In animal societies, individuals should optimize the way they behave in relation to the behavior displayed by their conspecifics. This social competence, i.e., the ability to adjust behavior to the social context, can vary between individuals, but also improve with age and experience. This aspect, although important, has rarely been studied. We tested whether the ability to adjust behavior to siblings develops with age in barn owl nestlings (Tyto alba). In this species, young siblings show intense social interactions referred to as Bsibling negotiation. Indeed, because parents bring a single indivisible food item at each visit to the nest, all the effort invested in sibling competition is only paid back in the nestling that is able to monopolize the food item. Therefore, before the arrival of parents, siblings vocally inform each other about their relative hunger level so that they can optimally invest in sibling competition, with the most vocal, and hence hungry, nestling momentarily deterring its siblings from competing. This process implies that siblings have the ability to adjust their behavior in relation to the behavior of their siblings, a process that could change with age. In a series of experiments, we examined how nestlings of different ages respond to the vocal behavior of siblings. We show here that older nestlings adjusted their vocal behavior more finely than younger nestlings in relation to the behavior of their siblings. Elders also more readily refrained from eating in front of a hungry sibling. These patterns could arise because owlets' social competence develops with age or because they adopt different competitive and cooperative strategies according to their age.
Significance statement
In sibling barn owls, competition for food brought by parents is settled by vocalization. Highly vocal owlets induce their siblings to call less and to let them eat in priority once parents are back with a prey item, a process referred to as Bsibling negotiation." Nestling barn owls adjust their investment in sibling competition according to two parameters: their hunger level and the vocal behavior of their siblings. We analyzed the relative importance of these two parameters in differently aged owlets. Younger owlets adjusted the intensity of vocalizing primarily in relation to their own hunger level, which was efficient in modifying older nestlings' behavior, as older nestlings readily withdrew from vocal contest and refrained from eating in front of highly vocal siblings. Hence, social adjustment changed with age in owlets, older ones being more sensitive to the signals of need of their siblings.