Sexe et âge ratios chez le canard siffleur Anas penelope L. en période hivernale en Europe de l'Ouest

Abstract

Data on the sex- and age-ratios of Wigeon were collected over five years. In the Camargue, data from three winters show that adult males arrived earlier than other birds ; that immature males passed through the delta in autumn and spring ; and that the sex-ratio remained remarkably stable (1.5 males per female). Short term observations over two winters covering western Europe (Spain-Holland, and Morocco-Holland) provided evidence for spatial segregation of the main sex- and age-classes. Adult males tended to remain further north in the wintering area, with immature males and the females further south. This difference in distribution was more pronounced between age-classes than between the sexes. It is suggested that aggression, through social hierarchies, may be one factor which causes these differences in distribution. Males dominate the Wigean population numerically even in the south of the wintering area. It is suggested that this unequal distribution of the ages and sexes, whatever its cause, may have important consequences for the species'demography2014-12-19T14:26:53