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Variation in the Effect of Corvid Predation on Songbird Populations

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Variation in the Effect of Corvid Predation on Songbird Populations Variation in the effect of corvid predation on songbird populations Submitted by Lucy Capstick to the University of Exeter as a thesis for the degree of Doctor of Philosophy in Psychology in May 2017 This thesis is available for Library use on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. I certify that all material in this thesis which is not my own work has been identified and that no material has previously been submitted and approved for the award of a degree by this or any other University. Signature: 1 2 TABLE OF CONTENTS TABLE OF CONTENTS ............................................................................................. 3 ABSTRACT ................................................................................................................ 8 LIST OF FIGURES ................................................................................................... 10 LIST OF TABLES ..................................................................................................... 12 ACKNOWLEDGEMENTS ........................................................................................ 14 DECLARATION ........................................................................................................ 16 Chapter One Variation in the effect of predators on bird prey species ……….. 19 1.1 INTRODUCTON .......................................................................................... 21 1.2 THE EFFECT OF DIFFERENCES IN PREDATOR AND PREY ECOLOGY AND BEHAVIOUR ON THE PREDATOR-PREY RELATIONSHIP .......................... 27 1.2.1 Differences in prey breeding ecology and behaviour ................................... 27 1.2.2 Differences in prey species’ demography .................................................... 29 1.2.3 Differences in predator ecology and behaviour ........................................... 31 1.3 THE EFFECT OF VARIATION IN HABITAT ON THE PREDATOR-PREY RELATIONSHIP ....................................................................................................... 34 1.3.1 Habitat variation and prey species’ vulnerability to predation ...................... 35 1.3.2 Habitat variation and predator species’ impact on prey ............................... 36 1.3.2.1 Landscape scale habitat variation ............................................................... 37 1.3.2.2 Local scale habitat variation ........................................................................ 38 1.3.2.3 Individual scale variation in habitat use ....................................................... 39 1.4 CONCLUSIONS .......................................................................................... 40 Chapter Two Factors predicting the susceptibility of songbirds to nest predation by corvids .............................................................................................. 43 ABSTRACT .............................................................................................................. 45 2.1 INTRODUCTION ......................................................................................... 46 2.2 METHODS ................................................................................................... 49 2.2.1 Literature search .......................................................................................... 49 2.2.2 Analysis of papers ....................................................................................... 49 2.2.3 Predation figures ......................................................................................... 50 2.2.4 Predator identification .................................................................................. 50 2.2.5 Prey species breeding biology parameters .................................................. 51 2.2.6 Study type.................................................................................................... 52 2.2.7 Statistical analysis ....................................................................................... 52 3 2.3 RESULTS .................................................................................................... 55 2.3.1 Factors affecting rates of predation ............................................................. 55 2.3.2 Model predictions ........................................................................................ 58 2.4 DISCUSSION .............................................................................................. 61 2.4.1 Factors influencing nest predation by corvids .............................................. 61 2.4.2 Implications of findings ................................................................................ 65 2.5 APPENDICES ............................................................................................. 68 2.5.1 Literature search method ............................................................................. 68 2.5.2 Inclusion criteria ........................................................................................... 70 Chapter Three Variation in the impact of corvid predation on songbird population numbers ............................................................................................. 85 ABSTRACT .............................................................................................................. 87 3.1 INTRODUCTION ......................................................................................... 88 3.2 METHODS ................................................................................................... 91 3.2.1 Literature search .......................................................................................... 91 3.2.2 Susceptibility to corvid predation ................................................................. 92 3.2.3 Response to corvid removal ........................................................................ 92 3.2.4 Long-term population trends ........................................................................ 93 3.2.5 Statistical analysis ....................................................................................... 93 3.3 RESULTS .................................................................................................... 94 3.3.1 Nesting mortality and susceptibility to corvid predation ............................... 95 3.3.2 Nesting mortality and response to corvid removal ....................................... 95 3.3.3 Mortality at different life history stages and long-term population trends ..... 95 3.4 DISCUSSION .............................................................................................. 96 3.4.1 Nesting mortality and susceptibility to corvid predation ............................... 97 3.4.2 Nesting mortality and response to corvid removal ....................................... 97 3.4.3 Mortality at different life history stages and long-term population trends ..... 98 3.4.4 Conclusions ............................................................................................... 100 Chapter Four Variation in magpie predation of artificial nests ........................ 101 ABSTRACT ............................................................................................................ 103 4.1 INTRODUCTION ....................................................................................... 104 4.2 METHODS ................................................................................................. 107 4 4.2.1 Field site .................................................................................................... 107 4.2.2 Identification of nest predators ................................................................... 107 4.2.3 Determining magpie territories ................................................................... 108 4.2.4 Measurement of nest predation ................................................................. 109 4.2.5 Measurement of habitat variation .............................................................. 111 4.2.6 Measurement of variation in magpie behaviour ......................................... 111 4.2.7 Statistical analysis ..................................................................................... 111 4.3 ETHICAL STATEMENT ............................................................................. 113 4.4 RESULTS .................................................................................................. 114 4.4.1 Predator identity ........................................................................................ 114 4.4.2 Factors affecting artificial nest predation ................................................... 115 4.5 DISCUSSION ............................................................................................ 120 4.5.1 Predators of artificial nests ........................................................................ 121 4.5.2 Effect of magpie presence on nest predation ............................................ 122 4.5.3 Effect of location on artificial nest predation .............................................. 124 4.5.4 Conclusions ............................................................................................... 127 Chapter Five Effect of magpie ecology and habitat variation on farmland songbird nest site choice and nest success ..................................................... 129 ABSTRACT ...........................................................................................................
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