The effects of farming intensification on an iconic grassland bird species, or why mountain refuges no longer work for farmland biodiversity

Agricultural intensification is threatening ecosystems and causing the collapse of farmland birds. Biodiversity-rich, semi-natural grasslands dramatically decreased in recent decades and were either intensified, replaced by more remunerative crops or abandoned. We investigated the factors driving habitat selection by corncrake Crex crex, a flagship species for grassland conservation, in Trentino (Italy, European Alps), considering topography, public payments through Rural Development Programme (RDP), agro-botanic grassland types and farming intensification, during 2010–2018. Topographical variables were the most important predictors, but a synthetic model combining different predictors was even more supported. Elevation (negatively) and solar radiation (positively) affected occurrence; untargeted subsidies for grassland mowing had a negative effect, whereas specific subsidies for the management of Natura 2000 grasslands had a positive effect. Stocking density (livestock units/ha), taken as a direct measure of intensification, had a negative impact on occurrence. Corncrakes preferred unfertilized grasslands, then species-rich grasslands with little fertilization; mountainside and, especially, valley-floor grasslands were under-selected. Corncrake has progressively disappeared from Trentino's valley-floors, ‘shifting’ to mountain areas, but the effects of topography remind it is a lowland species pushed towards uplands by farming intensification, which is now affecting also the ‘mountain refugia’. Grassland types are selected by the species according to a gradient from unmanaged to heavily managed; subsidized mowing and livestock units/ha, a proxy for the amount of fertilizers and timing/frequency of mowing, had negative impacts. The conservation of the Alpine corncrake population and associated biodiversity critically depends on the maintenance of low-intensity farming on a relevant portion of cultivated grasslands. The reduction of fertilization, the adaptation of mowing regimes (to avoid early mowing, close subsequent cuts and homogeneous cutting over large areas), and the broader adoption of biodiversity-targeted payment schemes are urgently required. Grasslands at relatively moderate elevation and sun-exposed are particularly important: lowering management intensity there is crucial for conservation.