Proximity measures of social play in the laboratory rat.

Litters of laboratory rats (Rattus norvegicus) were filmed between 21 to 60 days of age, and data on 700 social play bouts obtained. These were analyzed for information on how play bouts ended and on the spatial relationship between the players and their physical environment. The results suggest that social play in this species (a) does not appear to be a covert means of securing priority of access to resources such as food, females, or territory; and (b) does not appear to represent practice for behaving in the contexts within which "serious" adult aggression occurs (e.g., practicing being "territorial," etc.). Players showed a strong preference for playing close to cover and away from exposed areas; if this is also true for wild rats, it would minimize the potential costs of play in terms of increased conspicuity to predators.