Effects of grassland management on ground beetle (Coleoptera: Carabidae) assemblages and availability as prey for farmland birds

• Intensively managed grasslands had a higher ground beetle abundance, primarily due to a few dominant species sized >12mm. • Extensively managed AES grasslands provided a greater abundance and mean species-richness of diurnal ground beetles, particularly in the 4-12 mm size range. • Extensively managed AES grasslands support a more diverse ground beetle assemblage, with a higher abundance of ground beetles within the optimal prey size range (4-12 mm) and activity period for many farmland birds and their chicks. Ground beetles (Coleoptera: Carabidae) are an abundant surface-active arthropod family in agricultural systems, serving as an important food source for several insectivorous farmland birds in the breeding season. This study compares ground beetle assemblages, from the perspective as food source for farmland birds, in intensively managed (IM) and extensively managed (EM) grasslands. Ground beetles were sampled over two years (2017, 2019) using pitfall traps in ten intensively managed and ten extensively managed grasslands across five farms in the clay-peat district of Friesland, the Netherlands. We investigated the effect of management type on ground beetle assemblages and examined differences in species traits body length (<4mm; 4-8mm; 8-12mm and >12mm) and diel activity (nocturnal, diurnal). Ground beetle numbers were higher in IM fields, but there were pronounced differences between IM and EM grasslands regarding body size and diel activity. Diurnal ground beetles sized 4-12 mm were more abundant and species-rich in EM fields, while large nocturnal ground beetles (>12mm) were more numerous in IM grasslands. IM grasslands were dominated by a few large-bodied species (e.g. Pterostichus melanarius ) , whereas EM grasslands supported a more diverse community. We conclude that extensively managed AES grasslands support a more diverse ground beetle assemblage, with a higher abundance of ground beetles within the optimal prey size range (4-12 mm) and activity period for most farmland birds. This potentially improves ground beetle availability as prey item for farmland birds during the breeding season. Our study provides empirical support for policies such as AES that provide financial incentives biodiversity-friendly extensive farmland management.