Intraspecific competition in non-precocial birds may start during early developmental stages, when nestlings are still dependent on parental care. Despite it often leads to fatal outcomes, the physiological basis regulating the expression of agonistic behaviours has received scant attention. Among the physiological candidates regulating aggression and position in social hierarchies, testosterone and corticosterone (the “stress hormone”) have demonstrated to play an important role in adult birds. However, little is known on the role that these hormones may play within a context of sibling aggression. Considering that (1) competition for food is one of the first life challenges for neonate birds, and that (2) such competitive outcome constitutes a mayor selective force determining early survival (and thus individual fitness) the physiological basis regulating brood competition constitutes a research topic of prime relevance. Here we propose an experimental approach to test the endocrine modulation of sibling aggression and brood competition in bee-eaters, a model species that offers unique advantages to perform research on this topic.