When resources are limited and defensible, inter-group encounters in animals are often of aggressive nature. Individuals can participate in inter-group encounters to defend mates, infants, and food resources, but also to attract out-group individuals for additional mating opportunities. Since inter-group conflicts have mainly been studied in group-living species, we examined the mate, infant, and food resource defense and mate attraction hypotheses in pair-living Javan gibbons (Hylobates moloch) in Gunung Halimun-Salak National Park, Indonesia. To this end, we investigated factors influencing male and female participation and outcome of encounters (i.e., win vs. lose). We observed 234 complete encounters between three habituated and five unhabituated gibbon groups over 43 months, of which 72% were aggressive. Males were the main participants and they were more likely to participate when cycling females or dependent infants were present, supporting the mate and infant defense hypotheses. Males were also more likely to participate when more fruits were available, contradicting the food resource defense hypothesis. Females participated by singing more often when they were cycling and when there were singing opponents, suggesting an advertisement function of their reproductive status through songs. The probability of winning an inter-group encounter was only higher when cycling females were present, supporting the mate defense hypothesis. The intensity of space use or aggression level had no effect on the outcome of inter-group encounters. Our results highlight that mate and infant defense are crucial for male Javan gibbons, especially in view of their pair-living system, long interbirth intervals, and slow infant development. While animal groups interact aggressively with each other to defend valuable resources, they can also interact to increase additional mating opportunities. Here, we examined male and female participation and the outcomes of inter-group encounters in a wild pair-living primate, the Javan gibbon. Crucially, we found that the presence of cycling females had a significant impact on male participation, female singing, and the outcome of encounters. Our findings suggest that Javan gibbon females may advertise their reproductive status through singing during inter-group encounters while Javan gibbon males rather participate to defend their mates and infants.

中文翻译：

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为它的价值而战：一对生活的灵长类动物爪哇长臂猿（Hylobates moloch）的群体间遭遇的参与和结果

当资源有限且可防御时，动物的群体间遭遇通常具有攻击性。个体可以参与群体间的相遇来保护配偶、婴儿和食物资源，也可以吸引群体外的个体以获得额外的交配机会。由于主要研究群居物种的群际冲突，我们研究了印度尼西亚 Gunung Halimun-Salak 国家公园成对生活的爪哇长臂猿 (Hylobates moloch) 的配偶、婴儿和食物资源防御和配偶吸引假设。为此，我们调查了影响男性和女性参与和遭遇结果（即胜利与失败）的因素。在 43 个月内，我们观察到 3 个习惯性长臂猿和 5 个不习惯性长臂猿群体之间的 234 次完全遭遇，其中 72% 是攻击性的。男性是主要参与者，当骑自行车的女性或依赖婴儿在场时，他们更有可能参与，支持配偶和婴儿防御假设。当有更多水果可用时，男性也更有可能参与，这与食物资源防御假说相矛盾。女性在骑自行车时和有唱歌对手时更频繁地唱歌参与，通过歌曲暗示其生殖状态的广告功能。只有当骑自行车的女性在场时，赢得群体间遭遇的可能性才会更高，这支持了配偶防御假说。空间使用的强度或攻击性水平对群体间遭遇的结果没有影响。我们的结果强调，配偶和婴儿的防御对雄性爪哇长臂猿至关重要，尤其是考虑到他们的双胞胎生活系统、较长的生育间隔和缓慢的婴儿发育。在动物群体之间积极互动以保护宝贵资源的同时，它们也可以互动以增加额外的交配机会。在这里，我们检查了雄性和雌性的参与以及在野生双生灵长类动物爪哇长臂猿中群体间相遇的结果。至关重要的是，我们发现骑自行车的女性的存在对男性的参与、女性的歌唱和相遇的结果有显着影响。我们的研究结果表明，爪哇长臂猿雌性可能会在群体间相遇时通过唱歌来宣传它们的生殖状态，而爪哇长臂猿雄性则更愿意参与保护它们的配偶和婴儿。在动物群体之间积极互动以保护宝贵资源的同时，它们也可以互动以增加额外的交配机会。在这里，我们检查了雄性和雌性的参与以及在野生双生灵长类动物爪哇长臂猿中群体间相遇的结果。至关重要的是，我们发现骑自行车的女性的存在对男性的参与、女性的歌唱和相遇的结果有显着影响。我们的研究结果表明，爪哇长臂猿雌性可能会在群体间相遇时通过唱歌来宣传它们的生殖状态，而爪哇长臂猿雄性则更愿意参与保护它们的配偶和婴儿。在动物群体之间积极互动以保护宝贵资源的同时，它们也可以互动以增加额外的交配机会。在这里，我们检查了雄性和雌性的参与以及在野生双生灵长类动物爪哇长臂猿中群际相遇的结果。至关重要的是，我们发现骑自行车的女性的存在对男性的参与、女性的歌唱和相遇的结果有显着影响。我们的研究结果表明，爪哇长臂猿雌性可能会在群体间相遇时通过唱歌来宣传它们的生殖状态，而爪哇长臂猿雄性则更愿意参与保护它们的配偶和婴儿。我们研究了一对野生灵长类动物爪哇长臂猿的雄性和雌性参与以及群体间相遇的结果。至关重要的是，我们发现骑自行车的女性的存在对男性的参与、女性的歌唱和相遇的结果有显着影响。我们的研究结果表明，爪哇长臂猿雌性可能会在群体间相遇时通过唱歌来宣传它们的生殖状态，而爪哇长臂猿雄性则更愿意参与保护它们的配偶和婴儿。我们研究了一对野生灵长类动物爪哇长臂猿的雄性和雌性参与以及群体间相遇的结果。至关重要的是，我们发现骑自行车的女性的存在对男性的参与、女性的歌唱和相遇的结果有显着影响。我们的研究结果表明，爪哇长臂猿雌性可能会在群体间相遇时通过唱歌来宣传它们的生殖状态，而爪哇长臂猿雄性则更愿意参与保护它们的配偶和婴儿。