Key Habitat Factors of Breeding Birds in Agricultural Hedgerow Landscapes in East-Fryslân, the Netherlands, in European Perspective – Ecological Evaluation and Relation to Agri-Environmental Schemes

Modern agricultural landscapes suffer heavily from biodiversity loss. To counter this loss, it is important to understand the key factors that affect biodiversity in these landscapes. We studied the relationships between breeding birds and the habitat characteristics of the small-scale hedgerow landscapes of East-Fryslân, The Netherlands, a typical agricultural landscape that is under pressure from upscaling and habitat degradation. We questioned whether our findings collaborate the results of hedgerow studies from other countries. We also analysed whether agri-environmental schemes were effective for breeding birds. In this study, breeding birds and fifteen habitat factors were surveyed along 170 transects in two different regions in East-Fryslân in 2018. 37 bird species were identified, of which 19 were woodland species, 18 shrub species and 7 hedgerow specialists. We found five habitat characteristics to be key factors for breeding bird numbers. Four of these factors were intrinsic factors of the hedges (i.e. shrub cover, cover of brambles and nettles, crown width, hedge width at the base) and one spatial factor (i.e. number of hedge corners within a 150-m radius, corresponding to hedge intersections). Four key factors were the same for the two regions, but effect sizes differed between factors and species groups. As proxies for habitat volume (amount of habitat), the intrinsic key factors for hedgerow breeding birds in East-Fryslân correspond to those found in Britain and Eastern Europe, despite considerable differences in botanical composition, structure and management of the hedges. In contrast to studies on British hedges, we found mainly quantitative key factors and only one qualitative factor (cover of brambles and nettles). We found one spatial key factor (hedge intersections) and no correlation of bird numbers with density of hedges in the vicinity. We discuss the ecology of the key factors with respect to food provisioning and breeding. We also conclude that agri-environmental schemes favour key habitat factors and through this shrub birds. Implications of our findings are that traditional management favours breeding birds, but also that management should partly be extensified.