Abstract In the European captive population of western lowland gorillas (Gorilla gorilla gorilla), the harem social structure and an even sex ratio at birth result in a surplus of males and consequent management difficulties. This study seeks to assess the socialization differences between captive juvenile and adolescent male gorillas according to their fertility status (intact vs castrated) in different social compositions (familial vs bachelor groups), and to evaluate the suitability of castration as a management tool for the EEP gorilla population. We carried out social network analyses (SNA) to assess the “positive” proximity pattern of behaviour in 93 western lowland gorillas aged from 0 to 45 years old and housed in 11 social units (seven familial and four bachelor groups). We compared the data recorded for the 27 juvenile and adolescent (i.e. subadult and blackback) males included in our sample size. Although no differences were revealed between the intact juveniles and the castrated juveniles living in familial groups, our results showed that castrated adolescent individuals showed more cohesiveness within their familial group than their intact conspecifics in terms of their activity budget. They also displayed a “positive” proximity pattern of behaviour with all group members, including adults (silverback and females). Despite being significantly more isolated, the intact adolescent males living in bachelor groups do not differ from their castrated and intact counterparts of the same age class living in familial groups in terms of their strength of “positive” behaviour when close to group conspecifics. This effect highlights the social benefits of male-male interactions within gorilla species. Our results may be evidence that both of the management strategies compared here, i.e. bachelor groups and castration, could be appropriate socio-behavioural enrichments during juvenility and adolescence. These findings also highlight the need to continue investigations until the study subjects reach adulthood to validate and/or improve these tools for the welfare-compliant management of gorilla male surplus in captivity.

中文翻译：

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欧洲动物园雄性大猩猩（Gorilla gorilla gorilla）的社会亲缘关系：阉割和社会构成的后果

摘要 在西部低地大猩猩（Gorilla gorilla gorilla）的欧洲圈养种群中，后宫社会结构和出生时性别比例均匀导致雄性过剩和随之而来的管理困难。本研究旨在根据不同社会构成（家庭组与单身组）中的生育状况（完整与阉割）评估圈养的少年和青春期雄性大猩猩之间的社会化差异，并评估阉割作为 EEP 管理工具的适用性大猩猩种群。我们进行了社交网络分析 (SNA)，以评估 93 只年龄在 0 至 45 岁之间、居住在 11 个社会单位（七个家庭和四个单身汉群体）的西部低地大猩猩的“积极”接近行为模式。我们比较了 27 名青少年（i. e. 亚成年和黑背）男性包括在我们的样本量中。尽管生活在家庭群体中的完整幼鱼和被阉割的幼鱼之间没有发现差异，但我们的结果表明，就活动预算而言，被阉割的青少年个体在其家庭群体中比完整的同种个体表现出更多的凝聚力。他们还表现出与所有群体成员的“积极”接近行为模式，包括成年人（银背和雌性）。尽管明显更加孤立，但生活在单身汉群体中的完整青春期男性与生活在家庭群体中的同一年龄段的阉割和完整男性在接近群体同种物种时的“积极”行为强度方面没有区别。这种效应突出了大猩猩物种内雄性-雄性相互作用的社会效益。我们的结果可能证明这里比较的两种管理策略，即单身汉群体和阉割，可能是青少年和青春期适当的社会行为丰富。这些发现还强调了在研究对象成年之前继续调查的必要性，以验证和/或改进这些工具，以符合福利管理圈养大猩猩雄性过剩的管理。