Grassland breeding waders have been steadily declining across Europe. Recent studies indicating a dramatic decline in grassland invertebrates' abundance and biomass, the key food of most grassland wader chicks, suggest a likely driver of the demise of waders. While agricultural intensification is generally inferred as the main cause for arthropod decline, there is surprisingly little information on the relationship between land use intensity and total arthropod abundance in grasslands. Here, we explored those relationships across several key wader breeding habitats by surveying ground-active, aerial and soil-dwelling invertebrate communities in five European countries that range from natural undisturbed bogs to intensively managed grasslands. Using maximum vegetation growth and soil moisture content, we investigated how they shape the size of the invertebrate community within and across different countries. We found predominantly positive relationships between grassland invertebrate abundance, biomass and body weight with increasing vegetation growth and soil moisture. Maximum vegetation growth was strongly positively related to ground-active invertebrate abundance and biomass and abundance of soil-dwelling invertebrates (mainly earthworms). Body weight of aerial invertebrates furthermore increased with increasing maximum vegetation growth. Our results provide little support for the hypothesis that agricultural practices associated with intensification of grassland management result in an abundance decline of invertebrate prey for wader chicks. Conservation practices aiming to enhance wader chick survival require a careful balancing act between maintaining habitat productivity to secure high prey abundance and keeping productivity low enough to maintain open swards that do not need to be cut before chicks have fledged.

Data was collected in 64 sites in five countries across mainland Europe: France, the Netherlands, Poland, Estonia and Finland. To standardize habitat types and to make sure that results would be relevant for wader conservation, all sites had been hosting breeding waders (particularly the near-threatened black-tailed godwit) in the years before sampling, as indicated by local experts. Eighty-one percent of the sites hosted black-tailed godwit territories in the year we surveyed these sites; all contained at least one territory of a wader species, and breeding densities varied substantially. We aimed to include sites that varied as much as possible in land-use intensity both within countries and between countries, and sampled bogs and fens (natural habitats with no agricultural use), coastal and floodplain grasslands (semi-natural habitats that are grazed or mown but do not receive any inputs) and improved grasslands varying in management intensity (none to high fertilizer input). In each site, we surveyed aerial, ground-active and soil-dwelling invertebrates, sampled vegetation biomass and measured soil moisture content at twelve-day intervals throughout the local wader breeding season.