montana also recognized
the treaty rights of the Shoshone-Bannock Tribes and the Confederated Tribes of the Umatilla Indian Reservation to hunt bison on theselands (MFWP 2009, 2010b).
Public and treaty hunters harvest variable numbers of bison eachyear depending on the timing and extent of bison migration into Montana (White et al. 2011; Canfield et al. 2012; Jones et al. 2012; Clarke etal. 2014a). Starting in 2007, Montana Fish, Wildlife & Parks set a state
quota of 44 either-sex licenses allocated between hunting districts in
the Gardiner and West Yellowstone areas, with up to 100 additional
female–calf permits issued incrementally if warranted by conditions.
An increase in these quotas is expected in 2015. The tribes develop
and enforce their own harvest regulations, and there is no defined
limit on the number or type (age, sex) of bison the tribes may harvest(MFWP and MDOL 2013). However, federal, state, and tribal managers meet each summer to discuss objectives, no-shooting zones,
access, enforcement, and the sharing of harvest data (Interagency
Bison Management Plan Members 2013).
In addition, Montana Fish, Wildlife & Parks and the U.S. Department of Agriculture, Animal and Plant Health Inspection Service(2006) conducted a quarantine feasibility study during 2005 to 2010
with 214 Yellowstone bison calves that initially tested negative for brucellosis exposure. These bison were held at a research facility northHistorical Perspectiveof Yellowstone National Park to evaluate if they would remain free of
brucellosis through at least their first pregnancy and calving. The study
was successful and the surviving original bison and their offspring were
declared brucellosis free (MFWP 2010a, 2011; Clarke et al. 2014b). In
February 2010, 87 bison were transferred from the quarantine facility to the Green Ranch in Montana, owned by Turner Enterprises,
Inc., for five years of additional surveillance. In November 2014, theoriginal quarantine bison plus about 25 percent of their offspringwere transferred to the Fort Peck Indian Reservation in Montana.
The rest of the bison were retained by Turner Enterprises. In March
2012, Montana transferred 61 bison from the quarantine facility to
the Fort Peck Indian Reservation for five years of additional surveillance (MFWP 2011). Thirty-four of these bison were subsequently
transferred to the Fort Belknap Reservation in Montana.
Despite these successes, progress was initially slow in completing the Interagency Bison Management Plan’s three successive steps
to incrementally increase tolerance for bison moving outside thepark (White et al. 2011). Also, more than 1,000 bison (21 percent) were
removed from the population during winter 2006 and more than 1,700
bison (37 percent) were removed during winter 2008 because hazing
was no longer effective at keeping them in agreed-upon management
areas (White et al. 2011; Table 3.1). In 2006, 917 bison were captured
and shipped to meat processing facilities, 40 were shot by hunters, and87 were captured and shipped to a quarantine facility. In 2008, 1,448
bison were shipped to processing facilities, 166 were harvested, and 112
were shipped to quarantine. These culls removed a disproportionately
large number of females and reduced population growth — similar to
the effects of culls during earlier decades under different management
strategies (Meagher 1973; Halbert 2003; White et al. 2011; Treanor etal. 2013; Table 3.2). The federal government and the State of Montana
were criticized for these culls and for not consistently defining measurable objectives or applying adaptive management principles (Holling1978; U.S. Government Accountability Office 2008). In response, thepartners made several adjustments to the plan based on prevailing

59

0
0
0
0
0
0
0
22
79
5
119
344
358
11
94
0
6
202
13
15
96
56
4
160
4
0
0
0
0
0

0
88
41
0
2
567
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
32
47
59
1
4
Unk
15
148
258

13
0
16
7
37
2
3
14
0
0
0
0
0
0
0
0
0
0
0
0
0
0
8
12
107
0
0
Unk
13
81
64

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
87
0
112
0
0
53
0
0
60

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
17
0
0
0
0
0
0
0
0
0

0

Sent toquarantine
North
West
88
57
7
39
569
4
14
271
79
5
426
370c
1,083d
11
94
0
6
202
244
282
114
1,044
63
1,726
5
7
260
28
229
640

13

Total

42
42
5
27
295
0
0
113
9
0
77
100
329
0
44
0
6
60
75
58
23
205
53
516
5
7
106
14
116
200

4
37
15
2
7
221
0
0
95
8
0
66
71
330
0
49
0
0
42
98
179
54
513
6
632
0
0
102
12
85
284

7
8
0
0
0
53
0
0
41
9
0
31
10
144
0
1
0
0
16
43
23
20
245
0
332
0
0
52
2
28
152

0

1
0
0
5
0
4
14
22
53
5
252
189
280
11
0
0
0
84
28
22
17
81
4
246
0
0
0
0
4
4

2

Age and gender composition of culls/
harvests
Male
FemaleCalf
Unknown

National Park and nearby areas of Montana during winter (White et al. 2010, Geremia et al. 2014b).

Table 3.1. Annual removals of Yellowstone bison through harvests and management culls from the northern and western management areas in Yellowstone

2,247
2,351
2,776
2,976
NAb
2,477
3,021
3,112
3,357
3,321
4,114
3,928
3,378
2,170
1,892
2,444
2,432
3,283
3,715
3,811
4,215
5,015
3,889
4,694
2,969
3,301
3,898
3,720
4,230
4,924

0
0
0
0
0
0
0
249
0
0
307
26
725
0
0
0
0
0
231
267
1
861
0
1,288
0
3
6
0
0
258

1,552
1,609
1,778
2,036
NAb
1,885
2,203
2,290
2,676
2,635
2,974
3,062
2,593
1,715
1,399
1,904
1,924
2,564
2,902
2,923
3,339
3,531
2,512
2,624
1,469
1,462
1,653
1,406
1,561
1,504

0

695
742
998
940
NAb
592
818
822
681
686
1,140
866
785
455
493
540
508
719
813
888
876
1,484
1,377
2,070
1,500
1,839
2,245
2,314
2,669
3,420

1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014

Sent to slaughter/management
culls
Hunter harvesta
North
West
North
West

1970-84

Maximum no. bison counted
previous July-August
WinterNorth Central
Total

60
Yellowstone Bison: Conserving an American Icon in Modern SocietyHistorical Perspective
Central region
Abundance

Males:100 females

Juveniles:100 adults

2003

2,924 (2,768-3,084)

60 (53-68)

40 (36-44)

2004

3,396 (3,225-3,572)

110 (99-124)

34 (31-37)

2005

3,437 (3,281-3,595)

89 (80-99)

40 (36-43)

2006

2,422 (2,297-2,556)

112 (100-126)

35 (32-38)

2007

2,825 (2,680-2,974)

82 (73-92)

43 (39-47)

2008

1,379 (1,305-1,460)

101 (89-115)

26 (23-28)

2009

1,509 (1,428-1,592)

116 (103-132)

30 (27-33)

2010

1,690 (1,600-1,785)

126 (111-143)

31 (28-34)

2011

1,380 (1,302-1,459)

147 (129-166)

26 (24-29)

2012

1,584 (1,503-1,674)

129 (114-145)

28 (26-31)

2013

1,367 (1,296-1,443)

127 (113-145)

29 (26-32)

Northern region
Abundance

Males:100 females

Juveniles:100 adults

2003

895 (847-945)

96 (85-110)

33 (29-35)

2004

1,086 (1,013-1,148)

85 (77-96)

36 (32-39)

2005

1,308 (1,244-1,371)

86 (77-96)

34 (30-37)

2006

1,275 (1,211-1,342)

75 (66-84)

45 (41-50)

2007

1,807 (1,712-1,908)

52 (46-59)

47 (42-53)

2008

1,586 (1,507-1,669)

87

47

2009

1,674 (1,590-1,765)

101 (93-118)

42 (38-46)

2010

1,910 (1,813-2,016)

60 (54-68)

53 (47-60)

2011

2,296 (2,177-2,425)

61 (54-68)

45 (40-49)

2012

2,583 (2,458-2,720)

66 (58-75)

60 (53-68)

2013

3,204 (3,040-3,371)

63 (57-71)

56 (50-62)

Table 3.2. Estimated average and 95 percent range for the age and sex structureof bison in the central and northern regions of Yellowstone National Park during
2003 through 2013 (Geremia et al. 2013).

61

62

Yellowstone Bison: Conserving an American Icon in Modern Society

conditions and developed a long-term monitoring and research program to guide decision making (USDI, NPS et al. 2008; White et al.
2014). These adjustments (1) further described the circumstances forbison occupying habitats outside the park, (2) established a precedent
for minimizing the shipment of bison to meat processing facilities, (3)re-affirmed the commitment to vaccinating bison, (4) outlined a process for sharing decision documents with the public, and (5) specified
metrics for annual monitoring and reporting on management actions(USDI, NPS et al. 2008).
In 2009, an agreement with a private landowner removed livestockfrom the Royal Teton Ranch for 30 years to allow bison to access anduse habitats north of the park, including portions of the ranch and theGallatin National Forest (MFWP 2008a,b; NPS and MFWP 2008).
This agreement led to adjustments to the Interagency Bison Management Plan in 2011 and 2012 that increased tolerance for untested bison
north and west of the park (MFWP and MDOL 2012). During 2011
through 2014, 200 to 1,100 bison migrated to habitat in the Hebgen
and Gardiner basins of Montana during winter (Canfield et al. 2012;
Jones et al. 2012; Clarke et al. 2014a).
In 2010, the partners supported the organization of a working group
comprised of people from a diverse group of stakeholders to develop
collaborative ideas for managing Yellowstone bison. This Citizens
Working Group on Yellowstone Bison (2011) provided numerous
recommendations to bison managers regarding brucellosis risk reduction, bison population management, and bison habitat. Most of theserecommendations were subsequently implemented as part of theadaptive management plan (Jones et al. 2012). In return, the partners
involved with the Interagency Bison Management Plan provided theworking group and other interested citizenry with periodic updates
on the real impacts of bison and brucellosis management actions
compared to their anticipated effects. Through this framework, thepartners made adaptive management adjustments transparent andaccountable to stakeholders by: (1) soliciting public comment on
adaptive adjustments being considered by decision-makers, (2) postingHistorical Perspective

63

NPS/Neal Herbert

A bison grazes outside of thehistoric Yellowstone Lake Hotel.

64

Yellowstone Bison: Conserving an American Icon in Modern Society

monitoring reports on websites for the Interagency Bison Management
Plan (http://ibmp.info) and Yellowstone National Park (http://www.
nps.gov/yell/naturescience/bison.htm), (3) holding public information meetings, (4) publishing scientific articles, and (5) conducting
necessary analyses.

Conclusions
Moving forward, the extent to which bison can ultimately use theGreater Yellowstone Area will be defined by the tolerance of modern
society (Lott 2002; Franke 2005; Plumb et al. 2009; Bailey 2013). The
degree of tolerance will likely depend on active management to mediate conflicts between bison and humans — which is consistent withlarge mammal conservation programs worldwide where agriculture
and urbanization surround nature preserves (Plumb et al. 2009).
Though such management upsets some people, it has necessarily
occurred since the early part of the past century. In fact, human influences on bison behavior and demography extend much further backin time. For example, humans have been a significant predator on
bison for many centuries, as evidenced by kill sites in the Paradise
Valley north of Yellowstone National Park that were used repeatedly
over time (Cannon 2001).

Historical Perspective

65

Photograph courtesy of National Geographic by Michael Nichols

Bison moving north on
U.S. Route 89 outside of
Yellowstone National Park.

NPS/Jim Peaco

Bison moving in single filethrough unbroken snow
near Tower Junction in
the northern region of
Yellowstone National Park.

Chapter 4
SEASONAL DISTRIBUTIONS
AND MOVEMENTS
Chris Geremia, P.J. White, Rick L. Wallen,
and Douglas W. Blanton

Yellowstone bison can move long distances in relatively short periodsof time — occasionally traveling more than 30 kilometers (19 miles)
in a single day and annually ranging over areas of 100 to 750 square
kilometers (39 to 290 square miles; Meagher 1989b; Geremia et al.
2011, 2014b). They are considered migratory because most animals
move back and forth between seasonal ranges to better access foodresources (Senft et al. 1987; Mueller and Fagan 2008; Plumb et al.
2009). They have also dispersed between areas and expanded theirwinter ranges in recent decades. Dispersal refers to long-lasting or
permanent movements by animals from one area to another, whilerange expansion is the movement of animals beyond the limits ofthe traditional distribution for a population (Gates and Larter 1990;
Gates and Broberg 2011).

68

Yellowstone Bison: Conserving an American Icon in Modern Society

Migration and Dispersal
The primary factors influencing bison migrations are: (1) seasonal vegetation changes that affect food quality, (2) the breeding season, (3) the
distribution, size, and quality of foraging sites, and (4) snow accumulation that affects energy expenditures and access to food (Meagher 1973;
Bruggeman et al. 2009b; Gates and Broberg 2011; Geremia et al. 2011,2014b). Most bison show fidelity to seasonal ranges that are more than
50 square kilometers (19 square miles) in size and dominated by grassland and shrub steppe habitats. Individual bison do not segregate into
territories, but tend to aggregate into dynamic groups that form, merge,
and break-up as individuals feed, rest, and move across the landscape.
Group movements are correlated, with associations of groups making
back-and-forth movements across and between seasonal ranges overa span of days.5
As mentioned in Chapter 3, bison in the northern region of Yellowstone National Park traditionally spent summer on the Mirror Plateau
and slopes of the Absaroka Mountains along the eastern boundary,but spent winter in the Lamar or Pelican valleys (Meagher 1973).
However, progressive changes began in the mid-1970s when groups
began to move west and travel downslope along the Yellowstone
River and parallel road corridor to the Blacktail Deer Plateau andGardiner basin during winter (Meagher 1989b). As the number ofbison in northern Yellowstone increased, more bison spent summer
on the traditional wintering area of the Lamar Valley, which increased
the magnitude and extent of seasonal movements to lower-elevation
areas (Meagher 1989b).
Bison in central Yellowstone traditionally spent summer in the
Pelican or Hayden valleys and on the Mirror Plateau and upper Lamar
River drainage (Meagher 1973). They spent winter in these valleys
or the lower-elevation Firehole River drainage (Meagher 1973). For
decades, bison rarely moved between the Hayden and Pelican valleys
during any time of the year (Meagher 1973, 1989b). During the winterof 1982, however, groups of bison moved through the Pelican Valley to
5Portions of this chapter were adapted from Geremia et al. (2011, 2014b).

Seasonal Distributions and Movements

the northern shore of Yellowstone Lake and into the Hayden Valley(Meagher 1998). In subsequent years, regular movements between
the Hayden and Pelican valleys increased and bison that spent winterin the Pelican Valley stopped moving to the Mirror Plateau during
summer (Meagher 1998). More bison began moving west from the
Hayden Valley to the Firehole River drainage, and eventually, into theMadison Valley (Meagher 1998; Bruggeman et al. 2009c). By 1995, somebison from central Yellowstone made movements towards northern
Yellowstone along the river and roadway corridor connecting Mammoth Hot Springs and the interior of the park (Taper et al. 2000). By
2005, more than 1,000 bison from central Yellowstone moved to thenorthern region of the park during winter. During subsequent winters,
many of these animals were captured and shipped to meat processing
facilities after attempting to cross the northern boundary of the park
into Montana (White et al. 2011). The remaining bison either stayed innorthern Yellowstone or continued to seasonally migrate between thecentral and northern regions of the park (Geremia et al. 2011, 2014b).
Dispersal movements and range expansion by Yellowstone bison
were often associated with severe snow events that interacted withbison density to limit nutritional intake and foraging efficiency (Meagher 1989b, 1998; Coughenour 2005; Plumb et al. 2009). Changes in
distribution and seasonal movements continued as bison numbers
increased, and eventually led bison to expand their winter range tolower-elevation areas outside the park boundary (Taper et al. 2000;
Gates and Broberg 2011). Prior experience with particular routes andnew foraging areas likely contributed to a rapid increase in movements
by large numbers of bison during subsequent winters, even whensnow conditions were relatively mild (Meagher 1989b; Geremia etal. 2011, 2014b).
Range expansion can delay responses to food limitations since
new ranges provide additional forage (Larter and Gates 1990). As
a result, increases in winter range areas used by Yellowstone bisonfrom 1976 onwards contributed to sustained population growth inboth the central and northern regions of the park (Taper et al. 2000;

69

70

Yellowstone Bison: Conserving an American Icon in Modern Society

Photograph courtesy of National Geographic by Michael Nichols

Bison spread acrossYellowstone’s Lamar Valley.

Seasonal Distributions and Movements

Coughenour 2005; Plumb et al. 2009). However, culling and hazing
bison back into the park to reduce the risk of brucellosis transmission
to cattle in Montana limited range expansion by bison much beyond
the boundary of Yellowstone National Park (Gates and Broberg 2011;
White et al. 2011). Without this intensive management intervention,bison almost certainly would have continued to disperse to suitable
habitat areas further outside the park (Plumb et al. 2009; Gates andBroberg 2011).

Seasonal Movements
During summer, bison in northern Yellowstone are concentrated in
an approximately 40-kilometer (25-mile) long region along the Lamar
River from Cache Creek in the east towards the confluence of the
Yellowstone River in the west (Geremia et al. 2014b; Figure 4.1). A
portion of these bison make prolonged forays to the high-elevation
Specimen Ridge and Mirror Plateau areas, with occasional trips to thePelican and Hayden valleys. Bison from central Yellowstone returnto the Hayden Valley from wintering areas in western and northern
Yellowstone, with nearly all animals in the Hayden Valley during Julyand August. In late summer, large numbers of these bison travel backand forth between the Hayden Valley, northern shore of YellowstoneLake, and the Pelican Valley (Geremia et al. 2014b; Figure 4.1).
In early autumn, bison make brief trips from summer ranges tomost winter ranges, with nearly all animals subsequently returning
to the summer range (Figure 4.2). These exploratory trips may enablebison to assess food availability across winter ranges or access remaining high-quality food prior to vegetation becoming older and dying(Geremia et al. 2014b).
As winter progresses, bison in northern Yellowstone move
downslope to the lower Yellowstone River drainage (Tower, Slough
Creek, Hellroaring) and Blacktail Deer Plateau. From there, bison
may move further northwest to the lower-elevation Gardiner basin
where snow pack is lower and new vegetation growth begins earlier
in spring (Geremia et al. 2014b; Figure 4.3). These movements are

71

72

Yellowstone Bison: Conserving an American Icon in Modern Society
Gardiner Basin

Lower Yellowstone
Drainage
Lamar Valley
Blacktail Deer
Plateau
Hebgen Lake
Basin

MirrorPlateau
Gibbon River
Drainage

HaydenValleyPelicanValleyFirehole River
Drainage

Figure 4.1. Summer (June-August) utilization distribution of locations from 66 radio-collared,
adult, female bison in Yellowstone National Park during 2004 through 2012, with white areas
showing increased use and arrows showing the direction of most movements.

made along several pathways that follow the Yellowstone and Gardner
rivers. Bison often make brief return trips to higher-elevation winterranges before returning to lower elevations.
Bison in central Yellowstone leave the summer range and move tonorthern Yellowstone following the river and roadway corridor, orto western Yellowstone following a historic migration route (MaryMountain pass) that connects the Hayden Valley and Firehole Riverdrainage (Bjornlie and Garrott 2001; Geremia et al. 2014b; Figures 4.2
and 4.3). From the Firehole River drainage, bison move downslope
to access several meadows along the Firehole, Gibbon, and Madison rivers. Movements are relatively fluid between these meadows,
with short stays in any given meadow. Bison in central Yellowstone
predominantly access northern Yellowstone using the river and roadway corridor that connects the Gibbon Canyon with Mammoth Hot

Seasonal Distributions and Movements

73

Gardiner Basin

Lower Yellowstone
Drainage
Lamar Valley
Blacktail Deer
Plateau
Hebgen Lake
Basin

MirrorPlateau
Gibbon River
Drainage

HaydenValleyPelicanValleyFirehole River
Drainage

Figure 4.2. Autumn (September-November) utilization distribution of locations from 66
radio-collared, adult, female bison in Yellowstone National Park and nearby areas of Montana
during 2004 through 2012, with white areas showing increased use and arrows showing thedirection of most movements.

Springs. Some of these bison gradually move upslope to the Blacktail
Deer Plateau and lower Yellowstone River drainage, before moving
to lower-elevation wintering areas in the Gardiner basin (Geremia
et al. 2014b; Figure 4.3).
Movement patterns are reversed in spring as snow melts and bison
follow new vegetation growth from lower to higher elevations (Frankand McNaughton 1993; Frank et al. 2013; Wilmers et al. 2013; Geremia
et al. 2014b). The onset of new vegetation growth typically begins
three weeks earlier in northern Yellowstone than in central Yellowstone (Thein et al. 2009). Thus, return movements occur earlier innorthern Yellowstone and coincide with the time when many bisonin central Yellowstone are just reaching low-elevation wintering areas
along the Madison River and eastern portion of Hebgen Lake outside
the western boundary of the park (Geremia et al. 2014b; Figure 4.4).

74

Yellowstone Bison: Conserving an American Icon in Modern Society

Gardiner Basin

Lower Yellowstone
Drainage
Lamar Valley
Blacktail Deer
Plateau
Hebgen Lake
Basin

MirrorPlateau
Gibbon River
Drainage

HaydenValleyPelicanValleyFirehole River
Drainage

Figure 4.3. Winter (December-February) utilization distribution of locations from 66 radiocollared, adult, female bison in Yellowstone National Park and nearby areas of Montana
during 2004 through 2012, with white areas showing increased use and arrows showing thedirection of most movements.

Emergence of new vegetation in the Hebgen Lake basin coincides
with the calving period for bison, and several hundred bison moveto this winter range at this time. These animals remain in this area
during calving, before returning to higher-elevation summer ranges
inside Yellowstone National Park over the course of several days or
weeks during June.

Seasonal Movement Strategies
As numbers of bison increase, the abundance of bison and othergrazing ungulates may become sufficient to elicit increased competition for key resources (Coughenour 2005; Plumb et al. 2009; Franket al. 2013). Decreased food resources or foraging efficiency provide
an impetus for bison to move (Coughenour 2005; Gates and Broberg2011). Annual forage production and snow pack also influence foodSeasonal Distributions and Movements

75

Gardiner Basin

Lower Yellowstone
Drainage
Lamar Valley

Blacktail Deer
Plateau
Hebgen Lake
Basin

MirrorPlateau
Gibbon River
Drainage

HaydenValleyPelicanValleyFirehole River
Drainage

Figure 4.4. Spring (March-May) utilization distribution of locations from 66 radio-collared,
adult, female bison in Yellowstone National Park and nearby areas of Montana during 2004
through 2012, with white areas showing increased use and arrows showing the direction ofmost movements.

availability, foraging efficiency, and movements (Bruggeman 2006;
Geremia et al. 2011, 2014b). As snow depth increases, bison move towinter ranges with larger snow-free areas that increase foraging efficiency and allow for greater aggregations of animals (Meagher 1998;
Bjornlie and Garrott 2001; Bruggeman et al. 2009b; Fortin et al. 2009).
Large annual differences in the timing, extent, and hardness ofsnow pack, as well as the emergence of snow-free areas in spring,occur in northern Yellowstone. Consequently, bison are less likely to
track changes in food resources at broad scales because they cannot
depend on being able to access food in specific seasonal ranges during
similar times each year (Geremia et al. 2014b). Higher-elevation areas
with more available forage (due to high summer plant growth) andsome snow cover may provide increased access to food comparedto lower elevation areas with less snow but less available forage (dueYellowstone Bison: Conserving an American Icon in Modern Society

1000

2000

2100 m0

No. of Bison

Lamar Valley

07−11−09

01−11−10

07−11−10

01−11−11

07−11−11

01−11−12

500

1500

1800 m0

No. of Bison

Lower Yellowstone River Drainage

07−11−09

01−11−10

07−11−10

01−11−11

07−11−11

01−11−12

500

1500

2000 m0

No. of Bison

Blacktail Deer Plateau

01−11−10

07−11−10

01−11−11

07−11−11

01−11−12

07−11−11

01−11−121000 1500

Gardiner Basin

1600 m500

No. of Bison

07−11−09076

07−11−09

01−11−10

07−11−10

01−11−11

Date

Figure 4.5. Numbers of bison on winter ranges in the northern region of Yellowstone
National Park during 2009 through 2012 (adapted from Geremia et al. 2014b). The
Blacktail Deer Plateau and Gardiner Basin are lower-elevation areas and substantial between-year variations exist in numbers of bison moving to these winterranges. Solid and dashed lines represent medians and 95 percent credible intervals.
Date labels on the horizontal axis are numerically formatted as month-day-year.

1000 2000 3000

Hayden Valley

2400 m0

No. of Bison

Seasonal Distributions and Movements

07−11−09

01−11−10

07−11−10

01−11−11

07−11−11

01−11−12400

8002200 m0

No. of Bison

Firehole River Drainage

07−11−09

01−11−10

07−11−10

01−11−11

07−11−11

01−11−12400

8002100 m0

No. of Bison

Gibbon River Drainage

07−11−09

01−11−10

07−11−10

01−11−11

07−11−11

01−11−12400

8002000 m0

No. of Bison

Hebgen Lake Basin07−11−09

01−11−10

07−11−10

01−11−11

07−11−11

01−11−12

Date

Figure 4.6. Numbers of bison on winter ranges in the central region of Yellowstone
National Park during 2009 through 2012 (adapted from Geremia et al. 2014b).
Solid and dashed lines represent medians and 95 percent credible intervals. Dateis numerically formatted as month-day-year.

77

78

Yellowstone Bison: Conserving an American Icon in Modern Society

to lower summer plant growth). However, in years with high snow
cover, foraging efficiency in higher-elevation areas decreases and bisonmust move to lower-elevation areas. Bison learn to respond to thesechanges in foraging efficiency, and as a result, there are large annual
variations in numbers of bison on specific winter ranges (Geremia
et al. 2014b; Figure 4.5).
In central Yellowstone, bison exhibit regular seasonal distributions
because the timing and extent of snow conditions are similar among

Yellowstone bison canmove long distances inrelatively short periodsof time — occasionally
traveling more than
30 kilometers (19miles) in a single day.

years (Figure 4.6). Annual variations in snow pack and melt-out occur,
but overall, conditions are similar enough among years to decrease
foraging efficiency in a predictable manner. As a result, bison learn tomove to specific ranges at specific times of year to exploit differencesin food availability (Geremia et al. 2014b). This is most apparent in
the Hebgen Lake basin where several hundred bison from central
Yellowstone move during April and May to access newly emerging
vegetation after snow melt-out (Geremia et al. 2014b).

Conclusions
Large annual migrations of bison to low-elevation winter ranges northand west of Yellowstone National Park highlight the importance of
these areas (Plumb et al. 2009; Geremia et al. 2011). Most bison migration into Montana occurs in late February and March across thenorth boundary, and in April and May across the west boundary,as new grass begins to grow on lower-elevation ranges (Thein et al.
2009; Geremia et al. 2014b). Bison migration back to interior park
ranges typically occurs during April through June, following the waveof growing vegetation from lower to higher elevations (Thein et al.
2009; Wilmers et al. 2013).
If migration by bison into Montana is constrained by hazing animals
back into the park, then bison numbers will be ultimately determinedby food availability within the park. As a result, substantial winterkill could occur after bison reach high densities (Coughenour 2005;
Plumb et al. 2009; White et al. 2013b). To date, the total number ofbison in Yellowstone has not reached the estimated food-limited

Seasonal Distributions and Movements

carrying capacity of approximately 5,500 to 7,500 bison during winter(Coughenour 2005; Plumb et al. 2009). However, the population isprolific and still growing despite annual harvests and culling (White etal. 2011). As bison numbers approach or overshoot their food capacity in the park, there could be degradation of vegetation and soils,
increased competition with other ungulates, and deterioration of other
ecological processes (Coughenour 2005, 2008; Plumb et al. 2009).
Alternatively, managers could keep bison at low numbers to reduce
the likelihood of large migrations to the park boundary (Geremia
et al. 2011, 2014b; White et al. 2013b). Until the late 1970s, there wereless than 1,500 bison that generally remained in the park (Meagher
1989b, 1998).
An alternative to constraining bison within Yellowstone National
Park or artificially maintaining low numbers is to tolerate bison in
nearby areas of Montana, but manage them when they encroach on
cattle ranches, highways, and local communities (Treanor et al. 2013;
White et al. 2013b). Movements of bison to the northern and westernboundary areas of the park are affected by different dynamics, andas a result, require different management prescriptions (Geremia etal. 2014b). Large numbers of bison move across the western park
boundary each year and these movements correspond with the calving season when bison are most likely to transmit brucellosis. Thus,
space-and-time separation of bison and cattle is needed to reduce
the risk of brucellosis transmission, which can be accomplished by
fencing livestock and/or moving bison to suitable habitat away fromlivestock (Treanor et al. 2013; Geremia et al. 2014b).
In contrast, the timing and extent of bison movements across thenorthern park boundary depend on snow conditions, available forage,
and the density of bison in the park (Geremia et al. 2011, 2014b). Large
numbers of bison can rapidly move to the northern boundary whenconditions severely reduce foraging efficiency, but relatively few bisonexit the northern boundary when conditions are mild (Geremia etal. 2011, 2014b). When numbers of bison exceed 1,500 to 2,500 bisonin both the central and northern regions of Yellowstone, there is a

79

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Yellowstone Bison: Conserving an American Icon in Modern Society

significant chance that more than one-half will migrate to the northernboundary under severe snow conditions. With similar numbers andaverage snow conditions, only one-third of the bison are predicted tomigrate to the northern boundary; fewer than 200 bison are predicted
to move when snow conditions are below average (Geremia et al. 2011,2014b). If hunting in Montana is used to manage numbers of bison
leaving the park, then bison numbers in northern Yellowstone may
fluctuate widely over time because few bison are harvested during
years when migration is minimal (Geremia et al. 2014b). As a result, it
may at times be necessary to capture and remove some bison to meat
processing, quarantine, or research facilities to moderate fluctuations
in bison numbers (Geremia et al. 2013).

Seasonal Distributions and Movements

81

NPS/Jacob W. Frank

Bull bison near Obsidian Creek
in Yellowstone National Park.

NPS/Neal Herbert

Male and female bisonin the Lamar Valley of
Yellowstone National Park
during the midsummer rut.

Chapter 5
REPRODUCTION AND SURVIVAL
Chris Geremia, P.J. White, Rick L. Wallen,
and Douglas W. Blanton

Reproduction and survival are the key demographic drivers for Yellowstone bison because there is currently no immigration into the populationor emigration from the population. As a result, rates of birth and death
determine the number of bison. Both of these rates are strongly influenced by human intervention, through the introduction of a nonnative
disease (brucellosis) that reduces birth rates and removals of bison due toconcerns about the potential for large migrations of bison into Montana
and brucellosis transmission to cattle.

Gestation and Calving
Female bison typically reach sexual maturity and conceive their first calf
at 2 or 3 years of age (Meagher 1973; Gogan et al. 2013). Males are capableof breeding at this age, but generally do not until they are 5 or 6 years old
because older, larger, and more experienced males monopolize opportunities (McHugh 1958; Berger and Cunningham 1994). The estrus cycle

84

Yellowstone Bison: Conserving an American Icon in Modern Society

lasts about 3 weeks (19 to 26 days), with females being receptive for one or
two days and having one or two ovulations during the breeding season,
which mostly occurs from mid-July through mid-August (Meagher 1973;
Kirkpatrick et al. 1991, 1993). The gestation period lasts about 285 days (9½months) and fetal sex ratios appear biased towards slightly more males(Meagher 1973, 1986; Geremia et al. 2014a).6
Calves are born during March through June, with the majority of births
occurring during late April and May (Jones et al. 2010). Bison give birth
to a single calf that weighs between 15 and 30 kilograms (33 to 66 pounds;
Meagher 1986). Females often do not separate themselves from other bisonwhen giving birth (Jones et al. 2010). Newborn calves can stand and nurse
within 30 minutes, and feed, travel, and rest with groups of adult females
and other juvenile animals soon after birth (Meagher 1986). Calves begin
eating grass and drinking water within one week, and are usually weaned
between 7 and 12 months of age—though some calves have been observed
nursing more than 18 months after birth (McHugh 1958; Meagher 1986).
Females can adjust calving by several days to synchronize births andreduce predation risk to most calves through numerical dilution and group
defense (Rutberg 1984; Berger 1992; Berger and Cain 1999). However,
it is difficult for females in poor body condition to make these adjustments, and as a result, the birthing period is extended following winterswith deep snow and later emergence of new vegetation in spring (Berger1992). Calving dates for bison in northern Yellowstone precede those ofbison in central Yellowstone by about 14 days due to the earlier onset ofsnow melt and new plant growth in northern Yellowstone (Gogan et al.
2005; Figure 5.1). Seventy-two percent (47 of 65) of births in northern
Yellowstone occurred by May 7th, while 63 percent (50 of 79) of births incentral Yellowstone occurred after May 8th. The calving period in central
Yellowstone was prolonged, likely due to harsher winter conditions thatpredispose female bison to poorer body condition.
Yellowstone bison do not give birth in the same locale each year. Individual radio-collared females have given birth on high-elevation summer areas
6
The data and findings reported in this chapter reflect analyses revised from
Geremia et al. 2009 and include data collected during 2009-2014

Reproduction and Survival

Figure 5.1. Calving dates of 79 radio-collared bison in central Yellowstone during
2005-2012 and 65 radio-collared bison in the northern region of Yellowstone
National Park during 2008-2012 (Geremia et al. 2014a).

(e.g., Hayden and Lamar valleys) during some years and in lower-elevation
winter areas (Hebgen and Gardiner basins) during others. Calving often
overlaps with spring migrations from winter to summer ranges, and birth
locations likely depend on when these migrations commence—which
could be delayed due to prolonged snow pack or late emergence of newvegetation at higher elevations (Geremia et al. 2011, 2014b). As a result,many births occur on winter ranges near or outside the boundary of Yellowstone National Park during some years (Jones et al. 2010).

Reproductive Rates
After reaching sexual maturity, female plains bison generally produce one
calf every one or two years for the rest of their lives (Meagher 1973; Fuller
et al. 2007b; Geremia et al. 2009; Gogan et al. 2013). In central Yellowstone,
monitored females did not produce calves in sequential years during 1997
to 2003. Rather, most pregnancies were observed in animals greater

85

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Yellowstone Bison: Conserving an American Icon in Modern Society

than 3 years old that were not lactating (Kirkpatrick et al. 1996; Gogan etal. 2013). Lactating bison may not be able to replenish sufficient fat andprotein reserves to support pregnancy during summers when drought orcompetition with other herbivores limit their nutritional intake (Cook et
al. 2004a,b, 2013; Gogan et al. 2013; Middleton et al. 2013). However, 54
radio-collared bison monitored between two and nine sequential years
during 1997 through 2012 produced a calf more than 60% (136 of 211) of
the time, suggesting that bison in central Yellowstone may calve somewhat
more frequently than in alternate years. In contrast, sequential calving ismore common in northern Yellowstone where 39 radio-collared bisonmonitored between two and six sequential years produced a calf morethan 80% (110 of 132) of the time. Twenty of these females were monitored
for at least four consecutive years, with thirteen (60%) producing a calf
every year.
In recent decades, birth rates have been higher in northern Yellowstone(0.78; 95 percent Bayesian credible interval [CI] = 0.72 to 0.84) than incentral Yellowstone (0.63; CI = 0.56 to 0.69). The probability of giving
birth was lowest at 3 years of age and increased with age (Table 5.1; Figure5.2). A leveling off or decrease of birth rate in older animals has not been
detected, which may, in part, be due to limited observations of older animals. In many ungulate populations, birth rates decrease as abundance
increases towards the food-limited capacity of the environment to support them (Caughley 1976; Eberhardt 1977, 2002). The number of bison innorthern Yellowstone has varied between 400 and 3,500 since 1980, while
the number in central Yellowstone has varied between 1,400 and 3,600
bison, with no apparent effects of bison density on birth rates. Instead,
population growth has been limited by the capture and shipment of bison
to meat processing facilities, and to a lesser extent, hunting in Montana
during winter (White et al. 2011). Random variations in weather conditions such as drought or deep snows can limit the availability of forage
for bison and increase energetic costs (Clutton-Brock et al. 1985; Sæther
1997; Gaillard et al. 2000). Birth rates for Yellowstone bison were lower
following winters with deep or hard snow pack, but no drought-related
effects were detected.

Reproduction and Survival
Reproduction

Survival

Age

Birthed

Total

Survived

Total

1

0

0

5

6

2

0

1

58

58

3

27

47

64

66

4

38

53

76

78

5

43

61

73

77

6

35

57

63

66

7

31

44

53

55

8

28

32

50

52

9

22

28

49

53

10

18

24

26

32

11

13

16

20

24

12

8

11

13

16

13

5

7

5

6

14

3

4

3

4

15

1

2

4

4

16-20

2

4

7

9

Total

274

391

569

606

Table 5.1. One hundred and fifty-three adult female bison were repeatedly monitored
between two and nine years for birth and survival during 1996 through 2012 inYellowstone National Park (Geremia et al. 2014a).

Effects of Brucellosis
Some diseases rapidly influence the dynamics of wildlife populations
by reducing the survival and fecundity of infected animals (Hudson
et al. 1992; McCallum and Dobson 1995). Other diseases establish
long-term, endemic infections in populations that persist without anoticeable effect on survival and fecundity (Ewald 1994). Endemic
diseases are characterized by a relatively constant proportion of the
population being infected, with little variation in the prevalence of

87

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Yellowstone Bison: Conserving an American Icon in Modern Society

Figure 5.2. Age-specific probabilities of giving birth for radio-collared bison in thecentral and northern regions of Yellowstone National Park that were not exposed(red) and chronically exposed (blue) to Brucella abortus bacteria (see Chapter 2).
Birth probabilities for recently exposed, seroconverting bison are not reported byage but averaged near 0.48.

Reproduction and Survival

infection (Andersen and May 1979). Brucellosis has existed in the
Yellowstone bison population for about one century (Meagher andMeyer 1994). The disease does not significantly affect bison survival,
but females generally have decreased fecundity during their firstpregnancy following infection (Dobson and Meagher 1996; Thorne
2001; Joly and Messier 2005; Rhyan et al. 2009).
The probability of Yellowstone bison giving birth prior to infection
with brucellosis was 0.80 (CI = 0.73 to 0.86), but decreased to 0.48 (CI= 0.27 to 0.70) during the first pregnancy after infection (Figure 5.2).
However, there was large variability between individuals and about
one-half of pregnant bison that were recently exposed to Brucellabacteria successfully gave birth to live calves. Many Yellowstonebison are exposed to Brucella bacteria prior to reaching reproductive maturity (Treanor et al. 2011). This early exposure may allow
immature bison to develop some resistance to infection, thereby
reducing the occurrence of Brucella-induced abortions when they
become reproductively mature (Meyer and Meagher 1997; Geremia
et al. 2009).
There is some indication that the probability of Yellowstone bison
giving birth to a live calf remains suppressed (0.64, CI = 0.57 to 0.7)
for many years following exposure to Brucella bacteria due, in part,to lowered pregnancy rates (Figure 5.2). A Brucella-induced birth orabortion often results in a retained placenta that could predispose theuterus to infection and cause lower fertility due to delayed ovulationand lower conception rates (Geremia et al. 2009; Rhyan et al. 2009).
However, pregnancy rates of females culled at the boundary of Yellowstone National Park during 1997 to 2003 appeared unaffected bybrucellosis exposure (Gogan et al. 2013). Likewise, Joly and Messier(2005) did not detect effects of brucellosis exposure on pregnancy
rates in wood bison (Bison bison athabascae) in Canada. Further
research is necessary to resolve these disparate findings.

89

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Yellowstone Bison: Conserving an American Icon in Modern Society

Survival
Some female bison live for more than 20 years in Yellowstone (Udevitz
and Gogan 2010). Males rarely live past 12 years, perhaps due to higher
energetic costs and increased risk of injury when sparring for matesduring the breeding season (Meagher 1973). Newborn bison have an
increased risk of mortality from predation, disease, and harsh weather.
However, their survival has been remarkably high in recent decades,
especially compared to other ungulates such as elk (less than 0.3) following the recovery of grizzly bears and wolves (Barber-Meyer et al. 2008;
Hamlin et al. 2009). Neonate survival has been 0.75 (standard deviation= 0.06) during the first month of life and 0.87 (standard deviation = 0.05)
during the remainder of the first year (Geremia et al. 2014b).
The probability of an adult female bison surviving one year was 0.96
(CI = 0.94 to 0.98) in northern Yellowstone and 0.91 (CI = 0.88 to 0.94)
in central Yellowstone during recent decades (Figure 5.3). Survival rates
decreased during years with deep snow pack, but remained relatively
unchanged through substantial variations in bison abundance anddrought conditions. Survival remained consistently high for 3- to 9-yearold females in northern Yellowstone. There was some indication of lower
survival rates as females aged past 10 years, but additional data are needed
to better define this relationship (Figure 5.3). Lower survival was more
prominent in females from central Yellowstone after 9 years of age (Geremia et al. 2009, Figure 5.3). As bison age, tooth wear reduces their ability
to chew plant material into small enough particles to facilitate efficient
digestion by microbes in their rumen (Van Soest 1994; see Chapter 6). In
central Yellowstone this wear may be worsened by the abrasive action ofsilica present in rhyolite soils, some of which may be retained on plants
eaten by bison (Garrott et al. 2009b; Geremia et al. 2009).

Causes of Mortality
Since 1985, more than 6,000 bison have been removed from the population by humans, primarily through capture and shipment of bison tomeat processing facilities and secondarily through hunting (White et al.
2011). Overwhelmingly, these removals have been the principal causesReproduction and Survival

Figure 5.3. Age-specific probabilities of survival for radio-collared bison in thenorthern and central regions of Yellowstone National Park. Human removals
were not included in the analyses.

of bison mortality. Winter-kill can be a significant cause of mortality
during winters with severe snow pack (Fuller et al. 2007b; Geremia etal. 2009). Also, predation is becoming a larger factor following wolf
restoration and grizzly bear recovery (Smith et al. 2004, 2013; Becker et
al. 2009a,b). During 1993 through 2010, biologists from Montana State
University found 656 bison carcasses in central Yellowstone during
winter and spring and the apparent causes of death were 225 wolf predations, 181 winter-kills, 153 due to unknown causes, 46 grizzly bear
predations, 20 thermal/mud entrapments, 10 vehicle strikes, 7 accidents/
injuries, 7 birth/pregnancy complications, 6 due to unknown predators, and 1 coyote predation (R. A. Garrott, Montana State University,
unpublished data).
Wolves in northern Yellowstone primarily feed on elk, with bisoncomprising only 2 to 6 percent of kills (Metz et al. 2012). Since 1995
when wolves were initially restored, counts of northern Yellowstone
elk have decreased from about 19,000 to 4,000 while counts of bisonin this region have increased from about 900 to 3,500 (White et al. 2012;
see Chapter 1). Despite these changes, wolves have not begun preying

91

Infrared image of wolves feeding on a bison
carcass in Yellowstone National Park.

Photograph courtesy of National Geographic by Michael Nichols

94

Yellowstone Bison: Conserving an American Icon in Modern Society

substantially more on bison, even though wolf numbers in northern
Yellowstone decreased from 95 in 2007 to 34 by 2014 due to wolves
killing other wolves, malnutrition, and disease (Metz et al. 2012). Bison
are larger and employ group defenses that make them more difficult to
attack than elk, which are smaller and often run when attacked (Smithet al. 2000; MacNulty et al. 2007; Becker et al. 2009a).
Wolves in central Yellowstone also strongly prefer elk, even thoughbison are more abundant during winter and elk counts have decreased bySome female bison
live for more than 20
years in Yellowstone
National Park.

about 95 percent since wolf colonization in 1998 (Becker et al. 2009a,b;
Garrott et al. 2009a,c). Wolves kill more bison in late winter as snow
pack increases and its effects reduce bison condition and increase theirsusceptibility to attack (Becker et al. 2009a,b). As an example, bisoncomprised 53 percent wolf diets during 2006 when snow pack was severe,but only 15 percent of wolf diets during the relatively mild winter of 2007
(Becker et al. 2009a,b). Wolves also kill more bison as bison numbers
increase relative to elk and there are more bison calves in the population(Becker et al. 2009a,b). The average age of adult bison killed by wolves
was 10 years (Becker et al. 2009a,b). Wolves can exist almost entirely on
bison, as observed in Wood Buffalo National Park in Canada (Carbyn
and Trottier 1987). At this time, however, wolves in Yellowstone still preferelk and only tend to kill significant numbers of bison during winters withdeep and prolonged snow pack that make malnourished animals moreabundant and susceptible (Becker et al. 2009a).

Conclusions
An isolated population of wildlife that adapts to local environmental conditions and reproduces faster than individuals die will generally increasein abundance. Because habitat for many wildlife species is limited inmodern society, these types of populations often exhibit boom-and-bust
cycles with rapid population growth punctuated by sizeable mortality
events (e.g., starvation, culling) when food, other resources, or humantolerance become scarce (Caughley 1970). This is the situation in which
Yellowstone bison currently exist because: (1) there is a limited amountof winter range and forage for bison inside Yellowstone National Park, (2)Reproduction and Survival

there is limited space in Montana where bison are allowed to migrate anddisperse, (3) predation removes relatively few bison, and as a result, has
limited effects on population abundance, (4) under-nutrition (starvation)
only contributes to high mortality when bison abundance is high and/or
snow pack is above average, and (5) most bison migrate to lower elevation areas in response to such severe weather events—which eventuallybrings them into conflict with agriculture and residential development.
Managers could allow the Yellowstone bison population to continue
boom-and-bust cycles, and implement episodic, large removals whenpopulation abundance is high (e.g., more than 4,500 animals). These
removals would reduce migrations outside of the park for several years
as a substantially smaller population again increases in size. Alternatively,
managers could attempt to regulate the bison population within a range
where enough animals exit the park annually to implement harvests andsmaller management removals that offset growth. The target range should
be defined by ecological conditions that may vary over time, but undercurrent conditions is near an end-of-winter population of 3,000-4,000
bison (Geremia et al. 2014a). However, this approach necessitates tolerance for bison outside of the park, especially during years when severe
winter weather increases numbers of migrating animals.

95

NPS/Neal Herbert

Bison grazing among
the sagebrush near theBlacktail Deer Plateau in
Yellowstone National Park.

Chapter 6
NUTRITIONAL ECOLOGYJohn J. Treanor, Jessica M. Richards, and Dylan R. Schneider

The availability of an adequate food source is essential for the persistence of any wildlife population. Many species of herbivorous
mammals exist in dynamic environments in which the quality ofthis food source changes seasonally. Yellowstone National Park is
one such environment where seasonal fluctuations in environmental
conditions have a strong influence on key life events for large herbivores. In such a dynamic landscape, it is expected that individuals
maximize their ability to influence the outcomes of these life eventsby using different strategies within seasons (Barboza et al. 2009).
In this chapter, we describe how nutrition influences survival earlyin life, growth needed to reach reproductive maturity, and successful breeding during adulthood in Yellowstone’s bison population,with particular attention paid to how bison use seasonal strategies
to meet their nutritional needs.

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Yellowstone Bison: Conserving an American Icon in Modern Society

Forage Quality, Digestion, and Metabolism
Wild herbivores survive on forage that varies in quality and availability
throughout the year (Van Soest 1994). The preferred forage of Yellowstone bison is grasses and sedges, with forbs and shrubs making up lessthan 6 percent of their diets (Meagher 1973). Shrubs tend to retain ahigher nutrient content throughout the growing season, but they also
contain a variety of compounds, such as tannins, that limit digestibility(Rhoades 1979; Hanley et al. 1992). For Yellowstone bison, seasonalchanges in diet quality reflect the predictable phenology of grasses. The
high-elevation ranges in Yellowstone National Park are dominated bycool season grasses that tend to be high in nutrients in the spring, but
decrease as the growing season progresses.
The quality of forage is determined by environmental conditions
that influence plant growth and the stage of plant maturity (Van Soest
et al. 1978; Nelson and Moser 1994). Environmental factors such as
precipitation, summer temperatures, and winter severity influence thequality and growth of forage within a given year. During the growing
season, younger plants contain more soluble carbohydrates and lessfiber, which makes them more digestible than older plants. However,grasses mature quickly and become fibrous, which greatly reduces
their digestibility (Rinehart 2008). Thus, it takes more time for bison to
extract nutrients from ingested forage as the growing season proceeds.
Bison have a four-chambered stomach that can process bulky
amounts of fairly indigestible plant components (Hofmann 1989).
The fore stomach, or rumen, serves as a fermentation chamber where
millions of bacteria, protozoa, and fungi convert cellulose into energyyielding fatty acids that are digestible by bison (Owen-Smith 2002).
Dietary energy provides the nutrients for growth, heat production, andthe maintenance of body functions primarily through the metabolism
of glucose (Rinehart 2008; Barboza et al. 2009). The protein content
in forage provides rumen microbes with essential amino acids for thesynthesis of microbial proteins. These proteins are absorbed by bison as
they pass through the rumen and then used for the development of bodytissues and other vital functions. In other words, energy is supplied toNutritional Ecology

bison through the fermentation of dietary carbohydrates, while protein
is supplied through the digestion of rumen microbes (Van Soest 1994).
Gut capacity increases with body size in ruminants, which allows
larger animals to eat a diet high in fiber and retain and ferment forage
longer (Demment and Van Soest 1985; Gordon and Illius 1996; Larterand Nagy 2001). The amount of fibrous forage in bison diets increases
during winter when plant tissues are dead. As a result, forage is retained
longer in the gut because indigestible plant tissues must be reduced insize to pass through the openings in the rumen. Bison also ruminate,
whereby food is returned to the mouth from the gut for intensive chewing to further break down plant material. The frequency and durationof rumination bouts increase as diets become more fibrous (Renecker
and Hudson 1993; Sinclair et al. 2006). The ruminant digestive system is
not designed to maximize the flow of ingested forage (Hume 1989). As aresult, seasonal changes in the digestibility of forage plants correspondto a reduction in foraging time and the rate of forage intake (Spalinger
et al. 1986; Owen-Smith 2002). Small reductions in the quality of winterdiets have been associated with large declines in food intake, which
demonstrates that bison cannot compensate for low quality forage bysimply eating more (Gray and Servello 1995; Cook et al. 2004a).
In general, bison have peak forage intake and maintenance requirements during June through September (Rutley and Hudson 2000).
However, low temperatures and snow cover during winter createshigh energy demands at a time when less energy is available in forage
plants (Sinclair et al. 2006). Bison adjust by reducing food intake andmetabolism and decreasing their energy expenditures (Christopherson et al. 1979; Stuth 1993; Galbraith et al. 1998; Feist 2000; Signer et al.
2011). North American bison have adapted to survive winter conditions
when food is limited. Bison generate heat through digestive fermentation, especially from the high roughage diets that are available during
winter (Owen-Smith 2002). Body heat is then conserved by a layer ofsubcutaneous fat underneath a thick winter coat. In comparison, bison
are more tolerant of cold temperatures than cattle, with 6-month oldbison calves being as tolerant of cold as yearling cattle (Christopherson

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Yellowstone Bison: Conserving an American Icon in Modern Societyand Hudson 1978; Christopherson et al. 1979). Bison have developed
an effective strategy for meeting the nutritional demands of survival,
growth, and reproduction across seasons by selecting forage for highnutritional value from spring to autumn and minimizing nutritional
needs and the loss of body reserves during winter (Barboza et al. 2009;
Stephenson et al. 2002).

Seasonal Nutrition and Population Dynamics

The availability of highquality food duringlactation and the earlyyears of life could also
influence the social
status and lifetime
reproductive successof Yellowstone bison.

High quality diets are important during calf development because
protein requirements increase, particularly in late winter and early
spring when the fetus grows rapidly (Robbins and Robbins 1979; Robbins 1993; Cook 2002). In Yellowstone, the protein content of forageis lowest during late winter and early spring, which coincides with thehigh nutritional demands of late gestation (Treanor 2012). The survival
of newborn calves is reduced by low maternal diet quality, especially iffood is restricted for extended periods near parturition (Price and White
1985; Barboza et al. 2009; Cook et al. 2013). Pregnant bison mobilize
fat and protein body reserves during late gestation to meet increasing
nutritional demands (Treanor 2012). As a result, female bison lose asubstantial amount of body mass over winter, especially if winters aresevere and prolonged.
In spring, bison give birth to a single calf which must travel with theherd soon after birth (Renecker and Hudson 1993). Newborn calvesrequire milk of high nutritional quality to grow quickly. Thus, lactationis the most nutritionally demanding stage of reproduction in mammals,with protein requirements increasing 110 to 130 percent (Oftedal 1985;
Barboza and Parker 2008; Barboza et al. 2009). However, the onset of
lactation for bison frequently occurs when deep snow still impedes
plant emergence and access to high-elevation rangelands within Yellowstone National Park. Access to emerging forage is critical for thedevelopment of newborns because milk fat is primarily derived fromthe daily diet rather than body reserves (Sadleir 1987; Pond et al. 2005).
Milk production reaches a peak several weeks after parturition andgradually declines thereafter (Renecker and Hudson 1993). Thus, theNutritional Ecology

growth rate of bison calves and their body size entering winter reflects
the food available to their mothers for milk production.
Lactating females need to replenish body reserves that were depleted
the previous winter and spring to become pregnant in late summer (Cooket al. 2001). Ovulation in bison is influenced by the nutritional conditionof females and their access to summer forage with adequate digestible
energy (Schillo 1992; Gerhart et al. 1997; Cook et al. 2013). Therefore,
the accumulation of body fat through summer and autumn nutrition
plays an important role in reproductive success (Clutton-Brock et al.
1997; Russell et al. 1998; Cook 2002). After the metabolic needs of bison
are met by dietary nutrients, excess energy and protein are depositedin the form of fat and muscle. Fat is typically stored towards the end ofsummer because subcutaneous fat can limit the exchange of heat withthe environment (Owen-Smith 2002; Barboza et al. 2009).
The availability of high quality food during lactation and the earlyyears of life could also influence the social status and lifetime reproductive success of Yellowstone bison. Body mass is a reliable indicator of
female body condition and significantly correlated with dominance rank
in bison (Lott and Galland 1987; Green and Rothstein 1991; Vervaecke etal. 2005). A higher rank may improve feeding opportunities, especiallyduring periods of food restriction. Also, the maternal rank of bison ispositively related to offspring weight (Vervaecke et al. 2005). Bison thatare small at birth or grow more slowly because of inadequate nutrition
may become small adults and produce fewer offspring over their lifetimes(Gaillard et al. 2003; Barboza et al. 2009).
Reproduction has a cost that is mostly evident in animals in poor
nutritional condition (Festa-Bianchet et al. 1998). As a result, nutritional
condition can interact with bison density to influence the productivity ofthe population. For example, conception rates are lower in populations
at high density, which reduces mortality risk to reproductively mature
females in poor condition (Gaillard et al. 2000). Furthermore, nutritional
effects are subtle and influence many different aspects of reproduction
and survival. In combination, these effects may result in substantial limitations on population growth (Cook et al. 2013).

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NPS/Neal Herbert

Bison feeding near Lower Geyser
Basin in the west-central portionof Yellowstone National Park.

Nutritional Ecology

Seasonal Strategies
Yellowstone bison have responded to seasonal changes in forage availability and quality by overlapping the most nutritionally demanding phasesof their life cycle with the availability of high quality forage (Rutberg 1984;
Post et al. 2003; Treanor 2012). About 80 percent of their calving occurs
during April 25 through May 25, which coincides with the emergenceof growing forage on low-elevation winter ranges (Jones et al. 2010; Treanor 2012). Thus, lactation commences when forage high in protein anddigestible energy becomes available (Figure 6.1). The availability of highquality vegetation after birth increases the quality of milk and provides anadvantage for early born juveniles (Guinness et al. 1978; Festa-Bianchet1988). Over-winter mortality is typically lower for larger juveniles as aresult of better body condition (Clutton-Brock et al. 1982; Festa-Bianchet
1988; Keech et al. 2000; Côté and Festa-Bianchet 2001). Therefore, timing
the birth of calves with emerging vegetation is an effective strategy for
maximizing the growth of newborns in the early months of life, which
increases their ability to survive the upcoming winter.
In addition, Yellowstone bison adjust their nutritional intake throughhabitat selection and migratory movements as the availability and quality of forage changes seasonally across the landscape. They move fromsummer ranges at relatively high elevations to lower elevations during
autumn through winter, and then return to the summer ranges in June
(Meagher 1989b; Bjornlie and Garrott 2001; Bruggeman et al. 2009c).
Vegetation quality has little influence on the selection of foraging areasused by bison during winter because plant tissues have senesced and areof low nutritional value. Instead, factors that influence the availabilityof forage such as snow pack and bison density become more important(Bruggeman 2006). As a result, most bison move to foraging areas at lower
elevations and areas with thermally warmed ground as snow depths
increase at higher elevations (Meagher 1989b; Bruggeman et al. 2009c).
During spring, there are more energy-efficient foraging opportunities
for bison at lower elevations because snow melt and vegetation growthcommence earlier (Despain 1990; Thein et al. 2009). Thus, most calving
occurs in these areas (Jones et al. 2010). The return migration of bison

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Figure 6.1. Monthly percentage (mean ± standard error) of fecal crude protein fromYellowstone bison sampled during 2004 and 2005. The peak calving interval was
reported in Jones et al. (2010). Bison calving is synchronized with the emergenceof spring vegetation, which is high in protein and digestible energy. Sep-04 refers
to September 2004.

to higher-elevation summer ranges coincides with patterns of newvegetation growth on the landscape (see Thein et al. 2009 for detailed
descriptions and maps). Highly digestible plants eventually become
widely distributed, and as a result, energy intake by bison increases(Mysterud et al. 2001). As the growing season advances and grasses
mature there is a decrease in the proportion of higher-quality leaves
to lower-quality stems (Ball et al. 2001). As a result, bison become more
selective and consume the upper portions of grasses which are higher
in crude protein and digestible energy (Rutley and Hudson 2001).

Conclusions
Yellowstone bison have developed a set of strategies to meet theirnutritional needs across the year. The availability of high quality forage
during spring and summer promotes successful reproduction andthe accumulation of body reserves for winter survival, while winterNutritional Ecology

forage helps reduce the rate at which these reserves are mobilized. As
winter progresses, fat reserves may be needed for energy, especially for
pregnant females during late gestation. Calving is synchronized withthe emergence of spring forage, which allows bison to meet the highnutritional demands of lactation. The growth and survival of calves ispositively affected by the nutritional quality of summer forage. Therefore, bison increase forage intake during the growing season, which
enhances assimilation of nutrients. During the dormant season, foodintake is reduced and bison conserve body reserves by reducing activity and metabolic rates. Lower-elevation winter ranges provide bisonwith access to forage and reduce the energy expenditure of moving
through the deep snow found at higher elevations. Yellowstone bison
are adapted to seasonal changes in forage nutrition and winter conditions with digestive, physiologic, and behavioral strategies that allow
them to survive and reproduce in a dynamic environment.

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Bison and cowbirds during
the spring green-up in
Yellowstone National Park.

Chapter 7
ECOLOGICAL ROLE — BISON RELATIONSWITH OTHER ANIMALS AND EFFECTS
ON GRASSLAND PROCESSES
Rick L. Wallen, P.J. White, and Chris Geremia

Populations of large grazers like bison have strong influences onplant and animal communities (Knapp et al. 1999; Lott 2002; Bailey2013). Grazing often increases the availability and distribution of
nitrogen to plants, which in turn, can increase plant production(Frank and McNaughton 1993). Also, bison provide food for many
predators, scavengers, and decomposers, and their carcasses deposit
nutrients into the soil that create fertile patches for plant growth(Knapp et al. 1999). In addition, grazing and wallowing create specific environments that result in greater plant diversity across thelandscape by holding water in depressions, enabling colonization
by pioneering plant species, and increasing the diversity and use ofareas by other animals (Knapp et al. 1999; Truett et al. 2001; Fuhlendorf et al. 2006).

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Ecosystem Engineers
Bison inadvertently act as “ecosystem engineers” by creating andresponding to heterogeneity across the landscape (Gates et al. 2010).
They create greater plant diversity by preferentially feeding on grasses
and avoiding some flowering plants, while preventing plant community
succession through hoof action and horning or rubbing on trees andshrubs (Meagher 1973; Coppedge and Shaw 1998; Knapp et al. 1999).
Their heavy bodies and sharp hooves combine to till the soil and disturb
roots of grasses and grass-like plants (Frisina and Mariani 1995). This
prevents grassland succession to shrubs or trees and provides grasses
with greater access to sunlight, which is important for growth (Knappet al. 1999). Large groups of bison contribute to natural disturbancesthat influence plant species composition and distribution across large
portions of grasslands and shrub steppe, similar to fire, windthrow, andmass soil erosion events (Augustine and McNaughton 1998; Turner et
al. 2003; Collins and Smith 2006; McWethy et al. 2013). Fire can increase
grassland productivity through nitrogen cycling, but tends to reducethe diversity of plant species because not all species are fire tolerant.
Grazing by bison is more likely to retain a diversity of plant species
while redistributing nitrogen in the system (Knapp et al. 1999; Frank et
al. 2000). Moderate grazing induces the production of new grass tissue
and increases plant community production to the limits determined bywater and nitrogen availability (McNaughton 1983, 1984; Frank et al.
2013). Fire tends to burn fewer plants in grazed areas because ungrazed
grasses contain more flammable material. Thus, the combined effects
of grazing and fire — called pyric herbivory — can result in greater plant
diversity and habitat heterogeneity than either process alone (Fuhlendorf and Engle 2004; Fuhlendorf et al. 2008, 2012).

Food-Limited Carrying Capacity
Bison eat frequently due to their large body size, which combined with
their tendency to aggregate into herds, necessitates finding food sourcesthat are abundant or widely distributed. As a result, bison often congregate in large open grasslands for breeding, but then disband into smallerEcological Role109

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Bison wallowing in theLamar Valley of Yellowstone
National Park.

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Yellowstone Bison: Conserving an American Icon in Modern Society

groups and disperse widely on smaller patches of habitat through therest of the year (Berger and Cunningham 1994). The influence of bisongrazing on plant communities can be intense at times due to their grouping tendencies, but they rarely occupy the same foraging area for morethan a few days (McHugh 1972; Knapp et al. 1999). Bison select areas
with plants high in nutrients during the growing season, but transition
to areas with relatively high plant abundance and availability during
winter when grasses are past their growing period and there is relatively

Grazing and wallowing
create environmentsthat result in greater
plant diversity acrossthe landscape.

little variation in quality among areas (Wallace et al. 1995). Bison canmove more than 46 centimeters (18 inches) of snow by swinging their
massive heads in a side-to-side motion, which allows them to accessthe aged vegetation beneath and feed in areas where other ungulatescannot during winter (Barmore 2003; Picton 2005).
Grasses and grass-like plants are important foods for several ungulatesin Yellowstone National Park, including bison (97 to 99 percent of dietin winter), elk (81 to 86 percent), and bighorn sheep (Ovis canadensis; 61
to 67 percent; Singer and Norland 1994). As bison numbers in northern
Yellowstone increased during the 1970s and 1980s, they expanded theirgeographic range and began using more sedge meadows, grasslands,
and sagebrush areas (Jerde et al. 2001). As a result, their diet and habitat
overlap with other ungulates increased, including a moderate overlap
in diet and a large overlap in habitat with elk that could contribute tocompetition between them for food and space (Singer and Norland
1994; Coughenour 2005; Plumb et al. 2009). In turn, some people questioned whether bison had surpassed numbers that could be supportedby the forage in the park and nearby areas, considering year-to-year
variations in food production, habitat use, diet selection, competition,and energy use.
Dr. Michael Coughenour of the Natural Resource Ecology Laboratory at Colorado State University evaluated if bison had reacheda food-limited carrying capacity by developing and testing a modelof the Yellowstone system that incorporated abiotic variables (e.g.,soil nutrients, water, topography, weather) and biotic processes (e.g.,plant growth, herbivory, predation, and the abundance, distribution,

Ecological Roleenergy balance, and nutrition of bison and elk). Model output indicatedthe food-limited carrying capacity for bison in and near Yellowstone
National Park was as large as 10,000 bison during summer but varied
around 6,500 during winter, near which foraging efficiency and bison
condition should decrease (Coughenour 2005; Plumb et al. 2009). To
date, bison numbers have not reached this level, and several assessments of vegetation conditions by scientists and land managers haveindicated the park is not overgrazed (Boyce 1998; Huff and Varley 1999;
National Research Council 2002).
However, model output also predicted a substantial decrease in
the number of elk in northern Yellowstone could release bison in thisarea from competition and induce an increase in their numbers to as
many as 4,900 (Coughenour 2005; Plumb et al. 2009). This forecast
was supported as counts of northern Yellowstone elk decreased fromabout 19,000 in 1994 to 4,000 by 2013 following wolf restoration andgrizzly bear recovery, while bison numbers increased from approximately 870 to 3,500 (Frank et al. 2013; Garrott et al. 2013). The specificcauses of these coinciding trends remain unknown, but the numberof bison in northern Yellowstone is still increasing despite occasionalculling, with high calf production and survival of all age groups (Table
7.1). Bison will likely respond to increased competition and nutritional
stress as their numbers increase by moving to lower elevation winterranges outside the park in search of food (Coughenour 2005). Thisbehavior is consistent with large migrations of bison outside the park
during severe winters in the past decade (Coughenour 2005; Plumbet al. 2009). Scientists are studying the effects of this change from anelk- to a bison-dominated system on the ungulates and vegetation innorthern Yellowstone (Hebblewhite and Smith 2010; Garrott et al. 2013).

Effects of Grazing
Bison can enhance plant growth by making nitrogen and organic
matter more abundant and accessible to soil microbes, and distributing nutrients across the landscape (Frank and Evans 1997; Towne 2000;
Augustine and Frank 2001). During the 1980s and 1990s, the grazing of

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Yellowstone Bison: Conserving an American Icon in Modern Society
Growth rate
Average

95% range

2000-01

1.20

1.12 – 1.27

2001-02

1.20

1.13 – 1.26

2002-03

0.94

0.88 – 1.01

2003-04

1.10

1.03 – 1.16

2004-05

1.17

1.10 – 1.24

2005-06

0.75

0.69 – 0.81

2006-07

1.18

1.12 – 1.25

2007-08

0.55

0.48 – 0.61

2008-09

1.10

1.04 – 1.17

2009-10

1.17

1.10 – 1.23

2010-110.96

0.89 – 1.02

2011-12

1.12

1.06 – 1.19

2012-13

1.15

1.09 – 1.22

2013-140.99

0.92 – 1.05

AverageStandard deviation

Adult female survival

0.93

0.01

Neonate survival (1st month)

0.75

0.06

Calf survival (rest of 1st year)

0.87

0.05

Male survival

0.94

0.04

Probability of newborn calf

0.47

0.02

0.70

0.03

Vital rates

being female
Birth rate

Table 7.1. Population growth rate (including winter removals) and vital rates of
Yellowstone bison during the Interagency Bison Management Plan (Geremia etal. 2014b).

Ecological Rolegrasses and deposition of organic matter by migratory ungulates (primarily elk) in northern Yellowstone approximately doubled the rateof nitrogen mineralization and production of leaves, roots, and stems
by grasses (Frank and McNaughton 1993; Frank and Groffman 1998;
Frank et al. 2002). However, rates of ungulate grazing and nitrogen
cycling decreased by up to one-half during the late 1990s as the numbers of elk decreased substantially due to hunter harvest, predation,
and winter-kill (Frank 2008). Also, energy and nutrient dynamics wererearranged across the landscape, with grazing decreasing more in areas
with higher productivity (Frank 2008). Since that time, the numberof bison in northern Yellowstone has more than tripled, which could
reestablish the stimulating effects of grazing on nitrogen cycling andplant production (Frank et al. 2013). However, large groups of bisonthat repeatedly graze areas and remove plant tissue through the summer
growing season could have quite different effects on Yellowstone’s
grasslands than herds of elk that graze areas for relatively short periods
during their migration to higher-elevation summer ranges (Wallace et al.
1995). Scientists are currently studying the effects of this recent change.
Ungulate grazing and nutrient deposition generally increases grass
production from low to moderate grazing intensities, but decreases
production at higher grazing intensities because too much leaf tissue isremoved (Kie et al. 2003; Stewart et al. 2006). During 1998 to 2000, lessthan 50 percent of the herbaceous vegetation in the Hayden Valley ofcentral Yellowstone was consumed by herbivores during the growing
season, which approximates a moderate grazing rate (Olenicki and Irby2003). In some areas, however, bison removed more than 30 percentof new growth in spring and 70 percent of the remaining plants during
winter (Olenicki and Irby 2003). Higher consumption could decrease
plant production if bison numbers continue to increase and bison regraze the same plants during a single season or consecutive seasons(Olenicki and Irby 2003). As a result, the prevalence of grasses could
decrease while forbs and grazing-tolerant plants increase — though theoutcome will depend on the density of bison relative to the capacity ofthe environment to support them (Kie et al. 2003; Stewart et al. 2006).

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Apparent Competition
If the current trend of increasing bison numbers and decreasing elk
numbers continues, then wolves may begin to rely more on bison forsustenance; which could have indirect effects on elk and other ungulates(Garrott et al. 2009a, 2013; Hebblewhite and Smith 2010). Predation ona particular species can be strongly influenced by the presence of otherprey species that maintain predators at higher densities — a process
known as apparent competition (Holt and Lawton 1994). For example, an increase in the abundance of one prey species can result in adecrease in the abundance of another prey species due to an increase in
the number or distribution of predators (Holt 1977). This situation wasobserved in the Canadian Rocky Mountains where wolves primarily
fed on moose (Alces alces), but also killed woodland caribou (Rangifer
tarandus caribou) as alternate prey. An increase in moose numbers
resulted in more wolves that contributed to a range-wide decrease in
numbers of less abundant caribou (Wittmer et al. 2005). Garrott etal. (2009a) suggested that increased predation on abundant bison by
wolves in the Madison headwaters area of central Yellowstone would
also enable them to keep killing more of their primary prey, elk. In otherwords, abundant bison could sustain wolf hunting in the area despite
the scarcity of their preferred prey (Garrott et al. 2013). In turn, wolves
could keep the number of elk in the area low by occasionally killing
vulnerable animals, as annual counts suggest is currently happening(Garrott et al. 2013).
Elk populations in northern and west-central Yellowstone were near
the capacity of the environment to support them for several decades
prior to the restoration of wolves (Taper and Gogan 2002; Garrott etal. 2009c; White and Garrott 2013). Elk numbers decreased about 75
percent following wolf restoration due to predation and other factors(White and Garrott 2005; Garrott et al. 2009c; White and Garrott 2013).
It is uncertain if predation will ultimately regulate these elk populations
at a lower, alternate state or whether bison will become a significant
alternate prey for wolves (Garrott et al. 2009a, 2013). Bison are now
more abundant than elk in Yellowstone during winter, and wolf use ofEcological Role

115

Photograph courtesy of National Geographic by Michael Nichols

A bald eagle and ravens
feeding on a bison carcass inYellowstone National Park.

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NPS/Neal Herbert

Bison in the Lamar
Valley of Yellowstone
National Park.

Ecological Rolebison has increased in recent years (White and Garrott 2013). However,wolves still strongly prefer elk despite their decreased availability (Becker
et al. 2009a; Metz et al. 2012). Bison are much more formidable prey forwolves than elk because of their larger size and tendency to employ
group defenses whereby adults coalesce around and protect younger,
more-vulnerable animals (MacNulty et al. 2007; Becker et al. 2009a). As
a result, predation on bison is not currently sustaining more wolves in
Yellowstone which could contribute significantly to further decreases in
elk abundance (Garrott et al. 2013; White and Garrott 2013). However,scientists are continuing to evaluate the role of bison as an alternate prey
because wolves may begin to kill more bison if elk numbers decrease
further (Carbyn and Trottier 1987; Hebblewhite and Smith 2010; Garrott et al. 2013).

Conclusions
The role bison historically served in grassland ecosystems disappeared
as society killed them to near extinction and usurped most of theirhabitat for agricultural, recreational, and residential development (Lott2002; Franke 2005; Freese et al. 2007; Bailey 2013). While there are now
more than 400,000 bison in private and commercial herds used formeat production, the number of bison in conservation herds (less than
20,000) has not increased substantially since the 1930s (Freese et al.
2007). Thus, while the physical form of bison remains throughout theGreat Plains, most of these animals provide reduced ecological functions on a much smaller spatial scale (Plumb and Dodd 1993; Lott 2002;
White and Wallen 2012; Bailey 2013; Kohl et al. 2013). As a result, wild
land preserves like national parks and wilderness areas will continue
to provide the core conservation areas where wild bison fulfill the ecological role their ancestors played in shaping the species we see today(White and Wallen 2012). However, we are also encouraged that public
land agencies, non-governmental organizations, American Indian tribes,
and private landowners are working to build on this core by establishingor expanding wild, wide-ranging populations of bison in several areas
where conflicts with humans can be minimized across large landscapes.

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Bison moving snow with
its head to feed.

Chapter 8
ADAPTIVE CAPABILITIES AND GENETICS
Rick L. Wallen and P.J. White

Today, thousands of Yellowstone bison move across a large landscapeand are exposed to natural selection factors such as competition, predation, and severe environmental conditions (Darwin 1859; Plumb et
al. 2009). However, this population was nearly extirpated by humans in
the late 1800s and culled periodically during the last century (Cahalane
1944; Meagher 1973; White et al. 2011). As a result, there are concerns
about the genetic integrity of the population (Halbert et al. 2012). In
this chapter, we describe the existing genetic diversity in Yellowstonebison and discuss its preservation to ensure descendants have theability to adapt to a changing environment.

Near Eradication
Yellowstone bison experienced a population bottleneck in the late
1800s due to human exploitation (Plumb and Sucec 2006). There
were less than 25 indigenous bison in Yellowstone National Parkby 1902, all in the central region of the park (Pelican Valley). This

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Yellowstone Bison: Conserving an American Icon in Modern Society

population persisted at relatively low numbers (less than 500 bison)
for many decades (Meagher 1973). A population that is reduced toa small number of animals contains less genetic variation than theoriginal, larger population — known as the founder effect (Allendorf
and Luikart 2007). Thereafter, chance losses of genetic variation may
continue due to inadequate gene flow with other populations. Overtime, these losses can reduce the abilities of animals to adapt to newenvironmental challenges (Allendorf and Luikart 2007).
Fortunately, Yellowstone bison do not show the effects of inbreeding and they have retained significant amounts of genetic variation
as measured by heterozygosity and allelic diversity (Allendorf andLuikart 2007; Halbert et al. 2012; Wallen et al. 2013). This high genetic
diversity despite near extirpation may be due to the restoration of a
new herd in northern Yellowstone during 1902 from unrelated bisonthat eventually interbred with the indigenous bison in central Yellowstone (Dratch and Gogan 2010; White and Wallen 2012). The unrelatedbison came from the Pablo-Allard herd (18 females) in northwestern
Montana and the Goodnight herd (3 bulls) in Texas (Cahalane 1944;
Meagher 1973).
The remnant, indigenous bison in central Yellowstone were once
thought to be mountain bison or wood bison (Meagher 1973). However, Wilson and Strobeck (1999) concluded these bison were plainsbison based on genetic differences with other populations (also seeFranke 2005). Today, Yellowstone bison contribute an important
genetic lineage to plains bison that is not found elsewhere, except in
populations started with bison relocated from Yellowstone National
Park (Halbert and Derr 2008). Yellowstone bison have high genetic
diversity compared to many other populations of plains bison, and are
one of only a few bison populations with no evidence of interbreeding with cattle (Halbert 2003; Halbert and Derr 2007). However, thepopulation remains isolated because bison rarely move between Yellowstone National Park and the Jackson population in Grand Teton
National Park and the National Elk Refuge — even though there areno barriers to such movements.

Adaptive Capabilities and Genetics

121

NPS/Neal Herbert

Bull bison near Yellowstone’s
Lamar Valley.

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Yellowstone Bison: Conserving an American Icon in Modern Society

NPS/Neal Herbert

Bison scratching on waysidedisplay in Yellowstone’s
Hayden Valley.

Adaptive Capabilities and Genetics

Population Subdivision
Yellowstone bison congregate in two primary areas for breeding; theHayden and Pelican valleys in the central region of the park, and theLamar Valley and adjacent plateaus in the north (Olexa and Gogan
2007; Halbert et al. 2012). Analyses of mitochondrial DNA haverevealed a minimum of two haplotypes in Yellowstone bison (Wardet al. 1999; Gardipee 2007). Haplotype 6 was found in 88 of 94 (94percent) bison sampled from central Yellowstone and 29 of 57 (51percent) bison from northern Yellowstone. Haplotype 8 was foundin 6 of 94 (6 percent) bison from central Yellowstone and 28 of 57 (49percent) bison from northern Yellowstone (Gardipee 2007; Wallen etal. 2013). Bison with haplotype 6 carry a double mutation that affects
two genes: Cytochrome b and ATP6 (Pringle 2011). This mutation isinherited and could reduce aerobic capacity by affecting the production and transport of energy within cells (Pringle 2011). However, no
symptoms have been observed in Yellowstone bison, which have highbirth and survival rates despite living in a predator-rich environment
with severe winter conditions (see Chapter 5). Thus, it is unlikely
this mutation is being expressed and causing metabolic deficiencies.
Alternatively, there are often multiple pathways in biological systems
that alleviate or circumvent potential metabolic deficiencies. Regardless, the National Park Service is collaborating with Dr. James Derrof Texas A&M University to determine the diversity of mitochondrial
DNA haplotypes in the population and evaluate the consequences ofmutations that could lead to mitochondrial diseases.
Bison that live in the central and northern regions of Yellowstone
have significantly different distributions of alleles and genotypes,
and are genetically distinguishable based on 20 alleles only found in
one of the two regions (14 central; 6 northern; Halbert et al. 2012).
This substructure was likely created and sustained by several events,
including: (1) the population bottleneck caused by nearly extirpating
Yellowstone bison in the late 19th century, (2) the creation of anotherbreeding herd in northern Yellowstone from bison of unrelated breeding ancestry, and (3) human management thereafter (Meagher 1973;

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Yellowstone Bison: Conserving an American Icon in Modern Society

White and Wallen 2012). Analyses of mitochondrial DNA suggest theseregional genetic differences have been maintained by strong female
philopatry to breeding areas, with most females returning to the same
area each year (Gardipee 2007; Wallen et al. 2013). Also, analyses of
microsatellite DNA suggest there were only about two emigrants per
decade between the two regions during the 20th century (Halbert
et al. 2012).
In the past decade, there has been substantial dispersal of bison
between central and northern Yellowstone and subsequent gene flow
could lessen these regional genetic differences (White and Wallen2012). Since 2007, 22 of 114 radio-collared, female bison have emigrated
from central Yellowstone to the northern region, or vice versa, andremained through one or more breeding seasons (White and Wallen
2012; Wallen et al. 2013). Each of these females could represent morethan one dispersing individual because bison tend to move throughthe ecosystem in groups of 20 or more (USDI, NPS 2010). Monitoringdata supports that 18 of these 22 radio collared females got pregnant
on the destination range and produced 44 offspring over several years.
In addition, at least 6 of these females brought calves to their destination range that were conceived on their range of origin (White andWallen 2012; Wallen et al. 2013 updated). Many of these calves likely
survived to reproductive age given the high survival of Yellowstone
calves through their first year (0.65) and thereafter as adults (0.93; see
Chapter 5 and Table 7.1). These observations of female emigration andsubsequent reproduction on a new breeding range support estimatesof 10 to 20 genetic migrants per decade based on recent sampling of
microsatellite genotypes (Wallen et al. 2013).

Retention of Genetic Diversity
The rate at which genetic diversity is lost from populations is directly
related to generation time and the size of the breeding population(Allendorf and Luikart 2007). Increased loss of genetic diversity
can occur from non-random mating, large variations in abundance,skewed sex ratios, and non-random culling that disproportionately

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125

Photograph courtesy of National Geographic by Michael Nichols

Bull bison fighting during
the breeding season in
Yellowstone National Park.

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Yellowstone Bison: Conserving an American Icon in Modern Society

influences a particular population segment (Pérez-Figueroa et al.
2012). Population substructure, such as distinct breeding herds, canreduce rates of gene flow and the formation of new combinations ofgenes, as well as result in a non-random harvest or culling of animals
that increases the loss of genetic diversity (Allendorf and Luikart
2007; Allendorf et al. 2008). However, population subdivision withmoderate dispersal rates among subpopulations can minimize the rateof loss of genetic diversity (Allendorf and Luikart 2007). Thus, theThe future viabilityof Yellowstonebison depends on
maintaining large
enough breeding herds
to retain sufficient
genetic heterozygosity,
allelic diversity, andgene flow to enablebison to adapt to achanging environment.

future viability of Yellowstone bison depends on maintaining large
enough breeding herds to retain sufficient genetic heterozygosity,
allelic diversity, and gene flow to enable bison to adapt to a changing environment (Gross et al. 2006; Freese et al. 2007; Bailey 2013).
To preserve genetic variation over centuries, the bison conservation initiative by the U.S. Department of the Interior and the North
American conservation strategy for bison by the International Union
for the Conservation of Nature recommended that population (orsubpopulation) sizes should be at least 1,000 bison, with approximately equal sex ratios to ensure considerable competition between
breeding bulls (Dratch and Gogan 2010; Gates et al. 2010; Gross et al.
2010). These organizations also defined a wild bison population as one
with sufficient numbers to prevent the loss of genetic variation, lowlevels of cattle introgression, and exposure to some forces of natural
selection, including competition for breeding opportunities (Dratchand Gogan 2010; Gates et al. 2010). Currently, bison in Yellowstone are
the only population of plains bison that meet these objectives, withmore than 1,000 bison congregating in both the central and northern
regions of Yellowstone during the breeding season and hundreds ofmature males competing for breeding opportunities (Pérez-Figueroa
et al. 2012; Bailey 2013). However, analyses considering the importanceof male reproductive success and fluctuating population size on thepossible loss of genetic variation in Yellowstone bison indicate that it
may be prudent to manage for at least 3,000 to 3,500 total bison overdecades to preserve existing diversity for hundreds of years (PérezFigueroa et al. 2012). Though these estimates are derived from the bestAdaptive Capabilities and Genetics

available information, they incorporate a fair amount of uncertainty
due to the lack of validation over many bison generations and acrossvariations in abundance. Thus, this is an area of active research byscientists. There are currently minor concerns about the introgressionof cattle genes into Yellowstone bison given that spatial and temporalseparation is maintained between them and few cattle wander into
the park. However, such concerns may amplify if and when bison aretolerated outside the park during summer and autumn and cattle aregrazed in nearby areas.
Intensive management actions near the boundary of Yellowstone
National Park to reduce the risk of brucellosis transmission to cattle
could potentially result in a substantial loss of genetic diversity in
Yellowstone bison and affect population substructure (Halbert 2003;
Gates and Broberg 2011; Halbert et al. 2012; Bailey 2013). Sporadic
culls of more than 1,000 bison in some winters differentially affectedbison from the central region by removing more females and dampening productivity (White et al. 2011; Treanor et al. 2013). Similar
non-random culls could differentially influence the genotype diversity
and allelic distributions of bison living in the central and northern
regions of the park (Halbert et al. 2012). Therefore, managers agreed
to minimize future large-scale culls of bison, evaluate how the genetic
integrity of bison may be affected by management removals, and assess
the genetic diversity necessary to maintain a robust population thatis able to adapt to future conditions (USDI, NPS et al. 2008; PérezFigueroa et al. 2012; White and Wallen 2012). In addition, the National
Park Service developed a rigorous monitoring plan for Yellowstonebison that includes randomly sampling bison from the central andnorthern regions across decades to identify genetic subdivisions
and estimate gene flow within the population (White et al. 2014).
Furthermore, each winter biologists use radio telemetry, groundobservations, and aerial distribution surveys to track movementsof bison and attempt to differentiate animals from the central andnorthern regions when they approach the boundary of the park andbecome subject to management actions (White and Wallen 2012).

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Yellowstone Bison: Conserving an American Icon in Modern Society

This approach does not provide absolute certainty with respect
to region of origin, but it has been relatively effective for estimating
the proportion of culls from bison breeding in each region (Whiteet al. 2011).
Some scientists maintain the National Park Service should actively
manage to preserve genetic differences between bison in the central
and northern regions of Yellowstone (Halbert et al. 2012). We agree theconservation of genetic diversity is extremely important, but question
whether the preservation of a population or genetic substructure created and facilitated by humans should be the goal (White and Wallen2012). Rather, we propose ecological processes such as natural selection, migration, and dispersal be allowed to prevail and influence how
the population and genetic substructure is maintained into the future(White and Wallen 2012). Bison from the central region of Yellowstonebegan dispersing to northern Yellowstone in the 1980s and dispersal
movements between these regions have increased in the past decade(Fuller et al. 2007a; Geremia et al. 2011; White and Wallen 2012). Geneflow between these regions could lessen the effects of population
substructure and non-random culling on the loss of genetic diversity(Wallen et al. 2013). Current management actions attempt to preservebison migration to essential winter range areas within and adjacent toYellowstone National Park, as well as bison dispersal between the central and northern regions, which bison reestablished after a century ofprotection, husbandry, and intensive management (White et al. 2011).
The current population distribution and genetic substructure may or
may not be sustained over time through ecological and evolutionary
processes (White and Wallen 2012). The bison will determine that.

Conclusions
Debate about the population or breeding herd sizes necessary topreserve genetic diversity in Yellowstone bison is contentious at times,
and has been included in litigation proceedings (e.g., U.S. District
Court for the District of Montana, Missoula Division 2011). Genetic
variation is influenced by the interactions of: (1) natural selectionAdaptive Capabilities and Genetics

for individuals that survive environmental variability, (2) gene flow
through movement of individuals between populations, (3) mutations
that occur on the DNA of individuals, and (4) genetic drift due to therandom nature of mating (Allendorf and Luikart 2007). Some genetic
change due to culling by humans is inevitable (Allendorf et al. 2008).
Removals of Yellowstone bison via non-random harvest or culling
have the potential to cause genetic change by altering population-wide
allele frequencies and population subdivision characteristics (Halbert
et al. 2012). However, the maintenance of large breeding herds andtotal population size, along with monitoring genetic diversity overtime, will provide managers with information regarding the influenceof management actions on genetic diversity (White and Wallen 2012;
Wallen et al. 2013). Given the importance of male reproductive successand population size on the loss of genetic variation, we recommend
managing for at least 3,000 to 3,500 total bison over decades, while
minimizing selective culling and preserving opportunities for bison
migration and dispersal between the central and northern regions of
the park (Pérez-Figueroa et al. 2012). These genetic objectives should
be revised over time as new information is gained.

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NPS/Jim Peaco

Lakota Sioux spiritual leaders
conduct a ceremony in thenorthern region of Yellowstone
National Park to honor bison.

Chapter 9
CULTURAL IMPORTANCE
Rick L. Wallen, P.J. White, and Tobin W. RoopPortions of the Great Plains and Rocky Mountains in the Yellowstone area were part of the natural range of bison from prehistoric
times. This region is also the homeland of various native peoples whohunted bison as herds moved across the landscape. Archeologicalevidence indicates the earliest human occupation in the Greater Yellowstone Area occurred about 11,000 years ago, though the oral historyof some American Indian tribes suggests they occupied the lands
much longer (Nabokov and Loendorf 2002, 2004). At least 10 tribes
lived and hunted in the Greater Yellowstone Area during both historicand prehistoric times, including the Crow, Eastern Shoshone, Salish
and Kootenai, Shoshone-Bannock, Blackfeet, Nez Perce, Northern
Arapaho, and Northern Cheyenne (Nabokov and Loendorf 2002,
2004). An additional 16 American Indian tribes claim association with
the Yellowstone region and some First Nations of Canada (Blackfoot,Blood, Piegan, and Assiniboine) also hunted in the region. As late as
the 1880s, a band of Shoshone known as the Sheepeaters occupied

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Yellowstone Bison: Conserving an American Icon in Modern Society

portions of the area designated as Yellowstone National Park in 1872
(Nabokov and Loendorf 2002, 2004).7
After westward expansion by Euro-Americans, treaties with the
U.S. government limited the use of lands within the Greater Yellowstone Area by native peoples. Pursuant to the Treaty of Fort Laramie
in 1851, the areas now known as Yellowstone National Park, Gallatin
National Forest, Bridger-Teton National Forest, and Shoshone National
Forest were reserved for some Plains Indian tribes. The land west of

Bison are considered
ancestors and relatives
by some tribes who, in
response for the gift oflife provided by bison,
retain an obligation toserve as their guardians.

the Yellowstone River was used by the Blackfeet tribes (Piegan andBlood), land to the southeast was part of the Crow territory, and landnear the upper Missouri River was a common hunting area for thosetribes and the Gros Ventre, Flathead, Upper Pend d’Oreille, Kootenai,
and Nez Perce tribes (Nabokov and Loendorf 2002, 2004). AnotherFort Laramie Treaty in 1868 removed much of this land from tribal
control, but allowed hunting by the tribes on open and unclaimed
federal lands (Nabokov and Loendorf 2002, 2004). Treaties with the
Shoshone-Bannock tribes did not mention the Yellowstone area, but
did reference hunting on open and unclaimed lands in the UnitedStates. These tribes lived and hunted in the Yellowstone area until
the end of the 19th century (Nabokov and Loendorf 2002, 2004). By
the 1870s, most tribes were decimated by disease and rapid culturalchange, disorganized, and merely trying to survive Euro-American
expansion. After Yellowstone National Park was established in 1872,
administrators actively discouraged native peoples from using thepark, thereby ensuring their influences on the landscape waned andeventually disappeared (Nabokov and Loendorf 2002, 2004).

Importance of Bison to Native Peoples
Bison were central to the culture of native peoples living or hunting in
the Yellowstone area because they provided food, clothing, fuel, tools,
shelter, and spiritual value. However, the slaughter of bison herds bycolonizing Euro-Americans altered this relationship and resulted in
7
Portions of this chapter regarding native peoples and bison were adapted from
USDI, NPS (2010, 2014).

Cultural Importancedecimated, localized populations of both bison and American Indians(Isenberg 2000). Yellowstone bison are special to many tribes because
they are the last living link to the indigenous herds of bison that onceroamed across North America (USDI, NPS 2010). These tribes view
Yellowstone bison as inextricably linked to their existence and survival as indigenous peoples (Plumb and Sucec 2006). The bison are
considered ancestors and relatives by some tribes who, in response
for the gift of life provided by bison, retain an obligation to serve as
their guardians (Plumb and Sucec 2006). Bison represent power andstrength and are sometimes viewed as an earthly link to the spiritual
world (USDI, NPS 2010).
Some American Indians believe Yellowstone bison have been treatedunjustly, similar to native peoples during Euro-American colonizationof this country (USDI, NPS 2010). They accurately point out Yellowstone bison are managed differently than other wildlife because someindividuals have brucellosis, while elk infected with the same disease
are not subject to similar actions (USDI, NPS 2010). As a result, some
native people believe the treatment of bison reflects sentiments towards
American Indians (Stone 2013). The management of Yellowstone bisonhas also elicited protests by tribal members and governments (Ruppert
1997). In 1999, approximately 50 American Indians representing several
tribes walked from Rapid City, South Dakota to the north entranceof Yellowstone National Park. They performed a ceremony honoring
Yellowstone bison that included cutting the flesh on the backs of sometribal members and traditional songs and prayers (Joss 1999; Tarkaand Sattler 2008).
The federal government is charged with acting in the best interest(i.e., trust responsibility) of American Indian tribes to protect aboriginal
and treaty rights that stem from their original occupation of the landand negotiated and written treaties with the United States government(Meyers 1991; Garrott 2014). The National Park Service consults with
26 American Indian tribes that claim some level of association with
Yellowstone National Park (Figure 9.1). Twenty of these 26 groups
are current members of the InterTribal Buffalo Council, which is a

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Yellowstone Bison: Conserving an American Icon in Modern Society

federally chartered organization established in 1990 to restore bison to
American Indian tribes. Another 50 plus tribes across the United States
have some interest in bison management. Tribal representatives haverelated many concerns about the management of Yellowstone bison,
including: (1) respectful treatment of the bison, (2), allowing bison toroam freely without fencing or hazing, (3) transferring brucellosis-freebison to the tribes, (4) distributing meat, skulls, and hides of bison thatare killed to the tribes, (5) preservation of wickiups, stone alignments,and other cultural features associated with bison, and (6) employmentof tribal interns in bison management programs (USDI, NPS 2010).
The frequent occurrence of diabetes on American Indian reservations has motivated a return to a more-traditional, bison-based dietin recent years. As a result, meat from bison culled inside Yellowstone
National Park is distributed primarily to American Indian tribes.
During 2008, for example, about 258,548 kilograms or 570,000 poundsof bison meat was distributed to 46 tribes and civic food banks (Lewis
et al. 2009). The National Park Service currently has agreements withthree tribes and a tribal organization to periodically provide them with
Yellowstone bison for direct transfer to approved meat processing
facilities and subsequent distribution of meat, hides, horns, and otherbison parts to their members. Also, several tribes conduct subsistencehunts for bison on open and unclaimed federal lands adjacent to thepark in Montana (MFWP 2006a,b, 2009, 2010b). In addition, theNational Park Service and several American Indian tribes are exploring the establishment of quarantine facilities where Yellowstone bison
can undergo testing for exposure to Brucella bacteria and be released
elsewhere if they repeatedly test negative (Salazar 2012).

Euro-American Colonization
Bison also define the Euro-American experience because they were
central to national expansion and their products were importantelements of trade. Bison occupied the landscape of the Great Plains
in large numbers (25 to 30 million by some accounts; Shaw 1995;
McHugh 1972; Lott 2002). Early pioneers used bison trails to traverse

Cultural Importance135

the landscape, dung to build cooking fires, meat for food, and hides tomake clothes and blankets (Isenberg 2000). By 1820, bison became amarketable commodity and great numbers were killed so their hides
could be exported to the eastern United States and Europe (Hornaday 1889). Also, the government learned that many tribal cultures
depended on bison for their subsistence, and used this information
to exploit and conquer them (Wooster 1988; Isenberg 2000).
As numbers of plains bison dwindled, several people captured a
few animals to preserve the species (Coder 1975; Isenberg 2000). For
example, a Pend d’Oreille Indian named Walking Coyote brought four
calves across the continental divide to the Flathead Valley of Montana,where they were propagated by Michel Pablo and the descendants ofCharles Allard. Some of these bison were later reintroduced into thenorthern portion of Yellowstone National Park (Cahalane 1944). In
addition, the U.S. Army protected a small indigenous herd of bisonthat survived in the central region of Yellowstone (Cahalane 1944).
Public sentiment to prevent the extinction of bison was widespreadand restoration efforts gained momentum after the Lacey Act of 1894
provided legal protection for bison remaining in Yellowstone (Coder
1975; Gates and Broberg 2011). Thereafter, the American Bison Society,
Bronx Zoo, and the New York Zoological Society initiated programs
to propagate and restore bison elsewhere (American Bison Society
1909; Hornaday 1921; Coder 1975).
The debate over bison conservation contributed significantly tothe development of our national conservation ethic based on public
ownership of wildlife and the national park system (Plumb and Sucec
2006). Congress clearly indicated that the purpose of national parks
is to preserve cultural and natural resources, and bison became asymbol of this ideal. Bison restoration at Yellowstone National Parkwas underway by 1902, and in 1913 plains bison were introduced to
the Wind Cave Game Preserve, which was later incorporated intoWind Cave National Park (Sellars 1997). Thereafter, the American
Bison Society continued to establish preserves across the former
range of the species. Because bison were a well-known symbol for

NPS/Neal Herbert

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Yellowstone Bison: Conserving an American Icon in Modern Society

conservation, the National Park Service included a bison on its emblem
in 1952 (Workman 1997).

The Changing West
Many wildlife species are highly valued in rural areas of western North
America, and sportsman in these communities have been instrumental
in their conservation and restoration — including in the Greater Yellowstone Area (e.g., Picton and Lonner 2010). Agriculture, mining,
and timber harvest are traditional occupations and important to theeconomy (Montana Department of Commerce 2006; Bidwell 2010).
People are well aware that their livelihoods depend on conserving thenatural environment, but a good economy is often a higher priority
when conflicts arise (Bergstrom and Harrington 2013). As a result, large
ungulates like bison can be considered direct competitors for a valuable commodity — real estate and the grass that grows there (Isenberg
2002; Lott 2002; Franke 2005). Also, ranchers are more likely than otherresidents to believe that bison will infect cattle with brucellosis (Morrisand McBeth 2003). Therefore, restoring wild bison to public lands is
an appalling thought to some people because it is seen as a detriment
to the economy and a threat to their way of life, property rights, andability to graze cattle on public lands (McDonald 2001; Bienen and Tabor2006). Likewise, some members of American Indian tribes prefer toraise livestock to feed their families and generate income, rather thanrestore wild bison to tribal lands (Hatfield et al. 2013).
In recent decades, many rural areas in the intermountain west havebecome more demographically and economically diverse, with recreation, tourism, and amenity living competing with agriculture andnatural resource extraction economies (Haggerty and Travis 2006;
Hansen 2009). The Greater Yellowstone Area is no exception and many
new residents are migrants from other regions across the country where
living with wildlife is a novelty (Hansen et al. 2002; Johnson and Stewart2005). As a result, more residents in these communities now consider
the environment and wildlife viewing to be primary economic assets(Morris and McBeth 2003). These residents are also less likely to believe

Cultural Importancethat bison will transmit brucellosis to cattle (Morris and McBeth 2003).
Hence, there are often differences of opinion about bison management
between residents that are tourism-based and those that are agricultural-based (Bergstrom and Harrington 2013).
While these portrayals are exaggerated (Robbins 2006; Bidwell 2010),
there is little doubt tourism is now a major driver of the economy in the
Greater Yellowstone Area. Visitors to national parks and other public
lands provide substantial economic influx to surrounding communities(Cullinane Thomas et al. 2014). For example, visitors to Yellowstone
National Park during 2012 spent more than $400 million in local communities, which supported about 5,600 jobs and generated $473 million
in combined visitor and workforce sales (value of industry production/
output), $165 million in labor income (wages, salaries, payroll benefits),
and $272 million in value added (labor income plus profits, rents, andsales and excise taxes; Cullinane Thomas et al. 2014). About 50 percent
of surveyed resident and non-resident visitors indicated seeing bison
was a reason for their trip, and about 5 percent said they would not havecome to the area if bison had not been present (Duffield et al. 2000a,b).

Conclusions
Despite their biological and cultural importance, bison are the only wild
North American ungulate that has not been recovered across significant
portions of their historic range (Lott 2002; Freese et al. 2007; Bailey2013). Unlike bighorn sheep, caribou, deer, elk, moose, mountain goats(Oreamnos americanus), and pronghorn (Antilocapra americana), bison
receive little tolerance on private or public lands outside of nationalparks and refuges. Thus, they have failed to gain legitimate status as
wide-ranging wildlife and their conservation is constrained by real andperceived conflicts (Lott 2002; Plumb and Sucec 2006; Bailey 2013). For
most of the 20th century, as Yellowstone bison recovered from near
extirpation, they did not regularly and extensively venture outside Yellowstone National Park (Meagher 1973). This led to the beliefs bisonshould remain in the park, and they only leave when large numbers
overgraze the grasslands (Plumb et al. 2009; Becker et al. 2013). These

137

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Yellowstone Bison: Conserving an American Icon in Modern Society

beliefs have been reflected in the treatment of bison as livestock inmany areas outside the park (Franke 2005; Plumb et al. 2009; Bailey
2013; Becker et al. 2013).
Conflicts between agricultural, political, and wildlife conservation
values are a century old challenge for society. The most successful
wildlife conservation measures account for the diversity of values heldby society, and conflicts are resolved through education, negotiation,and creative actions. As the United States progresses further into thethird century of its existence, acknowledgment of the historical conditions that challenged native peoples and Euro-American pioneers
will be an important cultural value to society. Also, preservation of
one of the last unfenced, wide-ranging bison populations subject tonearly all the evolutionary pressures from which their descendants
evolved would be a tremendous achievement that could invigorate therestoration of the ecological role of plains bison as a species in western
North America (USDI, NPS 2011; Bailey 2013). As a worldwide leader
in wildlife conservation, the National Park Service will continue toadvocate for the conservation of wild bison and the processes thatsustain them at ecosystem scales. Long-term success in this endeavor
will come through effective partnerships with American Indian tribes,
federal and state agencies, private landowners, and other interested
stakeholders that incrementally increase tolerance for bison in moreareas based on successful management that addresses concerns andallows people’s perceptions of these icons of western America to change(White et al. 2013c).

Cultural Importance

Figure 9.1. American Indian tribes associated with Yellowstone National Park (YNP).

139

NPS/Jim Peaco

Staff on horseback hazing
bison near Undine Falls
in the northern region of
Yellowstone National Park.

Chapter 10
CURRENT MANAGEMENT — ATTEMPTINGTO BALANCE CONSERVATIONWITH DISEASE CONCERNS
P.J. White, Rick L. Wallen, David E. Hallac, Chris Geremia,
John J. Treanor, Douglas W. Blanton, and Tim C. Reid

The restoration of Yellowstone bison has been extremely successful,with many scientists considering them the only ecologically viable
population of plains bison in the United States (Freese et al. 2007;
Sanderson et al. 2008; Gates et al. 2010). There is local and national
support for allowing these wild bison to migrate and disperse to newareas outside Yellowstone National Park (Franke 2005; Bailey 2013).
However, there is also substantial resistance to this prospect, especiallyfrom the local agricultural community (Montana Sixth Judicial Court,
Park County 2013). Managing these massive, unfenced, wild animals
in close proximity to humans can be challenging at times and involve
substantial investments of time, effort, and money to keep bison awayfrom areas where they are not tolerated. Moreover, there are concerns

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Yellowstone Bison: Conserving an American Icon in Modern Society

about the safety of humans near bison; damage to property such as
fencing, landscaping, and vehicles; overgrazing of habitats also usedby livestock and other wild ungulates; and brucellosis transmission
to cattle (Lott 2002; Boyd 2003; Rhyan et al. 2009).

Interagency Bison Management Plan
Due to these concerns, the federal government and the State ofMontana agreed in 1992 to prepare a long-term management planfor Yellowstone bison. Progress on the plan was slower than anticipated, and in 1995, the State sued the National Park Service and theAnimal and Plant Health Inspection Service over the delay. The parties
subsequently agreed to a schedule for completing the plan, and a draft
was developed and released for public review in 1998. After reviewing
public comments, the federal agencies presented a modified plan to theState that allowed for a larger bison population and greater tolerance
for bison outside the park. The State did not agree and the parties
engaged a mediator to help resolve their differences. This mediation
resulted in the completion of the Interagency Bison Management
Plan in 2000 that established guidelines for cooperatively managing
the risk of brucellosis transmission from Yellowstone bison to cattle,
while conserving a wild bison population and allowing some bison to
occupy winter ranges on public lands in Montana (USDI, NPS and
USDA, USFS, APHIS 2000a; see Chapter 3 for details).
When the Interagency Bison Management Plan was developed, theState of Montana was under tremendous pressure to keep brucellosis
out of livestock to comply with free trade agreements benefitting
the cattle industry (Bidwell 2010). Therefore, any chance of brucellosis transmission from bison to cattle was unacceptable to livestock
regulators (Bidwell 2010). In fact, regulators and elected officials
intensified misperceptions that Yellowstone bison posed a high risk
to cattle by transferring authority for bison management in Montanafrom wildlife to livestock managers and making the brucellosis-freestatus of livestock a condition in trade agreements (Bidwell 2010).
These misperceptions and actions had substantial impacts on theCurrent Management

management of Yellowstone bison because the Interagency Bison
Management Plan is primarily about minimizing the risk of brucellosis transmission to cattle, not the conservation and restoration ofbison (Keiter 1997; Bidwell 2010).
Since 2000, many circumstances that influenced the derivationand implementation of the Interagency Bison Management Plan havechanged, and scientific knowledge regarding bison and brucellosis has
improved substantially. These changes and advances are summarized
in the following bullets (see Chapters 2 and 3 for details and citations):•

Four American Indian Tribes asserted their treaty rights to
conduct subsistence hunts of bison in southwestern Montana.

•

There are fewer cattle adjacent to Yellowstone National Park,
particularly on the Royal Teton Ranch (north) and Horse Butte(west). Also, cattle grazing may be delayed on the Watkins Creek
and South Fork allotments (west) if bison are present.

•

The Animal and Plant Health Inspection Service implemented
regulations whereby brucellosis outbreaks in cattle are dealt
with on a herd-by-herd basis. As a result, the entire state
does not lose its class-free brucellosis status due to one ormore outbreaks.

•

The states of Idaho, Montana, and Wyoming designated surveillance areas for brucellosis that were defined by occurrence of thedisease in elk. These areas benefit the livestock industry because
producers therein are reimbursed for brucellosis testing costs
and unnecessary testing is not required elsewhere in the states.

•

Calf-hood vaccination of cattle has been implemented with highcompliance in the designated surveillance area in Montana.

•Experimental studies indicated bull bison are not brucellosis
transmission vectors.

•

The prevalence of brucellosis in elk and the frequency of transmission from elk to cattle have increased. As a result, several
independent studies determined that the risk of brucellosis
transmission from bison to cattle was minute compared to therisk from elk.

143

144

Yellowstone Bison: Conserving an American Icon in Modern Society•

A quarantine feasibility study was conducted and successful,with the surviving bison and their offspring being declared brucellosis free and transferred elsewhere for conservation andcultural purposes.

•

There were significant changes in bison movement patterns anddistribution, with more bison migrating and dispersing to thenorthern portion of the park. Large migrations into Montana
during severe winters resulted in property damage and humansafety concerns, as well as large culls of bison.

•

There was increased concern by bison managers, American
Indian tribes, and the public about killing bison in the third
trimester of pregnancy.

•

Studies indicated many older bison testing positive for brucellosis exposure were no longer infectious and may have someresistance to the disease if reexposed.

•

American Indian tribes and a tribal organization became involved
with the management of Yellowstone bison, including developing an annual operating plan, conducting subsistence hunts,
relocating brucellosis-free bison to tribal lands, and distributing
meat, hides, and horns from culled animals to their members.

•

Several independent evaluations recognized that the substantial suppression of brucellosis through vaccination would be
extremely difficult with existing vaccines and delivery technologies. As a result, the National Park Service decided not to initiate
the remote vaccination of bison.

These changed circumstances and improved knowledge led toseveral adaptive management adjustments to the Interagency Bison
Management Plan. Annual public and tribal hunts were initiated inMontana. Actions such as strategic hazing of bison from conflict areas
to suitable habitat, and financial aid for fencing, were implemented toreduce conflict with landowners and livestock operators. In addition,
there was increased tolerance for more bison in Montana across alarger conservation area, especially for bull bison due to their lower
risk of brucellosis transmission. Furthermore, managers attempted toCurrent Management

reduce shipments of bison to meat processing plants by using alternate tools such as hazing, hunting, and increased tolerance. Detailsof these adaptive adjustments are provided in Chapter 3.

Management Tools and Operations
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. Bison numbers are supposed
to be regulated near an end-of-winter guideline of 3,000 (USDI, NPS
and USDA, USFS, APHIS 2000a; Interagency Bison Management Plan
Partner Agencies 2006). During June and July, biologists conduct counts
and age and gender classifications of bison in the central and northern
regions of Yellowstone (Hess 2002; Tables 10.1 and 10.2). Biologists
then use long-term weather forecasts and population and migration
models to predict bison abundance and composition by region at theend of the upcoming winter, as well as the numbers of bison likely to
migrate to the park boundary (Geremia et al. 2013, 2014a). The partners
use these predictions to establish annual removal objectives for bison
based on abundance, distribution, and demographic goals. During thefollowing winter, biologists use aerial and ground counts, snow model
projections, and revised weather forecasts to refine predictions of thetiming and magnitude of bison migrations and support decision-making(Interagency Bison Management Plan Members 2013).8
A variety of management tools are used to reduce bison numbers
towards 3,000, including: (1) public and treaty harvests in Montana,(2) capture and culling near the park boundary, and (3) shooting or
capture in Montana. Captured bison are shipped to meat processing
or research facilities. No quarantine facilities or terminal pastures are
currently operational. Biologists monitor bison abundance through thewinter and compile information on hunter harvest, management culls,
predation off-take, and winter-kill. If numbers of bison decrease to
8
Portions of this section contain excerpts, with permission, from various documents written in collaboration with the other members involved with the Interagency
Bison Management Plan. The cited documents are available at http://ibmp.info/.

145

146

Yellowstone Bison: Conserving an American Icon in Modern Society
Central herd

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

Northern herd

Total

AdultsCalves

Total

AdultsCalvesJune 4, 2000

2,060

1,734

326

553

460

93

July 13, 2000

2,118

590

August 31, 2000

2,084

529

June 21, 2001

2,599

553

104

July 25, 2001

2,564

June 25, 2002

3,100

477

71

July 29, 2002

2,901

813

August 22, 2002

3,238

807

July 10, 2003

2,905

748

125

August 8, 2003

2,923

888

August 28, 2003

2,772

994

July 21, 2004

2,811

July 28, 2004

3,027

968

August 4, 2004

3,339

876

July 19, 2005

3,553

1,266

July 26, 2005

3,394

1,353

August 1, 2005

3,531

1,484

July 19, 2006

2,430

July 26, 2006

2,512

1,377

August 2, 2006

2,496

1,279

June 14, 2007

2,734

1,499

321

July 30, 2007

2,390

1,569

August 6, 2007

2,624

2,070

June 14, 2008

1,115

1,463

325

July 8, 2008

1,540

1,341

July 15, 2008

1,469

1,500

June 12, 2009

1,462

1,520

319

July 9, 2009

1,544

1,433

July 16, 2009

1,535

1,648

June 14, 2010

1,653

1,890

355

July 8, 2010

1,735

1,980

July 22, 2010

1 ,7 1 3

1 ,8 5 0

2,190

469

657
719

2,560

2,471

2,310

2,146

2,385

1,052

1,293

1,426

540

434

501

284

349

103

169

227

548

873

1,337

1,283

1,820

1,788

1,839

2,245

Current Management
Central herd

2011

2012

2013

2014

Northern herd

Total

AdultsCalves

Total

AdultsCalvesJune 21, 2011

976

880

96

2,675

2,188

487

July 18, 2011

1,406

2,314

July 25, 2011

1,335

2,150

June 21, 2012

1,389

2,103

393

July 8, 2012

1,640

2,531

July 22, 2012

1,561

2,669

June 6, 2013

1,338

2,620

534

July 15, 2013

1,504

3,420

July 22, 2013

1,337

3,228

June 20, 2014

1,338

2,928

591

July 18, 2014

1,448

2,938

July 25, 2014

1,444

3,421

1,188

1170

1,190

201

168

148

2,496

3,154

3,519

Table 10.1. Annual counts of bison in the central and northern regions of Yellowstone
National Park during June through August from 2000 to 2014 (Geremia et al. 2014a).

2,300, managers have agreed to increase the use of non-lethal management measures. If numbers decrease to 2,100, managers would cease
harvests and management removals and use non-lethal measures tomaintain separation between bison and cattle (USDI, NPS et al. 2008).
Bison numbers and their distribution in Montana are managed
under the authority and discretion of the state veterinarian due to theirchronic exposure to brucellosis (81-2-120 Montana Code Annotated2011). The distribution of wild bison in Montana is currently limited tocertain lands located north (Gardiner basin) and west (Hebgen basin)of the park. Bison can move onto National Forest System and otherlands north of the park boundary and south of Yankee Jim Canyon(Figure 10.1) each winter and spring. Bison are not allowed north ofthe mountain ridge-tops between Dome Mountain/Paradise Valley
and the Gardiner basin on the east side of the Yellowstone River and

147

148

Yellowstone Bison: Conserving an American Icon in Modern Society

Tom Miner basin and the Gardiner basin on the west side of the Yellowstone River (MFWP and MDOL 2012). Bison approaching theseareas are hazed to other available habitat within the tolerance area,
captured, or killed. In addition, bison can move into the AbsarokaBeartooth Wilderness north of the park, including the upper portionsof Hellroaring and Slough Creek. West of Yellowstone National Park,
bison are allowed to move onto the Horse Butte peninsula at the eastend of Hebgen Lake and other nearby areas (USDI, NPS et al. 2008;

The restoration of
Yellowstone bisonhas been extremely
successful, withmany scientists
considering themthe only ecologicallyand genetically
viable populationof plains bison in
the United States.

Figure 10.2). Bison can also use the Eagle Creek/Bear Creek area,
Cabin Creek Recreation and Wildlife Management Area, and theMonument Mountain Unit of the Lee Metcalf Wilderness year-round(USDI, NPS and USDA, USFS, APHIS 2000a,b).
Hunting outside Yellowstone National Park is used to manage theabundance and distribution of bison in Montana, while providing
sport and subsistence harvest opportunities and cultural and spiritual engagement (Interagency Bison Management Plan Members2013). Each year, Montana Fish, Wildlife & Parks allocates permits forbison hunting from November 15 through February 15 in the northern
and western management areas (MFWP and MDOL 2004). Also,
American Indian tribes (Confederated Salish and Kootenai Tribesof the Flathead Nation, Nez Perce Tribe, Confederated Tribes of the
Umatilla Reservation, and Shoshone-Bannock Tribes) have rights,
reserved through treaties with the U.S. Government, to hunt bisonon certain federal lands in southwestern Montana (MFWP 2006a,b,
2009, 2010b). Montana Fish, Wildlife & Parks and these tribes coordinate each summer regarding bison removal objectives, permits, andharvests. Also, they enforce regulations and permit requirements fortheir respective hunters by sending game wardens to oversee hunts(Interagency Bison Management Plan Members 2013).
State and federal employees haze bison to prevent mingling withcattle, ensure human safety, prevent property damage, and preventthe movement of bison outside of agreed-upon tolerance zones oronto private property where landowners do not want bison. Hazingis accomplished primarily on horseback, but all-terrain vehicles,

Current Management

snowmobiles, and helicopters may be used at times (Interagency Bison
Management Plan Members 2013). Managers attempt to minimize
hazing in areas where hunting is ongoing. The partners involved withthe plan coordinate in April to compile information on bison movements and distribution, snow conditions, vegetation green-up, riverflows, logistical issues (e.g., staff, horse, and helicopter availability;
traffic control; visitation and road closures), and dates and locations
where cattle will be released for summer grazing (Interagency Bison
Management Plan Members 2013). Based on this information, thepartners devise a plan for hazing bison from the northern management area (Gardiner basin) back into Yellowstone National Park neara target date of May 1. They also devise a plan for hazing bison fromthe western management area (Hebgen basin) back into the park neara target date of May 15. These operations could occur earlier than
the target dates if forage and other conditions at higher elevations inYellowstone National Park are suitable or later if conditions preclude
safe and effective movements of bison to habitats that will hold/sustain
them. To avoid multiple hazing operations, the partners are exploring
private land management options with willing landowners, including
conservation easements, livestock grazing plans, and strategic fencing
to separate livestock and bison.
Bison have been captured (1) for brucellosis testing and vaccination,(2) to cull bison infected with brucellosis, (3) to reduce bison numbers,(4) because they have repeatedly resisted hazing to keep them withinagreed-upon tolerance zones, and (5) because there were already large
numbers of bison in the tolerance zones and additional bison could
induce movements into no-tolerance areas or cause human safety
and property damage issues (Interagency Bison Management Plan
Members 2013). As necessary, managers attempt to conduct captures
before pregnant bison are late in their third trimester (Interagency
Bison Management Plan Members 2013). Bison may be moved into
capture facilities by hazing and/or through enticement with weedfree hay. The National Park Service maintains a capture and handlingfacility at Stephens Creek within Yellowstone National Park in the

149

150
Date
July 7-15, 2003

July 14-18, 2004

Classified in mixed gender groups by age
Male1

Female>1

Female1

Calf

Bachelor

Mixedcentral

438

150

1426

241

498

380

2521

northern

159

23

176

12

46

77

795

133

11

227

15

110

638

179

1082

126

497

284

2594

523

125

932

131

397

247

35

331

33

164

125

1145

232

26

458

49

145

500

178

1098

162

430

674

175

1060

148

443

276

63

441

51

153

205

49

324

37

97

368

141

654

101

258

518

2078

386

152

757

111

301

northern

102

27

202

40

103

central

375

100

709

109

342

555

119

805

106

305

300

139

637

101

339

173

28

366

28

169

central

116

36

387

50

110

444

1101

northern

198

87

433

61

232

178

1158

central

145

63

427

73

158

480

1063

161

62

498

47

186

244

84

414

53

237

191

1239

224

83

391

53

179

340

72

517

57

219

342

1370

369

82

537

81

228

228

126

934

140

391

20

1755

298

150

679

121

344

centralcentralnorthern

July 11-13, 2006

July 10-17, 2007

centralnorthern

July 8-11, 2008

July 6-16, 2009

northern

July 6-20, 2010

Air count

Male>1northern

July 6-15, 2005

Yellowstone Bison: Conserving an American Icon in Modern Society

centralnorthernCurrent Management
Date
July 7-19, 2011

July 9-29, 2012

Classified in mixed gender groups by age
Male1

Female>1

Female1

Calf

Bachelor

Mixed

118

58

323

37

105

413

1407

163

53

309

40

106

northern

303

131

915

99

361

185

2103

central

282

68

493

41

173

398

1242

420

80

477

55

216

212

1349

375

187

876

165

466

80

2451

405

114

698

84

288

50

2619

287

101

415

82

197

342

1162

372

102

401

77

191

189

1148

457

231

1061

191

528

145

3275

608

249

1149

198

538

77

3151

275

113

565

69

206

280

1168

296

71

380

63

145

285

1159

310

155

1,023

126

422

141

2797

565

266

1,314

259

612

261

3163

centralcentralnorthern

July 14-25, 2014

Air count

Male>1northern

July 15-25, 2013

151

centralnorthern

Table 10.2. Annual ground and aerial composition surveys of bison in the central and northern regions of Yellowstone
National Park during July from 2003 through 2014. Ground composition columns represent total numbers of animals
observed in mixed age and sex groups (Geremia et al. 2014a).

152

Yellowstone Bison: Conserving an American Icon in Modern Society

Figure 10.1. Northern management area for the Interagency Bison Management Plan (IBMP) as
adjusted during 2012.

Current Management

153

Figure 10.2. Western management area for the Interagency Bison Management Plan (IBMP).

154

Yellowstone Bison: Conserving an American Icon in Modern Society

northern management area, while the State of Montana could maintainor erect one or more capture and handling facilities outside the park.
The 2000 Interagency Bison Management Plan called for the captureand serological testing of Yellowstone bison for brucellosis exposure,with those testing positive for antibodies to Brucella abortus being sent
to meat processing facilities and test-negative bison being vaccinated(USDI, NPS and USDA, USFS, APHIS 2000a,b). However, the operations plans for 2013 and 2014 (Interagency Bison Management Plan
Members 2013) modified the brucellosis testing and response protocol
somewhat to remove likely infectious bison, while retaining and vaccinating other bison to increase resistance to Brucella bacteria in the
population (Treanor et al. 2010, 2011; Ebinger et al. 2011). When bison
are captured and tested for antibodies to Brucella in their blood, animals identified as likely infectious could be shipped to meat processing
facilities up to the removal objectives for that year to help reduce brucellosis transmission (Interagency Bison Management Plan Members2013). Bison that have a lower risk of being actively infected, based on
negative test results or relatively low age-specific antibody levels for
Brucella, could be retained in the population (Geremia et al. 2013).
Bison selected for removal from the population are segregated fromother bison and transported to meat processing or research facilities
as soon as practical after capture and processing. Bison not selected
for removal are released from capture facilities when winter weather
moderates in spring or earlier to provide operational space and shorten
confinement (Interagency Bison Management Plan Members 2013).
Prior to their release, calf, yearling, and non-pregnant adult femalebison may be vaccinated for brucellosis via syringe with strain RB51.
Animals vaccinated with Brucella vaccine should not be consumed
within 21 days of vaccination; therefore, these animals are generally
held within the capture facility for at least this length of time if hunting
is ongoing (Interagency Bison Management Plan Members 2013). If
it is necessary to retain pregnant, likely infectious bison in captivity,
then staff segregate them from susceptible bison until after they have
calved and transmission risk is past.

Current Management

By June 15 each year, the Montana Department of Livestock and theAnimal and Plant Health Inspection Service determine the vaccination
status of all at-risk cattle in or coming into the Hebgen and Gardinerbasins (Interagency Bison Management Plan Members 2013). These
agencies use existing regulations and incentives to make sure that all
cattle are vaccinated as calves or adults. Furthermore, the partners
involved with the Interagency Bison Management Plan meet about
three times annually to publicly review, evaluate, and modify operatingprocedures (see meeting minutes at http://ibmp.info/).

Accomplishments and Failures
The conservation of Yellowstone bison has been successful under theInteragency Bison Management Plan, with overall abundance ranging
between 2,400 and 5,000 (average ~ 3,900; White et al. 2011; Geremia etal. 2014a). These bison are managed as wildlife and have relatively highgenetic variation (Plumb et al. 2009; Halbert et al. 2012). The population is prolific and has recovered rapidly from decreases in abundance
due to culling or natural mortality (Fuller et al. 2007b; Geremia et al.
2009; White et al. 2011). Also, adaptive management adjustments during
2005 to 2012 increased tolerance for bison on habitat in Montana by
expanding the northern and western management areas and allowing
more bison to occupy these areas during winter and spring (MFWP
and MDOL 2012). In addition, the transmission of brucellosis frombison to cattle has not occurred, due in part, to successful efforts byfederal and state agencies to maintain separation.
However, there has not been a reduction in brucellosis prevalence
within the Yellowstone bison population under the Interagency Bison
Management Plan. The proportion of adult females that test positive forbrucellosis exposure has remained approximately constant at about 60
percent (White et al. 2011; Hobbs et al. 2014). Several of the key assumptions in the plan were faulty or problematic to implement. Expectedadvances in vaccines, diagnostics, and delivery technologies did notoccur, and as a result, the plan overestimated the feasibility and effectiveness of vaccination (White et al. 2011, 2013b). Also, some aspects of the

155

156

Yellowstone Bison: Conserving an American Icon in Modern Societyplan such as test-and-slaughter at capture facilities were never completely
or consistently implemented for various reasons (see Chapter 2; Whiteet al. 2011). In addition, the plan underestimated bison reproduction andsurvival rates. As a result, more bison must be removed to regulate thepopulation towards 3,000. This has contributed to a continued relianceon the capture and shipment of bison to meat processing facilities toreduce abundance (White et al. 2011).
In addition, there is no guarantee of continued tolerance for bisonin Montana due to disease, political, and social concerns (Boyd 2003;
Franke 2005; Bailey 2013). In 2011, the Park County Stockgrowers Association filed a lawsuit to prevent additional tolerance for bison northof the park boundary. Also, during winters 2011 and 2013, the Montana
legislature proposed several bills intended to limit the distribution andrelocation of wild bison in Montana. Though the court dismissed thislawsuit in 2013 (Montana Sixth Judicial Court, Park County 2013), andto date, these bills have not become law, collectively these actions foretell that there may be little tolerance for bison in areas of Montana not
adjacent to Yellowstone National Park, regardless of their vaccination
or disease status.

Conclusions
The successes and failures of the Interagency Bison Management Plan
highlight the difficulties associated with managing for two competing
objectives — preventing brucellosis transmission from bison to cattle,
while conserving a wild population of bison (Treanor et al. 2013). Bison
managers implement actions to prevent brucellosis transmission each
winter, but unintended effects from these actions on the demography andgenetic diversity of bison may not be evident for many years (Treanor etal. 2013). To avoid undercutting conservation efforts, it is important toimplement proven and relatively non-intrusive management practices
such as maintaining separation between wildlife and cattle at the appropriate time of year to reduce brucellosis transmission risk (Nishi 2010).
Given current conditions and technology, it would be ineffective toimplement a vaccination program to suppress brucellosis in wildlife

Current Management

across the entire Greater Yellowstone Area (see Chapter 2). Federal
and state agencies have spent approximately $2 million annually to
implement the Interagency Bison Management Plan, and another $15
million to purchase land, conservation easements, and grazing rights(U.S. Government Accountability Office 2008; NPS and MFWP 2008).
Therefore, it is imperative to develop realistic objectives and rigorous
monitoring and research protocols to attain necessary information,measure progress towards objectives, and periodically assess theeffects and effectiveness of management actions (U.S. Government
Accountability Office 2008; Nishi 2010; White et al. 2013c).

157

NPS/Neal Herbert

Watching wild bisonin the Lamar Valley of
Yellowstone National Park.

Chapter 11
THE FUTURE — RECOMMENDATIONSFOR BISON CONSERVATION
P.J. White, Rick L. Wallen, Chris Geremia,
John J. Treanor, and David E. Hallac

Yellowstone bison comprise the largest conservation populationof plains bison and are one of only a few populations to have continuously occupied portions of their current distribution (Franke
2005; Plumb et al. 2009; Bailey 2013). They are managed as wildlife
in multiple large herds that move across extensive portions of thelandscape within and near Yellowstone National Park (Plumb et al.
2009; Gates and Broberg 2011; White et al. 2013b). Bison exist on thislandscape with a full suite of native ungulates and predators, while
being exposed to natural selection factors such as competition forfood and mates, predation, and survival in challenging environmental
conditions (Becker et al. 2009a,b; Plumb et al. 2009; Geremia et al. 2011;
Garrott et al. 2013). As a result, Yellowstone bison have likely retained
adaptive capabilities that may be diminished in other bison herds
across North America that are managed like domesticated livestock160

Yellowstone Bison: Conserving an American Icon in Modern Society

in fenced pastures with human-induced seasonal movements among
pastures, no predators, selective culling of older bulls to facilitate
easier management, and selection for the retention of rare alleles — thefunction and importance of which have not been identified (Berger
and Cunningham 1994; McDonald 2001; Lott 2002; Franke 2005;
Gates et al. 2010; White and Wallen 2012; Bailey 2013). Yellowstonebison also provide meat for predators, scavengers, and decomposers,
and allow visitors to observe this symbol of the American frontier ina wild, unfenced setting (Knapp et al. 1999; Franke 2005; Bailey 2013;
Frank et al. 2013; Garrott et al. 2013).

Lingering Issues
Despite this success, the management of bison near the boundary of
Yellowstone National Park is unsettling to many people. Park managers
are often asked why bison are managed differently from other wildlife
and not allowed to move freely into Montana and disperse to newareas. Conversely, other people believe bison should be kept in thepark and either managed like livestock or hunted to reduce numbers.
Many constituents are adamant that Yellowstone bison are so valuable they should be relocated elsewhere instead of being shipped tomeat processing facilities due to concerns about overabundance or
brucellosis transmission to cattle.
The debate about how to conserve and manage Yellowstone bison
involves a variety of issues, including:•Abundance — How many is too many (or too few)?

•

Brucellosis — What should be done and what can be done tosuppress 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?

The Future•

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 withina national park?

•

Cultural/Economic —What is the optimal abundance and distribution of bison for people that value them, and how muchare 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 otherstakeholders?

Incorporated in these overarching issues is a broad spectrum of
beliefs, concerns, and values held by a diverse range of stakeholders, including advocates, local community members, regulators andscientists, American Indian tribes, and the national and international
public. Most of these constituents support the conservation of wild
Yellowstone bison, but differ in their views regarding what constitutes conservation and responsible management actions to mitigate
conflicts. The challenge for managers is to consider this wide variety of viewpoints and reach a reasonable solution for the long-term
conservation of this ecologically important population, while accommodating the diverse policies and philosophies of various federal,state, and tribal agencies. In this chapter, we summarize key points
pertinent to the conservation of Yellowstone bison and make recommendations for management in the near future.

Key Points
Yellowstone Bison Are Migratory Wildlife, Not Livestock — A wildbison population can be defined as one that roams freely within adefined conservation area that is large and heterogeneous enoughto sustain ecological processes such as migration and dispersal, has
sufficient animals to mitigate the loss of existing genetic variation, and

161

162

Yellowstone Bison: Conserving an American Icon in Modern Society

is subject to forces of natural selection (White and Wallen 2012; Bailey2013). As demonstrated throughout this book, Yellowstone bison are
exceptional at meeting these criteria. Wildlife species in Yellowstone
National Park are not managed like domestic stock on a ranch and are
generally allowed to move freely. However, while the park provides
a large amount of habitat for bison and other wildlife, it does notencompass many of the lower-elevation winter ranges used by theseanimals when deep snow limits access to forage at higher elevations(Coughenour 2005; White et al. 2013b). As a result, some tolerance isnecessary outside the park for wild bison to access resources for theirsurvival — similar to the acceptance already provided to bears, bighorn
sheep, deer, elk, moose, pronghorn, wolves, and other wildlife.
Brucellosis Will Remain in the Greater Yellowstone Area for theForeseeable Future — As discussed in Chapter 2, the eradication or
substantial suppression of brucellosis in wild bison and elk is not
feasible at this time due to the absence of easily distributed and highly
effective vaccines, limitations of current vaccine delivery technologies, potential adverse consequences such as injuries and changes
in behavior from intrusive suppression activities, and chronic andincreasing infection in elk distributed across more than 8 million hectares (20 million acres; U.S. Animal Health Association 2006; Cross etal. 2010; Treanor 2012; White et al. 2013c; USDI, NPS 2014). Therefore,
brucellosis will remain endemic in the Greater Yellowstone Area formany decades to come.
Intensive Management of Yellowstone Bison Is Necessary atTimes — Yellowstone bison will continue to move into Montana during
winter, with more bison migrating as their numbers and winter severity
increase (Geremia et al. 2011, 2014b). Due to existing agricultural andresidential development, however, there is not sufficient low-elevation
habitat in areas where bison are currently tolerated that could sustain
many hundreds or thousands of animals for extended lengths of time.
Thus, bison attempt to migrate further during some winters, including
into areas occupied by hundreds of cattle. Also, bison will eventuallyattempt to pioneer new areas as their abundance increases, similar toThe Future163

Photograph courtesy of National Geographic by Michael Nichols

Bison leaving the national parkthrough the Roosevelt Archnear the northern boundary of
Yellowstone National Park.

164

Yellowstone Bison: Conserving an American Icon in Modern Society

the range expansion that occurred in the past (Taper et al. 2000; Plumbet al. 2009). When bison cross the park boundary into Montana their
management is the prerogative of the state, including coordinated management with the Gallatin National Forest on National Forest Systemlands (16 USC § 1604). Montana has allowed several hundred bison to
migrate outside Yellowstone National Park and occupy suitable winterrange in the state—and tolerance on additional range may occur in the
future (USDI, NPS et al. 2008; MFWP and MDOL 2012). However, massmigrations of bison have, at times, upset state and local governments andmany private landowners and cattle operators (Montana Sixth Judicial
Court, Park County 2013). If bison were allowed to disperse unimpeded
into cattle-occupied areas of Montana, it is likely those bison would be
lethally removed by state employees or during regulated hunts (U.S.
District Court for the District of Montana, Missoula Division 2011). Also,
the State might retract some tolerance for bison. Thus, management
practices such as hunting, hazing, capture, and culling are necessary attimes to limit the abundance and distribution of bison, while incrementally building acceptance for them in modern society (U.S. District Court
for the District of Montana, Missoula Division 2011; see Chapter 10).
Yellowstone Bison Can Support Conservation and Cultural Practices
Elsewhere—Yellowstone bison have high reproductive and survival rates
for a wild population exposed to numerous predators and relatively
severe environmental conditions (see Chapter 5). Thus, bison numbers
increase rapidly when environmental conditions are suitable (see Chapter 3), which could quickly fill available habitat and out-pace acceptancefor them in Montana. As a result, harvesting and culling bison is currently
necessary at times to keep the limited tolerance for them in Montanafrom being rescinded (U.S. District Court for the District of Montana,
Missoula Division 2011). Public and treaty harvests and the provisionof meat from culled bison to tribes and food banks could improve cultural, economic, nutritional, and social well-being (see Chapter 9). Also,
the use of quarantine to restore brucellosis-free Yellowstone bison to
public and tribal lands would enhance the conservation of the species
in North America.

The Future

Recommendations for Future Management
Objectives—Biologists at Yellowstone National Park have recommended
the following demographic, ecological, and genetic objectives for Yellowstone bison:•

Maintain 2,500 to 4,500 bison and average at least 3,000 to 4,000
over decades to preserve genetic diversity and reduce large-scale
culls;•

Minimize the effects of selective culling on bison and allow
numbers in the central and northern regions of the park to varydepending on dispersal rates and natural selection;•

Maintain similar proportions of males and females and an age
structure of about 70 percent adults and 30 percent juveniles tofacilitate competition for mates;•

Sustain ecological processes such as predation, migration, dispersal, and competition in the park and other agreed-uponconservation areas; and•Restore the contributions of bison to herbivore-grassland dynamics, the predator-prey-scavenger association, and many otherrelationships in the ecosystem (Plumb et al. 2009; Gross et al.
2010; Pérez-Figueroa et al. 2012; White and Wallen 2012; Franket al. 2013; Geremia et al. 2013; White et al. 2013c; Geremia et al.
2014a).

These objectives are consistent with the recommendations fromrecent reviews of ungulate management in national parks, but should
be reassessed periodically based on new information and changed circumstances (Demarais et al. 2012). Hobbs et al. (2014) recommended
managers use an adaptive management paradigm for Yellowstone bison,with the implementation of management actions for 3 to 5 years followed by assessments of progress, current knowledge and conditions,and updated model forecasts. Managers could then make an informed
decision regarding how to proceed.
Brucellosis Containment— Given current technology and existing
conditions, intrusive human actions such as vaccination or fertility control are unlikely to substantially decrease brucellosis infection in wild

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Yellowstone Bison: Conserving an American Icon in Modern Society

NPS/Neal Herbert

Bison calf in Yellowstone’s
Lamar Valley.

The Futurebison and elk. If disease regulators want to suppress brucellosis in
wildlife across the Greater Yellowstone Area, then they need to initiate
a dialogue with all the stakeholders regarding what should be done
based on various mandates, values, and viewpoints, and what can bedone based on consideration of existing conditions and technologies,
biological feasibility, and economic costs (Nishi 2010). In the meantime, the best alternative for suppressing brucellosis transmission
is to maintain separation between bison, elk, and cattle during thetransmission period from February to June (Keiter 1997; Bienen andTabor 2006; Nishi 2010; Cross et al. 2013; Godfroid et al. 2013; Treanor
et al. 2013; White et al. 2013c).
Tolerance — Allowing migratory bison to occupy public lands in
Montana until most calving is completed by early June would reducestress on pregnant or lactating females and newborn calves (Jones etal. 2010). It would also reduce the cost, duration, extent, and intensity of hazing needed to return bison to Yellowstone National Park
each spring or early summer. This tolerance would not significantly
increase the risk of brucellosis transmission to cattle because: (1) bison
parturition is typically completed weeks before cattle occupy nearby
ranges, (2) female bison consume most birthing tissues, (3) ultraviolet
light and heat degrade Brucella bacteria on tissues, vegetation, andsoil, (4) scavengers remove fetuses and remaining birth tissues, and(5) management maintains separation between bison and cattle (Joneset al. 2010; Schumaker et al. 2010; Aune et al. 2012; MFWP 2013).
One of the most vexing problems for the management of Yellowstone bison is the lack of available lower-elevation habitat in the
Gardiner basin and southern Paradise Valley north of Yellowstone
National Park. The valley bottoms in this area have more accessible
forage and less snow than surrounding mountains during winter,but are already used for agricultural and residential development(Hansen 2009). As a result, up to 800 bison have been held in theStephens Creek capture facility and other confinement pastures in andnear Yellowstone National Park and fed hay for months during some
winters to prevent their mass migration north of the park (White et

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Yellowstone Bison: Conserving an American Icon in Modern Society

al. 2011, 2013c). Confinement and feeding could unintentionally leadto food-conditioning, brucellosis transmission, and loss of migratory
knowledge (Franke 2005; Gates et al. 2010; Bailey 2013; White et al.
2013c). Thus, managers should develop and emphasize management
practices that avoid unnaturally concentrating bison during late winter,such as the enhancement and restoration of suitable forage plants in
the Gardiner basin where unpalatable, noxious weeds have proliferated (Plumb et al. 2009; White et al. 2013c). Seasonal or year-roundtolerance for wild bison should be attainable in some portions of
the Greater Yellowstone Area where brucellosis transmission risk
to cattle is low. Managers could use actions such as fencing, hazing,delaying cattle turn-on dates, and conservation easements or otherincentives to maintain separation between bison and cattle during
the transmission risk period (Kilpatrick et al. 2009). Federal and state
wildlife agencies have acquired some grazing rights and key habitat
for bison and other wildlife through agreements with willing landowners. They should continue to work with landowners to identify
areas with suitable habitat for bison and develop strategies to resolve
conflicts with livestock, human safety, and private property. These
strategies could include agreements to promote heifers or steers on
private lands and grazing allotments rather than cow-calf pairs. Also,
managers should continue successful efforts to subsidize fencing in
high-conflict areas and lower speed limits along highways crossed bybison. Nevertheless, human intervention will be necessary to manage
groups of bison that approach geographic or social boundaries oftolerance. These efforts will likely require additional funding andstaffing (MFWP and MDOL 2012).
Hunting — About 322 bison were harvested by public and treaty
hunters during the winter of 2014, most of which were shot near theboundary of Yellowstone National Park and along roads. Increasing this harvest will require increased tolerance (e.g., year-round insome areas) for bison in Montana, better access for hunters, creative
harvest strategies during non-traditional seasons, and commitments
by hunters to adjust harvest methods in response to bison habitat use

The Future

169

Photograph courtesy of National Geographic by Michael Nichols

Bison near Officers’ Row
in Mammoth Hot Springs,
Yellowstone National Park.

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Yellowstone Bison: Conserving an American Icon in Modern Society

patterns (White et al. 2011). State and tribal managers are discussing
strategies that would allow bison to migrate into more dispersed areas
across the landscape. They are also attempting to coordinate the overall
harvest of bison by age, breeding area (central, northern), and sex.
However, additional consultation is needed to effectively incorporate
tribal subsistence hunts into current management strategies. Modern
technology provides more efficient travel (vehicles), coordination (cellphones), gathering (rifles, winches), and long-term storage (freezers).
As a result, tribal subsistence hunts to procure large amounts of meat
appear unethical to some people in the complex and diverse social
landscape surrounding Yellowstone National Park. Ongoing discussions are focusing on how to effectively support tribal treaty harvests,
while respecting the concerns of other stakeholders about bison conservation, concentrations of gut piles near roads and residences, andhuman safety issues.
Hunting opportunities in Montana are limited in many years because
most bison do not migrate outside Yellowstone National Park until
March and April when public and tribal hunting seasons are closed due
to females being late in pregnancy. As a result, the State of Montana anda few American Indian tribes have recommended hunting bison inside
the park. Hunting in the park is not authorized by Congress and longstanding policy prohibits hunting in units of the National Park Service
system unless specifically authorized by Congress (NPS Organic Act of1916, 16 USC I, V § 26). Even if hunting were authorized, however, theNational Park Service is opposed due to concerns about wounding,behavioral changes (avoidance), unintended effects to other iconic andsensitive wildlife species, and decreased wildlife viewing opportunities
for visitors (Wenk 2012). Hunting just inside the park boundary would
probably not be much more effective than hunting outside the parkdue to the late-winter and spring migration patterns of bison. Rather,hunting during autumn and early to mid-winter would be most feasible
and effective in interior areas of the park (e.g., Blacktail Deer Plateau,
Firehole and Madison river drainages, Hayden Valley, Lamar Valley) andaway from roads. Even if these harvests were conducted by government

The Futureagents or government-supervised hunters, they would almost certainly
have unintended adverse effects to the bison population, other natural
resources, and visitor enjoyment (Wenk 2012).
Nonetheless, there is a need for further consultation between thefederal government and American Indian tribes associated with Yellowstone National Park to discuss recurring questions about potential
hunting rights inside the park and whether Yellowstone bison should
be managed as trust resources for the benefit of one or more specifictribes. One question is whether any tribes that signed treaties and landpurchases/sales reserved the right to hunt bison within the park. To
answer this question, it may be necessary to evaluate (1) whether thetribes understood the treaty agreements to mean that they retained
the right to hunt in the ceded lands that now encompass Yellowstone
National Park, and (2) whether Congress abolished these rights whenit created the park in 1872 or passed the National Park Protective Actof 1894 that specifically prohibited hunting in the park (Molloy 2000).
A separate question is whether the U.S. Department of the Interior hasa trust responsibility to consult with tribes that have recognized treaty
rights for hunting bison on open and unclaimed federal lands in Montana before removing Yellowstone bison to meat processing, research,or quarantine facilities. A few tribes have asserted that such removals
could affect the number of bison available for harvest by tribal huntersbecause fewer bison will migrate outside the park (Whitman 2012; YNP
2012). Two related questions are: (1) should tribes with recognized treaty
rights in Montana be preferentially provided with meat, hides, and otherproducts from Yellowstone bison that are shipped to meat processing
facilities over tribes that do not have treaty rights but are associatedwith Yellowstone National Park, and (2) should all brucellosis-free
Yellowstone bison that complete quarantine be relocated to open andunclaimed federal lands in Montana where tribes with recognized treaty
rights can hunt them (in lieu of relocating them elsewhere; YNP 2012)?
Capture and Culling — In some winters, several hundred bison
may need to be captured and culled at boundary facilities to regulate
population size (Geremia et al. 2013). Managers should cull animals in

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Yellowstone Bison: Conserving an American Icon in Modern Society

a non-selective manner to avoid potential adverse demographic andgenetic consequences that could compromise population viability(Halbert et al. 2012; Treanor et al. 2013). Culling bison in proportion
to their availability in the population may mimic natural mortality
events and help maintain an age structure close to historical distributions — though aboriginal harvests from horseback may havedisproportionately taken more females than bulls (Millspaugh et al.
2008; Clawson et al. 2013). Managers should avoid culling in a mannerthat artificially allows brucellosis or other factors to act as key selective forces (USDI, NPS and MFWP 2013).
If feasible, managers should implement smaller removals (25 to 50
bison) near the park boundary consistently through the migrationseason (Geremia et al. 2013). This stepwise approach would (1) limit
bison held within capture facilities and minimize effects on hunting
opportunities, (2) reduce logistical constraints of transporting large
numbers of bison to meat processing facilities over brief periods, (3)avoid transporting females late in pregnancy to meat processing facilities, and (4) lower the chances of out-of-park migrations surpassing
levels that exacerbate conflict (Geremia et al. 2013). If necessary, large
removals of 500 or more bison could be implemented during severe
winters and/or at high bison densities when large numbers of bison
naturally migrate to lower elevations (Geremia et al. 2013).
Quarantine Facilities and Terminal Pastures — The ecological andadaptive value of Yellowstone bison merits efforts to relocate animals
testing negative for brucellosis exposure to quarantine facilities forfurther testing and eventual release elsewhere (Treanor et al. 2013).
Quarantine facilities could be paired with terminal pastures so any
animals that test positive for brucellosis could be killed for food.
These paired facilities could reduce the frequency of large shipmentsof bison to meat processing facilities when females are late in pregnancy, while enhancing bison conservation and the cultural heritageand nutrition of American Indian tribes. If necessary, pregnant bison
could be held in terminal pastures through calving, with test-positive
animals eventually killed and test-negative calves and other animals

The Future

sent to quarantine. There is significant interest by federal and stateagencies, American Indian tribes, non-governmental organizations,and private entities in receiving brucellosis-free Yellowstone bisonand/or constructing and operating a quarantine facility on their lands(NPS, YNP and the Bureau of Indian Affairs 2012; Associated Press
2014). Also, the Department of the Interior recently identified 20
locations on federal lands within the historic range of plains bisonthat may be suitable for receiving Yellowstone bison completing quarantine (USDI 2014).
It is uncertain if periodically sending Yellowstone bison to quarantine will serve as a long-term tool for regulating the size of the
population. The minimum quarantine periods and testing requirements are logistically difficult and relatively expensive to implement
over several years (USDA, APHIS 2003; Clarke et al. 2014b). Also, there
are substantial political and social hurdles to overcome in many areas.
Thus, interest in obtaining Yellowstone bison is limited to groups that
greatly value their cultural and evolutionary significance. In addition,
recipients of brucellosis-free bison from quarantine could quickly
reach saturation of their facilities and lands through subsequent
breeding of these prolific animals. Thereafter, new herds formed
from brucellosis-free Yellowstone bison would only need the occasional infusion of a small group of bison to enhance or maintain their
existing genetic diversity. As a result, quarantine may not consistently
remove large enough numbers of bison to regulate the size of the
Yellowstone population.
Public Engagement — Most stakeholders are not satisfied with thelevel of involvement provided by the partners of the Interagency Bison
Management Plan, which primarily amounts to comment periods atpublic meetings. Rather, stakeholders want substantive input into thedecision-making process to influence management strategies before
they are adopted and implemented. As a result, managers should
consider alternate forms of public involvement such as stakeholder
workshops with presentations and discussion that allow information and ideas to be transferred and deliberated between managers,

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Yellowstone Bison: Conserving an American Icon in Modern Society

scientists, and the public (Bidwell 2010; Berger and Cain 2014). Management committees comprised of all interested stakeholders could
be formed and sustained to develop ideas and recommendations
similar to the Citizens Working Group on Yellowstone Bison (2011) andthe model used for managing the Book Cliffs and Henry Mountains
populations (Utah Department of Natural Resources 2014).
Scientific monitoring and research has greatly increased knowledge
regarding bison, brucellosis, and elk in the Greater Yellowstone Area.

A wild bison population
can be defined as one
that roams freely withina defined conservation
area that is large
and heterogeneousenough to sustain
ecological processes
such as migration anddispersal, has sufficientanimals to mitigate
the loss of existing
genetic variation, andis subject to forces ofnatural selection.

Gaining this knowledge was a critical step for bison conservation,
but also highlighted that human dimensions have a large influence
on policy changes when it comes to tolerance for large wildlife suchas bison outside national parks and refuges (Berger and Cain 2014).
Therefore, additional information is needed on political and socioeconomic factors such as: (1) comparative costs and public preferencesfor various management alternatives, (2) non-market values of wildbison, (3) the demand for bison removed from the population, (4)traditional knowledge from American Indians and local communities,and (5) public attitudes, behaviors, and knowledge of bison, brucellosis, and management (Nishi 2010; National Research Council 2013).
Also, public confidence in decisions could be enhanced by soliciting independent reviews of analyses and proposed plans, as well as
meeting with local officials to gain their input, and hopefully, support(National Research Council 2013; Berger and Cain 2014).

Conclusions
The overriding issue regarding the conservation of Yellowstone bisonand plains bison elsewhere in North America is whether the public
will support wild bison living outside preserves (Lott 2002; Franke
2005; Bailey 2013). Arguments against tolerance for Yellowstone bison,or their restoration elsewhere, are generally presented in terms of
disease, protection of property, and human safety concerns — eventhough elk have similar effects yet are tolerated without intrusive
management because they are economically valuable for hunting.
However, there are also underlying issues about grass (i.e., competition

The Futurewith cattle), political control (i.e., state versus federal rights), and thecontinuing transition of communities from traditional rural occupations and lifestyles such as ranching to tourism and the enjoyment of
natural amenities (i.e., locals versus outsiders; Haggerty and Travis
2006; Bailey 2013). While these characterizations are overly simplistic,
disease regulators and livestock interests have certainly perpetuatedmisperceptions regarding the risks posed by bison for decades (Robbins 2006; Bidwell 2010). Even today, these misperceptions strongly
influence the management of bison and severely limit their conservation and distribution across the landscape (Bidwell 2010).
The reluctance to allow Yellowstone bison onto more public landsin the Greater Yellowstone Area can no longer be justified solely basedon brucellosis risk to the cattle industry. There is recognition by bothdisease regulators and wildlife managers that the risk of brucellosis
transmission from bison to cattle is minute compared to elk which
are generally free to roam (Bienen and Tabor 2006; Kilpatrick et al.
2009; Schumaker et al. 2010). Also, the economic consequences ofoccasional brucellosis outbreaks in cattle are greatly reduced since
the Animal and Plant Health Inspection Service changed its regulations in 2010 to deal with outbreaks on a case-by-case (rather thanstate-wide) basis, and designated surveillance areas for brucellosis
were established (USDA, APHIS 2010; MDOL 2013). Despite several
detected transmissions of brucellosis from elk to cattle, the grossannual income from cattle sales in Montana surpassed $1 billion six
times during 2005 to 2013, with record-high cattle prices since 2010
(Lutey 2012, 2013). Furthermore, studies in Wyoming have clearly
demonstrated that the costs of measures to prevent brucellosis transmission from elk to cattle are exorbitant compared to the costs of an
occasional outbreak in cattle (Roberts et al. 2012; Kauffman et al. 2013).
Current conditions in the Greater Yellowstone Area present an
opportunity to manage bison similar to other wildlife in some areas
outside national parks and refuges. Tourism and recreational activities have a large and growing influence on the economy, and the vast
majority of visitors and hunters to the area enjoy seeing bison move

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Yellowstone Bison: Conserving an American Icon in Modern Society

across the greater landscape in large numbers. In fact, the Yellowstone
area provides a unique attraction — the opportunity to see bighorn
sheep, bison, deer, elk, pronghorn, and large predators such as bears
and wolves in close proximity on the landscape and within view frompaved roadways. Furthermore, American Indian tribes have become
more engaged with the management of bison in the area, sharing theirtraditional knowledge, restoring bison to tribal lands, and renewing
subsistence hunts to improve their cultural, nutritional, and social
well-being (Plumb and Sucec 2006; Hatfield et al. 2013). As a result,efforts to respect the presence of bison as wildlife on the larger landscape will be welcomed by native peoples and the majority of the local,
national, and international public. This vision is attainable because
decades of management have shown there are relatively few conflicts
between bison, residents, and the millions of visitors each year in
Grand Teton and Yellowstone national parks. Acceptance of bison as
wildlife in some areas outside parks and refuges will enhance bison
restoration, enrich visitor experience, improve public and treaty hunting opportunities, boost local and state economies, and hopefully,
elicit regional and national pride in this tremendous conservationaccomplishment. The time is right to recover bison, the iconic symbolof power and strength in our nation, as wildlife in appropriate locations of the Greater Yellowstone Area and elsewhere.

The Future

177

NPS/Neal Herbert

Bull bison in summer inYellowstone National Park.

Photograph courtesy of National Geographic by Michael Nichols

Bison calves with new horns
in Yellowstone National Park.

Acknowledgments
Special thanks to the following scientists for sharing their time and expertise
reviewing a draft version of this book:
Steve Cain, Grand Teton National Park, National Park Service; Curtis
Freese, Freese Consulting, Westport, Massachusetts; Dan Licht, Midwest
Region, National Park Service; John Nishi, EcoBorealis Consulting, Inc.,
Canada; Wes Olson, Grasslands National Park, Parks Canada (retired); Glen
Sargeant, Northern Prairie Wildlife Research Center, U.S. Geological Survey;
and Dirk Van Vuren, Wildlife, Fish, and Conservation Biology, Universityof California, Davis.
We also thank the Yellowstone Association for financial support to produce
both printed and electronic versions of this book; Sarah Garrott, Executive
Editor of Oregon Law Review, for guidance regarding the interpretation ofAmerican Indian treaty rights; and Robert Garrott, Montana State University,
for allowing us to use unpublished data on the causes of bison mortality.
Thanks also to Jim Peaco and Neal Herbert of the National Park Service
and Michael Nichols of the National Geographic Society for taking manyof the photographs used in this book.
The views and opinions in this book are those of the authors and should
not be construed to represent any views, determinations, or policies of the
National Park Service.

NPS/Neal Herbert

Bison feeding near theBlacktail Deer Plateau in
Yellowstone National Park.

Glossary of Terms

9

Acquired immunity: Immunity gained through prior exposure to a disease, vaccination, or some other manner than heredity.
Adaptive capabilities: Ability to adapt to a changing environment.
Adaptive management: A repetitive decision-making process that
includes: (1) describing the problem and desired outcomes, (2) modeling the system, (3) predicting the effects of management actions,(4) implementing management actions, (5) monitoring to evaluate
the effectiveness of actions, and (6) making adjustments based onlearning to enhance progress.
Allele: Alternative forms of a gene at a specific site (locus) on a chromosome.
Allelic diversity: The total number of possible alleles at each gene locus
in a population.
Amenity living: Residing in a place that is comfortable, convenient, and/or pleasing.
Analytic deliberation: Engaging stakeholders to discuss the technicalaspects, human dimensions (e.g., beliefs, values), and trade-offs ofvarious management alternatives; followed by recommendations todecision makers.
9
Portions of this glossary were adapted from USDI, NPS (2010, 2014). References are provided in the text.

182

Yellowstone Bison: Conserving an American Icon in Modern Society

Antibody: A protein molecule produced after exposure to an infectious disease that can combine with the disease organism.
Apparent competition: The rate of predation on a given prey species
is influenced by the presence of another prey species that allows
the predator to survive and reproduce at higher numbers than
could be sustained by one prey species alone.
ATP: Adenosine-5´-triphosphate which is produced by oxidative
phosphorylation in mitochondria and transports chemical energy
within cells for metabolism.
Bacteria: Unicellular microorganisms of the class Schizomycetes.
Bio-absorbable projectile: Remote delivery device where vaccine
is encapsulated into a bullet-like capsule that dissolves in liquid.
Birth: The process of bearing offspring, which is also known asparturition.
Bison management area: A zone where some bison are tolerated
for part or all of the year without increasing the risk of brucellosis
transmission to cattle.
Body condition: The state of fat and protein stores in an animal thatreflects nutritional intake and deposition or metabolism based on
their physiological requirements and environmental conditions.
Bovine/Bovinae: The subfamily of animals that includes bison, cattle,
oxen, European buffalo, water buffalo, and yaks.
Breeding herd: An aggregation of animals for breeding.
Brucella abortus: A species of bacteria that functions as a parasite
within cells to cause bovine brucellosis in bison, cattle, and elk.
Brucellosis: An infectious disease of cattle, dogs, goats, and pigs thatis caused by Brucella bacteria and can induce abortions in animals
and recurring (undulant) fever in humans.
Buffalo: Name commonly used to refer to bison.
Carnivore: Meat eater.
Carrion: Tissues of dead animals.
Carrying capacity: The number of animals that can be supported
in a given area based on the limits of available food, space, andother resources.

Glossary of Terms

Cattle: Domesticated animals of the family Bovidae (bison, cows,oxen) that are kept on a farm or ranch.
Cell-mediated (or cellular) immune response: The activation ofphagocytes, T-lymphocytes, and cytokines within cells in response
to disease-causing organisms.
Cellulose: Fibrous material that comprises the walls of plant cells.
Chromosome: A single piece of coiled DNA that contains many genes.
Competition: A direct or indirect interaction with another animal
decreases the ability of an animal to survive and reproduce.
Confederated Salish and Kootenai Tribes of the Flathead Nation:
The Bitterroot Salish, Kootenai, and Pend d’Oreilles tribes thatcurrently live on the Flathead Reservation in northwestern
Montana.
Conservation: The preservation and stewardship of natural resources
and the ecological processes that sustain them.
Contraception: A method of preventing fertilization or pregnancy.
Copulate: Sexual intercourse.
Culling: The removal of animals from a population for management
purposes.
Culture (disease tests): A method for detecting or increasing bacterial or viral organisms in a test sample.
Culture-negative: A culture test result that did not detect the organism of interest in a sample.
Culture-positive: A culture test result that detects the organism ofinterest in a sample.
Decomposers: Organisms that break down dead or decaying matter.
Demography: Statistics relating to births, deaths, emigration, andimmigration.
Density: The number of animals in a defined area.
Density-dependent: A response that occurs when there are a highnumber of animals within a given area.
Diagnostics: Procedures for detecting and/or identifying a disease.
Digestible energy: The portion of food that can be absorbed toprovide energy to an animal.

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Yellowstone Bison: Conserving an American Icon in Modern Society

Disease: An impairment of normal physiological function in partor all of an animal.
Dispersal: Movement to another area without returning shortly
thereafter.
DNA: Deoxyribonucleic acid which contains genetic instructions forthe development and functioning of animals.
Domestic (animal): A farm animal or pet that is not wild.
Dose: A prescribed amount of vaccine.
Ecological role: The relationships and interactions among animals
and their environment.
Ecology: The study of relationships among organisms and theirenvironment.
Efficacy: Effectiveness at producing a desired result.
Emigration: The movement of animals out of a population or area.
Endemic (disease): Sustained in an area or population without beingbrought in from outside sources.
Energetics: The movement and transformation of energy.
Epidemiology: The study of factors and mechanisms involved in the
spread of a disease.
Epizootic: An outbreak of disease that spreads quickly among animals
and could be transmitted to humans.
Euro-Americans: Americans with ancestry in Europe.
Exotic: Nonnative or introduced from a foreign place.
Extinction: A group of related organisms dies out.
Extirpation: Destroyed or wiped out.
Experimental challenge: The deliberate introduction of an infectious disease organism into a controlled environment.
Fecundity: The ability to produce offspring.
Fertility control: Devices or methods used to prevent fertilizationor pregnancy.
Fetal: Related to a fetus.
Fetus: An unborn, developing mammal.
Fidelity: See Philopatry.

Glossary of Terms

Field strain: A type of disease organism found in the wildlandenvironment.
Foraging: Searching for and ingesting food.
Forbs: Broad-leaved, herbaceous plants.
Foreign cells: Cells uncharacteristic of the organism.
Founder effect: The loss of genetic variation when a new population is established by a small number of individuals from a larger
population.
Free-ranging: See Wide-ranging.
Gene: The basic unit of heredity (inheritance) which consists of DNA
that contains instructions to make proteins.
Gene flow: The transfer of genes (alleles) from one population toanother.
Gene pool: The set of all genes in a population.
Generation time: The approximate time it takes individuals to replace
themselves in a population, or in other words, the time between
two successive generations (about 8 to 10 years in Yellowstonebison).
Genetic diversity: Variation of heritable characteristics in a
population which allows some animals to adapt to a changing
environment.
Genetic drift: A change in the frequency of alleles in a population
due to chance or random events rather than natural selection.
Genetic integrity: The preservation of existing genetic diversity andsubstructure.
Genetics: The study of heredity.
Genetic subdivision/substructure: See Population subdivision.
Genotypes: Genetic make-ups of individual animals.
Geothermal: Heat from the earth that flows to the surface and produces hydrothermal features (e.g., geysers, hot springs, fumaroles,
mud pots) in some areas, while warming more extensive portionsof the landscape and reducing or eliminating snow pack.
Gestation: Time of pregnancy.
Grass-like plants: Rushes and sedges.

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Yellowstone Bison: Conserving an American Icon in Modern Society

Grazing: Consume vegetation.
Grazing optimization: The production of grasses is increased bygrazing and the cropping of vegetation.
Greater Yellowstone Area: The general area surrounding Yellowstone and Grand Teton national parks where the states of Idaho,Montana, and Wyoming share a boundary (about 400 kilometers
north-to-south and 200 kilometers east-to-west).
Green-up (of vegetation): Commencement and continuation of
new growth by live green plants.
Group defense: Animals in a group cooperate to protect themselves
and their young.
Habitat: The environment in which an animal lives that includes
cover, food, space, water, and other resources necessary for an
animal to survive and reproduce.
Haplotype: Segments of DNA that are transmitted together andcontain closely linked gene variations.
Harvest: See Hunting.
Hazing (of bison): People with equipment moving animals awayfrom a location where they are not wanted.
Herbaceous: Plants without woody stems that die after each growing season.
Herbivore: Plant eater.
Herd: A group of animals from the same species that feed, travel, andinteract together for a period of time.
Heredity: Inheritance or the genetic transfer of traits to offspring.
Heterogeneity: Diversity or variation.
Heterozygosity: An index of genetic diversity that sums the proportion of genes with different alleles (alternative forms of a gene)across a representative sample of a population.
Hoof: Horny covering of the feet of animals such as bison, cattle, andelk (plural is hooves).
Horning: Rubbing horns against an object such as a tree or shrub.
Horns: One or more projections from animal’s head that consist ofa sheath of hardened protein covering bone.

Glossary of Terms

Hunting: Pursuing an animal to kill it for food (subsistence), sport,
and/or spiritual or cultural reasons.
Husbandry: The care and protection of animals in a manner similar
to livestock.
Immigration: Movement of animals into a population or area.
Immune protection: Resistance to a disease-causing organism that
may be natural (i.e., inherited) or acquired (e.g., vaccination).
Immune response: A bodily response that involves the recognitionof disease organisms by specific antibodies in blood, previously
sensitized lymphocytes, and/or phagocytes, T-lymphocytes, andcytokines within cells.
Immunity: The ability of an organism to defend itself against an
infectious disease.
Immunocontraception: The stimulation of an animal’s immune
system to cause infertility.
Inbreeding: Reproduction between individuals that are closely
related that often produces offspring with deleterious traits.
Indigenous: Originating from or belonging to a particular region
or place.
Infection: The invasion of, and proliferation within, an animal’s bodyby disease-causing microorganisms such as bacteria, viruses, andparasites.
Infectious disease: Diseases caused by infectious bacteria, viruses,
fungi, protozoa, and helminthes.
Infectious dose: The amount of disease-causing organism that stimulates an infection.
Inheritance: Traits transmitted from parents to their offspringthrough genes.
Interagency Bison Management Plan: A plan signed in 2000
between the State of Montana and the federal government thatprescribed collaborative actions to reduce the risk of brucellosis
transmission from Yellowstone bison to cattle, while conserving awild population of bison with some migration to lower-elevation
winter ranges on public lands in the state.

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Yellowstone Bison: Conserving an American Icon in Modern SocietyInterTribal Buffalo Council: A federally chartered organization
established in 1990 to restore bison to tribal lands.
Intracellular pathogens: Disease-causing organisms that operate
inside cells.
Introgression: Hybridization or the introduction of genes from one
species into the gene pool of another species.
Lactation: The production of milk by female mammals.
Latent disease: A disease characterized by periods of inactivity either
before symptoms appear or between attacks.
Litigation: A lawsuit brought in court to assert or defend a particular
right.
Livestock: Domesticated animals raised on farms or ranches forfood and other products.
Locus: Specific location of a gene (DNA sequence) on a chromosome (plural is loci).
Lymph node: An organ that is a part of the lymphatic (immune)system and contains white blood cells that trap foreign particles.
Lymphatic system: A bodily system that transports lymph throughtissues and organs for immune protection.
Lymphocyte cells (T-cells): Leukocytes (white blood cells) foundin large numbers in lymph tissues that contribute to immunity.
Management (wildlife): The conservation of populations of wild
animals and the ecological processes that sustain them, while considering other biological, economic, political, and social factors.
Meat processing facility: A facility where animals are killed and theirmeat and other parts are packaged and/or distributed.
Metabolic rate: The amount of energy expended by an animal duringa certain time period.
Metabolism: The chemical processes that convert food into energy
and other products necessary to sustain life.
Metabolizable energy: The amount of nutrients in food that can beabsorbed by an animal for energy.
Microsatellite DNA: Repeating sequences of DNA that result froma mixing of DNA from both parents.

Glossary of Terms

Migration: Seasonal, round-trip movements between separate areas
not used at other times of the year.
Mitochondrial DNA: Genetic information that is normally inherited
exclusively from the mother.
Mortality: Death or death rate.
Mutation: A change in a gene or chromosome that can produce aninherited trait.
Native peoples: Indigenous people that have certain inherent rights
based on their original occupation of an area.
Natural immunity/resistance: Ability to resist a disease due toinherited traits.
Natural selection: Animals with traits that make them better suited
to the environment tend to survive, reproduce, and transmit their
genetic characteristics to succeeding generations more than otheranimals.
Nez Perce Tribe: An American Indian tribe that currently governs
and lives within its reservation in Idaho.
Nitrogen cycling: The process by which nitrogen is converted into
one or more chemical forms that can be used by plants for photosynthesis and growth.
Nitrogen mineralization: The process by which microbes convert
proteins and other chemical compounds in organic matter into
forms that can be used by plants such as ammonium and nitrate.
Numerical dilution: The likelihood of an individual animal being
eaten decreases as the number of available prey animals increases.
Nutrients: Chemical substances in foods that enable animals to survive and reproduce.
Nutrition: The process of ingesting and using food substances.
Nutritional condition: See Body condition.
Nutritive quality: The amount of energy and nutrients in food.
Open and unclaimed federal lands: Public land in the United Statesthat is not being used in a manner inconsistent with tribal hunting.
Yellowstone National Park is not considered open and unclaimed
land because it exists to preserve native wildlife and hunting is

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prohibited. National Forest System lands are considered open
and unclaimed lands. Private property is not considered open
and unclaimed land.
Organic matter: The remains (carcasses) of dead plants and animals
or their waste products (feces, urine).
Organism: A life form (e.g., animal, bacteria, plant) composed ofinterdependent parts that maintain vital processes.
Ovulation: The release of ripe eggs from the female ovary.
Parasite: An organism that lives in or on an animal and benefits at
its expense.
Parturition: The process of giving birth.
Pathogen: Anything that causes disease such as a bacteria, virus, orother microorganism.
Phenology (of vegetation): Periodic life cycle events (e.g., leaf,bud, flower, and seed formation) that are influenced by seasonaland interannual variations in weather and other factors such as
elevation.
Philopatry: Tendency to stay in, or return to, a given area.
Physiology: The study of how cells, muscles, and organs work
together in animals.
Placenta: The organ in the womb to which the fetus is attached.
Plains bison: One subspecies of American bison (the other subspecies is the wood bison [Bison bison athabascae]).
Population: A collection of individuals of the same species that livein the same area and interbreed.
Population bottleneck: A drastic, temporary reduction in thenumber of animals in a population.
Population dynamics: Changes in the size and composition (age,sex) of populations, and the factors and processes influencing
those changes.
Population subdivision/substructure: Relatively independent subsets or separate groups within a population.
Predation: An interaction in which one organism (the predator)
attacks and feeds on another (the prey).

Glossary of Terms

Pregnancy: Female animal carrying one or more fetuses in her bodyfrom fertilization to birth.
Prevalence: The number of cases of a disease.
Productivity (wildlife): The number of young produced in a
population.
Pyric herbivory: Preferential grazing of burned patches that reduces
the likelihood of fires in the near future and promotes a shifting
pattern of disturbance across the landscape that supports a varietyof plants and animals.
Quarantine (bison): Animals are maintained in fenced enclosures
separate from other livestock and wildlife for a period of time
while they are repeatedly tested to evaluate if they remain freeof brucellosis.
Radio collar: See Radio telemetry.
Radio telemetry (wildlife): The transmission of information (e.g.,
direction, location) from a transmitter attached to an animal to areceiver where the information can be processed or downloaded.
Range expansion: The outward dispersal of animals beyond thelimits of the traditional distribution for a population.
Recruitment: The number of young that survive to enter a population in a given year.
Reintroduction: See Restoration.
Remote delivery (vaccination): Method of delivering a biological product such as a vaccine without physically capturing andrestraining individual animals.
Removals (of bison): The culling or harvest of animals from a
population.
Reproduction: Procreation or the process of creating new offspring.
Reproductive success: Breeding and passing on genes to the next
generation.
Reproductive synchrony: The birth of most offspring in a population within a short period of time each year.
Resistance (disease): Immunity or the ability of an animal to repel
infection from a disease.

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Resources (natural): A naturally occurring material that could be
used by humans or wildlife.
Restoration: The return of something that was removed or nearlyextirpated.
Riparian areas: Zones on or adjacent to rivers and streams that are
typically inhabited by a diversity of animals and plants.
Rumen: The first compartment of the four-chambered stomach of
ruminants.
Ruminants: Animals with a four-chambered stomach that includes
microorganisms such as bacteria and protozoa to break downplant material into volatile fatty acids and other compounds.
Ruminate: Regurgitating partially digested food and chewing it again
to further break down plant material.
Scale: The size of measurements at which ecological processes arestudied, including the area, number, duration, and frequency ofsampling (large-scale generally refers to observations over relatively long periods of time or extensive areas of space).
Scavengers: Animals that feed on dead or injured animals.
Select agent: Biological agents and toxins that could be packaged
as weapons by terrorists and used to threaten public health ornational security (www.selectagents.gov).
Senescent: Vegetation that has aged past maturity and is becoming
old and dying.
Serology: Tests to detect the presence of antibodies against a diseaseorganism in the blood serum (plasma).
Seronegative: The absence of specific antibodies in blood serum fora particular disease.
Seropositive: The presence of specific antibodies in blood serumthat indicate past exposure to a particular disease.
Seroprevalence: The proportion of a population that has been
exposed to a disease as determined by the presence of antibodies in the blood.
Shed: To discharge from the body.

Glossary of Terms

Shipment (of bison): The capture and transport of animals to meat
processing facilities, quarantine facilities, terminal pastures,
research facilities, or another location.
Simulation (computer): A program that attempts to replicate a modelof a particular system.
Slaughter: See Meat processing facility.
Social tolerance: See Tolerance.
Species: A group of populations that contain individuals that resemble
each other and can interbreed.
Stakeholders: People and organizations that use, influence, and/or
have an interest (or stake) in a given resource.
Summer range: The geographical area or region within which a population or species can be found during summer.
Survival: Continuing to live.
Susceptible: Not currently, but capable, of being affected or infectedby a disease.
T-cells: Leukocytes (white blood cells) found in large numbers inlymph tissues that contribute to immunity.
Terminal pasture: Fenced enclosure in which bison are maintained
separate from other livestock and wildlife, and harvested by shooting or transfer to a meat processing facility.
Test-and-slaughter: Animals are captured, tested for exposure and/or infection with a particular disease such as brucellosis, and killed
or otherwise removed from the population if they test positive.
Animals that test negative are often vaccinated for the disease andreleased.
Thermal: See Geothermal.
Tolerance: Acceptance of some animal or thing.
Transmission (disease): The passage or transfer of an infectious disease from one individual to another.
Treaty rights: Rights reserved by American Indian tribes through treaties
with the U.S. government that can include hunting, gathering, or conducting other activities on certain “open and unclaimed” federal lands.

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Trust responsibility: An obligation of the U.S. government to protect
tribal assets, lands, resources, and treaty rights.
Ungulates: Hooved mammals such as members of the orders Perissodactyla (horses, rhinos, and tapirs) and Artiodactyla (pigs, camels,
deer, antelope, cattle, and their kin).
Utilization distribution: A probability distribution derived fromdata identifying the locations of one or more animals at different
points in space and time.
Vaccination: Administration of vaccine to stimulate a protective
immune response against an infectious disease.
Vaccine: A suspension of living or inactivated organisms used toinduce a protective immune response against an infectious disease.
Variation in male reproductive success: Many males successfully
breeding and passing their genes on to the next generation (asopposed to one or a few males monopolizing breeding — which
could lead to a loss of genetic diversity).
Vegetation: Plants.
Virus: A submicroscopic, parasitic microorganism composed of
nucleic acid (DNA or RNA) inside a protein covering.
Wallowing: A behavior when bison roll to give themselves a dustbath, and in the process, create depressions in the soil.
Weaning: A mother stops nursing (milk) her offspring so it will begin
eating other foods.
White blood cells: B-cells, T-cells, macrophages, monocytes, andgranulocytes in the immune system that circulate in the blood andlymph and participate in defensive reactions to invading microorganisms or foreign particles.
Wide-ranging: Animals move across a vast landscape rather thanbeing confined to a feedlot or enclosure.
Wild (bison): A population that roams freely within a defined conservation area that is large and heterogeneous enough to sustain
ecological processes such as migration and dispersal, has sufficientanimals to mitigate the loss of existing genetic variation, and issubject to forces of natural selection such as predation, substantialGlossary of Terms

environmental variability, and competition for breeding opportunities and food.
Wildlife: Wild animals, birds, and other living things.
Windthrow: The uprooting, breakage, or toppling of trees by wind.
Winter-kill: Starvation.
Winter range: The geographical area or region within which a population (or part thereof) is found during winter.
Yearling: An animal between one and two years of age.
Yellowstone bison: Bison that primarily live in Yellowstone National
Park, but sometimes migrate to lower-elevation ranges in surrounding states during winter and spring.
Yellowstone National Park: The world’s first national park established in 1872 and located on 2.2 million acres in the states of
Idaho, Montana, and Wyoming.

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Bison in Yellowstone
National Park.

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241

NPS/Jim Peaco

A group of bison near
Soda Butte Creek in thenortheastern region of
Yellowstone National Park.

IndexAboriginal rights: 133, 172. See also American Indian tribes.
Absaroka-Beartooth Wilderness: 13, 68,148.
Abundance, of Yellowstone bison. See
Population dynamics.
Activities, of bison: 2-12, 67-78, 83-86, 100105, 107-113.
Adaptive capabilities: compared to cattle
or other bison populations, 119, 159160, 181.
Adaptive management: adjustments toalso Interagency Bison Management
Plan.
Age distribution/structure, of bison:
breeding/maturity, 2, 4, 83; of removals, 60-61; population objectives, 165;
sex and age composition, 4, 146-147,
150-151.
Aggression: artificial selection against, 160;
by breeding bulls and females, 4, 5.
See also Behavior.
American Bison Society: xiv, 135.
American Indian tribes: associated withthe management plan, 57-62, 144-145,

Yellowstone, 131-133, 139; bison kill

155; annual monitoring and report-sites, 64; bison use by, 49, 132-133;

ing, 57-62; changed circumstances,ceremonies, 130, 133; diabetes in, 134;

144-145; decision making, 62-64,

historical use of the Yellowstone

165; defined, 181; difficulties witharea, 131-132; involved with the Inter-

implementation, 155-157; plan foragency Bison Management Plan, 54,

Yellowstone bison, 57-62; public

144; ranching of bison and cattle,

involvement, 62-64; stakeholders,

136; significance and treatment of

62-64; uncertainty and, 126-127. See

Yellowstone bison, xi, xiii, 132-133;

244

Yellowstone Bison: Conserving an American Icon in Modern Society
subsistence hunts, 54, 58, 148, 170171; treaties with the United States

Indian tribes.
Augmentation, of bison: 14, 48.

government, 54, 58, 132, 143, 148, 171;
trust responsibility of the federal

Bacteria: anthrax type of, 13; bacterial

government, 133; views on bisondigestion of cellulose, 7, 98-99; bru-management, 134, 144, 170-171, 173, 176;

cellosis infection from, 19-43; effects

with treaty harvest rights for bisonon reproduction and survival, 87-89.

in southwestern Montana, 54, 58,

See also Brucellosis.

131-134, 143, 148, 171. See also Hunting;Interagency Bison Management Plan;
InterTribal Buffalo Council; Names ofindividual tribes.

Bears, predation/scavenging on bison: 17,
31-33, 90-91, 162, 176.
Behavior of bison: aggregation (herding/grouping), 2-5, 7, 123; aggressive,

Animal and Plant Health Inspection

4-5; associations between individu-

Service (APHIS): bison/brucel-

als, 2-4; calving, 84-87; dominancelosis management plan, 54, 142, 155;

hierarchies, 4-5; foraging, 7-10; groupcontraception study, 35; regulations

defense, 5, 84, 94, 117, 186; groupregarding brucellosis, 27-29, 143, 175;sizes, 2-4; herd composition, 150-151;

quarantine feasibility study, 58-59. Seemating, 4-5; rumination (chewing

also Interagency Bison Managementcud), 99, 192; social organization, 2-5;

Plan; U.S. Department of Agriculture.

traveling, 12-13; wallowing, 107-110,

Animal density: definition, 183; influence194.

on bison feeding, 103, 113; influence on

Bighorn sheep: 110, 137, 162, 176.

bison migration, 69, 79; influence on

Bio-bullets. See Remote vaccination;brucellosis transmission, 27, 30; influ-

Vaccination.

ence on reproduction and survival,

Bioterrorism: 42, 192.

86, 101; of elk and competition with

Birth control, of bison. See Fertility control.

bison, 14, 94, 111.

Birth, of bison calves: age and probabil-

Anthrax: 13.

ity of, 83, 85-88; birth rates, 85-88;

Antibodies, to Brucella bacteria. See Bru-

brucellosis effects on probability of,cellosis; Testing for brucellosis.

87-89; brucellosis transmission and,Anti-predator responses, of bison: 5, 84,

20-22; calving season, 84-85, 103-104;

94, 117, 186; of elk, 94.

calving in sequential years, 85-86,

Apparent competition. See Competition.

central versus northern region of Yel-

Archeological evidence: bison kill sites, 64;

lowstone, 84-86, 88; effect of bisonof native peoples, 131.
Assiniboine Tribe: 131. See also American

density, 86; effects of weather conditions, 86; fidelity to birthing location,

Index84-85; locations in and outside

management: contraception and,Yellowstone, 84-85; survival follow-

34-37, 165-167, 184; culling of bison

ing, 90-91, 94, 100-101, 103; relation

and, 14-15, 17, 29-31, 49, 52, 54, 57, 59,

to new vegetation growth, 103-104;

60, 126-129, 145, 149, 154, 156, 164-165,

synchrony in, 84-85, 103-105; timing

171-172; Interagency Bison Manage-of, 84-85, 103-104. See also Brucellosis;

ment Plan and, 15-17, 52-64, 142-157;

Demography; Nutrition; Nutritional

recommendations for, 159-176;

condition.

separation with cattle and, 26-27, 42,

Birth rate, of bison. See Demography.

54, 57, 79, 127, 147, 155-156, 167-168;

Bison: abundance of, 13-17, 60-61, 146-147,

vaccination and, 33-43, 54, 57, 143-144,

150-151, 165; athleticism of, 2; brucellosis infection of, 13, 19-43, 87-89;
competition with cattle, 17, 111, 174-175;
diets, 7-10, 98-105; diverse attitudes
toward, xiv, 26-27, 136-138, 141-142,

154-157, 162, 165, 167.
Blackfeet Tribes: 131-132. See also American
Indian tribes.
Body condition, of bison. See Nutritional
condition.

159-164, 174-176; domestication of,Book Cliffs, Utah: xiv, 174.

xiv, 13, 23, 27, 46-49, 59, 117, 159-160,

Breeding (rut), of bison: age of, 4, 83-84;

162, 183-184, 188; feeding, 7-13, 98-105;

effective population size for, 124-129;

habitat use, xiv, 5-6, 68-78, 100-104;

herds, 7, 123, 182; genetic diversity,

key life events, 2-5, 68-71, 83-85, 100-

124-129; inbreeding depression, 120;

105; livestock designation of outside

interbreeding with cattle, xiv; loca-

Yellowstone borders, 52-53; man-tions, 7, 123; mate competition, 1, 4,

agement of in differing eras, 45-64,

90, 125-126; season, 4; variable male141-157; numbers, 13-17, 60-61, 146-147,

reproductive success, 4, 126. See also

150-151, 165; physical attributes of, 2;

Behavior; Genetics.

population dynamics, 13-17, 60-61, 112,
146-147, 150-151, 165; privately owned,

Bridger-Teton National Forest: 132. See
also U.S. Forest Service.

xiv, 13, 23, 27, 33, 42-43, 59, 117, 162;

Bronx Zoo: xiii, 135.

ranges, 5-6, 8, 71-75; restoration of,

Brucella abortus. See Brucellosis.

xiv, 1, 19, 45-64, 159-176; size, 2; speed

Brucellosis: abortions caused by, 20, 22,of, 2; wolf predation and, 90-94;

24, 30, 33-34, 43, 49, 89, 182; age ofscavenging of, xiv, 31-33, 107, 160. See

exposure and infection, 20, 23-23, 35,also Brucellosis; Demography; Yel-89, 144; antibodies to, 21-23, 192; Bru-

lowstone bison.

cella abortus bacteria as cause of, 13,

Bison conservation initiative: 126.

19-21; bulls and, 20, 57; chronic infec-

Bison management and brucellosis risktion, 13, 19, 23, 27, 52, 87, 89, 147, 162;

245

246

Yellowstone Bison: Conserving an American Icon in Modern Society
class-free status, 27, 29; culture of,162; progression of, 20-21; quarantine

22; degradation of Brucella bacteria,

for, 58-59, 134, 144, 172-173;recovery

31-33, 57, 167; designated surveillancefrom or resistance to infection, 20,

area for, 27-29, 33, 143, 175; diagnostic

33-34; reinfection of bison from elk,

tests for, 22-23, 33, 42; effects on bison

20; research, 26, 35, 37, 41, 57, 143-144,

behavior and population viability,

175; resistance to transmission, 21,

30-31, 35-38, 57, 71; effects on bison

30, 33-34, 89; risk management, 19,

restoration and recovery, 13, 19, 41, 49,

23-24, 27, 33-34, 41-43, 49, 51-54, 59,

57, 71, 137, 147-148; effects on genetic

79, 142-155, 160-161, 165-167, 175; risk

diversity of bison, 127, 171-172; effectsof transmission to cattle, x, 13, 17, 19,

on pregnancy, birthing, recruitment,

22-24, 26-27, 33-34, 41-43, 52-53, 57, 59,

and survival, 13, 19, 22, 35-37, 39,

79, 142-157, 160-162, 165-167, 175; select83, 89; effect of under-nutrition on

agent, 42, 192; serology, 22-24, 33, 42,

infection risk, 21-22, 39; epidemiol-54, 192; shedding of Brucella bacteria,ogy (or spread), 21-23; eradication

20-22, 24, 33-34; source of in Yellow-of (or inability to eradicate), 39-42,

stone, 19, 22-23; strategies to contain,

162; fertility control, 34-37; hunting

15, 23-24, 27-38, 41-43, 49, 51-57, 59, 79,

and, x, 30-31, 52, 57-58, 148; immune

142-157, 160-162, 165-168, 175; suppres-protection, 20-21, 33-34, 38; in bison,sion objectives, 23, 29, 42, 144, 156-157,

x, 19-43; in elk, 19, 23-24, 27, 26, 29-30,

160-162, 165; tools/practices, x, 15, 23,

33-34, 53, 133, 144, 162, 175; in other27, 29-38, 52-64, 133, 142-155, 160-162,

wildlife, 23; in the Greater Yellow-

165-174; transmission between bisonstone Area, 19, 23-24, 26-27, 29, 38, 41,

and elk, 20, 22, 49; transmission

174-176; in Idaho, 19, 27-28, 42, 143; incycle, 20-22; transmission period,

Montana, 19, 27-29, 42, 51, 143, 147;

20-22, 24; transmission to livestockin Wyoming, 19, 24, 27-31, 33, 42, 143,

and humans, 19, 22-24, 27, 41-43, 49,

175; infection, 20-21, 23-24, 33-35, 43,

52, 167, 175; uncertainties regarding

144; introduction to bison and elk,

feasibility of suppression, 29, 38-43,

19; management objectives/strategies

59, 144, 155-157, 160-162; vaccination

for, 15, 23-24, 27-38, 41-43, 49, 51-54,

for, 21, 27, 29, 33-43, 54, 57, 62; views

142-155; metritus (inflammation of theon suppression, 17, 27, 39-43, 49, 53,

uterus), 89; misperceptions regard-64, 133-134, 136-148, 155-157, 160-162,

ing, x, 23, 136-138, 142-143, 174-176;

165-168, 174-176. See also Designatedmodes of transmission, 20, 24; persis-

Surveillance Area; Human Healthtence, 20-22, 23, 26, 33-34, 38, 57, 89,

and Safety; Management; Nutritional

162; prevalence, 24, 26, 30, 144, 155,

condition; Vaccination.

IndexBuffalo. See Bison; Plains bison; Yellowstone bison.
Buffalo Ranch: 46-48.
Bulls, bison: aggression by, 4-5; appear-exceeding, 78-79; food limited, 78-79,
108-111; of bison in Yellowstone, 78-79,
111.
Cattle. See Livestock and cattle.

ance, xvi, 81, 121, 177; breeding

Cellulose. See Nutrition.

variances of, 4-5, 126, 129; female’s

Census. See Counts.

choice of, 4; management of, 57-58,

Central: breeding herd of bison, ix, 7, 10,144, 160; rutting behavior of, 4-5;

12-14, 17, 46, 48-49, 51, 60-61, 68-69,

seasonal grouping behavior of, 4-5.

71-77, 79-80, 84-86, 88, 90-91, 113, 119-See also Behavior; Demography;

120, 123-124, 127-128, 146-147, 150-151,

Genetics.

170; range/region, 5, 7, 9-10, 13-15, 46,
51, 69, 77, 78-80, 91, 94, 102, 113-114, 123,

Cabin Creek Recreation and Wildlife
Management Area: 148. See also U.S.
Forest Service.
Calves, bison: birth/nursing of, 83-85, 103-

126-129, 135, 145, 165.
Citizens Working Group on Yellowstone
Bison: 40, 62, 174. See also Interagency
Bison Management Plan.

104; brucellosis infection of, 20; wolf

Climate: drought, 86, 90; of Yellowstone,

predation on, 94. See also Behavior;

7; precipitation, 7; temperature, 7,

Brucellosis; Demography.

weather, 7.

Capture and confinement, of bison: alternatives to, 148, 168; Buffalo Ranch, 148;

Color, of bison: 2.
Competition: apparent, 114-117, 182;

concerns about, 148, 154, 168; coordi-

between elk and bison for food andnation of, 145, 149; effects on bison,

space, 110-111; between bison and big-168; locations, 148, 154; methods used,horn sheep for food, 110; interspecific149; numbers held, 60, 167; objectives(with other species), 78-79, 110-111;

of, 149; release from, 154; Stephensintraspecific (with other bison), 4-5,

Creek, 149, 154; timing of, 149. See also

9, 69, 74-75, 78-79, 103, 110-111.

Management.

Condition, of bison: 14, 182; effects on

Caribou: 114, 137.

birthing and reproduction, 84, 101;

Carnivores, 182; bison as food for, 31, 94;energetic expenditures, 10-12; influ-

effects of bison numbers on, 94-95;

ence on susceptibility to brucellosis,

predation on bison, 91-95, 114-116;

21-22, 39-40; mortality and, 103;

scavenging on bison, 31, 92-93, 115.

predation and, 94; relationship to car-Carrion, for scavengers: 31, 182.
Carrying capacity: concept, 14, 182; culling and, 79; effects or reaching or

rying capacity, 111.
Confederated Salish and Kootenai Tribesof the Flathead Nation: 54, 58, 131,
148, 183.

247

248

Yellowstone Bison: Conserving an American Icon in Modern Society
Confederated Tribes of the Umatilla
Indian Reservation: 58, 148.

Culling: alternatives to, 30, 143-144, 148149, 167-173; definition, 183, 191; effects

Congress: 46, 135, 170-171.

on demography, 13, 19, 79, 111, 127, 155;

Conservation and management implica-

effects on genetics, 119, 124-126, 127-

tions, for bison: conservation ethic,

129; effects on population dynamics

xiii, 135; demographic concernsand substructure, 17, 79, 94-95, 111,of, 59-62, 156, 160-161, 165, 171-172;

155; evaluation of effects, 59, 71, 129;

domestication effects of, 167-168;

frequency in Yellowstone, 14, 60,

ecological approach to, 49-52, 165,

119; managers desire to reduce large

174-176; genetic concerns of, 127-129,

culls of Yellowstone bison, 29-30, 49,

171-172; Interagency Bison Manage-

59-62, 165; of bison, 15, 30, 52, 60; ofment Plan, 52-64, 142-155; of ungulateelk, 29-30; process, 145, 149; random

grazing on grasslands, 107-113; ofversus non-random, 124-126, 128-

migration and dispersal, 69-71, 78-80,

129, 165, 171-172; recommendations

137-138; Contraception, of bison. Seeregarding, 126-129, 164-165, 171-172;

Fertility control.

selective culling of infected bison toCounts: central herd (bison), 46, 48-49,

reduce brucellosis prevalence, 57, 154;

60-61, 150-150; northern herd (bison),strategies for, 129, 154, 160, 165, 171-172.

46-48, 60-61, 150-151; of bison, 14-17,

See also Brucellosis; Demography;

45-51, 60-61, 150-151; of elk, 91, 94, 111,

Genetics; Interagency Bison Manage-

114; of wolves, 94.

ment Plan; Management; Population

Courts. See Litigation.
Cows, bison: birth rates of female bison,

dynamics; Survival.
Cultural heritage: of American Indian

85-89; brucellosis infection of, 19-22,

tribes, 132-134, 172; of Euro-Ameri-

24; choice of mate, 4; estrus in, 83-84;

cans, 134-137.

gestation in, 84; proportion of, 61,
150-151; selective culling or huntingof, 59-60; stocking of, 14, 46, 120; vaccination of, 29, 33-34, 38-43, 57, 144,

Cultural importance, of bison: 132-135,
137-138.
Culture, of Brucella bacteria. See testingfor brucellosis.

156-157, 165-167. See also Behavior;
Brucellosis; Demography; Livestockand cattle.
Coyotes, predation or scavenging ofbison: 33, 91.
Crow Tribe: 131-132. See also American
Indian tribes.

Decomposers, of bison carcasses: xiv, 107,
160, 183.
Deer: 137, 162, 176, 194.
Demography, of bison: age structure, 61,
146-147, 150-151, 165; birth rates, 85-89;
carrying capacity, 78-79, 108-111;

Indexcounts, 14-17, 45-51, 60-61, 150-151;

seasonal distributions, 68-78; sur-dispersal (emigration), 68-69, 124,

veys, 145, 71-78. See also Migration

128; effects of brucellosis on, 19, 87,

and dispersal; Movements; Range

89; effects of culling on, 49, 59-60,

expansion.

90-91, 165; lifespan/longevity, 90;

Domestication, of bison: xiv, 159-160.

male to female ratio, 61, 146-147, 150-

Drought, effects on reproduction and sur-

151; mortality, 90-94; recruitment, 112;

vival: 86, 90.

reproduction, 83-88; population size,
15, 150-151, 165; population growth
rates, 112; population models, 112, 145;

Eagle Creek/Bear Creek: 148. See also U.S.
Forest Service.

removals, 49, 59-60, 90-91, 165; senes-

Eastern Shoshone Tribe: 131. See also

cence, 85-88, 90-91; survival, 90-91.

American Indian tribes.

Density, of bison: effects on brucellosis

Ecological process management: 49-52.

transmission, 27, 30, 37; effects on

Ecological role, of bison: 107-117.

competition, 108-111, 114; effects

Economics, cost of brucellosis outbreaks:

on demography and population

13, 19, 27-29; costs of brucellosis

dynamics, 86, 101; effects on forag-

management actions, 37-38, 167, 174-

ing efficiency, 69, 103, 113; effects on

175; in the Greater Yellowstone Area,

migration, 69, 79; effects on dispersal

136-137; natural resource extraction,and range expansion, 69, 79. See also

136-137; sustained costs of brucellosis

Demography; Nutrition; Nutritional

suppression, 23, 27-29, 37-38; tourism,

condition; Population dynamics.

136-137, 175-176.

Derr, James: 123.

Ecosystem. See Greater Yellowstone Area.

Designated Surveillance Areas (for bru-

Elk: brucellosis in, 19, 21-24, 26, 41, 49, 162;

cellosis): 27-29; 33, 143, 175. See also

brucellosis management strategies

Brucellosis.

and, 19-20, 24, 26-29, 37-40, 42, 53,

Diet, of bison. See Food; Food habits;
Foraging.

133, 137, 143, 160, 162, 165, 167, 174-175;
counts of, 14, 17, 24, 29, 94, 111, 113-

Digestion. See Nutrition.

114; culling of, 29-30; feed grounds

Disease: See Brucellosis.

in Wyoming, 24, 26-27, 29-30;

Dispersal. See Migration and dispersal

fertility control of, 35-37; grassland

Distribution: annual variations in, 68-78;

ecosystems and, 49, 110-111, 113-114,

constraints in modern society, 19,117; hunting of, 29-31; increasing

41, 52-57, 64, 78-80; historical, xiii,

brucellosis prevalence in, 23, 26-27,

5-6, 45; of plains bison, xiii; of Yel-

143; population dynamics, 14, 17, 29;

lowstone bison, 7-8, 45-52, 68-78;

predation on, 31-33, 90, 94; resource

249

250

Yellowstone Bison: Conserving an American Icon in Modern Society
competition with bison and, 110-111,

Fertility control: 34-37, 165-167, 184.

114, 117; transmission of brucellosis

Fidelity (Philopatry), to breeding areas:

to cattle and domestic bison, 20-24,

123-124; contribution to genetic dif-

26-29, 175; vaccination of, 33-35,

ferences between breeding herds

38-40, 42-43.

in Yellowstone, 123-124; to seasonal

Emigration. See Migration and dispersal.
Energetics, of bison: digestible energy

ranges, 68.
Fire, as critical ecological process: 108;

intake, 10, 99-100; effects of gestation

habitat management with, 191.

and lactation, 100-101, 103-104; effects

First Nations of Canada (Blackfoot,of weather conditions, 12-13, 99-100;

Blood, Piegan, Assiniboine): 131. Seeenergy costs (activities, seasonal),

also American Indian tribes.

10-12; metabolic rates, 10, 99-100;

Flathead Tribes (Flathead, Salish, Upper

nutritional deprivation, 12, 39; travel

Pend d’Oreille, Kootenai): 54, 58, 132,

costs, 12-13.

135, 148, 183. See also American Indian

Eradication. See Brucellosis; Extinction.
Erosion, bison and: 108.
Euro-Americans: colonization and settle-

tribes.
Fluorescent Polarization Assay. See Testingfor brucellosis.

ment, 45-46, 132, 134-135; commercial

Food: calves, 4, 12, 84, 100-101, 103; con-hunting of bison, 134-135; definition,

sumption or daily intake of, 10-12,184; treatment of native peoples, 132-

98-99; nutritional quality of, 10,133, 135; use of bison, 134-135.

98-99, 104; quantity consumed, 113;

Evolution. See Adaptive capabilities;

rate of intake, 10-12, 98-99; summer

Genetics.
Exponential growth, of bison. See Demography, of bison.
Extinction: ecologically extinct, bison,(growing season), 9, 98, 100-104;
winter (dormant season), 9, 99. See
also Nutrition.
Food habits: composition, 7, 9-10, 98, 104;

xiv, 117; definition, 184; genetics of,

by forage classes, 7, 9-10, 98, 104;

119-120; of bison on the Great Plains,

selection of plants, 7, 9-10, 98, 104;

1, 135.

Forage. See Food; Food habits; Foraging.
Foraging, by bison: behavior, 7, 9, 98-105;

Fat. See Nutrition.

bison density and, 69, 103, 113; byFeces: fertilizing effects of, 111-113.

bison, 7-13, 98-105; displacement

Fecundity, of bison. See Birth;of snow, 2, 9-10, 110, 118; efficiency,

Demography.

9-12, 98-99; green wave and, 100-105;

Fencing: xiv, 37, 46, 48, 53, 79, 134, 138, 141-

selection of foraging areas and plants,

142, 144, 149, 159-160, 168, 191, 193.

7, 9-10, 98, 104; snowpack and, 2, 4,

Index
9, 74-75, 78, 100, 103-105; strategies, 9,

herds in Yellowstone, 123, 128-129;

98-104; time spent, 9, 98-99.

recommended population size andForbs. See Food; Food habits; Grassland

demography, 126, 161-162, 165; reten-

ecosystems; Habitat; Vegetation andtion of genetic diversity, 126, 129,vegetation phenology

161-162, 165, 173; variable male repro-

Forests. See Habitat.

ductive success, 126, 129, 194; viable

Fort Belknap Indian Community: 59. See

population size, 126, 129. See also

also Quarantine.
Fort Peck Indian Reservation: 59. See also
Quarantine.

Adaptive capabilities; Movements.
Geothermal influence: on bison, 5, 7, 9, 11,49; on snow pack, 5, 12, 185.
Gestation, in bison. See Pregancy.

Gallatin National Forest: 62, 132, 164. See
also U.S. Forest Service.
Gardiner basin: x, 7, 45, 55, 57, 62, 68,

Goodnight, Charles: 46, 120.
Grand Teton National Park: 6, 52, 120,
176, 186.

71-76, 85, 147-149, 155, 167-168.

Grasses. See Food; Food habits; Grassland

Genetics, of bison: allelic diversity,

ecosystems; Habitat; Vegetation and120, 123-124, 126, 128-129, 155, 185;

vegetation phenology.

bottleneck, 119-120; disease, 123;

Grassland ecosystems: bison and, xiii,

domestication’s dilution of, 159-

68, 108; competitive interactions

160; effects of culling, 127, 129, 172;

among plant species, 107-108, 113;

effects of management, 37, 127,

composition of plant species over

156, 160, 172; effects of population

time, 107-108, 113; grazing optimiza-

fluctuations, 129; founder effect,tion function, 107, 111-113; phenology

119-120, 185; gene flow, 124, 128-129;

of grasses, 78, 98; turnover of soil

generation time, 185; genetic diversity

nutrients, 107-108; ungulate grazing(and loss thereof), 119-120, 123-124,

and, 9-10, 78, 113; wolf predation and,

126, 155; genetic drift, 119-120, 185;

111-117;

haplotypes, 123; heterozygosity,

Gray wolves. See Wolves.

120, 123, 186; human influence on,

Grazing: by bison, 7; competition with

119-120, 123; inbreeding effects, 120,

livestock, 17, 174-175; ecosystem

187; interbreeding with cattle, 120,influences, 107-108, 165; effects on

127; lineages, 120; microsatellites,

biodiversity and heterogeneity,

124, 188; mitochondrial DNA, 123-

108; effects on plants (colonization,

124, 189; mutations, 128-129, 189;

nutrients, production, succession),

population/genetic subdivision107-108; effects on the soil, 108;and differences between breeding

intensity of, 9-10, 113; optimization

251

252

Yellowstone Bison: Conserving an American Icon in Modern Society(stimulating) effects on plants, 107, 111-

Hayden Valley: 4, 7, 10, 13-14, 48-49, 51,

113; other ungulates, 110, 113; repeated

68-69, 71-77, 85, 113, 122-123, 170.

removal of plant tissue, 9-10, 113. See

Hazing: alternatives to, 57-62, 148-149, 167-

also Foraging; Grassland ecosystems;

168; coordination of, 148-149; effects

Heterogeneity; Wallowing.

on bison, 78-80; methods used, 54;

Great Plains: xiii, 45, 117, 131, 134.

objectives of, 54, 71, 144-145, 148-149,

Greater Yellowstone Area: xi, xiv, 13, 17, 19,

164; of bison, 54, 148-149; of elk, 37;

21, 23-24, 26-32, 37-42, 45, 64, 131-132,

timing of, 149. See also Helicopters;

136-137, 157, 162, 167-168, 174-176, 186.

Management.

Green-up, of vegetation: 71-78, 106; bisonHebgen basin, Montana: 147, 149.

management and, 149; bison migra-

Horse Butte, Montana: 143, 148, 153.

tion and, 24, 71-78, 103-104; definition,

Helicopters, used to haze bison: 54,

186; phenology, 73, 78, 103-104.

148-149.

Grizzly bear. See Bears.

Hemorrhagic septicemia: 13.

Gros Ventre Tribe: 132. See also American

Henry Mountains, Utah: xiv, 174.

Indian tribes.

Herbivores: 14: 38, 86, 97-98, 110, 113, 165;

Group sizes, of bison: 2-4.

definition, 186; pyric herbivory, 108,

Growth, of bison: 2; rates of, 12, 100-101,

191.

103-105.

Herd segments, of bison: ix, 7, 14, 45-52, 61,
68-78, 84-85, 88, 90-91, 119-120, 123-

Habitat, for bison: conservation ease-124, 127-128, 146-147, 150-151, 165.

ments/incentives, 30, 149, 157, 168;

Heterogeneity, definition of: 186; effects ofcost of, 157; effects of snow depth,

grazing, 108, 111-113; need for, 161. See

2, 4, 9, 74-75, 103; effects of springalso Grazing.

vegetation green-up on use, 71-78,

Hides, from bison: distribution of, 134-135,

100-106; grazing rights, 62, 143, 168;

144, 171; fur characteristics, 2, 99.

selection of, 5, 7-10, 97, 103-105; loss

History, of Yellowstone bison: 45-64.

of due to human land use, xiv, 17,Home ranges, of bison, 67; seasonal24, 41, 49, 78-79, 95, 117, 149, 162, 167;

ranges, 71-78.

overlap with other ungulates, 110-111;

Horns, of bison: 2, 5, 108, 134, 144, 178, 186.

shortage of low-elevation winterHuman activities: effects on bison of, 19,

habitat, xiv, 17, 24, 41, 49, 78-79, 95,

24, 30, 54, 83, 90-91, 119, 129, 165, 174;

117, 149, 162, 167; summer habitat foreffect on ecosystem, xiv, 17, 117, 162,

bison, 71-77; winter habitat for bison,

167; hunting, xiii, 15, 29, 31, 52, 54,

71-77.

57-59, 60, 64, 86, 131, 132, 134, 143, 148-

Harvests. See Hunting.

149, 168-171; livestock grazing, 57, 62,Index95, 136-138; recreation and tourism,

and breeding herd, 60; commercial,

17, 117, 136-138, 174-176. See also Cli-

xiii, 46, 132; concerns about, 170;

mate change; Culling; Hunting.

coordination of, 58, 145, 148, 154, 170-

Human health and safety: brucellosis and,

171; cultural and spiritual engagement

13; interactions with bison, 141-142;

in, 148, 187; effects on brucellosis

perceived risks from bison, 17, 141-142,

prevalence, 29-31; effects on bison

144, 148-149, 161, 168, 170, 174; selectdistribution, 31, 38; ethics of, 161,

agent, 42, 192; vaccination and, 57;

170; factors influencing hunter suc-

Human intervention: effects of, 59-60,

cess, 80, 168-170; fair chase, 58; game64, 71, 79, 83, 129; in wildlife popula-wardens, 148; gut piles, 170; neartions during ecological managementpark boundary, 168; near roads, 168;

period, 46-59; minimizing as man-objectives, 58, 148; permits, 58, 148;

agement goal, 30, 117, 127, 149, 161, 165,

poaching, 46; prohibition of inside

172; occasional need for, 80, 141, 145-

Yellowstone National Park, 31, 170-

155, 168. See also Culling; Hunting.

171; public sport hunting, 52, 57-58,

Human land use practices: agriculture and148; seasons and regulations for hunt-

livestock ranching, 57, 62, 95, 136-138;

ing bison, 58, 148; subsistence/treaty

amenity ranching, 136-138, 174-176, 181;

hunting, 54, 58, 131-132, 134, 143-144,

development, 57, 62, 95, 136-138; rec-148, 168-171, 176; tactics and practices,

reation and tourism, 136-138, 174-176;

168-170; unregulated, xiii, 46, 132.

switch from agriculture/extraction to

Husbandry, of bison: 187; commercial

amenities/tourism, 137-138, 174-176.
Humans: conflicts with bison, xiv, 17, 30,

herds, xiv, 117; in Yellowstone, 46-49,
128. See also Management.

64, 95, 141-142, 168; diverse attitudes
toward bison, 136-138, 174-176; in the

Idaho: 5, 23, 27-28, 33, 42, 52, 143, 186.

Greater Yellowstone Area, 136-138,

Immigration. See Migration and dispersal.

174-176; perceptions regarding, 17, 128,

Immune protection and response: age

136-138, 174-176; property damage,and, 20-21; definition, 183, 187-188,

17, 141-142, 144, 148-149; visitation to194; of bison to vaccination, 33-34,

Yellowstone, 137, 174-176. See also

38-40, 42; of cattle to vaccination,

American Indian tribes; Recreation;

33-34,42-43; of elk to vaccination,

Human activities; Human health and33-34, 38-40, 42; resistance to bru-

safety; Human intervention; Humancellosis infection and transmission,

land use practices; Hunting.

20-22, 38-40.

Hunting, of bison: annual harvests ofbison, 52, 58-60, 80, 168; by age, sex,

Immunocontraception. See Fertility
control.

253

254

Yellowstone Bison: Conserving an American Icon in Modern Society
Inbreeding. See Genetics.

164, 167-168, 174-176; tools/practices,

Indians. See American Indian tribes.

54, 57-59, 62, 64, 143-155, 162, 164;

Infection, by brucellosis. See Brucellosis;

vaccination, 54, 57, 143, 149, 154-155,

Testing for brucellosis.
Interagency Bison Management Plan:

156-157, 162, 165, 167; website, 62-64,
145, 155. See also American Indian

adaptive management, 52-64, 143-145,

tribes; Bison; Brucellosis; Citizens

155, 165; authorities and jurisdictions,

Working Group for Yellowstone

15, 52-53, 147, 164; capture and con-

Bison; Demography; Hunting;finement, 54, 57, 149, 167-168, 171-172;

Management; Population dynamics;

cost of, 157; culling, 54, 57, 60, 154,

Quarantine; Vaccination.

164-165, 171-172; development of, 15,International Union for the Conservation

54, 57-64, 142; effects on demographyof Nature and Natural Resources

and population dynamics, 60-61, 112,

(IUCN): 126.

146-147, 150-151, 155; failures of, 59, 62,

InterTribal Buffalo Council: agreement155-157, 160-161; genetic concerns, 119,to transfer Yellowstone bison, 134;

123, 126-129, 165; hazing, 54, 148; his-mission of, 133-134, 188; members

tory of, 15, 54, 57-64, 142-157; hunting,of, 133-134; Interagency Bison

57-58, 143, 148-149, 168-171; litigation

Management Plan and, 54. See alsoof, 128, 156, 164; management com-

Interagency Bison Management Plan;

pared to other ungulates, 19-20, 26,

Management; Yellowstone bison.

133, 137, 162; management steps, 54,
57; members of, 54; monitoring andresearch needs for, 57, 145, 157; objectives of, 54, 129, 145, 157, 165; public

Lacey Act (National Park Protective Act of1894): 46, 135, 171. See also Hunting.
Lactation, of bison: 188; costs of, 37, 100-

involvement with, 62-64, 161, 173-174;

103; effects on brucellosis resistance,

quarantine, 57-59, 144-145, 164, 172-21-22, 39; effects on subsequent preg-

173; risk of brucellosis transmission

nancy, 101; fertility control and, 35-37;

to cattle, 54, 57-58, 143-144, 155; spatial

milk production, 100-101; timing of,separation of bison and cattle, 54, 57,

100, 103. See also Nutrition; Nutri-156, 167; State Veterinarian, 29, 37, 40,

tional condition.

52-53, 147; success of, 57-59, 62, 64,

Lamar Valley: xvi, 4, 7, 13-14, 36, 45-48,

155-157, 159-160; terminal pastures,

51, 68, 70, 72-76, 82, 85, 109, 121, 123,

145, 172-173; test-and-slaughter, 54, 57,

166, 170.

60, 145, 154, 156, 172-173, 193; tolerance

Landscape-scale processes. See Grassland

for bison in Montana, 54, 57-58, 62,

ecosystems; Migration and dispersal;

143-144, 147-149, 152-153, 155-156, 162,

Vegetation and vegetation phenologyIndexLand use of humans: 136-137, 138, 167;
effects on bison, xiv, 17, 95, 117, 162,
174-176; effects on brucellosis, 24-27,
37-38.

Maintenance. See Nutrition; Nutritional
condition.
Mammoth Hot Springs: bison enclosure,44, 46; bison movements, 69, 72-73.

Learning, by bison: 9, 12, 78; by elk, 31.

Management, of bison: adaptive manage-

Lee Metcalf Wilderness (Monument

ment, 52-64, 143-145, 155, 165; annual

Mountain Unit): 148. See also U.S.

removal objectives, 145, 165; capture

Forest Service.

and facilities, 54, 57, 60, 145, 148-149,

Litigation: over bison management, 128,

154, 167-168, 171-172; compared to164, 188; rights of American Indians,

other ungulates, 19-20, 23, 26, 53, 133,

171.

137143, 160, 162, 174-176; conserva-

Livestock and cattle: abundance in thetion areas, 53, 72-75, 147-148, 152-153;

Yellowstone area, 26, 62, 143; brucel-

controversy over, 17, 41, 49, 59, 64,

losis regulations regarding, 13, 27-29,

94-95, 126-129, 133-134, 136-138, 141-

51-57, 142-143, 145-155; causes of bru-

144, 148-149, 155-157, 160-165, 170-171,

cellosis in, 13, 17, 19-20, 22-24, 26-27,

173-176; culling, 13-14, 17, 19, 29-30, 49,

33, 37-38, 42, 51-53, 57-58, 143, 155-156,

57, 59-62, 79, 94-95, 111, 119-129, 145,

160, 167-168; class-free brucellosis

149, 154-155, 160, 165, 171-172, 183, 191;

status, 27-29, 142-143; competition

feeding, 167-168; hazing/herding, 54,

with bison, xiv, 17, 99, 141-142, 162-163,

57-62, 71, 78-80, 144-145, 148-149, 164,

168; consideration of bison as, xiv,

167-168; hunting, xiii, 29-31, 38, 46, 52,

46-49, 52-54, 137-138, 159-162; defini-54, 57-60, 80, 131-132, 134, 143-145, 148,

tion, 183, 188; domesticated bison,

154, 161, 168-171, 176, 187; husbandry,

xiv, 13, 23, 27, 48, 159-160, 162, 183;

xiv, 46-49, 128, 187; issues regarding,fencing of, xiv, 79, 144, 149, 159-160,

17, 41, 49, 59, 64, 94-95, 126-129, 133-

168; industry, 13, 19, 23, 27-29, 41, 136,

134, 136-138, 141-144, 148-149, 155-157,

168, 175; interbreeding with bison,160-165, 170-171, 173-176; jurisdiction,

xiv, 120, 126, 127; stakeholder views

15, 17, 52-53, 147, 164; meat process-on brucellosis and wild bison, 41-42,

ing facilities, xiv, 29-30, 52, 59, 90,

79, 136-138, 142-143, 161-162, 164, 174-

117, 134, 144-145, 164, 171; migration

176; tolerance with elk, 19-20, 26-27;

predictions, 71-78, 145; monitoring

vaccination of, 33-34, 40, 42-43, 57,

and research needs for, 27-29, 33,

143, 155. See also Designated Surveil-

58-62, 129, 143-145, 157; operations

lance Area.

plans, 145-155, 165-174; population
guidelines and objectives, 57, 126, 129,

Madison Valley: 51, 69.

142, 145, 156, 165-174; principles of,

255

256

Yellowstone Bison: Conserving an American Icon in Modern Society
x, 29, 50, 128, 133-134, 174-176; quarantine and facilities, 55-60, 80, 134,

also Nutrition.
Metabolism, of bison: 12, 98-100, 188;

144-145, 164, 171-173, 191; relocation of

metabolic needs, 10-12; relation tobison, 14, 41, 46, 48, 58-59, 120, 135,

Brucella infections, 39; seasonal156, 172-173, 174-176; risk of brucel-

variations, 98-105.

losis transmission to livestock, x, 13,

Microbes. See Bacteria.

17, 19, 22-24, 26-27, 33-34, 41-43, 49,

Migration and dispersal, of bison: brucel-

52-54, 57-59, 79, 142-157, 160-162, 165-

losis and, 22, 23-24, 26, 30, 38-39;

168, 175-176; separation of bison andconservation and management impli-

livestock, 26-27, 42, 54, 57, 79, 127, 147,

cations, 69-71, 78-80; defined, 67, 189;

155-156, 167-168; shooting, 58, 145, 193;

effects of restricting, 78-80; factors

terminal pastures, 145, 172-173, 193;

influencing, 68-71, 74-80; from cen-tolerance, for bison, 17, 30, 41, 49, 53,

tral to northern Yellowstone, 68-69,

57-59, 60-62, 64, 94-95, 137-138, 144-

71-75; gene flow, 124, 128, 165; green

145, 147-149, 155-156, 162, 164, 167-168,

wave and, 73-74, 78; into Montana,

174-176; tools/practices, x, 15, 23, 27,

51-52, 74-75, 162-164; predictions of,

29-38, 52-64, 133, 142-155, 160-162, 164-71-78, 145; snowmelt and, 73-74, 78;

174; views on, 17, 27, 39-43, 49, 53, 64,

snowpack and, 69, 71, 75, 78; timing,

79, 133-134, 136-148, 155-157, 160-162,

68, 71-78.

164-168, 174-176. See also American

Mirror Plateau: 7, 13, 48, 51, 68-69, 71-75.

Indian tribes; Brucellosis; Hunting;Monitoring. See Management;Interagency Bison Management Plan;
Quarantine.

Surveillance.
Montana: bison hunting in, 31, 52, 58, 134,

Mary Mountain: 49, 51, 72.

143, 168-171; bison management in,

Mating, of bison. See Breeding, of bison.

14-15, 53-54, 58-59, 69, 142, 145-157,

Meadows. See Foraging; Habitat.

162-164, 171-173; bison numbers in, 15,

Meagher, Mary: xv.

62, 76-77; brucellosis containment

Meat, from bison: distribution of, 29-30,

in, 23, 27, 31, 40, 42, 51; cattle in, 33,

52, 59, 90, 134, 144-145, 171; for preda-

143, 155; designated surveillance area

tors, scavengers, and decomposers,in, 27-29, 33, 143; importation of Yel-

107, 160; production of, xiv, 117;

lowstone bison, 58-59; jurisdiction,

quality of, 134, 164; use of, 132-135;

17; legislature, 52; litigation, 128, 141,

vaccination and consumption of, 154.

156, 164; politics in, ix-x, 52-53, 142;

See also Human health and safety;

state veterinarian, 40; tolerance for

Vaccination.

(or against) bison in, 5, 54, 75, 78-79,

Metabolizable energy intake: 10-12, 188. See

95, 144, 167-168, 174-176; treaty rights

Indexin, 54, 58; See also Interagency Bisonof, 135-136; mission, 29; Organic Act

Management Plan.

of 1916, 170; policies regarding con-Montana Department of Livestock: 29,
53-54, 155.
Montana Fish, Wildlife & Parks: 52-54,
58, 148.

traception of wildlife, 37, 165. See also
Fertility control; Interagency Bison
Management Plan.
National Research Council: on fertility

Moose: 114, 137, 162.

control, 35, 37; on ecological process

Mortality: 90, 112; causes of, 90-94. See

management, 29, 49, 111; on publicalso Survival.
Mountain goats: 137.
Mountain (Wood) bison: differing opin-

involvement, 174.
Native Americans. See American Indian
tribes.

ions about subspecies in Yellowstone,

Native peoples in Yellowstone: 131-134.

120, 190.

Natural disturbance dynamics, 107-108;

Movements: annual, 67; between thecentral and northern regions of
Yellowstone, 68-69, 71-75; daily, 67;

droughts and, 86, 90.
Natural selection: 119, 126, 128, 159, 162, 165,
174, 185, 189.

factors influencing, 9-10, 68-71, 74-80,

New York Zoological Society: 135.

103; historical, 51-52, 74-75; influence

Nez Perce Tribe: 54, 58, 131-132, 148, 189.

of calving, 73-74, 84-85, 100-101, 103-

Nitrogen cycling: 107-108, 111-113, 189.

104; influence of competition andNorth American conservation strategy forbison density, 9-10, 74-80, 103; influence of forage availability and snow

bison: 126, 135.
Northern: breeding herd of bison, 7, 10,pack, 9-10, 74-80, 103; influence of

12-14, 17, 46, 48-49, 51, 60-61, 68-69,

roads and streams, 12-13; patterns and

71-76, 79-80, 85-86, 88, 90-91, 110-111,

routes, 71-78; seasonal, 71-78. See also

113, 120, 123-124, 127-128, 145-147, 150-

Distribution; Migration and disper-

151, 170; range/region, 3, 5, 7, 11, 14,sal; Range expansion.

31-32, 45-46, 50-51, 55, 66, 69, 79-80,

Mule deer: 137, 162, 176, 194.

91, 94, 111, 114, 126-130, 135, 140, 144,
148-149, 154-155, 163, 165.

Natality, of bison. See Demography.
National Academy of Sciences. See
National Research Council.
National expansion: xiii, 132, 134.
National Park Protective Act of 1894. See
Lacey Act.
National Park Service: bison as a symbol

Northern Arapaho: 131. See also American
Indian tribes.
Northern Cheyenne: 131. See also American Indian tribes.
Norris, Philetus: 45.
Numerical responses, of bison. See
Demography; Population dynamics.

257

258

Yellowstone Bison: Conserving an American Icon in Modern Society
Nursing, of calves. See Lactation.

100-101, 103-105; muscle anabolism

Nutrient cycling: xiv, 107-108, 111-113, 189.

and catabolism, 12, 100, 104-105;

Nutrition: annual variations in, 98, 100-

nutritional deprivation/restriction

104; calving dates and, 103-104;(under-nutrition), 12, 39, 104-105; pro-cellulose, 98-99, 104; dietary energy

tective immune responses and, 21-22,

and protein, 98-99, 104; digestion

34, 39; protein metabolism, 12, 100,and digestive capacity, 98-99; diges-

104-105; seasonal strategies, 100-104;

tive efficiency compared to othersusceptibility to brucellosis infection,

ungulates, 99; effects on juvenile

21-22, 34, 39. See also Brucellosis;

growth and survival, 12, 100-101, 103;

Pregnancy; Survival.

effects on fat and protein reserves,
12, 99-100; effects on pregnancy andOperations plans, for bison. See

lactation, 100-101, 103-105; effects on

Management.

reproduction and survival, 100, 103;

Organic Act of 1916: 170.

energy content of forage, 10, 98-99,

Overabundance, of bison, 14-15, 50; of

104; grasses and sedges, 7, 9-10, 98,

other ungulates, 14-15, 50, 110-111;

104; influence of plant maturity

concerns about, 14-15, 50, 78-80, 110-

(senescence), 9, 98-99, 104; protein

111, 137, 160; culling herds to address,

content of forage, 98; production of
fatty acids, 98; rumen and microbes,
7, 98; rumen processing rates, 99;
seasonal changes in, 98-99, 100-105;

50-52, 59-60.
Over-snow vehicles. See Snowmobiles andcoaches.
Ovulation. See Pregnancy.

secondary compounds, 98; shrubs,
98; spring and summer nutrition forbison, 98, 100-104; winter nutrition
for bison, 99.
Nutritional (body) condition, of bison:body mass and dominance rank, 101;
central versus northern Yellowstone,
10, 12; effects on juvenile growth andPablo-Allard (Michel Pablo, Charles
Allard): 46, 120, 135.
Paradise Valley: 64, 147, 167.
Parasites. See Disease.
Park County Stockgrowers Association:
156, 164.
Partnerships among state and federal

survival, 12, 99-101, 103; effects on

agencies, 29, 54, 59-60, 62, 138, 145,

pregnancy and lactation, 100-101, 103;

149, 155, 173. See also Interagency

factors influencing, 10, 12, 101, 104-105;

Bison Management Plan.

fat deposition and metabolism, 12,Parturition. See Birth.

101, 104-105; interaction with popula-

Pelican Valley: 7, 14, 45-46, 48-49, 51, 58,

tion density, 101; lactation effects on,

68-69, 71-75, 119, 123.

Index
Perceptions (and misperceptions) of park
management, 138, 141-144, 174-176.
Phenology. See Vegetation and vegetation

winter’s impact on, 91; wolves impact
on, 91, 94.
Precipitation: 7, 9, 10-12, 15, 49, 68-71, 74-75,

phenology

78, 80, 84-86, 90, 94-95, 99-100, 103,

Philopatry. See Fidelity.

105, 162, 167; effects of drought on

Physiology, of bison: 10, 12, 35, 98-105, 190.

ungulates, 86, 90. See also Snow and

Pink Mountain, Canada: xiv.
Plains bison: commercial herds, xiv; con-snowpack.
Predation: alternate prey, 114-117; anti-

servation herds, xiv; current status of,predator responses, 5, 84, 94, 117, 186;

xiv-xv; disappearance of, xiii, 45-46;

prey switching in multiple predator

ecological role, 107-110, 117; genetics,

ecosystems, 114-117; risk or vulner-

120; historical distribution of, xiii, 132,

ability, 90-94; ungulates as prey and,

134; restoration of, 135, 138, 141, 173,

90-94, 117. See also Competition;

174-176; symbolism, xiii, 132-133. See

Population dynamics; Wolf predation

also Bison.
Plains Indian tribes. See American Indian
tribes.
Plant communities and populations. See
Vegetation and vegetation phenology.

and restoration.
Pregnancy, of bison: effects of brucellosis,
87-89; effects of lactation, 86, 101;
estrus, 83-84; fetal sex ratios, 84; gestation length, 84; ovulation, 84; rates

Plant-herbivore systems: 107-113.

of, 85-87. sexual maturity, 4, 83; See

Plant phenology. See Vegetation and veg-

also Demography; Nutrition; Nutri-

etation phenology.

tional condition.

Poaching, of bison: xiii, 14, 48.

Prince Albert, Canada: xiv, 10.

Politics, of bison: ix-x, xiii-xv, 17, 138, 156-

Productivity. See Demography; Vegetation

157, 173-176.
Population dynamics, of bison: effects ofcompetition with elk, 108-111, 114-117;
effects of culling, 52, 59-60, 90-91;

and vegetation phenology.
Pronghorn: 137, 162, 176.
Property damage and public safety. See
Humans; Human health and safety.

effects of disease, 19, 29-30, 41; effects

Protein, crude. See Nutrition.

of harvest, 31, 52, 59-60; effects of

Public, Yellowstone management strate-

road grooming, 12-13; historical esti-

gies and, 40-41, 62-64, 126-127, 135,

mates, 14-17; population subdivision,

165, 173-174.

123-128; population size and range,
15, 60-61, 146-147, 150-151, 155, 165;

Quarantine, of bison: alternative to reduce

population viability, 126-127, 129; rates

shipments to meat processing facili-of increase, 112; regulation, 145, 147;

ties, 59-60, 164, 172; definition, 191;

259

260

Yellowstone Bison: Conserving an American Icon in Modern Society
facilities, 58-59, 145; feasibility study,

Relocation, of bison: factors limiting

58-60, 144; interest in obtaining Yel-the translocation of Yellowstone

lowstone bison, 173; limitations of,bison, 41, 58-59, 156, 172-173, 174-176;

145, 171, 173; minimum quarantine

northern to central Yellowstone, 14,periods, 173; proposed for Yel-

48; from Yellowstone, 41, 58-59, 156,

lowstone bison, 80, 134; protocols

172-173, 174-176; into Yellowstone, 14,

and designs for, 57-59; testing for
brucellosis exposure, 58-60; reloca-

46, 120, 135.
Remote vaccination, of bison: 57, 191;

tion of brucellosis-free Yellowstone

bio-bullet, 182; evaluation of, 38, 144;bison, 59-60. See also Brucellosis;

impacts of, 38-40; recommenda-

Interagency Bison Management Plan;

tions regarding, 40-41, 144. See also

Management; Testing for brucellosis.

Vaccination.
Removals, of bison. See Culling; Hunting;Radio-collaring, of bison. See Telemetry.
Ranching, of bison: 14, 46-49, 59, 162; ofcattle, 57, 62, 79, 136, 143, 175, 183, 188.
Range expansion, of bison: defined, 67,

Shipments.
Reproduction. See Pregnancy.
Research. See Management; Surveillance.
Resources, for bison: density and, 9-10, 69,

191; effects of culling on, 69; effects

103; snow pack and, 9, 68-69, 74-75,

of bison density, 14, 51, 69, 110; factors

78, 84-86; influence on migration,

influencing, 69-71, 162-164; effects ofdispersal, and range expansion, 9, 15,learning, 69; influence on popula-

67-71, 73; limitation and, 9-10, 69, 74;

tion growth, 69-71; influence of roadpartitioning among different species

grooming, 12-13; into Montana, 14, 51,of ungulates, 9, 108-111; predators

69; timing of in Yellowstone, 49-51,

and, 9-10; selection of, 5, 7, 9, 98-105,

69, 110. See also Migration and dis-111-113.

persal; Movements.

Restoration, of bison: plains bison, xii-xiv,

Recovery, of bison: factors influencing,135-136, 137-138, 159-160, 165, 174-176;

xv, 13, 19, 141-144, 155-156, 159-161; inin the Greater Yellowstone Area, 17,

Yellowstone, 1, 57-59, 141-144, 155-156,

19-20, 135-136, 174-176; in Yellowstone

159-161; lack thereof, xiv, 59, 137-138;

National Park, 1, 46-52, 119-120, 135-

Plains bison, xiv, 137-138.
Recreation, effects on bison habitat: 17, 117,
136; road grooming and bison travel,
12-13; wildlife viewing, 175-176.
Recruitment, of bison. See Demography.
Reintroduction, of bison. See Restoration.

136, 141-145, 159-160, 165.
Road grooming, winter. See Recreation.
Roads, bison use of: 12-13, 16, 65, 68-69, 72,
149, 168, 170, 176.
Rocky Mountains, bison distribution in:xiii, 114, 131.

IndexRoyal Teton Ranch: 57, 62, 143.
Rumen. See Nutrition.
Ruminant. See Nutrition.
Rut. See Breeding.

Sheepeaters, band of Shoshone in Yellowstone: 131-132. See also American
Indian tribes.
Shipments, of bison to meat processing
facilities: agreements with Ameri-

Sagebrush communities: 96, 110.

can Indians, 134; alternatives to, 30,

Scale: xiv, 9, 39, 43, 75,165, 192; culling

144-145, 160, 172-173; authorities, 49;of bison and, 127, 165; population

concerns about pregnancy, 149, 172;

dynamics and, 138; spatial and tem-coordination of, x, 171; effects onporal scale, 117.

bison demography, genetics, andScientific information, need for in man-

population dynamics, 49, 59, 86,agement of Yellowstone: 59, 62, 157,

90-91; likely infectious bison, 154;

174.

numbers, 29-30, 49, 52, 59-60; objec-

Secretary of the Interior: consultation

tives of, 52, 59; protocols for, 154;

with and support of American Indian

public reaction to, 30, 52, 59; strate-

tribes, 134; disposition of surplus

gies for, 30, 49, 62, 154, 156; timing of,bison, 49; quarantine of bison, 134.

145. See also American Indian tribes;

See also American Indian Tribes;

Demography; Genetics; Manage-

Trust resources.
Sedges. See Food; Food habits; Grassland
ecosystems; Habitat; Vegetation andvegetation phenology
Select agent. See Brucellosis.
Selective breeding and/or culling, of bison:30, 129, 160-161, 165, 171-172. See also
Breeding; Culling.
Senescence: in bison reproduction, 85-87;
in bison survival, 90-91; in plants/

ment; Population dynamics.
Shoshone-Bannock Tribes: 58, 131-132, 148.
Shoshone National Forest: 132. See also
U.S. Forest Service.
Shrubs. See Food; Food habits; Grassland
ecosystems; Habitat; Vegetation andvegetation phenology
Sioux tribes: 130, 133. See also American
Indian tribes.
Snow and snowpack: birth rates/calv-

vegetation, 39, 103, 192. See also

ing and, 84-86; differences between

Demography; Vegetation and vegeta-

central and northern Yellowstone,tion phenology.

7, 49, 71; displacement by bison, 2,

Serology. See Testing for brucellosis.

9, 110, 118; effects on energetics andSex and age composition, of bison. See

survival, 90-91, 99-100; foraging and,Age distribution.

2, 4, 9, 74-75, 103; geothermal impacts,

Sexual maturity: 2, 4, 83.

5; grooming of, 12-13; hazing and, 148-

Sheep, bighorn. See Bighorn sheep.

149; influence on movements, 9, 15, 31,

261

262

Yellowstone Bison: Conserving an American Icon in Modern Society
74-75, 78-79, 95, 162, 167; influence on

Surveillance: annual monitoring andnutrition, 10-12, 39; melt, 78, 103-105;

reporting, 58-62, 157; brucellosis,

migration and, 24, 68-69, 73, 79-80;

27-29, 33, 58-62, 143-145; plan for Yel-model projections, 145; travel throughlowstone bison, 58-62, 129. See also

by bison, 12-13, 66; wolf predation

Management.

of bison and, 10, 94-95. See also Dis-

Survival, of bison: adults, 87, 90-94, 112;

tribution; Foraging; Migration andcalves, 87, 90, 112; central versus

dispersal; Movements; Nutrition;

northern region of Yellowstone,

Nutritional condition; Predation.

90-91; effects of capture and con-

Snowmobiles and coaches: 12, 148-149. See

finement on, 167-168; effects ofalso Recreation.
Social organization, of bison. See
Behavior.
Social tolerance, for bison: 17, 30, 41, 49, 53,bison density on, 14-15, 90; effectsof brucellosis on, 13-15, 19, 87-89,
155-157; effects of culls and harvests
on, 94-95, 155-157; effects of drought

57, 59, 62, 64, 94-95, 137-138, 142, 144-

on, 90; effects of fertility control

145, 148-149, 155-156, 162, 164, 167-168,

on, 36-37; effects of nutrition on,

174, 193.

97, 100-101, 103-105; effects of road

Soils, diseases and: 13, 167; effects of bisongrooming on, 12-13; effects of preda-

on, 79, 107-111; effects on teeth wear,

tion on, 90-91; effects of snow on,

9, 90; wallowing effects on, 107, 194.

90; senescence in, 90-91. See also

Spatial separation, of bison and cattle:

Demography; Mortality.

26-27, 42, 54, 57, 79, 127, 147, 155-156,
167-168. See also Brucellosis; Inter-

Teeth, of bison: eruption patterns, 2;agency Bison Management Plan.

senescence and wear, 9, 90.

Starvation, of bison: 78, 90-91, 94-95, 113,

Telemetry, of bison, 8, 72-75, 84-91, 124,

145, 195.
State Veterinarian, of Montana. See Inter-

127, 191.
Temperature, air. See Climate; Weather

agency Bison Management Plan.

Terminal pastures, for bison: 145, 193: alter-

Stephens Creek: 149, 167. See also Capture.

native to reduce shipments to meat

Strain RB51 vaccine. See Vaccination.

processing facilities, 172-173; defined,

Subspecies controversy: 120, 190. See also

193. See also Management; Shipments

Mountain bison.
Summer ranges, for bison. See
Distribution.
Supplemental feeding, of bison: 14, 24, 48,
167-168.

of bison; Quarantine.
Test-and-slaughter. See Brucellosis; Interagency Bison Management Plan;
Management; Testing.
Testing, for brucellosis. See Brucellosis

Index(culture, diagnostics, serology).
Tolerance, for bison: beliefs and values,

Ungulates: See Bighorn sheep; Bison; Elk;
Moose; Mountain goats; Mule deer;

60-62, 137-138, 174, 176; effects on risk

Pronghorn; White-tailed deer.

of brucellosis transmission to cattle,

Urine, fertilizing effects of: 111-113

49, 149, 168, 175-176; effects on bison

U.S. Animal Health Association: 23, 26-27,

calving and migration, 62, 95; effects

162.

on the costs of bison management,

U.S. Army: 135; cavalry in Yellowstone, 46.

167; in Montana, 53, 147-148, 155, 162,

U.S. Department of Agriculture: 15, 58. See

164; issues regarding,64, 94-95, 149;

also Animal and Plant Health Inspec-lack of, 17, 41, 49, 59, 94-95, 137-138,tion Service (APHIS); U.S. Forest

148, 156, 174; misperceptions regard-

Service.

ing bison, 137-138, 174-175; tools to

U.S. Department of the Interior: ix, 4, 126,

increase, 30, 57-58, 62, 64, 144-145,

171, 173. See also National Park Ser-

148, 155, 164, 168.

vice; Yellowstone National Park.

Tools, for managing bison and brucellosis.

U.S. Forest Service: grazing allotments,

See Brucellosis; Interagency Bison

26, 37, 143, 168; management of wild-

Management Plan; Management.

life with the State of Montana, 15,

Tourism: 136-137, 175-176.
Transfer, of bison. See Shipments.
Travel corridors, of bison: 7, 12-13, 67-68,
71-78. See also Recreation.

52, 54. See also U.S. Department ofAgriculture.
U.S. Government Accountability Office:59, 157.

Treaties of Fort Laramie (1851, 1868): 132.

Utilization (Use) areas, by bison: 8, 72-75,

See also American Indian tribes.

194. See Distribution; Movements;

Treaty rights to hunt bison: 54, 58, 132-133,

Migration and dispersal; Range

143, 145, 161, 164, 170-171, 176. See also

expansion.

American Indian tribes; Hunting;Interagency Bison Management Plan.

Vaccination: antibodies to Brucella, 22-24,

Tribes. See American Indian tribes.

33, 35, 182; booster, 34, 37; calfhood,

Trust resources, bison as: 133-134, 171.

29, 143, 155; cost effectiveness, 37-38,

Turner Enterprises, Inc.: 59.

175; definition, 194; delivery of, 35,
38-39, 40-41, 57, 144, 154, 182, 191;

Umatilla. See Confederated Tribes of the

difficulties with and unintended

Umatilla Indian Reservation.

effects of, 33, 38-43, 155-157; efficacy

Uncertainty: 41, 126-127.

of, 33-34, 43,; effort required, 38-39,

Undernutrition, of bison. See Energetics;

42-43; experiments versus field

Nutrition.

application, 33-34, 39; evaluations of

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Yellowstone Bison: Conserving an American Icon in Modern Society
effects, 39-41; feasibility, 38-41, 155-

types of, 5, 7, 71-78, 100-106; ungulate

157, 165, 167; fertility control, 34-37,

grazing and, 97-105, 107-113. See also

165, 167; human consumption of

Grassland ecosystems.

meat and, 154; immune protection

Vigilance. See Behavior.

(resistance to Brucella infection),

Visitors and interactions with wildlife:

20-22, 38-40; influence of nutrition/ix, xv, 160; economic benefits, 137;

condition on immune responses,

effects of management on, 38-40, 149,

21-22, 39; influence of pregnancy on

170-171; numbers to Yellowstone, 176;

immune responses, 22, 39; modelingreasons for visiting, 137, 175-176.

evaluations of effectiveness, 41; ofVital rates. See Demography.

Yellowstone bison, 33-34, 38-40, 42,149; of cattle, 29, 33-34,42-43, 143, 155;

Walking Coyote: 135.

of elk, 33-34, 38-40, 42; oral delivery,

Wallowing: xvi, 107-110; description of,35, 38; predictions of effectiveness,
39-41; proportion of population

194; influence on soils and vegetation,
107. See also Behavior.

needed, 38; reduction in brucellosis

Water: 9, 84, 107-108, 110.

prevalence and transmission, 33-34,

Weaning, of bison: 84, 194.

43; remote delivery, 35, 38-39, 40-41,

Weather, 29, 41, 49; effects of on bison

57, 144, 182, 191; research on, 41, 143;

populations, 69, 74-75, 78-80, 86, 90,

safety, 57; strategies, 42-43, 154, 162,

95, 110-111, 145, 154; effects of on veg-

165, 167; timing of delivery, 38-39;

etation, 98-105, 190; ungulate foraging

vaccines, 33-34. See also Interagency

and, 69, 75-78, 90. See also Climate

Bison Management Plan; Livestockchange; Drought; Yellowstone

and cattle; Management.

National Park.

Vaccines. See Vaccination.
Vegetation and vegetation phenology:
dormant season, 71, 98-100, 103-105;

Weights, of bison: adults, 2; birth, 84;
calves, 2, 84; gain/loss, 12; importanceof, 101; yearlings, 2.

effects of bison on, 97-105, 107-113;

West Yellowstone, Montana: 58.

effects of variations in temperature

White-tailed deer: 137, 162, 176, 194.

and precipitation on, 2, 4, 9, 74-75,

Wild, wide-ranging: definition, 126, 161-

103; green-up, 71-78, 100-106; grow-

162, 194; ecological role, xiv, 49-52,

ing season, 71-74, 78, 100-101, 103-105;

107-117; genetic recommendations of,measurements of, 9-10, 113; natural

126; processes that sustain them, 119,

disturbance dynamics and, 108;

126, 128, 159, 161-162, 189; public sup-plant phenology, 71-78, 100-106;

port (or lack of ) for, xiv, 17, 52-53, 57,

senescence, 9, 39, 98-99, 103-104, 192;

136-138, 141-142, 147-148, 156, 160-161,

Index174-176; Yellowstone bison, x, xiv, 1,

Brucellosis; Demography; Genetics;

46-49, 133, 142, 155, 159-162, 167-168.

Interagency Bison Management Plan;

See also Adaptive capabilities.
Wind Cave National Park: 135.

Management; Population dynamics.
Yellowstone ecosystem: distribution of

Winter-kill. See Starvation.

forage in, 2, 4, 7-13, 69, 74-75, 78,

Winter ranges, for bison. See Distribution.

98-105, 110, 113, 118; geography of,

Wolves: age of bison kills, 94; appar-

5-8, 28, 53, 72-75, 139, 152-153; plantent competition, 114-117; effects on

phenology in, 24, 73, 71-78, 103-104,

bison abundance and distribution

106, 149; pre-European Americans in,patterns, 10, 90-94, 114; effects on

131-134; rivers in, 5, 7, 14, 45, 48-49, 51,

elk abundance and distribution pat-68-69, 71-77, 83, 132, 137, 147-149, 170;

terns, 17, 94; carrion abundance and,scale and, xiv, 9, 39, 43, 75, 117, 138,

31; elk and, 94; factors influencing

192; soils in, 9, 13, 79, 90, 107-108, 110-kills of bison, 10, 90-94; grassland

111; See also Fires of 1988; Grassland

ecosystems and, 111-117; numbers inecosystems; Natural disturbanceYellowstone, 91; percent bison in

dynamics; Riparian ecosystems; Veg-

wolf diets in Yellowstone, 94; preda-

etation and vegetation phenology.

tion on bison, 5, 90-94; scavenging of

Yellowstone Lake: 51, 63, 69, 71.

bison, 31-32. See also Predation.

Yellowstone National Park: area of, 195;

Wood bison: 89, 120,190. See also Mountain bison.
Wood Buffalo National Park, Canada,
23, 94.

boundary of, 6, 8; brucellosis controversy in, 19-43; establishment of,45, 132, 171, 195; historical narrativesof, 45-64; hunting in, 31, 46, 170-171;

Woodland caribou. See caribou.

low-elevation winter habitat for

Wyoming: bison in, 5-7, 52, 131; brucellosis

ungulates, 71-77; map of, 6, 8; military

in cattle, 23, 27; brucellosis in elk,management of, 46, 135; poaching in,

27-30, 33, 42, 143; economic evalu-

xiii, 46, 48; predators in, 17, 90-94;

ations of brucellosis management

purpose of, 46, 138; size of, 195; U.S.

actions, 37-38, 175; feed grounds in,

Cavalry in, 46; website for bison, 64.

24, 29-33. See also Elk.

Yellowstone National Park Act (1872): xiii,
46, 171, 195.

Yankee Jim Canyon: 147.
Yellowstone bison: See also Bison;

Yellowstone River: 7, 45, 51, 68, 71, 73, 76,
132, 147-148.

265

The iconic bison deserves our best efforts to assure its place on the American
landscape. I am grateful to the authors for clearly articulating the issues we face
as we collectively determine the future of these animals. The authors have given
us a chance to advance our discussions based on a common understanding of
the science, culture, and politics surrounding bison.

— From the Preface by Daniel N. Wenk