Population Dynamics 1994Т98, and Management, of Kaimanawa Wild
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Population dynamics 1994–98, and management, of Kaimanawa wild horses Frontispiece - Colourphoto of horses; centre on page Victa's band relaxing on a ridge above the Argo Basin, Autumn 1997. View is towards south-west and Auahitotara Peak Population dynamics 1994–98, and management, of Kaimanawa wild horses SCIENCE FOR CONSERVATION 171 E. Z. Cameron, W. L. Linklater, E. O. Minot and K. J. Stafford Published by Department of Conservation P.O. Box 10-420 Wellington, New Zealand Science for Conservation presents the results of investigations by DOC staff, and by contracted science providers outside the Department of Conservation. Publications in this series are internally and externally peer reviewed. This report was prepared for publication by Science Publications, Science & Research Unit; editing and layout by Jaap Jasperse. Publication was approved by the Manager, Science & Research Unit, Science Technology and Information Services, Department of Conservation, Wellington. © March 2001, Department of Conservation ISSN 1173–2946 ISBN 0-478-22022-7 Cataloguing-in-Publication data Population dynamics 1994-98, and management, of Kaimanawa wild horses / E.Z. Cameron ... [et al.]. Wellington, N.Z. : Dept. of Conservation, 2001. viii, 165 p. ; 30 cm. (Science for conservation, 1173-2946 ; 171). Cataloguing-in-Publication data. - Includes bibliographical references. ISBN 0478220227 1. Kaimanawa wild horse herd. 2. Wild horses--Control-- New Zealand. 3. Population biology. I. Cameron, E. Z. Series: Science for conservation (Wellington, N.Z.) ; 171. CONTENTS Abstract 1 Executive summary 3 1. Literature review 5 1.1 Breeding group terminology 5 1.2 Wild horse ecology 6 1.3 Kaimanawa wild horse population history 11 1.4 Contraception for wildlife management 11 1.5 Wild horse population control using immunocontraception 15 2. Focal population 17 2.1 Identified horses 17 2.2 Bands—Methods 18 3. Study area 21 3.1 Scales of measurement 21 3.2 Horse range and extensive study area 21 3.3 Vegetation 22 3.4 Climate 24 3.5 Focal population’s range and intensive study area 26 4. Social behaviour 27 4.1 Objectives 27 4.2 Methods 27 4.2.1 Focal population 27 4.2.2 Records of group composition 27 4.2.3 Activity, spacing, associative and social behaviour 28 4.2.4 Mare pregnancy status 29 4.2.5 Statistical analyses 29 4.3 Results 30 4.3.1 Types of groups 30 4.3.2 Band types 32 4.3.3 Social structure of single and multi-stallion bands compared 33 4.3.4 Social behaviour in single and multi-stallion bands compared 35 4.3.5 Band stallion loyalty, effort and risk taking during mare retrieval 36 4.3.6 Formation of bands 36 4.3.7 Disbanding 37 4.3.8 Reproduction related to band types 37 5. Range use 41 5.1 Objectives 41 5.2 Methods 41 5.2.1 Records of focal band membership and location 41 5.2.2 Defining mare group stability 41 5.2.3 Horse density 42 5.2.4 Horse habitat use 44 5.2.5 Diet 46 5.2.6 Home range 47 5.2.7 Forage production and carrying capacity of the low- altitude Argo Basin grassland sward 48 5.3 Results 49 5.3.1 Accurately measuring home range size and structure 49 5.3.2 Accurately estimating the rate of band membership change 51 5.3.3 Habitat use 51 5.3.4 Diet 53 5.3.5 Home range size and structure 54 5.3.6 Relative home range quality 56 5.3.7 Horse movement 56 5.3.8 Forage production and carrying capacity in the southern and low-altitude Argo Basin 66 6. Health and condition 69 6.1 Objectives 69 6.2 Methods 69 6.2.1 Visual body condition scores 69 6.2.2 Parasites 70 6.2.3 Equine herpes virus (EHV) 1 and 4 70 6.2.4 Blood trace element analyses 70 6.2.5 Blood typing 71 6.2.6 Osteoarthritis in the metacarpophalangeal joints 71 6.2.7 Collagen crimp patterns in the superficial digital flexor tendon (SDFT) core region 71 6.3 Results 72 6.3.1 Body condition 72 6.3.2 Parasites 75 6.3.3 Equine herpes 77 6.3.4 Blood trace elements 77 6.3.5 Blood typing 77 6.3.6 Osteoarthritis in the metacarpophalangeal joints 78 6.3.7 Collagen crimp patterns in the superficial digital flexor tendon (SDFT) core region 78 7. Reproduction and maternal behaviour 79 7.1 Objectives 79 7.2 Methods 79 7.2.1 Parental investment 80 7.3 Results 82 7.3.1 Pregnancy rates 82 7.3.2 Foetus survival 83 7.3.3 Foaling rates 83 7.3.4 Foal survival 83 7.3.5 Estimates of annual reproduction 84 7.3.6 Extent of breeding season 85 7.3.7 Differences in parental investment between band types 85 7.3.8 Differences in parental behaviour with paternity in a single-stallion band 88 7.3.9 Differences in parental investment with mare age and experience 88 7.3.10 Differences in parental investment with foal sex 90 7.3.11 Sex ratios 92 7.3.11 Parental investment summary 94 7.3.12 Implications 94 8. Demography 95 8.1 Objectives 95 8.2 Demographic measures: Methods 95 8.3 Results 96 8.3.1 Population density and size 96 8.3.2 Population structure 99 8.3.3 Survival by age and sex classes 99 8.4 Demographic model: Methods 100 8.5 Modelling results 102 8.5.1 Population simulations with and without human- induced mortality 102 8.5.2 Checking demographic parameters from simulations 103 8.5.3 Population growth rates 103 9. Immunocontraception 109 9.1 Objectives 109 9.2 Methods 109 9.2.1 Vaccine and biobullets 109 9.2.2 Design of field experiment 109 9.2.3 Administration of vaccine and placebo 112 9.3 Results 112 9.3.1 Treatment effects of vaccination 112 10. Strategies for population management 115 10.1 Objectives 115 10.2 Methods 115 10.2.1 Designing conceptual management strategies 115 10.2.2 Management strategies and population sex ratio 116 10.2.3 Population management strategy simulations 117 10.2.4 Mustering protocols 117 10.2.5 The size, age and sex composition, of musters 120 10.2.6 Population decline and the diminishing returns of mustering protocols 120 10.2.7 Shooting protocols 121 10.2.8 Contraceptive protocols 121 10.3 Results 122 10.3.1 Muster size and composition 122 10.3.2 Simulated management strategies 122 10.3.3 Conclusions 126 11. Summary 129 11.1 Kaimanawa wild horse ecology 129 11.2 Social behaviour 130 11.2.1 Harassment of mares by stallions and multi-stallion bands 130 11.3 Range use 131 11.3.1 Home range size and structure 131 11.3.2 Population dispersal 131 11.3.3 Band membership changes 131 11.3.4 Habitat use 132 11.4 Health and condition 132 11.5 Reproduction and demography 133 11.6 Factors influencing population growth 134 11.7 The immunocontraception trial 135 11.8 Strategies for population management and monitoring 136 11.8.1 Ground or helicopter shooting 137 11.8.2 Mustering 137 11.8.3 Contraception 138 11.8.4 Combining musters and contraception 139 11.8.5 Population monitoring strategies 139 12. Acknowledgements 140 13. References 142 Appendix 1 155 Population dynamics 1994–98, and management, of Kaimanawa wild horses E. Z. Cameron, W. L. Linklater, E. O. Minot and K. J. Stafford Ecology Group, Institute of Natural Resources, and Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North ABSTRACT Feral horses of the southern Kaimanawa ranges, New Zealand, were studied from 1994 to 1998. Social, range use and maternal behaviour, and population health, reproduction and demography, were described. We also report on a field trial of immunocontraception and computer simulations of strategies to control population size. Kaimanawa feral horses behaved similarly to free- ranging horse populations throughout the world. We contribute new information and perspectives on maternal investment and multi-stallion breeding groups in horses. Maternal investment varied according to foal sex and maternal condition. Multi-stallion breeding groups suppressed mare fecundity due to higher levels of harassment by stallions. Body condition varied with season, reproductive status and social context. Reproduction varied between years and with mare age and social context. Population growth of around 9% per annum resulted from moderate fecundity (49% of mares 2+ years old foaled each year); high survivorship e.g., adult (5+ years old): female 94%, male 97%, and foal (<1 year old): female 87%, male 79%; and high foetal-neonate mortality (31% of pregnancies to adult mares lost). Resource limiting density and sex ratio parity contributed to comparatively low population growth. Comparisons of management strategies using computer simulations of a population model showed shooting or mustering for removal were the most, and immunocontraception the least, effective strategies for controlling population size. Hormonal contraceptives combined with mustering to remove juveniles appeared to be a useful compromise between strategies that decrease survivorship or fecundity. We discuss the implications of our findings for feral horse population management. © March 2001, Department of Conservation. This paper may be cited as: Cameron, E.Z.; Linklater, W.L.; Minot, E.O.; Stafford, K.J. 2001. Population dynamics 1994–98, and management, of Kaimanawa wild horses. Science for conservation 171. viii + 165 p. Science for conservation 171 1 2 Cameron et al.—Kaimanawa horse population and management EXECUTIVE SUMMARY We report on the social and range use behaviour, health and condition, and demography of the Kaimanawa feral horse population in the southern Kaimanawa Mountains, New Zealand, from 1994 to 98.