The effects of the 1989/1990 drought on the colonial waterbirds nesting at Lake Mikri Prespa, Greece, with special emphasis on pelicans

From 1986 to 1991, four heron species and Pygmy Cormorants (Phalacrocorax pygmeus) which form mixed-species bleeding colonies shifted their colony site in relation to wet and dry conditions. The total number of nesters was probably lower than in other years. Cormorants moved to a new nesting site, the number of nesters remaining within observed fluctuations. Egg laying was not delayed. Some early nests of pelicans (Dalmatian, Pelecanus crispus, and Great White, P. onocrotalus) at traditional sites were destroyed by predators due to connection with land. Both pelican species delayed egg laying and finally nested on artificial islands not available in normal years. The number of nesting attempts was high for Dalmatian and low for Great White Pelicans. The inverse was observed for bleeding success.