Agonistic intergroup interactions can cause individual costs such as physical injuries, increased physiological stress, and disrupted intragroup social relationships. Therefore, individuals should employ behavioral strategies to minimize the cost associated with aggressive intergroup encounters (IGEs). We investigated the behavioral strategies of territorial, pair-living Javan gibbons ( Hylobates moloch ) in response to intergroup aggression, including 1) changes in activity budgets, 2) affiliative behaviors within pairs, and 3) potential intergroup avoidance strategies, such as sleeping tree selection. We observed 129 encounters in three habituated gibbon groups surrounded by four unhabituated groups in Gunung Halimun-Salak National Park, Java, from 2014 to 2016. Overall, gibbons significantly altered their activity budgets during IGEs: they foraged less and were less active than when there was no encounter. We also found a decrease in grooming within pairs following IGEs compared to a matched-control period. However, we did not find any effects of the intensity of aggression, outcome, length of, or female participation in IGEs on grooming within pairs in the hour after an encounter. Male gibbons slept farther away from the IGE location after aggressive IGEs than after neutral encounters. Our results suggest that not only primates living in large groups but also primates living in small groups, such as Javan gibbons, may develop behavioral strategies to deal with direct (during encounters), immediate (within 1 h after encounters), and possibly longer (at the end of a day with encounters) effects of intergroup interactions.

中文翻译：

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群际相互作用对爪哇长臂猿（Hylobates moloch）群内行为变化的影响

激烈的群体间互动会导致个人成本，例如身体伤害、生理压力增加和群体内社会关系的破坏。因此，个人应该采用行为策略来最小化与激进的群际遭遇 (IGE) 相关的成本。我们调查了领土、成对生活的爪哇长臂猿 (Hylobates moloch) 响应群际攻击的行为策略，包括 1) 活动预算的变化，2) 成对内的从属行为，以及 3) 潜在的群际回避策略，例如睡眠树选择。从 2014 年到 2016 年，我们在爪哇哈利蒙-萨拉克国家公园的三个习惯性长臂猿群中观察到了 129 次遭遇，周围是四个无人居住的群。总的来说，长臂猿在 IGE 期间显着改变了它们的活动预算：与没有遭遇时相比，它们觅食更少，也更不活跃。我们还发现，与匹配的对照期相比，IGE 后成对的梳理减少了。然而，我们没有发现攻击强度、结果、持续时间或女性参与 IGE 对相遇后一小时内成对梳理的任何影响。与中性遭遇相比，雄性长臂猿在攻击性 IGE 后睡得离 IGE 位置更远。我们的结果表明，不仅生活在大群体中的灵长类动物，而且生活在小群体中的灵长类动物，如爪哇长臂猿，可能会发展出行为策略来应对直接（在遭遇期间）、立即（在遭遇后 1 小时内）和可能更长时间（在一天结束时遇到）群际互动的影响。