African elephants can detect water from natural and artificial sources via olfactory cues

Water is vital for mammals. Yet, as ephemeral sources can be difficult to find, it raises the question, how do mammals locate water? Elephants (Loxodonta africana) are water-dependent herbivores that possess exceptional olfactory capabilities, and it has been suggested that they may locate water via smell. However, there is no evidence to support this claim. To explore this, we performed two olfactory choice experiments with semi-tame elephants. In the first, we tested whether elephants could locate water using olfactory cues alone. For this, we used water from two natural dams and a drinking trough utilised by the elephants. Distilled water acted as a control. In the second, we explored whether elephants could detect three key volatile organic compounds (VOCs) commonly associated with water (geosmin, 2-methylisoborneol, and dimethyl sulphide). We found that the elephants could locate water olfactorily, but not the distilled water. Moreover, they were also able to detect the three VOCs associated with water. However, these VOCs were not in the odour profiles of the water sources in our experiments. This suggests that the elephants were either able to detect the unique odour profiles of the different water sources or used other VOCs that they associate with water. Ultimately, our findings indicate that elephants can locate water olfactorily at small spatial scales, but the extent to which they, and other mammals, can detect water over larger scales (e.g. km) remains unclear.

对于哺乳动物而言，水是生命必需之物。然而，临时水源往往难以寻觅，这引出了一个核心问题：哺乳动物是如何定位水源的？非洲象（Loxodonta africana）是依赖水源的草食性动物，拥有卓越的嗅觉能力，此前有研究推测它们可通过嗅觉定位水源，但尚无相关证据支撑这一论断。为探究这一问题，我们对半驯化非洲象开展了两项嗅觉选择实验。第一项实验中，我们测试大象是否仅依靠嗅觉线索即可定位水源：实验所用水源取自两处天然水坝以及大象日常使用的一处饮水槽，同时以蒸馏水作为对照组。第二项实验中，我们探究了大象能否检测到三种与水源密切相关的关键挥发性有机化合物（VOCs）：土臭素（geosmin）、2-甲基异茨醇（2-methylisoborneol）与二甲基硫醚（dimethyl sulphide）。实验结果显示，大象可通过嗅觉定位天然水源，但无法识别蒸馏水；此外，它们同样能够检测出上述三种与水源相关的VOCs。但值得注意的是，本次实验的水源气味特征谱中并未检测到上述三种VOCs。这表明，大象要么能够识别不同水源独特的气味特征谱，要么借助了其他与水源相关的VOCs来定位水源。综上，本研究结果表明，大象可在小空间尺度上通过嗅觉定位水源，但它们（以及其他哺乳动物）在大尺度范围（例如数公里级别）内检测水源的能力上限仍有待进一步阐明。