Why do elephants use seismic communication?

值得注意的是，大象交流的一种方法是通过地面振动或地震振动。我们知道，大象会产生微小的地震，并对此做出反应，通过被称为“隆隆声”的发声在彼此之间传递信息，这种声音同时会产生声学振动。然而，缺乏这些神秘的地震信号在自然环境中的生物学作用的证据。研究它们的生物学作用对于了解濒危大象可能会受到土地利用变化的影响很重要，包括基础设施发展导致的人为地震噪声增加。关于大象地震振动的生物学作用，我们有两个假设。首先，地震信号可以实现千米级的远距离通信，超出了空气传播的声音、气味或视觉所能提供的范围。对这一点的支持是基于理论和轶事证据，例如，理论上的振动比空气体积在地面上传播得更远。其次，地震振动可以作为声学信号的“后备”，以促进信息在任何空间尺度的不同环境中的传输。这得到了动物通讯理论和建模工作的支持，这些工作表明，地震和声学成分受到不同环境因素的影响，如风或地质。为了解决这个难题，我们将窃听大象隆隆声产生的地震和声学信号。这使我们能够了解振动信号在传播过程中的信息含量是如何变化的，特别是地质、噪声、风向等环境因素的不同影响，并与理论进行比较。我们的第二种方法将测试大象对地震振动的反应，无论是由大象自己产生的，还是通过允许我们操纵信息内容的回放实验。通过操纵声振动和地震振动的位置和噪声含量，我们可以近距离检验这两种振动的信息和噪声的相对重要性，结合这一点，这将为验证我们的两个假设提供证据。特别是，地震振动是否对大象的交流具有生物学作用，取决于传播距离和/或环境因素。如果两者都不是，这支持地震和声波振动形成一种通信模式，这对于理解振动通信系统的演变是重要的。我们的目标是了解大象为什么使用地震振动进行交流。除了功能上的重要性外，了解大象使用地震信号的目的将为在自然和圈养环境下保护和管理大象提供决策依据，包括人为噪音给大象带来的挑战。通过这项研究，我们还将开发新的方法，通过窃听大象隆隆发声的声学成分来实时远程监控大象，这将有助于未来大象的保护。

Remarkably, one method through which elephants communicate is via ground-based, or seismic vibrations. We know that elephants generate, and respond to, mini-earthquakes to transfer information between each other using vocalisations known as 'rumbles' that concurrently generate an acoustic vibration. Yet evidence for the biological role of these enigmatic seismic signals in the natural environment is lacking. Investigating their biological role is important for understanding how endangered elephants might be affected by changes in land-use, including increasing anthropogenic seismic noise due to infrastructure development. We have two hypotheses for the biological roles of seismic vibrations for elephants. Firstly, seismic signals could enable long-distance communication at the kilometre scale, beyond what air-borne sound, smell or sight could offer. Support for this is based on theory and anecdotal evidence, for example vibrations in theory propagate further through the surface of the ground compared to the volume of air. Secondly, seismic vibrations could act as a 'back-up' for acoustic signals to promote transfer of information over variable environments at any spatial scale. This is supported by animal communication theory and modelling work, which show that seismic and acoustic components are influenced by different environmental factors such as wind or geology. To solve this puzzle, we will eavesdrop on the seismic and acoustic signals generated by elephant rumbles. This allows us to understand how information content of vibrational signals changes during propagation, specifically the different influences of environmental factors such as geology, noise, wind direction, and compare to theory. Our second approach will test how elephants respond to seismic vibrations, both when generated by the elephants themselves and via playback experiments that allow us to manipulate the information content. By manipulating the position and noise content of acoustic and seismic vibrations, we can test for the relative importance of information and noise of these two vibration types at close range.Combined, this will provide evidence to test our two hypotheses. Specially, whether seismic vibrations have biological roles for elephant communication that are dependent on propagation distance and/or environmental factors. If neither is the case, this supports that seismic and acoustic vibrations form one communication mode, which is important for understanding the evolution of vibration communication systems. Our goal is to understand why elephants use seismic vibrations for communication. In addition to its functional importance, understanding what elephants use seismic signals for will inform decisions about elephant conservation and management in natural and captive contexts, including the challenges imposed on elephants by anthropogenic noise. Through this study, we will also develop novel methods to monitor elephants remotely in real-time by eavesdropping on the acoustic component of their rumble vocalisations, which can aid elephant conservation in the future.