Investigating the causes of the decline of the urban House Sparrow Passer domesticus population in Britain Kate E. Vincent (BSc.) A thesis submitted for the degree of Doctor of Philosophy Awarded by De Montfort University Funded by English Nature, RSPB and De Montfort University October 2005 ABSTRACT In Britain and parts of northwest Europe, House Sparrow Passer domesticus populations have declined markedly in urban-suburban landscapes since the mid-1980s. Little is known about the demographic mechanisms or environmental causes of these population declines, although lack of winter seed has been implicated as a cause of the decline in House Sparrow numbers on English farmland (Hole, 2001). This study focused on factors affecting nesting success and annual productivity of nesting House Sparrows along an urban-suburban-rural gradient centred on the city of Leicester, England. Chick diet (inferred from faecal remains), habitat selection by foraging adults and over-winter survival were also studied. Data were collected during 2001-2003 from 9 study areas spread along the urbanisation gradient. Most sparrows in most study areas nested in or close to domestic gardens. Counts of territorial males declined by 28% between 2001 and 2003, with the largest declines in rural villages (25%) and suburban fringe (16%) and a small increase (4%) in the urban centre. Annual productivity (the estimated number of fledged young/pair/year) was 25% lower in suburban areas and 18% lower in rural areas than that measured during a recent study of farmland House Sparrows in Oxfordshire. The main cause of this lower productivity was starvation of chicks, (usually the first 5-6 days after hatching) during June and July. Chicks were more likely to starve if their diet contained a high proportion of vegetable material (mainly supplementary food) or ants, and less likely to starve if their diet contained a high proportion of spiders. The number of young sparrows successfully fledging, and the aggregate chick biomass, per nesting attempt were greater in home ranges containing relatively high proportions of deciduous shrub, trees and grass, and relatively little concrete. During June and July 2003, more young fledged from home ranges containing a higher density of aphids. Dipteran prey (Tipulids and other flies) constituted a higher proportion of the chick diet in rural localities than in urban-suburban localities, while Homopteran prey (mainly aphids) constituted a higher proportion of chick diet in urban-suburban localities. After allowing for effects of weather, nestling body mass and condition were negatively correlated to local levels of nitrogen dioxide air pollution. Since body mass at fledging is known to be a good predictor of immediate post-fledging survival, I predicted that the lower average body mass at fledging among suburban broods (compared to rural broods) would result in lower survival during the first 10 days after fledging (57% for suburban fledglings, compared to 70% for rural fledglings). The combined effects of lower annual productivity and lower predicted post-fledging survival in suburban localities were large enough to result in rapid predicted population decline, given plausible annual survival rates of adults and first-year sparrows and no net immigration. Under the same set of assumptions, productivity and predicted post- fledging survival were high enough in rural localities to maintain and even increase adult population size. Deciduous shrubbery, grassy areas and concrete were the main summer foraging habitats of suburban and rural House Sparrows, with trees being heavily utilised in 2003. Ornamental and evergreen shrubs were strongly avoided by foraging sparrows. Stable isotope ratios of nitrogen (δ15N scores) in chick feathers are proposed to constitute a useful integrated measure of the quality of the chick diet. δ15N scores differed markedly between the vegetable (2.7), herbivorous invertebrate (4.7-6.4) and carnivorous invertebrate (7.1-7.7) components of chick diet. δ15N scores in sparrow chick feathers averaged 7.7 1 suggesting that the average δ15N score of ingested diet was approximately 4.7 (i.e. was probably dominated by vegetable material and herbivorous invertebrates). Feather δ15N scores were lower in home ranges containing relatively large areas of concrete and evergreen vegetation, and were a positive predictor of chick growth rate and body condition. The data presented in this thesis suggest that the abundance of invertebrate prey within home ranges of House Sparrows breeding within suburban and rural garden habitats limits the quantity and quality of chicks raised to fledging. The combined effects of relatively high rates of chick starvation and low body masses at fledging (and consequently low post-fledging survival) observed in suburban localities are large enough to result in rapid population declines. Invertebrate abundance in suburban areas is probably determined, at least in part, by the availability of suitable habitat including native deciduous shrubbery, tress and grassland. Although there is no evidence that the abundance of key invertebrate prey have declined in urban-suburban landscapes, such declines do provide a plausible mechanism for the observed declines in urban-suburban House Sparrow populations. Management techniques, which increase densities of key invertebrate prey during summer, have the potential to increase the annual productivity and possibly the breeding densities of House Sparrows in urban-suburban landscapes. 2 DEDICATION Janet Linda Vincent 1949 - 2005 This thesis is dedicated with love to the memory of my Mum, who instilled in me the drive and determination to follow my dreams and pursue my goals and realise my full potential. Thank you for your enduring encouragement throughout my life. I hope I have made you proud. ACKNOWLEDGEMENTS ‘The spirited horse which will try to win the race of its own accord, will run even faster if encouraged’ - Publius Ovidius Naso Thank you to all my family, for their financial help and encouragement. They never gave up on me in what seemed like a never-ending quest. Because of them all, I came out the other end in one piece. There are a number of people without whom this thesis might not have been written. Firstly, I must thank all the householders who kindly allowed me to put nest boxes on their houses and gave me access to their properties. Without them all, the fundamental task of gathering data would not have been possible. Secondly, my sincerest thanks must go to my supervisors, Jim Fowler of De Montfort University and Will Peach of the RSPB, for their guidance, support and ultimately their faith in this worthwhile project. Particular thanks must go to Phil Grice of English Nature who also supported me throughout this undertaking by giving his time, knowledge and expertise. These three institutions have supported me financially throughout the project. I must thank those people who aided me when out in the field – Alison Smith, Kim Fenton, Rosie Cleary, Louise Cussen and Kelly Thomas, for making those three years carrying out fieldwork so much more enjoyable and easier. I am also grateful to Derek Gruar of the RSPB and David Hole of Oxford University for giving their assistance and expertise so willingly. All the Leicester and Rutland Ornithological Society members must be thanked. In particular, a mention must go to Ken and Jean Goodrich, whose time, enthusiasm and interest for this project showed no bounds. I must not fail to mention the sparrow guru himself, Denis Summers-Smith, whose passion and enthusiasm for the House Sparrow has rubbed off on me. His immense knowledge on the subject was given to me so freely and he has always been available whenever I needed ideas, advice and opinions. Finally, thank you to all my friends for still talking to me, after what must seem like a never- ending excuse for not coming out for a beer. So now I can turn round and say get the drinks in! 3 CONTENTS Abstract 1 Acknowledgements 3 Contents 4 Chapter 1: General Introduction 9 1.1 Thesis aim and objectives 10 1.2 The urban environment 11 1.3 The House Sparrow 15 1.3.1 Habitat 16 1.3.2 Behaviour 16 1.3.3 Diet 17 1.3.4 Breeding ecology 18 1.3.5 Dispersal 20 1.3.6 Population trends 20 1.4 Suggested causes of decline 24 1.4.1 Predation 24 1.4.2 Competition 30 1.4.3 Lack of nest sites 32 1.4.4 Disease 34 1.4.5 Food availability 39 1.4.6 Environmental pollutants 42 1.4.6.1 The possible link between pollution and invertebrate abundance 44 1.4.7 Multiple environmental causes 46 Chapter 2: Methodology of Fieldwork 48 2.1 Establishing the study sites 50 2.2 Field methodologies 52 2.2.1 Erection of nest-boxes 52 2.2.2 Nest recording and biometric data collected 53 2.2.3 Census methodology 54 2.2.4 Habitat selection and utilisation 55 2.2.5 Provisioning watches 56 2.2.6 Aphid abundance 57 2.2.7 Habitat composition 59 2.2.8 Capture and resighting 61 2.3 Collecting and processing the air pollution data 62 2.4 Intercorrelates and associations between variables used in multivariate analyses 64 Tables and Figures 66 Chapter 3: The status of the House Sparrow Passer domesticus across a number of study areas within Leicester between 2001 and 2003 74 3.1 Introduction 76 3.2 Methods 76 3.2.1 Census methodology 76 4 3.2.2 Statistical analysis of the census data 2001-2003 78 3.3 Results 79 3.3.1 Population change at each site over study period 79 3.3.2 Temporal changes in relative abundance 80 3.4 Discussion 81 3.4.1 Population changes of House Sparrows within Leicester 81