Predictors of farmland bird species richness in intensively used agricultural landscapes: habitat heterogeneity, crop type, and food supply matter

Abstract Context Biodiversity in agroecosystems has experienced significant declines in species richness due to intensive agricultural practices. Historically, diverse agricultural landscapes have been replaced by nutrient-rich monocultures. To improve the situation, it is important to find out what are the attributes of these landscapes that support the highest species richness. Objectives This study investigates the relationships of farmland bird species richness to field size, diversity of crop types and landscape elements (expressing different kinds of habitat heterogeneity), areas of winter and spring crops (i.e., crops sown in the autumn and in the spring, respectively), and invertebrate food availability. The research objective is to find out which of these factors are linked to the highest richness. Methods Bird species were surveyed using point counts during the breeding season at 52 sites of varying field sizes, landscape element composition, and crop types in open agricultural landscapes in northwestern Hungary, Europe. Food availability was expressed as invertebrate abundance, diversity, and biomass, respectively. Results Bird species richness increased with landscape element diversity and invertebrate abundance, while the field size showed opposing effects depending on crop type. Smaller field sizes were more beneficial in the case of winter crops, but larger fields supported more farmland bird species in the case of spring crops. The abundance of invertebrates was particularly high in alfalfa and fallow fields. Conclusions The value of open farmland for farmland bird species richness can be improved by enhancing diversity of landscape elements (e.g. by adding small water bodies to landscape mosaic), increasing invertebrate abundance (e.g. by reducing pesticide use), reducing the size of fields covered by winter crops and supporting the spring crops.