TITL BTO RESEARCH REPORT 531 Estimates of breeding bird abundance and habitat use in Thetford Forest Park. Greg Conway & Ian Henderson BTO Research Report No. 531 Estimates of Breeding Bird Abundance and Habitat Use in Thetford Forest Park Authors Greg Conway & Ian Henderson Report of work carried out by The British Trust for Ornithology for the Forestry Commission England March 2009 © British Trust for Ornithology British Trust for Ornithology, The Nunnery, Thetford, Norfolk, IP24 2PU Registered Charity No. 216652 CONTENTS Page No. List of Tables ......................................................................................................................................... 3 List of Figures ........................................................................................................................................ 5 List of Appendices ................................................................................................................................. 7 1. INTRODUCTION.................................................................................................................... 9 2. METHODS ............................................................................................................................. 11 2.1 Survey Sampling Design ........................................................................................................ 11 2.2 Field Methods ......................................................................................................................... 11 2.3 Habitat Structure ................................................................................................................... 11 2.4 Data Methods and Analysis ................................................................................................... 11 2.5 Relative Density Estimates and Habitat Association .......................................................... 12 2.6 Comparison of Bird Densities with the Deer Project .......................................................... 12 2.7 Population Estimates ............................................................................................................. 12 3. RESULTS ............................................................................................................................... 15 3.1 Survey Coverage .................................................................................................................... 15 3.2 Bird Data ................................................................................................................................ 15 3.2.1 Relative density estimates and habitat association ................................................ 15 3.2.2 Species richness ......................................................................................................... 15 3.2.3 Species of conservation concern .............................................................................. 16 3.2.4 Comparison with the Deer Project results .............................................................. 16 3.2.5 Population estimates ................................................................................................. 16 4. DISCUSSION ......................................................................................................................... 17 4.1 Survey Coverage .................................................................................................................... 17 4.2 Species Richness ..................................................................................................................... 17 4.3 Species of Conservation Concern ......................................................................................... 17 4.4 Relative Density Estimates for Growth Stages and Habitats ............................................. 17 4.5 Comparison of breeding bird densities with other studies………………………….……18 4.6 Comparison with the Deer Project Results.......................................................................... 18 4.7 Limitations .............................................................................................................................. 18 References ............................................................................................................................................ 21 Acknowledgements ............................................................................................................................. 22 Tables ................................................................................................................................................. 23 Figures ................................................................................................................................................. 33 Appendices ........................................................................................................................................... 41 BTO Research Report No. 531 1 Draft March 2009 BTO Research Report No. 531 2 Draft March 2009 LIST OF TABLES Page No. Table 1 Definition of forest growth stages and habitats, derived form the Forestry Commission sub-compartment database ................................. 23 Table 2 Number of 1-km survey squares covered in each forest block............................. 23 Table 3 (part 1) Summary of all species encountered, excluding flight only records, and Maximum counts for singing and all individuals from all records and distance band up to 75 m ..................................................... 24 Table 3 (part 2) (As above) ............................................................................................................ 25 Table 4 Area of each primary habitat in Thetford Forest Park and area surveyed ........................................................................................................ 26 Table 5a Breeding population estimates and 95% confidence intervals for Thetford Forest Park. (A) Males .................................................................... 27 Table 5b (As above) (B) All registrations ........................................................................... 28 Table 6 Species richness within primary habitats ............................................................. 28 Table 7 Summary of associations between species and habitat structure derived from mixed models .................................................................................. 29 Table 7a Comparative bird density estimates, with confidence intervals, for Pre-Thicket, Thicket and Pre-fell growth stages, derived from GLMM’s using Deer Project (2007 & 2008) and breeding birds monitoring (2008) data ................................................................................ 30 Table 7b Comparative bird density estimates, with confidence intervals, for Pre-Thicket, Thicket and Mature growth stages, derived from GLMM’s using Deer Project (2007 & 2008) and breeding birds monitoring (2008) data ......................................................................................... 31 Table 8 Densities estimates (individuals per hectare) and confidence intervals (ci’s), of selected non-forest species, as derived from the Breeding Bird Survey (BBS) for Norfolk (n=66 1-km squares) and Suffolk (n=53 1-km squares) in 2006…………………………………………...32 BTO Research Report No. 531 3 Draft March 2009 BTO Research Report No. 531 4 Draft March 2009 LIST OF FIGURES Page No. Figure 1 Location of 1-km squares where line transects were surveyed ............................ 33 Figure 2a-f Relative density estimates (from maximum single count per Visit), across growth stages and habitats ......................................................................... 34 Figure 3a-d Relative density estimates (from maximum single count of, singing or all, individuals per Visit), across growth stages and habitats........................... 35 Figure 4a-f Relative density estimates (from maximum single count of, singing or all, individuals per Visit), across growth stages and habitats........................... 36 Figure 5a-f Relative density estimates (from maximum single count of, singing or all, individuals per Visit), across growth stages and habitats........................... 37 Figure 6a-f Relative density estimates (from maximum single count of, singing or all, individuals per Visit), across growth stages and habitats........................... 38 Figure 7a-e Relative density estimates (from maximum single count of, singing or all, individuals per Visit), across growth stages and habitats........................... 39 BTO Research Report No. 531 5 Draft March 2009 BTO Research Report No. 531 6 Draft March 2009 LIST OF APPENDICES Page No. Appendix 1a Species Lists and relative abundance for each growth stage/ habitat class (all registrations) .............................................................................. 41 Appendix 1b Species Lists and relative abundance for each growth stage/ habitat class (all registrations) .............................................................................. 42 Appendix 1c Species Lists and relative abundance for each growth stage/ habitat class (all registrations) .............................................................................. 43 Appendix 2 Woodland growth stage / Distribution and type of understorey within stand / Mature woodland structure ............................................................ 44 BTO Research Report No. 531 7 Draft March 2009 BTO Research