Spatial and temporal variation of habitat and prey utilization in the Great White Egret Ardea alba alba at Lake Neusiedl, Austria

Abstract

Capsule In eastern Austria, Great White Egrets used the extensive reed beds of Lake Neusiedl not only as nesting sites, but also as a major foraging area. Aims To investigate habitat and prey utilization in a growing population of Great White Egrets in different periods of the breeding season and in relation to the water level at the foraging sites. Methods During three breeding seasons, we quantified the utilization of feeding areas and prey by means of aerial surveys and observations on the ground. Results Fish of open water areas within the reed beds of Lake Neusiedl is the main type of prey during the breeding season. Variation in habitat utilization was higher within breeding seasons than among years. The number of foraging individuals in fish-dominated habitats increased linearly during the season, corresponding to decreasing water levels. The utilization of amphibian-dominated habitats showed two peaks related to the spawning period and larval development of prey items. Conclusion The availability of fish within the reed beds of Lake Neusiedl is crucial for the largest population of Great White Egrets in western and middle Europe. The recent increase of this population is probably, in part, caused by an increase of fish availability due to local habitat changes.