Increasing group size decreases social bonding in young Japanese quail, Coturnix japonica

Social bonds between groupmates and social motivation can influence the stability of the social structure among domestic birds. Group size may also influence social stability, but no information is available about its influence on social bonding. We investigated the effect of group size and social motivation on the strength of social bonds between familiar Japanese quail chicks. The behaviour of quail selected for high (HSR) or low (LSR) social reinstatement behaviour and housed in different group sizes (6, 15 and 30 individuals) was recorded during two successive 10 min situations: separation and return of a cagemate or an unfamiliar conspecific. In both lines and for all group sizes, chicks formed social bonds with cagemates, shown by disturbance at separation and a greater calming effect of the return of a familiar versus an unfamiliar quail. LSR chicks might form stronger social bonds than HSR ones but our results do not allow us to conclude confidently on that point. With increasing group size, the calming effect and especially the positive social interactions decreased in both lines, indicating a weakening of the social bond between familiar conspecifics, perhaps because of the larger number of potential partners or the establishment of a tolerant social strategy based on less aggression, less time spent in contact and weaker bonds. Further investigations of the relationship between group size and social bonding in this species may allow us to determine why their social behaviour changes with increasing group size and to make more suitable social environments for domestic birds.