Abstract
Seismic waves - vibrations within and along the Earth's surface - are ubiquitous sources of information. During propagation, physical factors can obscure information transfer via vibrations and influence propagation range [1]. Here, we explore how terrain type and background seismic noise influence the propagation of seismic vibrations generated by African elephants. In Kenya, we recorded the ground-based vibrations of different wild elephant behaviours, such as locomotion and infrasonic vocalisations [2], as well as natural and anthropogenic seismic noise. We employed techniques from seismology to transform the geophone recordings into source functions - the time-varying seismic signature generated at the source. We used computer modelling to constrain the propagation ranges of elephant seismic vibrations for different terrains and noise levels. Behaviours that generate a high force on a sandy terrain with low noise propagate the furthest, over the kilometre scale. Our modelling also predicts that specific elephant behaviours can be distinguished and monitored over a range of propagation distances and noise levels. We conclude that seismic cues have considerable potential for both behavioural classification and remote monitoring of wildlife. In particular, classifying the seismic signatures of specific behaviours of large mammals remotely in real time, such as elephant running, could inform on poaching threats.
Highlights
Seismic waves — vibrations within and along the Earth’s surface — are ubiquitous sources of information
We selected a few examples of each observed behaviour type, as well as car noise, which were processed to determine the corresponding source function — the force strength and pattern generated by the elephant ‘at the source’ (Supplemental Information)
Differences in elephant behaviour caused detectable changes in source function properties, which remained distinguishable during modelled seismic wave propagation up to 1000 metres regardless of the noise level and terrain type (Figure 1; Supplemental Information)
Summary
Beth Mortimer1,2,*, William Lake Rees, Paula Koelemeijer, and Tarje Nissen-Meyer. Seismic waves — vibrations within and along the Earth’s surface — are ubiquitous sources of information. We selected a few examples of each observed behaviour type, as well as car noise, which were processed to determine the corresponding source function — the force strength and pattern generated by the elephant ‘at the source’ (Supplemental Information). Differences in elephant behaviour caused detectable changes in source function properties, which remained distinguishable during modelled seismic wave propagation up to 1000 metres regardless of the noise level and terrain type (Figure 1; Supplemental Information). Seismic information transfer is affected by physical factors during propagation, such as background seismic noise and terrain type [1]. Using the set of source functions and a seismological detectability technique, we determined the maximum propagation range where cues could be detected above recorded background noise levels. For our set of source functions, vocalisation behaviours gave higher input forces and larger propagation ranges compared to locomotion (Supplemental Information).
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