NESTLING CALL MODIFICATION DURING EARLY DEVELOPMENT IN A COLONIAL PASSERINE

Parental dependence on the nest's spatial cues in offspring recognition decreases with nestling growth in the azure-winged magpie

In altricial birds, to address which cues are used by parents to recognize their offspring, and when they switch between cues during reproduction, it has not been well determined. In this study, we address this question in a Tibetan population of the azure-winged magpie Cyanopica cyanus, by examining the dependence of parents on a nest's spatial position in offspring recognition. During the egg and nestling phases, azure-winged magpie nests were translocated to new positions across various distances from their original site, and parental responses to the translocated nests were investigated. Our findings show that a nest's spatial position is not connected with the survival of its young, but might be used as a cue in parental offspring recognition. When nests are translocated to a new position within a certain distance, parents could recognize their nests and returned to resume their parenting behaviors. Parental dependence on the nest's spatial position in offspring recognition is higher during the egg phase than during the nestling phase, and it decreases with the growth of nestlings. After nestlings reach a certain age, the nest' s spatial position was no longer used by parents as the single cue for offspring recognition. These findings suggest that azure-winged magpies switch their cues in offspring recognition during the different stages of reproduction. After parent-offspring communication has been established, the offspring's phenotypic traits may become a more reliable cue than the nest's spatial position in offspring recognition.

Individual vocal signatures in barn owl nestlings: does individual recognition have an adaptive role in sibling vocal competition?

To compete over limited parental resources, young animals communicate with their parents and siblings by producing honest vocal signals of need. Components of begging calls that are sensitive to food deprivation may honestly signal need, whereas other components may be associated with individual-specific attributes that do not change with time such as identity, sex, absolute age and hierarchy. In a sib-sib communication system where barn owl (Tyto alba) nestlings vocally negotiate priority access to food resources, we show that calls have individual signatures that are used by nestlings to recognize which siblings are motivated to compete, even if most vocalization features vary with hunger level. Nestlings were more identifiable when food-deprived than food-satiated, suggesting that vocal identity is emphasized when the benefit of winning a vocal contest is higher. In broods where siblings interact iteratively, we speculate that individual-specific signature permits siblings to verify that the most vocal individual in the absence of parents is the one that indeed perceived the food brought by parents. Individual recognition may also allow nestlings to associate identity with individual-specific characteristics such as position in the within-brood dominance hierarchy. Calls indeed revealed age hierarchy and to a lower extent sex and absolute age. Using a cross-fostering experimental design, we show that most acoustic features were related to the nest of origin (but not the nest of rearing), suggesting a genetic or an early developmental effect on the ontogeny of vocal signatures. To conclude, our study suggests that sibling competition has promoted the evolution of vocal behaviours that signal not only hunger level but also intrinsic individual characteristics such as identity, family, sex and age.