Sexual differences in reproductive effort: time-activity budgets of monogamous killdeer, Charadrius vociferus

Abstract

By measuring the time allocated to various reproductive and somatic activities it was possible to look at differences in the strategies of the sexes for killdeer, a monogamous species. Killdeer time-activity budgets supported the general hypothesis that males and females maximize fitness in different ways. Males allocated more time than females to mating activities: mate attraction and territorial defence. However, the parental roles of the sexes were not those predicted for a monogamous species; males allocated more time than females to parental activities throughout a nesting attempt. Males appeared to be less time-constrained, and better able to perform parental activities. Females allocated more time to foraging than did males. It is suggested that the amount of time females allocated to parental activities is limited by the high energy demands of egg production. Further, high nest-failure rates may select for females maintaining good condition for re-nesting. The costs of desertion for killdeer were considerable. Adult removal experiments supported the hypothesis that two parents were necessary for successful reproduction. No individuals managed to raise offspring alone successfully. Lone males, however, were able to hatch chicks while females were not. The need for continuous parental attentiveness may results in selection for biparental care for killdeer.