Durham E-Theses Aspects of the ecology of gulls in the urban environment Raven, Susan Jane How to cite: Raven, Susan Jane (1997) Aspects of the ecology of gulls in the urban environment, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/5069/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk Aspects of the ecology of gulls in the urban environment Susan Jane Raven The copyright of this thesis rests with the author. No quotation from it should be published without the written consent of die author and information derived from it should be acknowledged. Presented in candidature for the degree of Doctor of Philosophy. University of Durham, Department of Biological Sciences, 1997. II I FEB 1998 The copyright of this thesis rests with the author. No quotation from it should be published without her prior written consent and information derived from it should be acknowledged. No part of this thesis has previously been submitted for a degree at this or any other University. Acknowledgements The work presented in this thesis was made possible by the assistance and co-operation of a great many people. The British Trust for Ornithology and the Seabird Group endorsed the survey of roof-nesting gulls and by doing so greatly increased the number of volunteers who became involved. Dr. Richard Gregory and the Regional Representatives of the British Trust for Ornithology were of particular help in the organisation of the survey. Paul Walsh and Mark Tasker of the Joint Nature Conservation Committee provided roof-nesting gull data from the Seabird Colony Register as well as much useful advice. The many people who actually carried out counts of roof-nesting gulls in their local areas are too numerous to mention here but their work was greatly appreciated. Ken Smith and Bob Walters, Ecology Officers at ICI Wilton, worked hard to enable me to have access to the roof of the warehouse on the Wilton site and the Teesside Ringing Group, particularly Eric Woods and Geoff Myers, worked with me while ringing chicks on this roof. Dr. David Thompson of Glasgow University assisted with the identification of fish otoliths. The Port of Tyne Authority kindly allowed me to accompany their patrols along the River Tyne and I am grateful for the help given and interest shown by Captain Andrew Nelson and all the patrol crews. Northumbrian Water and the Environment Agency made available information concerning the input of treated and untreated sewage to the River Tyne. In the Department of Biological Sciences I would like to thank Dr. John Coulson and Dr. Keith Hamer for their constructive advice while supervising the work in this thesis. Also in the department thanks must go to Eric Henderson, Dr. Mark O'Connell and Robin Ward for answering countless questions, and John Carter, Justin Maude and Katherine Webb for their assistance with fieldwork. Finally, I must thank the following people for their constant support and help during the last four years; my mother, Michael Ioannou, Louise Revell, Karen Haysom, Michelle Nickerson and Takebumi Itagaki. Contents Abstract 1 Chapter 1: General Introduction 2 Chapter 2: The distribution and abundance of Larus gulls 8 nesting on buildings in Britain and Ireland 2.1 Introduction 9 2.2 Review of roof-nesting by Larus gulls 10 2.2.1 Britain and Ireland 10 2.2.2 Europe 16 2.2.3 North America 17 2.2.4 Other continents 18 2.3 Methods 19 2.4 Results 20 2.4.1 Herring Gulls and Lesser Black-backed Gulls 20 2.4.1.1 Abundance and distribution 20 2.4.1.2 Changes since 1976 24 2.4.1.3 Regional variation 27 2.4.1.4 Coastal and inland nesting 32 2.4.1.5 Effect of colony size on rate of increase 33 2.4.1.6 Loss of colonies 33 2.4.1.7 Nest site types 35 2.4.2 Common Gulls and Great Black-backed Gulls 36 2.4.3 Responses of local authorities 38 2.5 Discussion 39 Chapter 3: Breeding success of Herring Gulls and Lesser Black 43 -backed Gulls on a large warehouse 3.1 Introduction 44 3.2 Study Site 46 3.3 Methods 47 3.4 Results 50 3.4.1 Use of the roof 50 3.4.1.1 Number of breeding pairs 50 3.4.1.2 Distribution over the roof 50 3.4.1.3 Types of nest sites 52 3.4.1.4 Nest density 56 3.4.2 Breeding success 57 3.4.2.1 Initiation of laying 57 3.4.2.2 Clutch size 57 3.4.2.3 Egg volumes 59 3.4.2.4 Hatching success 59 3.4.2.5 Survival to fledging 62 3.4.3 Adult mortality due to botulism 66 3.4.4 Factors potentially influencing breeding success 67 3.4.4.1 Nest density 67 3.4.4.2 Nest site type 69 3.4.4.3 Elevation 70 3.4.4.4 Grouped and dispersed nesting 70 3.5 Discussion 70 Chapter 4: The diet of Herring Gulls nesting on a large warehouse 81 4.1 Introduction 82 4.2 Methods 83 4.3 Results 86 4.3.1 Adults 86 4.3.1.1 Diet 86 4.3.1.2 Changes through the season 92 4.3.2 Chicks 92 4.3.2.1 Diet 92 4.3.2.2 Changes through the season 95 4.3.3 Review of dietary studies of roof-nesting gulls 98 4.4 Discussion 98 Chapter 5: The effect of improvements to sewage treatment on the 108 numbers and distribution of gulls on the River Tyne 5.1 Introduction 109 5.2 Study Area 111 5.2.1 The River Tyne 111 5.2.2 Use of the polluted river 112 5.2.3 Improvements to sewage treatment 115 5.3 Methods 115 5.4 Results 117 5.4.1 Changes in sewage input since 1969/70 117 5.4.2 Other changes on the river since 1969/70 117 5.4.3 Use of the river by gulls in 1993/94 119 5.4.3.1 Black-headed Gull 120 5.4.3.2 Common Gull 120 5.4.3.3 Lesser Black-backed Gull 120 5.4.3.4 Herring Gull 123 5.4.3.5 Great Black-backed Gull 123 5.4.3.6 Kittiwake 123 5.4.4 Comparing abundance - 1969/70 and 1993/94 124 5.4.5 Sections 10 -14 128 5.4.6 Comparing distribution - 1969/70 and 1993/94 129 5.4.7 Factors affecting the distribution of gulls in 1993/94 132 5.5 Discussion 135 Chapter 6: General Discussion 142 Summary 151 References 158 Appendices 172 Appendix 1 Herring Gulls and Lesser Black-backed Gulls nesting 173 on buildings in Britain and Ireland in 1994 Appendix 2 Common Gulls nesting on buildings in Britain and 183 Ireland in 1994 Appendix 3 Great Black-backed Gulls nesting on buildings in 184 Britain and Ireland in 1994 Appendix 4 Towns where roof-nesting gulls definitely absent 185 in 1994 Appendix 5 Counties where no records of roof-nesting gulls 186 had been received by 1994 Abstract A survey in 1994 recorded nearly 14,000 pairs of Larus gulls of four species nesting on buildings in Britain and Ireland. The majority of these records involved Herring Gulls, although large numbers of Lesser Black-backed Gulls were also observed. Since the last such survey in 1976, Lesser Black-backed Gulls had shown the highest rate of increase. Despite the sharp decline in the numbers of Herring Gulls breeding in Britain and Ireland since the mid-1970s, numbers nesting on roofs had continued increasing, albeit at a lower rate than before. New developments since 1976 included increasing numbers nesting inland and on the roofs of large industrial buildings. The study of a colony of Herring Gulls and Lesser Black-backed Gulls nesting on one such industrial building showed that the breeding success of these birds, although lower than that found for roof-nesting birds at more dispersed colonies, was higher than that at many traditional colonies. Low nest density, shelter for chicks and safety from predators were thought to be important contributors to this success. In addition, the colony was situated very close to the sources of food, agricultural land and urban areas, found to be most important in the diet of Herring Gulls nesting there. A review of dietary studies of roof-nesting Herring Gulls found that, despite the location of such colonies in urban areas, urban sites were not always an important source of food. The reduction in availability of one urban source of food, untreated sewage, was found to have little effect upon the gulls using an urban stretch of river. In particular, neither of the species causing most problems in urban areas, the Herring Gull and Lesser Black- backed Gull, decreased in number; in fact, numbers of these species nesting on buildings in the area increased considerably.