Recent changes in bird populations in British broadleaved woodland

摘要

This paper presents estimated national and regional changes in numbers of breeding woodland birds in predominantly broadleaved woodland in Britain between the mid 1980s and 2003-04, derived from the Repeat Woodland Bird Survey (RWBS). A total of 405 sites across Britain for which historical data on bird populations were available were re-surveyed by BTO and RSPB fieldworkers during the RWBS. Changes were estimated separately for sites surveyed by the RSPB (n = 252) and BTO (n = 153) because of differences between the two groups in the field methods used in the original surveys. Changes between the 1960s and 1970s and 2003-04 were also estimated with the BTO data set only. The BTO and RSPB sites provide geographically complementary coverage of Britain and together provide much more widespread coverage than did the Common Bird Census (CBC), the former national monitoring scheme. Nationally, between the 1980s and 2003-04, six species declined significantly and three increased significantly based on the RSPB data, whereas eight declined and 13 increased according to the BTO data, with good correspondence between the changes recorded by the two data sets (only seven of 34 species showing trends differing in direction). Eight species showed large national declines (> 25%) according to both data sets: Garden Warbler Sylvia borin, Lesser Redpoll Carduelis cabaret, Lesser Spotted Woodpecker Dendrocopos minor, Spotted Flycatcher Muscicapa striata, Tree Pipit Anthus trivialis, Willow Tit Poecile montanus, Willow Warbler Phylloscopus trochilus and Wood Warbler P. sibilatrix. Eleven species showed large national increases (> 25%) in both data sets: Blackcap Sylvia atricapilla, Blue Tit Cyanistes caeruleus, Common Chiffchaff Phylloscopus collybita, Coal Tit Periparus ater, Great Spotted Woodpecker Dendrocopos major, Great Tit Parus major, Green Woodpecker Picus viridis, Goldcrest Regulus regulus, European Robin Erithacus rubecula, Eurasian Treecreeper Certhia familaris and Winter Wren Troglodytes troglodytes. Analysis of the longer-term changes using the BTO data set showed significant declines between the 1960s and 2003-04 in seven species and increases in 12 species. The large declines detected by the national monitoring schemes (CBC/BBS) for Lesser Spotted Woodpecker, Lesser Redpoll, Spotted Flycatcher, Tree Pipit, Willow Tit, Willow Warbler and Wood Warbler were all confirmed by the RWBS but the declines of the Common Bullfinch Pyrrhula pyrrhula, Marsh Tit Poecile palustris and Mistle Thrush Turdus viscivorus were not clearly supported. The declines detected by the RWBS for Garden Warbler, Pied Flycatcher Ficedula hypoleuca and Common Redstart Phoenicurus phoenicurus were not evident from the national monitoring schemes. Most of the increases detected by the monitoring schemes were confirmed by the RWBS. However, the large increases detected by the RWBS for Coal Tit, Goldcrest, Great Tit and Eurasian Treecreeper were unexpected. All long-distance migrants have declined whilst medium-distance migrants (Blackcap and Common Chiffchaff) have increased. Also, rare and specialist woodland species have fared less well than common and generalist species.