Data from: Strategic use of affiliative vocalizations by wild female baboons

Although vocal production in non-human primates is highly constrained, individuals appear to have some control over whether to call or remain silent. We investigated how contextual factors affect the production of grunts given by wild female chacma baboons, Papio ursinus, during social interactions. Females grunted as they approached other adult females 28% of the time. Supporting previous research, females were much more likely to grunt to mothers with young infants than to females without infants. Grunts also significantly increased the likelihood of affiliative interactions among all partners. Notably, however, grunts did not simply mirror existing social bonds. Instead, they appeared to perform a very different function: namely, to serve as signals of benign intent between partners whose relationship is not necessarily close or predictable. Females were less likely to grunt to their mothers or adult daughters—the individuals with whom they shared the closest and least aggressive bonds—than to other females. In contrast, patterns of grunting between sisters were similar to those between nonkin, perhaps reflecting sisters’ more ambivalent relationships. Females grunted at higher rates to lower-ranking, than to higher-ranking, females, supporting the hypothesis that grunts do not simply signal the signaler’s level of arousal or anxiety about receiving aggression, but instead function as signals of benign intent. Taken together, results suggest that the grunts given by female baboons serve to reduce uncertainty about the likely outcome of an interaction between partners whose relationship is not predictably affiliative. Despite their limited vocal repertoire, baboons appear to be skilled at modifying call production in different social contexts and for different audiences.

尽管非人灵长类的发声行为受到高度约束，但个体似乎能够一定程度上控制是否发出叫声或保持静默。本研究探讨了社会互动过程中，情境因素如何影响野生雌性南非狒狒（Papio ursinus）发出咕哝叫声（grunt）的行为。雌性狒狒在靠近其他成年雌性时，有28%的概率发出咕哝叫声。与此前研究结果一致，雌性狒狒向带有幼崽的雌性个体发出咕哝叫声的概率，远高于向无幼崽雌性个体的概率。咕哝叫声还显著提升了所有互动伙伴之间的亲和性互动概率。但值得注意的是，咕哝叫声并非简单反映已有的社会联结。相反，其功能似乎截然不同：具体而言，它充当了关系未必亲密或可预测的伙伴之间的善意信号。相较于其他雌性，雌性狒狒向自己的母亲或成年女儿发出咕哝叫声的概率更低——而这些个体正是与其拥有最亲密、攻击性最弱的社会联结的对象。与之相反，雌性狒狒姐妹间的咕哝叫声模式与非亲属间的模式相似，这或许反映了姐妹间关系更为矛盾复杂的特点。雌性狒狒向低等级雌性发出咕哝叫声的频率高于高等级雌性，这支持了如下假说：咕哝叫声并非简单传递发出者因可能遭受攻击而产生的唤醒水平或焦虑情绪，而是作为善意信号发挥作用。综合来看，研究结果表明，雌性狒狒发出的咕哝叫声，旨在降低那些关系无法被预测为亲和性的互动伙伴之间，关于互动可能结果的不确定性。尽管狒狒的发声库有限，但它们似乎能够熟练地根据不同社会情境和不同受众调整发声行为。