When Should Avian Parents Differentially Provision Sons and Daughters?

Abstract

Given the scarcity of data on sex differences in the behavior, provisioning, growth, and development of young birds, this paper is necessarily speculative. Definitive treatments of the topic will have to wait until more empirical data are available. However, at this point, it is clear that factors besides relative body size can affect the food requirements and provisioning rates of young male and female birds. Relationships between food intake and growth rates can be affected by a number of factors, and in species with sexual size dimorphism, these functional relationships are probably different for young males and females. Several hypotheses predict relatively egalitarian feeding of both sexes in sexually size-dimorphic species or preferential feeding of the members of one sex in sexually size-monomorphic species. These include hypotheses related to competition among the siblings for parental provisioning, competition between young around the time of independence, and sex-biased dispersal in the period immediately following independence. In addition, there are suggestions that male and female young of the same age might allocate food to different components of growth and development, as a result of different developmental schedules or of selection for the early maturation of structures that enhance competitive ability. Hence, the topic of sex-biased provisioning in birds would seem to be a fertile field for further discussion and empirical studies.