National agri-environment schemes (AESs) aim to promote sustainable farming and protect farmland biodiversity. For efficient maintenance of biodiversity, it is essential to understand the habitat requirements of fauna, and its responses to farming practices. This study examined the importance of different habitat characteristics and habitat heterogeneity for farmland birds in boreal agricultural landscapes, focusing on species in open arable habitats (true field species) and bushy field-edge habitats. Density, species richness, and species composition were studied in a multivariate space, and along environmental gradients. The relevance of the biodiversity-related measures of the Finnish AES regarding the habitat needs of farmland birds was examined. Non-cropped habitat heterogeneity (especially open ditches and habitat patch richness) increased the density and species richness. Crop diversity increased the species richness of true field species. Ordinations revealed a gradient from large open arable to small field areas, and a relation to habitat heterogeneity. The AES places insufficient emphasis on biodiversity issues.