Population estimates of birds in Great Britain and the United Kingdom Andy Musgrove, Nicholas Aebischer, Mark Eaton, Richard Hearn, Stuart Newson, David Noble, Matt Parsons, Kate Risely and David Stroud l l e w o P y r a m e s o R Abstract Population estimates of birds have a wide range of practical conservation uses, as well as being of enduring interest to many birdwatchers. Following previous reports by the Avian Population Estimates Panel, in 1997 and 2006, we present the third collation of population estimates of birds in Great Britain and the United Kingdom. There are now thought to be about 84 million breeding pairs of birds in the UK. The ten commonest species contribute 57% of this total, with Wren Troglodytes troglodytes alone providing one in ten of our breeding birds. In all, 23 species exceed one million breeding pairs. The individual population estimates come from a wide variety of sources, many from extrapolation of previous estimates by recognised trend measures, others from new surveys and novel analytical approaches developed since the last report. Despite the exceptional level of detail available for some species, many gaps in our knowledge remain. Recommendations are made to allow a continuing improvement in our understanding of the numbers of birds in GB and the UK. There are many opportunities for volunteer and amateur birdwatchers to make a significant contribution. 64 © British Birds 106 • February 2013 • 6 4–100 Population estimates of birds in Great Britain and the United Kingdom ow many birds are there in a popula - (Baker et al. 2006, APEP 2 ). Their purpose tion? Sometimes the most straight - was to present a consensus view on the most Hforward of questions can be the most appropriate estimates for a range of conser - difficult to answer. For most species, it is vation applications. In 2002, the Joint Nature impossible to count every individual and so Conservation Committee (JNCC) acknowl - bird numbers are estimated from sample edged the value to conservation agencies of a counts, using a variety of statistical tech - single, quality-assured source of population niques and assumptions about behaviour and estimates for statutory conservation purposes detectability. Yet bird numbers are inherently and endorsed the APEP process (Stroud et al. dynamic, fluctuating within and between 2002). years as a result of reproduction, mortality, The significance of the APEP’s work has immigration and emigration (Newton 1998). increased with recent developments in Euro - Consequently, the emphasis of much popula - pean bird conservation policy. Article 12 of tion-based research involves generating and the European Union’s (EU) Directive on the understanding population trends , rather than conservation of wild birds (2009/147/EC) total numbers. Nonetheless, the absolute size requires Member States to submit a triennial of an animal population is still important in report on the implementation of the Direc - conservation terms, in particular for the tive. Previous such reports (e.g. Defra 2007) rarest species, which may be under threat of focused on processes, with little or no assess - extinction (Mace 1994). ment of the efficacy of Directive implemen - The UK statutory conservation agencies tation. However, a new reporting format has and relevant non-governmental organisa - now been agreed, which moves Article 12 tions have previously collaborated through reporting to a six-year cycle and focuses on the Avian Population Estimates Panel (APEP) assessment of species status (population to collate the best estimates of the size of sizes, trends and distributions, and changes breeding and non-breeding bird populations. in these parameters over time). The first such Both previous reports were published in BB , reporting cycle is being undertaken jointly in 1997 (Stone et al. 1997, APEP 1 ) and 2006 with BirdLife International, and thus will s t e l l i W e m e a r G 56. White-tailed Eagle Haliaeetus albicilla , Mull, Argyll, September 2012. This spectacular raptor, successfully reintroduced to Scotland in the late twentieth century, is well monitored by the RBBP and we have a very good estimate of its current population. British Birds 106 • February 2013 • 6 4–100 65 Musgrove et al. contribute to a wider assessment of the status sidered endemic to parts of the UK. However, of birds in Europe (and the third edition of because of a lack of knowledge of distribu - Birds in Europe ; see BirdLife International tion, it was not possible to give estimates for 2004). To encourage national joint assess - three currently recognised endemic sub - ments between Member State authorities and species: Meadow Pipit Anthus pratensis whist - the respective BirdLife partners, the Euro - leri , Linnet Carduelis cannabina autochthona pean Commission has promoted the APEP as and Yellowhammer Emberiza citrinella caligi - a model of good working. nosa (and estimates for some other sub - This, the third APEP report, presents the species are similarly problematic). For some most recent population estimates for both waterbirds, it is common practice to treat Great Britain and the United Kingdom. clearly delineated biogeographic populations These, together with other data and informa - separately, and we follow Musgrove et al. tion, will support the UK’s Article 12 report (2011) in this regard. to the EU due for submission in December 2013. However, we hope that the estimates Geographic area are also interesting and informative for a As far as possible, separate estimates have much wider range of users. been produced for Great Britain (GB) and the United Kingdom (UK). All estimates exclude Scope the Channel Islands. The Isle of Man (IoM) is Species, subspecies and biogeographic not part of GB or the UK, but its exclusion populations from most population estimates is generally All species in Categories A and C of the not straightforward and most estimates are British List were considered but other non- actually for GB+IoM and UK+IoM. For most native species were excluded. Population esti - species, this makes very little difference to the mates were principally sought at species level estimates, especially following rounding. but for some species it was possible to give However, for five species (Hen Harrier Circus separate estimates of different subspecies. cyaneus , Peregrine Falcon Falco peregrinus , This was of particular interest for subspecies Ringed Plover Charadrius hiaticula , Herring with a distinct legal status and/or those con - Gull Larus argentatus and Red-billed Chough h c t a w d r i B / g n u o Y e v e t S 57. Little Gull Hydrocoloeus minutus , Lancashire & N Merseyside, April 2012. One of the most difficult groups, in terms of estimating national population size, is that of non-breeding seabirds. 66 British Birds 106 • February 2013 • 6 4–100 Population estimates of birds in Great Britain and the United Kingdom m o c . s e g a m i - b p s r 58. Barn Owl Tyto alba , Northumberland, February 2010. In many parts of the UK, this is the most frequently encountered owl, hunting in daylight in a variety of open habitats; and yet, in terms of estimating population size, it is surprisingly poorly known. Pyrrhocorax pyrrhocorax ) the Isle of Man con - where statutory site protection and reporting tributes a significant and calculable propor - is based around non-breeding estimates. In tion of the GB/UK total; for these, separate some cases (such as Blackbird Turdus merula IoM estimates are presented (together with and Common Chaffinch Fringilla coelebs ), strict GB and UK estimates). Estimates mostly common residents are supplemented by exclude offshore areas out of sight of land, large-scale autumn arrivals, but estimates of although this definition may be stretched by non-breeding numbers have not been aerial survey data incorporated into Common attempted for these species owing to a lack of Scoter Melanitta nigra and Red-throated suitable data sources. However, estimates Diver Gavia stellata estimates. have been produced for species that are sub - stantially more numerous outside the Seasons breeding season. These include scarce win - Breeding-season estimates are presented for tering species (such as Great Grey Shrike all species with at least one case of proven Lanius excubitor ) but not scarce passage breeding from 2006 onwards. Appendix 3 migrants (such as Barred Warbler Sylvia covers those other species where there was a nisoria ). Rare migrants and vagrants (species lower level of breeding evidence, plus a covered by BBRC) were excluded unless there number of historical breeding species that were recent breeding records. exhibited no breeding evidence, over the Estimating non-breeding numbers of same period. seabirds is particularly difficult, both in terms It was harder to define those species for of monitoring species away from breeding which non-breeding estimates should be pre - colonies and in terms of the passage of many sented. The precise definition of the non- species through UK waters. In most cases, breeding season varies according to species such estimates have been omitted. Estimates and estimation technique (as set out in this of passage numbers of other species are also paper and in those referenced) and this excluded, with the exception of the globally should be taken into account. In general, threatened Aquatic Warbler Acrocephalus non-breeding estimates were omitted for paludicola , which occurs here only at this largely resident species, except for waterbirds point in its life-cycle. British Birds 106 • February 2013 • 6 4–100 67 Musgrove et al. Timescale APEP 3 , although this will be a key source of The aim has been to collate the most recently information for APEP 4 . However, prelimi - published estimates. However, many of the nary data from the new atlas was helpful in estimates presented here are based on novel some instances, particularly where discrepan - analyses that extrapolate from previously cies arose between multiple estimates derived published estimates.