Understanding Population Dynamics of Feral Horses in the Tuan and Toolara State Forest for Successful Long-Term Population Management
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Understanding population dynamics of feral horses in the Tuan and Toolara State Forest for successful long-term population management Magdalena Anna Zabek Bachelor of Equine Science A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2015 School of Veterinary Science i Abstract Feral horses (Equus caballus) in Australia are a growing problem despite implementation of management strategies. The increasing number of feral horses within the Tuan and Toolara State Forest (TTSF), a coniferous plantation on the Sunshine Coast, Queensland, and particularly near major public roads, has been recognised as a problem in the last decade. Desensitised to road traffic, horses are a serious distraction for motorists, and have potential to cause serious animal-vehicle accidents. The primary objective of the study was to characterise the essential demographics of the TTSF feral horses, so that the most suitable methods for long-term population management could be determined. The study was conducted from 2012 – 2014 and determined social structure, reproductive performance and survival, and population growth rate. The estimation of population distribution, abundance and density together with assessment of habitat use and home range size were also addressed. The studied population did not show significant annual variation in demographics, which is consistent with measurements in other unmanaged feral horse populations in Australia and abroad. The overall size and age composition of social groups remained stable during the study period. The average harem size was estimated as 4.95 (95%CI 4.53-5.41), and usually consisted of 1 stallion, 2 - 3 adult females, and 2 immature offspring (≤ 3 years of age). Males not associated with harems consisted of adult (≥ 3 years old) and sub-adult (2 years old) individuals, either forming groups of 2 – 6 or living by themselves. The population showed a stable age distribution, with adult horses constituting the largest group (68%; n = 247). The sex ratio of adult female to male horses was nearly equal (0.99:1.00). The mean annual fecundity was 0.23 ± 0.07 SD and was comparable to those obtained for other feral horse populations where the environment imposed nutritional limitations. Adult females were observed to foal on average every second year. The overall nutritional status of the population expressed as body condition score (BCS; 0 - 5) was 2.55 ± 0.51 SD with adult females having poorer scores than other age and gender groups. Survival estimates were consistently high (0.92 – 0.95) across all age groups. The average annual finite rate of population increase (λ) for the three years of the study was 1.088 which was lower than the maximum reported for populations living in the most favourable conditions. Elasticity ii analysis demonstrated that the TTSF population growth rate was almost seven times more sensitive to changes in adult survival compared with juvenile survival, and almost twice more sensitive than changes in fecundity. Assessment of the population distribution based on a strip transect survey using horse dung on forest tracks indicated that the majority of the forestry was occupied by horses, with the highest population density being located in the central region of the plantation. Abundance and density of horses were estimated by distance line transect survey of dung counts, dung disappearance rate of 444 (± 150.7 SD) days and individual defecation rates of 7.97 (± 8.74 SD) over 24 hours. The analysis indicated that the TTSF was occupied by 1321 horses (95%CI 940 - 1965), which corresponded to a density of 1.8 horses/km2. Habitat use quantified by visual detection of horses, dung counts, and Global Positioning System (GPS) tracking, identified a preference for open habitats of young pine forest and harvested areas, and avoidance of closed canopy habitats of juvenile and mature pine. Home range size determined by GPS tracking was greater than that measured by direct observation (mean ± SD; 16.90 ± 9.11 km2 and 6.71 ± 3.30 km2 respectively). All harems were loyal to their home ranges; harem members occupied one core area more than other parts of their range, and home ranges highly overlapped. The findings of this thesis confirm that there is a gradual increase in feral horse distribution and population size within the TTSF. It is evident that the design and implementation of a program to manage feral horses in the TTSF will need to consider a combination of approaches, which will need to satisfy a number of criteria including efficacy, cost- effectiveness, occupational safety, environmental impacts and animal welfare. Continued monitoring of the population growth is essential to measure the effectiveness of chosen management strategies. iii Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis. iv Publications during candidature Conference abstracts Zabek MA, Berman DM, and Collins CW (2012). Population growth analysis of feral horses in a coastal forest environment. Proceedings of the Australian and New Zealand College of Veterinary Scientists, Gold Coast, p.49. Zabek MA, Berman DM, and Collins WC (2012). Determination of feral horse density in a forest environment of Toolara State Forest. Proceedings of the International Wild Equid Conference, Vienna, p.33. Zabek MA, Berman DM, Wright J, Blomberg S, and Collins CW (2014). Understanding population dynamics of the feral horse in a coniferous environment in southeast Queensland. Proceedings of the 16th Australasian Vertebrate Pest Conference, Brisbane, p.142. Berman DM, Marshall D, Garrett T, Scriven J, Morgan N, Hosie H, and Zabek MA (2014). Monitoring tools and techniques for intelligent management of vertebrate pests. Proceedings of the 16th Australasian Vertebrate Pest Conference, Brisbane, p.84. Publications Zabek MA, Wright J, Berman DM, Hampton JO, and Collins CW (2014). Assessing the efficacy of medetomidine and tiletamine-zolazepam for remote immobilisation of feral horses (Equus caballus). Wildlife Research, 41, 615 - 622. Zabek MA, Collins CW, Berman DM, Blomberg S, and Wright J (2015). Population dynamics of feral horses in the Tuan and Toolara State Forest (2011 – 2014). Report for FPQPlantations. Publications included in the thesis Zabek MA, Wright J, Berman DM, Hampton JO, and Collins CW (2014). Assessing the efficacy of medetomidine and tiletamine-zolazepam for remote immobilisation of feral horses (Equus caballus). Wildlife Research, 41, 615 - 622. v Zabek MA, Collins CW, Berman DM, Blomberg S, and Wright J (2015). Population dynamics of feral horses in the Tuan and Toolara State Forest (2011 – 2014). Report for the FPQPlantations. The University of Queensland, Gatton. Contributions by others to the thesis The project advisors provided ongoing discussion and feedback on research planning and project design. Dr David Berman taught me how to estimate population distribution, density and abundance by the dung count method; performed remote immobilisation of horses in the field; and offered continuous support and feedback on the study design and content of my written work. Dr Christina W. Collins assisted with the research planning, project design and read through my written work to provide feedback on its content. Dr Simon Blomberg was involved in the design of the algorithm used in habitat use analyses and assisted with statistical analyses included in the thesis. Dr John Wright provided veterinary assistance during remote immobilisation of horses and read through my written work to provide feedback and proof-reading on the content. Statement of parts of the thesis submitted to qualify for the award of another degree None vi Acknowledgements I am deeply grateful to Dave Berman for his guidance and unfailing support over the duration of this study. His trust in my skills and determination was inspiring and his knowledge of feral horse ecology is remarkable. I am very grateful to John Wright for his fantastic mentoring over the last two and a half years of this study and enormous patience during the editing process of my written work. I am very glad that I had the opportunity to work with such great advisor. I would also like to thank Chris Pollitt for assistance with project design, Wynne Collins for assistance with research planning, project design and feedback to my written work, and Simon Blomberg for his assistance with statistical design and analyses and continuous support of the project. The Forestry Plantation Queensland (FPQ) provided financial and logistical support in the field, in particular Steven Husband, Brad Kennedy, Bart Schneemann, Colleen Hair, Michael Robinson, and Garthe Russell.