Survival Explains Sex Ratio in an Introduced Mandarin DuckAix galericulataPopulation

Abstract

Adult sex ratio in ducks is male-biased, probably due to higher mortality of incubating females. In an introduced population of Mandarin Ducks Aix galericulata in Berlin and Potsdam, adult sex ratio (proportion of males) was 0.65 (95% confidence interval 0.64–0.67). Annual apparent survival of 163 colour-ringed birds during 2003–2012 was 0.65 (0.55–0.76) for first year and 0.66 (0.60–0.72) for adult males, and 0.47 (0.25–0.69) for first year and 0.57 (0.48–0.66) for adult females. Female mortality but not male mortality peaked during the breeding season. A Leslie matrix model based on productivity and survival rates in the study population estimated an adult sex ratio of 0.64, or 0.67 when first-year birds were excluded. The similarity between observed adult sex ratio and model estimates based on survival suggests that the male-bias might be fully explained by sex differences in survival.