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