Sex Ratio and Survival of Mandarin Ducks in the Tachia River of Central Taiwan

Sound management of the Mandarin Duck (Aix galericulata) requires an understanding of its survival and cause-specific mortality, yet these parameters have not been studied in Taiwan. From January 1999 to December 2002, a study was conducted along the Tachia River, in central Taiwan, where the largest population of Mandarin ducks resides. The sex ratio was male-biased for adults (average 2.10:1) but not for juveniles (average 0.92:1). Ducks (34 males and 42 females) were radio-tagged and monitored two to three times per month for 1-47 months. Annual survivorship was 0.80 and 0.44 for male and female ducks, respectively; lower female survival may lead to a male-biased sex ratio. Forty-three ducks died, the greatest proportion from unknown causes, followed by avian predators, mammalian predators and anthropogenic activity. Mortality occurred year-round, but female mortality was greatest from spring to fall, 9-10 carcasses, while male mortality (seven) was greatest in the winter. Received 20 May 2011, accepted 26 September 2011.