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.

Mirror reflections can elicit various behavioral responses ranging from social behavior, which suggests that an animal treats its own reflection as a conspecific, to mirror-guided self-directed behaviors, which appears to be an indication for mirror self-recognition (MSR). MSR is scarcely spread in the animal kingdom. Until recently, only great apes, dolphins, and elephants had successfully passed this test. The range of convergence was, however, expanded by an avian species, the Eurasian magpie (Pica pica). Efforts to find MSR in other corvid species have so far failed, and with only a few studies conducted, the cause of these discrepancies is difficult to identify. In the present study, we examined the responses to mirrors and the ability of MSR in hitherto untested species: the carrion and hooded crows (Corvus corone ssp.). These crows showed a pronounced and lasting interest in the mirror; unlike many species, they did not exhibit social behaviors on their first encounters but immediately started investigating the mirror. Some crows showed contingent behaviors in front of the mirror, but none of the crows showed significant mirror-guided self-directed behaviors nor mark-directed behavior during the subsequent mark test. This lack of mark-directed behavior could not be explained by a lack of interest in the mirror nor in the mark. These findings could indicate that crows lack a concept of self, or the need for other means of investigating self-recognition and self-awareness in avian species.

Mirror self-recognition (MSR) assessed by the Mark Test has been the staple test for the study of animal self-awareness. When tested in this paradigm, corvid species return discrepant results, with only the Eurasian magpies and the Indian house crow successfully passing the test so far, whereas multiple other corvid species fail. The lack of replicability of these positive results and the large divergence in applied methodologies calls into question whether the observed differences are in fact phylogenetic or methodological, and, if so, which factors facilitate the expression of MSR in some corvids. In this study, we (1) present new results on the self-recognition abilities of common ravens, (2) replicate results of azure-winged magpies, and (3) compare the mirror responses and performances in the mark test of these two corvid species with a third corvid species: carrion crows, previously tested following the same experimental procedure. Our results show interspecies differences in the approach of and the response to the mirror during the mirror exposure phase of the experiment as well as in the subsequent mark test. However, the performances of these species in the Mark Test do not provide any evidence for their ability of self-recognition. Our results add to the ongoing discussion about the convergent evolution of MSR and we advocate for consistent methodologies and procedures in comparing this ability across species to advance this discussion.

No abstract

No abstract