Predictable males and unpredictable females: sex difference in repeatability of parental care in a wild bird population

Repeatability of parental care, let alone heritability of care, has been rarely measured, although there has been much research linking sexual selection to male parental care and also examining biparental care in relation to game theory models. We investigated within- and between-year repeatabilities of incubation and nestling provisioning and how these two types of parental care were related in a sexually dimorphic species, the house sparrow, Passer domesticus. We found that between- and within-year repeatabilities of feeding rate were high in males and low to moderate in females, but that between- and within-year repeatabilities of incubation time were low to moderate in both sexes. Interestingly, the amount of time during which neither sex incubated significantly predicted the subsequent male feeding rate but not the female feeding rate. Our results suggest a need for a new theoretical framework that encompasses variation in the predictability and plasticity of parental investment by individuals.