Vegetation Structure and Invertebrate Food Availability for Birds in Intensively Used Arable Fields: Evaluation of Three Widespread Crops

Arable land covers a large part of the European landscape, and its biodiversity is declining rapidly due to agricultural intensification. Among the most threatened groups of organisms are insectivorous ground-foraging farmland birds. To reverse their decline, it is necessary to understand the impact of agriculture on the factors potentially shaping their populations. This study therefore evaluates the invertebrate food availability and vegetation structure of three widespread crops-wheat, maize and rapeseed-during their breeding. This research took place in Slovakia, the country with the largest average field size in the EU. Wheat overlapped bird habitat preferences for the longest part of their breeding season by vegetation structure, but it also had the most limited food supply due to frequent treatment with insecticides. Maize and rapeseed provided higher invertebrate abundance and biomass, but their stands created unsuitable vegetation structures for farmland bird nesting and foraging over a major part of the breeding season. The food supply improved closer to the field edges, but the birds' ability to use these benefits could be considerably limited by the large field sizes. Therefore, conservation measures should include reduction of field size and insecticide application to improve the food supply and switch to spring sowing to improve the vegetation structure.