Article

Do you hear what I hear? Implications of detector selection for acoustic monitoring of bats

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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.

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... In addition, contrary to capture methods, radio tracking methods, roost surveys and the use of ultrasonic detectors, all non-intrusive methods, are often the only logistically feasible methods (Stahlschmidt and Brühl 2012). Thus, since the two last decades, these approaches have been widely used by researchers working for environmental consulting firms or government agencies (Adams et al. 2012), for example, during the evaluation of development projects. Acoustic detectors have become increasingly used by academic researchers to investigate the differential use of habitats by bats (Sherwin et al. 2000;Russo and Jones 2003) or to test various anthropogenic pressures such as the following: (i) agricultural intensification based on high levels of agrochemicals (Wickramasinghe et al. 2003); (ii) non-lethal impacts of wind turbines, such as the disturbance of commuting and migration routes and local habitat loss (Hötker et al. 2006;Millon et al. 2015); or (iii) artificial light at night (Stone et al. 2009;Azam et al. 2016). ...
... However, temperature and humidity could also indirectly influence the behaviour of bats due to their impact on feeding prey (O'Donnell 2000;Ciechanowski et al. 2007). In addition, acoustic recordings are expected to be influenced by technical choices such as the following: the detector microphone (Waters and Walsh 1994;Adams et al. 2012), bat detector height (Weller and Zabel 2002;Baerwald and Barclay 2009;Collins and Jones 2009;Jones et al. 2009), detector orientation (Weller and Zabel 2002) and distance of the signal from the detector (Adams et al. 2012). Moreover, long-term acoustic monitoring involves also considering the wear of the microphones. ...
... However, temperature and humidity could also indirectly influence the behaviour of bats due to their impact on feeding prey (O'Donnell 2000;Ciechanowski et al. 2007). In addition, acoustic recordings are expected to be influenced by technical choices such as the following: the detector microphone (Waters and Walsh 1994;Adams et al. 2012), bat detector height (Weller and Zabel 2002;Baerwald and Barclay 2009;Collins and Jones 2009;Jones et al. 2009), detector orientation (Weller and Zabel 2002) and distance of the signal from the detector (Adams et al. 2012). Moreover, long-term acoustic monitoring involves also considering the wear of the microphones. ...
... Les conditions météorologiques défavorables aux relevés, tel que le vent, la pluie ou les températures inférieures à 10°C, ont été évitées (Parsons & Bat Conservation Trust, 2007). Les enregistreurs de type SM2BAT sont adaptés à l'enregistrement de l'ensemble des espèces dans un rayon d'environ 50 mètres (Adams et al., 2012) ce qui correspond à la surface des placettes du réseau FunDiv Europe (Baeten et al., 2013). ...
... Each plot was defined as a square area of 50 x 50m with homogeneous tree species distribution. The plot size matched with the theoretical range of bat detector efficiency (Adams et al., 2012). In all plots we recorded tree species richness and mean basal area of broadleaved trees. ...
... Our findings may therefore be used to adapt their management in order further improve their conservation value. Adams, A.M., Jantzen, M.K., Hamilton, R.M., Fenton, M.B., 2012 Evol. 3, 992-998. ...
Thesis
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Les chiroptères sont reconnus comme de potentiels régulateurs des populations d’insectes. Ce sont aussi les mammifères européens pour lesquels les enjeux de conservation sont les plus importants. Ils trouvent dans les forêts des habitats favorables qui sont cependant menacés par les changements climatiques et la fragmentation. Il convient donc de mieux comprendre lesrelations entre les communautés de chiroptères, leurs habitats et leurs proies en forêt. L'objectif de cette thèse est de quantifier les effets, à différentes échelles spatiales, desprincipales composantes de l’habitat forestier sur l’activité, la richesse spécifique, la diversité fonctionnelle et la composition des communautés de chiroptères européens. Les résultats reposent sur des données collectées grâce à des protocoles expérimentaux en Aquitaine et dans les six pays du réseau de placettes forestières organisé par le projet FunDivEurope. De la parcelle au continent, l'accroissement de la diversité des essences forestières, de la proportion de feuillus et du bois mort, en augmentant les ressources en proies et en gîtes, ont des effets positifs sur les communautés de chiroptères. Ces effets, non stationnaires, se renforcent vers le nord avec la rigueur du climat. Nous confirmons également que les chiroptères forestiers, par leur réponse numérique et fonctionnelle aux densités de proie, peuvent limiter la démographie d’un insecte défoliateur. Des mesures de gestion, visant le renforcement des structures-clés des habitats forestiers, sont proposées pour favoriser la conservation des communautés de chiroptères et leur capacité de régulation des insectes ravageurs.
... These record the sounds bats produce during navigation, foraging or social behaviour. Ultrasound sounds in general have limited reach, and depending on the species, habitat and weather conditions (Adams et al. 2012, Barataud 2015) and can vary from less than 5 m to 100 m (Barataud 2015). A bat detector will, to a large extent, be able to record sounds that will enable bat-species identification. ...
... Next to the position and the mounting-direction of the microphone, the choice of the recording device (both microphone and recorder) are of great importance. (Adams et al. 2012, Lagerveld et al. 2019. Note that the sensitivity of microphones decreases over time and therefore regular replacement or re-calibration is required. ...
... Flight calls of birds should be recorded with a bird sound recorder. Note that the detection distance of some species is rather limited (Adams et al. 2012, Barataud 2015 and therefore multiple ultrasound and regularly placed microphones are needed to monitor bat and bird activity at various tower heights (Lagerveld et al. 2017A, Bach et al. in press A). Even so, it is not likely that the entire RSA can be monitored. ...
... comm.). Compared to the ZCA detectors we used, full-spectrum detectors, as employed by Pottie et al. [33] generally record more calls and offer greater resolution [49]. For species-identification purposes, we expect those differences to be minimal in our context, but we identified calls based on measured parameters, such as minimum frequency, slope and duration [see also 47]. ...
... Therefore, we strongly encourage studies using methods suited to fruit bats. Third, it should be noted that our use of ZCA (as opposed to full-spectrum) detectors may have limited our ability to detect certain species whose calls are typified by steep, FM sweeps [49]. However, based on occurrence data in the paper we used as a reference for bat identification [33], we did not expect to find these bats along roads. ...
... However, based on occurrence data in the paper we used as a reference for bat identification [33], we did not expect to find these bats along roads. Full-spectrum detectors may also record more feeding buzzes [49]. However, in reviewing each file visually and by sound, we aimed to mitigate this issue. ...
Article
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Cities around the world are transitioning to more efficient lighting schemes, especially retrofitting traditional, high-pressure sodium (HPS) streetlights with light-emitting diode (LED) lights. Although these initiatives aim to address the problems of urban sustainability and save money, the ecological impacts of these retrofits remain poorly understood, especially in brightly lit cities and in the tropics, where urbanisation is most rapid. We performed an experimental study of the retrofit in Singapore–focusing on insectivorous bats, whose activity we monitored acoustically along paired control (HPS-lit) and treatment (LED-lit) streets. We recorded seven species along these streets, but only obtained enough recordings to measure the effect of light type for three of them–all of which can reasonably be described as urban adapters. The strongest predictor of bat activity (an index of habitat use) was rainfall–it has a positive effect. Light type did not influence bat activity or species composition of the bat assemblage along these streets, though it did interact with the effects of rainfall and traffic noise for one bat species. Ultimately, the retrofit may be ecologically meaningless to urban-adapted, tropical insectivores that already experience high levels of light pollution as they do in Singapore. However, while our findings may appear reassuring to those concerned with such retrofits in other tropical and/or brightly-lit cities, they also highlight the contextual nature of ecological impacts. We point out that they should not be prematurely generalised to other locales and systems. In particular, they do not imply no impact on species that are less urban-adapted, and there is a clear need for further studies, for example, on responses of other foraging guilds and of bats (and insects) throughout the tropics.
... Bats are also important keystone species providing many ecosystem services such as pest control, pollination and seed dispersal Voigt 2016, Jones et al. 2013). Unfortunately, about one quarter of all bat species are threatened with extinction and due to their nocturnal behaviour, use of multiple (difficult to access) roosts, and their variation in flight patterns, bats can be difficult to survey and are often overlooked in diversity studies (Adams et al. 2012, Monadjem and Reside 2008, Berry et al. 2004, Mickleburgh et al., 2002, Gelderblom et al. 1995. Most African bat species are poorly studied with about 15% of all bat species in southern African listed under Data Deficient by the IUCN (Monadjem et al. 2010). ...
... SM4 and SM2 Songmeters (Wildlife Acoustics, USA) were used to record the echolocation calls of insectivorous bats in northern KNP (Adams et al. 2012). Each detector was equipped with a waterproof case and an SMM-U1 or SMX-US ultrasonic full spectrum, omni-directional microphone (Wildlife Acoustics, Concord, MA, USA), which was placed at a 45-degree angle, at least 1.5 meters above the ground, by mounting it onto a pole or a tree (Clement et al. 2014). ...
... Bat detectors are able to detect a greater species richness over a shorter period of time compared to live -capture(O'Farrell & Gannon 1999). However, when identifying recorded echolocation calls, it is important to know and understand the call parameters from species within the study area(Taylor et al. 2013, Adams et al. 2012). Through live-capture, echolocation calls for call reference libraries can be collected(Taylor et al. 2013). ...
Article
The Kruger National Park (KNP) is considered an important biodiversity hotspot, with insectivorous bats representing about twenty percent of the total mammalian diversity of South Africa. Historically, 40 bat species have been documented in the northern region of the Park between 1960 and 1990. However, it has been three decades since the last comprehensive assessment. To aid the long-term monitoring of bats within KNP, our study re-surveyed the bat community of northern KNP over two years , incorporated the latest acoustic technologies, compared changes in bat species richness with historical data, and tested the use of an automated classifier for the acoustic data. We captured bats and recorded echolocation calls at 26 sites ), between March and October in 2017 and 2018. Kaleidoscope Pro software was used to identify each bat call series recorded. To enhance the accuracy of this tool, a northern KNP-specific classifier was developed. We recorded 27 distinct species during this study, of which 13 were live-captured. The historical data therefore show a much higher richness of bat species within the study area (40 species) than recorded during our study (27 species), although the former were collected over a much longer period of time during numerous collecting trips by staff of the former Transvaal Museum (Ditsong National Museum of Natural History). Total sample effort, environmental effects, biological aspects and overall study limitations likely contributed to the observed differences. The classifier tool had a relatively high percentage accuracy (80%) but manual identification was required to avoid the misidentification of rare species and to detect new species not previously recorded. Future studies should focus more effort on live-capturing, given the high species richness of the region and the limitation of bat detectors to record high frequency and low intensity echolocation calls, which are common in many southern African species.
... With increasing reliance on acoustic methods comes a greater need to understand and quantify sources of variation related to the process of detecting and recording bats. Broadly, changes in acoustic bat activity can represent biologically interesting variation in the number, species, or behavior of bats, or can stem from factors such as the characteristics of the sampled airspace and associated influence on the propagation of ultrasound through air, and the equipment used to record the sound (Adams et al 2012;Goerlitz 2018). Some sources of potential nuisance variation cannot be controlled for under natural monitoring conditions. ...
... Bat detectors use a variety of microphone elements and algorithms/technologies to transform ultrasonic echolocation pulses of bats into the range of human hearing, and associated variation in sensitivity among detector types can have profound effects on detection range and volume of sampled airspace (Parsons 1996;Parsons and Szewczak 2009;Adams et al. 2012), ...
... Intra-pair variation in recorded bat activity was substantially smaller in our study than in comparisons among different types of detectors (e.g. Adams et al. 2012), which can differ substantially in microphone type, detection pattern, signal to noise ratios and other factors affecting sensitivity. As detectors and associated analysis methods continue to develop, comparisons to previous datasets recorded with older equipment will introduce yet additional sources of variation, potentially complicating long-term monitoring programs that rely on autonomous acoustic monitors (Rempel et al. 2013;Shonfield and Bayne 2017). ...
Article
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Bat populations in North America face novel threats from white-nose syndrome and widespread turbine-related mortality related to the rapidly expanding wind power industry in addition to long-standing pressures from habitat loss and degradation. Bats, unlike most small mammals, are long-lived and slow to reproduce, highlighting the importance of understanding and managing anthropogenic sources of mortality. My dissertation research used acoustic bat detectors to measure bat activity at commercial wind projects, predict patterns in risk, and design strategic measures to reduce fatality rates by curtailing turbine operation during periods when bats are most active. Bats collide with wind turbines only when their rotors are spinning, and risk of turbine-related fatality is therefore a dynamic factor that can be manipulated by curtailing turbine operation when bats are active. We first measured inter-detector variation in metrics of acoustic bat activity to understand how the acoustic detection process may affect inferences related to spatial and temporal variation in bat activity. Using acoustic detectors mounted on top of wind turbines at two commercial wind farms in West Virginia, we then demonstrated that the amount of bat activity recorded when turbines were operating aligned closely with bat fatality rates on multiple scales. Accordingly, the metric of bat activity exposed to turbine operation provides a meaningful, quantitative indicator of turbine-related bat fatality risk. Further, bats responded consistently to changing wind speed and temperature at turbines in both wind farms across multiple years, enabling exposed bat activity to be predicted accurately among turbines and years. Building on these results, we simulated exposure of bats to turbine operation and energy loss for curtailment strategies recommended by state and federal agencies in the United States and Canada. By adjusting parameters such as cut-in wind speeds and temperature thresholds, we demonstrated the ability to design strategic curtailment programs that achieve equivalent or greater predicted reductions in bat activity exposure for substantially less energy-production loss. Characterizing fatality risk on a finer scale using acoustics will help regulatory agencies and the wind industry alike reduce risks of population-level impacts to vulnerable bat species while continuing to expand large-scale renewable energy generation.
... Broders et al. [11] suggested a need for additional testing in flight cages for more precise manipulation of experimental conditions and to record over a continuous range of clutter conditions. Acoustic studies aimed at investigating detector placement in relation to clutter, omnidirectional versus directional microphones, bat sonar beam characteristics, and detector waterproofing have largely been conducted in field rather than controlled laboratory conditions with live bats [15,[23][24][25][26][27][28]. In field studies, clutter has been assessed by a variety of habitat metrics including forest canopy closure and height [20,29], distance to vegetation from the detector [11], live tree basal area [30], and clutter volume indices and qualitative clutter categories assigned by an observer [6]. ...
... While microclimate differences on acoustics throughout the day are thought to be small, it is possible that different atmospheric conditions between the plots could have further compounded the plot variability [32]. Adams et al. [24] investigated the implications of bat detector selection for recording bats by broadcasting synthesized ultrasound signals at different frequencies and recording the signals on bat detectors placed at varying distances and angles in relation to the broadcast source in an open field. Detection was most influenced by frequency of the broadcast signal and the distance; however, recording angle was also an important factor. ...
... Through the use of the anechoic chamber, we assessed the effect of receiver angle and measures of clutter condition on the recording and classification of an echolocation signal using a standardized synthetic echolocation pulse without the uncertainty associated with field studies. Although our results were aligned with our prediction and previous studies that detector angle would play an important role in echolocation call quality received [24,25], our findings that stem density and basal area did not influence outcomes as much were contrary to our expectations based on previously reported field studies [6,11,20,39]. The overall poor classification probabilities, the fact that all of the angles significantly differed from angle 0°, and the marginal significance of the two clutter metrics imply that proximity and angle of the emitter to the receiver might be the more important factors for recording high-quality, identifiable echolocation calls. ...
Article
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Ultrasonic bat detectors are useful for research and monitoring purposes to assess occupancy and relative activity of bat communities. Environmental “clutter” such as tree boles and foliage can affect the recording quality and identification of bat echolocation calls collected using ultrasonic detectors. It can also affect the transmission of calls and recognition by bats when using acoustic lure devices to attract bats to mist-nets. Bat detectors are often placed in forests, yet automatic identification programs are trained on call libraries using echolocation passes recorded largely from open spaces. Research indicates that using clutter-recorded calls can increase classification accuracy for some bat species and decrease accuracy for others, but a detailed understanding of how clutter impacts the recording and identification of echolocation calls remains elusive. To clarify this, we experimentally investigated how two measures of clutter (i.e., total basal area and number of stems of simulated woody growth, as well as recording angle) affected the recording and classification of a synthesized echolocation signal under controlled conditions in an anechoic chamber. Recording angle (i.e., receiver position relative to emitter) significantly influenced the probability of correct classification and differed significantly for many of the call parameters measured. The probability of recording echo pulses was also a function of clutter but only for the detector angle at 0° from the emitter that could receive deflected pulses. Overall, the two clutter metrics were overshadowed by proximity and angle of the receiver to the sound source but some deviations from the synthesized call in terms of maximum, minimum, and mean frequency parameters were observed. Results from our work may aid efforts to better understand underlying environmental conditions that produce false-positive and -negative identifications for bat species of interest and how this could be used to adjust survey accuracy estimates. Our results also help pave the way for future research into the development of acoustic lure technology by exploring the effects of environmental clutter on ultrasound transmission.
... The standardization of international bat monitoring programs, data management and analysis protocolsabove all, in acoustic surveys (Adams et al., 2012;Jones et al., 2013) is vital as it is not often possible to compare results from studies conducted using different methodologies (Adams et al., 2012). For example, the large number of possible settings on acoustic detectors (Adams et al., 2012;Fenton, 2000;Larson and Hayes, 2000) and the variety of notions of what the term 'bat pass' constitutes in acoustic surveys (Kerbiriou et al., 2019;Miller, 2001) hinder comparisons and parallel-running projects. ...
... The standardization of international bat monitoring programs, data management and analysis protocolsabove all, in acoustic surveys (Adams et al., 2012;Jones et al., 2013) is vital as it is not often possible to compare results from studies conducted using different methodologies (Adams et al., 2012). For example, the large number of possible settings on acoustic detectors (Adams et al., 2012;Fenton, 2000;Larson and Hayes, 2000) and the variety of notions of what the term 'bat pass' constitutes in acoustic surveys (Kerbiriou et al., 2019;Miller, 2001) hinder comparisons and parallel-running projects. ...
... The standardization of international bat monitoring programs, data management and analysis protocolsabove all, in acoustic surveys (Adams et al., 2012;Jones et al., 2013) is vital as it is not often possible to compare results from studies conducted using different methodologies (Adams et al., 2012). For example, the large number of possible settings on acoustic detectors (Adams et al., 2012;Fenton, 2000;Larson and Hayes, 2000) and the variety of notions of what the term 'bat pass' constitutes in acoustic surveys (Kerbiriou et al., 2019;Miller, 2001) hinder comparisons and parallel-running projects. Similarly, the variability in sonotypes in bat species classification (Walters et al., 2012;Wickramasinghe et al., 2003) and the quantifying of assemblage diversity using a wide range of diversity indices also prevent the comparison of results from different studies (Cosson et al., 1999;Moreno and Halffter, 2000;Rex et al., 2008). ...
Article
BACKGROUND The fact that bats suppress agricultural pests has been measured for some particular dyads of predator and prey species both in economic and food security terms. The recent emergence of new molecular techniques allows for wide screenings of bat diet and provide a further evidence that bats consume an ample array of agricultural pest species. The main focus about the regulatory services that bats provide in agroecosystems has been on crop pests that cause yield losses. Rice paddies constitute a particular agronomic system with specific challenges, not only related to crop productivity but also to human health. Dipteran density in such ecosystems poses a serious threat to human wellbeing and hinders crop production. Mosquitoes cause direct harm to human populations transmitting a number of infectious diseases. Non‐biting midges (Chironomidae) can consume and weaken rice seedlings and can cause major yield losses. RESULTS Mosquito populations and bat activity were assessed in rice paddies of Montgrí, Medes i Baix Ter Natural Park (NE Iberian Peninsula). Molecular analyses of bats faeces (6 weekly samples of 15 faeces each between mid‐August and September) proved the presence of both mosquitoes and non‐biting midges in all of the diet samples. Furthermore, bat activity at the sampling locations was related to adult mosquito density. CONCLUSION Our results suggest that bats actively exploit the emergence of adult mosquitoes and further prove that they prey on mosquitoes, non‐biting midges and other deleterious insects. Promoting the presence of bats next to human settlements in such agroecosystems may constitute a biological control system with direct impact on both human health and crop yield. This article is protected by copyright. All rights reserved.
... 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 ...
... 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. ...
Article
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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.
... 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]. ...
Article
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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 km 2 , and producing >300,000 sound files) to validate MaxEnt outputs for six neo-tropical 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.
... Each has its tradeoffs. Zero-crossing is a quick, simple method, but detects fewer echolocation calls than the information-rich Fourier analysis (Adams et al. 2012). Fourier analysis requires more battery life and data storage than zerocrossing analysis, but can analyze an entire call, including harmonics and amplitude information. ...
... If you are not using a call analysis software package, manual identification using a reference library is easier if calls are recorded in the same format as the reference library. If you plan to compare data with those from past surveys, choose similar hardware as detectors vary in detection efficacy, which results in different depictions of the same bat community and may limit the value of comparisons among surveys (Adams et al. 2012). ...
... 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). ...
Article
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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.
... Each has its trade-offs. Zero-crossing is a quick, simple method, but detects fewer calls than the information-rich Fourier analysis (Adams et al. 2012). Fourier analysis requires more battery life and data storage than zerocrossing analysis, but can evaluate an entire call, including harmonics and amplitude information. ...
... If you are not using a call analysis software package, manual identification using a reference library is easier if calls are recorded in the same format as the reference library. If you plan to compare data with those from past surveys, choose similar hardware, as detectors vary in detection efficacy (e.g., sensitivities), which can result in different depictions of the same bat community, limiting the value of comparisons among surveys (Adams et al. 2012). ...
Book
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The Handbook summarizes all the key steps in conducting an acoustic survey of a bat community, including project planning, strategies for data collection, approaches to analysis and interpretation, a guide to purchasing a bat detector, and a series of case studies. Chapter 1 (“Introduction to bat echolocation”) provides a broad introduction to the theme, including a discussion of why and how bats echolocate, and a brief description of acoustic data, as well as what can be discerned about a bat community using acoustic techniques. Chapter 2 (“Acoustic survey design”) focuses on acoustic survey design, stressing the importance of identifying a clear research question and approach, and summarizing some of the most common questions that researchers investigate using acoustic techniques. Chapter 3 (“Bat detector choice and deployment”) discusses the difficult task of choosing the appropriate detector and summarizing the different technological approaches, as well as the trade-offs involved with selecting one style of detector over another. Chapter 4 (”Echolocation call identification”) focuses on strategies for identifying recordings of echolocation calls, starting with a discussion of the challenges associated with this task, an overview of both manual and automated approaches, and a section on using and creating call libraries, which is crucial for researchers working in areas where bat communities have received little or no study. Chapter 5 “Data, analysis, and inference”) deals with data management, analysis, and inference. It includes a discussion about strategies for data management that contains a section on the nature and use of databases. Furthermore, it describes different approaches to statistical analyses, many of which are intuitively linked to the suggestions for study design in Chapter 2. Chapters 2 through 5 each conclude with a “Some additional suggestions” section, which were sent to us when we asked a group of bat acoustic experts what they considered to be some common pitfalls associated with the technique. The final chapter of the Handbook (“Case studies”) includes five case studies, each of which summarizes a previously published study or studies that used acoustic survey techniques. The goal of this section is to demonstrate how many of the principles discussed throughout the Handbook have been applied in real-life scenarios. We selected the case studies to provide examples from a range of geographic locations, using various detecting technologies, and asking diverse questions about bat communities. Throughout the Handbook, when photos or recordings of individual species are provided and labeled, we have identified the species of interest by scientific name and by the common name provided by the online resource, Bats of the World: A Taxonomic and Geographic Database (Simmons and Cirranello 2020), unless stated otherwise. On behalf of all contributors to the Handbook, we hope that this guide will help demystify the process of eavesdropping on bats and promote high standards in future acoustic studies of bat activity. Erin Fraser, Alex Silvis, Mark Brigham, and Zenon Czenze
... In recent years, acoustic methods-the use of ultrasound detectors to record bat echolocation calls-have gained popularity in bat studies (Adams et al. 2012;Jones et al. 2013;Walters et al. 2013). The advantages of acoustic over capture methods include the ability to set up automatic detectors to record bats without the need to have personnel on site manipulating the equipment and the possibility of documenting bat activity without any direct observation or manipulation. ...
... Massive deployment of passive acoustic sensors helped to answer ecological questions about echolocation behavior, patterns of distribution and habitat use, among others. Soon, several brands of passive recorders with different microphone sensitivities and recording features became available (see Adams et al. (2012) for a comparison of passive detectors). Since then, full-spectrum handheld detector technology has evolved, gaining field portability (lowering weight and increasing durability) and incorporating built-in screens for sonogram display. ...
Chapter
Full-text available
The study of bat acoustic signals requires specialized equipment with microphones capable of recording high frequencies. There has been growing interest in bat acoustics and a rapid evolution in ultrasonic recording equipment, from the pioneering work using detectors weighing several kilograms, to the current pocket-sized and open source recorders. The increasing accessibility of bat detectors has extended the field of bat acoustics from simple activity detection to acoustic species identification and experimental research. Traditional call analysis was based on multivariate statistical techniques such as discriminant function analysis. However, technological improvements have led to expanding knowledge regarding the complexity and versatility of bat echolocation, and have kindled the evolution of signal processing methods with new approaches (i.e. deep learning) and more powerful computational techniques. Free access to reference libraries that permit adequate and extensive algorithm comparisons have emerged as a cornerstone for the refinement of automated acoustic analysis. Acoustic surveys have provided important insights into the effects of anthropogenic activities and urbanization on bat activity and diversity. Understanding how human activities affect biodiversity is a crucial prerequisite for the development and application of effective species conservation programs.
... Due to logistic constraints, acoustic monitoring was often limited to only recording bat activity during the first part of the night, however, modern automatic bat detectors are now widely available and can record bat calls overnight (e.g. Adams et al., 2012). ...
... Future studies in the area should aim at finding R. ferrumequinum, Otonycteris hemprichii and Plecotus gaisleri, which were reported in arid areas to the north and south-east of the Chott region in Tunisia (Dalhoumi et al., 2011;Puechmaille et al., 2012), and from similar zones of neighbouring countries (Kowalski and Rzebik-Kowalska, 1991;Ahmim and Oubaziz, 2017;Aulagnier et al., 2017). However, these species are difficult to detect during a short survey with a Song Meter detector (SM2+) because they emit signals with low intensity (Holderied et al., 2011;Barataud, 2012); this detector has a significant rate of attenuation with distance (Adams et al., 2012). Nyctinomus aegyptiacus was only reported in Ksar Ghilane (south Tunisia), where a dead specimen was identified (Bendjeddou et al., 2016); the echolocation calls of this bat have not been described previously in North Africa. ...
Article
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Riquesa d’espècies i activitat de ratpenats al Parc Nacional de Dghoumes (sud-oest de Tunísia): estudi preliminar Es va portar a terme un estudi de la fauna de ratpenats en vuit dels principals tipus d’hàbitats del Parc Nacional de Dghoumes utilitzant xarxes de boira, detecció acústica i cerca de refugis. Els ratpenats van estar actius durant la nit i es van localitzar prop de masses d’aigua i fanals d’enllumenat públic. Es van registrar sis espècies de ratpenats: Eptesicus isabellinus, Pipistrellus kuhlii, Vansonia rueppellii, Asellia tridens, Tadarida teniotis i Rhinopoma cystops. Es van localitzar dues colònies, una de R. cystops amb 111 individus penjats a la cova de Jebel Morra i una altra amb 54 individuos d’A. tridens al sostre de l’Ecomuseu. Davant la possible pertorbació causada pels visitants del museu, suggerim reforçar les mesures de gestió del públic per garantir l’ús d’aquest lloc de descans dels ratpenats, la qual cosa impactaria positivament en la conservació d’A. tridens. Dades publicades a GBIF (Doi: 10.15470/0u03uz)
... Due to logistic constraints, acoustic monitoring was often limited to only recording bat activity during the first part of the night, however, modern automatic bat detectors are now widely available and can record bat calls overnight (e.g. Adams et al., 2012). ...
... Future studies in the area should aim at finding R. ferrumequinum, Otonycteris hemprichii and Plecotus gaisleri, which were reported in arid areas to the north and south-east of the Chott region in Tunisia (Dalhoumi et al., 2011;Puechmaille et al., 2012), and from similar zones of neighbouring countries (Kowalski and Rzebik-Kowalska, 1991;Ahmim and Oubaziz, 2017;Aulagnier et al., 2017). However, these species are difficult to detect during a short survey with a Song Meter detector (SM2+) because they emit signals with low intensity (Holderied et al., 2011;Barataud, 2012); this detector has a significant rate of attenuation with distance (Adams et al., 2012). Nyctinomus aegyptiacus was only reported in Ksar Ghilane (south Tunisia), where a dead specimen was identified (Bendjeddou et al., 2016); the echolocation calls of this bat have not been described previously in North Africa. ...
Article
Bat species richness and activity in Dghoumes National Park (Southwest Tunisia): a preliminary survey. Bat fauna in eight of the main habitat types of Dghoumes National Park was inventoried using mist–netting, acoustic detection and roost search. Bats were active at night and recorded near water bodies and street lamps. We recorded the echolocation calls of six bat species: Eptesicus isabellinus, Pipistrellus kuhlii, Vansonia rueppellii, Asellia tridens, Tadarida teniotis and Rhinopoma cystops. Two bat colonies containing 111 individuals of R. cystops were found roosting in Jebel Morra cave and 54 individuals of A. tridens were found roosting in the ceiling of the Ecomuseum. Due to potential disturbance by visitors to the museum, we suggest strengthening management practices to ensure the usage of this roosting site in order to promote the conservation of A. tridens.
... Audible bats are infrequent within regional faunas but are found globally, especially, but not exclusively, within the Molossidae family (Barclay & Brigham, 1991;Jones, 1999;Jones, 2005). Audible bats tend to be fast-flying aerial hawkers of large moths (Jones, 2005;Rydell & Arlettaz, 1994) and are often not easily surveyed using traditional (e.g., Kunz & Parsons, 2009) capture methods and acoustic recording devices because they fly above survey equipment in wide open airspace (e.g., Best, Kiser, & Freeman, 1996;Luce & Keinath, 2007;Rodhouse, McCaffrey, & Wright, 2005;Strahan, 1995) at distances greater than the recording sensitivities of current commercially-available bat detector microphone technology Adams, Jantzen, Hamilton, & Fenton, 2012). Notable species include the western North American member of the Vespertilionidae family, Euderma maculatum (Figure 1; Fenton, Tennant, & Wyszecki, 1987;Fullard & Dawson, 1997), and the Molossids Tadarida teniotis in Eurasia (Russo & Jones, 2002;Rydell & Arlettaz, 1994;Zbinden & Zingg, 1986), Otomops martiensenii in southern Africa (Fenton et al., 2002), and Tadarida (Austronomus) australis in Australia (Barclay & Brigham, 1991). ...
... E. maculatum is a strikingly-colored ( Figure 1) but rarely seen obligate cliff-roosting bat ranging broadly across arid regions of western North America (Wai-Ping & Fenton, 1989;Watkins, 1977). The species routinely emits 10 Khz search-phase calls at >60 dB which can be heard by humans with undamaged hearing >60 m, whereas commercially-available bat acoustic recording units are limited to <40 m (Adams et al., 2012;Fullard & Dawson, 1997;Luce & Keinath, 2007). We also considered A. pallidus as an additional target species because it also roosts sympatrically in large desert cliffs and emits distinctive audible social calls in the vicinity of maternity colonies (Hermanson & O'Shea, 1983). ...
Article
Full-text available
Bat conservation has been impeded by a lack of basic information about species’ distributions and abundances. Public participation in closing this gap via citizen (community) science has been limited, but bat species that produce low-frequency calls audible to the unaided human ear provide an overlooked opportunity for collaborative citizen science surveys. Audible bats are rare in regional faunas but occur globally and can be under-surveyed by traditional methods. During 2019-2020, we were joined by community members to conduct aural surveys and expand our knowledge of rare audible desert bats in western North America through a structured survey design broadly adaptable for practitioners across the globe where audible bats occur. Our study was integrated into a statistically robust but flexible master sample in use by the North American Bat Monitoring Program (NABat), ensuring representativeness of data contributions. We used survey results to update a Bayesian species distribution model for the rare spotted bat, Euderma maculatum, accounting for imperfect detection and including land cover occupancy predictors. Detection probability was estimated ~ 0.7 ± 0.1. Informative priors from a previous attempt to model E. maculatum were leveraged with the new citizen science data to support spatial predictions of occurrence previously impeded by data sparsity and which reinforced the biogeographic importance of arid cliffs and canyons. Our results are preliminary but encouraging, and future surveys can scale up through the NABat design structure and Bayesian modelling framework. We encourage future surveys to use recording devices to obtain voucher calls and double-observer methods to address false-positive detection errors that arise with inexperienced volunteers. Our design and model supported approach to integrating citizen science surveys into bat conservation programs can strengthen both the scientific understanding of rare species and public engagement in conservation practices.
... When it was necessary to place recorders within the same area (e.g. in Sidmouth Wood for the four sites cleared from rhododendron), they were situated facing away from each other to minimise any overlap of their recording fields (Sleep and Brigham, 2003). Although it was not possible to perform ultrasonic attenuation surveys for the RPA2, Adams et al. (2012) found that, for synthetic bat calls of constant amplitude, three out of five commercial bat detectors failed to detect frequencies of 25 kHz beyond 30 m when the source was directly in front of the recorder, and 15-20 m when the source was at a 90°angle. At 55 kHz, the maximum detection range fell to 20 m and 15 m directly in front of the detector and at 90°, respectively; however, in both cases, only one of the five detectors tested achieved this level of performance and ranges were typically shorter (Adams et al., 2012). ...
... Although it was not possible to perform ultrasonic attenuation surveys for the RPA2, Adams et al. (2012) found that, for synthetic bat calls of constant amplitude, three out of five commercial bat detectors failed to detect frequencies of 25 kHz beyond 30 m when the source was directly in front of the recorder, and 15-20 m when the source was at a 90°angle. At 55 kHz, the maximum detection range fell to 20 m and 15 m directly in front of the detector and at 90°, respectively; however, in both cases, only one of the five detectors tested achieved this level of performance and ranges were typically shorter (Adams et al., 2012). While these authors did not test response at an angle of 180°, it is reasonable to assume that detection ranges would be even shorter than those at 90°and that any overlap in detections between nearby recorders facing in opposite directions should be minimal. ...
Article
Full-text available
Biological invasions pose a significant threat to biodiversity, yet the severity and direction of impacts differs between taxa. The non-native evergreen shrub Rhododendron ponticum has colonized large areas of woodland understorey in the UK and is currently undergoing widespread clearance due to its negative impacts on native flora and as a potential host reservoir for harmful pathogens. Presence of rhododendron significantly increases the amount of structural clutter in the understorey and, hence, modifies microhabitat structure, which might have an impact on bat foraging activity. Here, for the first time, we investigated the effects of rhododendron on activity of British bat species by performing autonomous acoustic surveys at twelve sites in Richmond Park, London, where rhododendron was either present, absent or recently removed. The effects of other microhabitat characteristics likely to influence bat activity (e.g. tree diversity, canopy cover, distance to water and the pre- sence/absence of deer) were also considered. We predicted that the increased understorey clutter present in areas invaded by rhododendron would reduce the activity of larger, less agile bats Nyctalus noctula, Eptesicus serotinus and Nyctalus leisleri (NSL), whereas the activity of bat species able to forage within, or at the edges of, clutter (e.g. Myotis spp. and Pipistrellus spp.) would not be negatively affected. While our results indicated a significant reduction in the activity of larger, open space foragers (NSL) in rhododendron-invaded areas, deer presence had a stronger negative effect than woody understory density and canopy cover on these bat species. Activity of other bats recorded was not negatively impacted by the presence of rhododendron. However, sites where rhododendron had been removed demonstrated higher bat activity levels than sites where rhododendron was present and absent with the exception of Pipistrellus pygmaeus, which displayed higher activity levels in the presence of woody understorey. NSL and P. pipistrellus also demonstrated more frequent commuting/roosting activity in sites without rhododendron, although P. pygmaeus and Myotis spp. appeared to be regularly utilising at least some rhododendron sites for this purpose. To mitigate potential negative effects of rhododendron removal on some bat species, we therefore suggest restriction of deer access to sites to enable recovery of native woody understorey.
... In the second sampling period, we used the ultrasound Song Meter SM2BAT+ recording device with an SMX-US omnidirectional microphone sensitive to frequencies up to 192 kHz (Wildlife Acoustics Inc., USA) placed on a 3 m-high base at the fragment edge. As this equipment samples a wider area than the one used in the first sample period (Adams et al. 2012), we sampled three points each for 1 h at each site to obtain the same site sampling effort (N = 3 h) for both sampling time periods. Sampling points were located at least 50 m from each other to avoid overlapping recordings between sites because the detection range of these recorders tends to be less than 30 m (Adams et al. 2012). ...
... As this equipment samples a wider area than the one used in the first sample period (Adams et al. 2012), we sampled three points each for 1 h at each site to obtain the same site sampling effort (N = 3 h) for both sampling time periods. Sampling points were located at least 50 m from each other to avoid overlapping recordings between sites because the detection range of these recorders tends to be less than 30 m (Adams et al. 2012). During both sampling periods, we sampled only one site per night and all points at the same sampling site were pooled for the analyses. ...
Article
Full-text available
Tropical forests are being lost and modified at an unprecedented rate, with extant biodiversity increasingly restricted to human-modified landscapes. Resulting changes in landscape structure are shaping diversity patterns, with features such as habitat amount, edge density, and matrix quality determining species persistence. We assessed the importance of landscape composition (forest amount and matrix composition) and configuration (edge density) on diversity patterns of aerial insectivorous bats in Brazilian Atlantic Forest landscapes. We sampled 40 sites in two nearby sub-regions, one contained more forest cover and shade cacao plantations while the other was less forested and dominated by pastures. Based on echolocation calls, we detected 17 sonotypes that could be attributed to at least 13 species belonging to three families. The two sub-regions comprised bat assemblages similar in species richness but different in species composition and activity levels (a surrogate for abundance). Whereas species richness was not influenced by landscape structure at the largest spatial scale of study, activity levels were shaped by changes in landscape composition and configuration, with different responses for forest and open-area foragers. Decreasing activity of forest foragers was the most evident response of bat diversity to landscape structure at different spatial scales. Given the value of this biological group for key ecosystem services such as pest control, our findings highlight the importance of considering regional landscape features for management and prediction of future scenarios of anthropization.
... In contrast, in ecoacoustics, little attention has been paid to the microphone specifications. Some studies have evaluated the effectiveness of different recorder types for birds (Rempel et al., 2013;Pérez-Granados et al., 2019a;Pérez-Granados et al., 2019b) and bats (Adams et al., 2012), and it has been reported that a recording system with the lowest SNR detected the least birds (Rempel et al., 2013). Finally, Bardeli et al. (2010) mentioned that automated detection of animal sounds could be impeded by worn microphones. ...
... Possibly, results of previously published comparisons of bird and bat recorders (Adams et al., 2012;Rempel et al., 2013), which did not explicitly consider microphones, could be explained quantitatively by simple differences in detection ranges caused by differing microphone SNR values. We consider that by definition, sensitivity is secondary compared to self-noise or SNR values with respect to their impact on detection ranges, in slight contrast to previous findings about the importance of microphone sensitivity (Turgeon, Van Wilgenburg & Drake, 2017). ...
Article
Full-text available
Background Automated sound recorders are a popular sampling tool in ecology. However, the microphones themselves received little attention so far, and specifications that determine the recordings’ sound quality are seldom mentioned. Here, we demonstrate the importance of microphone signal-to-noise ratio for sampling sonant animals. Methods: We tested 12 different microphone models in the field and measured their signal-to-noise ratios and detection ranges. We also measured the vocalisation activity of birds and bats that they recorded, the bird species richness, the bat call types richness, as well as the performance of automated detection of bird and bat calls. We tested the relationship of each one of these measures with signal-to-noise ratio in statistical models. Results: Microphone signal-to-noise ratio positively affects the sound detection space areas, which increased by a factor of 1.7 for audible sound, and 10 for ultrasound, from the lowest to the highest signal-to-noise ratio microphone. Consequently, the sampled vocalisation activity increased by a factor of 1.6 for birds, and 9.7 for bats. Correspondingly, the species pool of birds and bats could not be completely detected by the microphones with lower signal-to-noise ratio. The performance of automated detection of bird and bat calls, as measured by its precision and recall, increased significantly with microphone signal-to-noise ratio. Discussion: Microphone signal-to-noise ratio is a crucial characteristic of a sound recording system, positively affecting the acoustic sampling performance of birds and bats. It should be maximised by choosing appropriate microphones, and be quantified independently, especially in the ultrasound range.
... 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 ...
Article
Full-text available
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.
... In contrast, in ecoacoustics, little attention has been paid to the microphone specifications. Some studies have evaluated the effectiveness of different recorder types for birds (Rempel et al., 2013;Pérez-Granados et al., 2019a;Pérez-Granados et al., 2019b) and bats (Adams et al., 2012), and it has been reported that a recording system with the lowest SNR detected the least birds (Rempel et al., 2013). Finally, Bardeli et al. (2010) mentioned that automated detection of animal sounds could be impeded by worn microphones. ...
... Possibly, results of previously published comparisons of bird and bat recorders (Adams et al., 2012;Rempel et al., 2013), which did not explicitly consider microphones, could be explained quantitatively by simple differences in detection ranges caused by differing microphone SNR values. We consider that by definition, sensitivity is secondary compared to self-noise or SNR values with respect to their impact on detection ranges, in slight contrast to previous findings about the importance of microphone sensitivity (Turgeon, Van Wilgenburg & Drake, 2017). ...
Article
Full-text available
Background Automated sound recorders are a popular sampling tool in ecology. However, the microphones themselves received little attention so far, and specifications that determine the recordings’ sound quality are seldom mentioned. Here, we demonstrate the importance of microphone signal-to-noise ratio for sampling sonant animals. Methods We tested 12 different microphone models in the field and measured their signal-to-noise ratios and detection ranges. We also measured the vocalisation activity of birds and bats that they recorded, the bird species richness, the bat call types richness, as well as the performance of automated detection of bird and bat calls. We tested the relationship of each one of these measures with signal-to-noise ratio in statistical models. Results Microphone signal-to-noise ratio positively affects the sound detection space areas, which increased by a factor of 1.7 for audible sound, and 10 for ultrasound, from the lowest to the highest signal-to-noise ratio microphone. Consequently, the sampled vocalisation activity increased by a factor of 1.6 for birds, and 9.7 for bats. Correspondingly, the species pool of birds and bats could not be completely detected by the microphones with lower signal-to-noise ratio. The performance of automated detection of bird and bat calls, as measured by its precision and recall, increased significantly with microphone signal-to-noise ratio. Discussion Microphone signal-to-noise ratio is a crucial characteristic of a sound recording system, positively affecting the acoustic sampling performance of birds and bats. It should be maximised by choosing appropriate microphones, and be quantified independently, especially in the ultrasound range.
... Bat activity was surveyed using two Wildlife Acoustics Inc. (Maynard, MA) bat detectors: an SM2BAT+ equipped with an SMX-UT microphone at GSB and an SM4BAT FS with an SMM-U1 ultrasonic microphone at PSB. These instruments have a similar sensitivity to bat calls and it has been demonstrated that SM2 performs similarly to Batcorder 2.0 (Adams et al., 2012). Both bat detectors were positioned on the outside of isolated buildings, at about 5 m from the ground, with the microphones oriented towards each alpine pass. ...
Article
Full-text available
Information about bat migration routes across the Alps is generally scarce and there is no existing data available for the Italian part of the chain. Through acoustic surveys, we explored the possibility that even a region characterized by high Alpine mountains may be crossed by migrant bats. Data were recorded in August–September 2016 at two sites located near mountain passes in the Aosta Valley (NW Italy), respectively for 29 and 53 entire nights. Activity of different species/acoustic groups of species was associated with period and weather variables, the most important of which was wind speed (negatively related), followed by temperature (positively related). Only the acoustic group N. leisleri/N. noctula/V. murinus/E. serotinus, at both sites, showed a significant increase in activity in the period 31 August–14 September. Additional elements suggesting the occurrence of a late-summer migratory flow involving this group were the fact that it mainly consists of migratory species; the attribution to N. leisleri of the sequences that could be identified at the species level; and the timing of activity through the night (generally later than the other bats) and some characteristics of the recorded calls. Contacts with B. barbastellus were recorded at both study sites, possibly due to migrating individuals or, as an alternative, to resident bats using open environments located far from woods during the summer. The occurrence of P. kuhlii was ascertained at the highest elevation so far reported for this species in the Alps (2208 m a.s.l.).
... We also include two opportunistic findings. We installed recorders in open areas at an approximate height of one meter above ground level, at an inclination of 45° (Adams et al. 2012), the recordings started at 18:00 h and ended at 22:00 h on nights without strong winds or rain. Sounds were recorded in a waveform audio format (WAV). ...
Preprint
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We present the first record of leucism of Molossus nigricans a chromatic disorder rarely documented in mammals of Honduras, as well as species' biological and ecological information. In addition, we present the currently known distribution and altitudinal range of M. nigricans in Honduras, based on acoustic records, opportunistic findings and previous records. We confirm the presence of M. nigricans in sixteen departments of which four are new departmental records.
... As all recordings of echolocation calls have been converted to zero-crossing files, the main differences in sampling techniques is related to bat detector design. In comparison, the AnabatSD2 detector was used with the 'AnaBat stainless steel microphone' recording directional signals up to 200 kHz, while the SM4BAT+ detector with the 'SMM-U1' microphone records omni-directional up to 500 kHz [57,58]. We, therefore, decided to take a cautious approach in using the number of passes (bat activity) as a random factor in our analysis to control for a bias in sampling effort instead of´true activity levels´ [59]. ...
Article
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The Okavango River Basin is a hotspot of bat diversity that requires urgent and adequate protection. To advise future conservation strategies, we investigated the relative importance of a range of potential environmental drivers of bat species richness and functional community composition in the Okavango River Basin. During annual canoe transects along the major rivers, originating in the central Angolan highlands, we recorded more than 25,000 bat echolocation calls from 2015 to 2018. We corrected for possible biases in sampling design and effort. Firstly, we conducted rarefaction analyses of each survey year and sampling appeared to be complete, apart from 2016. Secondly, we used total activity as a measure of sample effort in mixed models of species richness. Species richness was highest in the Angola Miombo Woodlands and at lower elevations, with higher minimum temperatures. In total, we identified 31 individual bat species. We show that even when acoustic surveys are conducted in remote areas and over multiple years, it is possible to correct for biases and obtain representative richness estimates. Changes in habitat heterogeneity will have detrimental effects on the high richness reported here and human land-use change, specifically agriculture, must be mediated in a system such as the Angolan Miombo Woodland.
... The correspondence between acoustic and visual detection events were examined at three scales: the entire night (averaging approximately 12 hours), a 2-hour period (i.e., an acoustic detection 1 hour before or after a visual detection), and a 10-minute period (i.e., an acoustic detection 5 minutes before or after a visual detection). Bat passes at any point during a visual detection were noted if they occurred at a distance of approximately 15 m or less from the turbine nacelle, a range within which the probability of acoustic detection is high, particularly for low-frequency echolocation calls (Adams et al. 2012, Gorresen et al. 2017, and used to conservatively assess the proportion of visual detections lacking a corresponding acoustic detection. ...
... However, the frequency range captured by a recording system is also limited by the maximum sampling rate, transducer sensitivity, and filters of the audio recorder and microphone (Merchant et al., 2015). It is important to consider that even a partial mismatch between the frequency range of the recording system and the frequency range of the signal of interest can distort the recorded signal (Adams, Jantzen, Hamilton, & Fenton, 2012). Moreover, microphones and loudspeakers often have varying frequency sensitivities instead of a flat frequency response with equal sensitivity to all frequencies. ...
Article
The multifaceted ability to produce, transmit, receive, and respond to acoustic signals is widespread in animals and forms the basis of the interdisciplinary science of bioacoustics. Bioacoustics research methods, including sound recording and playback experiments, are applicable in cognitive research that centers around the processing of information from the acoustic environment. We provide an overview of bioacoustics techniques in the context of cognitive studies and make the case for the importance of bioacoustics in the study of cognition by outlining some of the major cognitive processes in which acoustic signals are involved. We also describe key considerations associated with the recording of sound and its use in cognitive applications. Based on these considerations, we provide a set of recommendations for best practices in the recording and use of acoustic signals in cognitive studies. Our aim is to demonstrate that acoustic recordings and stimuli are valuable tools for cognitive researchers when used appropriately. In doing so, we hope to stimulate opportunities for innovative cognitive research that incorporates robust recording protocols. This article is categorized under: • Neuroscience > Cognition • Psychology > Theory and Methods • Neuroscience > Behavior • Neuroscience > Cognition
... As such, larger forest patches may be expected to host higher bat species richness. This relationship was not addressed here but is investigated in relation to bat functional diversity in Chapter 3. Lastly, different species demonstrate differences in detectability by acoustic recorders which limits the ability to compare relative activity levels between species, families, or functional groups (Adams et al., 2012). Detection distances, and the relevant correction factors, have been developed for bats in savanna habitats in Eswatini (Monadjem et al., 2017) but not yet for forested habitats in South Africa or for the acoustic recorders and associated omni-directional microphones utilised in this study. ...
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Bats are a highly diverse mammalian order and are some of the most economically important non-domesticated vertebrates, providing many ecosystem services that contribute to the global economy. Yet, they remain a largely understudied taxon, particularly in the Eastern Cape province of South Africa, in which basic surveys of bat assemblages utilising indigenous forests are lacking. Indigenous forests constitute South Africa’s smallest and most fragmented biome yet support disproportionally high biodiversity. They have been fragmented throughout most of their evolutionary history due to global palaeoclimatic shifts; the responses of bats to forest fragmentation and historical climatic shifts in this habitat have been poorly studied. This study addresses these gaps with the broad aims of compiling a species inventory from 17 forests across the Eastern Cape and KwaZulu-Natal provinces; assessing the effects of fragmentation and biogeography on taxonomic and functional diversity of bat assemblages; and determining how genetic diversity and population genetic structure are informed by forest habitat associations and fragmentation. A multi-faceted approach of sampling methods, including capture and acoustic recording, and species identification techniques (morphology, acoustics, and DNA barcoding) were used to assemble an inventory of 25 species, with range extensions noted for six species. The first reference call library of hand released bats for forests in this region is presented, which may be used for species identification in further acoustic surveys. A minimum acoustic monitoring period of 6 to 7 nights per forest is recommended for future surveys. Forest biogeography was an important determinant of the functional diversity of insectivorous bat assemblages. Forest edge effects were found to demonstrate a positive relationship with functional evenness, thus motivating for maintenance and conservation of forest edges, particularly in temperate regions. Larger forearm length and low wing loading were identified as morphological traits exhibiting greater sensitivity to fragmentation, flagging species exhibiting these traits as potentially vulnerable to habitat fragmentation. The effect of historical climate-induced fluctuations of forest extent on population genetic structuring and demographic histories for six species was investigated using two mitochondrial markers, cytochrome b and D-loop. Population genetic trends were not informed by forest habitat associations, but rather by species-specific traits of dispersal ability, philopatry, and roost utilisation. Low genetic diversity and high population structure identify two species, Rhinolophus swinnyi and Laephotis botswanae, for conservation priority. Demographic responses to the Last Glacial Maximum (LGM) were not detected, with all six species displaying population expansions over this time. It appears that volant insectivores in eastern South Africa were less affected by the harsh conditions of the LGM than elsewhere. The dusky pipistrelle (Pipistrellus hesperidus) was used as a model organism to investigate the gene flow, genetic diversity, and migration of a forest-utilising species across the region with the use of eight microsatellite markers. The effects of urbanisation and agricultural development on gene flow were also examined. Findings of low population structure, low migration rates, and two genetic discontinuities were presented. This species does not depict dependence on forested habitats to maintain genetic connectivity on the landscape. The data also suggest that agricultural development and urbanisation have not yet had an impact on gene flow, thus providing a baseline with which to monitor the effects of future anthropic development on this species. Overall, this study has provided novel insights into the taxonomic, functional, and genetic diversity of forest-utilising bats in relation to biogeographical history and fragmentation within eastern South Africa.
... An Anabat Chirper (Titley Scientific, Australia) was used to calibrate the microphones, which were expected to detect bat calls mostly within 25-30 m in all directions (Wildlife Acoustics, 2007Agranat, 2014;Wildlife Acoustics, 2014-2020. However, the probability of detecting bat calls would have been affected by the dominant frequency and distance of calls from the microphones, the directionality and frequency response of the detectors (Adams, Jantzen, Hamilton & Fenton, 2012), and other unavoidable factors like weather. The number of microphones installed near ground level or in turbine rotor sweep within each ecoregion is indicated in Table 1. ...
Article
We provide a comparison of bat activity levels recorded during long-term acoustic monitoring through 188 microphones at pre-construction wind energy facility (WEF) sites in 12 South African ecoregions, and discuss the implications of the results for wind energy development. We summed all bat passes and detector hours over microphones, sites and years for each month, and fitted a negative binomial regression model with total bat passes as the response and ecoregion as the predictor. Overall, there was a significant effect of ecoregion on the number of bat passes per detector hour recorded near ground level, and in the turbine rotor sweep. Pairwise comparisons revealed that the sites in Maputaland coastal forests and woodlands, and KwaZulu-Natal-Cape coastal forests, were most distinct due to exceptionally high levels of recorded activity. As such, we strongly advise against WEF development in these ecoregions. In lowland fynbos and renosterveld, Limpopo lowveld, and Albany thickets, where intermediate to high bat activity was recorded, we recommend that the conditions of WEF-authorizations must include rigorous bat impact mitigation measures. For operational WEFs, our results provided valuable benchmark information for devising bat fatality thresholds that reflect the variation in bat activity across South Africa's diverse landscape.
... ARUs recorded directly to.wav format. The individual ARU equipment and settings varied between the hardware platforms (SM3BAT vs. SM2BAT+), with detection distances of approximately 20-30 meters [33], depending on the frequency of the source and other environmental variables (i.e., temperature and humidity) [34]. The equipment and settings were consistent for a given site throughout the study. ...
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Traditional pathogen surveillance methods for white-nose syndrome (WNS), the most serious threat to hibernating North American bats, focus on fungal presence where large congregations of hibernating bats occur. However, in the western USA, WNS-susceptible bat species rarely assemble in large numbers and known winter roosts are uncommon features. WNS increases arousal frequency and activity of infected bats during hibernation. Our objective was to explore the effectiveness of acoustic monitoring as a surveillance tool for WNS. We propose a non-invasive approach to model pre-WNS baseline activity rates for comparison with future acoustic data after WNS is suspected to occur. We investigated relationships among bat activity, ambient temperatures, and season prior to presence of WNS across forested sites of Montana, USA where WNS was not known to occur. We used acoustic monitors to collect bat activity and ambient temperature data year-round on 41 sites, 2011–2019. We detected a diverse bat community across managed (n = 4) and unmanaged (n = 37) forest sites and recorded over 5.37 million passes from bats, including 13 identified species. Bats were active year-round, but positive associations between average of the nightly temperatures by month and bat activity were strongest in spring and fall. From these data, we developed site-specific prediction models for bat activity to account for seasonal and annual temperature variation prior to known occurrence of WNS. These prediction models can be used to monitor changes in bat activity that may signal potential presence of WNS, such as greater than expected activity in winter, or less than expected activity during summer. We propose this model-based method for future monitoring efforts that could be used to trigger targeted sampling of individual bats or hibernacula for WNS, in areas where traditional disease surveillance approaches are logistically difficult to implement or because of human-wildlife transmission concerns from COVID-19.
... Yet, the type of AUD may have a strong influence on its ability to differentiate between echolocation calls and background noise. Testing five typical ultrasonic detectors in a field situation revealed that detectors recorded between 40 and 93% of all broadcast calls (Adams et al. 2012), showing that some detectors may miss a substantial proportion of bats passing by. When combined with sufficient memory, real-time AUDs can be left unattended for extended periods of time at nacelle height. ...
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Wind turbines (WTs) frequently kill bats worldwide. During environmental impact assessments, consultant ecologists often use automated ultrasonic detectors (AUDs) to estimate the activity and identity of bats in the zone of highest mortality risk at WTs in order to formulate mitigation schemes, such as increased curtailment speeds to prevent casualties. While acknowledging the potential of acoustic monitoring, we evaluate the limitations of AUDs for monitoring bats at WTs and highlight directions for future research. We show that geometric attenuation and atmospheric attenuation of ultrasonic echolocation calls, in conjunction with limited sensitivity of ultrasonic microphones, severely constrain detection distances of bats at WTs. Taking into account the acoustic shadow produced by the nacelle, AUDs cover only approximately 23% of the risk zone for a bat calling at 20 kHz and 4% for a bat calling at 40 kHz, assuming a 60 m blade length. This percentage will further decrease with increasing blade lengths in modern WTs. Additionally, the directionality of echolocation calls and the dynamic flight behaviour of bats constrain the detectability of bats. If a call can be detected, the low interspecific and high intraspecific variation of echolocation call characteristics may impair species identification, limiting the power to predict population‐level effects of fatalities. We conclude that technical, physical, and biological factors severely constrain acoustic monitoring in its current form. We suggest the use of several AUDs, installed at complementary sites at WTs, and the testing of other techniques, such as radar, cameras, and thermal imaging, to inform stakeholders on the mortality risk of bats at WTs.
... 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). ...
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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. ...
Article
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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]. ...
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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]. ...
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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.
... A bat recorder (Song Meter SM3Bat +) was used with an omnidirectional ultrasound microphone SMX-US (Wildlife Acoustics, Maynard, Massachusetts, USA). The recorder was installed in open urban areas at a height of approximately one meter above ground level, with an inclination of 45° (Adams et al., 2012) oriented towards the flight path of the bats. All vocalizations were recorded through the heterodyne system, with frequencies between 20 and 100 kHz and in a WAV (Waveform Audio Format) audio format. ...
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In Honduras, most bat inventories have been carried out with mist nets as the main sampling method, skewing knowledge towards the Phyllostomidae family, therefore the diversity and distribution of insectivorous bats is underrepresented. In order to have a more complete knowledge of the diversity of bats in the municipality of Yuscarán and mainly in the Yuscarán Biological Reserve, an inventory was carried out using the techniques of mist-netting and acoustic monitoring. The samplings were carried out between 910 and 1,827 masl, covering agroecosystems, broadleaf forest, pine forest and urban environment. A total of 32 species of bats were registered, which represents 28% of the species diversity present in Honduras. Species belonging to five families were recorded: Emballonuridae (6.25%), Mormoopidae (15.22%), Phyllostomidae (56.25%), Molossidae (9.37%) and Vespertilionidae (12.5%). With the mist nets, a sampling effort of 7,128 m²/h was reached, which allowed the capture of 20 species and 186 individuals. Through the acoustic method, with 84 h/r, 13 species of insectivorous bats were recorded. The values of the acoustic parameters analysed from the search phase of each insectivorous species are provided, which can serve as a reference for the identification of species from Honduras. To advance our understanding of the distribution patterns, composition, and vocal signatures of insectivore bats, we suggest the complementary use of mist nets and acoustic recorders in the inventories.
... With the recent progress in data storing capacity, the decrease in the cost of acoustic devices and the improvement of species detection and identification, the use of passive acoustic monitoring (PAM) offers promising opportunities in biodiversity assessments, especially for elusive and/or nocturnal taxa (Barré et al. 2019;Gibb et al. 2019). PAMs offer a wide range of applications to policy makers and environmental consultant firms (Adams et al. 2012;Claireau et al. 2019a, b) as well as to academic researchers in studies of vocal species such as amphibians (Rosa et al. 2012), birds (Gregory et al. 2004), cetaceans (Nowacek et al. 2016), nocturnal arthropods (Jeliazkov et al. 2016) and echolocating bats (Stahlschmidt and Brühl 2012). Beyond providing support for inventories, PAMs enable studies of species habitat use (Russo and Jones 2003) and assessment of anthropogenic pressure (e.g. ...
Article
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Passive Acoustic Monitoring offers promising opportunities for biodiversity assessments and species conservation and is still in development. The robustness of community metrics depends on sampling effort, and acoustic surveys should be adjusted for cost-effectiveness. Using a large-scale acoustic survey of bat assemblages conducted along 5,487 survey nights across France, we assessed the effect of sampling duration on the level of confidence of four community metrics (total bat activity, species of conservation concern activity, species richness, and community specialisation index). We further investigated this effect varied across habitat and seasons. Overall, a high level of confidence (i.e., 95% similarity between consecutive survey nights) was reached after 2 to >20 sampling nights, depending on the community metric, the habitat and the season considered. CSI required the lowest sampling duration. A higher sampling duration was required in three-dimensionally structured habitats (e.g., forests) and habitats unfavourable to bats (e.g., intensive farmlands), while a high degree of confidence was reached earlier in more favourable habitats and non-intensive farmlands, and during the season of higher activity. Beyond providing recommendations for the design of context-dependent minimum sampling duration in acoustic surveys, we show that weighted community indices such as the CSI are efficient summary measures, and advocate for their use when monitoring resources are limited.
... Estos, además de su función básica de captar la voz para las comunicaciones, también permiten el registro de otros sonidos ambientales y se han usado ampliamente en investigaciones. Los estudios con estos micrófonos han ido desde aplicaciones bioacústicas sofisticadas para la identificación de especies y sonidos con procedimientos de aprendizaje de máquina, similares al de las aplicaciones Siri de Apple y Alexa de Android (Adams & al. 2012, Mennill & al. 2012, hasta estudios enfocados en la medición de las intensidades sonoras (Figura 4). ...
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Los teléfonos celulares han irrumpido en todos los aspectos de la vida de la mayor parte de la humanidad, incluyendo las actividades profesionales y científicas. Numerosas aplicaciones apoyan al investigador en el seguimiento de protocolos experimentales, manejo de bibliografía y como vía de conexión inalámbrica con otros equipos. Pero la amplia gama de sensores miniaturizados integrados que poseen, de alta precisión y que actúan en aspectos ocultos del funcionamiento del equipo, no ha sido aún lo suficientemente explotada. Los celulares modernos contienen potentes cámaras digitales, micrófonos, receptores GPS/GNSS, acelerómetros, giroscopios, sensores de magnetismo, luxómetros, barómetros, termómetros, sensores de humedad, sensores biométricos y muchos otros, que tienen el potencial de convertirse en importantes aliados para la recolecta de datos durante el trabajo de un investigador. A partir de ellos han aparecido las aplicaciones de brújulas, altímetros, escáneres, lectores de códigos de barras o QR, identificadores de rostros, sonidos o especies, detectores de metales, de movimientos o de vibraciones, podómetros, colorímetros, espectrómetros y muchas más. Todas estas herramientas están impactando un amplio espectro de campos científicos como la medicina, las ciencias sociales, el monitoreo ambiental, el transporte y la industria. Sin embargo, aún existe desconocimiento de sus ventajas y posibilidades, por lo cual, en este trabajo, se hace una revisión de las potencialidades que brindan estos sensores y sus aplicaciones en las investigaciones biológicas. En condiciones donde el equipamiento tecnológico es limitado, los celulares, sus sensores y las aplicaciones correspondientes pueden ser alternativas eficientes para sobrellevar la brecha tecnológica y aumentar la calidad de las investigaciones.
... Though methods vary for each of the aforementioned monitoring programs, all make the assumption that they have implemented a robust and repeatable survey design that will allow for reliable inference regarding bat population changes over time. However, the challenges associated with reliably detecting bats come in many forms, including seasonal and daily variation in bat activity (Hayes, 1997;Skalak et al., 2012), variation from type and sensitivity of bat detector (Adams et al., 2012;Barclay, 1999;Barlow et al., 2015), variation in automated classification systems (Russo and Voigt, 2016), and roadside detection bias (Berthinussen and Altringham, 2012;D'Acunto et al., 2018;de Torrez et al., 2017;Roche et al., 2011;Stahlschmidt and Brühl, 2012). Automated classification could be particularly problematic in this case as we must assume that call filtering parameters and classifiers produced no false negative or false positive species identifications within the BCID software program. ...
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Bat populations in eastern North America have experienced precipitous declines following the spread of white-nose syndrome (WNS) and other population stressors. It is imperative to understand changes in bat populations as WNS spreads to provide appropriate guidance for species management. We developed generalized linear mixed-models of population trend and habitat associations for five indicator bat species on U.S. Fish and Wildlife Service Mobile Acoustic Bat Monitoring program routes across 86 sites in the southeastern United States from 2012 to 2017. We estimated substantial declining annual trends in relative abundance of tricolored bat (Perimyotis subflavus; −15.1% [−20.6 to −9.1% 95% CI]) and little brown bat (Myotis lucifugus; −13.9% [−22.9 to −3.8% 95% CI]). Relative abundance of bat species increased throughout the summer, and associated positively with the amount of woody cover along survey routes in all but P. subflavus. Fewer evening bats (Nycticeius humeralis) and eastern red bats (Lasiurus borealis) were detected along more developed routes. Using these models, we conducted a prospective power analysis to examine sampling effort necessary to detect moderate to catastrophic population changes in bat populations. We estimated that it would require 10–20 years of surveys on 50–100 routes to detect 5% annual declines in all species at 80% power and α = 0.1. Detecting a 2.73% annual decline may require >200 surveys over >20 years; whereas a 1.14% annual decline was nearly impossible to detect via our program. We demonstrate and caution that underpowered monitoring programs may misrepresent the magnitude and/or sign of population trajectories. We recommend project-specific power analysis continue to be emphasized as an important study design component for effective long-term monitoring programs.
... We then graphed the proportion presence for each species over time. Detectability can be influenced by recording equipment (Adams et al. 2012); however, the proximity of the microphones to the entrances (< 5 m) enhanced the detectability of emergent bats' calls and should minimize equipment bias. ...
Article
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The seasonal roost use of Philippine horseshoe bats (Family: Rhinolophidae) is poorly known. Here, we monitored an undisturbed rock crevice roost comprised of four Rhinolophus species on Mount Makiling, Philippines, to document seasonal changes in colony size and species composition. Evening emergences were videotaped using an IR spotlight and an IR-sensitive camera and were acoustically recorded using an ultrasonic detector. Emergence counts ranged from an average of 7,965 bats in the wet season to 177 bats in the dry season. Higher emergence counts in the wet season, and the presence of post-lactating females and juveniles, together indicated that Rhinolophus arcuatus and Rhinolophus inops used the rock crevice as a maternity roost. Rhinolophus macrotis and Rhinolophus virgo were detected during all survey months but comprised a smaller proportion of the wet-season emergence than R. arcuatus and R. inops. These data, while limited in scope, provide the first evidence of seasonal cave use by Philippine horseshoe bats and highlight the potential conservation value of this particular roost as a maternity site for horseshoe bats within the Makiling Forest Reserve.
... Acoustics have been at the forefront of chiropteran research for decades (Griffin et al. 1960;Neuweiler 1989) because the detection of species-specific echolocation calls is a convenient and standardised method for determining the composition of bat community assemblages (Yates and Muzika 2006;MacSwiney et al. 2008;Adams et al. 2012). At present the role of sound in bat social communication is receiving increased attention, with bats now known to produce a variety of function-specific calls and songs (e.g. ...
Article
The ghost bat (Macroderma gigas) is a colonial and highly vocal species that is impacted by human visitation of caves. The ability to document behaviours inside the roost by recording vocalisations could provide an important new tool for the management of this disturbance-prone species by removing the need for in-person confirmation of reproductive activity, and, in turn, identifying roosts of conservation importance. To assess whether vocalisations are indicators of daily and seasonal behavioural events, we aimed to determine whether total vocal activity significantly varied by time of day and time of year and, further, how the relative frequencies of occurrence of three common social vocalisations ('Chirp-trill', 'Squabble' and 'Ultrasonic Social') aligned with previously reported seasonal reproductive behaviour. We recorded sound inside the largest known maternity roost, extracted all vocal signals and classified them into types using semiautomated methods. Total vocal activity varied significantly by time of day and time of year, peaking around sunrise and sunset, and during the mating and nursing seasons. The relative frequencies of occurrence of vocalisation types varied significantly seasonally, with the Chirp-trill and Squabble produced most during the mating season and first flight periods, whereas the Ultrasonic Social peaked during parturition and weaning periods. This timing aligns with a previously suggested vocalisation function, providing further evidence that these signals are important in mating and maternity behaviours. Further, this suggests that peaks in the relative frequency of occurrence of distinct social vocalisations may act as indicators of in-roost reproductive and pup development behaviours and provides a low-disturbance, semiautomated method for using long-term acoustic recordings to study and monitor behaviour in this sensitive species.
... The acoustic recordings were made using a bat recorder (Song Meter SM2Bat+) with an omnidirectional ultrasonic SMX-US microphone (Wildlife Acoustics, USA). We installed the recorder in open areas at an approximate height of one meter above ground level, at an inclination of 45° (Adams et al. 2012), oriented towards the flight path of bats. The recordings started at 18:00 h and ended at 06:00 h on nights without strong winds or rain (Parsons and Szewczak 2009). ...
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Information on the distribution of the Northern Ghost Bat, Diclidurus albus, in its natural distribution range, is scarce. In Honduras, four previous records are known. Here we add seven new locations, corresponding to five departments: Atlántida, Choluteca, Copán, Cortés, and Valle. We document the first records in the insular zone of the Gulf of Fonseca. We confirm the presence of D.albus on the northern coast, through records in San Pedro Sula and Jardín Botánico Lancetilla. We expand the distribution range towards the west zone of Honduras, in Copán Ruinas, approximately 63 km from the closest previous record from the year 1937. We update the distribution and perform ecological niche modelling that suggest, a wider presence, mainly in ecosystems associated with aquatic environments and dry forest below 1500 m.a.s.l. We provide the values of the different acoustic parameters, which can serve as a reference for the identification of D. albus at the local level. In addition, morphological, and ecological information is contributed thereby advancing the natural history knowledge of this species.
... In the Neotropics, many research groups have implemented ultrasonic detection as a sampling method for bats; however, they usually follow different analytical procedures that can prevent cross-studies comparisons. This situation can be attributed to many factors, but an obvious one is the availability of detection devices that vary in performance, with direct implications on the characteristics of the recording (see Fenton 2000, Adams et al. 2012. Moreover, the measurement criteria of acoustic parameters are not set by the recording device itself but during postprocessing, so standardization is important. ...
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Ultrasound detectors are becoming an increasingly used tool in bat research. Still, the lack of standardization of measurement criteria in the analysis of recordings is problematic when attempting identifications. For instance, the analytical procedures depend on the technique for obtaining the spectral content of an echolocation pulse (eg. zero-crossing, Fourier analysis)-which is directly related to the detection device and software-, and they should be as consistent as possible among studies' and observers' to allow comparisons. Using full-spectrum recordings of a Myotis species, we measured the minimum frequency and maximum frequency on the spectrogram, as well as considering four thresholds on the power spectrum: at-55 and-50 decibels from 0 decibels, and at 18 and 6 decibels below peak frequency. Focusing on the minimum frequency, we found statistically significant differences of measurements obtained on the spectrogram vs. power spectrum, with higher mean values in the latter as product of pulse truncation, as well as statistically significant differences between two trained observers. The measurements relative to the peak frequency were less variable. Without proper considerations, these issues may represent confounding factors and derive data unsuitable for cross-studies comparisons and potential misidentifications. We make recommendations about measurement criteria and emphasize the importance of replication and more rigorous reports.
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Acoustic methods are largely used for monitoring the impact of land-use changes on bats, particularly during the erection and operation of wind turbines. Over the past ten years, the automation of detectors and call analysis turned this technique into a cost-effective tool for consultants, which is now recommended by all national guidelines. Acoustic monitoring allows the collection of high quality data, e.g. when several instruments are deployed simultaneously over long periods. Nevertheless acoustic monitoring has its drawbacks and limitations. The physics of sound propagation constrains the detection range of bats, which varies with the behavior and species under consideration. These limits are beyond the control of users. Furthermore the specific use of detectors strongly influences the resulting data, for example by the choice of detector placement, recording settings and programming protocol. Here users may optimize the application of detectors to some degree. Nevertheless it is likely that the resulting data will be highly variable. Recorded echolocation calls are not always easy to identify on the species level, since inter- and intraspecific variability complicate call analysis. Only a few evaluation schemes are available, most of which are rather subjective and lack the possibility to control for the aforementioned constraints during data acquisition. Therefore, it is mandatory to follow a balanced approach when interpreting data. To make reports suitable and legally sound for environmental impact assessments, it seems mandatory to have an excellent understanding of the involved method. Simple generalized conclusions are usually impossible. Nevertheless, even when considering all limitations, acoustic monitoring techniques bear great advantages for the monitoring of bats during the planning and operation of wind turbines. When applied correctly, acoustic monitoring imposes rarely strong limitations.
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The presence of bat species is commonly determined by placing acoustic bat detectors that record bat echolocation calls in the habitat they are likely to use. Detection rates are affected by variables including type of detection unit used. We compared detection rates of long-tailed bat (Chalinolobus tuberculatus) echolocation calls between two types of automated bat detectors: Wildlife Acoustics SMZC Zero Crossing Bat Recorders (ZC), and Frequency Compression Automated Bat Monitoring units (FC) produced by New Zealand's Department of Conservation. Units were placed in locations where bats were known to be present, but not all detected bats. The median number of bat passes recorded by FC units over 10 nights was 20 compared with a median of 3 bat passes for ZC units. ZC units also detected bats over significantly fewer nights than FC units. These results suggest FC units are more sensitive and therefore better to use where long-tailed bats are expected to be at low abundance or only present infrequently. Because of inconsistencies in detection rates, we recommend the use of only one model of the detector within a monitoring project. Our data also suggests that surveys should take place over long periods to maximise likelihood of detecting bats, if present.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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) .
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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.
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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
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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 oil 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 level, 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.
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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.
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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.
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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.
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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.
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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.
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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.
Book
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.
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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.