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Thompson, Katherine Russell (1987) The ecology of the Manx shearwater Puffinus Puffinus on Rhum, West Scotland. PhD thesis. https://theses.gla.ac.uk/636/ Copyright and moral rights for this work are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This work cannot be reproduced or quoted extensively from without first obtaining permission in writing from the author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Enlighten: Theses https://theses.gla.ac.uk/ [email protected] THE ECOLOGY OF THE MANX SHEARWATER PUFFINUS PJJFFINUS ON RHUM, WEST SCOTLAND KATHERINE RUSSELL THOXPSON Presented in candidature for the degree of Doctor of Philosophy to the Faculty of Science, University of Glasgow, July 1987. K. R. Thompson, 1987. There is a great deal of stormy magnificence about the lofty cliffs, as there is generally round the shores of Runi; and they are, in most places, as abrupt as they are inaccessible from the sea. The interior is one heap of rude mountains, scarcely possessing an acre of level land. It is the wildest and most repulsive of all the islands. The outlines of Halival and Haskeval are Indeed elegant, and render the island a beautiful and striking object from the sea. If it is not always bad weather in Rum, it cannot be good very often." Ma.cCulloch, 1824. u yet the birds which hover so closely over the bosom of the deep at times ascend in the air to an elevation of many hundred feet as, for example, when the individuals which nest in the interior of Rum return to their well-nigh Inaccessible burrows among the mountain crags of that island deer-forest." H.A. XJc Pherson, 1898. ACKNOWLEDGEMENTS I was first introduced to Manx shearwaters by Neville McKee and I thank him for encouraging my Interest in seabirds. I thank the N.C.C. for allowing me to work on Rhum, and all the island's residents for helping to make It such an enjoyable place to live. In particular, I am grateful to Laughton and Patricia Johnston, Richard and Janet Jewell, Wilf and Rosemary Nelson, Ian and Cathy Simpson and all the members of the red deer research team for their help and ever-open doors. I thank also John Love and Peter Wormell for valuable and stimulating discussions about my work on Rhum. Many visitors to Rhum were willing assistants and in particular, I thank Bob and Sue Furness and "Earthwatch" volunteers for their help in capturing birds and Jim Hanson for his assistance in gathering data on chick growth. For invaluable constructive comment and discussion during the preparation of this thesis I thank Bob Furness. and Peter Jones. I am most grateful to the Department of Education in Northern Ireland for providing the necessary funding for this research and to Prof. Keith Vickerman for the use of facilities within the Department of Zoology at Glasgow University. I thank Anne Hudson for being such a cheerful and helpful friend throughout my time at Glasgow. Bob Swann gave me invaluable data from the Canna colony and Dave Ireland of the Meteorological office also provided useful information. Jim Baird and Martin Burns provided expert assistance in the construction of the maze used In olfaction experiments. Most of all, I thank my husband, Dann Hale, for unstinting help in the field, for pancake breakfasts after long nights out on the hill, and for his endless patience, support and encouragement through it all. CANDIDATE' S DECLARATION I declare that the work recorded in this thesis is entirely my own, unless otherwise stated, and that it is of my own composition. No part of this work has been submitted for any other degree. Kate Thompson CONTENTS ABSTRACT . I 1. INTRODUCTION ............................................. 1 Taxonomy of the Manx shearwater ........................ 1 Distribution of the )tanx shearwater .................... 1 The breeding cycle ..................................... 2 Thestudy area ......................................... 3 History of shearwaters on Rhum......................... 4 Past and present sliearwater research on Rhum ........... 5 Methods ................................................ 7 Nomenclature ........................................... 8 2. BIOMETRICS OF MANX SHEARWATERS ON RHUI( ................... 9 Introduction ........................................... 9 Methods ................................................ 9 Results ............................................... 10 Comparison of male and female dimensions......... 10 Seasonal changes in weight ........................ 12 Pre-laying weights on Rhum and Skokholm ........... 15 Discussion ............................................ 15 Size difference between the sexes ................. 15 Differences in body dimensions between Skokholm and Rhum.......................................... 16 Seasonal changes in weight ........................ 17 3. BREEDING SUCCESS AND BURROW QUALITY ..................... 21 Introduction .......................................... 21 Methods ............................................... 21 Results ............................................... 24 Burrow density in relation to habitat type....... 24 Breeding success .................................. 24 Burrowquality .................................... 29 Relationship between bird quality and burrow quality ........................................... 33 Burrow selection .................................. 37 Discussion ............................................ 4. TIMING OF BREEDING, EGG DIMENSIONS, AND FLEDGING WEIGHTS.................................................45 Introduction..........................................45 Methods...............................................45 Results................................................47 Relationship between fledging weight and date.....47 Timing of laying..................................48 Eggsize..........................................52 Incubation periods................................54 Role of fat reserves carried by fledglings............55 Discussion ...........................................60 5. FEEDING ECOLOGY AND CHICK GROWTH........................70 Introduction..........................................70 A) Adult and Chick Diets..............................70 Methods...........................................70 Results...........................................73 B) Chick Feeding and Growth...........................77 Methods...........................................77 Results...........................................77 Chickgrowth..................................77 Feed sizes....................................79 Feeding frequency.............................81 Food conversion efficiency....................85 Factors influencing growth rates..............86 Discussion............................................85 Diet and food conversion efficiency...............86 Chick growth rates................................89 Desertion period..................................91 6. PREDATION AND POPULATION DYNAMICS.......................95 Introduction..........................................95 A) Rat Predation......................................95 Introduction......................................95 Methods...........................................98 Results..........................................100 Discussion.......................................109 B) Avian Predators 113 Introduction ..................................... 113 Golden eagles .................................... 113 Golden eagle breeding success in relation todiet ...................................... 120 Great black-backed gulls ......................... 123 Peregrine falcons ................................ 124 C) Population Dynamics ............................... 124 7. DISCUSSION: POPULATION REGULATION AD LIMITATION...... 128 SUMJ(ARY ................................................... 137 APPENDIX 1. NAVIGATION TO THE BURROW ...................... 143 Introduction ......................................... 143 Methods .............................................. 145 Results and conclusions .............................. 146 APPENDIX 2. SCIENTIFIC NAMES OF SPECIES MENTIOfED IN THETEXT ...................................... 149 REFERENCES ................................................ 151 ABSTRACT The aim of this project was to investigate the ecology of Hanx shearwaters on Rhuiu, with particular emphasis on the influence of predation and other extrinsic factors upon breeeding success and population dynamics. Brown rats were not found to be active predators of shearwaters on Rhum. Few rats were present in the shearwater colony during the birds' breeding season, but larger numbers scavenged on the remains of shearwater eggs and chicks during the autumn and early winter. Rats are apparently prevented from becoming established in the shearwater colony by food shortage in late winter and by the colony's location within Rhum. Golden eagles, peregrine falcons and great black- backed gulls do prey upon shearwaters on Rhum but have an insignificant effect upon the shearwater population. Hatching success in the colony varies markedly from year to year and is significantly negatively correlated with the incidence of heavy rain during the incubation period. This arises from the variation in