Long-distance vocalizations form an integral part of intergroup spacing mechanisms. The decision to approach, retreat, or ignore loud calls of neighboring groups might be influenced by resource availability, location in the home range, presence of fertile females or infants, or differential resource-holding potentials, and can alter intergroup encounter rates. During a 19-mo study (February 2016–August 2017), we examined navigation decisions relative to neighbor’s loud calls for five groups of black howler monkeys (Alouatta pigra) in Palenque National Park, Mexico. Study groups encountered any of their neighbors at a mean rate of one every 3.5 days and the same neighbor at a mean rate of one every 16.7 days, which was significantly more frequent than would be expected based on a simulation model that randomized observed daily paths. These results are consistent with mutual attraction. Based on 368 travel bouts relative to nearby (50–300 m) calls of neighbors, study groups were more likely to approach calls of neighbors than would be expected by chance, but only when neighbors were close by (50–150 m), suggesting that the imminence of threat by opponents played a role. Of the nine social and ecological predictor variables considered, availability of ripe fruits and of flowers was an important driver of their navigation choices and groups were more likely to move toward neighbors’ calls when ripe fruits were scarce and to move away when flowers were abundant. We found no evidence that the presence of fertile females or unweaned infants influenced navigation decisions. Nor did relative competitive abilities of opposing groups, measured as numeric superiority in group size or male group size, affect navigation decisions. This study provides evidence that black howler monkeys incorporate information on resource availability and neighbors’ current locations into their navigation decisions and intergroup spacing patterns.

中文翻译：

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大声呼叫对黑吼猴（Alouattapigra）群际间隔机制的影响

长距离发声是群际间隔机制的一个组成部分。接近、撤退或忽略邻近群体的大声呼叫的决定可能会受到资源可用性、家庭范围内的位置、可育雌性或婴儿的存在或不同的资源持有潜力的影响，并可能改变群体间相遇率。在一项为期 19 个月的研究（2016 年 2 月至 2017 年 8 月）中，我们检查了与邻居对墨西哥帕伦克国家公园的五组黑吼猴 (Alouattapigra) 的大声呼叫相关的导航决策。研究组以每 3.5 天的平均频率遇到他们的任何邻居，每 16.7 天遇到一个相同的邻居，这比基于随机观察到的日常路径的模拟模型所预期的频率要高得多。这些结果与相互吸引是一致的。基于与附近 (50-300 m) 邻居呼叫相关的 368 次旅行，研究组比偶然预期更有可能接近邻居呼叫，但仅当邻居靠近 (50-150 m) 时，表明对手威胁的迫在眉睫发挥了作用。在考虑的九个社会和生态预测变量中，成熟水果和鲜花的可用性是他们导航选择的重要驱动因素，当成熟水果稀缺时，群体更有可能转向邻居的呼唤，而当鲜花丰富时，他们更有可能离开。我们没有发现有生育能力的雌性或未断奶婴儿影响导航决策的证据。对立群体的相对竞争能力也没有，以群体规模或男性群体规模的数字优势来衡量，影响导航决策。这项研究提供的证据表明，黑吼猴将有关资源可用性和邻居当前位置的信息纳入其导航决策和群际间距模式。