Sex Roles in the American Oystercatcher

Abstract

AbstractAmerican oystercatchers have extensive parental care. As a result sex roles are similar and highly complementary. During the pre-laying period the roles of males and females, except during copulation, are indistinguishable. During the laying period the roles diverge slightly with males spending more time chasing conspecifics. Presumably the similarity during pre-laying, and the differences during laying, function to prevent the male from being cuckolded. Males begin assisting in incubation as soon as the females begin incubating and then consistently perform the same proportion of incubation throughout this breeding stage. During incubation, females incubate more often than males, and consequently rest less, preen less and fly less than males. During chick-rearing males are involved in more chases than females and take more foraging trips to provision young but wait longer between successive trips. The pattern of foraging by each sex is complementary. Breeding season energy expenditure is approximately equal in both sexes. There is no evidence for conflict between the sexes over the contributions to parental care. Where sex roles diverge the differences in behaviour can be partly explained by the relative energetic efficiencies of each sex performing different tasks.