Data from: The importance of size, location and vegetation composition of perennial fallows for farmland birds

Across Europe, patches of un-cropped land (field margins, fallows etc.) have been established and managed as part of agri-environment schemes (AES) to counteract the decrease of farmland biodiversity. Various studies demonstrate a positive impact of such un-cropped land on different taxa. However, there is potential to further improve the efficiency of fallow options for farmland birds. In a long-term monitoring, 12 breeding farmland bird species and sizes of perennial fallows were recorded from 1992 to 2015 in a 6.1 km2 area in Switzerland. Furthermore, habitat composition and fallow characteristics were mapped in 2012. We calculated population trends, analysed habitat associations and revealed the impact of fallow habitat characteristics on territory density. The proportion of fallows in the study site increased from 1.4 % (1992) to 8.5 % (2012). Population trends of six out of 12 censused species increased significantly over the same time, four species showed no trend and trends of two species decreased. Seven species were analysed in more detail, for five of them fallows were overrepresented around their territory centre-points compared to arable fields and grassland. The overall territory density of these five species was higher in small fallows which were not placed next to a wood and which held bramble rubus spp., shrubs and the tall-growing forb goldenrod (Solidago canadensis and S. gigantea). Our study confirms that perennial fallows are a highly suitable option to support different farmland birds in arable landscapes. Yet, we recommend optimising fallows through careful site selection and management, such that they are not established on shady locations and are structurally diverse by allowing brambles, shrubs and tall-growing forbs to occur. We suggest adapting the Swiss AES in this regard. Biodiversity-related advisory services available for farmers could increase the probability that fallow options are implemented and managed properly for targeted species.territory numbers of priority farmland birds in champagne genevoiseTerritory numbers of 12 farmland bird species of conservation concern in Switzerland, collected in the field in the study site in the champagne genevoise between 1992 and 2015.territory_numbers_priority_farmland_birds_genevoise.csvhabitat within pseudoterritories of priority farmland birds in 2012Amount (square meter) of each land-use type in the pseudoterritories of seven farmland bird species of conservation concern in the Study site in 2012. Pseudoterritories were established with ArcGIS, laying a buffer with radius 50m around each territory centre-point.habitat_pseudoterritories_genevoise2012.zipfallow characteristics and territory numbers in champagne genevoise 2012Characterisitcs (vegetation composition, size, age, distance to wood) of fallows in 2012 and territory numbers of six farmland bird species of conservation concern in each fallow. Vegetation data was mapped in the field, distances and areas were calculated in ArcGIS.data_fallow_characteristics_and_territory_numbers_genevoise2012.cs