TARGETS, TACTICS, AND THE OPEN MOUTH FACE DURING PLAY FIGHTING IN 3 SPECIES OF PRIMATES

The play fighting of many mammals involves the nonserious use of behav ior patterns derived from serious fighting. A major question of theore tical importance has been that of holy, given this overlap in patterns of behavior, the animals can distinguish between playful and nonplayf ul intent. One proposed solution is that animals use play signals to i nform each other about the playful intent of their actions. The most w idely reported play signal amongst primates is the open mouth play fac e. The manner in which this so-called signal functions is based on cor relational evidence, with most reports simply noting its presence or a bsence in a given species. This study involved a detailed video-based analysis of the occurrence of open mouths during the play fighting of three species of primates. One captive troop each of ring-tailed lemur s, black-handed spider monkeys, and patas monkeys was used. By examini ng all open mouths in the context of the species-typical style of play fighting, several conclusions were empirically verified. 1) Most open mouths occur as a functionally necessary precursor for biting. 2) Som e open mouths occur as a defensive threat which deters further contact . 3) The residual open mouths which may function as contact promoting play signals, constituted about 20-25% of all open mouths by the lemur s and patas monkeys, but less than 5% for spider monkeys. These specie s differences appeared to arise from two causes. Firstly, the spider m onkeys used another signal, the head shake, in situations where lemurs and patas monkeys used open mouths. Secondly, the style of play fight ing greatly influenced the frequency and duration of open mouths. This was most marked in the face-to-face combat style of patas monkeys. Th ese findings show that comparative studies of the occurrence and funct ion of play signals need to take into account species-typical styles o f playful combat. (C) 1997 Wiley-Liss Inc.