The breeding season is of paramount importance to the population size of waterfowl. All of the increase in population size occurs, as does much of the mortality during that season, which is often but a fraction of the entire year. Population of a species is indicative of the environmental factors of that area which strictly influences the species. The study includes the population size of the Cotton Pygmy-goose Nettapus coromandelianus Gmelin, a least concern anatid of South-east Asia and near relatives of Pygmy-goose of New South Wales which is under threatened condition. The study also includes the parameters influencing the population sizes. Two hundred and three (203) Cotton Pygmy-geese were observed during breeding season in 2006 and 2009 in study sites of Assam. Adult survival rates were found high 0.99 to 0.94 (SE < 0.005), but duckling survival was much lower, varying from approximately 0.1 to 0.3 during 2007 to 2009. No naturally died specimens have been collected during the study period, but 7 specimens have been reported to be killed by hunters among a total of 22 gooses were killed during 2006 to 2008. The present paper deals with the population dynamics of Cotton Pygmy-goose with special mention of the factors affecting their survival.
Key words: Breeding, environmental, mortality, population, waterfowl.
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