Listening and watching: do camera traps or acoustic sensors more efficiently detect wild chimpanzees in an open habitat?

1. With one million animal species at risk of extinction, there is an urgent need to regularly monitor threatened species. However, in practice this is challenging, especially with wide-ranging, elusive and cryptic species or those that occur at low density. 2. Here we compare two non-invasive methods, passive acoustic monitoring (n=12) and camera trapping (n=53), to detect chimpanzees (Pan troglodytes) in a savanna-woodland mosaic habitat at the Issa Valley, Tanzania. With occupancy modelling we evaluate the efficacy of each method, using the estimated number of sampling days needed to establish chimpanzee absence with 95% probability, as our measure of efficacy. 3. Passive acoustic monitoring was more efficient than camera trapping in detecting wild chimpanzees. Detectability varied over seasons, likely due to social and ecological factors that influence party size and vocalization rate. The acoustic method can infer chimpanzee absence with less than ten days of recordings in the field during the late dry season, the period of highest detectability, which was five times faster than the visual method. 4. Synthesis and applications: Despite some technical limitations, we demonstrate that passive acoustic monitoring is a powerful tool for species monitoring. Its applicability in evaluating presence/absence, especially but not exclusively for loud call species, such as cetaceans, elephants, gibbons or chimpanzees provides a more efficient way of monitoring populations and inform conservation plans to mediate species-loss.

1. 目前有100万种动物面临灭绝风险，亟需对受威胁物种开展常态化监测。但实际操作中该工作颇具挑战，尤其是针对活动范围广、行踪隐秘、隐蔽性强或种群密度较低的物种。2. 本研究针对坦桑尼亚伊萨河谷的稀树草原-林地镶嵌生境，对比了两种非侵入式监测方法：被动声学监测（passive acoustic monitoring，n=12）与红外相机陷阱监测（camera trapping，n=53），以检测黑猩猩（Pan troglodytes）的存在。我们通过占用模型（occupancy modelling）评估两种方法的有效性，以"以95%概率确定黑猩猩未出现所需的最小采样天数"作为有效性衡量指标。3. 研究结果显示，被动声学监测在检测野生黑猩猩方面的效率高于红外相机陷阱监测。检测率随季节发生变化，这可能受影响种群社群规模与发声频率的社会及生态因素驱动。在检测率最高的晚旱季，声学监测仅需开展不到10天的野外录音即可推断黑猩猩未出现，这一速度是视觉监测方法的5倍。4. 综合与应用：尽管存在部分技术局限，本研究证实被动声学监测是一种用于物种监测的高效工具。该方法可用于评估物种存在与否，尤其（但不限于）适用于鲸类、大象、长臂猿、黑猩猩等会发出响亮叫声的物种，为种群监测提供了更高效的途径，也可为制定缓解物种灭绝的保护方案提供科学依据。