Recent behavioural studies in corvids (i.e. crows and jays) have demonstrated their sophisticated cognitive abilities such as mental-time travel, theory-of-mind-like ability, reasoning, and tool manufacture and use. These abilities are thought as a case of cognitive convergence which has been evolutionary driven by the social complexity common between corvids and primates. However, 'complexity' of the social life of corvids has been less understood. Here I review the social ecology of crows and

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... jays with focusing on the social relationships and inter-individual interactions. Particular attentions are paid to affiliative relationships, including social bonds and friendships, and cooperation styles as the foundation of the conflict management which should evolutionarily work as a socio-ecological demand for cognitive-processing power of corvids.