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Is a low-cost recorder going to open new doors to studies with a smaller budget?

Acoustic recorders are an effective non-invasive tool to study sounds of interest. They were originally developed to study marine ecosystems, but have been recently used in terrestrial ecosystems as well. Especially in documenting biodiversity, studying animal behavior and other wildlife. However, their usage can be found in localizing poachers and logging illegal activity via sounds they give out as well. Until now, studies have been using high-end acoustic recorders, called Wildlife acoustics Song meter (SMs), but Loretta Schindlerová from the Faculty of Science, Charles University, was part of a team, that compared this high-end acoustic recorder with a newly developed low-cost recorder (CARACAL) and focused on the differences. If they were minor, being able to use the cheaper recorder without loss of precision in the obtained data would open many new doors, not only in research

The advantage of acoustic recorders is, that the animals don’t have to be caught nor manipulated and the recorded information is about many individuals of multiple species if needed. When monitoring animals, researchers usually need to know their precise location, which is quite problematic in acoustic surveys. The solution to that is, that three or more recorders are placed not far from each other and the localization of a sound is calculated from the time difference of arrival of the sound to these recorders. This however requires the recorders to have precisely synchronized clocks, which is usually achieved by GPS receivers. 

SMs and CARACALs, were placed in a generally flat region in Wisconsin, USA, where domestic dogs, grey wolves, coyotes, and barred owls were monitored, and the effectiveness of the recorders was determined. The focus was on detection ability and range (if the sound is detected by the recorder and from how far) and acoustic localization (if and how precisely is the recorder able to detect where the sound comes from).

CARACAL recorder in action. Author: Bethany Smith

Since SMs are high-end recorders, data were analyzed from them first. Afterwards, data from CARACAL, the low-cost recorder, were obtained and compared with SMs. The detection ability of the CARACAL recorder was defined as a percentage of vocalizations corresponding with data from SMs, them being considered the gold standard.

It was found, that the low-cost recorder detected fewer vocalizations when compared to the high-end one. Also, recordings of wolves weren’t sufficient enough and they were excluded from the analysis. The reason for the lack of data about wolves might be that they use long-distance communication and the recorders can’t detect sounds coming from so far away. In contrast, domestic dogs provided the highest number of detected vocalizations, probably because the recorders were placed near a farm, where dogs live. 

Spectrogram comparison of wolves (a), coyotes (b), dogs (c) and owls (d). Source: original study.

In contrast to detection ability, which is different between CARACAL and SM recorders, localization precision was not significantly different between them. Therefore, vocal species can be studied with this recorder, but it has to be kept in mind that if a studied species uses long-distance communication, its vocalizations might be completely missed with the CARACAL recorder and the obtained data would be deceptive. Moreover, habitat type plays a role in data perception as well. Sound travels worse in a dissected landscape and the CARACAL recorder might not be the best option in such a place.

All in all, the low-cost CARACAL recorder is good at localizing perceived sounds, but their number doesn’t correspond with reality, since the detection ability is quite small. However, that doesn’t degrade the recorder as this problem can be solved by using more recorders or having a smaller study area. CARACAL recorders, as well as SM recorders, are suitable for wildlife studies, the researchers just need to consider all the factors when choosing the technology to make the data reliable.

Smith, B., Root-Gutteridge, H., Butkiewicz, H., Dassow, A., Fontaine, A., Markham, A., Owens, J., et al. (2022). Acoustic localisation of wildlife with low-cost equipment: Lower sensitivity, but no loss of precision. Wildlife Research https://doi.org/10.1071/WR21089

Eliška Leštinová


Published: Dec 05, 2022 07:50 AM

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