Breeding and dispersal implications for the conservation of the Southern Ground Hornbill Bucorvus leadbeateri Kate Carstens Thesis presented for the degree of Doctor of Philosophy FitzPatrick Institute of African Ornithology DST-NRF Centre of ExcellenceTown Department of Biological Sciences, Faculty of Science University of CapeCape Town of October 2017 University Supervised by Professor Peter Ryan Co-supervised by Dr Rob Little and Dr Robert Thomson The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non- commercial research purposes only. Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author. University of Cape Town Declaration This thesis reports original research that I conducted under the auspices of the Percy FitzPatrick Institute, University of Cape Town. All assistance received has been fully acknowledged. This work has not been submitted in any form for a degree at another university. Signature Removed Kate Carstens i Table of Contents Abstract .................................................................................................................................... iii Acknowledgements .................................................................................................................... v Chapter 1 An introduction to artificial nests as a conservation tool .......................................... 1 Chapter 2 Reproductive productivity of Southern Ground Hornbills in an area supplemented with nest boxes ......................................................................................................................... 19 Chapter 3 Variation in the timing of egg-laying ...................................................................... 56 Chapter 4 Natal dispersal in the Southern Ground Hornbill .................................................... 73 Chapter 5 Synthesis.................................................................................................................. 89 References ................................................................................................................................ 99 ii Abstract Populations of secondary tree-cavity nesting bird species are often limited by a shortage of natural nesting sites. For the Southern Ground Hornbill Bucorvus leadbeateri that typically nests in natural tree cavities, the shortage of nesting sites is one factor potentially limiting population growth. The species is listed as endangered in South Africa, and vulnerable throughout the rest of its range. Nest boxes can improve the conservation status of threatened birds that are limited by nest-site availability. However, nest boxes or other types of artificial nests are not always beneficial to the target species, and their value as a conservation tool needs to be tested for each species. Wooden nest boxes were installed for ground hornbills in a study area in north eastern South Africa with a paucity of natural nest sites. In this thesis, I assess productivity, timing of breeding, and dispersal in the Southern Ground Hornbill in a study area supplemented with nest boxes and discuss the implications for the conservation of this endangered species. Nest boxes are an effective conservation tool to improve productivity in areas lacking natural tree cavity nesting sites. Breeding success (calculated as the proportion of nesting attempts that fledged a chick) and predation levels were similar for groups using nest boxes and natural nests. Natural nests were more buffered against cooling night temperatures, but otherwise nest boxes provided nesting conditions that were no better than natural nests. Timing of breeding for nests in natural tree cavities and nest boxes were similar. However, groups with access to a nest box attempted breeding more often than groups with access to a natural nest only, resulting in an 15 % increase in the number of fledglings per group compared to an adjacent protected area with no artificial nests. The number of breeding groups in the study area increased by 460 % over 12 years. However, there is a limit to the density of breeding groups. Breeding success was highest when breeding density was one breeding group per 90–120 km2, so nests should be spaced ~10 km apart. Given that the threats to ground hornbills include persecution and poisoning, increasing the reproductive rate by providing nest boxes should assist in slowing the decline by the increased recruitment of offspring into the population. Timing of breeding varied across years. The first eggs laid each year ranged from 9 September to 14 November, and median lay date was 03 November. Breeding attempts that were initiated early in the season were more likely to fledge a chick than those initiated later iii in the season. Timing of breeding was delayed during warmer springs, particularly under dry conditions. In savannas, hotter spring temperatures could limit food availability, for example, if higher temperatures cause the vegetation to dry out, resulting in a rapid decline in insect flush, especially in the phytophagous insect groups that form a large part of the ground hornbill diet. Factors to consider when constructing and placing nest boxes include thickness of the cavity walls, entrance height above ground and density of nest boxes placed in the landscape. Breeding attempts in natural nests and nest boxes with thicker nest walls and those positioned with higher entrances above the ground increased breeding success. Therefore, nests should be constructed with cavity walls at least 6 cm thick and placed so that the entrances are situated > 6 m above the ground. With 186 ringed chicks fledging from the study area after the installation of nest boxes, it was possible to observe their dispersal within the study area and farther away into the adjacent Kruger National Park. There was no evidence for sex-biased dispersal. Males and females dispersed at similar ages, and over similar distances, raising interesting questions about inbreeding avoidance mechanisms in this species. If females do not disperse beyond the range of related males, how do related individuals avoid pairing, and what forms of individual recognition exist? iv Acknowledgements I owe a great deal to the many people who were involved in the making of this PhD. First and foremost, my significant other, Cassie Carstens, for being by my side every step of the way. I am grateful that he shares my fascination with these modern-day pterodactyls, and for his love and support during this journey. To my supervisor, Peter Ryan, for his impeccable guidance. He allowed me to shape this PhD in my own way, but at the same time provided just enough steering to make sure my thoughts didn’t drift too far of course. To Rob Little, who gave me the chance to do this PhD, and who assisted me to edit countless versions of chapters. His help and guidance from the very beginning made this journey fun. To Robert Thomson, who came on board as an unofficial co-supervisor a little later during my PhD journey, but who provided useful comments on the chapters when my logic was sometimes flawed. To the support staff of the Fitz: Hilary Buchanan, Anthea Links, Tania Jansen, Chris Tobler, Margaret Koopman, Susan Mvungi, Denise Scheepers and Gonzalo Aguilar; knowing they were there to help was always a huge relief. And to Phil Hockey for his support during my early days with the study. To the many academic staff who not only made helpful comments on draft versions of these chapters, but who also provided insightful discussions when I was interpreting my results. I would like to thank Alan Kemp, whose in-depth knowledge of ground hornbills never ceases to amaze me, and who provided many useful and enjoyable discussions either in person or electronically. To Rita Covas for her discussions and comments on dispersal, as well as her contagious enthusiasm during our few discussions on behaviour and cooperative breeding systems. I am most indebted to Reshma Kassanjee for her advice and assistance with the statistical side of this PhD. She patiently worked through my data with me, and showed a quick mind when it came to understanding the complex nature of these birds. Also to Susie Cunningham and Martha Nelson-Flower for their help with my frequent questions on statistical modelling in the early days, and to Chevonne Reynolds for her help with my statistics questions toward the end. The field work for this study took place in reserves comprising private farms. I am extremely grateful to the landowners of the Klaserie, Timbavati, Umbabat, Balule and Jejane, for making their properties open to the Fitz’ Ground Hornbill Project. Thank you to the wardens, Colin Rowles, Jacques Britz, Brian Havermann, Glen Thomson, Mark Griffiths and Henri v Hibbett, for their help with various aspects of the day-to-day running of the Project. Many thanks to the ecologist, Almero Bosch, for his help when it came to arranging extra pairs of hands and eyes in the field, and for the opportunity to walk the Timbavati from east to west: an adventure I will never forget. To the reserve staff for all their help with project technicalities: Eric Manyike, Hennie Jacobs, Sipho Mdluli, Abel Matjie and Abel Strydom. Thank you to the various field assistants and friends whose help in the field made field work feel more like an adventure than work: Cassie Carstens and