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Ecology of a Non-Native Invasive Species, the Norway Or Common Rat

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Ecology of a Non-Native Invasive Species, the Norway Or Common Rat ANGLIA RUSKIN UNIVERSITY FACULTY OF SCIENCE AND TECHNOLOGY RUM RATS: ECOLOGY AND BEHAVIOUR SEAN BENJAMIN JAMES CARLISLE A thesis in partial fulfilment of the requirements of Anglia Ruskin University for the degree of Doctor of Philosophy This research programme was carried out in collaboration with the Animal and Plant Health Agency Submitted: May 2019 Acknowledgments I would firstly like to thank Dr. Mark Lambert for his continued invaluable professional support throughout all phases of this project (and hopefully beyond). I would also like to thank Dr. Sheila Pankhurst for her help initialising the project and welcoming me into the Life Sciences Department at Anglia Ruskin University; Dr. Charlie Nevison for her regulatory, editorial, motivational, and determined supervision throughout; Dr. William Hoppitt for his support with everything statistical; the numerous Anglia Ruskin University advisors (official and otherwise) for providing a support network; and the postgraduate departmental cohort for keeping me in touch. None of this would have been possible without the financial and practical support from Scottish Natural Heritage (SNH), Scottish Environmental Protection Agency (SEPA), and the collaborating partner the Animal and Plant Health Agency (APHA) - to all I am extremely grateful. In particular Dr. Andy Douse (SNH) provided exceptional professionalism, understanding, and encouragement throughout; Dr. Lesley Watt (SNH) gave continuous operational management and support, and Mike Ingram (SNH) offered practical and personal support beyond the call of duty. I would also like to thank all of the various people whom have volunteered their time in the field, especially (but not exclusively); Mikis Bonnett, Jed Cossar, Tadhg Gennery, Jessica Hodnett, Julian Michaelis, Raquel Baraut Riu, and the SNH reserve staff. Thank you also to the Isle of Rum residents for allowing the smooth running of my research, accepting me into their community, and providing essential sustenance and laughter. In particular, Dave Beaton and Jed Cossar whose friendship kept me motivated. A special thank you to Nicola Rodgers whose personal, practical, and theoretical support kept my feet on the ground throughout. Lastly I would like to thank the rats of Rum, for allowing me a slice of their wisdom. i ANGLIA RUSKIN UNIVERSITY ABSTRACT FACULTY OF SCIENCE AND TECHNOLOGY DOCTOR OF PHILOSOPHY RUM RATS: ECOLOGY AND BEHAVIOUR SEAN BENJAMIN JAMES CARLISLE May 2019 The Isle of Rum hosts approximately 25% of the global population of Manx shearwaters, Puffinus puffinus. Potential for negative impacts on the shearwater colonies from introduced Norway rats, Rattus norvegicus, has highlighted the need to better understand the ecology of this island invader. Abundance and population estimates are often central to effective conservation and invasive species management. Despite their potentially catastrophic impacts on seabird populations, the ecology of Norway rats on islands is poorly understood. Developing an appropriate tool to measure rat population size is therefore important. Furthermore, an understanding of the movement patterns and diet of introduced Norway rats is vital to establishing the nature of their relationship with native species. Optimisation (transect duration/length) of two common rodent activity survey techniques (tracking plates and chocolate-flavoured wax blocks) was carried out to derive parameters that resulted in a standard deviation of the bootstrapped distribution of the mean (precision) of less than 0.2. Activity survey scores were then calibrated against capture- mark-recapture population estimates for linear (coast, river, wall) and non-linear (grassland, heath, woodland) sites. An island-wide population estimate of Norway rats on Rum was calculated using extrapolated density estimates for linear features (boundary strip method) and non-linear vegetation types (SECR models). Home range size of 17 Norway rats, across three study sites (coast, heath, river) was estimated. Jacob’s Index was used to compare vegetation availability (home range) with use (location points), and Spearman’s correlation for a relationship between capture rates (C100TN) and distance to linear features. Stomach content analysis was used to describe the diet of 29 rats across three ecotopes (coast, grassland, urban) on Rum. Activity indices reached an acceptable level of precision after three days and a grid size of 35 x 10m2 from tracking plate (linear and non-linear sites) and wax block (non-linear sites only) surveys. Total population size of Norway rats on Rum was estimated at 11,844 ± 5,685 for non-linear/linear sites combined. Mean home range size (MCP100) was estimated at 2.32 ± 0.86 hectares, with differences between sex and site found. Distance to coast had a strong negative correlation with mean capture rates. Vegetation and invertebrates were the most frequent/abundant food types across all ecotopes. Calibrated tracking plates are preferable for the use of estimating population size of Norway rats on islands. Coastal environments are likely to be an important resource for introduced rats; woodland may offer intra-island refugia to rats on Rum. Overall, Norway rats are unlikely to be a current threat to Manx shearwaters on Rum. Key words: Isle of Rum, Norway rats, invasive species, stomach content analysis, habitat preference, home range size. ii This thesis is dedicated to my family (past and present), without whom meaning would be lost. Anaesthetised female rat ‘Wanda’, with a GPS tag attached (the rat was released after recovery from anaesthesia and re-trapped two weeks later to remove the tag). Table of Contents Acknowledgments..................................................................................................... i ABSTRACT ............................................................................................................... ii Table of Contents .................................................................................................... iii List of Figures and Tables .................................................................................... viii Copyright ................................................................................................................ xii Chapter 1 Introduction ............................................................................................. 1 1.1 General ....................................................................................................................... 1 1.1.1 What is an invasive non-native species? ............................................................... 1 1.1.2 Rodents as invasive non-natives ........................................................................... 2 1.2 Impacts of Invasive Rodents .................................................................................... 4 1.2.1 Socio-economic and health ................................................................................... 4 1.2.2 Conservation ......................................................................................................... 5 1.3 Behavioural and Ecological Context of Rats ........................................................... 6 1.4 Rat Management: Tools and Use .............................................................................. 7 1.4.1 Rodenticides ......................................................................................................... 7 1.4.2 Island eradications ................................................................................................ 8 1.5 Impact of Norway Rats on Manx Shearwaters in Britain....................................... 10 1.6 The Island of Rum ................................................................................................... 11 1.7 Rationale and Research Questions ........................................................................ 13 Chapter 2 - Optimisation of Two Common Rat Activity Survey Techniques: How Long is a Piece of Transect? ........................................................................ 15 2.1 Introduction ............................................................................................................. 15 2.1.1 General ............................................................................................................... 15 2.1.2 Tools for studying populations: transects and plots ............................................. 15 2.1.3 Activity indices .................................................................................................... 17 2.1.4 Transect parameters – how much is enough? ..................................................... 19 2.2 Rationale and Research Questions ........................................................................ 19 2.3 Methods.................................................................................................................... 20 2.3.1 Health and safety ................................................................................................ 20 2.3.2 Study sites .......................................................................................................... 21 2.3.2.1 Preliminary site visits ..................................................................................................... 21 iii 2.3.2.2 Site selection ................................................................................................................. 21 2.3.3 Transects ...........................................................................................................
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