Durham E-Theses Determinants of habitat and site use by turnstones and purple sandpipers in N.E. England, and possible eects of the removal of coastal nutrients Eaton, Mark A. How to cite: Eaton, Mark A. (2001) Determinants of habitat and site use by turnstones and purple sandpipers in N.E. England, and possible eects of the removal of coastal nutrients, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/3986/ 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 2 Determinants of habitat and site use by Turnstones and Purple Sandpipers in N.E. England, and possible effects of the removal of coastal nutrients by Mark A. Eaton, M.Sc (Durham) This thesis is presented in candidature for the degree of Doctor of Philosophy Department of Biological Sciences University of Durham 2001 The copyright of this thesis rests with the author. No quotation from it should be published in any form, including Electronic and the Internet, without the author's prior written consent. All information derived from this thesis must be acknowledged appropriately. 2 MAR 200^ Abstract Determinants of habitat and site use by Turnstones and Purple Sandpipers in N.E. England, and possible effects of the removal of coastal nutrients PhD. thesis by Mark Eaton, 2001 Purple Sandpipers and Turnstones were studied on the coast of south Northumberland, with regard to the possible effects of reductions in sewage inputs into inshore waters along the Northumberland coast as a result of new European legislation. Multivariate analysis of bird density in relation to 33 habitat variables indicated that Purple Sandpiper distribution was positively correlated with the abundance of intertidal musselbeds, but negatively correlated with raptor density. Turnstone density was positively correlated with several intertidal habitats such as bare and barnacle-covered rock, as well as the amount of detached wrack deposited on the strandline. Analysis of stable carbon and nitrogen isotopes in particulate organic matter in inshore waters indicated that sewage contributed up to 60% of the total organic matter in the immediate vicinity of outfalls, and hence probably supported increased intertidal invertebrate densities. Purple Sandpiper numbers were unlikely to be limited by food resources, but birds sought to feed in areas that offered the highest food intake rates, in order to reduce the time spent feeding and therefore minimise the risk of predation by raptors. Social status determined where birds could feed, with larger and older birds excluding subordinates to poorer feeding areas. Social status in Turnstones was determined by sex and age. By feeding on the richest intertidal food resources, dominant individuals (males and adults) minimised the time spent foraging on ephemeral deposits of strandline wrack over high water, which carried a greater risk of predation. Dominant individuals of both species were able to carry less stored fat and hence improved their chances of escaping attacks by raptors. While both species are unlikely to decline in numbers as a direct response to lower food densities, subsequent changes in foraging behaviour and distribution could result in greater mortality. Contents Page Chapter One: General introduction, study area and species 1.1 Introduction 1 1.2 The effects of sewage inputs on coastal ecosystems 2 1.3 Objectives 4 1.4.1 The study area 5 1.4.2 Changes in treatment levels and locations of sewage discharges 8 1.5. The study species 10 1.5.1 Purple Sandpiper 11 1.5.2 Turnstone 14 Chapter Two: Relationships between bird density and environmental variables 2.1 Introduction 17 2.1.1 Factors determining Purple Sandpiper and Turnstone distribution 17 2.1.2 Spatial scales 20 2.1.3 Temporal scales 20 2.2 Methods 22 2.2.1 Environmental variables 22 2.2.2 Spatial scales 25 2.2.3 Statistical techniques 26 2.2.4 Testing models 26 2.3 Results 32 2.3.1 Purple Sandpiper principal component regression at the larger spatial scale 32 2.3.2 Purple Sandpiper principal component regression at the small spatial scale 34 2.4.1 Turnstone principal component regression at the larger spatial scale 35 2.4.2 Turnstone principal component regression at the small spatial scale 35 2.5.1 Testing the accuracy of model predictions 36 2.5.2 Accuracy of models of Purple Sandpiper density 36 2.5.3 Accuracy of models of Turnstone density 37 2.6 Discussion 38 2.6.1 Purple Sandpiper 38 2.6.2 Turnstone 43 Chapter Three: Measuring the relative inputs of particulate organic matter from sewage outfalls and from dead macroalgae using stable isotopes 3.1 Introduction 46 3.2 Methods 49 3.2.1 Sampling locations 49 3.2.2 Sampling methods 52 3.3 Results 54 3.3.1 Variation between replicated samples 54 3.3.2 Isotope ratios for sources of inshore POM 56 3.3.2.1 Sewage 56 3.3.2.2 Macroalgae 57 3.3.3 Sewage and algae values used in calculations of input to POM in the inshore water column 59 3.3.4 The relative contribution of sewage to particulates in inshore waters 60 3.3.4.1 Spring sampling 61 3.3.4.2 Autumn sampling 64 3.4 Discussion 67 3.4.1 Errors, problems and possible solutions 67 3.4.2 Isotope ratios of POM and its sources 68 3.4.3 Estimates of the percentage of sewage in POM 69 Chapter Four: Use of the south Northumberland coast by Purple Sandpipers 4.1 Introduction 71 4.2 Methods 73 4.2.1 Counts 73 4.2.2 Habitat use and behaviour 74 4.2.3 Faecal samples 75 4.3 Results 76 4.3.1 Counts of Purple Sandpipers 76 4.3.1.1 Variation in total numbers 76 4.3.1.2 Distribution between sites 79 4.3.2 Purple Sandpiper foraging behaviour 85 4.3.2.1 Foraging substrate choice 85 4.3.2.2 Behaviour over the tidal cycle 89 4.3.3 Faecal samples as an indicator of Purple Sandpiper diet 91 4.4 Discussion 99 4.4.1 Purple Sandpiper distribution and overall numbers 99 4.4.2 Purple Sandpiper foraging behaviour 105 4.4.3 Purple Sandpiper diet 107 4.4.4 Summary 109 Chapter Five: Use of the south Northumberland coast by Turnstones 5.1 Introduction 111 5.2 Methods 111 5.2.1 Counts and analyses 112 5.2.2 Habitat use and behaviour 113 5.2.3 Faecal samples 113 5.3 Results 114 5.3.1 Counts of Turnstones 114 5.3.1.1 Seasonal and annual variation in total numbers 114 5.3.1.2 Distribution between sites 117 5.3.1.3 Turnstone numbers at Amble and Hauxley in relation to wrack deposits 126 5.3.2 Turnstone behaviour and foraging substrate use over the tidal cycle 126 5.3.2.1 Substrate choice 126 5.3.3 Turnstone faecal samples 134 5.3.4 Observations of feeding Turnstones 135 5.4 Discussion 137 5.4.1 Turnstone distribution and overall numbers 137 5.4.2 Turnstone distribution within the study area 141 5.4.3 Turnstone foraging behaviour 143 5.4.4 Variation in Turnstone behaviour between the six rocky shore sites 145 5.4.5 Conclusions 147 Chapter Six: Individual variation in the behaviour and site and habitat u of Purple Sandpipers 6.1 Introduction 149 6.1.1 Individual variation in behaviour 149 6.1.2 Site fidelity and mortality 151 6.1.3 Nocturnal behaviour 152 6.2 Methods 154 6.2.1 Catching birds 154 6.2.2 Molecular sexing of Purple Sandpipers 155 6.2.3 Radio-telemetry 155 6.2.4 In-field observations 157 6.2.4.1 Age, sex and breeding population of Purple Sandpipers 157 6.2.4.2 Observations of colour-ringed Purple Sandpipers 158 6.3 Results 159 6.3.1 The sex ratio and origins of Purple Sandpipers in the study area 159 6.3.1.1 Biometric measurements 159 6.3.1.2 In-field assessment of bill lengths 161 6.3.1.3 Ages 164 6.3.2 Mortality 165 6.3.3 Site fidelity 166 6.3.4 Bird mass in relation to site fidelity 171 6.3.5 Arrival and departure dates 174 6.3.6 Difference in the behaviour and use of sites by individuals 174 6.3.6.1 Roosting and other behaviour over high water 174 6.3.6.2 Foraging behaviour over low water 175 6.3.6 Nocturnal behaviour 176 6.3.7 Nocturnal diet 180 6.4 Discussion 181 6.4.1 Composition of the wintering population of Purple Sandpipers in south Northumberland 181 6.4.2 Mortality and recruitment 183 6.4.3 Variation in the behaviour of individual Purple Sandpipers, and possible determinants 184 6.4.3 Individual variation in behaviour 187 6.4.4.