Male-biased Sex Ratio and Body Size of a Wintering Roost of Brambling, Fringilla montifringilla Linnaeus, 1758
Male-biased Sex Ratio and Body Size of a Wintering Roost of Brambling, Fringilla montifringilla Linnaeus, 1758
Liping Liu and Pengfei Liu*
ABSTRACT
Sex ratio and age composition are important parameters in population biology, related to life history and difference in mortality and behavior of male and female. Sexual dimorphism indicates divergence selective pressure between two sexes. We determined the sex and age through plumage coloration and measured 6 body measurements of each bird in 122 Brambling Fringilla montifringilla individuals in a wintering roost, which were captured randomly with mist nets. We found both the sex ratios of juveniles and adults were male-biased in this roost, which possible originated from different migrating strategies with sex and age. Culmen length, wing length and tail length of male is longer than female, male is heavier than female in body mass, these differences showed slight male-biased sexual size dimorphism, the larger body size of male may have resulted from sexual selection, while pressure of natural selection may not be significant as the males and females were observed almost always foraging together closely on same substrates in one flock during non-breeding season.
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