RESUMO
Breeding biology of the Great Cormorants Phalacrocorax carbo sinensis is assessed in the southern coasts of the Caspian Sea, Iran during the years 2008-2010. About 84 nests located on 63 trees were examined. Nests were built on large trees located in Abbas abad marsh, Gilan Province. Initially, eggs were found on first week of April and egg laying continued until the last week of May. Clutch size varied from 2 to 5 eggs, with a mean clutch size of 2.8 +/- 0.69. Mean shape index for all eggs were 1.68 +/- 0.035 and 1.706 +/- 0.048, respectively. The length of the incubation period was estimated at 26.6 +/- 2.2 days. in 2010 of the 84 eggs laid, 26.6% were lost. In 2009 of 92 eggs laid, 62% were lost. Number of eggs hatched per nest averaged at 1.57 +/- 0.57 in small ones and 1.8 +/- 1.6 in large nest. Mean weight of eggs was estimated at 46.8 +/- 1.28g [N=10, mean =48.9, min=45.2]