Longitudinal studies of play in <italic>Rattus norvegicus</italic>

This thesis describes experiments and observational studies of social play in Rattus norvegicus. focussing on two aspects of play which have received relatively little attention: the relationship of play to other behaviours during development, and the immediate causation of play, Chapter two looks at play in relation to other social and non-social behaviours. Social play showed a distinctive inverted "U"-shaped ontogenetic trend (as did exploration), and was the major form of social interaction for young rats. However, social behaviours accounted for little of the developing animal's overall time-budget. No evidence was found for a relationship between play and the agonistic behaviours it is traditionally supposed to resemble. Experiments two and three provide further data on this point. Chapter three looks at temporal and contextual aspects of play—features which have been studied very little. Most play-bouts were found to be very short, and to show little reciprocity between interactants. Play occurred in a context of exploration, play, and activity, and was not associated with sedentary or agonistic behaviours. Experiments on play's immediate causation highlight the importance of environmental factors in determining whether play will occur. Experiment one shows that the "rebound" effect (increased play induced by prior short-term social deprivation) is not ameliorated by non-playful social contact. Experiment two looks at the effects on play of environmental change. Experiment three shows that food-deprivation selectively suppresses play. These results suggest that play's "costs" may have been overestimated; that play may have immediate benefits (exercise and allo-grooming); and that of the plethora of benefits which play could provide for this particular species, practice of agonistic activities seems the least plausible