The Sex Ratio of Orange-flanked Bush-robins (Aves: Passeriformes: Muscicapidae) from a Winter Population in Central China

ABSTRACTThe sex ratio of a population is an important demographic parameter, but compared with breeding populations, the sex ratios of avian winter populations have received relatively little attention. The orange-flanked bush-robin (Tarsiger cyanurus) is a migratory species whose plumage is sexually dimorphic with delayed plumage maturation wherein first-year males show female-like plumage. We investigated the sex ratio of an orange-flanked bush-robin population wintering in Dongzhai National Nature Reserve located in central China. The results show that most (> 85%) orange-flanked bush-robins of this population have female-like plumage, implying that the population sex ratio might be female-biased. However, genetic analysis revealed that most (c. 70%) individuals with female-like plumage were males, resulting in a significantly male-biased population sex ratio. Among the individuals with female-like plumage, the males were found to have significantly longer wings and tails than females, but the accuracy...