Autonomous Recorders Research Articles

Evaluation of an autonomous acoustic surveying technique for grassland bird communities in Nebraska.

Monitoring trends in wildlife communities is integral to making informed land management decisions and applying conservation strategies. Birds inhabit most niches in every environment and because of this they are widely accepted as an indicator species for environmental health. Traditionally, point counts are the common method to survey bird populations, however, passive acoustic monitoring approaches using autonomous recording units have been shown to be cost-effective alternatives to point count surveys. Advancements in automatic acoustic classification technologies, such as BirdNET, can aid in these efforts by quickly processing large volumes of acoustic recordings to identify bird species. While the utility of BirdNET has been demonstrated in several applications, there is little understanding of its effectiveness in surveying declining grassland birds. We conducted a study to evaluate the performance of BirdNET to survey grassland bird communities in Nebraska by comparing this automated approach to point count surveys. We deployed ten autonomous recording units from March through September 2022: five recorders in row-crop fields and five recorders in perennial grassland fields. During this study period, we visited each site three times to conduct point count surveys. We compared focal grassland bird species richness between point count surveys and the autonomous recording units at two different temporal scales and at six different confidence thresholds. Total species richness (focal and non-focal) for both methods was also compared at five different confidence thresholds using species accumulation curves. The results from this study demonstrate the usefulness of BirdNET at estimating long-term grassland bird species richness at default confidence scores, however, obtaining accurate abundance estimates for uncommon bird species may require validation with traditional methods.

Using autonomous recording units for vocal individuality: insights from Barred Owl identification

Using autonomous recording units for vocal individuality: insights from Barred Owl identification

Mocking Bird ( Mimus polyglottos ) calls potentially confound acoustic indices of bird diversity and provide a potential heuristic to distinguish them.

This study explores the increasing use of autonomous recording units (ARUs) in wildlife surveys. While ARUs offer cost-effective and efficient data collection, challenges arise in analyzing large datasets and accurately assessing species abundance. Our research focuses on avian communities, emphasizing the impact of vocal mimicry by Northern Mockingbirds ( Mimus polyglottos ) on survey accuracy. Utilizing the Merlin Bird ID application, we found an average accuracy rate of ~81.3%, with mockingbirds contributing ~31% of false positive identifications. Finding potential solutions for distinguishing mimics in bioacoustic survey data is crucial for enhancing accuracy as researchers increasingly adopt this methodology in the future.

Using bioacoustics to enhance the efficiency of spotted owl surveys and facilitate forest restoration

AbstractThe California spotted owl (Strix occidentalis occidentalis) is an older‐forest associated species that resides at the center of forest management planning in the Sierra Nevada and Southern California, USA, which are experiencing increasingly large and severe wildfires and drought‐related tree mortality. We leveraged advances in passive acoustic survey technologies to develop an acoustically assisted survey design that could increase the efficiency and effectiveness of project‐level surveys for spotted owls, allowing surveys to be completed in a single year instead of in multiple years. We deployed an array of autonomous recording units (ARUs) across a landscape and identified spotted owl vocalizations in the resulting audio using BirdNET. We then evaluated spatio‐temporal patterns in spotted owl vocalizations near occupied territories and the ability of a crew naïve to the location of occupied territories to locate spotted owls based on patterns of acoustic detections. After only 3 weeks of acoustic surveys, ≥1 ARU within 750 m of all 17 occupied territories obtained spotted owl detections across ≥2 nights. When active surveys using broadcast calling were conducted near ARUs with spotted owl detections by surveyors naïve to territory occupancy status and locations, surveyors located owls in 93% to 100% of occupied territories with ≤3 surveys. To further improve the efficiency of spotted owl surveys, we developed a statistical model to identify and prioritize areas across the Sierra Nevada for different survey methods (active only, acoustically assisted, no surveys) based on the expected probability of occupancy predicted from remotely sensed measurements of tree height and historical occupancy. Depending on managers' tolerance for false negatives, this model could help identify large areas that might not benefit from surveys based on low expected occupancy probabilities and areas where acoustically assisted surveys might enhance survey effectiveness and efficiency. Collectively, these findings can help managers streamline the survey process and thus increase the pace of forest restoration while minimizing potential near‐term adverse effects on California spotted owls.

Listening Beyond the Human: The Autonomous Recording Unit and the Ethics of Sound in Biodiversity Conservation

Sound technologies and sound sensor networks play a crucial role in our understanding of biodiversity loss in conservation biology and the environmental sciences. Among these technologies, the autonomous recording unit (ARU) has been widely used for studying longitudinal biodiversity loss. This article draws on fieldwork conducted in 2016 and 2017 at a bioacoustics research laboratory to explore the significance of the ARU, developed by Wildlife Acoustics, as the central component of the research network for biodiversity conservation. While it is commonly acknowledged in Science and Technology Studies (STS) that research instruments are not neutral data collectors, this article examines how the ARU is deployed and programmed, and how it transcends the limitations of human-centered listening by (a) shifting the focus away from the perceiving human subject and (b) promoting a global ethic of response and responsibility as sound becomes more democratized in scientific practices.

Simultaneous passive acoustic monitoring uncovers evidence of potentially overlooked temporal variation in an Amazonian bird community

The vocal activity and detectability of tropical birds are subject to high levels of temporal heterogeneity, but quantifying patterns of diel and day‐to‐day variation in complex systems is challenging with traditional point count methods. As a result, research concerning stochastic temporal effects on tropical bird assemblages is limited, typically offering only broad conclusions, such as that overall activity is highest in the first few hours of the morning and some species are active at different times of the day. Passive acoustic monitoring introduces several advantages for studying temporal variation, particularly by enabling simultaneous and continuous data collection across adjacent sites. Here, we employed autonomous recording units to quantify temporal variation in bird vocal activity and observed species richness at an Amazonian reserve in Madre de Dios, Peru, a region featuring some of Earth's richest, most complex bird assemblages. We manually annotated 18 dawn hour recordings, collected simultaneously from three separate days at the same six sites, which represent various microhabitats and bird community compositions. We documented significant and consistent temporal variation in avian vocal activity levels and observed species richness within the dawn hour and across days. We found that temporal effects were stronger for vocal activity than for observed species richness and that vocal activity patterns over the course of the dawn hour varied between species. Our results indicate that overlooked temporal variation in Amazonian soundscapes may obfuscate the results of surveys that do not sufficiently account for temporal variables with simultaneous monitoring. While manual analysis of large volumes of soundscape data remains challenging, such data should be collected to supplement traditional surveys whenever possible. Rapid advances in the automated processing of acoustic data could lead to more efficient methods for reducing temporal bias and improving the calibration and accuracy of tropical bird surveys.

Software-dependent biases in the recognition of di- and tri-syllabic bird songs can create false interpretations of bird abundance and singing activity

The use of autonomous recording units (ARUs) for passive acoustic monitoring has recently gained a lot of importance. It is now widely used for scientific purposes and has been increasingly applied in the field of conservation biology. However, while ARUs may greatly increase cost-effectiveness in monitoring, they are not exempt from possible biases. In this study, we compared the performances of three different software in recognizing bi- and tri-syllabic bird songs and tested if their results varied significantly in a real setting. We focused on the interpretation of the relative abundance among habitats and the time of vocal activity, also using different numbers of training records to assess if the results of the software improved. Even with the quality measures of the recognizer being consistent with those of previously published studies, in several cases the results produced significantly different interpretations depending on the software used. While increasing the number of training records slightly improved the overlap in the estimates of activity among the different software, differences in the relative abundance of each song were present even with a fairly solid number of training records. Our results suggest that reliable biological interpretations might only be attained with a large number of training records and very high values of precision, recall, and the F-score. In fact, even with very high precision and F-scores, lower values for recall led not only to statistically significant differences, but also to different interpretations of relative abundance and time of activity between the two best-performing software. Thus, great caution must be taken in interpreting the results of bioacoustics studies that use automated recognition, and standards of minimum quality should be created for recognizers in scientific and technical studies.

Optimizing detection of the bobwhite reproduction call using passive acoustic monitoring

AbstractNorthern bobwhite (Colinus virginianus) populations have declined across much of their range. In response to these declines, wildlife biologists and managers have increased survey efforts and tried to optimize detection and capitalize on technological advances to improve population estimates and cost‐effectiveness. Our objective was to determine how environmental conditions influence detection of the reproduction call, or whistle, of masked bobwhite (C. v. ridgwayi), an endangered subspecies of northern bobwhite, using autonomous recording units (ARUs). We estimated the call intensity of the masked bobwhite reproduction call as 112 ± 0.5 decibels (mean ± SE) at 10 cm. We then broadcasted 16,284 calls during 17 trials to compare manual and automated call detection in recordings collected with ARUs. We used these data to model detectability of a bobwhite reproduction call, for when the bird is present and available, as a function of distance and weather conditions using generalized linear mixed models with trial as a random effect. Regardless of detection type, one model structure was competitive and suggested detection probability was a function of distance, wind speed, and wind direction. Detectability decreased with increased distance and wind speed and was influenced by wind direction. We demonstrate the use of our results to predict the probability of detecting a reproduction call during ARU‐based monitoring efforts. By understanding the effects of environmental factors on the detection of a bobwhite reproductive call, bobwhite surveys can be improved.

Large‐scale bioacoustic monitoring to elucidate the distribution of a non‐native katydid

Abstract For animals that produce species‐specific audible sounds, environmental recordings combined with automated acoustic monitoring software (passive acoustic monitoring [PAM]) may be an effective monitoring tool because it allows audio data from many, widely distributed autonomous recording units (ARUs) to be processed in a relatively short period of time. Males of many insect species produce loud, species‐specific mating songs, yet acoustic insects have received less attention from PAM relative to vertebrates. We evaluated the use of PAM to monitor, Roeseliana roeselii (Orthoptera, Tettigoniidae), an acoustic insect that has expanded its range to Alberta, Canada, far outside its naturalized North American range. We analysed environmental recordings from ARUs: (1) at two control sites known to be occupied by R. roeselii and (2) across Alberta established by the Alberta Biodiversity Monitoring Institute (ABMI) to search for new populations. PAM successfully detected R. roeselii at the two control sites, but not at any of the 73 ABMI sites that we analysed. Despite the failure to detect new locations of R. roeselii, our analysis of ABMI environmental recordings detected several other species of acoustic insects, including Orchelimum gladiator, Gryllus sp. and Allonemobius spp. Our results add to the growing body of work showing the feasibility of using PAM for acoustic insects. We make suggestions for how to maximize the effectiveness of this monitoring tool for the conservation and management of singing insects in North America.

Bioacoustic monitoring to determine addiction levels of primates to the human sphere: A feasibility study on Japanese macaques.

Some nonhuman primate species, whose original habitats have been reclaimed by artificial activities, have acquired boldness toward humans which is evident based on the diminished frequency of escape behaviors. Eventually, such species have become regular users of human settlements, and are referred to as "urban primates." Considering this, we developed a noninvasive technique based on bioacoustics to provide a transparent assessment of troop addiction levels in anthropogenic environments, which are determined by the dependence on agricultural crops and human living sphere for their diets and daily ranging, respectively. We attempted to quantify the addiction levels based on the boldness of troops when raiding settlements, characterized by a "landscape of fear" because of the presence of humans as predators. We hypothesized that the boldness of troops could be measured using two indices: the frequency of raiding events on settlements and the amount of time spent there. For hypothesis testing, we devised an efficient method to measure these two indices using sound cues (i.e., spontaneous calls) for tracing troop movements that are obtainable throughout the day from most primate species (e.g., contact calls). We conducted a feasibility study of this assessment procedure, targeting troops of Japanese macaques (Macaca fuscata). For this study, we collected 346 recording weeks of data using autonomous recorders from 24 troops with different addiction levels during the nonsnowy seasons. The results demonstrated that troops that reached the threshold level, at which radical interventions including mass culling of troop members is officially permitted, could be readily identified based on the following behavioral characteristics: troop members raiding settlements two or three times per week and mean time spent in settlements per raiding event exceeding 0.4 h. Thus, bioacoustic monitoring could become a valid option to ensure the objectivity of policy judgment in urban primate management.

A multi-sensor array for detecting and analyzing nocturnal avian migration.

Avian migration has fascinated humans for centuries. Insights into the lives of migrant birds are often elusive; however, recent, standalone technological innovations have revolutionized our understanding of this complex biological phenomenon. A future challenge for following these highly mobile animals is the necessity of bringing multiple technologies together to capture a more complete understanding of their movements. Here, we designed a proof-of-concept multi-sensor array consisting of two weather surveillance radars (WSRs), one local and one regional, an autonomous moon-watching sensor capable of detecting birds flying in front of the moon, and an autonomous recording unit (ARU) capable of recording avian nocturnal flight calls. We deployed this array at a field site in central Oklahoma on select nights in March, April, and May of 2021 and integrated data from this array with wind data corresponding to this site to examine the influence of wind on the movements of spring migrants aloft across these spring nights. We found that regional avian migration intensity is statistically significantly negatively correlated with wind velocity, in line with previous research. Furthermore, we found evidence suggesting that when faced with strong, southerly winds, migrants take advantage of these conditions by adjusting their flight direction by drifting. Importantly, we found that most of the migration intensities detected by the sensors were intercorrelated, except when this correlation could not be ascertained because we lacked the sample size to do so. This study demonstrates the potential for multi-sensor arrays to reveal the detailed ways in which avian migrants move in response to changing atmospheric conditions while in flight.

Evaluating factors affecting species detection using passive acoustic monitoring in neotropical forests: a playback experiment

ABSTRACT Passive acoustic monitoring (PAM) has become a popular approach for terrestrial species monitoring. Studies determining detection ranges and predictors of detection probability are needed for accurate ecological modelling based on PAM data. We conducted a playback experiment to evaluate factors affecting call detectability in a neotropical forest. We used Geoffroy´s spider monkeys as a model species and broadcast their contact calls at seven distances from autonomous recording units (ARUs) positioned at different heights, in forest patches of different ages, and controlled for climate conditions during broadcasting trials. Using GLMMs (N = 1,342 data points), we found that call detectability increased the smaller the difference between the ARU and speaker height. We further found detection range to be wider the younger a surveyed forest patch is. To test whether these effects were related to structural signal characteristics, we included vocalisations from seven sympatric species in the experiment (N = 9,394). We found peak frequency to modulate the effect of ARU height difference, and peak frequency and bandwidth to modulate the effect of forest age on call detectability. Our study sheds light on factors influencing acoustic signal detectability and emphasises the need to consider climatic and habitat variables when designing PAM programmes.

Influence of sanctuary disturbance, weather, and landscape characteristics on waterfowl harvest opportunity in western Tennessee

AbstractThe North American Waterfowl Management Plan (NAWMP) recognizes waterfowl hunters and non‐consumptive users as important stakeholders to sustain waterfowl populations through economic and political support for habitat conservation initiatives. Opportunities to shoot at and harvest ducks are key determinants of achievement‐oriented hunt satisfaction and quality. Therefore, identifying factors influencing harvest opportunity would help hunters and wildlife managers identify optimal days afield and promote hunter recruitment, retention, and reactivation (R3) efforts in support of NAWMP. Waterfowl extensively use spatial sanctuaries during hunting seasons, especially diurnally, which could limit their perceived availability to hunters. Thus, a possible management action to support R3 is allowing limited public access on sanctuaries, which could offer diverse recreational opportunities for non‐consumptive users and potentially increase harvest opportunities for hunters in traditional hunting areas if the limited disturbance caused waterfowl to leave sanctuaries. Therefore, we evaluated to what extent experimental sanctuary disturbance, landscape characteristics, and weather influenced local harvest opportunities. We conducted disturbance treatments including travel by a covered truck (i.e., truck with enclosed cab), a pedestrian on foot, and an uncovered vehicle (e.g., motor boat or all‐terrain vehicle [ATV]). To measure harvest opportunity, we used autonomous recording units (ARU) to enumerate daily shotgun volleys at a landscape‐scale across western Tennessee, USA, during 2019–2021 waterfowl hunting seasons. We identified 339,391 distinct shotgun volleys ( = 73 shotgun volleys/day/ARU). Shotgun volleys decreased 50% within 2 weeks of opening day and did not notably increase for the remainder of the hunting season. Contrary to our predictions, sanctuary disturbance decreased harvest opportunity. Specifically, the pedestrian disturbance and covered vehicle disturbance decreased daily shotgun volleys by 32% and 31%, respectively. Additionally, harvest opportunity decreased 20% with every 5‐km increase in distance from a sanctuary. Harvest opportunity increased 2% for every 1°C decrease from mean low temperatures and 9% with every 10‐hPa increase in barometric pressure from the previous day. Conversely, harvest opportunity was unaffected by changes in cloud cover, daily precipitation, waterfowl abundance, or surface water inundation. Our results suggest disturbing sanctuaries decreases harvest opportunity and, in turn, may reduce hunt quality and satisfaction. If increasing harvest opportunity is a primary management objective, we recommend limiting sanctuary disturbance to maximize local harvest opportunities. Furthermore, greater harvest opportunity nearer sanctuaries indicates that additional disturbance‐free areas may increase local harvest opportunities and hunter satisfaction.

Effects of landscape and distance in automatic audio based bird species identification.

The present work focuses on how the landscape and distance between a bird and an audio recording unit affect automatic species identification. Moreover, it is shown that automatic species identification can be improved by taking into account the effects of landscape and distance. The proposed method uses measurements of impulse responses between the sound source and the recorder. These impulse responses, characterizing the effect of a landscape, can be measured in the real environment, after which they can be convolved with any number of recorded bird sounds to modify an existing set of bird sound recordings. The method is demonstrated using autonomous recording units on an open field and in two different types of forests, varying the distance between the sound source and the recorder. Species identification accuracy improves significantly when the landscape and distance effect is taken into account when building the classification model. The method is demonstrated using bird sounds, but the approach is applicable to other animal and non-animal vocalizations as well.

The utility of coded very high frequency telemetry for monitoring reintroduced mammal populations.

Very high frequency (VHF) radio tracking technology deployed on terrestrial vertebrates has been well utilized in ecology without much evolution since the 1960s. With the advent of multi-species rewilding projects, and the new field of reintroduction biology, there has been an increase in requirements for telemetry systems to monitor survival and mortality for many animals simultaneously. Common, pulsed VHF can only monitor one individual on each radio frequency, and the number of individuals monitored is constrained by the amount of time spent on each frequency to facilitate a detection and the number of receivers. Coded VHF largely removes these constraints by using a digital code that can simultaneously monitor up to 512 individuals on a single frequency. Incorporated into an autonomous monitoring system, the coded VHF system also greatly reduces time in the field to confirm the status of individuals. Here we demonstrate the utility of coded VHF technologies applied to monitoring a reintroduced population of brush-tailed bettong (Bettongia penicillata) on the Southern Yorke Peninsula in southern Australia. A system of autonomous monitoring towers was able to monitor 28 different individuals simultaneously without having to change frequency on any of the towers. During a single 24-h period, one individual was recorded 24,078 times. Key benefits of the high detection rate and autonomous recording are, a timely response to mortalities or a predation event, the detection of nocturnal, cryptic, or burrowing species whenever they are active, and the reduced need for personnel to be in the field.

A Quantitative Evaluation of the Performance of the Low-Cost AudioMoth Acoustic Recording Unit.

The AudioMoth is a popular autonomous recording unit (ARU) that is widely used to record vocalizing species in the field. Despite its growing use, there have been few quantitative tests on the performance of this recorder. Such information is needed to design effective field surveys and to appropriately analyze recordings made by this device. Here, we report the results of two tests designed to evaluate the performance characteristics of the AudioMoth recorder. First, we performed indoor and outdoor pink noise playback experiments to evaluate how different device settings, orientations, mounting conditions, and housing options affect frequency response patterns. We found little variation in acoustic performance between devices and relatively little effect of placing recorders in a plastic bag for weather protection. The AudioMoth has a mostly flat on-axis response with a boost above 3 kHz, with a generally omnidirectional response that suffers from attenuation behind the recorder, an effect that is accentuated when it is mounted on a tree. Second, we performed battery life tests under a variety of recording frequencies, gain settings, environmental temperatures, and battery types. We found that standard alkaline batteries last for an average of 189 h at room temperature using a 32 kHz sample rate, and that lithium batteries can last for twice as long at freezing temperatures compared to alkaline batteries. This information will aid researchers in both collecting and analyzing recordings generated by the AudioMoth recorder.

Passive acoustic monitoring indicates Barred Owls are established in northern coastal California and management intervention is warranted

Abstract Barred Owls (Strix varia) have recently expanded westward from eastern North America, contributing to substantial declines in Northern Spotted Owls (Strix occidentalis caurina). Passive acoustic monitoring (PAM) represents a potentially powerful approach for tracking range expansions like the Barred Owl’s, but further methods development is needed to ensure that PAM-informed occupancy models meaningfully reflect population processes. Focusing on the leading edge of the Barred Owl range expansion in coastal California, we used a combination of PAM data, GPS-tagging, and active surveys to (1) estimate breeding home range size, (2) identify patterns of vocal activity that reflect resident occupancy, and (3) estimate resident occupancy rates. Mean breeding season home range size (452 ha) was reasonably consistent with the size of cells (400 ha) sampled with autonomous recording units (ARUs). Nevertheless, false-positive acoustic detections of Barred Owls frequently occurred within cells not containing an activity center such that site occupancy estimates derived using all detected vocalizations (0.61) were unlikely to be representative of resident occupancy. However, the proportion of survey nights with confirmed vocalizations (VN) and the number of ARUs within a sampling cell with confirmed vocalizations (VU) were indicative of Barred Owl residency. Moreover, the false positive error rate could be reduced for occupancy analyses by establishing thresholds of VN and VU to define detections, although doing so increased false negative error rates in some cases. Using different thresholds of VN and VU, we estimated resident occupancy to be 0.29–0.44, which indicates that Barred Owls have become established in the region but also that timely lethal removals could still help prevent the extirpation of Northern Spotted Owls. Our findings provide a scalable framework for monitoring Barred Owl populations throughout their expanded range and, more broadly, a basis for converting site occupancy to resident occupancy in PAM programs.

Soundscape components inform acoustic index patterns and refine estimates of bird species richness

Ecoacoustic monitoring has proliferated as autonomous recording units (ARU) have become more accessible. ARUs provide a non-invasive, passive method to assess ecosystem dynamics related to vocalizing animal behavior and human activity. With the ever-increasing volume of acoustic data, the field has grappled with summarizing ecologically meaningful patterns in recordings. Almost 70 acoustic indices have been developed that offer summarized measurements of bioacoustic activity and ecosystem conditions. However, their systematic relationships to ecologically meaningful patterns in varying sonic conditions are inconsistent and lead to non-trivial interpretations. We used an acoustic dataset of over 725,000 min of recordings across 1,195 sites in Sonoma County, California, to evaluate the relationship between 15 established acoustic indices and sonic conditions summarized using five soundscape components classified using a convolutional neural network: anthropophony (anthropogenic sounds), biophony (biotic sounds), geophony (wind and rain), quiet (lack of emergent sound), and interference (ARU feedback). We used generalized additive models to assess acoustic indices and biophony as ecoacoustic indicators of avian diversity. Models that included soundscape components explained acoustic indices with varying degrees of performance (avg. adj-R2 = 0.61 ± 0.16; n = 1,195). For example, we found the normalized difference soundscape index was the most sensitive index to biophony while being less influenced by ambient sound. However, all indices were affected by non-biotic sound sources to varying degrees. We found that biophony and acoustic indices combined were highly predictive in modeling bird species richness (deviance = 65.8%; RMSE = 3.9 species; n = 1,185 sites) for targeted, morning-only recording periods. Our analyses demonstrate the confounding effects of non-biotic soundscape components on acoustic indices, and we recommend that applications be based on anticipated sonic environments. For instance, in the presence of extensive rain and wind, we suggest using an index minimally affected by geophony. Furthermore, we provide evidence that a measure of biodiversity (bird species richness) is related to the aggregate biotic acoustic activity (biophony). This established relationship adds to recent work that identifies biophony as a reliable and generalizable ecoacoustic measure of biodiversity.

Passive acoustic survey reveals the abundance of a low-density predator and its dependency on mature forests

ContextEven though habitat use is essential information for conservation management strategies, studying it in elusive and scarce forest species has proven challenging. Passive acoustic monitoring allows collecting accurate presence-absence data even for species that typically exhibit low detectability. It further provides tools for long-term and cost-effective biodiversity monitoring, and may also be used to infer population estimates at the landscape level.ObjectivesWe aimed to demonstrate the application of passive acoustic monitoring to the problem of detecting elusive species, especially in forests, using the Eurasian pygmy owl as a model species. We explored its habitat selection, and estimated occupancy and density at the landscape level in the managed boreal forest.MethodsWe conducted a wide-scale autonomous recording units (ARUs) survey, involving 292 sites in a single season, in a study area covering approx. 370 km2 in south-western Finland. We clustered the detections into territories of males to infer population size by also taking into account the size of home ranges derived from GPS-tags data. Since we were simultaneously monitoring the occupancy of a network of nest boxes and previously estimated the abundance of natural cavities, we could also estimate the proportion of pygmy owls nesting in natural cavities.ResultsIncreasing availability of mature forests was consistently the most critical habitat variable both for calling and nesting sites, increasing occupancy probability of the pygmy owls in a landscape dominated by managed forests. The proportion of sites showing occupancy by the pygmy owls was 20.9%, corresponding to an estimate of ca. Six territorial males/100 km2.ConclusionOur results confirmed that the pygmy owl can be considered a species of mature and old forests, and we provide the first data-based estimate of the total density of territorial males of this species. Passive acoustic monitoring proved to be an efficient method in detecting the presence of pygmy owls, and may overcome weaknesses of other methods, such as nest box surveys, in order to quantify population numbers.

A wireless and battery-less implant for multimodal closed-loop neuromodulation in small animals.

Fully implantable wireless systems for the recording and modulation of neural circuits that do not require physical tethers or batteries allow for studies that demand the use of unconstrained and freely behaving animals in isolation or in social groups. Moreover, feedback-control algorithms that can be executed within such devices without the need for remote computing eliminate virtual tethers and any associated latencies. Here we report a wireless and battery-less technology of this type, implanted subdermally along the back of freely moving small animals, for the autonomous recording of electroencephalograms, electromyograms and body temperature, and for closed-loop neuromodulation via optogenetics and pharmacology. The device incorporates a system-on-a-chip with Bluetooth Low Energy for data transmission and a compressed deep-learning module for autonomous operation, that offers neurorecording capabilities matching those of gold-standard wired systems. We also show the use of the implant in studies of sleep-wake regulation and for the programmable closed-loop pharmacological suppression of epileptic seizures via feedback from electroencephalography. The technology can support a broader range of applications in neuroscience and in biomedical research with small animals.