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WILD AND FREE-ROAMING HORSES AND BURROS: Current Knowledge and Recommended Research Phase I Final Report of the Committee on Wild and Free-Roaming Horses and Burros Board on Agriculture and Renewable Resources Commission on Natural Resources National Research Council NATIONAL ACADEMY PRESS "' ? Washington, D.C. l980 MAY 0 8 1981 L1BRARY
£1l 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 report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Research Council was established by the National Academy of Sciences in l9l6 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and of advising the federal government. The Council operates in accordance with general policies determined by the Academy under the authority of its congressional charter of l863, which establishes the Academy as a private, non-profit, self-governing membership corporation. The Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in the conduct of their services to the government, the public, and the scientific and engineering communities. It is administered jointly by both academies and the Institute of Medicine. The National Academy of Engineering and the Institute of Medicine were established in l964 and l970, respectively, under the charter of the National Academy of Sciences.
COMMITTEE ON WILD AND FREE-ROAMING HORSES AND BURROS Frederic H. Wagner (Chairman), Utah State University Gail L. Achterman, Portland, Oregon John L. Artz, University of Nevada, Reno Francisco J. Ayala, University of California, Davis Wilbert H. Blackburn, Texas A&M University Walter H. Conley, New Mexico State University L. Lee Eberhardt, Kennewick, Washington Warren E. Johnston, University of California, Davis Stephen R. Kellert, Yale University John C. Malechek, Utah State University Patricia D. Moehlman, University of Wisconsin Ulysses S. Seal, VA Medical Center, Minneapolis J.W. Swan, Rogerson, Idaho Sally K. Fairfax, BARR Liaison Philip Ross, Staff Officer iii
BOARD ON AGRICULTURE AND RENEWABLE RESOURCES George K. Davis, Chairman, University of Florida Chester O. McCorkle, Jr., Vice Chairman, University of California, Davis John D. Axtell, Purdue University Neville P. Clarke, Texas A & M University Sally K. Fairfax, University of California, Berkeley John E. Halver, University of Washington Robert O. Herrmann, Pennsylvania State University Minoru Hironaka, University of Idaho Laurence R. Jahn, Wildlife Management Institute Bernard S. Schweigert, University of California, Davis George R. Staebler, Weyerhaeuser Company Paul E. Waggoner, Connecticut Agricultural Experiment Station Philip Ross, Executive Secretary iv
COMMISSION ON NATURAL RESOURCES Robert M. White, Chairman, University Corporation for Atmospheric Research Timothy Atkeson, Steptoe & Johnson Stanley I. Auerbach, Oak Ridge National Laboratory Norman A. Copeland, E.I. du Pont de Nemours and Company, Inc. (retired) George K. Davis, University of Florida Edward D. Goldberg, Scripps Institution of Oceanography Charles J. Mankin, Oklahoma Geological Survey Chester O. McCorkle, Jr., University of California, Davis Norton Nelson, New York University Medical Center Daniel A. Okun, University of North Carolina David Pimentel, Cornell University John E. Tilton, Pennsylvania State University Alvin M. Weinberg, Oak Ridge Associated Universities E. Bright Wilson, ex officio, Harvard University Wallace D. Bowman, Executive Director
CONTENTS PREFACE Xi ACKNOWLEDGMENTS xi EXECUTIVE SUMMARY l l: INTRODUCTION 13 The Committee's Charge l3 Subdivision and Timing of the Task l4 Structure and Basis of the Report l6 2: BIOLOGY OF HORSES AND BURROS l9 Information Needs l9 State of Knowledge 20 Information Sources 20 History and Paleontology of Equids in North America 2l Behavioral Ecology of Equids 23 Equid Demography 33 Demography-Related Characteristics of the Mare Reproductive Cycle 86 Genetic Polymorphism 89 Food Habits of Horses and Burros 93 Equid Forage Requirements and Nutrition 97 Nutritional Value of Diets Consumed on Rangelands l0l Habitat Preference and Use, and Interspecific Competition l04 Needed Research l07 Overview l07 Project l. Habitat Preference and Use by Co-occurring and Separately Occurring Feral Equids and Cattle l10 Project 2. Food Consumption Rates and Nutrition of Wild and Free-Roaming Horses and Burros and Their Associated Species ll2 Project 3. Nutritional Plane, Condition Measures, and Reproductive Performance in Domestic Mares ll4 Project 4. Blood Assay of Experimental Equids and Livestock in Projects l, 2, 3, 5, and 8 ll8 Project 5. Demography of Wild Horses and Burros ll9 Project 6. Social Structure, Feeding Ecology, and Population Dynamics of Wild and Free-Roaming Horses and Burros l24 Project 7. Genetic Polymorphism l28 vii
3: EFFECTS OF EQUIDS ON OTHER ECOSYSTEM COMPONENTS l3l Information Needs l3l State of Knowledge l32 Information Sources l32 Range-Plant-Community Impacts l32 Competitive Effects on Other Animals l40 Effects of Equids on Range Hydrology l44 Needed Research l63 Overview l63 Project 8. Grazing Impacts of Equids and Cattle on Range-Plant Communities l64 Project 9. Hydrologic Impacts l67 Project l0. Riparian-Zone Impacts l70 4: SOCIOECONOMIC AND POLITICAL ISSUES l72 Information Needs l72 State of Knowledge l73 Information Sources l73 Economic Considerations l74 Legal and Political Issues l76 Sociological Aspects l78 Needed Research l78 Levels of Inquiry l78 Project ll. Public Attitudes l79 Project l2. Analysis and Evaluation of Demands for Excess WFRHB l83 Project l3. Management Costs of WFRHB Alternatives l85 Project l4. Economic Considerations for Management Alternatives Drawn from Proposed Research Programs l86 Project l5. Nonmarket Values for WFRHB l87 Project l6. Conceptual Development of Public Rangeland Management Models l88 5: WILD EQUID RESEARCH AND MANAGEMENT METHODOLOGY l90 Information Needs l90 State of Knowledge l90 Information Sources l90 Census l9l Review of Range-Survey Methodology 20l Limitations of Techniques for Diet Analysis 203 Determining Range-Forage Digestibility in Equids 206 Blood Assays as Possible Indices of Nutritional State in Horses and Burros 207 Behavioral Sampling: Methods for Comparison between Treatments and Experiments . 2l0 Behavioral Sampling for Specific Experiments 2l4 Contraception in the Horse 2l8 Chemical Immobilization and Capture of Wild Equids 220 viii
Needed Research 222 Project l7. Census Methods for Wild Horses and Burros 222 Project l8. Contraception Studies 224 REFERENCES 227 APPENDIXES Appendix A. Digestive Physiology of the Horse 259 Appendix B. Annotated Bibliography on Grazing Hydrology 302 Appendix C. Annotated Bibliography on Economic and Socio-Political Issues 348 ix
PREFACE The Public Rangelands Improvement Act of l978 directs in part that the Bureau of Land Management and the National Academy of Sciences contract for performance of a research study on wild horses and burros. This report, which is submitted in partial compliance with the Act, is the final report on Phase I. It assesses the current state of our relevant knowledge and sets forth in detail the kind of research effort that could provide information now lacking but essential to sound management of wild and free-roaming horses and burros. Phase II of the study is now under way, and a final report from the Academy will be submitted to the Bureau in l98l (see Chapter l for a more detailed discussion of the study). ACKNOWLEDGMENTS Several people contributed time and effort to the work of the committee. Maureen J. Seidman, Executive Secretary at Utah State University, typed, edited, collated, and supervised the printing of the drafts of the interim and final reports. She also organized travel and meeting arrangements for the Committee and conducted correspondence and telephone communications. David R. Anderson, Leader of the Cooperative Wildlife Research Unit at Utah State University, provided critical advice on parts of the final report, assisted in formulating the RFP on census research, and helped review the resulting proposals. Milton Frei of the BLM in California attended two meetings of the Committee at its request, and accompanied Walter Conley to a number of BLM offices around the West to obtain some of the horse and burro data analyzed in the report. Montague Detriment of the University of Wisconsin acted as consultant to the Committee on horse nutrition and wrote Appendix A. Other individuals of the University of California, Davis, New Mexico State University, and Utah State University, who assisted with data analyses, library searches, and literature reviews, were Jeri Aamodt, Martha Bryant, William B. Collins, Micheline Devaws, Margot Garcia, Allen Kraus, Jennifer Lewis, Cindy Rebar, Paul Smyth, Everett Springer, Janice Stevenson, Gwen Thomas, Thomas Thompson, Raul Valdez, Thomas Watts, and Glenn Yost. xi
Michael Zagata and Yvonne Hudson provided staff support for the project until November l, l980, after which Philip Ross saw the task through to completion. Marsha Elliott and Estelle Miller assisted in a broad range of editorial tasks in preparing the manuscript for the printer. NOTE The section of the report on equid demography (see Chapter 2) was rewritten after its initial drafts following considerable Committee discussion. The Committee, with the exception of Dr. Patricia Moehlman, reviewed the rewritten section and approved it. The Committee had earlier agreed that if, during preparation of the report, any Committee member was out of the country, and if his or her review of new material would hold up the release of the report, that member would be asked to forego additional review. Since Dr. Moehlman was out of the country at the time the rewritten material on demography became available, she did not review it, but she may if she so desires, provide additional reactions or information at a later date. xii
