Urban species often adjust their behavior to survive in urban environments, characterized by the proximity of humans, habitat fragmentation and heterogeneous, fluctuating ecological resources. Several hypotheses have been put forth to explain how species manage living in heterogeneous and complex anthropogenic habitats. The ability of individuals or species to beneficially modify their behaviors in response to changes in the environment has indeed been alternatively explained based on phylogenetic, adaptive, and ontogenic arguments. In this study we investigated the role of sociality as a driver of behavioural flexibility in urban birds. Sociality can be defined as the tendency to associate with conspecifics or form a group and may influence a species' ability to survive in an urban ecosystem to the extent that it represents advantages to species or individuals in terms of resource exploitation, fitness, and predation risk-avoidance. Given the potential benefits of sociality we hypothesized that sociality is a further characteristic that may explain how species have successfully expanded their range into urbanized areas. Based on this hypothesis, we predicted that pigeons (Columba livia) will show higher behavioural flexibility when in larger groups, whatever their genetic background and living-circumstances. Using pigeons as a model system, we compared 27 groups in France and Italy composed of four different genetic strains and varying living-conditions: free-living feral pigeons in urban areas, free-living domestic pigeons at the property of a local breeder captive, feral pigeons in a French ecological field station, captive domestic pigeons in an Italian ecological station. We tested two standardized behavioral measures of behavioural flexibility: thresholds for fear or neophobia and rates of problem solving. We found that group number affects neophobia and to a lesser extent problem-solving, suggesting that sociality is a factor enhancing birds' faculties to establish in and cope with heterogeneous urban environments. We consider this hypothesis here as compatible and complementary to existing hypotheses on species' adaptation to urban ecosystems.