N.R. Chalmers

The ontogeny of play in feral olive baboons (Papio anubis)

Abstract Behaviours that always appear playful (play markers) are distinguished from behaviours that appear playful in some contexts, but not others (context-dependent play components). Age changes in the frequency of performance of both kinds of playful behaviours are described, as are age changes in the frequency with which context-dependent play components accompany play markers in baboon social interactions. Some quantitative properties of social interactions containing and lacking play markers are compared. Interactions with play markers last longer and have a higher rate of change of constituent behaviours than interactions without. Animals are also more persistent in the face of changes in their partners behaviour in interactions with play markers. It is suggested that an attempt to produce a definition of play is not a useful enterprise, but that it is important to investigate causal mechanisms underlying behaviours that appear playful to human observers, and to clarify the relationships among those mechanisms. Data are presented suggesting that at least two sets of mechanisms, not totally separate, underly the performance of baboon social play. Functions of the behaviours controlled by these mechanisms are discussed.

Temporal patterns of play bouts in captive common marmosets (Callithrix jacchus)

Abstract An objective method for defining a play bout is derived and applied to data collected from six 143–146-day old captive marmosets living in family groups. Temporal patterns within and between play bouts are investigated. There is a tendency for play bouts to occur in sessions. Play sessions are terminated by short rather than long play bouts. The pattern of components within play bouts is nonrandom. Chasing tends not to be performed either at the beginning or at the end of a play bout. Typical latencies from play bout onset to the onset of components within the bout vary from one component to another. It is argued that mechanisms controlling social play must operate at two levels: at the level of the play session, and at the level of the play bout.

Developmental pathways in behaviour

Abstract Much behaviour changes gradually in frequency during development. It is possible to argue for the existence of rules that govern such changes, to distinguish between directing and stopping rules, and to identify several different kinds of directing and stopping rules. Directing rules can be postulated that involve an instantaneous assessment of rate of performance of behaviour by the young animal or a cumulative assessment of amount of behaviour performed, and that also involve age-dependent or age-independent set points. Stopping rules may be performance-dependent or performance-independent. The evidence for these various rules is discussed, together with their functional significance.