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Do you hear what I hear? Implications of detector selection for acoustic monitoring of bats
Methods in Ecology and Evolution
Abstract
Summary
The probability of detecting the echolocation calls of bats is affected by the strength of the signal as well as the directionality and frequency response of the acoustic detectors. Regardless of the research question, it is important to quantify variation in recording system performance and its impacts on bat detection results. The purpose of this study was to compare the detection of echolocation calls among five commonly used bat detectors: AnaBat SD2 (Titley Scientific), Avisoft UltraSoundGate 116 CM16/CMPA (Avisoft Bioacoustics), Batcorder 2·0 (ecoObs), Batlogger (Elekon AG) and Song Meter SM2BAT (Wildlife Acoustics).
We used playback of synthetic calls to optimize detection settings for each system. We then played synthetic signals at four frequencies (25, 55, 85 and 115 kHz) at 5-m intervals (5–40 m) and three angles (0°, 45°, 90°) from the detectors. Finally, we recorded free-flying bats (Lasiurus cinereus), comparing the number of calls detected by each detector.
Detection was most affected by the frequency dominating the signal and the distance from the source. The effect of angle was less apparent. In the synthetic signal experiment, Avisoft and Batlogger outperformed other detectors, while Batcorder and Song Meter performed similarly. Batlogger performed better than the other detectors at angles off-centre (45° and 90°). AnaBat detected the fewest signals and none at 85 kHz or 115 kHz. Avisoft detected the most signals. In the free-flying bat experiment, Batlogger recorded 93% of calls relative to Avisoft, while AnaBat, Batcorder and Song Meter recorded 40–50% of the calls detected by Avisoft.
Numerous factors contribute to variation in data sets from acoustic monitoring; our results demonstrate that choice of detector plays a role in this variation. Differences among detectors make it difficult to compare data sets obtained with different systems. Therefore, the choice of detector should be taken into account in designing studies and considering bat activity levels among studies using different detectors.
... hot, humid weather (Griffin 1971;Lawrence and Simmons 1982;Goerlitz 2018) and where there are high levels of vegetative clutter near the microphone (Patriquin et al. 2003). Microphones must be designed specifically to detect ultrasonic frequencies (Parsons and Szewczak 2009), but microphones from different manufacturers have varying sensitivities and do not record bat echolocation calls equally (Adams et al. 2012;Smith et al. 2020). Microphones can be omnidirectional or directional, which impacts what is recorded. ...
... There are not many published studies in the last two decades that compare passive acoustic devices. However, discrepancies in passive acoustic devices to record bat echolocation have been noted in previous work (Downes 1982;Forbes and Newhook 1990;Waters and Walsh 1994;Parsons 1996;Fenton et al. 2001;Adams et al. 2012;Kaiser and O'Keefe 2015). For example, some Anabat passive acoustic devices (models II and SD2, now retired) record fewer high-frequency calls, like those emitted by Myotis, and calls of lower quality (i.e., lower highest frequency, shorter bandwidth, and shorter duration) . ...
... Further, the disparity we observed could be explained by the fact that some microphones may be more sensitive to certain frequency ranges than others; e.g. Anabats are more sensitive to low-frequency (<30 kHz) sounds (Adams et al. 2012;Kaiser and O'Keefe 2015). Weatherproofing can also affect how PAM devices record sound (Britzke et al. 2010;Osborne et al. 2023). ...
... Since the emergence of automatic recorders and their use to study chiropteran activity, which is becoming increasingly common, indeed exclusive, there have been very few studies comparing the products and their performance. The most famous, by Adams et al (2012) -Do you hear what I hear? Implications of detector selection for acoustic monitoring of bats -, is already 10 years old, whereas several generations of new detectors and microphones have arrived on the market and are widely used. ...
... Pour mieux comparer les différents enregistreurs, même si les process de réglages sont différents, nous avons réglé les paramètres propres à chacun des appareils en suivant certaines préconisations tirées de Adams et al. (2012). Pour le Batlogger, un « gain » à 18 dB, une gamme de sensibilité de 8 à 160 kHz, un « Crest factor » déterminant la sensibilité du Trigger réglé à 4, la « Période » (Period trigger) permettant de distinguer des fréquences sinusoïdales de chiroptères des insectes est gardée à sa valeur par défaut, le seuil de déclenchement est fixé à 25 dB SPL ; les autres réglages adoptés par défaut sont indiqués sur la Fig. 3. ...
... Une erreur d'appréciation aurait donc été faite sur l'activité rare qui a eu lieu pour certaines espèces à basse température en novembre (Fig. 42). E n premier lieu, les résultats, comme pour ceux d' Adams et al. (2012), montrent clairement des disparités de fonctionnement d'un système d'appareil à l'autre. Bien que les microphones soient globalement équivalents et proches en caractéristiques, on obtient des écarts importants en nombre et en taille ou durée de fichiers délivrés. ...
Since the advent of automatic recording devices and their use to study the activity of chiropterans, which have become increasingly common, even exclusive, there have been few studies comparing the products and their performance. The best known, by Adams et al. (2012) - Do you hear what I hear? Implications of detector selection for acoustic monitoring of bats -, is already 10 years old, while several generations of new detectors and microphones have come to market and are widely used. However, it is easy to imagine, and some have found, biases at all levels of the detection chain between an emitting bat and the writing of a digital file. They may be due to the variety of microphones, their degree of wear, the various sensitivity settings, the choice of trigger function, etc. So it's a fair question to ask whether it's really useful to compare the results of different recording devices and what they mean.
The consulting company Biotope therefore conducted an initial study in collaboration with a wind farm operator to test and compare five devices installed on measurement mast in southern France over a period of one and a half months: a Batlogger WE -X, a GSM Batcorder, a BatmodeS+ and two SM3BAT equipped with different microphones.
Several things emerge from this test. First, there are major differences in the quality of the recordings delivered, even though the microphone capsules used are of comparable technology. On this point, the Batlogger WE-X and the SM3BAT with SMM-U2 microphones come out on top. Secondly, there was a significant disparity in terms of detectability. This means, depending on the device, more or less pronounced detection errors and thus significantly different generation of the number of files corresponding to chiropteran contacts. In addition to the different settings for gain, sensitivity, etc. and filtering problems, the quite different trigger designs of the individual devices tested are probably also the cause of the different results.
Thus, the choice of equipment can have a major impact on the results of a study and its analysis. To demonstrate this, we decided to analyse the results of the 5 devices to establish scenarios for wind turbine curtailment. This involves correlating the activity data obtained with the wind and temperature parameters recorded in order to produce cumulative or affinity functions. The discrepancies in the data provided by the various devices have resulted in modelings of varying degrees of accuracy, with errors in estimation and limited relevance for devices that have supplied few positive files.
Finally, this comparative study highlights the low relevance of counting files as a unit of contact when using passive recorders to study chiropteran activity, and rehabilitates the idea of the positive minute proposed by Miller and Haquart.
... Bat acoustic detectors record the ultrasound calls emitted by bats, which can be used in combination with bat identification software to depict frequency range and call shape on a spectrogram. These detectors are non-invasive, with some capable of continuously recording and saving large volumes of data in nearly every environment and condition (Adams et al., 2012;Skalak, 2012;Broset, 2018). The range of acoustic detection varies with the model of detector, parameters of the detector, bat species, and weather (Goerlitz, 2018;Adams et al., 2012). ...
... These detectors are non-invasive, with some capable of continuously recording and saving large volumes of data in nearly every environment and condition (Adams et al., 2012;Skalak, 2012;Broset, 2018). The range of acoustic detection varies with the model of detector, parameters of the detector, bat species, and weather (Goerlitz, 2018;Adams et al., 2012). To decrease bias in detection, detectors have been elevated to altitudes, such as over the forest canopy, with masts, balloons, kites, pulleys, and towers (Plank et al., 2012;Froidevaux et al. 2014;August & Moore, 2019). ...
... Using drones requires a much smaller bat detector than has been traditionally used, which is why we used the lightweight Echo Meter Touch 2. Even so, the capabilities of bat detectors vary widely (Adams et al., 2012). To compare the sensitivity and reliability of the Echo Meter ...
Advances in operational simplicity and cost efficiency have promoted the rapid integration of unoccupied aerial vehicles (UAVs) into ecological research, yet UAVs often disturb wildlife, potentially biasing measurements. Studies of UAV effects on wildlife to date have focused on UAV trajectory or distance; however, UAV size and noise could be critical variables influencing wildlife responses.
Bats are cryptic aerial species that are difficult to survey using conventional means, and so we tested the effectiveness of drone‐based acoustic surveys for bats. We recorded the number of acoustic bat detections with and without a UAV present. We used three small, commercial rotary UAVs varying in size and noise intensity (249, 907, 1,380 g).
Larger and louder UAVs deterred significantly more bats, with no effect of take‐off distance on bat activity. The smallest and quietest UAV model had a similar change in bat activity compared with control measurements. Drone noise increased with drone size, but all drones emitted in a similar range of frequencies that overlapped with the larger bat species that were also those most impacted by the UAV. During the 5‐minute surveys, there was no evidence of bat habituation to UAVs although bats returned quickly once the UAV survey ended.
We urge wildlife researchers to consider drone size during wildlife surveys. Smaller and quieter models have negligible impacts on wildlife, eliminating the impact of drones on wildlife in some cases.
... Despite its utility, acoustic monitoring has limitations that must be considered in monitoring efforts. For example, the determination of species presence can vary depending on the detector type and identification algorithms used (Adams et al. 2012, Russo et al. 2018, Perea & Tena 2020. Echolocation calls of individual bats can vary based on habitat, presence of conspecifics, or environmental noise (Walters et al. 2012, Russo et al. 2018, influencing species detection and identification efficacy (Adams et al. 2012, Russo & Voigt 2016). ...
... For example, the determination of species presence can vary depending on the detector type and identification algorithms used (Adams et al. 2012, Russo et al. 2018, Perea & Tena 2020. Echolocation calls of individual bats can vary based on habitat, presence of conspecifics, or environmental noise (Walters et al. 2012, Russo et al. 2018, influencing species detection and identification efficacy (Adams et al. 2012, Russo & Voigt 2016). ...
BioBlitzes, rapid field studies conducted by a collaborative team of scientists and conservation professionals in specific geographic areas, offer an opportunity to enhance research capabilities, foster partnerships, and provide learning opportunities for scientists, conservation professionals, and non-professional volunteers. Since the detection of white-nose syndrome (WNS) in North America, populations of cave-dwelling bats have declined significantly. However, most studies documenting declines have occurred in the core of the WNS-affected area in the eastern United States. To examine changes in capture rates along the periphery of the WNS-affected region, we examined captures from Bat Blitz events (i.e., a subset of a BioBlitz focused exclusively on bats) in northern Alabama and Georgia, USA, before (n = 2; 2008, 2010) and after (n = 2; 2022, 2023) WNS detection. Pre-WNS detection, we captured 676 bats from 11 species, contrasting with post-WNS, where only 283 bats from seven species were captured. Our results show significant declines in captures of the federally endangered northern long-eared bat (Myotis septentrionalis) and the proposed endangered tricolored bat (Perimyotis subflavus), with decreases of 99,4% and 87,7%, respectively. While other common species showed no significant changes, eastern red bat capture rates declined by 35,4%, and captures of big brown and evening bats increased by 8,0% and 15,0%, respectively. In addition, we observed decreases of > 99% for most myotis species. Overall, our results support documented declines observed for WNS-affected species in northern regions, emphasizing the urgent need for conservation measures for northern long-eared and tricolored bats. Furthermore, we highlight the value of BioBlitz events to conduct surveys at broad spatial and temporal scales efficiently.
... However, there are technical decisions researchers must make that can influence the results they will obtain from passive acoustic monitoring. Choice of detector (Adams et al. 2012), detector settings (Fraser et al. 2020), microphone (Darras et al. 2020), equipment placement (Britzke et al. 2010), and analysis software (Lemen et al. 2015) can all affect outcomes. ...
... At least 10 models of acoustic bat detectors are currently available, differing widely in their technical specifications. Previous studies have compared different brands and models of detectors, identifying significant differences in the number of bat echolocation calls recorded, detection probabilities, and species richness (Adams et al. 2012, Kaiser and O'Keefe 2015, Perea and Tena 2020, Phinney 2020, Kunberger and Long 2023. Because each brand of detector is paired with its own proprietary microphone, one cannot determine whether differing outcomes are a result of the detector's capabilities, user-selected detector settings, microphone specifications, or a combination of all three. ...
Passive acoustic monitoring is a standard technique for studying bat ecology and behavior. However, an issue that has received little attention is how to appropriately analyze data within a long‐term acoustic monitoring dataset when the equipment has been replaced and updated. Equipment changes are often inevitable, especially for microphones, which need to be replaced regularly due to extended weather exposure and associated reductions in recording quality. We compared 2 ultrasonic microphone models (Wildlife Acoustics SMM‐U1 and SMM‐U2) by deploying them side‐by‐side with the same acoustic detector unit. We tested 9 or 10 microphones per model in field deployments lasting an average of 9 nights. We compared triggering frequency, species classification, detection rates, and echolocation call parameters (as indicators of signal quality) from both microphones. The vast majority (97%) of our 25,949 paired recordings were captured simultaneously by both microphones. Yet, the SMM‐U2 outperformed the SMM‐U1 in terms of proportion of files classifiable to the species level (70% versus 61%), rate of bat detections per night (1–6.5 more detections per night depending on species), and recording quality. Based on our results, we propose a correction factor to facilitate direct comparison of datasets collected with these 2 different microphones. Our study will assist bat researchers in selecting appropriate equipment and accounting for potential biases in long‐term acoustic monitoring programs.
... Recently, acoustic monitoring has gained great popularity as a potentially useful tool in fowl of bats tracking programs (Ahlén and Baagøe, 1999;Parsons and Jones, 2000;Fukui et al., 2004;Jones et al., 2013); it became possible due to the widespread use of passive acoustic sensors (ultrasonic detectors, microphones). At the same time, monitoring of echolocation signals is applicable not only to study the diversity, but also to study the peculiarities of ecology and problems of bat conservation (Fenton, 1997;Adams et al., 2012;Russo and Voigt, 2016). ...
... It is known that the signal characteristics vary depending on the sex (Russo et al., 2001;Puechmaille et al., 2014), age (Jones and Ransome, 1993), size class of an animal (Jones et al., 1992;Puechmaille et al., 2014), geographic location (Russo et al., 2007), the presence of other bats nearby (Obrist, 1995), habitat (Neuweiler, 1989;Barataud, 2015;Russo et al., 2017), and the type of foraging activity (Parsons et al., 1997;Barataud, 2015;Russo et al., 2017). The appearance of the signal structure can also differ depending on the type of equipment used in their recording (Adams et al., 2012). Therefore, the identification of bats by echolocation signals requires extensive experience and a priori knowledge of the local fauna, peculiarities of the biology and vocalization of bats, all possible variations of echolocation signals, and a critical attitude to the results obtained. ...
... Step-1: Signal resampling Sampling frequency differences are often disregarded, Adams et al. (2012); Rempel et al. (2013). For example, SM4 recorders commonly employ a sampling rate of 44.1 kHz for audible ranges, while AudioMoth recorders do not allow configuring this sampling rate, being 48 kHz the closest possible value. ...
... Contrasted with the studies elucidated in the literature review depicted in Table Appendix A, our full methodology distinguishes itself through its all-encompassing approach to rectifying the bias introduced by recording devices in acoustic indices. As gleaned from the literature, intra-brand evaluations predominantly concentrate on diagnosing the issue instead of proposing an effective remedy to counteract the bias stemming from recording devices (Adams et al., 2012;Rempel et al., 2013;Pérez-Granados et al., 2019). Furthermore, certain studies delve into the variability of acoustic indices, often emphasizing filtering techniques without specifying precise frequency ranges or protocol modifications to alleviate the bias (Metcalf et al., 2021b;Cifuentes et al., 2021;Hyland et al., 2023a). ...
Due to the complexity of soundscapes, Ecological Acoustic indices (EAI) are frequently used as metrics to summarize ecologically meaningful information from audio recordings. Recent technological advances have allowed the rapid development of many audio recording devices with significant hardware/firmware variations among brands, whose effects in calculating EAI have not yet be determined. In this work, we show how recordings of the same landscape with different devices effectively hinder reproducibility and produce contradictory results. To address these issues, we propose a preprocessing pipeline to reduce EAI variability resulting from different hardware without altering the target information in the audio. To this end, we tested eight EAI commonly used in soundscape analyses. We targeted three common cases of variability caused by recorder characteristics: sampling frequency, microphone gain variation, and frequency response. We quantified the difference in the probability density functions of each index among recorders according to the Kullback-Leibler divergence. As a result, our approach reduced up to 75% variations among recorders from different brands (AudioMoth and SongMeter) and identified the conditions in which these devices are comparable. In conclusion, we demonstrated that different devices effectively affect EAI and show how these variations can be mitigated.
Graphical Abstract
Highlights
Addressing recorder-induced biases in acoustic indices for improved reproducibility.
Proposing an effective method to mitigate recorder-related biases.
Evaluating pipeline proposed performance via acoustic index distribution analysis.
... The microphone was placed on a stick at 150 cm approx. above-ground level and with an angle of c. 45° with respect to the soil surface (Adams et al., 2012;Lisón & Calvo, 2011). The microphone was turned off between points. ...
... Bat activity was measured counting the number of bat passes and feeding buzzes in each listening point. Bat passes are defined as a series of 5 or more echolocation pulses, and feeding buzzes are distinctive sound patterns indicating a capture attempt (Adams et al., 2012;Lisón & Calvo, 2011;Lisón & Calvo, 2014). ...
Resumen
A pesar de su importancia ecológica y económica, en Chile se desconocen muchos aspectos de la ecología de los murciélagos y de su distribución. Esta situación no permite una correcta implementación de los esfuerzos de conservación aún cuando son legalmente reconocidos por sus beneficios para la agricultura. En este trabajo estudiamos la actividad y la comunidad de murciélagos en dos tipos de paisaje agrícola (homogéneo vs. heterogéneo) en un hotspot de biodiversidad en el centro‐sur de Chile. Para ello, monitoreamos cuatro transectos de 10 km en cada tipo de paisaje, con 10 puntos de escucha separados por 1 km. Estos transectos se repitieron 5 veces, una vez al mes. Evaluamos la actividad de los murciélagos según el tipo de cobertura forestal (nativa, mixta y plantaciones) y la densidad de árboles aislados. Nuestros resultados mostraron que el paisaje heterogéneo fue dominado por Tadarida brasiliensis mientras que el paisaje homogéneo fue dominado por Lasiurus spp. Sin embargo, sólo la especie T. brasiliensis fue afectada por el tipo de paisaje. En el paisaje heterogéneo, sólo las variables de cobertura forestal tuvieron un impacto significativo en la actividad de las especies de murciélagos, donde Lasiurus spp. y Myotis chiloensis tuvieron una respuesta positiva para bosque nativo y mixto, así como Lasiurus spp. tuvo una respuesta negativa para plantaciones. La densidad de árboles aislados tuvo un efecto negativo sobre la actividad de T. brasiliensis y Lasiurus spp. en el tipo de paisaje homogéneo. Nuestros resultados muestran la importancia de considerar los elementos forestales en el paisaje agroforestal para conservar las comunidades de murciélagos.
... In the first step, since we compiled data produced by different contributors, we expected the existence of multiple combinations between the recorder type and the trigger sensitivity. However, these recording methods deeply affect the number of bat passes recorded (Adams et al., 2012). Confounding effects between recording methods and factors of interest (e.g. ...
... All gradients of drivers strongly varied among recorder type/trigger sensitivity combinations, thus preventing any modelling of the effects of drivers on bat activity based on the full dataset due to confounding effects. Indeed, different recorder type/trigger sensitivity combinations can lead to very different levels of bat activity between sites due to the different detection distances generated by the material specificities and settings (Darras et al., 2020;Adams et al., 2012). We opted to compensate for this problem by modelling the effect of the drivers on bat activity after separating the recorder type/trigger sensitivity combinations. ...
Wind turbine development is growing exponentially and faster than other sources of renewable energy worldwide. While multi-turbine facilities have small physical footprint, they are not free from negative impacts on wildlife. This is particularly true for bats, whose population viability can be threatened by wind turbines through mortality events due to collisions. Wind turbine curtailment (hereafter referred to as "blanket curtailment") in non-winter periods at low wind speeds and mild temperatures (i.e. when bats are active and wind energy production is low) can reduce fatalities, but show variable and incomplete effectiveness because other factors affect fatality risks including landscape features, rain, turbine functioning, and seasonality. The combined effects of these drivers, and their potential as criteria in algorithm-based curtailment, have so far received little attention. We compiled bat acoustic data recorded over four years at 34 wind turbine nacelles in France from post-construction regulatory studies, including 8619 entire nights (251 ± 58 nights per wind turbine on average). We modelled nightly bat activity in relation to its multiple drivers for three bat guilds, and assessed whether curtailment based on algorithm would be more efficient to limit bat exposure than blanket curtailment based on various combinations of unique wind speed and temperature thresholds. We found that landscape features, weather conditions, seasonality, and turbine functioning determine bat activity at nacelles. Algorithm-based curtailment is more efficient than blanket curtailment, and has the potential to drastically reduce bat exposure while sustaining the same energy production. Compared to blanket curtailment, the algorithm curtailment reduces average exposure by 20 to 29 % and 7 to 12 % for the high-risk guilds of long- and mid-range echolocators, and by 24 to 31 % for the low-risk guild of short-range echolocators. These findings call for the use of algorithm curtailment as both power production and biodiversity benefits will be higher in most situations.
... The microphone was placed on a stick at 150 cm approx. above-ground level and with an angle of c. 45° with respect to the soil surface (Adams et al., 2012;Lisón & Calvo, 2011). The microphone was turned off between points. ...
... Bat activity was measured counting the number of bat passes and feeding buzzes in each listening point. Bat passes are defined as a series of 5 or more echolocation pulses, and feeding buzzes are distinctive sound patterns indicating a capture attempt (Adams et al., 2012;Lisón & Calvo, 2011;Lisón & Calvo, 2014). ...
In Chile, many aspects of the ecology of bats and their distribution are unknown, despite their ecological and economic importance. This situation does not allow a correct implementation of conservation efforts even when they are legally recognized as beneficial animals for agriculture. Here, we studied the bats' activity and community in two agricultural landscape types (homogeneous vs. heterogeneous) in a hotspot of biodiversity in the centre-south of Chile. We monitored
four transects of 10 km per landscape type with 10 listening points separated by 1 km. These transects were repeated 5 times, once per month. We evaluated the bats activity according to the forest cover type (native, mixed and plantations) and the isolated trees density. Our results showed that the heterogeneous landscape was dominated by T. brasiliensis while the homogeneous landscape was by Lasiurus spp. However, only the species T. brasiliensis was affected by the landscape type. In the heterogeneous landscape, only the forest cover variables had significance in the activity of the bat species, where Lasiurus spp. and M. chiloensis had a positive response for native and mixed forest, as well as Lasiurus spp. had a negative response for plantations. The density of isolated trees had a negative effect on the activity of T. brasiliensis and Lasiurus spp. in the homogeneous landscape type. Our results showed the importance of considering the forest elements in agroforestry landscape to conserve bat communities.
... популярность приобретает акустический мониторинг (Ahlén, Baagøe, 1999;Parsons, Jones, 2000;Fukui et al., 2004;Jones et al., 2013), ставший возможным благодаря широкому распространению пассивных акустических датчиков (ультразвуковые детекторы, микрофоны). При этом мониторинг эхолокационных сигналов применим не только для изучения разнообразия, но и для исследования особенностей экологии и проблем сохранения рукокрылых (Fenton, 1997;Adams et al., 2012;Russo, Voigt, 2016). ...
... Известно, что характеристики сигналов варьируют в зависимости от пола (Russo et al., 2001;Puechmaille et al., 2014), возраста (Jones, Ransome, 1993) и размерного класса животного (Jones et al., 1992;Puechmaille et al., 2014), географического положения (Russo et al., 2007), наличия поблизости других рукокрылых (Obrist, 1995), среды оби-тания (Neuweiler, 1989;Barataud, 2015;Russo et al., 2017), а также от типа кормодобывающей деятельности (Parsons et al., 1997;Barataud, 2015;Russo et al., 2017). Внешний вид структуры сигналов может также различаться в зависимости от типа оборудования, используемого при их записи (Adams et al., 2012). Поэтому для идентификации рукокрылых по эхолокационным сигналам необходимы большой опыт и априорные знания о местной фауне, особенностях биологии и вокализации рукокрылых, всех возможных вариаций эхолокационных сигналов, а также критическое отношение к полученным результатам. ...
The results of calculating the echolocation signals of bats performed using an Echo Meter Touch 2 PRO ultrasonic
detector are presented. The signals were recorded using the time-expansion mode and identified
manually with BatSound software. The work was carried out in June–August 2019–2020 in the northwest of
the Voronezh Region within the Federal Voronezh State Nature Reserve. Four types of habitat were used as
model territories to identify the species composition, occurrence and biotopic association: a river bank, a forest
lake, a formerly burnt area, and a village. A total of 2332 audio recordings of ultrasonic signals were made.
After manual verification, 1615 records (69.3%) belonging to 13 bat species were identified with high probability,
found in the following descending order: N. noctula > N. leisleri > P. pygmaeus > V. murinus > P. nathusii >
M. dasycneme > M. daubentonii > N. lasiopterus > P. auritus > P. pipistrellus > M. brandtii > E. nilssonii. The
latter species, E. nilssonii was recorded from the study territory for the first time. From a habitat point of view,
near-water spaces were the most attractive to bats, where the greatest diversity was observed. However, the
species distribution there was not the same, as M. brandtii, P. pygmaeus, E. nilssonii and M. dasycneme showed
greater preferences to river habitats, being virtually absent from or indifferent to spaces near the lake. The
greatest preference to a near-lake area was noted for M. daubentonii, V. murinus, P. nathusii and E. serotinus.
Burnt forests were unattractive to most bat species, with the exception of N. noctula and E. serotinus. The attitude
of species to the territory of the village was either indifferent or it was avoided. Alpha diversity increased
in the following succession: a formerly burnt area–a village–a river bank–a forest lake, where the highest
number of species was observed with their better alignment in terms of relative occurrence. The differences
revealed in the biotopic confinement were discussed in connection with the spatial location of the habitats.
... For several reasons, detection probability in bats is often lower than 1 (Meyer 2015). Firstly, detection probability can be detector-specific (see for example Adams et al. 2012). Secondly, for the same species, probability of detection may differ between different locations within the same general area to habitat or weather, as these impact flying behaviour and echolocation (Rydell 1993;Duchamp et al. 2006;Schaub and Schnitzler 2007;Kaiser and O'Keefe 2015;Richardson et al. 2019). ...
... This is problematic because a detected absence of a function for a species after performing these surveys is considered a true absence, as opposed to scientific studies where problems caused by detection differences are minimised by adapting the sampling design or in the strategy for the data analysis (e.g. Adams et al. 2012;Froideveaux et al. 2014;Andrews 2018). ...
Different bat species are known to differ in their detectability. Having available presence-absence data from 100 randomly stratified selected 1 km² squares in the north of the Netherlands, collected during autumn 2009 and spring 2010 following Environmental Impact Assessment protocols, we calculated probabilities of occupancy and detection for ten bat species. Not only did we investigate their presence in general but also of the three main functions a landscape has for a bat: roosting, commuting and foraging. The four most commonly detected species were Pipistrellus pipistrellus, Pipistrellus nathusii, Eptesicus serotinus and Myotis daubentonii. For all species, roosting was the function detected least while the function of foraging was detected most for most species. Probability of detection was highest for P. pipistrellus (0.79), followed by P. nathusii and E. serotinus. They are all relatively loud species, whose presence is hardly missed. For the other seven species, probability of detection was below 0.4 with the lowest value for Plecotus auritus (0.11). The latter species has a very soft echolocation call and is thus often not detected even when present. Our study is the first to use occupancy modelling for European bats. Our results show that the number of visits required to obtain a reliable approximation of occupancy differs widely: from two visits for both Pipistrellus species, to three for E. serotinus and M. daubentonii and even ten for P. auritus. Especially for the latter species, other survey methods may be better employed. This has implications for the design of surveys for Environmental Impact Assessments.
... Only the bats survey assemblage displayed a significant change in list lengththe number of species within an assemblage recorded at a given site and dateover time. This increase in list length coincides with the increased use of broad-spectrum acoustic recording devices and automatic species identification software, which permits easier detection and identification of a wide range of bat species (Adams et al., 2012;MacSwiney et al., 2008). Although sample sites were distributed across the UK, sampling was not uniform or random: for small mammals and bats, most sites were in England and Wales; for deer, most sites were in England and Scotland; whereas the sites for mid-sized mammals were from across the UK (Fig. 2). ...
... This information should be considered when interpreting these results, and efforts should be made to collect information on survey methods in the future. For example, acoustic bat detectors have advanced in recent years with microphone types and their unique frequency responses resulting in differences between detectability of different bat species (Adams et al., 2012), with consequent effects on bat trend analyses . In addition, season (phenology), landscape variables (e.g. ...
Conservation action is usually triggered by detecting trends in species’ population size, geographical range, or occupancy (proportion of sites occupied). Robust estimates of these metrics are often required by policy makers and practitioners, yet many species lack dedicated monitoring schemes. An alternative source of data for trend estimation is provided by biological records, i.e., species presence information. In the UK, there are millions of such records, but biological trend assessments are often hindered by biases caused by the unstructured way in which they are collected. Recent advances in occupancy modelling that account for changes in survey effort and detectability over time mean that robust occupancy trends can now be estimated from these records. By grouping mammal species into survey assemblages — species likely to be recorded at the same time — and applying occupancy models, this study provides estimates of long-term (1970 to 2016) occupancy trends for 37 terrestrial mammal species from the UK. The inter-annual occupancy growth rates for these species ranged from -4.26% to 11.25%. This information was used to classify two species as strongly decreasing, five as decreasing, 12 as no change, 11 as increasing and seven as strongly increasing. Viewing the survey assemblages as a whole, the occupancy growth rates for small mammals were, on average, decreasing (-0.8% SD 1.57), whereas bats and deer (0.9% SD 1.30) were increasing (3.8% SD 3.25; 0.9% SD 1.30 respectively), and mid-sized mammals were stable (-0.3 SD 1.72). These results contribute much-needed information on a number of data deficient species, and provide evidence for prioritising conservation action.
... All bat detectors were set to high sensitivity ('crest advanced') while recording was triggered automatically (15 kHz to 155 kHz, crest factor ≥ 7, post trigger time: 1 s). We placed one bat detector each at the wildflower and the crop field, at a distance of more than 60 m to each other, i.e. 30 m infield from the shared hedge, to avoid an overlap of the recording radius ( Fig. 1B; Adams et al., 2012;Heim et al., 2018;Kelm et al., 2014). We attached the microphones to wooden poles at a height of about 2.5 m in order to reduce acoustical clutter echoes produced by vegetation (Schnitzler and Kalko, 2001). ...
... Patterns of bat species composition were very similar to findings of previous studies on bat activity above agricultural fields in North-East Germany, where N. noctula and pipistrelle bats were most frequently recorded (Heim et al., 2015(Heim et al., , 2016(Heim et al., , 2017; but see Adams et al., 2012). This pattern of bat activity largely mirrors species-specific habitat preferences of the prevailing bat species since all dominant species were either open-space (NEV group and N. noctula;about 70%) or edge-space foragers (pipistrelle bats; about 26%) and thus, common bat species in agricultural landscapes (Heim et al., 2016;Schnitzler and Kalko, 2001). ...
While land-use change threatens insectivorous bats, there is a lack in conservation measures targeting bats in temperate agro-ecosystems. Further, there is no consensus on shared benefits of existing conservation measures either. To unravel the causal factors behind the failure and success of conservation measures, we studied whether sown wildflower fields create sufficient ecological contrast and adequate foraging habitats for insectivorous bats and if potential benefits depend on landscape context.
From June to September 2020, we simultaneously monitored insects and bats on paired wildflower and crop fields in landscapes with increasing complexity, here shares of semi-natural habitats such as hedgerows. We compared insect and specifically moth abundance as well as overall bat and foraging activity between wildflower and crop fields and studied effects of prey abundance on bat activity.
During summer, insect and moth abundances were two- to fourfold higher on wildflower than crop fields. On wildflower fields, insect abundances increased with wildflower cover, while moth abundances increased with shares of semi-natural habitats. Bat activity on wildflower compared to crop fields was higher during the beginning and lower towards the end of summer. Both bat and foraging activity increased with insect abundance and decreased with patch size of wildflower fields.
Wildflower fields seem to be a promising tool to provide adequate foraging habitats for insectivorous bats in agro-ecosystems but sufficient prey availability may be key, particularly during times of high food demand. Moreover, it seems vital to target complex landscapes and foster the retention and reintroduction of hedgerows in agro-ecosystems.
... Between March 2014 and January 2020, we employed passive acoustic monitoring to sample bat echolocation calls in the 129 sampling points (Fig 1, and S3 Table), using a combination of two SM2Bat+, two SM3BAT, and two SM4BAT-FS ultrasound recorders (Wildlife Acoustics Inc., Massachusetts, USA). We set the microphones at 45º to the ground, avoiding highly cluttered areas [16,45,46]. Since the highest frequency used by the studied species is~60 kHz (Noctilio leporinus) [19], we configured the bat detectors with a minimum sampling rate of 384 kHz and 16 bit audio depth, enough to detect and record our focal species without distortions (e.g., aliasing). ...
... format in the SD cards with a preset maximum duration of 1 minute if any sound above 7 kHz exceeded at least 6 dB. Since bat activity and the reception of the calls can be affected by weather and local conditions, we sampled only during nights with temperature > 15ºC, without strong winds (< 5 m/s) or rain [16,45,46]. ...
Species distribution modelling (SDM) gained importance on biodiversity distribution and conservation studies worldwide, including prioritizing areas for public policies and international treaties. Useful for large-scale approaches and species distribution estimates, it is a plus considering that a minor fraction of the planet is adequately sampled. However, minimizing errors is challenging, but essential, considering the uses and consequences of such models. In situ validation of the SDM outputs should be a key-step—in some cases, urgent. Bioacoustics can be used to validate and refine those outputs, especially if the focal species’ vocalizations are conspicuous and species-specific. This is the case of echolocating bats. Here, we used extensive acoustic monitoring (>120 validation points over an area of >758,000 km², and producing >300,000 sound files) to validate MaxEnt outputs for six neotropical bat species in a poorly-sampled region of Brazil. Based on in situ validation, we evaluated four threshold-dependent theoretical evaluation metrics’ ability in predicting models’ performance. We also assessed the performance of three widely used thresholds to convert continuous SDMs into presence/absence maps. We demonstrated that MaxEnt produces very different outputs, requiring a careful choice on thresholds and modeling parameters. Although all theoretical evaluation metrics studied were positively correlated with accuracy, we empirically demonstrated that metrics based on specificity-sensitivity and sensitivity-precision are better for testing models, considering that most SDMs are based on unbalanced data. Without independent field validation, we found that using an arbitrary threshold for modelling can be a precarious approach with many possible outcomes, even after getting good evaluation scores. Bioacoustics proved to be important for validating SDMs for the six bat species analyzed, allowing a better refinement of SDMs in large and under-sampled regions, with relatively low sampling effort. Regardless of the species assessing method used, our research highlighted the vital necessity of in situ validation for SDMs.
... Notably, data from Rhinolophus sp. indicate manoeuvring flight can be more metabolically demanding than horizontal flight, although this may depend on wing-loading 49 . Regardless, any impact would necessarily be proportional to the number of trains passing per unit time, which varied substantially between lines. ...
... Detector-train distances were 10.6 (3.2) m (mean (SD)), minimum = 5.2 m, maximum = 16.8 m, and train widths were 2.8 (0.1) m. Consequently, as the detectors have an approximate maximum 20-25 m range 49 , detected bats would be within 26.6-43.2 m of the track centre on the side facing the microphone, and within 1.8-18.4 ...
Rail transport is expanding, with a global increase in infrastructure of up to one-third predicted by 2050. Greater reliance on rail is expected to benefit the environment at a planetary level, by mitigating transport-related carbon emissions. However, smaller-scale, more direct consequences for wildlife are unclear, as unlike roads, railway impacts on animal ecology are rarely studied. As a group, bats frequently interact with transport networks due to their broad distribution and landscape-scale movements. Additionally, their nocturnality, and use of echolocation mean bats are likely to be affected by light and noise emitted by trains. To investigate whether passing trains affect bat activity levels, we monitored the two most abundant UK species using ultrasonic detectors at 12 wooded rail-side sites in southern England. Activity fell by ≥ 30–50% each time a train passed, for at least two minutes. Consequently, activity was reduced for no less than one-fifth of the time at sites with median rail traffic, and two-thirds or more of the time at the busiest site. Such activity changes imply repeated evasive action and/or exclusion from otherwise favourable environments, with potential for corresponding opportunity or energetic costs. Hence, disturbance by passing trains may disadvantage bats in most rail-side habitats.
... I compiled data to train the feeding buzz classifier from recordings of bats made at five locations throughout Ontario, Canada, with three different recording devices over three separate years ( Table 1). The three devices were the Song Meter SM2BAT+ coupled with an SMX-US or SMX-UT microphone, the Song Meter SM4BAT-FS coupled with a SMM-U2 microphone, and the Song Meter Mini Bat with an integrated microphone, all manufactured by Wildlife Acoustics Inc. Variation among recorder types and microphones leads to differences in the amplitude, spectral characteristics, and noise profiles of their recordings which can also lead to differences in their ability to sample bat activity [24]. As such, data from more than one device were used to improve the generalizability of the classifier and to test whether recorder type affected classifier accuracy. ...
Quantification of bat communities and habitat heavily rely on non-invasive acoustic bat surveys the scope of which has greatly amplified with advances in remote monitoring technologies. Despite the unprecedented amount of acoustic data being collected, analysis of these data is often limited to simple species classification which provides little information on habitat function. Feeding buzzes, the rapid sequences of echolocation pulses emitted by bats during the terminal phase of prey capture, have historically been used to evaluate foraging habitat quality. Automated identification of feeding buzzes in recordings could benefit conservation by helping identify critical foraging habitat. I tested if detection of feeding buzzes in recordings could be automated with bat recordings from Ontario, Canada. Data were obtained using three different recording devices. The signal detection method involved sequentially scanning narrow frequency bands with the “Bioacoustics” R package signal detection algorithm, and extracting temporal and signal strength parameters from detections. Buzzes were best characterized by the standard deviation of the time between consecutive pulses, the average pulse duration, and the average pulse signal-to-noise ratio. Classification accuracy was highest with artificial neural networks and random forest algorithms. I compared each model’s receiver operating characteristic curves and random forest provided better control over the false-positive rate so it was retained as the final model. When tested on a new dataset, buzzfindr’s overall accuracy was 93.4% (95% CI: 91.5%– 94.9%). Overall accuracy was not affected by recording device type or species frequency group. Automated detection of feeding buzzes will facilitate their integration in the analytical workflow of acoustic bat studies to improve inferences on habitat use and quality.
... Such data collection methods have been used for bats, whose complex echolocation system exhibits significant variability influenced by numerous factors [2]. Bats navigate and perceive their surroundings through the echoes returned from their environment by utilizing high-frequency pulses ranging from 9 kHz to 200 kHz, which is well beyond human hearing [3]. As nocturnal creatures, these echolocation calls serve as a crucial tool for researchers to study various aspects of bat populations. ...
Bats play a pivotal role in maintaining ecological balance, and studying their behaviors offers vital insights into environmental health and aids in conservation efforts. Determining the presence of various bat species in an environment is essential for many bat studies. Specialized audio sensors can be used to record bat echolocation calls that can then be used to identify bat species. However, the complexity of bat calls presents a significant challenge, necessitating expert analysis and extensive time for accurate interpretation. Recent advances in neural networks can help identify bat species automatically from their echolocation calls. Such neural networks can be integrated into a complete end-to-end system that leverages recent internet of things (IoT) technologies with long-range, low-powered communication protocols to implement automated acoustical monitoring. This paper presents the design and implementation of such a system that uses a tiny neural network for interpreting sensor data derived from bat echolocation signals. A highly compact convolutional neural network (CNN) model was developed that demonstrated excellent performance in bat species identification, achieving an F1-score of 0.9578 and an accuracy rate of 97.5%. The neural network was deployed, and its performance was evaluated on various alternative edge devices, including the NVIDIA Jetson Nano and Google Coral.
... A direct assessment of detection ranges of the various species of bats in our study area would have been beyond the scope of this study. Species that echolocate at different frequencies are expected to have different detection probabilities 57 . As we were mostly interested in relative differences in time and space and the same devices were deployed randomly on all meadows, we believe our approach is sufficient. ...
Increasing agriculture and pesticide use have led to declines in insect populations and biodiversity worldwide. In addition to insect diversity, it is also important to consider insect abundance, due to the importance of insects as food for species at higher trophic levels such as bats. We monitored spatiotemporal variation in abundance of nocturnal flying insects over meadows, a common open landscape structure in central Europe, and correlated it with bat feeding activity. Our most important result was that insect abundance was almost always extremely low. This was true regardless of management intensity of the different meadows monitored. We also found no correlation of insect abundance or the presence of insect swarms with bat feeding activity. This suggests that insect abundance over meadows was too low and insect swarms too rare for bats to risk expending energy to search for them. Meadows appeared to be poor habitat for nocturnal flying insects, and of low value as a foraging habitat for bats. Our study highlights the importance of long-term monitoring of insect abundance, especially at high temporal scales to identify and protect foraging habitats. This will become increasingly important given the rapid decline of insects.
... The Wildlife Acoustics Song Meter Mini Bat, a widely popular bat detector, was used as a control tool during the tests. As sensitivity and performance can vary among different bat detectors (Adams et al. 2012;Kunberger and Long 2023), results might differ if the tests were carried out using alternative models. In the Song Meter Mini Bat, the maximum gain that can be set is 12 dB, whereas in other detectors it can be higher (Kaiser and O'Keefe 2015). ...
Citizen science has become a crucial tool in biodiversity monitoring, often facilitated by the diffusion of mobile devices, such as smartphones and tablets. High costs of professional equipment often limit large-scale monitoring, particularly in bat monitoring programmes based on acoustic surveys. Here we present the potential of using mobile devices for bat monitoring, allowing for large-scale, volunteer-based monitoring programmes. We initially compared mobile devices’ performance with a professional bat detector for recording low-frequency bat calls. We then conducted a citizen science pilot study to test the method’s feasibility in a real-world setting, recording echolocation and social calls of nine European bat species. We found high similarity in spectrogram quality (0.74 ± 0.09 for Samsung, 0.90 ± 0.01 for Huawei, 0.86 ± 0.09 for Xiaomi, 0.69 ± 0.09 for Apple) and average peak frequency (differences of 0.2 ± 0.5 kHz for Samsung, 0.1 ± 0.7 kHz for Huawei, 0.5 ± 1.0 kHz for Xiaomi, 0.1 ± 0.8 kHz for Apple) between calls recorded by mobile devices and professional bat detectors. The number of recorded bat calls per sampling session was also similar. However, differences in sound quality and effectiveness among mobile device brands were found. iOS devices outperformed professional detectors at recording bat calls at increasing distances. The citizen science pilot study tested 35 mobile device models, all of which effectively recorded bats. This study suggests that mobile devices could be an accessible, no-cost tool for large-scale bat monitoring. Incorporating mobile devices into existing monitoring networks or creating new dedicated programmes could not only enhance data collection, but also boost public knowledge and awareness about bats, ultimately promoting informed decision-making and better conservation strategies.
... All continuous variables were standardized to a mean of 0 and standard deviation of 1. We also included study site (factor with 20 levels) and monitoring night as Julian day (fac-tor with 62 levels) as random effects and detector model (factor with 2 levels: SM2 and SM4) and year (factor with 2 levels: 2019 and 2020) as fixed effects in all models because these variables could have a nonnegligible effect on bat species activity detection and need to be included to control for their potential effects (Adams, 2012;Hayes, 1997;Smith et al., 2021). After observing trends in the residuals of the initial models, we transformed the stream area term by taking the square root and found that this effectively corrected the model fit. ...
Climate refugia, areas where climate is expected to remain relatively stable, can offer a near‐term safe haven for species sensitive to warming temperatures and drought. Understanding the influence of temperature, moisture, and disturbance on sensitive species is critical during this time of rapid climate change. Coastal habitats can serve as important refugia. Many of these areas consist of working forestlands, and there is a growing recognition that conservation efforts worldwide must consider the habitat value of working lands, in addition to protected areas, to effectively manage large landscapes that support biodiversity. The sensitivity of forest bats to climate and habitat disturbance makes them a useful indicator taxon. We tested how microclimate and forest management influence habitat use for 13 species of insectivorous bats in a large climate refugium in a global biodiversity hotspot. We examined whether bat activity during the summer dry season is greater in forests where coastal fog provides moisture and more stable temperatures across both protected mature stands and those regularly logged. Acoustic monitoring was conducted at a landscape scale with 20 study sites, and generalized linear mixed models were used to examine the influence of habitat variables. Six species were positively associated with warmer nighttime temperature, and 5 species had a negative relationship with humidity or a positive relationship with climatic moisture deficit. Our results suggest that these mammals may have greater climate adaptive capacity than expected, and, for now, that habitat use may be more related to optimal foraging conditions than to avoidance of warming temperatures and drought. We also determined that 12 of the 13 regionally present bat species were regularly detected in commercial timberland stands. Because forest bats are highly mobile, forage over long distances, and frequently change roosts, the stewardship of working forests must be addressed to protect these species.
... daubentonii) with capture data. Similarly to how mist nets are made of mesh of different thicknesses, various models of bat detectors may also differ strongly in sensitivity, and these differences are not evenly distributed among call frequencies [64,65]. Additional bias may result from the fact that-at least at close-canopy sites-some high-flying species, like noctules, may not even represent the habitat in which their calls were recorded, as they often use the open space above the canopy but their calls easily reach the microphone located at ground level. ...
Woodland bat assemblages are usually structured in a space according to the distance from the ground, water, and obstacles, features that often define chiropteran hunting tactics. Consequently, the bat species composition differs strongly among various habitats, even within the same forest patch. However, when conducting local bat surveys in Wolin National Park (WPN), we revealed an unexpected uniformity in the qualitative and quantitative structure of bat assemblages, based on mist netting and ultrasound recording. In total, 10 vespertilionid species were detected. Across all methods and sampled habitats, a single species, Pipistrellus pygmaeus, predominated, while no Barbastella barbastellus, an old forest specialist, were detected, despite the abundance of their preferred daily roosts. We also reviewed the literature for mist-netted bat samples in four different habitats in lowland Polish forests. The samples usually clustered based on habitats, and the same habitat classes often clustered very closely despite representing geographically distant forests. The exception was WPN, where all four habitat classes formed a tightly packed cluster. We hypothesize that P. pygmaeus might act as a hyperabundant native species, a successful generalist that reduces the contribution of more specialized taxa in the assemblage. It probably benefits from both forest renaturation and anthropogenic cross-boundary subsidy.
... We also suggest that research continues to use a paired method design to continue to explore how detection rates change with TA B L E 2 Occupancy and detection models, including the number of parameters (K), Akaike's information criteria adjusted for small sample sizes (AICc), the difference in AICc from the most parsimonious model (ΔAICc), model weight (w), and log-likelihood (LL) estimates. species, abundance, region, equipment and software used (Adams et al., 2012;Lemen et al., 2015). ...
Using acoustics to survey for bats has increased as the need for data on increasingly rare species has also increased. We set out to better understand the difference between mist netting and acoustic detection probabilities between these two methods for the little brown bat ( Myotis lucifugus ), a species highly impacted by white‐nose syndrome and currently considered for federal listing in the United States. We also analyzed occupancy relationships with local and landcover variables. We surveyed 15 sites using mist netting paired with an acoustic recorder for multiple nights to estimate detection probability of this species. We also deployed acoustic recorders at another 73 sites. We found that detection rates for mist netting were very low but increased with day of year and decreased from proximity to water. Acoustic surveys had higher detection rates, but there was an approximately 30% likelihood of false‐positive detections. At the mean distance to water and day of year, acoustic surveys had a detection rate 55 times higher than mist netting. There were not significant factors influencing occupancy of little brown bats, only a slight positive relationship between forested largest patch, landscape patch richness and forest basal area. Given the declines in little brown bat populations since white‐nose syndrome, it is even more critical that we consider the very low detection rate of mist netting compared to acoustic surveys.
... In a study on Hawaiian hoary bats (Gorresen et al., 2017), the authors found that most flying bats recorded with video cameras were not detected using acoustics, which is particularly surprising regarding the relatively lowfrequency long-range calls of the species. Trawling Myotis bats present frequency-modulated calls that are usually above 40 kHz of peak frequency (van de Sijpe, 2011), which makes the detection distance of their calls relatively low (Adams et al., 2012;Monadjem et al., 2017). ...
Mediterranean habitats will be one of the Eurasian ecosystems more strongly affected by Climate Change, especially their riverine systems. Monitoring these ecosystems, which are endemism hotspots and extremely sensitive to changes in rain regimes and extreme weather events like droughts, is of crucial importance. Decades of citizen science projects have proven their utility in highlighting ecological shifts and conservation action priority areas. The Bat Monitoring Programme ( www.batmonitoring.org ), for instance, has already been used to develop ecological indicators to evaluate the evolution and conservation status of Mediterranean ecosystems. However, using bats as ecological indicators for aquatic ecosystems has resulted in contradicting results, making its application a little controversial. In the present study, we compared two citizen science protocols (visual counting vs. passive acoustic monitoring) used in the Bat Monitoring Programme to test the utility of trawling bats as indicators of Mediterranean riverine habitat quality at both local and landscape scales. By doing so, we aimed to build a specific ecological indicator to determine habitat quality through visual and acoustic counts. Although both protocols presented similar positive significant responses to riverine forest quality, visual counts are suggested as the best sampling approach due to their simplicity and potential within citizen science projects. Moreover, for the first time, we defined threshold values of trawling bat activity to assign different levels of habitat quality to the sampled rivers. We applied them in NE Iberia to exemplify the benefits of using them in a Mediterranean region and discussed the potential, pros and cons of these two citizen science methodologies to establish a pan‐European river biomonitoring programme using trawling bats.
... Several strategies exist for monitoring bats, from more intrusive techniques that may result in increased investigator disturbance, resulting in a potential for additional energy expenditure for the bat, such as physical counts, to more passive methods, such as acoustic monitoring (e.g., Hayes et al., 2009;Kloepper et al., 2016Kloepper et al., , 2017, videography (e.g., Betke et al., 2008), and camera traps (e.g., Krivek et al., 2022). Acoustic monitoring has been tested in surface environments (e.g., Adams et al., 2012;Hogue & McGowan, 2018) and there is some consensus on appropriate methodologies. When comparing the effectiveness of different monitoring techniques, there was a positive, although not significant, effect on bat populations. ...
Bats frequently inhabit caves and other subterranean habitats and play a critical role in subterranean food webs. With escalating threats to subterranean ecosystems, identifying the most effective measures to protect subterranean‐roosting bats is critical. We conducted a meta‐analysis to evaluate the effectiveness of conservation and management interventions for subterranean‐roosting bats. We used network analyses to determine to what extent interventions for bats overlap those used for other subterranean taxa. We conducted our analyses with data extracted from 345 papers recommending a total of 910 conservation interventions. Gating of roost entrances was applied to preserve bat populations in 21 studies, but its effectiveness was unclear. Habitat restoration and disturbance reduction positively affected bat populations and bat behavior, respectively, in ≤4 studies. Decontamination was assessed in 2 studies and positively affected bat populations, particularly in studies focused on reducing fungal spores associated with white‐nose syndrome in North America. Monitoring of bat populations as an effective conservation strategy was unclear and infrequently tested. Only 4% of bat studies simultaneously considered other subterranean organisms. However, effective interventions for bat conservation had similarities with all other organisms. If other subterranean organisms are considered when applying interventions to conserve bats, they might also benefit.
... These curtailments are usually initiated through monitoring bat activities using acoustic devices such as ultrasonic recorders placed at nacelle height or ground level [2]. Due to the limited recording radius of these devices, it is usually hard to monitor the entire area of wind farms [3]. UAVs may help to tackle this problem. ...
The goal of this study is to monitor the number and type of bats located in a specific, hard-to-reach area, without disturbing their natural flight behaviour. This can be achieved by acoustic monitoring of the bat’s ultrasonic echoes. By attaching an acoustic sensor to an unmanned aerial vehicle (UAV), a large area can be covered. However, it has been shown that bats may be either attracted or deterred by UAVs. What specifically is causing this effect is still unclear. Our hypothesis is that the bats can hear the UAV’s ”whining”. We measure the sound level of drone drivetrains up to 100 kHz in the laboratory and apply an environmental damping model of sound. Our findings suggest that dedicated species of gleaning bats can still hear much of the UAV noises, whereas the ”non-gleaning” bats are less affected. We
further researched, which parameters have the most influence on the emitted noise by varying the type of Electronic
Speed Controller (ESC), motor, and diameter of propeller blades. An optimum drone drivetrain setup for further in-situ
investigations is presented in this paper.
... Having popularized acoustic bat surveys (Fenton 1970;Barclay et al. 1979;Adams et al. 2012), Brock and colleagues applied acoustics to compare impacts of WNS on M. lucifugus and Lasiurus cinereus in a heavily impacted region (Dzal et al. 2011). These surveys demonstrated reduced summer activity of susceptible M. lucifugus, which was attributed to WNS mortality during hibernation. ...
Bats are hosts to a range of pathogens, which include zoonotic pathogens and pathogens of conservation concern. Brock Fenton’s research on bat ecology has always balanced clear communication of potential health risks associated with bats and the need to communicate these risks precisely to avoid unnecessary persecution of bats. Here, we integrate Brock’s work in the field of disease ecology with that of his students and collaborators and consider the potential advantages of studying disease ecology of bats within the Canadian context. The broad distribution of a few common species across the vast landscape of present-day Canada provides an opportunity to untangle the impacts of environmental variation on host–pathogen interactions and disease severity, particularly in the context of climate change. The varying migratory strategies and social structure of the bat species found in Canada could also facilitate informative interspecific studies to better understand how bat health is affected by interactions among rapid environmental changes, physiological traits, and the social behaviour of different species. We propose a series of priority research questions and approaches that could further our understanding of bat health and disease ecology in Canada, inspired by the work of Brock, his colleagues, and students.
... comm.; see also Barataud, 2015, pp. 38ff;Adams et al., 2012). However, the relatively high flight speed of P. nathusii in Pape of 6.9 m/s (Troxell et al., 2019) suggests that many bats in the pre-and post-playbackphases passed the location of the speaker, yet never heard any of the playback files; with such speed, bats may have left the audible range (37-42 kHz; 60 m) in approximatly 10 s. ...
In late summer, migratory bats of the temperate zone face the challenge of accomplishing two energy-demanding tasks almost at the same time: migration and mating. Both require information and involve search efforts, such as localizing prey or finding potential mates. In non-migrating bat species, playback studies showed that listening to vocalizations of other bats, both con-and heterospecifics, may help a recipient bat to find foraging patches and mating sites. However, we are still unaware of the degree to which migrating bats depend on con-or heterospecific vocalizations for identifying potential feeding or mating opportunities during nightly transit flights. Here, we investigated the vocal responses of Nathusius’ pipistrelle bats, Pipistrellus nathusii, to simulated feeding and courtship aggregations at a coastal migration corridor. We presented migrating bats either feeding buzzes or courtship calls of their own or a heterospecific migratory species, the common noctule, Nyctalus noctula. We expected that during migratory transit flights, simulated feeding opportunities would be particularly attractive to bats, as well as simulated mating opportunities which may indicate suitable roosts for a stopover. However, we found that when compared to the natural silence of both pre-and post-playback phases, bats called indifferently during the playback of conspecific feeding sounds, whereas P. nathusii echolocation call activity increased during simulated feeding of N. noctula. In contrast, the call activity of P. nathusii decreased during the playback of conspecific courtship calls, while no response could be detected when heterospecific call types were broadcasted. Our results suggest that while on migratory transits, P. nathusii circumnavigate conspecific mating aggregations, possibly to save time or to reduce the risks associated with social interactions where aggression due to territoriality might be expected. This avoidance behavior could be a result of optimization strategies by P. nathusii when performing long-distance migratory flights, and it could also explain the lack of a response to simulated conspecific feeding. However, the observed increase of activity in response to simulated feeding of N. noctula, suggests that P. nathusii individuals may be eavesdropping on other aerial hawking insectivorous species during migration, especially if these occupy a slightly different foraging niche.
... Other studies (e.g. Adams et al., 2012) comparing detectors show similar dependency of the amount of recordings dependent on the recording device and trigger method but are using different settings in suburban environments. ...
Localizing bats is a common task in many research projects. But working in the
field with this equipment is often challenging since these tracking devices consist
of numerous parts, require calibration and power supplies. Many researchers even
have no access to localization instruments due their price and availability. This thesis
describes new approaches for localizing bats. An eight channel microphone array
which does not require laptops or computers and runs entirely on battery power
was developed from scratch, from new low cost and small size microphones over
the analog-to-digital conversion up to the software and hardware implementation
of real-time detection and recording of all channels. The resulting system allowed
sampling eight channels simultaneously with 1MHz at 16 bit and running 50 h on
battery while real-time detecting echolocation calls. A second method to localize bats
during the absence of light are near infrared video recordings. Based on the popular
Raspberry Pi single board computer, a low cost stereo camera system is introduced
that enables localization of bats in the field at minimum costs. Ten stereo-infrared
cameras were assembled to asses flight behavior of bats around small wind turbines
in northern and southern Germany. An object detection was implemented that
allowed processing of nearly 550 h of stereo video and triangulate all detections
resulting in three dimensional flight trajectories.
... Protection from temperature extremes, rain or humidity may therefore be required for both microphone and recording unit 68 -this may consist of the standard case normally provided as part of the recording system, potentially with other modifications to protect the unit further from rainfall, wind and animals. Procedures for the regular inspection, maintenance and calibration of recording systems are also needed to support field studies 69,70,71 . Microphone management, calibration and checking is very important before and after field deployments, as degradation in microphone quality over time can significantly affect results. ...
Passive acoustic monitoring has great potential as a cost-effective method for long-term
biodiversity monitoring. However, to maximise its efficacy, standardisation of survey protocols is
necessary to ensure data are comparable and permit reliable inferences.
The aim of these guidelines is to outline a basic long-term acoustic monitoring protocol that
can be adapted to suit a range of projects according to specific objectives and size. Here we
summarise some basic recommendations for audible-range terrestrial ecosystem monitoring -
more detail can be found in the following chapters. A ‘Quick start guide’ giving further rationale
for these recommendations can be found in Appendix 1.
... To calculate this distance, the authors used a threshold of 60 dB sound pressure level (SPL; the lower the threshold the more sensitive the recorder), which is commonly used with the acoustic recording device 'Batcorder' (produced by one of Voigt's co-authors) at wind turbines. Other detectors specifically designed to sample bats at wind turbines (BATmode, bioacoustictechnology; Batlogger WEX, Elekon) have a substantially lower threshold at 37 dB SPL and thus record much more activity than the Batcorder (Adams et al. 2012. When compared to figure 2 in Voigt et al. (2021), the detection ranges of these detectors are twice as far as those of the Batcorder, resulting in eight times larger volumes. ...
Voigt et al. (2021) provide a thorough analysis of the restrictions inherent to the estimation of bat abundance from acoustic surveys, and conclude that limitations of acoustic monitoring impede the reliable evaluation of bat fatalities at wind turbines. We argue that acoustic data recorded at the nacelle of wind turbines have been experimentally validated as a useful and appropriate measure of bat collisions. Therefore, acoustic data can be used to estimate bat fatalities at wind turbines, provided a referenced and standardised protocol for data acquisition and analysis is used.
... Simultaneous monitoring by an Avisoft detector and a Batcorder indicated a much better performance of the Avisoft. This corresponds with the findings ofAdams et al. (2012) which evaluated the performance of several types of batdetectors, including Avisoft and Batcorder. ...
... However, ultrasonic recorders, power requirements (battery supplies), memory cards and hard drives are becoming increasingly cheaper (Hill et al., 2018). Automated identification software is not yet reliable for neotropical bats (Rydell et al., 2017;Menon et al., 2018) and the identifications need to be validated manually (Adams et al., 2012;Hintze et al., 2016;Lopéz-Baucells et al., 2019). Indeed, there are some limitations such as the imperfect detection of certain species (Duchamp et al., 2006;Torrez et al., 2017), the inability to quantify individuals and obtain bat abundance (Adams et al., 2015) and difficulties to separate sonotypes with similar echolocation call structure (Jung et al., 2007(Jung et al., , 2014López-Baucells et al., 2016). ...
Mist nets set at ground level is the traditional method of surveying bats and in the Amazon, almost half of the bat surveys used this methodology. The sole use of ground-level mist nets biases surveys because of the lack of records of aerial insectivorous bats, which forage above the canopy or in other open areas. Canopy mist nets, roost searches and acoustic surveys are methods to survey bat assemblages, but their efficiency compared to ground-level mist nets has not been fully evaluated in the Amazon, the world's largest tropical rainforest. Here, we test how the complementarity of sampling methods contributes to the number of species recorded in bat surveys in the Amazonian rainforest. We simultaneously sampled bats using ground mist nets and ultrasonic recorders at the Ducke Reserve (Central Amazon) in Brazil and did a literature review of bat surveys conducted in the Amazon to assess how these methods have been used in field research during the recent decades. Forty-three bat species were identified using ground mist nets, and seventeen species and five acoustic sonotypes were identified using ultrasonic recorders in Ducke Reserve. The combination of ground mist nets and acoustic recorders registered the largest number of bat species. However, for phyllostomid species the sole use of mist nets was efficient in recording the highest number of species, whereas for aerial insectivores acoustic surveys was the most effective. Of the 54 bat surveys made in the Amazon, 27 localities used complementary methods: roost search, canopy mist nets, harp traps and acoustic surveys. The combination of ground and canopy nets, and ground nets with roost search did not record more phyllostomid bat species than the use of ground nets alone. However, the sole use of acoustic surveys recorded more aerial insectivorous species than any other combination of sampling methods. Using mist nets and acoustic surveys simultaneously, as in our study, results in a dramatic increase in species diversity and different guilds than using only mist nets in the Amazon. Canopy nets and roost search did not increase the total number of species or the number of phyllostomid species in bat surveys. By combining different survey methodologies, we can optimize the recorded diversity of bats, especially using both mist nets and acoustic monitoring.
... First, the costs of microphones, especially those sensitive in the ultrasonic range, are too high to further increase the number of array elements. An industry standard microphone with appropriate frequency responses for bioacoustic research often costs well over 1000 US Dollar 28,29 . Secondly, as these microphones are analog they require a data-acquisition device (DAQ) for analog to digital conversion to record the data. ...
Microphone arrays are an essential tool in the field of bioacoustics as they provide a non-intrusive way to study animal vocalizations and monitor their movement and behavior. Microphone arrays can be used for passive localization and tracking of sound sources while analyzing beamforming or spatial filtering of the emitted sound. Studying free roaming animals usually requires setting up equipment over large areas and attaching a tracking device to the animal which may alter their behavior. However, monitoring vocalizing animals through arrays of microphones, spatially distributed over their habitat has the advantage that unrestricted/unmanipulated animals can be observed. Important insights have been achieved through the use of microphone arrays, such as the convergent acoustic field of view in echolocating bats or context-dependent functions of avian duets. Here we show the development and application of large flexible microphone arrays that can be used to localize and track any vocalizing animal and study their bio-acoustic behavior. In a first experiment with hunting pallid bats the acoustic data acquired from a dense array with 64 microphones revealed details of the bats’ echolocation beam in previously unseen resolution. We also demonstrate the flexibility of the proposed microphone array system in a second experiment, where we used a different array architecture allowing to simultaneously localize several species of vocalizing songbirds in a radius of 75 m. Our technology makes it possible to do longer measurement campaigns over larger areas studying changing habitats and providing new insights for habitat conservation. The flexible nature of the technology also makes it possible to create dense microphone arrays that can enhance our understanding in various fields of bioacoustics and can help to tackle the analytics of complex behaviors of vocalizing animals.
... First, observing bats via acoustics contain potential biases in that the physics of ultrasonic sound (bat echolocation pulses) change with atmospheric conditions [92]. This, plus the fact that non-occurrence does not necessarily equate to absence (i.e., detection probability is not reliably 1; [93]), may over or underestimate probabilities of occurrence depending on the conditions, time of year, among other factors. Additionally, acoustic activity of bats and wind turbine collision risk are not always analogous [52]. ...
Abstract: In eastern North America, "tree bats" (Genera: Lasiurus and Lasionycteris) are highly susceptible to collisions with wind energy turbines and are known to fly offshore during migration. This raises concern about ongoing expansion of offshore wind-energy development off the Atlantic Coast. Season, atmospheric conditions, and site-level characteristics such as local habitat (e.g., forest coverage) have been shown to influence wind turbine collision rates by bats onshore, and therefore may be related to risk offshore. Therefore, to assess the factors affecting coastal presence of bats, we continuously gathered tree bat occurrence data using stationary acoustic recorders on five structures (four lighthouses on barrier islands and one light tower offshore) off the coast of Virginia, USA, across all seasons, 2012-2019. We used generalized additive models to describe tree bat occurrence on a nightly basis. We found that sites either indicated maternity or migratory seasonal occurrence patterns associated with local roosting resources, i.e., presence of trees. Across all sites, nightly occurrence was negatively related to wind speed and positively related to temperature and visibility. Using predictive performance metrics, we concluded that our model was highly predictive for the Virginia coast. Our findings were consistent with other studies-tree bat occurrence probability and presumed mortality risk to offshore wind-energy collisions is highest on low wind speed nights, high temperature and visibility nights, and during spring and fall. The high predictive model performance we observed provides a basis for which managers, using a similar monitoring and modeling regime, could develop an effective curtailment-based mitigation strategy.
... In our monitoring schemes, we include specific methodologies to overcome these biases, such as the video recording of the emergence with synchronized ultrasound detectors and infrared lights or a combination of techniques in bat surveys in foraging habitats. Because bioacoustics is gaining momentum worldwide, special care must be taken in acoustic surveys; the availability of detectors and microphones in the market has been increasing dramatically in recent last decades, but acoustic surveys are somewhat difficult to compare, as each detector is optimized under certain conditions and for specific aims, having quite different sensitivities [49]. We recommend using only one or two models (one economic version for volunteers and another more advanced version for professionals), because direct side-by-side comparisons between detectors' performance is crucial for modelling any data resulting from various devices collected from different sources [40]. ...
The Biodiversity and Bioindicators research group (BiBIO), based at the Natural Sciences Museum of Granollers, has coordinated four long-term faunal monitoring programmes based on citizen science over more than two decades in Catalonia (NE Spain). We summarize the historical progress of these programmes, describing their main conservation outputs, the challenges overcome , and future directions. The Catalan Butterfly Monitoring Scheme (CBMS) consists of a network of nearly 200 recording sites where butterfly populations have been monitored through visual censuses along transects for nearly three decades. This programme provides accurate temporal and spatial changes in the abundance of butterflies and relates them to different environmental factors (e.g., habitat and weather conditions). The Bat Monitoring Programme has progressively evolved to include passive acoustic monitoring protocols, as well as bat box-, underground-and river-bat surveys, and community ecological indices have been developed to monitor bat responses at assemblage level to both landscape and climatic changes. The Monitoring of common small mammals in Spain (SEMICE), a common small mammal monitoring programme with almost 80 active live-trapping stations, provides information to estimate population trends and has underlined the relevance of small mammals as both prey (of several predators) and predators (of insect forest pests). The Dormouse Monitoring Programme represents the first monitoring programme in Europe using specific nest boxes for the edible dormouse, providing information about biological and demographic data of the species at the southern limit of its distribution range. The combination and com-plementarity of these monitoring programmes provide crucial data to land managers to improve the understanding of conservation needs and develop efficient protection laws.
This study examines the impact of habitat management on the seasonal and spatial activities of bat species in Mediterranean scrublands of southern France. Three study sites, presenting managed and unmanaged scrublands, were sampled by acoustic recording to assess their ecological potential for bat conservation. General linear mixed models (GLMMs) were used to identify the key factors driving variation in activity patterns of these areas. A total of 16 bat species were recorded, and no significant differences in taxonomic composition were found between managed and unmanaged areas. Bats have an opportunistic tendency to explore different habitats over long distances. In addition to the strong seasonal dynamics observed in most species, we found evidence of a shift in activity rhythms suggesting species adaptation to seasonal thermal variations and prey availability. In this study, the impact of managed areas on activity patterns depends on the functional traits of each species. Level of activity differed considerably from one species to another, suggesting that the ‘management’ effect is not the only ecological parameter involved in conditioning bats' preferred occupancy patterns.
Key words: acoustic, species richness, season, habitat, conservation, France
We document the first visual observation of a Lasiurus cinereus (Hoary Bat) flying over the open ocean, 49 km from the northern California coast. This observation provides further evidence that this migratory species at times utilizes offshore habitat. Hoary Bats face significant, population level threats from collisions with onshore wind turbines, particularly during late-summer and autumn migration periods. The location of this sighting within a leased offshore wind-energy area highlights the potential for Hoary Bats to be impacted by planned offshore wind-energy development.
Woodland bat assemblages are usually structured in space by distance from the ground, water and obstacles, features often defining chiropteran hunting tactics. Consequently, bat species composition differs strongly among various habitats even within the same forest patch. However, when conducting local bat survey in Wolin National Park (WPN), we revealed unexpected uniformity in qualitative and quantitative structure of bat assemblages, based on mist netting and ultrasound recording. In total, 10 vespertilionid species were detected. In all methods and sampled habitats a single species, Pipistrellus pygmaeus, predominated, while no Barbastella barbastellus, an old forest specialist, was detected, despite the abundance of preferred daily roosts. We also reviewed literature for mist netted bat samples in four different habitats of lowland Polish forests. Samples usually clustered based on habitats and the same habitat classes often clustered very closely, despite representing geographically distant forests. The exception was WPN, where all four habitat classes formed a tightly packed cluster. We suppose that P. pygmaeus might act as a hyperabundant native species, a successful generalist that reduces the contribution of more specialized taxa in the assemblage. It probably benefits from both forest renaturation and anthropogenic cross-boundary subsidy, the latter including both roost availability and prey abundance.
Monitoring and surveying of bat populations is becoming increasingly important for identifying environmental changes. Although there are numerous approaches for analysing changes in bat groups, from visual counts to genetic research, bats have typically been studied using capture techniques including mist nets, harp traps, and/or hand nets. These techniques are widely used because they don't require a lot of expensive equipment and eliminate any potential uncertainty in the identification of the species in the future. Bats experience discomfort and invasion from capture techniques. In bat studies, acoustic technologies that record bat echolocation sounds using ultrasound detectors are becoming more and more common. Two pocket-sized acoustical bat detectors were comparatively reviewed in this study, Audio Moth from open acoustic devices and Echo Meter Touch 2 Pro for Android (EMT 2 Pro) from wildlife acoustics. Each device has benefits and drawbacks of its own. Our results suggest that if we are doing sampling in a closed environment or in a well-known site (i.e.) in a Drive count method, we can prefer Audio Moth and if the study is taking place in an open and unknown environment (i.e.) in a transect method then we prefer EMT 2 Pro. The active monitoring with an EMT 2 Pro records more bat call sequences and produces higher-quality call recordings, resulting in a more complete bat community survey than Audio Moth.
Guidance to quantify and manage traffic-related effects on bat populations, commissioned by the BMVBS (German ministry of traffic)
Bat movement and behaviour are still mostly understudied over large scales. High‐altitude, nocturnal activity makes visual identification of bats from the ground virtually impossible, dramatically hindering our ability to study their movement ecology. Despite the wide use of radar in aeroecology, its application to study specific taxa is limited due to incomplete target classification abilities. BATScan is a bat classifier for vertical‐looking radar data, which enables identifying bats and characterizing their unique aeroecology.
We constructed the classifier using data from 10 radar deployments, covering a wide range of habitats on a central bird migration flyway over a 7‐year period, comprising ~18 million observations. We analysed animal migration above the Hula Valley, home to over 30 species of bats spanning a range of 5–150 g in size and exhibiting a variety of ecological characteristics. We distinguished bat‐labelled radar echoes for training according to phenology, morphology and movement ecology of bats, birds and insects. Several non‐bat datasets were constructed and joined to train classifiers under increasing levels of difficulty. Class imbalance in the resulting training data was handled using a generative adversarial network for up‐sampling the much smaller bat dataset.
The resulting classification tool reached a high level of accuracy and precision, and was further scrutinized with an extensive set of ecological validations.
Bats perform seasonal migrations over long distances, but little is known about the spatial and temporal characteristics of this movement, and the ability to study it at a large scale has so far been limited. We present the Israeli BATScan dataset, containing over 60,000 bat observations spanning the entire country and representing multiple habitats. Using this data, we produce an unprecedented large scale, highly detailed documentation of the yearly movements of bats on a major migration flyway, and distinguish this pattern from bird migration over space and time.
So far, radar aeroecology dealt primarily with birds, increasingly with insects, and only rarely with bats. We present BATScan, a classification tool that can incorporate bats into the framework of radar aeroecology to finally enable a comprehensive description of animal aeroecology.
Recent advances in low-cost automated recording unit (ARU) technology have made large-scale bat monitoring projects more practical, but several key features of ARUs (e.g., microphone quality, triggering thresholds) can influence their ability to detect and record bats. As such, it is important to quantify and report variation in ARU performance as new recording systems become available. We used the automated classification software SonoBat to compare the number of call files, number of echolocation pulses, and number of species recorded by a commonly used, full-spectrum bat detector—the Song Meter SM4BAT-FS—and a less expensive, open-source ARU that can detect ultrasound—the AudioMoth. We deployed paired ARUs across several forest types in Louisiana during breeding (June–August) and non-breeding (December–February) periods in 2020 and 2021. Weatherproof cases were unavailable for AudioMoths at the time of our study. Thus, we used disposable plastic bags and plastic boxes recommended by the manufacturer and other AudioMoth users to house our monitors. We lost several AudioMoths to water damage using both methods and subsequently placed these monitors in waterproof smartphone bags for the remainder of our study. We compared data collected by AudioMoths in the three enclosures and found no differences in the number of call files identified to species or species richness. We found that SM4BATs recorded more call files identifiable to species, call files with high-frequency bat calls, echolocation pulses, and higher species richness than AudioMoths. Our results likely reflected differences in microphone sensitivities, recording specifications, and enclosures between the ARUs. We recommend caution when comparing data collected by different ARUs, especially through time as firmware updates and new enclosures become available, and additional research to examine variation in monitor performance across a wide range of environmental conditions.
The knowledge of fish assemblage in submarine environments is a keystone for fishery management but remain poorly monitored due to heavy methodological requirements for scientific fish sampling. Passive acoustic monitoring appeared as a promising non intrusive alternative to fish sampling, potentially providing more objective data at a reduced cost, but still rely on heavy expert analysis of the acoustic signal. We propose in this paper to improve passive acoustic monitoring efficiency with deep learning. Using convolutional recurrent neural networks, we built and tested models able to detect two types of fish vocalizations as well as motor engine sounds. The detector had a high F1 score and an error rate . These methods are promising tools for the fish communities management as they allow automatic fish sounds detection and classification.
In late summer, migratory bats of the temperate zone face the challenge of accomplishing two energy-demanding tasks almost at the same time: migration and mating. Both require information and involve search efforts, such as localizing prey or finding potential mates. In non-migrating bat species, playback studies showed that listening to vocalizations of other bats, both con-and heterospecifics, may help a recipient bat to find foraging patches and mating sites. However, we are still unaware of the degree to which migrating bats depend on con-or heterospecific vocalizations for identifying potential feeding or mating opportunities during nightly transit flights. Here, we investigated the vocal responses of Nathusius’ pipistrelle bats, Pipistrellus nathusii, to simulated feeding and courtship aggregations at a coastal migration corridor. We presented migrating bats either feeding buzzes or courtship calls of their own or a heterospecific migratory species, the common noctule, Nyctalus noctula. We expected that during migratory transit flights, simulated feeding opportunities would be particularly attractive to bats, as well as simulated mating opportunities which may indicate suitable roosts for a stopover. However, we found that when compared to the natural silence of both pre-and post-playback phases, bats called indifferently during the playback of conspecific feeding sounds, whereas P. nathusii echolocation call activity increased during simulated feeding of N. noctula. In contrast, the call activity of P. nathusii decreased during the playback of conspecific courtship calls, while no response could be detected when heterospecific call types were broadcasted. Our results suggest that while on migratory transits, P. nathusii circumnavigate conspecific mating aggregations, possibly to save time or to reduce the risks associated with social interactions where aggression due to territoriality might be expected. This avoidance behavior could be a result of optimization strategies by P. nathusii when performing long-distance migratory flights, and it could also explain the lack of a response to simulated conspecific feeding. However, the observed increase of activity in response to simulated feeding of N. noctula, suggests that P. nathusii individuals may be eavesdropping on other aerial hawking insectivorous species during migration, especially if these occupy a slightly different foraging niche.
Bat arousals during hibernation are related to rises in environmental temperature, body water loss and increasing body heat. Therefore, bats either hibernate in cold places or migrate to areas with mild winters to find water and insects to intake. During winter, insects are abundant in wetlands with mild climates when low temperatures hamper insect activity in other places.
However, the role of wetlands to sustain winter bat activity has never been fully assessed. To further understand bat behaviour during hibernation, we evaluated how the weather influenced hibernating bats, assessed the temperature threshold that increased bat arousals, and discussed how winter temperatures could affect bat activity under future climate change scenarios.
The effects of weather and landscape composition on winter bat activity were assessed by acoustically sampling four different habitats (wetlands, rice paddies, urban areas and salt marshes) in the Ebro Delta (Spain).
Our results show one of the highest winter bat foraging activities ever reported, with significantly higher activity in wetlands and urban areas. Most importantly, we found a substantial increase in bat activity triggered when nocturnal temperatures reached ca. 11 °C. By contrasting historical weather datasets, we show that, since the 1940s, there has been an increase by ca. 1.5 °C in winter maximum temperatures and a 180% increase in the number of nights with mean temperatures above 11 °C in the Ebro Delta.
Temperature trends suggest that in 60–80 years, winter months will reach average temperatures of 11 °C (except maybe in January), which suggest a potential coming interruption or disappearance of bat hibernation in coastal Mediterranean habitats. This study highlights the significant role of wetlands in bat conservation under a climate change scenario as these humid areas represent one of the few remaining winter foraging habitats.
Offshore wind energy is a growing industry in the United States, and renewable energy from offshore wind is estimated to double the country's total electricity generation. There is growing concern that land-based wind development in North America is negatively impacting bat populations, primarily long-distance migrating bats, but the impacts to bats from offshore wind energy are unknown. Bats are associated with the terrestrial environment, but have been observed over the ocean. In this review, we synthesize historic and contemporary accounts of bats observed and acoustically recorded in the North American marine environment to ascertain the spatial and temporal distribution of bats flying offshore. We incorporate studies of offshore bats in Europe and of bat behavior at land-based wind energy studies to examine how offshore wind development could impact North American bat populations. We find that most offshore bat records are of long-distance migrating bats and records occur during autumn migration, the period of highest fatality rates for long-distance migrating bats at land-based wind facilities in North America. We summarize evidence that bats may be attracted to offshore turbines, potentially increasing their exposure to risk of collision. However, higher wind speeds offshore can potentially reduce the amount of time that bats are exposed to risk. We identify knowledge gaps and hypothesize that a combination of operational minimization strategies may be the most effective approach for reducing impacts to bats and maximizing offshore energy production.
Ultrasonic detectors are powerful tools for the study of bat ecology. Many options are available for deploying acoustic detectors including various weatherproofing designs and microphone orientations, but the impacts of these options on the quantity and quality of the bat calls that are recorded are unknown. We compared the impacts of three microphone orientations (horizontal, 45 degrees, and vertical) and two weatherproofing designs (polyvinyl chloride tubes and the BatHat) on the number of calls detected, call quality, and species detected by the Anabat II bat detector system at 17 sites in central Kentucky in May and June 2008. Detectors with BatHat weatherproofing recorded significantly fewer call sequences, pulses per file, species per site, and lower quality calls. Detectors in the horizontal position also tended to record fewer files, fewer species, and lower quality calls. These results illustrate potential impacts of deployment method on quality and quantity of data obtained. Because weatherproofing and orientation impacted the quality and quantity of data recorded, comparison of results using different methodologies should be made with caution.
Crassulacean acid metabolism (CAM) is one of three metabolic pathways found in vascular plants for the assimilation of carbon dioxide. In this study, we investigate the occurrence of CAM photosynthesis in 200 native orchid species from Panama and 14 non-native species by carbon isotopic composition (δ 13 C) and compare these values with nocturnal acid accumulation measured by titration in 173 species. Foliar δ 13 C showed a bimodal distribution with the majority of species exhibiting values of approximately −28‰ (typically associated with the C 3 pathway), or −15‰ (strong CAM). Although thick leaves were related to δ 13 C values in the CAM range, some thin-leaved orchids were capable of CAM photosynthesis, as demonstrated by acid titration. We also found species with C 3 isotopic values and significant acid accumulation at night. Of 128 species with δ 13 C more negative than −22‰, 42 species showed nocturnal acid accumulation per unit fresh mass characteristic of weakly expressed CAM. These data suggest that among CAM orchids, there may be preferential selection for species to exhibit strong CAM or weak CAM, rather than intermediate metabolism.
The islands of the West Indies are home to 56 species of bats, half of which are endemic to the region. Recently, researchers have begun to characterize the echolocation calls of the bat fauna of the West Indies. However, the majority of species have not yet been characterized and no studies have been conducted on most West Indian islands, including the islands of the Bahamas. Exuma, a small island in the Bahamas, has six species of bats classified in four families (Molossidae, Natalidae, Phyllostomidae, and Vespertilionidae). We used an ultrasonic detector (Avisoft UltraSoundGate 116) to study the echolocation calls of these bats, focusing on three species whose calls have not been previously described, Erophylla sezekorni, Macrotus waterhousii, and Nyctiellus lepidus. Each of these species uses low-intensity, frequency modulated echolocation calls and exhibits intraspecific call variation both among individuals and within individual call sequences. Despite this variation, we were able to accurately classify each species using discriminant function analysis. Accuracy rates varied from 94% (M. waterhousii) to 100% (E. sezekorni, N. lepidus). We also provide a preliminary description of the echolocation calls of two additional Exuman bat species, Lasiurus borealis and Tadarida brasiliensis. The echolocation calls of L. borealis and T. brasiliensis appear similar to their mainland counterparts; however, more study is needed to characterize the calls of these two species on Exuma.
Wind energy is a rapidly growing sector of the alternative energy industry in North America, and larger, more productive turbines are being installed. However, there are concerns regarding bird and bat fatalities at wind turbines. To assess the influence of turbine size on bird and bat fatalities, we analyzed data from North American wind energy facilities. Diameter of the turbine rotor did not influence the rate of bird or bat fatality. The height of the turbine tower had no effect on bird fatalities per turbine, but bat fatalities increased exponentially with tower height. This suggests that migrating bats fly at lower altitudes than nocturnally migrating birds and that newer, larger turbines are reaching that airspace. Minimizing tower height may help minimize bat fatalities. In addition, while replacing older, smaller turbines with fewer larger ones may reduce bird fatalities per megawatt, it may result in increased numbers of bat fatalities.
Variation in carbon-isotope composition among and between wheat genotypes was correlated with variation in water-use efficiency in separate pot experiments conducted in spring-summer and in winter. In the main, winter experiment, the water-use efficiencies ranged from 2.0 to 3.7 mmolC/mol H2O (means of four replicates) while the corresponding isotope effects for leaf material ranged from 1.0225 to 1.0194. 13C was more abundant in grain than in leaves and stems. It is suggested that carbon-isotope analysis may be a useful tool in selection for improved water-use efficiency in breeding programmes for C3 species.
Non-photosynthetic, or heterotrophic, tissues in C 3 plants tend to be enriched in 13 C compared with the leaves that supply them with photosynthate. This isotopic pattern has been observed for woody stems, roots, seeds and fruits, emerging leaves, and parasitic plants incapable of net CO 2 fixation. Unlike in C 3 plants, roots of herbaceous C 4 plants are generally not 13 C-enriched compared with leaves. We review six hypotheses aimed at explaining this isotopic pattern in C 3 plants: (1) variation in biochemical composition of heterotrophic tissues compared with leaves; (2) seasonal separation of growth of leaves and heterotrophic tissues, with corresponding variation in photosynthetic discrimination against 13 C; (3) differential use of day v. night sucrose between leaves and sink tissues, with day sucrose being relatively 13 C-depleted and night sucrose 13 C-enriched; (4) isotopic fractionation during dark respiration; (5) carbon fixation by PEP carboxylase; and (6) developmental variation in photosynthetic discrimination against 13 C during leaf expansion. Although hypotheses (1) and (2) may contribute to the general pattern, they cannot explain all observations. Some evidence exists in support of hypotheses (3) through to (6), although for hypothesis (6) it is largely circumstantial. Hypothesis (3) provides a promising avenue for future research. Direct tests of these hypotheses should be carried out to provide insight into the mechanisms causing within-plant variation in carbon isotope composition.
Euphorbiaceae is among the large flowering plant families consisting of a wide variety of vegetative forms some of which are plants of great importance. Its classification and chemistry have of late been subjects of interest possibly because of the wide variety of chemical composition of its members, many of which are poisonous but useful. In this review, we have tried to demonstrate why Euphorbiaceae are important medicinal plants. Two important issues have come up. The worldwide distribution of the family exposes its members, to all sorts of habitats to which they must adapt, therefore inducing a large variety of chemicals (secondary substances) that are employed for survival/defense. Succulence and the CAM (crassulacean acid metabolism) pathway that characterize a good number of its members were quoted as some of the adaptations that aid colonization and survival to achieve this induction. We have also found out that medicinal properties of some of its species may be due to stress factors that characterize most habitats of the family. Varying stress factors like temperature, salinity, drought and others were seen to operate in tandem with genetic factors such as gene expression and mutation loads to bring about synthesis of a wide assemblage of secondary substances that may probably be responsible for the family's medicinal nature. It was concluded that the family is a good starting point for the search for plant-based medicines.
Photosynthetic carbon gain in plants using the C(3) photosynthetic pathway is substantially inhibited by photorespiration in warm environments, particularly in atmospheres with low CO(2) concentrations. Unlike C(4) plants, C(3) plants are thought to lack any mechanism to compensate for the loss of photosynthetic productivity caused by photorespiration. Here, for the first time, we demonstrate that the C(3) plants rice and wheat employ a specific mechanism to trap and reassimilate photorespired CO(2) . A continuous layer of chloroplasts covering the portion of the mesophyll cell periphery that is exposed to the intercellular air space creates a diffusion barrier for CO(2) exiting the cell. This facilitates the capture and reassimilation of photorespired CO(2) in the chloroplast stroma. In both species, 24-38% of photorespired and respired CO(2) were reassimilated within the cell, thereby boosting photosynthesis by 8-11% at ambient atmospheric CO(2) concentration and 17-33% at a CO(2) concentration of 200 µmol mol(-1) . Widespread use of this mechanism in tropical and subtropical C(3) plants could explain why the diversity of the world's C(3) flora, and dominance of terrestrial net primary productivity, was maintained during the Pleistocene, when atmospheric CO(2) concentrations fell below 200 µmol mol(-1) .
The leafless spurgeEuphorbia aphylla (Euphorbiaceae), an endemic species restricted to several of the Canary Islands where it inhabits coastal and arid localities, expresses Crassulacean Acid Metabolism (CAM) when it is subjected to summer drought. A flexible CAM is consistent with the general ecology of the species. It is the only member of sect.Tirucalli native to the Canary Islands and is at the north-western edge of the section''s biogeographical range. The other members of the section have a paleotropic distribution and are found throughout Africa. Many of them are regarded as obligate CAM plants, includingE. tirucalli which was used as a comparison in ecophysiological experiments examining the response ofE. aphylla to drought and temperature.
In the terrestrial bromeliad, Puya floccosa, a value of carbon isotopic composition (δ13C) of −22‰ has been previously reported, suggesting the operation of weak and/or intermediate (C3-CAM) crassulacean acid metabolism (CAM). In order to characterize the operation of CAM in P. floccosa and its possible induction by drought, plants were grown in Caracas and subjected to four independent drought cycles. Additionally,
since plants of this species grow in Venezuela in a large range of elevations, leaf samples were collected at elevations ranging
from 725 to 2,100 m a.s.l. in the Venezuelan Andes and the Coastal Range, in order to evaluate the effect of elevation on
CAM performance. Even though nocturnal acid accumulation occurred in both watered and droughted plants, mean ΔH+ was higher in droughted than watered plants [ΔH+ = 60.17.5 and 22.9 ± 5.2 μmol g−1(FM), respectively]. The majority of plants from all the natural populations sampled had low values of δ13C not differing significantly from those of C3 plants collected as standards and δ13C did not change with elevation. We conclude that P. floccosa is capable of a weak CAM activity, with a large variability among populations and drought experiments probably due to local
and temporal differences in microclimatic variables and drought stress; elevation bears no influence on values of δ13C in this species.
Additional key words
Bromeliaceae
-elevation-nocturnal acid accumulation
Echolocation calls of most bats are emitted at high intensities and subject to eavesdropping by nearby conspecifics. Bats may be especially attentive to feeding buzz calls, which are emitted immediately before attack on airborne insects and indicate the potential presence of prey in the nearby area. Although previous work has shown that some species are attracted to feeding buzzes, these studies did not provide a well-controlled test of eavesdropping, as comparisons were made between responses to natural and altered signals (e.g., forward versus backward broadcasts of calls). In this study, I assessed the importance of feeding buzzes by conducting playbacks of controlled echolocation stimuli. I presented free-flying Brazilian free-tailed bats, Tadarida brasiliensis (I. Geoffroy, 1824), with echolocation call sequences in which feeding buzz calls were either present or absent, as well as a silence control. I determined levels of bat activity by counting the number of echolocation calls and bat passes recorded in the presence of each stimulus, and found significantly greater bat activity in response to broadcasts that contained feeding buzzes than to broadcasts without feeding buzzes or to the silence control. These results indicate that bats are especially attentive to conspecific feeding buzz calls and that eavesdropping may allow a bat to more readily locate rich patches of insect prey.
In habitats where prey is either rare or difficult to predict spatiotemporally, such as open habitats, predators must be adapted to react effectively to variations in prey abundance. Open-habitat foraging bats have a wing morphology adapted for covering long distances, possibly use information transfer to locate patches of high prey abundance, and would therefore be expected to show an aggregative response at these patches. Here, we examined the effects of prey abundance on foraging activities of open-habitat foragers in comparison to that of edge-habitat foragers and closed-habitat foragers. Bat activity was estimated by counting foraging calls recorded with bat call recorders (38,371 calls). Prey abundance was estimated concurrently at each site using light and pitfall traps. The habitat was characterized by terrestrial laser scanning. Prey abundance increased with vegetation density. As expected, recordings of open-habitat foragers clearly decreased with increasing vegetation density. The foraging activity of edge- and closed-habitat foragers was not significantly affected by the vegetation density, i.e., these guilds were able to forage from open habitats to habitats with dense vegetation. Only open-habitat foragers displayed a significant and proportional aggregative response to increasing prey abundance. Our results suggest that adaptations for effective and low-cost foraging constrains habitat use and excludes the guild of open-habitat foragers from foraging in habitats with high prey abundance, such as dense forest stands.
Zamioculcas zamiifolia (Araceae), a terrestrial East African aroid, with two defining attributes of crassulacean acid metabolism (CAM) (net CO(2) uptake in the dark and diel fluctuations of titratable acidity) is the only CAM plant described within the Araceae, a mainly tropical taxon that contains the second largest number of epiphytes of any vascular plant family. Within the Alismatales, the order to which the Araceae belong, Z. zamiifolia is the only documented nonaquatic CAM species. Zamioculcas zamiifolia has weak CAM that is upregulated in response to water stress. In well-watered plants, day-night fluctuations in titratable acidity were 2.5 μmol H(+)·(g fresh mass)(-1), and net CO(2) uptake in the dark contributed less than 1% to daily carbon gain. Following 10 d of water stress, net CO(2) uptake in the light fell 94% and net CO(2) uptake in the dark increased 7.5-fold, such that its contribution increased to 19% of daily carbon gain. Following rewatering, dark CO(2) uptake returned to within 5% of prestressed levels. We postulate that CAM assists survival of Z. zamiifolia by reducing water loss and maintaining carbon gain during seasonal droughts characteristic of its natural habitat.
This study investigated whether Euphorbia subgenus Chamaesyce subsection Acutae contains C3–C4 intermediate species utilizing C2 photosynthesis, the process where photorespired CO2 is concentrated into bundle sheath cells. Euphorbia species in subgenus Chamaesyce are generally C4, but three species in subsection Acutae (E. acuta, E. angusta, and E. johnstonii) have C3 isotopic ratios. Phylogenetically, subsection Acutae branches between basal C3 clades within Euphorbia and the C4 clade in subgenus Chamaesyce. Euphorbia angusta is C3, as indicated by a photosynthetic CO2 compensation point (Г) of 69 μmol mol−1 at 30 °C, a lack of Kranz anatomy, and the occurrence of glycine decarboxylase in mesophyll tissues. Euphorbia acuta utilizes C2 photosynthesis, as indicated by a Г of 33 μmol mol−1 at 30 °C, Kranz-like anatomy with mitochondria restricted to the centripetal (inner) wall of the bundle sheath cells, and
localization of glycine decarboxlyase to bundle sheath mitochondria. Low activities of PEP carboxylase, NADP malic enzyme,
and NAD malic enzyme demonstrated no C4 cycle activity occurs in E. acuta thereby classifying it as a Type I C3–C4 intermediate. Kranz-like anatomy in E. johnstonii indicates it also utilizes C2 photosynthesis. Given the phylogenetically intermediate position of E. acuta and E. johnstonii, these results support the hypothesis that C2 photosynthesis is an evolutionary intermediate condition between C3 and C4 photosynthesis.
In this paper we report for the first time the occurrence of an inducible weak CAM in leaves of Talinwn triangulare (Jacq.) Willd. This plant is a terrestrial perennial deciduous herb with woody stems and succulent leaves which grows under
full exposure and in the shade in northern Venezuela. Plants grown in a greenhouse (‘sun’ plants) and a growth cabinet (‘shade’
plants) with daily irrigation showed CO2 uptake only during the daytime (maximum rate, 4·0 μmol m−2 s−1) and a small acid accumulation during the night (6·0 μmol H+g−1 FW). Twenty-four hours after cessation of irrigation, no CO2 exchange was observed during part of the night. Dark fixation reached a maximum (1·0 μmol CO2 m−2 s−1, 100 μmol H+ g−1 FW) on day 9 of drought. By day 30 almost no gas exchange was observed, while acid accumulation was still 10 μmol H+ g−1 FW. Rewatering reverted the pattern of CO2 exchange to that of a C3 plant within 24 h. Daytime and night-time phosphoenolpyruvate carboxylase activity increased up to 100% (shade) and 62% (sun)
of control values after 10 and 15 d of drought, respectively. Light compensation point and saturating irradiance were similar
in well-watered sun and shade plants, values being characteristic of sun plants. CAM seems to be important for the tolerance
of plants of this species to moderately prolonged (up to 2 months) periods of drought in conditions of full exposure as well
as shade, and also for regaining high photosynthetic rates shortly after irrigation.
Background:
In obligate Crassulacean acid metabolism (CAM), up to 99 % of CO(2) assimilation occurs during the night, therefore supporting the hypothesis that CAM is adaptive because it allows CO(2) fixation during the part of the day with lower evaporative demand, making life in water-limited environments possible. By comparison, in facultative CAM (inducible CAM, C(3)-CAM) and CAM-cycling plants drought-induced dark CO(2) fixation may only be, with few exceptions, a small proportion of C(3) CO(2) assimilation in watered plants and occur during a few days. From the viewpoint of survival the adaptive advantages, i.e. increased fitness, of facultative CAM and CAM-cycling are not obvious. Therefore, it is hypothesized that, if it is to increase fitness, CAM must aid in reproduction. Scope An examination of published reports of 23 facultative CAM and CAM-cycling species finds that, in 19 species, drought-induced dark CO(2) fixation represents on average 11 % of C(3) CO(2) assimilation of watered plants. Evidence is discussed on the impact of the operation of CAM in facultative and CAM-cycling plants on their survival--carbon balance, water conservation, water absorption, photo-protection of the photosynthetic apparatus--and reproductive effort. It is concluded that in some species, but not all, facultative and cycling CAM contribute, rather than to increase carbon balance, to increase water-use efficiency, water absorption, prevention of photoinhibition and reproductive output.
This study empirically tests the prediction that the echolocation calls of gleaning insectivorous bats (short duration, high frequency, low intensity) are acoustically mismatched to the ears of noctuid moths and are less detectable than those of aerially hawking bats. We recorded auditory receptor cell action potentials elicited in underwing moths (Catocala spp.) by echolocation calls emitted during gleaning attacks by Myotis septentrionalis (the northern long-eared bat) and during flights by the aerial hawker Myotis lucifugus (the little brown bat). The moth ear responds inconsistently and with fewer action potentials to the echolocation calls emitted by the gleaner, a situation that worsened when the moth's ear was covered by its wing (mimicking a moth resting on a surface). Calls emitted by the aerial-hawking bat elicited a significantly stronger spiking response from the moth ear. Moths with their ears covered by their wings maintained their relative hearing sensitivity at their best frequency range, the range used by most aerial insectivorous bats, but showed a pronounced deafness in the frequency range typically employed by gleaning bats. Our results (1) support the prediction that the echolocation calls of gleaners are acoustically inconspicuous to the ears of moths (and presumably other nocturnal tympanate insects), leaving the moths particularly vulnerable to predation, and (2) suggest that gleaners gain a foraging advantage against eared prey.
Clusia is the only dicotyledonous tree genus with crassulacean acid metabolism (CAM), and in some cases all variants of CAM can be expressed in one given species. These unique features as well as Clusia's extreme flexibility have put it in the limelight of international research. The studies presented in this volume embrace anatomy, morphology and plant architecture, phytogeographical distribution and community ecology, phylogeny and genetic diversity, physiology and metabolism, physiological ecology and functional diversity, circadian rhythmicity and biological timing. Covering all aspects of tree biology, this richly illustrated volume is an invaluable source of information for any plant scientist.
Direct field comparisons revealed that in any time period, a bat detecting system using zero-crossing period meter analysis (the Anabat II Bat Detector with Anabat ZCAIM and Anabat 6 software) detected significantly fewer bat echolocation calls than a time-expansion bat detecting system (Pettersson D980 detector with BatSoundPro software). Furthermore, the features of 81 echolocation calls (highest frequency, in kHz; lowest frequency, in kHz; duration, in ms) recorded and analyzed on both systems differed significantly. Regression analyses indicated no consistent, frequently unpredictable differences between Anabat and Pettersson values for the lowest frequencies in echolocation calls, but a significant correlation for their highest frequencies and durations. In a variety of field settings in Israel and in southern Ontario, Canada involving both foraging bats and bats emerging from a cave roost, the Pettersson system recorded echolocation calls not detected by the Anabat system. When many Myotis bats were emerging from a cave roost in Israel, the Anabat system did not detect the calls of a Rhinolophus species or those of another vespertilionid which were detected by the Pettersson system. The differences in performance between the two kinds of systems reflect differences in sensitivity and operation between zero-crossing period meters and time-expansion systems. Data on bat activity or echolocation calls detected and analyzed by a zero-crossing period meter system like Anabat are not as consistent or as reliable as those obtained by a time-expansion system like the Pettersson. Differences in performance of bat detectors coincide with considerable difference in costs, from about USS 650 for an Anabat system, to over USS 2,000 for a Pettersson system, which involves digital time-expansion. A time-expansion system involving a high speed tape recorder will cost over USS 30,000. When it comes to bat detectors and analysis systems, the quality of data that will be obtained is a direct reflection of cost - buyers get what they pay for.
Use of bat detectors can be an effective method of comparing relative amounts of activity of bats among areas. If multiple detectors are used, differences in sensitivity of detectors could bias results. We investigated the variability in sensitivity and field of detection of 14 Anabat II bat detectors. Levels of sensitivity varied among detectors, greatly affecting relative sizes of the fields of detection. Calibration using an ultrasonic signal source can minimize variability in sensitivity among detectors.
Using the technique of carbon isotopic ratio determinations, 20 selected species of Euphorbia (s. lat.) have been investigated to determine their metabolic status. Previous work is reviewed, and as found by previous investigators, enriched 13C values -- indicating Crassulacean acid metabolism or C4 photosynthesis -- have been detected only in subgenera Euphorbia and Chamaesyce, respectively. All taxa investigated in subg. Chamaesyce except two species of subsect. Acutae show the Kranz syndrome and C4 photosynthesis; the probable phylogenetic origin of the subgenus is therefore pinpointed within this subsection. Apparently taxa with Crassulacean acid metabolism and C4 photosynthesis have arisen independently within the genus.
We present behavioural data demonstrating that the little brown bat, Myotis lucifugus, and the northern long-eared bat, M. septentrionalis, can glean prey from surfaces and take prey on the wing. Our data were collected in a large outdoor flight room mimicking a cluttered environment. We compared and analysed flight behaviours and echolocation calls used by each species of bat when aerial hawking and gleaning. Our results challenge the traditional labelling of M. lucifugus as an obligate aerial-hawking species and show that M. septentrionalis, which is often cited as a gleaning species, can capture airborne prey. As has been shown in previous studies, prey-generated acoustic cues were necessary and sufficient for the detection and localization of perched prey. We argue that the broadband, high-frequency, downward-sweeping, frequency-modulated calls used by some bats when gleaning prey from complex surfaces resolve targets from background. First, because calls of lower frequency and narrower bandwidth are sufficient for assessing a surface before landing, and second, because there are few, if any, simple surfaces in nature from which substrate-gleaning behaviours in wild bats would be expected. © 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.