Sex-specific parental care during postfledging in common ravens

Abstract

Parents face a trade-off when allocating limited resources to reproduction and self-maintenance, and this can result in differential investment in individual offspring when rearing multiple offspring simultaneously. In birds with biparental care, it is not well understood how each parent allocates its resources to different chicks of the same brood. Theory suggests that parental investment depends on offspring quality and brood size, but empirical quantification of parent–offspring interactions during the postfledging stage is often difficult. We worked with captive common ravens, Corvus corax, a slightly dimorphic songbird with extended periods of biparental care, to investigate the effects of offspring sex, body mass, brood age and brood size on the feeding probability by both parents. We further investigated the influence of the same factors on offspring begging behaviour and affiliative interactions between parent and offspring. Mothers were more likely to feed and affiliate with their offspring than fathers. Fathers were more likely to feed and affiliate with sons than daughters, whereas mothers showed no preference. When more than one son was present, fathers were more likely to feed and affiliate with heavier sons than light sons. Brood size increased the begging probability of chicks, but decreased their probability of being fed. Our results suggest that biparental care in ravens is skewed towards the mother and that paternal care is selective. Selective paternal investment in the heaviest son may be adaptive in a system where heaviest males better compete for resources during dispersal.