The Western Barbastelle is one of the rarest, most endangered and most specialised bat species in Western Europe (COUZENS et al. 2017). Bavaria is the species’ stronghold within Germany which means that the state bears a special responsibility for the conservation of the species. While its occurrence all over the north, east and south-east of Bavaria has been verified there are larger gaps in the distribution in central and south-western Bavaria (LFU 2020b). Several nursery roosts of the species were known in the northern administrative district of Swabia (Günzburg) in the 1950s. Since then the Western Barbas-telle seemed to have withdrawn from this region for a long time (RUDOLPH 2004). In the last few years, probably also due to the improved technical possibilities in bat observation and numerous mappings in the context of wildlife conservation assessments (saP), an increasing number of acoustic recordings and nursery roost findings occurred (LFU 2020b).
The present study also revealed numerous new locations of call records and nursery roosts of the spe-cies for the administrative district of Swabia, which suggests that the Western Barbastelle is again more widespread in the region. Examples from Italy (ANCILLOTTO et al. 2015), Portugal (REBELO & JONES 2010) and Latvia (PĒTERSONS, VINTULIS & ŠUBA 2010) show that targeted searches can lead to unexpected densi-fication and expansion of distribution maps.
In order not to endanger the populations of the Western Barbastelle again, regional-specific data and knowledge are required so that the species can be adequately taken into account in forestry and agri-culture as well as in projects. Even if many secrets have been disclosed from the Western Barbastelle in recent years, its ecology and behaviour have by no means been conclusively researched. In addition, findings cannot be transferred to all occurrence areas without restrictions because the populations are adapted to different habitat conditions (ANCILLOTTO et al. 2014, REBELO & JONES 2010, SIERRO 1999, RU-DOLPH 2004). Accordingly, it is not surprising that the studies, individual observations and expert assess-ments available to date give a partly contradicting impression of the species and make it difficult to predict land use and project-related effects on the species.
Expectations and observations regarding the influence of light on the habitat of the Western Barbas-telle go in different directions (VOIGT et al. 2019, RUSSO et al. 2017, LACOEUILHE et al. 2014, ANCILLOTTO et al. 2014, STONE 2013, ZINGG 1999), which is why the reaction of the species to light emissions in the Bavarian administrative district of Swabia was experimentally investigated with the present study. For a field test it was hypothesized that the species avoids artificial light and its acoustically detectable activi-ty is reduced under the influence of light.
The experiment was carried out at ten locations in the districts of Neu-Ulm, Günzburg and Unterallgäu, with individuals of at least five different nursery communities being sampled. The intensely used hunting areas and flight routes were illuminated with two LED spotlights (4.500 lumens, 5.000 Kelvin, 50 W) in phases (15-minute intervals) while bat activity was measured in both the illuminated area and two non-illuminated control areas. During unlit phases, the activities were almost evenly distributed over the three recording locations, whereas the recording time was significantly reduced under the influence of the lighting.
Lateral and vertical evasive manoeuvres as well as turning around in the illuminated area were the most frequently observed behavioural patterns, but apparently unimpaired through-flights were also occa-sionally recorded. For the also recorded species group Pipistrellus (mainly Pipistrelle bat) no significant effect of the lighting could be determined but was found for the genus Myotis. On average, 32.5% of the Barbastelle´s activities occurred during the illuminated phases. This proportion differed significantly from the genus Myotis (9.2%) but not compared to the genus Pipistrellus (44.6%), which suggests that the Western Barbastelle reacts light-shy, but apparently less strongly than the genus Myotis.
The results of the present study provide a further contribution to the problem of “light emissions and bats” related to the German (Bavaria). They give clear indications that the Western Barbastelle is dis-turbed by new light sources on its flight routes and in its hunting habitats. The disturbance causes the species to fly detours and leave hunting habitats rich in food such as structured forest edges.
Since there are no explicit data on the extent to which such disturbances lead to stress, energy loss, i.e. restrictions in fitness, it must be assumed that light emissions in preferred hunting habitats and traditio-nal flight routes negatively effect the conservation status of local populations thus the disruption ban according to BNatschG § 44 paragraph 2 is fulfilled. In addition, it has not been conclusively clarified which factors trigger collisions in the Barbastelle.
The species is agile, fast and can orient over longer distances than the genera "Myotis" and "Plecotus", sometimes flies freely over highways, but also uses underpasses (SCHEWE 2015, KERTH & MELBER 2008). Nevertheless, it appears in the lists of road traffic victims (FENSOME & MATHEWS 2015). Irritations trigge-red by dynamic light (vehicle lights) could play a role, which temporarily disorientate the species in fast flight, lead to evasive action and, in the worst case, to collisions (ORBACH & FENTON 2010).
Important sub-habitats of the species such as structurally rich forests and forest edges, riparian vege-taion, hedges and old trees in settled areas should also be taken into account for projects in the admi-nistrative district of Swabia at least within 7 kilometers of the nursery roosts. To minimize light-related impairments from street lamps, the methods described in VOIGT et al. (2019) are required. In addition, the effects of dynamic, vehicle-generated light in road planning should be estimated by modeling lighting scenarios and taken into account in route planning.