Sexually Different Parental Inputs in Pheasant-tailed Jacanas and the Correlates with Brood Success

Parental care and territoriality are crucial components for the success of avian reproduction. Biparental care with female-biased efforts prevails in avian species, whereas breeding territories in most birds are male- or bisexual-defended. In social-polyandrous birds, however, females trade parental care for mating through sex-role reversal. On the other hand, managing multiple broods or mating events exposes females to physiological/environmental constraints of energetic-nutritional demands, which in turn may result in variations in egg mass and subsequent egg fates. This study assessed sexual differences in parental efforts, including territoriality, time allocation of parental behaviors, and egg-laying (reflected by egg mass) in sex-role-reversed pheasant-tailed jacanas, Hydrophasianus chirurgus, and their relationships with brood success. Females monopolized small ponds but shared larger ones with female neighbors by holding larger territories. In contrast, male territories were within those of their mates, the size was not affected by the presence of male neighbors, and was associated with the total hatchlings and fledglings obtained through multiple clutches. The time allocated in parental behaviors differed between the sexes and across the pre-laying, incubation, and post-hatching stages. The breeding duration, territory size, female breeding order, and male mating order, however, had no effects on parental time allocation. While male time spent chick-attending was positively correlated with brood success, preening negatively correlated with the fledging rate, other behaviors had no effects on reproductive outputs. The egg mass varied slightly, but showed no effect of year, nor the season of laying date until late August. The fourth egg in a clutch was lighter and, among clutches, the egg mass tended to be greater in later clutches and clutches from polyandrous females. We found positive correlations between mean egg mass and the numbers of hatchlings and fledglings gained per clutch. Our results suggest a substantial pre-laying parental input through egg production in polyandrous females. Brood success, however, appears to be determined by the combined effects of multiple factors, including male devotion and environmental conditions.