“Conversation rules” such as overlap avoidance and coordinated overlap have been reported in nonhuman animals, and seem to be adaptive responses to the requirements of social life. Some species display both patterns in an apparently flexible way, but the social factors mediating their respective usage remain poorly documented. We investigated the potential social factors guiding the usage of these temporal rules during collective howling in six free-ranging groups of black howler monkeys (Alouatta pigra). First, we found that adult males' vocalizations rarely overlap those of other callers while most adult females' calls overlap other members' calls, especially that of other females. Second, whereas some call types (notably affiliative calls) are typically emitted without overlap, roars (agonistic loud calls) overlap more frequently. Third, coordinated overlap is more frequent during intergroup competition. Our findings support the hypothesis that overlap avoidance and coordinated overlap are two different (here sex-related) vocal alliance social behaviors, at least for some nonhuman primates. More comparative investigations are now needed to explore further their evolutionary trajectories in this lineage.

中文翻译：

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自由放养的黑吼猴之间声音互动的社会中介重叠

在非人类动物中已经报道了诸如避免重叠和协调重叠的“对话规则”，并且似乎是对社会生活要求的适应性反应。一些物种以明显灵活的方式展示这两种模式，但调节它们各自使用的社会因素仍然缺乏记录。我们调查了在六个自由放养的黑吼猴群（Alouattapigra）。首先，我们发现成年男性的发声很少与其他呼叫者的声音重叠，而大多数成年女性的声音与其他成员的声音重叠，尤其是其他女性的声音。其次，虽然某些呼叫类型（特别是从属呼叫）通常没有重叠地发出，但咆哮（激动的大声呼叫）重叠的频率更高。第三，群际竞争中，协同重叠更加频繁。我们的研究结果支持这样的假设，即避免重叠和协调重叠是两种不同的（此处与性别相关的）声音联盟社会行为，至少对于某些非人类灵长类动物而言。现在需要更多的比较研究来进一步探索它们在这个谱系中的进化轨迹。