Research Interests and Main Results
Título de la Tesis en castellano: Relaciones sociales y formación de grupos con reproducción cooperativa en la Corneja negra (Corvus corone corone).
Título de la Tesis en inglés: Social relationships and group formation in cooperatively breeding Carrion crows (Corvus corone corone).
Cooperatively breeding societies are characterized by individuals providing care to young that are not their offspring. Natal delayed dispersal is typically a prerequisite for cooperative behaviour in birds, because helpers are often offspring that remain in the natal territory past the age of independence and aid their parents in rearing new siblings. The evolutionary explanation of cooperative breeding therefore lies in identifying factors influencing offspring delayed dispersal and their subsequent decision to help at the nest. The hypothesis of “parental facilitation” or “nepotism” suggests that offspring delay dispersal because of the benefits obtained from the prolonged association with their parents through, for example, preferential access to the resources of the territory and/or defence against predators. Regarding helping behaviour, the “pay to stay” hypothesis proposes that it represents a ‘rent’ that subordinates pay to the dominants in order to be tolerated in their territory. This implies that dominant breeders should ‘punish’ helpers that do not provide sufficient help, or, as recently suggested, that ‘lazy’ helpers should prevent punishment by displaying submissive behaviours.
In My PhD thesis, I analysed both hypotheses by studying the social dynamics in cooperatively breeding groups of carrion crow during the access to an experimental food source. Social groups comprised two types of helpers at the nest, namely offspring of the breeding pair, which can stay on the natal territory for up to four years and immigrants. Results showed that the access to food was regulated by linear dominance hierarchies that remained stable through the breeding season and over the years. Breeding males were always at the top of the hierarchy, followed by male immigrants and male offspring, which were dominant over all the females in their group. According to the hypothesis of nepotism, dominant breeding males provided their offspring with a preferential access to food resources of the territory by (1) attacking male immigrants with more frequency and intensity than offspring and (2) associating preferentially with their offspring on the feeding spot and sharing food with them. This parental facilitation allowed the offspring to spend more time feeding than higher-rank immigrants. Moreover, breeding males were fast approaching a novel food resource, followed by male immigrants, whereas retained offspring and breeding females were last.
Results showed that this order, which matched the dominance ranks, was unlikely to be enforced through social interference but derived form differences in individual level of neophobia among group members. In groups that were simultaneously presented with two identical novel food sources that could not be monopolized by one individual, subordinates only used the one that was first explored by the dominant male. This indicates that the explorative behaviour of the dominant breeding male provided cues that helped subordinates to overcome their neophobia. Therefore, retained offspring may benefit from living in families with their nepotistic father by gaining access to food without incurring the risk of exploring.
Finally, I found no evidences of ‘pay to stay’ in cooperative groups. Contrarily to predictions, neither the aggressive behaviour of the dominant breeding males nor the submissive behaviour of helpers (retained offspring / immigrants) correlated with the level of contribution at the nest of the latter. Instead, at the end of the breeding season, dominant breeding males reduced significantly their aggressions towards immigrant males, who reduced the frequency of submissive behaviours accordingly and increased the time spent eating together with the dominant male, whereas alpha male/offspring relationships did not change over time. I suggest that the seemingly lack of ‘pay to stay’ in crows arises because of the important insurance function of ‘lazy’ helpers, which can fully compensate for a sudden reduction in the provisioning effort of the group, avoiding a decrease in reproductive success during unfavourable circumstances.
Chiarati, E., Canestrari, D., Vera, R. & Baglione, V. 2012.
Chiarati, E., Canestrari, D., Vila, M., Vera, R., Baglione.V. 2011.
Baglione, V., Canestrari, D., Chiarati, E., Vera, R. & Marcos, J. M. 2010. Lazy group members are substitute helpers in carrion crows. Proceedings of the Royal Society B-Biological Sciences, 277, 3275-3282
Chiarati, E., Canestrari, D.,Vera, R., Marcos, J.M., Baglione, V. 2010.
Canestrari, D., Vera, R., Chiarati, E., Marcos, J. M., Vila, M., Baglione, V. 2010. False feeding: the trade-off between chicks' hunger and care-givers' needs in cooperative crows. Behavioral Ecology, 21: 233-241
Canestrari, D., Chiarati, E., Marcos, J. M., Ekman, J. & Baglione, V. 2008. Helpers but not breeders adjust provisioning effort to year-round territory resource availability in carrion crows. Animal Behaviour, 76-243-249