Effect of water level fluctuations on wading bird foraging habitat use at an irrigation reservoir, Lake Kerkini, Greece

Lake Kerkini, a Ramsar site in Macedonia, Greece, is an irrigation reservoir with water level fluctuations exceeding 5 m annually. We determined the effect of water level fluctuations on the area of available Ciconiiformes' foraging habitat at low, intermediate and high lake stages. Log-linear analysis assessed the changes in the patterns of foraging habitat use by Great Egrets, Little Egrets and Grey Herons in response to the interactions of foraging habitat type and lake stage. At low lake stage Ciconiiformes mainly foraged in non-vegetated habitats or in lacustrine and palustrine habitats with submerged vegetation, while at intermediate lake stages they used palustrine habitats with emergent or submerged vegetation. At high lake stage birds shifted to riverine habitats that constituted the main available foraging grounds. The coexistence of three wetland systems enhances habitat heterogeneity at Lake Kerkini and enables large heron populations to thrive, despite the relatively small foraging area compared to other Mediterranean wetlands. Only Great Egrets seem to face constraints related to the limited availability of marshes - habitats linked to the species feeding and nesting requirements - during the breeding period.