Habitat analysis from infra-red aerial photographs and the conservation of birds in Swedish agricultural landscapes

The populations of many farmland birds have declined with the modernization of agriculture, particularly specialization in a few arable crops which often require the removal of the habitats associated with traditional farming and the remnants of seminatural habitats. It is difficult to identify habitats and map all birds in large areas and consequently most studies have been constrained to small areas (≤ 100 ha) that fail to include all the rural habitats or the rare species that are of interest to conservationists. We describe a new technique in which by considering only indicator or rare species we were able to study two much larger areas ($22\ {\rm km}^{2}$) in central Sweden, and could identify their habitats by interpreting infrared aerial photographs. We compare a small-scaled and varied rural landscape, of the traditional type, with a modern large-scale landscape, and show that features of the traditional landscape (meadows, scrubland and deciduous woodland) support higher bird diversity and densities than modern landscape features (coniferous plantations and clear-cuts). Combining large-scale mapping and habitat analysis thus enables us to quantitatively define which habitat components are the most important for supporting a high diversity of birds and hence are of the greatest conservation interest. Furthermore, habitat analysis from infrared aerial photographs might be used as a means of predicting the densities of birds and hence the conservation value of areas that have not been censused.