Sleeping tree selection and related behaviours of a family group and a solitary female siamang ( Symphalangus syndactylus ) were investigated over a 5-month period in northern Sumatra, Indonesia. We performed all day follows, sleeping tree surveys and forest plot enumerations in the field. We tested whether: (1) physical characteristics of sleeping trees and the surrounding trees, together with siamang behaviours, supported selection based on predation risk and access requirements; (2) the preferences of a solitary siamang were similar to those of a family group; and (3) sleeping site locations within home ranges were indicative of home range defence, scramble competition with other groups or other species, or food requirements. Our data showed that (1) sleeping trees were tall, emergent trees with some, albeit low, connectivity to the neighbouring canopy, and that they were surrounded by other tall trees. Siamangs showed early entry into and departure from sleeping trees, and slept at the ends of branches. These results indicate that the siamangs’ choice of sleeping trees and related behaviours were strongly driven by predator avoidance. The observed regular reuse of sleeping sites, however, did not support anti-predation theory. (2) The solitary female displayed selection criteria for sleeping trees that were similar to those of the family group, but she slept more frequently in smaller trees than the latter. (3) Siamangs selected sleeping trees to avoid neighbouring groups, monopolise resources (competition), and to be near their last feeding tree. Our findings indicate selectivity in the siamangs’ use of sleeping trees, with only a few trees in the study site being used for this purpose. Any reduction in the availability of such trees might make otherwise suitable habitat unsuitable for these highly arboreal small apes.

中文翻译：

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印度尼西亚苏门答腊热带低地雨林中 siamang（Symphalangus syndactylus）的睡眠树和睡眠相关行为

在印度尼西亚苏门答腊北部的 5 个月内调查了一个家庭群体和一只独居雌性 siamang ( Symphalangus syndactylus ) 的睡眠树选择和相关行为。我们进行了一整天的跟踪，在野外进行树木调查和林地调查。我们测试了：（1）睡眠树木和周围树木的物理特征，以及 siamang 行为，是否支持基于捕食风险和访问要求的选择；(2) 独居族群的喜好与家族族群的喜好相似；(3) 栖息地内的栖息地位置表明栖息地防御、与其他群体或其他物种的争夺竞争或食物需求。我们的数据显示 (1) 沉睡的树木是高大的、挺拔的树木，有些树木虽然矮小，连接到邻近的树冠，并且它们被其他高大的树木包围。Siamangs表现出早进早出睡眠树，睡在树枝的末端。这些结果表明，siamangs 对睡眠树木的选择和相关行为受到捕食者回避的强烈驱动。然而，观察到的睡眠场所的定期重复使用并不支持反捕食理论。(2) 独居雌性对睡眠树的选择标准与家族相似，但比后者更频繁地睡在较小的树上。(3) Siamangs 选择沉睡的树，以避免相邻的群体，垄断资源（竞争），并靠近他们最后的觅食树。我们的发现表明暹罗人对沉睡树的使用具有选择性，研究地点只有几棵树用于此目的。此类树木可用性的任何减少都可能使原本合适的栖息地不适合这些高度树栖的小型猿类。