Variations in nest-site parameters were studied at Lake Zarivar, Kurdistan Province, Western Iran in 2007 and 2008. This study was applied for six breeding waterbird species: Great-crested Grebe (Podiceps cristatus), Little Grebe (Tachybaptus ruficollis), Moorhen (Gallinula chloropus), Coot (Fulica atra), Water Rail (Rallus aquaticus) and Whiskered Tern (Chlidonias hybrida). A total of 205 nest-sites were studied in terms of five environmental factors: vegetation density and height, water depth, distance to open water, as well as distance to the nearest nest of the conspecific species were measured. Great-crested Grebes selected areas of deeper waters, possibly to increase feeding efficiency. All species were directly dependent on water for nesting, except for the Water Rail, which established its nest in muddy areas with higher vegetation density and height. Nests were at a higher density for the Whiskered Terns than in other species. Overall, mean water depth at nesting sites was lower in the 2008 breeding season and total breeding population of waterbirds decreased. Evaluating and monitoring of habitat quality of breeding species urges conservation measures with regard to transformations occurring at this freshwater lake ecosystem.
