An investigation of individual, age and sexual differences in the play of Rattus norvegicus (Mammalia: Rodentia)

Eight litters of Rattus norvegicus of the PVG/C hooded strain were observed in order to investigate the roles of individuality, sexuality and age in playful behaviour.
Three measures of social play, namely, initiations, numbers of play bouts and numbers of playful elements performed were all found to be positively correlated. The incidence of social and solitary play were also positively correlated so that a concept of "playfulness" appeared to be justifiable. Playfulness showed no correlation with the general level of non-playful locomotor activity.
Male rats were more playful than females but only minor sex-related differences were found to occur in the sequential organisation of play.
Older rats showed longer play bouts and a higher degree of temporal organisation. Considerable individual differences in playfulness were recorded and in single sex litters playful rats were found to play together.
The majority of opponents, in playfighting, alternated between the roles of attacker and defender.