Analysis of Islay Greenland White-Fronted Anser Albifrons Flavirostris and Barnacle Branta Leucopsis Goose Datasets
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BTO Research Report No. 420 Analysis of Islay Greenland White-fronted Anser albifrons flavirostris and Barnacle Branta leucopsis Goose datasets Authors Chris Pendlebury, Chris Wernham and Mark Rehfisch A report by the British Trust for Ornithology under contract to the Scottish Executive Environment and Rural Affairs Department (Environment Research Group 2004/05 Project No: ENV/BTO/001/04) December 2006 ©British Trust for Ornithology BTO Scotland, School of Biological and Environmental Science, Cottrell Building, University of Stirling, Stirling, FK9 4LA Registered Charity No. 216652 British Trust for Ornithology Analysis of Islay Greenland White-fronted Anser albifrons flavirostris and Barnacle Branta leucopsis Goose datasets BTO Research Report No. 420 Chris Pendlebury, Chris Wernham and Mark Rehfisch Published in December 2006 by British Trust for Ornithology (Scotland) School of Biological & Environmental Sciences, Cottrell Building, University of Stirling, Stirling. FK9 4LA Copyright British Trust for Ornithology 2006 ISBN 978-1-908581-40-2 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form, or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publishers TABLE OF CONTENTS LIST OF TABLES ............................................................................................................................ 3 LIST OF FIGURES ........................................................................................................................... 5 LIST OF APPENDICES .................................................................................................................... 7 EXECUTIVE SUMMARY ............................................................................................................... 11 A Appraisal of the International Paired Count Data .......................................................... 11 B Effectiveness of Goose Scaring on Islay ......................................................................... 12 1 INTRODUCTION ................................................................................................................ 15 1.1 Background .................................................................................................................... 15 1.2 The Islay Situation .......................................................................................................... 15 1.3 Greenland White-fronted Goose ................................................................................... 15 1.4 Greenland Barnacle Goose............................................................................................. 16 1.5 Goose Monitoring on Islay ............................................................................................. 16 1.6 Factors Influencing Field Preferences Shown by Geese ................................................ 16 1.7 Scaring Programme ........................................................................................................ 17 1.8 Project Aims ................................................................................................................... 19 2 METHODS ......................................................................................................................... 21 2.1 Use of International Paired Count Data to Assess Count Quality and Significance of Population Trends .................................................................................. 21 2.1.1 Data selection and calculation of count discrepancy ........................................... 21 2.1.2 Correlates of count discrepancy ........................................................................... 22 2.1.3 Population trends and their significance ............................................................. 23 2.1.4 Value of paired counts ......................................................................................... 25 2.2 Factors Influencing Field Usage by Geese on Islay ......................................................... 26 2.2.1 Selection of data for field use modelling: whole-island analyses ........................ 26 2.2.2 Models of field use: whole-island analyses .......................................................... 26 2.2.3 Models of field use: Loch Gruinart analyses ........................................................ 29 2.3 Investigation of the Effects of Scaring on Field Use by Geese ....................................... 30 2.3.1 Predicted versus observed numbers of geese ..................................................... 30 2.3.2 Models to assess any effects of scaring ............................................................... 31 2.4 Effects of Scaring on the Distribution of Geese on Islay ................................................ 33 2.5 Statistical Analyses ......................................................................................................... 34 3. RESULTS ........................................................................................................................... 35 3.1 Use of International Paired Count Data to Assess Count Quality and Significance of Population Trends .................................................................................. 35 3.1.1 Count discrepancy and its correlates ................................................................... 35 3.1.2 Estimates of count discrepancy ............................................................................ 35 3.1.3 Derivation and significance of population trends for Greenland White-fronted Goose ......................................................................... 36 3.1.4 Derivation and significance of population trends for Greenland Barnacle Goose ................................................................................... 37 3.2 Factors Influencing Field Usage by Geese on Islay ......................................................... 37 3.2.1 Greenland White-fronted Goose (whole-island data) ......................................... 37 3.2.2 Greenland Barnacle Goose (whole-island data) ................................................... 38 BTO Research Report 420 1 December 2006 3.2.3 Loch Gruinart RSPB reserve data ......................................................................... 39 3.3 Effects of Scaring on Field use by Geese on Islay ........................................................... 40 3.3.1 Effects of scaring on field usage by Greenland White-fronted Geese ................. 40 3.3.2 Effects of scaring on field usage by Greenland Barnacle Geese .......................... 40 3.3.3 Effects of scaring on field usage by the two goose species combined ................ 41 3.4 Effects of Scaring on the Distribution of Geese on Islay ................................................ 42 4. DISCUSSION ...................................................................................................................... 43 4.1 Use of International Paired Counts to Assess Count Quality and Significance of Population Trends .................................................................................. 43 4.1.1 Limitations of count discrepancy as a measure of count ‘quality’ ....................... 43 4.1.2 Magnitude of count discrepancy and its influences ............................................ 43 4.1.3 Population trends and their significance ............................................................. 44 4.1.4 Value of paired counts ......................................................................................... 45 4.1.5 Future monitoring recommendations .................................................................. 45 4.2 Predicting Patterns of Field Usage by Geese on Islay .................................................... 47 4.2.1 Data quality and model fit .................................................................................... 47 4.2.2 Variables influencing field usage .......................................................................... 47 4.3 Effects of Scaring on Field Usage by Geese on Islay ...................................................... 49 4.3.1 Comparisons of scaring and non-scaring areas .................................................... 49 4.3.2 Comparisons of scaring techniques...................................................................... 50 4.3.3 Limitations in the assessment of scaring effects .................................................. 51 4.4 Effects of Scaring on the Distribution of Geese on Islay ................................................ 52 4.5 Recommendations for Future Work on Scaring............................................................. 53 5 ACKNOWLEDGEMENTS ..................................................................................................... 55 6 REFERENCES ..................................................................................................................... 57 BTO Research Report 420 2 December 2006 LIST OF TABLES Table 1.5.1 Annual summaries of the number and dates of counts used in our analyses of population trends .................................................................................. 61 Table 2.1.1.1 Annual summaries of the number and dates of paired counts used in our analyses of count discrepancy .......................................................................... 62 Table 2.2.3.1 Crop types and numbers of fields that received fertiliser