The number of males per group varies substantially in group-living primates, both between and within species. In blue monkeys (Cercopithecus mitis), males may temporarily join groups during annual mating seasons when sexually receptive females are present. A likely determinant of the number of males per group is female group size (the number of adult females in a group). To clarify the role of female group size in driving variation in the number of males per group, we expanded on earlier observations of a wild population in the Kakamega Forest, Kenya with a larger sample of groups that varied fivefold in female group size. We found considerable flexibility in social organization, with groups experiencing multimale episodes both during and outside mating seasons, some persisting over multiyear periods. The dichotomy between single- and multimale mating seasons was less distinct than previously reported, suggesting greater variation in multimale states. Across 65 group-specific conception periods, female group size strongly influenced how often multiple sexually active females and multiple males were present in a group. The number of sexually active females present on a given day related closely to the number of males in the group that same day, especially during conception periods. Results suggest that males join and remain in larger groups where mating opportunities are greater and costs of joining or staying may be lower than in smaller groups. This longitudinal study highlights intraspecific social variation within and across groups while confirming that female group size influences the number of males.

中文翻译：

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雌性群体规模对蓝猴（Cercopithecus mitis）群体中雄性数量的影响

在群体生活的灵长类动物中，每组雄性的数量在物种之间和物种内都有很大差异。在蓝猴 (Cercopithecus mitis) 中，当存在性接受的雌性时，雄性可能会在一年一度的交配季节暂时加入群体。每组雄性数量的一个可能决定因素是雌性组的大小（一组中成年雌性的数量）。为了阐明雌性群体规模在推动每组雄性数量变化方面的作用，我们扩展了对肯尼亚 Kakamega 森林中野生种群的早期观察，扩大了雌性群体规模变化五倍的群体样本。我们发现社会组织具有相当大的灵活性，在交配季节期间和之外，群体都会经历多雄性事件，有些会持续多年。单雄性和多雄性交配季节之间的二分法不如之前报道的那么明显，表明多雄性状态的差异更大。在 65 个特定于群体的受孕期中，女性群体的规模强烈影响了一个群体中多个性活跃女性和多个男性出现的频率。某一天出现的性活跃女性的数量与同一天该组中男性的数量密切相关，尤其是在受孕期间。结果表明，雄性加入并留在较大的群体中，在那里交配机会更多，加入或停留的成本可能低于较小的群体。这项纵向研究强调了群体内部和群体之间的种内社会差异，同时证实了女性群体的规模会影响男性的数量。