Reed cutting affects arthropod communities, potentially reducing food for passerine birds

Winter cutting of Common Reed Phragmites australis (Poaceae) is increasing in Camargue, southern France, potentially affecting wetlands of high conservation value. We studied its impact on arthropods by comparing four cut and uncut sites with special respect to avian prey availability in the breeding season. The two most important prey groups for breeding passerines, spiders (Araneida) and beetles (Coleoptera), were identified to species in trap catches and diet samples. The arthropod assemblages differed significantly between cut and uncut sites. Phytophagous and saprophagous species showed contrasting responses. Numbers of homopterans increased in cut reed beds, where green Phragmites stem density was higher. Saprophagous woodlice decreased, presumably due to the reduced amount of litter. Densities of some vegetation-dwelling spider and beetle species were lower at cut sites, including two of the most preferred prey species for passerine birds. Consequently, large-scale mechanically harvested reed beds host altered arthropod communities, missing major food components used by vulnerable passerines. However, reed cutting on a small scale may increase habitat heterogeneity and species richness on a landscape level. To contribute to reed bed conservation, EU schemes should reward management that leaves uncut reed patches in the proximity of cut areas to permit their recolonization by arthropods.