Functions of multiple play signals in free-ranging juvenile rhesus macaques (Macaca mulatta)

Some mammals, including some nonhuman primates, use multiple play signals during social play that convey the playful mood or intention of the signaler. However, why single species use multiple play signals has not been investigated. We recently identified seven such signals among free-ranging juvenile rhesus monkeys (Macaca mulatto) on Cayo Santiago, Puerto Rico, all of which predict the imminent occurrence of play. Here we ask whether the use of these multiple signals may have more precise or multiple functions. Specifically, we ask whether different play signals are associated with different (1) types of play to come, (2) intensities of play, (3) initiators of play and/or (4) distances at which the signal is given. Our results indicate that most signals were disproportionately associated with one or more aspects of play. For example, gamboling was associated with play that is initiated at a distance, crouch-and-stares were associated with chasing play and intense play, and leg-peeks were associated with play initiated by the receiver, as opposed to the signaler. These nonrandom associations suggest that play signals, most of which are conspicuous body signals, are not merely redundant variants of a single general function to transmit a playful mood. Rather they may be used more selectively in a variety of play contexts in which it may be beneficial to reinforce, clarify or emphasize the playful intention of the signaler. At the same time, most are not associated with particular contexts in a highly exclusive or simple manner. As such further research is needed to determine whether they are examples of functionally referential signaling.