Communication is the link between individuals of one species and represents the essence of social life. Vocal communication is one of the most studied forms of information exchange, although it also comes with interspecific barriers that are still tricky to overcome. While we are able to understand the meaning of another human’s words, we fail to understand an animal’s utterances. Among these, bird song has become a field of particular interest. However, little is known yet about many species’ vocalizations, and even less about their significance or how different factors influence them. The presented study establishes the vocal repertoire of a group of rooks and further investigates the importance of contact calls between partners in an experiment. We found that test subjects and other group members produced more contact calls after than before partners had been separated from each other, indicating stress induced by physical isolation and/or the lack of visual contact as an important factor influencing the call frequency. Separating certain individuals seemed to affect the group differently, which indicates that the ‘importance’ of the animal to the group influences the group call rate. In this study, we have shown how social and environmental factors play a role in vocal communication in birds.

Comparing oneself to others is a key process in humans that allows individuals to gauge their performances and abilities and thus develop and calibrate their self-image. Very little is known about its evolutionary foundations. A key feature of social comparison is the sensitivity to other individuals' performance. Recent studies on primates produced equivocal results, leading us to distinguish a 'strong' variant of the social comparison hypothesis formulated for humans from a 'weak' variant found in nonhuman primates. Here, we focus on animals that are distantly related to primates but renowned for their socio-cognitive skills, birds from the family Corvidae. We were interested in whether crows' task performances were in uenced i) by the presence of a conspeci c co-actor performing the same discrimination task and ii) by the simulated acoustic cues of a putative co-actor performing better or worse than themselves. Crows reached a learning criterion quicker when tested simultaneously as compared to when tested alone, indicating a facilitating effect of social context. The performance of a putative co-actor in uenced their performance: crows were better at discriminating familiar images when their co-actor was better than they were. Standard extremity, i.e., how pronounced the difference was between the performance of the subject and that of the co-actor, and category membership (i.e., a liation status and sex), of the putative co-actors had no effect on their performance. Our ndings are in line with the 'weak' variant of social comparison and indicate that elements of human social comparison can be found outside of primates.