Testosterone is known to be essential for sexual maturation as well as for the display of behavioural traits linked to reproduction. At the same time, external factors such as the presence of receptive females may affect testosterone levels, stressing the hormone’s substantial role in reproductive success. It is therefore of major interest to investigate the links between androgens, behaviour and the social environment especially in species that rely on a resilient reproduction rate, such as the white rhinoceros (WR). We collected faecal samples of 16 male Southern WR (Ceratotherium simum simum) aged between 1 and 44 years from 11 European zoos. Audio and video recordings were simultaneously taken from five of the study males that were sexually mature and had direct contact with receptive females. Our results showed a positive correlation of faecal testosterone metabolite (fTM) concentrations and progressing age up until adulthood followed by a decline in older males. While previous reproductive success did not show any effect, the access to receptive females resulted in higher fTM levels. Thereby, fTM concentrations remained at the same level regardless of the receptivity phase, while social cohesion with respective females, affiliative behaviour as well as call rates of Pant and Hiss distinctly peaked during the receptive compared to the non-receptive periods. Conclusively, the immediate presence of receptive females poses a female effect that enhances the overall androgen levels in males and, thus, might facilitate their reproductive success. However, androgens do not seem to be the main driver of behavioural changes during courtship or mating. By linking endocrinological and socio-behavioural factors, we were able to provide an applicable basis for non-invasive monitoring of reproductive behaviour in male WR in captivity, thereby contributing to deeper understanding of potential reproduction impairments in a species whose population in captivity remains not fully self-sustaining.

中文翻译：

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雌性效应——雌性接受能力如何影响雄性南方白犀牛的粪便睾酮代谢物水平、社会积极行为和发声

众所周知，睾酮对于性成熟以及与生殖相关的行为特征的展示至关重要。同时，外在因素，如接受雌性的存在可能会影响睾酮水平，强调激素在生殖成功中的重要作用。因此，研究雄激素、行为和社会环境之间的联系具有重要意义，特别是在依赖弹性繁殖率的物种中，例如白犀牛 (WR)。我们从 11 个欧洲动物园收集了 16 头年龄在 1 至 44 岁之间的雄性南方 WR (Ceratotherium simum simum) 的粪便样本。同时从五名性成熟并与接受性女性直接接触的研究男性中获取音频和视频记录。我们的研究结果显示，粪便睾酮代谢物 (fTM) 浓度与成年男性的年龄增长呈正相关，随后老年男性下降。虽然之前的繁殖成功没有显示出任何影响，但接触到接受性的雌性会导致更高的 fTM 水平。因此，无论接受期如何，fTM 浓度都保持在同一水平，而与非接受期相比，接受期与各自女性的社会凝聚力、亲和行为以及 Pant 和 Hiss 的呼叫率明显达到峰值。最终，接受雌性的立即存在会产生一种雌性效应，从而提高雄性的整体雄激素水平，因此可能会促进它们的繁殖成功。然而，雄激素似乎不是求偶或交配期间行为变化的主要驱动力。通过将内分泌和社会行为因素联系起来，我们能够为圈养雄性 WR 的生殖行为的非侵入性监测提供适用的基础，从而有助于更深入地了解圈养种群仍未完全恢复的物种的潜在生殖障碍自我维持。