The impacts of non-native gamebird release in the UK: an updated evidence review Lucy R. Mason, Jake E. Bicknell*, Jennifer Smart, Will J. Peach RSPB Research Report No. 66 October 2020 RSPB Centre for Conservation Science RSPB, The Lodge, Sandy, Bedfordshire SG19 2DL Suggested citation: Mason, L.R., Bicknell, J.E., Smart, J. & Peach, W.J. (2020) The impacts of non-native gamebird release in the UK: an updated evidence review. RSPB Research Report No. 66. RSPB Centre for Conservation Science, Sandy, UK. This report updates an earlier review: Bicknell, J., Smart, J., Hoccom, D., Amar, A., Evans, A., Walton, P. & Knott, J. (2010) Impacts of non- native gamebird release in the UK: a review. RSPB Research Report 40. RSPB: Sandy, Bedfordshire. *J. E. Bicknell current address: Durrell Institute of Conservation and Ecology (DICE), School of Anthropology and Conservation, University of Kent, Canterbury, UK. Cover images: © Mike Langman (rspb-images.com) 1 Contents List of Tables and Figures .................................................................................................................... 4 Common abbreviations ........................................................................................................................ 7 Scientific names of species mentioned in the text ............................................................................ 8 SYNOPSIS 10 1.1 Executive Summary..................................................................................................... 10 1.2 Background ................................................................................................................. 11 1.3 Methods ....................................................................................................................... 12 1.4 Results overview ......................................................................................................... 13 Ecological impacts ....................................................................................................... 13 Socio-economic impacts ............................................................................................. 14 1.5 Conclusions ................................................................................................................. 15 Ecological impacts ....................................................................................................... 15 Socio-economic impacts ............................................................................................. 15 1.6 Key knowledge gaps requiring further study ............................................................... 15 1.7 Impact theme summary tables .................................................................................... 17 Table 2: Ecological impacts ......................................................................................... 17 Table 3: Socio-economic impacts ............................................................................... 22 MAIN REPORT 24 2 Background .................................................................................................................................... 24 2.1.1 Annual release of non-native gamebirds ......................................................... 24 2.1.2 The lowland game shooting industry ............................................................... 32 2.1.3 Best-practice guidelines for sustainable gamebird releasing .......................... 35 2.1.4 Impacts of gamebird releasing ........................................................................ 36 3 Review methods ............................................................................................................................. 38 3.1 Aims and scope ........................................................................................................... 38 3.2 Literature search .......................................................................................................... 38 3.3 Assessing the impacts of gamebird release ................................................................ 40 3.3.1 Quantifying the evidence for ecological impacts ............................................. 40 3.3.2 Quantifying the evidence for socio-economic impacts .................................... 45 4 Ecological impacts ........................................................................................................................ 46 4.1 Ecological impact score results overview .................................................................... 46 4.2 Game estate management .......................................................................................... 52 4.2.1 Impact summary .............................................................................................. 52 4.2.2 Background ..................................................................................................... 54 4.2.3 Farmland management ................................................................................... 55 4.2.4 Woodland management .................................................................................. 59 4.2.5 Woodland creation and retention .................................................................... 65 4.2.6 Supplementary feeding ................................................................................... 66 4.2.7 Legal predator control ..................................................................................... 68 4.2.8 Rodent pest control ......................................................................................... 70 4.2.9 Key knowledge gaps and recommendations .................................................. 72 4.3 Shooting practices ....................................................................................................... 73 4.3.1 Impact summary .............................................................................................. 73 4.3.2 Background ..................................................................................................... 74 4.3.3 Accidental shooting of non-target species ...................................................... 77 4.3.4 Direct ingestion of lead by wildlife ................................................................... 79 4.3.5 Environmental lead concentrations ................................................................. 80 4.3.6 Secondary poisoning of predators .................................................................. 81 4.3.7 Key knowledge gaps and recommendations .................................................. 83 4.4 Illegal persecution........................................................................................................ 85 2 4.4.1 Impact summary .............................................................................................. 85 4.4.2 Background ..................................................................................................... 85 4.4.3 Impacts of illegal persecution on protected species........................................ 86 4.4.4 Key knowledge gaps and recommendations .................................................. 89 4.5 Direct impacts of gamebirds ........................................................................................ 91 4.5.1 Impact summary .............................................................................................. 91 4.5.2 Background ..................................................................................................... 92 4.5.3 Browsing by gamebirds ................................................................................... 92 4.5.4 Predation by gamebirds .................................................................................. 95 4.5.5 Resource competition ...................................................................................... 98 4.5.6 Soil enrichment .............................................................................................. 100 4.5.7 Density dependent effects of pheasant releasing ......................................... 102 4.5.8 Key knowledge gaps and recommendations ................................................ 104 4.6 Disease transmission to wildlife ................................................................................ 106 4.6.1 Impact summary ............................................................................................ 106 4.6.2 Background ................................................................................................... 107 4.6.3 Diseases and parasites carried by gamebirds .............................................. 109 4.6.4 Key knowledge gaps and recommendations ................................................ 114 4.7 Impacts on predators and predation.......................................................................... 116 4.7.1 Impact summary ............................................................................................ 116 4.7.2 Background ................................................................................................... 117 4.7.3 Food source for predators and scavengers .................................................. 117 4.7.4 Impacts of gamebird release on predator abundance................................... 121 4.7.5 Predation rates: impacts on native prey species ........................................... 125 4.7.6 Key knowledge gaps and recommendations ................................................ 126 5 Socio-economic impacts 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