In traditional human societies (e.g. Dogon, Kirundi, Yoruba ethnic groups), ageing is a sign of wisdom and the speech of an elder elicits specific respect and attention (Bascom 1942; Albert 1964; Calame-Griaule 1965). Intergenerational conversations in modern societies are regulated by several factors, including culture (Giles et al. 2002), age-difference (Hummert et al. 1998; Williams & Garett 2002) and the context of the interaction (Ervin-Tripp 1964). Even though it is not true in all contexts, at the workplace, younger people are particularly respectful to elders regardless of their eastern/western culture (McCann & Giles 2006). Children respect more turn-taking rules and respond more to their mothers than to other individuals, probably a solid necessary basis for respect to elders when older (Fitch 2004).

We observed female Campbell's monkeys living in a group composed of one male (13 years old), seven adults (3–15 years old) and one subadult (2 years old) females. Females belonged to two matrilines and were nulliparous apart from the older one. The group composition matched the ones observed in the wild (Ouattara et al. 2009). The group was housed in an indoor (21 m² × 3 m)—outdoor (21 m² × 4 m) enclosure enriched with litter and perches. Monkeys were fed two meals per day (fruits, vegetables, pellets). Water was available ad libitum.

Vocal exchanges corresponded to series of successive calls from different females (2 or 3, 43–31%; sometimes 4 or 5, 15–5%), since 74% of the exchanges were composed of one call from each individual and the same individual almost never produced two consecutive calls (0.48%). The individuals who emitted several calls within a given exchange were the youngest (five times more for the female under 5 years old). Recordings confirmed that vocal exchanges were characterized as series of calls given by different individuals typically trailing each other with short intercall intervals of up to 1 s (figure 1). No call overlap was observed and individuals responded to each other with a latency rarely (7.7%) less than 260 ms (average contact call duration). Age appeared as a major factor in the contribution of individuals to vocal exchanges. In nulliparous females (n = 7), call production was negatively correlated with age (Spearman test: r = −0.893, p = 0.0068; figure 2a), indicating that elders were less ‘loquacious’ than younger individuals. Despite that, they received more responses from their younger conspecifics. Age was positively correlated with the rate of responses received (r = 0.929, p = 0.0025; figure 2b). Elders called less but when they called, they almost always received a response. The oldest individual, who was the mother of some of the nulliparous females, for some reason presented a particular profile with a high call production (figure 2a). Including this female in the analysis cancelled the ‘call rate–age’ correlation (n = 8, r = −0.57, p = 0.14). But, interestingly, including this female did not change the significance of the correlation between age and rate of responses received (n = 8, r = 0.857, p = 0.0065; figure 2b). Call rate and response rate were not correlated with dominance status, with or without the mother (−0.5 < r < 0.57, 0.13 < p < 0.32).

Observations of spontaneous vocal exchanges in a group of Campbell's monkeys revealed that, like other species, they perform temporally well-organized interactions, respecting turn-taking rules (Hauser 1992; Hausberger et al. 2008). More interesting still is the finding that age is an important regulating factor, with elders, regardless of dominance status, eliciting more responses from their younger counterparts despite a lower call production. Obviously, elders received more attention than younger adults. As delays were very short, age identification was probably related to the observed changes of sound structure with age (Lemasson 2003) as also found in marmosets (Chen et al. 2009), although here sight identification cannot be excluded. Only hypotheses can be raised at this stage to explain the high call rate of the old mother (particular social status/hormonal profile, re-increase of loquacity after a certain age-threshold, idiosyncrasy). This is an interesting question deserving further investigation. But these results show for the first time that ‘attention to elders’ constitutes an integral part of the daily social life of a non-human primate species and suggest that this may be more than a purely cultural human product.