Using Science to Improve the

BLM WILD HORSE AND
BURRO PROGRAM

A WAY FORWARD

Committee to Review the Bureau of Land Management
Wild Horse and Burro Management Program

Board on Agriculture and Natural Resources

Division on Earth and Life Studies

NATIONAL RESEARCH COUNCIL
OF THE NATIONAL ACADEMIES

THE NATIONAL ACADEMIES PRESS

Washington, D.C.

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Committee to Review the Bureau of Land Management Wild Horse and Burro Management Program Board on Agriculture and Natural Resources Division on Earth and Life Studies

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THE NATIONAL ACADEMIES PRESS  500 Fifth Street, NW  Washington, DC 20001 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This study was supported by Contract L11PC00058 between the National Academy of Sciences and the Bureau of Land Management. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project. International Standard Book Number-13: 978-0-309-26494-5 International Standard Book Number-10: 0-309-26494-4 Additional copies of this report are available for sale from the National Academies Press, 500 Fifth Street, NW, Keck 360, Washington, DC 20001; (800) 624-6242 or (202) 334-3313; http://www.nap.edu/. Cover: Design by Michael Dudzik. Horse photo courtesy of the Bureau of Land Management. Burro photo courtesy of Michael Gallagher. Back cover photo courtesy of the Bureau of Land Management. Copyright 2013 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal govern- ment on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. C. D. Mote, Jr., is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertain- ing to the health of the public. The Institute acts under the responsibility given to the National Acad- emy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to asso­ ciate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the N ­ ational Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is admin- istered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. C. D. Mote, Jr., are chair and vice chair, respectively, of the National Research Council. www.national-academies.org

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COMMITTEE TO REVIEW THE BUREAU OF LAND MANAGEMENT WILD HORSE AND BURRO MANAGEMENT PROGRAM GUY H. PALMER, Chair, IOM,1 Washington State University, Pullman CHERYL S. ASA, St. Louis Zoo, St. Louis, Missouri ERIK A. BEEVER, U.S. Geological Survey, Bozeman, Montana MICHAEL B. COUGHENOUR, Colorado State University, Fort Collins LORI S. EGGERT, University of Missouri, Columbia ROBERT GARROTT, Montana State University, Bozeman LYNN HUNTSINGER, University of California, Berkeley LINDA E. KALOF, Michigan State University, East Lansing PAUL R. KRAUSMAN, University of Montana, Missoula MADAN K. OLI, University of Florida, Gainesville STEVEN PETERSEN, Brigham Young University, Provo, Utah DAVID M. POWELL, Wildlife Conservation Society, Bronx Zoo, New York City DANIEL I. RUBENSTEIN, Princeton University, Princeton, New Jersey DAVID S. THAIN, University of Nevada, Reno (retired) Staff KARA N. LANEY, Study Director JANET M. MULLIGAN, Senior Program Associate for Research KATHLEEN REIMER, Senior Program Assistant ROBIN A. SCHOEN, Director, Board on Agriculture and Natural Resources NORMAN GROSSBLAT, Senior Editor 1  Institute of Medicine v

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BOARD ON AGRICULTURE AND NATURAL RESOURCES NORMAN R. SCOTT, Chair, NAE,1 Cornell University, Ithaca, New York (Emeritus) PEGGY F. BARLETT, Emory University, Atlanta, Georgia SUSAN CAPALBO, Oregon State University, Corvallis GAIL CZARNECKI-MAULDEN, Nestlé Purina PetCare, St. Louis, Missouri HAROLD L. BERGMAN, University of Wyoming, Laramie RICHARD A. DIXON, NAS,2 University of North Texas, Denton GEBISA EJETA, Purdue University, West Lafayette, Indiana ROBERT B. GOLDBERG, University of California, Los Angeles FRED GOULD, NAS,2 North Carolina State University, Raleigh GARY F. HARTNELL, Monsanto Company, St. Louis, Missouri GENE HUGOSON, University of Minnesota, St. Paul MOLLY M. JAHN, University of Wisconsin, Madison ROBBIN S. JOHNSON, Cargill Foundation, Wayzata, Minnesota JAMES W. JONES, NAE,1 University of Florida, Gainesville A. G. KAWAMURA, Solutions from the Land, Washington, DC STEPHEN S. KELLEY, North Carolina State University, Raleigh JULIA L. KORNEGAY, North Carolina State University, Raleigh PHILIP E. NELSON, Purdue University, West Lafayette, Indiana (Emeritus) CHARLES W. RICE, Kansas State University, Manhattan JIM E. RIVIERE, IOM,3 Kansas State University, Manhattan ROGER A. SEDJO, Resources for the Future, Washington, DC KATHLEEN SEGERSON, University of Connecticut, Storrs MERCEDES VAZQUEZ-AÑON, Novus International, Inc., St. Charles, Missouri Staff ROBIN A. SCHOEN, Director CAMILLA YANDOC ABLES, Program Officer KARA N. LANEY, Program Officer JANET M. MULLIGAN, Senior Program Associate for Research KATHLEEN REIMER, Senior Program Assistant EVONNE P. Y. TANG, Senior Program Officer PEGGY TSAI, Program Officer 1  National Academy of Engineering 2  National Academy of Sciences 3  Institute of Medicine vi

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Preface 千里之行,始于足下 Lao-tzu, The Way of Lao-tzu T he above quotation has been translated most commonly as “A journey of a thousand miles begins with a single step” and, alternatively, as “Even the longest journey must begin where you stand.” In both interpretations, there is relevance to moving forward to improve management of free-ranging horses and burros on public lands in the western United States. Although there is a broad spectrum of public opinion regarding how horses should be managed on the land, there is also common ground as to the goal of sustaining healthy equid populations managed on healthy rangeland. In light of the charge to our committee and in the course of our public engagement, it is clear that the status quo of continually removing free-ranging horses and then maintaining them in long-term holding facilities, with no foreseeable end in sight, is both economically unsustainable and discor- dant with public expectations. It is equally evident that the consequences of simply letting horse populations, which increase at a mean annual rate approaching 20 percent, expand to the level of “self-limitation”—bringing suffering and death due to disease, dehydration, and starvation accompanied by degradation of the land—are also unacceptable. Those facts define the point from which we must begin the journey. However, it also provides a direction for the next steps: how can the natality be effectively managed so as to ensure that genetically viable, physically and behaviorally healthy equid populations are maintained on the land while preserving the ecosystem itself? The committee has endeavored to examine the full array of options to meet that goal by reviewing prior National Research Council reports on the Wild Horse and Burro Pro- gram, studying existing data and current program procedures used by the Bureau of Land Management, and inviting experts to present evidence related to equid behavior, genetics, and reproduction as well as management approaches. Importantly, the committee did not limit itself to free-ranging horses and burros in the western United States but incorporated knowledge derived from the study of equid populations as diverse as donkeys in Sicily, zebras in Africa, and horses on Assateague Island and other barrier islands of the eastern United States. In a similar vein, the committee included studies of diverse ecosystems in which multiple species overlap, such as Yellowstone and the Serengeti, and lessons learned vii

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viii PREFACE in resolution of environmental issues in which different sectors of the public held views that once seemed irreconcilable. The committee took seriously the public’s valuation of free-ranging horses and burros on public lands, the importance of promoting a healthy multiple-use ecosystem, and the economic consequences of simply continuing the status quo. On behalf of the committee, I want to express my appreciation to each and every per- son who took the time, effort, and expense of providing public comment and to those who shared their “citizen science” data with the committee. A study of this magnitude requires a tremendous commitment from the commit- tee members. All have sacrificed evenings, weekends, and vacations—without financial c ­ ompensation—in this commitment and in their desire to bring the best possible science to bear on a challenging issue. Individually and collectively, they brought a wealth of experi- ence and knowledge and engaged in vigorous intellectual debate to meet the challenge. On behalf of the committee, I express our thanks and appreciation to the study director, Kara Laney; to Robin Schoen, director of the Board on Agriculture and Natural Resources; to Janet Mulligan, senior program associate for research; and to Kati Reimer, senior program assistant. Without their planning, organization, and editing expertise, this report would not have been possible. I also want to recognize the valuable contributions of Dr. Irwin Liu, who provided expertise on equid fertility. Science alone, even the best science, cannot resolve the divergent viewpoints on how best to manage free-ranging horses and burros on public lands. Evidence-based science can, however, center debate about management options on the basis of confidence in the data, predictable outcomes of specific options, and understanding of both what is known and where uncertainty remains. I am confident that this study provides a centerpoint and hope that it will serve as a guide for the first step in the journey toward ensuring that genetically viable, physically and behaviorally healthy equid populations can be maintained while preserving a thriving, balanced ecosystem on public lands. Guy Hughes Palmer Chair, Committee to Review the Bureau of Land Management Wild Horse and Burro Management Program

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Acknowledgments T his report is the product of the cooperation and contribution of many people. The mem- bers of the committee thank all the speakers who provided briefings to the committee (Appendix C contains a list of presentations to the committee). Members also wish to express gratitude to Dr. Irwin Liu, University of California, Davis, for his time and input. This report has been reviewed in draft form by persons chosen for their diverse per- spectives and technical expertise in accordance with procedures approved by the National Research Council’s Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards of objectivity, evidence, and responsiveness to the study charge. The review com- ments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following for their review of this report: Barry Ball, Gluck Equine Research Center, University of Kentucky David Berman, Ozecological Pty. Ltd. Elissa Z. Cameron, University of Tasmania C. Rex Cleary, Bureau of Land Management (retired) Leonard Jolley, U.S. Department of Agriculture, Natural Resources Conservation ­Service (retired) Robin C. Lohnes, American Horse Protection Association Robin K. McGuire, Lettis Consultants International, Inc. John McLain, Resource Concepts Inc. Colleen O’Brien, Australian Brumby Alliance Greg Olsen, GHO Ventures, LLC Oliver A. Ryder, San Diego Zoo Institute for Conservation Research Donald B. Siniff, University of Minnesota (Emeritus) Thomas Webler, Social and Environmental Research Institute Gary C. White, Colorado State University (Emeritus) ix

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x ACKNOWLEDGMENTS Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations, nor did they see the final draft of the report before its release. The review of this report was over- seen by coordinator, Dr. Stephen W. Barthold, University of California, Davis, appointed by the Division on Earth and Life Studies, and monitor, Dr. May R. Berenbaum, University of Illinois, Urbana-Champaign, appointed by the National Research Council’s Report Re- view Committee. The coordinator and monitor were responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.

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Contents SUMMARY 1 1 FREE-RANGING HORSES AND BURROS IN THE WESTERN UNITED STATES 13 Committee Charge and Approach, 14 Bounds of the Study, 19 Status of Free-Ranging Horses and Burros Under Bureau of Land Management Jurisdiction, 21 Organization of the Report, 26 References, 28 2 ESTIMATING POPULATION SIZE AND GROWTH RATES 31 Estimating the Size of Free-Ranging Equid Populations, 32 Equid Population Growth Rates, 48 Conclusions, 53 References, 57 3 POPULATION PROCESSES 61 Density-Dependent Factors, 62 Density-Independent Population Controls, 69 Effects of Predation, 72 Consequences and Indicators of Self-Limitation, 74 Management Factors, 81 Conclusions, 84 References, 87 xi

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xii CONTENTS 4 METHODS AND EFFECTS OF FERTILITY MANAGEMENT 93 Equine Social Behavior and Social Structure, 94 Reproduction in Domestic Horses and Donkeys, 95 Potential Methods of Fertility Control in Free-Ranging Horses and Burros, 96 Adjustment of Sex Ratio to Limit Reproductive Rates, 97 Female-Directed Methods of Fertility Control, 98 Male-Directed Methods of Fertility Control, 122 Additional Factors in Evaluating Methods of Fertility Control, 128 Identifying the Most Promising Fertility-Control Methods, 129 Conclusions, 133 References, 135 5 GENETIC DIVERSITY IN FREE-RANGING HORSE AND BURRO POPULATIONS 143 The Concept and Components of Genetic Diversity, 143 Research on Genetic Diversity in Free-Ranging Populations Since 1980, 144 The Relevance of Genetic Diversity to Long-Term Population Health, 145 Is There an Optimal Level of Genetic Diversity in a Managed Herd or Population?, 150 Management Actions to Achieve Optimal Genetic Diversity, 161 Conclusions, 169 References, 170 6 POPULATION MODELS AND EVALUATION OF MODELS 175 Utility of Population Models, 175 Population Models Applied to Horses and Burros, 176 Population-Modeling Framework Used by the Bureau of Land Management, 179 The Wild Horse Management System Model, 183 Alternative Modeling Approaches, 184 Conclusions, 188 References, 191 7 ESTABLISHING AND ADJUSTING APPROPRIATE MANAGEMENT LEVELS 195 The History of Appropriate Management Levels, 196 Evaluation of the Handbook Approach, 199 Establishing and Validating Appropriate Management Levels: Science and Perceptions, 213 Conclusions, 226 References, 230 8 SOCIAL CONSIDERATIONS IN MANAGING FREE-RANGING HORSES AND BURROS 239 Disparate Values Related to Free-Ranging Horses and Burros, 240 The Case for Public Participation, 243 Opportunities for the Bureau of Land Management to Engage the Public, 257 Conclusions, 259 References, 260

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CONTENTS xiii 9 A WAY FORWARD 265 The Problem with “Business as Usual”, 265 The Toolbox, 266 A New Approach, 269 References, 270 APPENDIXES A Biographical Sketches 271 B Previous National Research Council Reports on Free-Ranging Horses and Burros 277 C Presentations to the Committee 285 D Questions and Requests from the Committee 287 E Herd Management Areas 293 F Pairwise Values of Genetic Distance (Fst) 307

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