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Artificial light at night (ALAN) affects biodiversity conservation through its impacts on spatio-temporal distribution patterns of species, in particular bat species. The development of this threat underlines the urgency to adopt lighting practices (characteristics) that have the least impact on species, in particular the most vulnerable species still present in semi-natural areas. It is therefore crucial to better assess the relative effects of the different light parameters for a wide variety of species. Our study investigates the relative effects of streetlights characteristics, i.e. height, lamps type (HPS, LED), illuminance, and the distance to a streetlight on the activity of a variety of species (15) according to their flight traits. We compared bat species activity in lit and dark conditions along streets and in hedges at less than 200 m away from streetlights of various characteristics, in a Mediterranean protected area.Lighting had contrasting effects on the activity of clutter and aerial bat species, with a strong negative effect on clutter species (90% reduction of bat activity), half of which are strictly protected. Illuminance particularly affected their activity.Among the possible management options to reduce the effect of light pollution at night (reduction of light intrusion by modifying the height of street lamps, lighting intensity, spectral composition), the removal of light sources, or at least the reduction of illuminance, seems to be the most effective option. Due to its strong impact on highly protected species, we urge the need to manage lighting, in particular in protected areas. Capsule: Artificial light at night had a negative effect on clutter bats activity (90% reduction of bat activity) and among streetlight characteristics illuminance was the most relevant. Data accessibility: Data used for statistical analysis are include in Appendix C. Acoustic row data was delivered to the citizen science program “VigieChiro” (https://vigiechiro.herokuapp.com/).

Additional file 1.

Slides and abstract from the BCC2020 talk "Producing biodiversity indicators from citizen science projects: update of birds and bats monitoring schemes on Galaxy-E" Video capture of the talk is available here: https://vimeo.com/437705490, Video capture of the talk is available here: https://vimeo.com/437705490

Few reports have been published on detection distances of bat calls because the evaluation of detection distance is complicated. Several of the approaches used to measure detection distances are based on the researcher’s experience and judgment. More recently, multiple microphones have been used to model flight path. In this study, the validity of a low-cost and simple detectability metric was tested. We hypothesize that the duration of an echolocating-bat-pass within the area of an ultrasonic bat detector is correlated with the distance of detection. Two independent datasets from a large-scale acoustic bat survey—a total of 25,786 bat-passes from 20 taxa (18 species and two genera)—were measured. We found a strong relationship between these measures of bat-pass duration and published detection distances. The advantages of bat-pass duration measures are that, for each study, experimenters easily produce their own proxy for the distance of detection. This indirect measure of the distance of detection could be mobilized to monitor the loss in microphone sensitivity used to monitor long-term population trends. Finally, the possibility of producing an index for distance of detection provides a weight for each bat species’ activity when they are aggregated to produce a bat community metric, such as the widely used “total activity„.

International audience; Suite à une demande européenne de contribution à la construction d’un indicateur des tendances de populations de Chauves-souris à partir des comptages hivernaux, une réflexion a été menée en France depuis 2015, pour évaluer la faisabilité du réseau français à contribuer à cet indicateur européen. Plusieurs questions se sont alors posées sur les approches à développer pour mobiliser les observateurs et les données, les méthodologies à mettre en œuvre pour prendre en compte les biais inhérents à ce type de suivi. Des formations spécifiques à destination des groupes Chiroptères ont été proposées ainsi que la production d’outils (script R) dans le but de les accompagner dans la structuration de leurs données, l’identification des problèmes potentiels dans les données et les analyses des tendances aux différentes échelles. Les données analysées sur les vingt anciennes régions administratives françaises concernent 9 106 sites dont en moyenne sur la période 2000-2015, plusde 2 000 sites sont suivis annuellement. L’implication des groupes Chiroptères dans ces suivis hivernaux est en très nette augmentation comme en témoigne l’augmentation du nombre de sites suivis. Il a été possible d’obtenir suffisamment de tendances locales pour permettre de produire des tendances locales puis nationales pour douze espèces. Parmi celles-ci, huit espèces ont une tendance significative à l’augmentation (Barbastella barbastellus, Myotis mystacinus, M. myotis, M. emarginatus, M. natterreri, Rhinolophus ferrumequinum, R. hipposideros, R. euryale), une seule espèce (Miniopterus schreibersii) présente une tendance significative à la diminution. Aucune tendance significative n’a été détectée pour trois autres espèces (Myotis daubentonii; Myotis bechsteinii et Plecotus auritus).

Monitoring biodiversity over large spatial and temporal scales is crucial for assessing the impact of global changes and environmental mitigation measures. Bats often have high conservation prioritisation owing to their trophic position, habitat associations and threat level, and many have dedicated management plans. However, poor knowledge of species' ecology, identification issues and surveying challenges mean that large-scale monitoring to produce required distribution and abundance information is less developed than for some other taxa. Exciting possibilities applicable to professional and citizen science are offered by new recording techniques and methods of semi-automated species recognition based on sound detection. Static detectors deployed to record bats throughout whole nights have been recommended for standardised acoustic monitoring but until recently cost and lack of software to support the analyses of such data has prohibited wide uptake. Such monitoring schemes have recently been deployed in both Britain and France allowing the fast and standardized collection of millions of bat records together with very interesting data on non-targeted taxa such as bush-crickets. Such data management led us to develop generic and open tools: (1) the Tadarida software toolbox providing a generic detection and classification of sound events, and (2) an open dedicated web portal (www.vigiechiro.herokuapp.com) to allow participants to manage and upload their data, then being processed trough Tadarida to get a quick feedback on the content of the data. We demonstrate how such data can accurately describe pronounced ecological patterns for numerous species at different scales: spatial variation in activity as a proxy for relative abundance, habitat selection and phenology of seasonal and nocturnal activity. If maintained in the long term, such schemes will also greatly improve estimates of species temporal trends and hence the assessment of conservation priorities. The feedback produced by these two monitoring schemes allows us the opportunity to provide recommendations for the sustainability of long-term acoustic monitoring of bats. These include a database that is adaptively managed to allow all raw data to be re-analysed every time automatic identification makes significant progress, while keeping the link with expert validation to ensure consistency in the semi-automated process. More importantly, there are real benefits of developing long-term acoustic monitoring within a collaborative framework. Specifically, (1) for collaboration among bat scientists for the collection of reference sound data, because diversity and quantity of the reference library remains a limiting factor for automatic identification, and (2) for work on bats to consider the wider acoustic monitoring of other species groups by working with other zoologists to share resources and costs.

International audience; Acoustic detectors have become increasingly used by bat workers to investigate bat ecology and assess impacts of anthropogenic pressures. Within these studies, the metric used, "bat activity," is based on the number of bat passes, without considering the bat pass duration (i.e., each event of a bat detected within the volume of an ultrasonic detector); we expected that bat pass duration may contain information about site quality in terms of potentialities for foraging. Because bats are expected to have a more sinuous trajectory and slower velocity when they exhibit foraging behaviour, as opposed to commuting behaviour, we hypothesize a greater bat pass duration in favourable habitats; during seasons with important energetic demands; or during night pic activity. We datasets from a large-scale acoustic bat survey (n=2890 sites), allowing a total of 24597 bat pass measures from 6 taxa, and performed GLMM modelling. We detected a significant effect of habitat type on bat pass duration for five taxa. Smaller bat pass durations were detected in the beginning of the night. We detected longer pass durations during the lactation period or just before hibernating, while weather conditions or ageing and wear of the detector rarely influenced bat pass duration. Bat pass duration appears to be a simple and easy measure for position calls on a gradient between commuting vs. foraging behaviour. We suggest that the traditional measure of bat activity may be weighted by bat pass duration by giving more weight to the events with potentially greater links to foraging behaviour.