Acoustic localisation of wildlife with low-cost equipment: lower sensitivity, but no loss of precision

Abstract

Context. Synchronised acoustic recorders can be used as a non-invasive tool to detect and localise sounds of interest including vocal wildlife and anthropogenic sounds. Due to the high cost of commercial synchronised recorders, acoustic localisation has typically been restricted to small or well-funded surveys. Recently, low-cost acoustic recorders have been developed, but their efficacy has yet to be compared to higher specification recorders.Aims. This study aimed to compare the efficacy of a newly developed low-cost recorder, the CARACAL, with an established, high-end recorder, the Wildlife Acoustics Song Meter (SM).Methods. We deployed four recorders of each type in a paired set-up across five nights in Wisconsin, USA. We manually identified domestic dog (Canis familiaris), grey wolf (Canis lupus), coyote (Canis latrans), and barred owl (Strix varia) calls on the recordings then compared the ability of each recorder type to detect and localise the vocalising animals.Key results. The CARACALs were less sensitive detecting only 47.5% of wolf, 55% of coyote, 65% of barred owl, and 82.5% of dog vocalisations that were detected on the paired SMs. However, when the same vocalisations were detected on both recorders, localisation was comparable with no significant difference in the precision or maximum detection ranges. Conclusions.Low-cost recording equipment can be used effectively for acoustic localisation of both wild and domestic animals. However, the lower sensitivity of the CARACALs means that a denser network of these recorders would be needed to achieve the same efficacy as the SMs. Deploying a greater number of cheaper recorders increases the labour time in the field and the amount of data to process and store. Thus, there is trade-off between cost and time to be considered. Implications.The ability to use low-cost recorders for acoustic localisation provides new avenues for tracking, managing and researching a wide range of wildlife species. At present, we suggest that CARACALs are more suited to monitoring species that have small home ranges and high amplitude vocalisations, and when a large time investment for in situ equipment checks and data processing is feasible.

Combining acoustic localisation and high-resolution land cover classification to study predator vocalisation behaviour

“…When up-scaled further, entire populations across large regions could be studied. With further development of low-cost acoustic devices (Smith et al 2022) and automated acoustic data processing using artificial intelligence (Christin et al 2019;Dufourq et al 2021), such large-scale applications of acoustic monitoring are becoming increasingly feasible.…”

“…(2019) and Smith et al . (2022). We analysed only recordings taken between 1700 and 0600 hours to speed up data processing, because coyotes and wolves are more likely to be active at night (Harrington and Mech 1982; Okoniewski and Chambers 1984).…”

“…The location of vocalising animals can be calculated based on the arrival times of the sound's acoustic waves at three or more synchronised devices set at distant points, a process known as acoustic localisation (Wilson et al 2014;Kershenbaum et al 2019). It has been applied to biological contexts, particularly for monitoring marine mammals (Zimmer 2011), birds (Frommolt and Tauchert 2014), and (recently) canids (Papin et al 2018;Kershenbaum et al 2019;O'Gara et al 2020;Smith et al 2022). Although localisation requires several recorders to permit the detection of signals from multiple angles, it can provide unique insight into the behaviour of species in situ without impacting their behaviour.…”

A ready-to use workflow for automated, sound-based bird identification and localization

“…In recent years, various studies used microphone arrays to localize individuals of single species (Wilson & Bayne, 2018, Avots et al, 2022 or limited numbers of species (Smith et al, 2022). They used expensive technology (beyond 1000 $ per ARU; Avots et al, 2022) in combination with manual species identification (Smith et al, 2022), and laborious manual detection of time delays (Wilson & Bayne, 2018.…”

Localizing wild chimpanzees with passive acoustics

“…There are commercial options available for such work (namely, Song Meters (Wildlife Acoustics, 2022)), but these systems are either expensive or lack the flexibility in design necessary for adapting them to novel applications. Other and more affordable options are being introduced regularly, for example, CARACAL (Wijers et al, 2019), but offer a lower sensitivity (i.e., detecting fewer calls) and thus require more acoustic sensors and consequently a higher quantity of data to analyze (Smith et al, 2021).…”