Maternal encouragement of infant locomotion in pigtail macaques, Macaca nemestrina

This study investigated whether pigtail macaque mothers encourage their infants’ independent locomotion by increasing distance from them and displaying a retrieval signal, the pucker face. Fifteen mother–infant pairs living in a large captive social group were focally observed during the first 12 weeks of infant life. Mothers puckered to their infants only when out of contact with them, and the pucker was followed by reduction in distance by the mother or the infant. The pucker was significantly associated with an increase in distance initiated by the mother, and mothers that frequently puckered to their infants were also those that frequently left them. Multiparous mothers puckered to their infants more than primiparous mothers. The infant’s initiative in reducing distance after the pucker increased with its age, and the latency of its response gradually decreased in the first 6–7 weeks of life. Infants that received more puckers from their mothers spent less time in contact with them and approached and left them more frequently than infants that received fewer puckers. The evidence is insufficient to assess unequivocally whether developmental changes in infant responses to the pucker reflect social learning or maturation of motor skills. ? 1996 The Association for the Study of Animal Behaviour In recent years, there has been a growing interest in social transmission of information in animals (Whiten 1989; Galef 1992; Tomasello et al. 1993). Social information transfer can take different forms and be broadly categorized as active or passive. Active information transfer, also referred to as instruction or teaching, differs from passive forms of information transfer such as local enhancement or imitation, because it requires the active participation of an individual in the role of ‘instructor’ (King 1991; Caro & Hauser 1992). Although observational learning and local enhancement are not uncommon in animals, the question of whether animals engage in active information transfer is still debated (Tomasello et al. 1993). In a recent review of putative cases of teaching in animals, Caro & Hauser (1992) noted that most if not all of these cases involve parent–offspring interactions. Among the best known examples are mother cats, Felis catus, teaching their kittens hunting techniques (Ewer 1969) and mother chimpanzees, Pan troglodytes, assisting their infants in nut-cracking activities (Boesch 1991). Several authors have also suggested that primate mothers encourage their infants to walk independently, to follow or climb on, through complex behavioural sequences involving the use of communicative signals. The typical sequence, as observed in a number of cercopithecine monkeys and chimpanzees, involves the mother placing her infant on the ground, moving a few steps away from it, and displaying facial expressions (e.g. lip-smacking, teeth-chattering or pucker; Redican 1975), gestures (e.g. extending one arm towards the infant) and body postures (e.g. presenting the hindquarters) that serve a retrieval function; mothers have occasionally been seen walking backwards bipedally while supporting the infant with one hand (Maestripieri 1995a; Maestripieri & Call, in press). Unfortunately, all reports of these interactions in primates are qualitative and anecdotal, and the notion that the mother may encourage the behaviour of her infant is based on the subjective impression of a human observer rather than on quantitative evidence. One exception is provided Correspondence: D. Maestripieri, Yerkes Regional Primate Research Center, Emory University, 2409 Taylor Lane, Lawrenceville, GA 30243, U.S.A. (email: [email protected]). 0003–3472/96/030603+08 $18.00/0 ? 1996 The Association for the Study of Animal Behaviour