Spontaneous vocal coordination of vocalizations to water noise in rooks (Corvus frugilegus): An exploratory study.

The ability to control one's vocal production is a major advantage in acoustic communication. Yet, not all species have the same level of control over their vocal output. Several bird species can interrupt their song upon hearing an external stimulus, but there is no evidence how flexible this behavior is. Most research on corvids focuses on their cognitive abilities, but few studies explore their vocal aptitudes. Recent research shows that crows can be experimentally trained to vocalize in response to a brief visual stimulus. Our study investigated vocal control abilities with a more ecologically embedded approach in rooks. We show that two rooks could spontaneously coordinate their vocalizations to a long-lasting stimulus (the sound of their small bathing pool being filled with a water hose), one of them adjusting roughly (in the second range) its vocalizations as the stimuli began and stopped. This exploratory study adds to the literature showing that corvids, a group of species capable of cognitive prowess, are indeed able to display good vocal control abilities.

Early social environment affects attention to social cues in juvenile common ravens, Corvus corax.

Social competence, i.e. defined as the ability to adjust the expression of social behaviour to the available social information, is known to be influenced by early-life conditions. Brood size might be one of the factors determining such early conditions, particularly in species with extended parental care. We here tested in ravens whether growing up in families of different sizes affects the chicks' responsiveness to social information. We experimentally manipulated the brood size of 13 captive raven families, creating either small or large families. Simulating dispersal, juveniles were separated from their parents and temporarily housed in one of two captive non-breeder groups. After five weeks of socialization, each raven was individually tested in a playback setting with food-associated calls from three social categories: sibling, familiar unrelated raven they were housed with, and unfamiliar unrelated raven from the other non-breeder aviary. We found that individuals reared in small families were more attentive than birds from large families, in particular towards the familiar unrelated peer. These results indicate that variation in family size during upbringing can affect how juvenile ravens value social information. Whether the observed attention patterns translate into behavioural preferences under daily life conditions remains to be tested in future studies.

Dominance in a socially dynamic setting: hierarchical structure and conflict dynamics in ravens' foraging groups.

Dominance hierarchies typically emerge in systems where group members regularly encounter and compete for resources. In birds, the 'open' and dynamic structure of foraging groups may prevent the emergence of structured hierarchies, although this assumption have hardly been tested. We report on agonistic data for ravens Corvus corax, collected over two 18-month periods for 183 marked individuals of a wild (fluid) population and 51 birds from six captive (stable) groups. We show that the dominance structure (steep and transitive) in wild foraging groups is strikingly similar to that found in captivity. In the wild, we found that higher ranks are mainly occupied by males, older and more aggressive individuals that also tend to receive fewer aggressions. Exploring the mechanisms sustaining the wild dominance structure, we confirmed that males are more aggressive than females and, with age, tend to receive fewer aggressions than females. Males that are about to leave the foraging groups for some months are less aggressive than newcomers or locals, while newcomers are specifically targeted by aggressions in their first year (as juveniles). Taken together, our results indicate that the socially dynamic conditions ravens face during foraging do not hinder, but provide opportunities for, using (advanced) social cognition. This article is part of the theme issue 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies'.

Early evidence for emotional play contagion in juvenile ravens.

Perceiving, evaluating and reacting towards conspecifics' emotional states are important challenges of social group living. Emotional contagion describes an alignment of emotional states between individuals and is widely believed to be based on behavioral synchronization, i.e., behavioral contagion. As basic empathy-like processes, the occurrence of both forms of contagion seems to underlie early ontogenetic trajectories in humans and non-human species. In the present study, we assessed play as a context for studying the development of emotional contagion and its interlink with behavioral contagion in ten juvenile common ravens. Ravens are exceptional players that engage in all three forms of play: object, locomotion and social play. To assess potential ontogenetic patterns of both behavioral and emotional contagion, we tested juvenile ravens at two different periods of early development, at three- and six-month post-hatching. We elicited object play in one or several ravens (demonstrators) in a standardized experimental environment, using a playground setup. At both test ages, we found evidence for emotional contagion as observer ravens showed an increase of locomotion and social play after we provided the demonstrator(s) with the playground setup, but no significant changes in the amount of object play. Hence, observers did not copy motor patterns from demonstrator(s) but engaged in other forms of play. Our findings speak for a transfer of a general mood state in the context of play in ravens as young as 3 months and against behavioral mimicry as a precondition for emotional contagion.

Effect of rearing style on the development of social behaviour in young ravens (Corvus corax).

Early social experiences can affect the development and expression of individual social behaviour throughout life. In particular, early-life social deprivations, notably of parental care, can later have deleterious consequences. We can, therefore, expect rearing procedures such as hand-raising-widely used in ethology and socio-cognitive science-to alter the development of individual social behaviour. We investigated how the rearing style later affected (a) variation in relationship strength among peers and (b) individuals' patterns of social interactions, in three captive groups of juvenile non-breeders consisting of either parent-raised or hand-raised birds, or a mix of both rearing styles. In the three groups, irrespectively of rearing style: strongest relationships (i.e., higher rates of association and affiliations) primarily emerged among siblings and familiar partners (i.e., non-relatives encountered in early life), and mixed-sex and male-male partners established relationships of similar strength, indicating that the rearing style does not severely affect the quality and structure of relationships in young ravens. However, compared to parent-raised ravens, hand-raised ravens showed higher connectedness, i.e., number of partners with whom they mainly associated and affiliated, but formed on average relationships of lower strength, indicating that social experience in early life is not without consequences on the development of ravens' patterns of social interaction. The deprivation of parental care associated with the presence of same-age peers during hand-raising seemed to maximize ravens' propensity to interact with others, indicating that besides parents, interactions with same-age peers matter. Opportunities to interact with, and socially learn from peers, might thus be the key to the acquisition of early social competences in ravens.

What constitutes "social complexity" and "social intelligence" in birds? Lessons from ravens.

In the last decades, the assumption that complex social life is cognitively challenging, and thus can drive mental evolution, has received much support from empirical studies in nonhuman primates. While extending the scope to other mammals and birds, different views have been adopted on what constitutes social complexity and which specific cognitive skills are selected for. Notably, many avian species form "open" groups as non-breeders (i.e., seasonally and before sexual maturity) that have been largely ignored as potential sources of social complexity. Reviewing 30 years of research on ravens, we illustrate the socio-ecological conditions faced by these birds as non-breeders and discuss how these relate to their socio-cognitive skills. We argue that the non-breeding period is key to understand raven social life and, to a larger extent, avian social life in general. We furthermore emphasize how the combination of the large-scale perspective (defining social system components: e.g., social organization, mating system) and the individual-scale perspective on social systems allows to better capture the complete set of social challenges experienced by individuals throughout their life, ultimately resulting on a more comprehensive understanding of species' social complexity.

Erratum: A longitudinal network analysis of social dynamics in rooks Corvus frugilegus: repeated group modifications do not affect social network in captive rooks.

[This corrects the article DOI: 10.1093/cz/zow083.].

A longitudinal network analysis of social dynamics in rooks corvus frugilegus: repeated group modifications do not affect social network in captive rooks.

Numerous studies have investigated the remarkable variation of social features and the resulting structures across species. Indeed, relationships are dynamic and vary in time according to various factors such as environmental conditions or individuals attributes. However, few studies have investigated the processes that stabilize the structures within a given species, and the behavioral mechanisms that ensure their coherence and continuity across time. Here, we used a dynamic actor-based model, RSiena, to investigate the consistency of the temporal dynamic of relationships of a group of captive rooks facing recurrent modifications in group composition (i.e., the loss and introduction of individuals). We found that changes in relationships (i.e., formation and removal) followed consistent patterns regardless of group composition and sex-ratio. Rooks preferentially interacted with paired congeners (i.e., unpopular attachment) and were more likely to form relationships with individuals bonded to a current social partner (i.e., "friends of friends", or triadic closure). The sex of individuals had no effect on the dynamic of relationships. This robust behavioral mechanisms formed the basis of inter-connected networks, composed of sub-structures of individuals emerging from the enmeshment of dyadic and triadic motifs. Overall, the present study reveals crucial aspects of the behavioral mechanisms shaping rooks social structure, suggesting that rooks live in a well-integrated society, going far beyond the unique monogamous pair-bond.