Foraging habitat availability and diet composition of the Grey Heron (Ardea cinerea) at two spatial scales

Habitat composition on foraging ground is one of the crucial factors determining diet diversity in colonially breeding avian predators. Studies on habitat and diet composition at different spatial scales (regional and local inter-colonial) may help to better understand drivers of diet composition. In this study we reconstructed from pellets diet composition of an opportunistic predator, the Grey Heron ( Ardea cinerea ) and compared it among 21 colonies in two different regions of Poland differing in foraging habitat presence/absence and composition. We used multivariate statistical techniques to analyze the relationship between diet and habitat compositions in a 20 km radius around the studied colonies. We found significant inter-regional and inter-colony differences in the Grey Heron diet and habitat composition in foraging areas. We found that some taxa were present in diet only in one of the studied regions. The heronries with predominance of farmland habitats in the vicinity were characterized by low frequency of the European water vole ( Arvicola amphibius ) and terrestrial invertebrates and high contribution of the Field striped mouse ( Apodemus agrarius ). Voles ( Microtus sp.) were more frequent in colonies with prevalence of non-irrigated arable land around the colony, in contrast to the Bank vole ( Myodes glareolus ) which was less common in heronries with higher contribution of this habitat type. Remains of aquatic invertebrates were less abundant in colonies surrounded by extensive forests. Conducted study indicates opportunistic character of the diet of the Grey Heron adapted to the local foraging habitat and prey availability other than fish.