The investigation of prosocial behavior is of particular interest from an evolutionary perspective. Comparisons of prosociality across non-human animal species have, however, so far largely focused on primates, and their interpretation is hampered by the diversity of paradigms and procedures used. Here we present the first systematic comparison of prosocial behavior across multiple species in a taxonomic group outside the primate order, namely the bird family Corvidae. We measured prosociality in 8 corvid species, which vary in the expression of cooperative breeding and colonial nesting. We show that cooperative breeding is positively associated with prosocial behavior across species. Also, colonial nesting is associated with a stronger propensity for prosocial behavior, but only in males. The combined results of our study strongly suggest that both cooperative breeding and colonial nesting, which may both rely on heightened social tolerance at the nest, are likely evolutionary pathways to prosocial behavior in corvids.

Highlights d Neophobia, i.e., fear of novel stimuli, impacts adaptability, and survival d Individual and species-level variation found in object and food neophobia in corvids d Urban habitat, adult sociality, max flock size, and caching influenced object neophobia

In long-range fission-fusion complex societies, individuals are often recognized by audiovocal signals because of long-range propagation. The signature voice system is a well-known mechanism involving both acoustic individuality of a certain call type and discrimination ability. Previous studies on vocal individual recognition of birds have emphasized its involvement in breeding contexts such as mate, parent and offspring, and territorial-neighbour recognition. However, there has been less focus on the recognition of non-breeding flock members despite the socio-ecological demand of such ability in the complex social lives of highly social birds including corvids. Here we report a signature voice system in jungle crows by showing both acoustic individuality of contact calls and discrimination ability. We first performed a discriminant functional analysis on contact ka calls of five crows to examine their discriminatory potential and demonstrate inter-individual distinctions. We next used an operant conditioning to verify the perceptual ability to discriminate non-breeding familiar conspecifics based on ka calls. Four of the five crows successfully transferred discrimination of individual calls to the novel ka calls. Our results provide the first evidence of a signature voice system as a perceptual mechanism for individual recognition of familiar individuals in non-breeding flocks of a highly social crow.

Behavioural responses to novelty, including fear and subsequent avoidance of novel stimuli, behaviours referred to as neophobia, determine how animals interact with their environment. Neophobia aids in navigating risk and impacts on adaptability and survival. There is variation within and between individuals and species, however, lack of large-scale, comparative studies critically limits investigation of the socio-ecological drivers of neophobia. In this study, we tested responses to novel objects and food (alongside familiar food) versus a baseline (familiar food alone) in 10 corvid species (241 subjects) across 10 labs worldwide. There were species differences in the latency to touch familiar food in the novel object and food conditions relative to the baseline. Three of seven socio-ecological factors influenced object neophobia: 1) use of urban habitat (vs not), 2) territorial pair vs family group sociality and 3) large vs small flock size (whereas range, caching, hunting live animals, and genus did not); while only flock size influenced food neophobia. We found that, overall, individuals were temporally and contextually repeatable (i.e. consistent) in their novelty responses in all conditions, indicating neophobia is a stable behavioural trait. With this study, we have established a network of corvid researchers, demonstrating potential for further collaboration to explore the evolution of cognition in corvids and other bird species. These novel findings enable us, for the first time in corvids, to identify the socio-ecological correlates of neophobia and grant insight into specific elements that drive higher neophobic responses in this avian family group.

No abstract