Department of Anthropology, University of Zurich, 8057 Zurich, Switzerland.
School of Human Evolution and Social Change and Institute of Human Origins, Arizona State University, AZ 85281, USA.
Biol Lett. 2019 Jul 26;15(7):20190209. doi: 10.1098/rsbl.2019.0209. Epub 2019 Jul 17.
The communicative function of primates' self-directed behaviours like scratching has gained increasing attention in recent years, but their intentional use is still debated. Here, we addressed this issue by exploring the communicative function of 'loud scratches' in wild Sumatran orangutans. Building on previous studies in chimpanzees, we examined the prediction that audio-visual loud scratches are used communicatively in mother-infant travel coordination. Specifically, we examined whether individual, social and scratch features affected the use of pre-move scratches, markers of intentional signal use and approach responses. We analysed a total of 1457 scratching bouts, produced by 17 individuals (including four mothers and their dependent offspring) observed during 305 h of focal follows. Overall, we found that scratching bouts preceded departure mainly when these were produced by mothers and showed features of exaggeration. If the scratching individual was a mother, associates were more likely to be visually attentive during pre-move scratches than in other contexts. Approach or follow responses to scratches by individuals in association were predicted by context, the relationship with the scratcher (i.e. offspring) and the associate's attentional state. We conclude that orangutan mothers use loud scratches as communicative strategies to coordinate joint travel with their infants.
近年来，灵长类动物自我指向行为（如抓挠）的交际功能受到了越来越多的关注，但它们的意图使用仍存在争议。在这里，我们通过探索野生苏门答腊猩猩的“大声抓挠”的交际功能来解决这个问题。基于黑猩猩的先前研究，我们检验了音频视觉大声抓挠在母婴旅行协调中的交际作用的预测。具体来说，我们研究了个体、社会和抓挠特征是否影响预移动抓挠、有意信号使用和接近反应的使用。我们分析了总共 1457 次抓挠，这些抓挠由 17 只个体（包括 4 只母亲及其依赖的后代）在 305 小时的焦点跟踪中产生。总体而言，我们发现，当抓挠是由母亲发出的，并且具有夸张特征时，抓挠通常会在离开前发出。如果抓挠的个体是母亲，那么在预移动抓挠期间，同伴更有可能比在其他情况下更注意视觉信息。对与抓挠者（即后代）相关联的个体的接近或跟随反应，由背景、与抓挠者的关系（即后代）以及同伴的注意状态来预测。我们的结论是，猩猩母亲使用大声抓挠作为交际策略，与它们的幼崽协调联合旅行。
