Acoustic localization at large scales: a promising method for grey wolf monitoring

Abstract

BackgroundThe grey wolf (Canis lupus) is naturally recolonizing its former habitats in Europe where it was extirpated during the previous two centuries. The management of this protected species is often controversial and its monitoring is a challenge for conservation purposes. However, this elusive carnivore can disperse over long distances in various natural contexts, making its monitoring difficult. Moreover, methods used for collecting signs of presence are usually time-consuming and/or costly. Currently, new acoustic recording tools are contributing to the development of passive acoustic methods as alternative approaches for detecting, monitoring, or identifying species that produce sounds in nature, such as the grey wolf. In the present study, we conducted field experiments to investigate the possibility of using a low-density microphone array to localize wolves at a large scale in two contrasting natural environments in north-eastern France. For scientific and social reasons, the experiments were based on a synthetic sound with similar acoustic properties to howls. This sound was broadcast at several sites. Then, localization estimates and the accuracy were calculated. Finally, linear mixed-effects models were used to identify the factors that influenced the localization accuracy.ResultsAmong 354 nocturnal broadcasts in total, 269 were recorded by at least one autonomous recorder, thereby demonstrating the potential of this tool. Besides, 59 broadcasts were recorded by at least four microphones and used for acoustic localization. The broadcast sites were localized with an overall mean accuracy of 315 ± 617 (standard deviation) m. After setting a threshold for the temporal error value associated with the estimated coordinates, some unreliable values were excluded and the mean accuracy decreased to 167 ± 308 m. The number of broadcasts recorded was higher in the lowland environment, but the localization accuracy was similar in both environments, although it varied significantly among different nights in each study area.ConclusionsOur results confirm the potential of using acoustic methods to localize wolves with high accuracy, in different natural environments and at large spatial scales. Passive acoustic methods are suitable for monitoring the dynamics of grey wolf recolonization and so, will contribute to enhance conservation and management plans.

Tracking cryptic animals using acoustic multilateration: A system for long-range wolf detection

“…Using simulated howls to estimate the accuracy of a localization system has previously had mixed results (Papin et al, 2018) with mean position errors of 315 m. One possible explanation for the improved precision and accuracy in our study is the use of frequency modulated simulated signals (police sirens), which not only more closely match the characteristics of wolf howls, but also allow for more precise measurement of the time differences between recorders than using flat single-frequency signals. For example, identifying the start of the howl as the common event between multiple recording channels can be inaccurate if more distant detectors do not pick up early low intensity howl onset.…”

“…We present here a complimentary system for studying wolves in the wild based on passive acoustic localization. The possibility of using passive acoustic localization for wolf tracking was investigated recently using simulated wolf howls (Papin et al, 2018), but ours is the first study to test this possibility with field recordings of animal vocalizations. We deployed multiple acoustic detectors in YNP over a period of two years and analyzed wolf howls and those of the related coyote Canis latrans to locate the source of the sound.…”

Acoustic localization of terrestrial wildlife: Current practices and future opportunities

“…Bioacoustic studies tended to occur over smaller areas (e.g., Fujioka, Mantani, Hiryu, Riquimaroux, & Watanabe, 2011; Patricelli, Dantzker, et al, 2008). Loud, far‐ranging animals such as wolves and orangutans were localized on arrays covering large spatial extents (e.g., Kershenbaum et al, 2019; Papin, Pichenot, Guérold, & Germain, 2018), whereas the quickly attenuating vocalizations of bats were typically localized using arrays that surveyed smaller areas (e.g., Ratcliffe, Jakobsen, Kalko, & Surlykke, 2011). Spatial scale of arrays is discussed in greater depth in Section “Placement”.…”

“…Multi‐ARU arrays had a median spacing between ARUs of about 31 m (Table ). The maximum area surveyed by any one array was 30 km 2 in a test of a system intended for localizing wolf howls (Papin et al, 2018). The area enclosed within the boundaries of the microphones is sometimes referred to as the “hull” of the array.…”

Listening and watching: Do camera traps or acoustic sensors more efficiently detect wild chimpanzees in an open habitat?

“…However, recent advances in bioacoustics have expanded the applications of acoustic sensors for terrestrial species (Blumstein et al, ; Wrege, Rowland, Keen, & Shiu, ). More recently, applications include the study of gibbons Nomascus gabbrielae (Vu & Tran, ), and wolves Canis lupus (Papin, Pichenot, Guérold, & Germain, ) among others. Both methods allow for diverse applications (Burton et al, ; Gibb, Browning, Glover‐Kapfer, & Jones, ; Sugai et al, ), ranging from revealing occurrence and occupancy (Campos‐Cerqueira & Aide, ; Rovero, Collett, Ricci, Martin, & Spitale, ), population size and density (e.g.…”