Reproductive Success and Daily Survival Rate in Great Cormorant Phalacrocorax carbo at Ramsar Colony, North Iran

Great Cormorants are dependent on marine and freshwater wetlands, and are top-predators in the ecological food-web and are thus particularly exposed to habitat loss, pollution and other human activities affecting such habitats. Reproductive performance in Great Cormorant was studied during the 2003 breeding season (early March-late July) at Ramsar colony. Factors influencing breeding success were taken in study. Mayfield and Maximum Likelihood methods were used to estimate nest survival during incubation stage and nestling stages. Mean brood size was 3.03 and early-breeder pairs had significantly larger broods. A positive relationship found between nest size and both brood size and number of chicks fledged. Breeding success was 2.88 per nesting attempts (80% of initial eggs).The difference in reproductive success between early and late breeders was not significant. There were higher Daily Survival Rate in later stages of chick rearing than the incubation stage and main losses occurred in incubation stage. Results suggest that Ramsar colony site provide more favorable situation for breeding Great Cormorants´ than other studied colonies.