Reichard U
Center for Conservation Biology, Department of Biology, Mahidol University, Bangkok, Thailand.
Am J Primatol. 1998;46(1):35-62. doi: 10.1002/(SICI)1098-2345(1998)46:1<35::AID-AJP4>3.0.CO;2-W.
The sleeping habits of wild white-handed gibbons (Hylobates lar) were investigated to assess the risk of predation and predation-avoidance behavior. Sleeping sites were distributed throughout home ranges, including areas where they overlapped with neighbors, and appeared to be selected independently of habitat characteristics. Individuals did not build night nests or otherwise manipulate the vegetation around the sleeping place but slept on open branches. Group members usually slept in separate trees, and, except for females with infants, they never shared a sleeping place. Sleeping trees were entered several hours before dusk and were used for about 14-17 h. The majority of sleeping trees were used only once, and fewer were selected repeatedly by the same or other group members. Usually females with infants went into a sleeping tree first, then juveniles, and last were mostly subadult and adult males. Intragroup competition over access to a sleeping place was observed once. Average time difference between the first and last group member to enter a sleeping tree was 13 min. The sequence of departure from sleeping trees was more variable. Gibbon sleeping habits seem to primarily reflect adaptations to minimize predation risk. The predation-risk hypothesis was indirectly supported by observations of mobbing pythons, alarm calls given in response to birdes of prey flying low over the canopy, and more importantly by 1) the predominant use of large sleeping trees, which were among the tallest trees available, particularly by adult females with small infants and juveniles, 2) an unpredictable long-term pattern of reuse of sleeping places, and 3) inconspicuous presleep behavior.
对野生白掌长臂猿（白掌长臂猿属）的睡眠习惯进行了调查，以评估被捕食风险和避免被捕食的行为。睡眠地点分布在整个活动范围内，包括与邻居重叠的区域，并且似乎是独立于栖息地特征而选择的。个体不会搭建夜巢，也不会以其他方式操纵睡眠地点周围的植被，而是睡在开阔的树枝上。群体成员通常睡在不同的树上，除了带着幼崽的雌性，它们从不共享睡眠地点。在黄昏前几个小时进入睡眠树，并且使用约14 - 17小时。大多数睡眠树只被使用一次，较少被同一或其他群体成员重复选择。通常带着幼崽的雌性首先进入睡眠树，然后是幼猿，最后大多是亚成年和成年雄性。观察到一次群体内关于进入睡眠地点的竞争。第一个和最后一个群体成员进入睡眠树的平均时间差为13分钟。离开睡眠树的顺序更具变化性。长臂猿的睡眠习惯似乎主要反映了为将被捕食风险降至最低而做出的适应。通过观察对蟒蛇的围攻、对低空飞过树冠的猛禽发出的警报叫声，更重要的是通过以下几点间接支持了捕食风险假说：1）主要使用高大的睡眠树，这些树是可获得的最高的树之一，尤其是带着小幼崽的成年雌性和幼猿；2）睡眠地点不可预测的长期重复使用模式；3）不显眼的睡前行为。
