Distributions of birds in lowland agricultural landscapes of England andWales: How distinctive are bird communities of hedgerows and woodland?

摘要

Within agricultural landscapes many species of birds depend on hedgerows and woodland, but few studies have examined their relative importance as habitats for breeding birds. Breeding bird communities in hedgerows and woodland in lowland England and Wales were compared in terms of species richness and similarity of species composition. The preference of individual species for hedgerows and woodland was also assessed. The data were drawn from 33 farmland and 35 woodland Common Birds Census plots for 3 years: 1990, 1993 and 1996. Woodland plots were significantly richer in species than farmland plots. Species number on farmland plots increased linearly with the cover of farm woodland and non-linearly with density of total hedgerow. Species number increased with density of non-roadside hedgerows, but not with density of roadside hedgerows. Although the farmland and woodland plots supported distinctive bird communities, there was considerable overlap between them in species composition. The similarity between the species composition on individual farms and that theoretically possible for woodland increased significantly with the cover of farm woodland, hedgerow density and the total amount of woody habitat present within the farmland plot. Canonical correspondence analysis and preference indices indicated that seven species could be regarded as hedgerow specialists: Dunnock Prunella modularis. Whitethroat Sylvia communis, Lesser Whitethroat S. curruca, Linnet Carduelis cannabina, Goldfinch C. carduelis, Greenfinch C. chloris and Yellowhammer Emberiza citrinella. Species showing clear preferences for woodland were: Tawny Owl Strix aluco, Marsh Tit Parus palustris, Coal Tit P. ater, Goldcrest Regulus regulus, Spotted Flycatcher Muscicapa striata. Treecreeper Certhia familiaris, Nuthatch Sitta europaea, Great Spotted Woodpecker Dendrocopos major, Chiffchaff Phylloscopus collybita and Blackcap Sylvia atricapilla. The habitat needs of the hedgerow specialists show considerable variation and do not always coincide with the hedgerow structures that support the greatest numbers of bird species and highest densities of birds. Management strategies that maintain a diversity of hedgerow structures are, therefore, desirable. Hedgerow and woodland bird communities are essentially complementary and habitat creation initiatives in lowland agricultural landscapes should not be excessively weighted towards one habitat or the other.