Parental roles and mating system in the black-winged stilt

Abstract

The breeding behaviour of black-winged stilts (Himantopus himantopus) was studied in southwestern Spain. In the prelaying period males devoted more time than females to agonistic encounters, locomotion, and nest building. During egg laying, males spent more time than females at the nest, mostly building the nest and covering the eggs, while females spent more time foraging than males. During late incubation, females spent significantly more time at the nest than males. These results suggest very similar parental investment by the sexes. During part of the female's fertile period, males stayed at the nest while females were foraging, which precluded efficient mate guarding. However, females were reluctant to engage in extra-pair copulations, being always very aggressive towards conspecifics except for their mates. Even in two cases of extra-pair copulation, the first described for this species, the female continuously attacked the intrusive male and did not cooperate in copulation. Male parental care seems to be essential for reproductive success and females are probably faithful in order to assure male parental investment. The need for parental care from both males and females would maintain social, and perhaps also genetic, monogamy in this species.