Agricultural land-use and the spatial distribution of granivorous lowland farmland birds

Current agricultural practices are believed to have contributed to the decl ines of many farmland bird species. especially seed-eaters, throughout Euro pe. We investigated associations between the spatial distribution of fourte en granivorous farmland bird species and agricultural land-use in Britain, using breeding bird atlas data and national agricultural statistics. Analys es were spatially-referenced by 10 x 10 km square and variation due to broa d-scale geography and spatial auto-correlation was controlled for. Generali zed linear modelling analyses were used to select models describing variati on in distribution explained by the available land-use variables. The resul ts show that relationships between distribution and agriculture tend to be species-specific. but that some general effects can be identified. Features of intensive arable farming including large areas of sugar beet, wheat and oilseed rape tended to be associated with low frequencies of occurrence fo r 9-11 species, while large areas of younger (re-seeded) grassland and high sheep stocking densities were associated with low frequencies in pastoral farmland for up to 12 species. One key feature of lower intensity farming, the presence of larger areas of fallow land, was positively related to freq uency index for up to 11 species. The proportion of barley sown in spring a nd agricultural diversity were each associated with a range of complex rela tionships with frequency index across species, probably reflecting combinat ions of positive influences and artefacts of scale and geography. A variabl e describing the heterogeneity of farmland (the extent to which it is a mix of arable and pastoral land-use) was negatively related to frequency index for eight species, but other results suggested that farming which is mixed at a smaller spatial scale is widely beneficial. The results reveal relati onships between agriculture and the occurrence of granivorous farmland bird species which suggest both hypotheses for the causes of population change and directions for management action. However, data on several key features of agricultural practice (such as pesticide use) were unavailable, so thei r effects could not be tested, and the effects of the variables included co uld not be separated from those of other factors which are subject to compl ex geographical variation. Experimental comparisons of the effects of land- use at the farm scale are needed to investigate such confounded influences on farmland bird occurrence.