Variability of clutch size in Cormorant (Phalacrocorax carbo sinensis) at the Jeziorsko Reservoir (Central Poland) in 2004

The analysis of the clutch size variability in Cormorant (P. carbo sinensis) was based on study results in colony at the “Jeziorsko Reservoir” (central Poland) in 2004. There were used 328 broods controlled 3-5 times in the season. Number of eggs in a single clutch ranged from 1 to 7, although Cormorants mostly laid 3 to 5 eggs. Mean clutch size was 3.80 (SD = 1.0 0). The size of clutch depended on time of laying eggs and the part of colony where the nest with brood was localised. The clutch size was bigger for pairs that started laying eggs earlier and lower for birds bred in the part of colony where the number of nests and their density were low.