Spatial and temporal variation in farmland bird nesting ecology: Implications for effective Corn Bunting Emberiza calandra conservation

Farmland bird populations continue to decline despite intense conservation efforts, possibly also because of incomplete knowledge on the drivers of local productivity. We therefore investigated spatial and temporal variation in nest site selection, breeding phenology, and nest survival for 225 nests of the Corn Bunting, a species of conservation concern in Central and Western Europe, in cropland-dominated, mixed, and grassland-dominated landscapes in SW Central Europe. Nesting phenology spread from April to August, started earlier at lower altitudes and progressed from grassland habitats to arable crops and eco-scheme flower fields. Most nests were placed in cultivated land, with substantial variation between landscape types but also between years within sites, so that large fractions of breeding attempts are prone to fail through land use operations in particular years. When nests were individually protected from land use, 'apparent' and 'Mayfield' survival rates differed substantially between nest habitats, with lowest survival in 2nd year flower fields and highest survival in fallow grassland. Accounting for land use survival from patch-specific mowing, harvesting, and grazing dates, 'total Mayfield nest survival' estimates dropped by about half to 21 %, 13 %, and 20 % for (hay) meadows, alfalfa / clover-grass leys, and pastures, respectively, which held about 2/3 of nests in mixed landscapes. To enhance productivity beyond the thresholds required for local population persistence, we propose refined conservation schemes that improve survival within production farmland, best coupled with the development of prolific 'Corn Bunting Landscapes'.