Food availability and offspring demand influence sex-specific patterns and repeatability of parental provisioning

Few studies have examined interactions between resource availability, life-history traits and sexual conflict on species-specific provisioning rates, and within-individual variation of parental care. To this end, we used 1129 nest observation periods from 118 nests across 4 populations to examine how parental nest visitation varied according to sex, food availability, and offspring need (brood size and age) in the stitchbird (hihi: Notiomystis cincta). Males increased their provisioning proportional to brood size regardless of food availability, whereas females did not increase provisioning to larger broods unless food supplemented. Male provisioning consistently followed the age-dependent energy requirements of the nestlings, whereas females showed little or no brood age–provisioning relationships. Thus, males were more sensitive than females to changes in the energy demands of their offspring; however, this was probably because females were already providing food at a high rate and could not respond to increased demand unless given additional food. Sex and habitat-specific repeatability estimates of parental effort suggest that variation in female provisioning behavior tends to be driven by differences in the local environment, whereas variation in male provisioning is more related to differences in individual quality. These sex-specific responses of parental care can be largely explained by the relative benefits of provisioning; females provisioned at a high rate to offspring they knew to be their own, based on available resources. In contrast, when food was abundant, males did not increase their provisioning to offspring probably because of the opportunity for additional matings via forced extrapair copulations.