School of Natural Sciences and Psychology, Liverpool John Moores University, Liverpool, United Kingdom.
Greater Mahale Ecosystem Research and Conservation (Project), Tanzania.
Am J Phys Anthropol. 2018 Jul;166(3):530-540. doi: 10.1002/ajpa.23609.
Much is known about chimpanzee diurnal call patterns, but far less about night-time vocal behavior. I deployed a passive acoustic monitoring (PAM) system to assess 24-hr temporal acoustic activity of wild, unhabituated chimpanzees that live in a woodland mosaic habitat similar to hominin landscapes from the Plio-Pleistocene. A primary aim was to apply findings to our broader understanding to chimpanzee 24-hr activity patterns, and what implications this may have for reconstructing hominin adaptations to similarly hot, dry, and open landscapes. I also tested whether chimpanzees conform to the acoustic adaptation hypothesis, and produce loud calls during periods of optimal sound transmission.
Nine custom-made solar-powered acoustic transmission units (SPATUs) recorded continuously for 250 days over 11 months in the Issa Valley, western Tanzania. I complemented acoustic data with environmental data from weather stations as well as behavioral data collected on chimpanzee nest group sizes to assess the relationship between party size and calling.
Chimpanzees called at all hours of the day and night in both wet and dry seasons, and night and day calls exhibited parallel rates/month, although twilight calls were produced significantly more in the dry, compared to the wet season. Calls were more likely during warmer temperatures and lower humidity. Call rate was positively associated with (nest) party size and counter-calls exhibited no temporal variation in their origins (similar vs. adjacent valleys).
Chimpanzees were acoustically active throughout the 24-hr cycle, although at low rates compared to diurnal activity, revealing night-time activity in an ape otherwise described as diurnal. Chimpanzee loud calls partially, and weakly, conformed to the acoustic adaptation hypothesis and likely responded to social, rather than environmental factors. Call rates accurately reflect grouping patterns and PAM is demonstrated to be an effective means of remotely assessing activity, especially at times and from places that are difficult to access for researchers.
关于黑猩猩的日间叫声模式已经了解很多，但关于夜间的发声行为却知之甚少。我使用被动声学监测（PAM）系统评估了生活在类似于更新世人类景观的林地镶嵌栖息地中的野生、未驯化黑猩猩的 24 小时时间声学活动。主要目的是将研究结果应用于我们对黑猩猩 24 小时活动模式的更广泛理解，以及这可能对重建人类适应类似炎热、干燥和开放景观的方式产生的影响。我还测试了黑猩猩是否符合声学适应假说，即在最佳声音传输时段发出响亮的叫声。
在坦桑尼亚西部伊萨谷的 11 个月中，9 个定制的太阳能供电声学传输单元（SPATU）连续记录了 250 天。我将声学数据与气象站的环境数据以及在黑猩猩巢群大小上收集的行为数据相结合，以评估群体大小与叫声之间的关系。
黑猩猩在干湿两季的白天和夜晚的所有时间都在鸣叫，夜间和白天的叫声每月的发生率相同，尽管在干燥季节，黄昏时的叫声明显多于潮湿季节。叫声更可能在温度较高和湿度较低时出现。叫声率与（巢）群体大小呈正相关，而回应叫声的起源在时间上没有变化（相似的山谷与相邻的山谷）。
黑猩猩在 24 小时周期内一直保持声学活跃，尽管与日间活动相比，其活跃度较低，但这揭示了原本被描述为日间活动的猿类在夜间也有活动。黑猩猩的大声叫声部分且微弱地符合声学适应假说，可能是对社会因素而非环境因素的反应。叫声率准确反映了分组模式，并且 PAM 被证明是一种有效的远程评估活动的手段，尤其是在研究人员难以进入的时间和地点。
