Abstract
Acoustic sensors are increasingly being used in ecological and conservation research, but the choice of sensor can be fraught with trade-offs. In this work we assess the performance of the Raspberry Shake and Boom (RS&B) sensor package for detecting and monitoring African elephants (Loxodonta africana). This is the first documented test of this particular unit for recording animal behavior; the unit was originally designed for detecting tectonic earthquakes and low frequency (<50 Hz) atmospheric acoustics. During a four day deployment in South Africa we tested five RS&B units for recording acoustic and seismic vocalizations generated by a group of African elephants. Our results highlight a varied degree of success in detecting the signals of interest. The acoustic microphone recorded fundamental frequencies of low-frequency (<50 Hz) harmonic vocalizations that were not clearly recorded by more sensitive instruments, but was not able to record higher frequency harmonics due to the low sampling rate (100 Hz). The geophone was not able to consistently record clear seismic waves generated by vocalizations but was able to record higher harmonics. In addition, seismic signals were detected from footsteps of elephants at <50 m distance. We conclude that the RS&B unit currently shows limited potential as a monitoring tool for African elephants and we propose several future directions and deployment strategies to improve the sensitivity of the sensor package.
Highlights
Acoustics are an important component of many habitats and in-situ sound recordings offer potentially rich information about the abundance, distribution, and behavior of vocalizing animals in the target area
We include a section detailing examples of non-elephant related seismic and acoustic signals, and how these signals were used to assess the performance of the Raspberry Shake and Boom (RS&B) unit
In the acoustic spectrogram recorded by the RS&B unit at station P5, multiple vocalizations can be seen in Reunion 2 from one or more individual elephants with fundamental frequencies modulated at 19–25 Hz
Summary
Acoustics are an important component of many habitats and in-situ sound recordings offer potentially rich information about the abundance, distribution, and behavior of vocalizing animals in the target area. Cost-effective and scalable acoustic sensors are being increasingly used in ecological research and conservation efforts for monitoring animals (Blumstein et al, 2011; Browning et al, 2017) Results from these studies are providing new insights into animal acoustic signal features (e.g., Stoeger and Baotic, 2016), communication processes within social groups (e.g., Poole et al, 1988), seasonal variability in acoustic behaviors, and spatio-temporal variability of acoustic habitats in which the animals reside (e.g., Thompson et al, 2010a). Elephants remain at risk due to poaching, habitat loss, and human-elephant conflict arising from damaged crops and buildings, along with infrequent human fatalities (DouglasHamilton, 2008; Zeppelzauer et al, 2015)
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