Modelling the Relationship Between Bird Population Variables and Hedgerow, and Other Field Margin Attributes. II. Abundance of Individual Species and of Groups of Similar Species

Abstract

1. An earlier paper related bird species richness to hedgerows and other field boundary attributes including adjacent land use. The study was over several years (winter and summer) at two sites, Huntingdon and Swavesey, in East Anglia UK. 2. The present paper deals with similar relationships, but the bird variables used are the abundance of individual species, of groups of species (all finches, all raptors, etc.) and of all birds, as well as Simpson's index of diversity. This required extensive modelling - 105 models for Huntingdon and 174 for Swavesey. 3. The results of all 279 models are presented in a condensed form, highlighting the importance of given field boundary attributes to particular species or groups of species. 4. Like bird species richness in the earlier paper, the abundance of many species was strongly influenced by the land use, and by the main vegetation variables (tree height and number, hedgerow length, height and width). Land use was important to a larger majority of species, the exceptions being carrion crow, pheasant, reed bunting and wren. 5. Verge width appeared important for small insectivores (blue tit) and was particularly important for seed eating birds, e.g. most finches and buntings, red-legged partridge in summer, and carrion crow and skylark in winter. 6. Ditch dimensions were associated with the abundance of some seed eaters (linnet, reed bunting and goldfinch) and insectivores (blackbird, great tit, skylark, song thrush and wren). Kestrel and the groups raptors, corvids, waders and aquatics were associated with large ditches. 7. Though the general management prescriptions to benefit the majority of farmland birds were found to be similar to those in the earlier paper, the detailed species specific modelling made it possible to examine the habitat requirements of particular species. 8. Ecological evaluation of the results from the two studies are presented in a form considered to be of value for practical management. Bird species and groups of birds are categorised with respect to their likely requirements of particular attributes of the field boundaries.