Spatial behavior in rehabilitated orangutans in Sumatra: Where do they go?

Wildlife restoration is one of the key components of conservation strategies, and this includes the rehabilitation and release of animals confiscated from wildlife traffickers. When primates are re-introduced, most individuals need a pre-release training to acquire the skills needed to survive in the wild. Pre-release training may either negatively or positively affect primate post-release behavior and survival. Post-release behavior, however, has rarely been monitored even though it is the only means to assess the survival of released individuals. Here, we present a thorough analysis of data from a 3-year radio tracking study on 32 orangutans (Pongo abelii) released in Sumatra after their rehabilitation. We investigated whether and how the age at release, the duration of the pre-release rehabilitation and training, and the release location affected the post-release individual spatial behavior. Orangutans released at older age exhibited post-release habitat selection patterns that were more comparable to that shown by wild conspecifics, i.e., they chose areas closer to rivers and at lower elevations (150–250 meters a.s.l.) where previous research had documented greater food availability. In contrast, individuals released at younger age showed a stronger spatial dependency on the rehabilitation station and exhibited disrupted habitat selection patterns; although after several months after the release all individuals tended to decrease their spatial reliance on the rehabilitation facility. This study indicates that the rehabilitation of individuals for a longer period and their release further from the rehabilitation station have facilitated the subsequent development of more natural spatial behavior, i.e. driven by food availability rather than by the dependence on care-giving human facility. Our study provides indications on how to improve the rehabilitation and release of confiscated orangutans, highlighting the importance of the age at release, the length of the rehabilitation program, and the location of the release site.

野生动物恢复是保护策略的核心组成部分之一，其中涵盖对从野生动物走私者手中查获的动物实施康复与放归工作。针对灵长类动物的放归行动而言，多数个体需接受放归前训练，以掌握野外生存必需的技能。放归前训练可能对灵长类的放归后行为与存活状况产生正向或负向影响。然而，尽管放归后行为是评估放归个体存活情况的唯一手段，相关监测工作却鲜有开展。
本研究对一项为期3年的无线电追踪研究数据进行了全面分析，该研究针对在苏门答腊地区放归康复后的32只苏门答腊红毛猩猩（Pongo abelii）展开。我们探究了放归年龄、放前康复与训练时长，以及放归地点，是否以及如何影响个体的放归后空间行为。
研究结果显示，较晚放归的个体，其放归后的生境选择模式与野生同种个体更为相似——即它们会选择距离河流更近、海拔更低（150–250米）的区域，过往研究已证实该区域的食物可获得性更高。与之相反，较早放归的幼年个体则对康复站表现出更强的空间依赖性，生境选择模式也更为紊乱；不过在放归数月后，所有个体对康复设施的空间依赖程度均呈现下降趋势。
本研究表明，延长个体的康复周期，并将其放归至距离康复站更远的区域，有助于其后续形成更符合自然规律的空间行为模式——即行为驱动因素转为食物可获得性，而非依赖人类提供照料的设施。
本研究为如何优化查获红毛猩猩的康复与放归流程提供了科学参考，同时强调了放归年龄、康复项目时长以及放归地点的重要性。