Effects of grazer density, season and land cover on bird guilds in a restored conservation area

Abstract

Abstract Context Grazing by large herbivores is an increasingly used management tool in European nature reserves. A challenge in grassland conservation is to maintain both the openness and the heterogeneity of the habitat, to support their animal communities, including birds. Horses and cattle are often used to create and maintain patchy landscapes, especially in rewilding projects, but the influence of grazers on birds is often debated by conservationists. Objectives We studied how the abundance and species richness of birds of four foraging guilds are related to the area use of Highland cattle and Konik horses in an alluvial grassland. We also investigated how season and land cover influences the spatial distribution of individuals and species of different bird guilds on the grazed area. Methods We equipped all grazers with GPS-collars to assess the density of their hourly positions. We made weekly transect counts of birds to describe their distribution and carried out land cover surveys to describe the habitat. We used GAMM models in a spatially explicit framework. Results Open-area foraging birds were clearly associated with higher grazer densities, and aerial, wetland and woodland birds also seemed to profit from low-intensity year-round grazing. Most bird species and individuals were observed on open landscapes scattered with woody patches and waterbodies, and on areas with moderate grazer density. The number of birds on the grazed area was about twice the number on the ungrazed control area. Conclusions A heterogenous landscape maintained by low-intensity grazing seems to fulfil the needs of birds with different feeding ecologies.