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Clutter‐adaptation of bat species predicts their use of under‐motorway passageways of contrasting sizes – a natural experiment
Journal of Zoology
Abstract
Bat populations may be vulnerable to the barrier impacts of roads, including habitat restriction and traffic mortality. Under‐road passageways may reduce these impacts, but little is known about the ecological factors influencing their use by bats. The study area provided a natural experimental design, in that adjacent under‐motorway passageways had contrasting dimensions (two long, narrow drainage pipes within Rhinolophus hipposideros, Myotis nattereri and Plecotus auritus flew through the narrow drainage pipes. These species are adapted for flight and foraging in cluttered airspace, in terms of wing morphology and echolocation signal design. Edge‐space species (Pipistrellus pipistrellus, Pipistrellus pygmaeus) were highly active in the area but never flew through the narrow pipes. All species, except the open‐adapted Nyctalus leisleri, flew through the large underpass. Simultaneous recordings made above and below this underpass (16 nights) also indicated that species' tendency to cross over, rather than under, the structure was inversely related to the degree of clutter‐adaptation. If motorways are built through bat habitat, trade‐offs between optimal mitigation of impacts on protected bats and cost/engineering practicality are inevitable. Large underpasses are advisable where possible as they accommodate a wider range of species, and bats are less likely to fly over them. However, their construction is costly and is dependent on landscape topology. If the target species for mitigation are clutter‐adapted bats, our findings indicate that incorporation of a greater number of suitably located small tunnels into new roads may facilitate safe passage more effectively than fewer large underpasses.
... Flight characteristics can be useful for a general description of the types of risk to which different bat species are most vulnerable, and, therefore, which types of mitigation measures may be most effective in mitigating risk (aBBott et al. 2012b, BhardWaJ et al. 2017. For example, the disruption or removal of habitat features used as navigation aids for clutter adapted species may reduce their access to foraging resources (Kyheröinen et al. 2019). ...
... Bridges and viaducts (long extended bridges, usually supported by pillars) built to support traffic infrastructure across a watercourse or a valley are not usually specifically designed to mitigate the barrier effect for wildlife, but they can provide large and suitable underpasses for a range of taxa (iuell et al. 2003). Since they are built over the landforms that often define bat commuting and migration routes (and where foraging activity is also highly concentrated), they are likely to be effective for many bat species, providing that the clearance height above water or vegetation is sufficient to avoid putting open-space foraging bat species at risk of collision (altringham 2008, Berthinussen & altringham 2012, aBBott et al. 2012a, aBBott et al. 2012b). . They pose a particular danger to bats, especially if they sever treelines where bats flying at canopy height enter the collision risk zone as they cross the road . ...
... Species-specific effectiveness of underpass is determined by the cross-sectional area, and height in particular rather than length (Boonman 2011, aBBott et al. 2012a, aBBott et al. 2012b, Berthinussen and altringham 2012b thus leading to published recommendations on the required species-specific dimensions of underpasses (e.g. limpens et al. 2005(e.g. ...
The continuing global expansion of the traffic infrastructure network has a detrimental impact on bats and other wildlife through indirect effects such as loss of habitats and roost sites, increased habitat fragmentation, avoidance of habitats (the
barrier effect) and directly through collisions with vehicles. Some impacts can be avoided or minimised through an effective planning process and good design. Mitigation features are used to promote permeability whilst reducing mortality,
however, solutions should be species-specific and site-specific.
These guidelines bring together information on the impact on bats of road, rail and air traffic infrastructure. There is a need for transport commissioning authorities to work with researchers to better understand how traffic infrastructure and operation
affect bat behaviour, and impact bats at the population level. Robust survey and monitoring of traffic infrastructure projects are required to improve the effectiveness of avoidance and mitigation measures (EUROBATS Resolution 7.9).
... As a result, at the planning approval stage, the design engineers would have at hand the exact minimum dimensions of the height and width of a given culvert or underpass. The study reported in [19] presented the aggregate results of dimensions of underpasses and culverts recommended for certain European bat species, based on the data obtained from many research studies [45,[77][78][79][80][81][82]. Based on the confrontation of the road structures built on the S3 expressway and the conclusions from the studies and the reports formulated in [45,[76][77][78][79][80][81][82], regarding the recommended dimensions of underpasses and culverts on bat commuting and migration routes, the authors believe that the minimum dimensions of culverts should be determined as early as at the stage of preliminary considerations based on the results of pre-construction monitoring surveys, taking into account the species of bats and the heights of their flight that had been confirmed in the monitoring. ...
... The study reported in [19] presented the aggregate results of dimensions of underpasses and culverts recommended for certain European bat species, based on the data obtained from many research studies [45,[77][78][79][80][81][82]. Based on the confrontation of the road structures built on the S3 expressway and the conclusions from the studies and the reports formulated in [45,[76][77][78][79][80][81][82], regarding the recommended dimensions of underpasses and culverts on bat commuting and migration routes, the authors believe that the minimum dimensions of culverts should be determined as early as at the stage of preliminary considerations based on the results of pre-construction monitoring surveys, taking into account the species of bats and the heights of their flight that had been confirmed in the monitoring. Additionally, depending on the terrain conditions, the vertical alignment of the designed road, the landscape and development features of the local geography, the possible need for mesh screens, and new supplementary plantings along the treelines or watercourses should be considered before the start of road works, and the lines of natural funnels for bats to fly through should be designated. ...
... Examples of inadequate landscape and land development features at locations where several bat carcasses were found and suggestions for improving this land development are shown in Appendix D. Figure A8 in Appendix D shows a proposal for extending the treeline and the natural funnel installed at culverts. Figure A9 in Appendix D shows a proposal for a natural funnel to be installed before a small wildlife underpass, taking into account the minimum dimensions based on the study results given in [19,20,46,76,77,[79][80][81]. Figure A10 in Appendix D shows a proposal for a natural funnel to be installed before a medium-size underpass, considering the minimum dimensions based on the study results given in [19,46,77]. Figure A11 in Appendix D shows a proposal for a natural funnel to be installed before a large-size underpass, considering the minimum dimensions based on the study results given in [10,19]. ...
The continuing increase in motorisation and the resulting development of the road infrastructure puts increasing demands on environmental protection, and on the protection of bats in particular. One of the available mitigation measures is mesh screen structures installed on dual carriageways. However, not all the mitigating measures turn out to be effective and functional. Mesh screens were installed along a road section over a dozen kilometres long near a large bat reserve in Poland (40,000 bats). As part of post-construction work, bat mortality monitoring was conducted over a 3–4 year period in order to assess the effectiveness of the mesh screens in raising the height of bat flyways. An analysis of the mortality surveys and the locations of bat carcasses found along the expressway allowed the authors to confirm that the screens may contribute to raising the height of bat flyways, yet this effect should be considered in combination with other determinants identified during the surveys. The article presents the main determinants, which together with the mesh screens installed along a dual carriageway road over the length of several kilometres, can contribute to the effective raising of the height at which bats fly across the road. The most important determinants included: retaining the continuity of linear landscape features along the confirmed bat commuting and migration routes, no gaps in the tree line greater than 30 m, use of natural funnels for bats to fly through, and sizing of culverts and underpasses appropriate for the specific bat species, as identified in the pre-construction surveys. The conclusion drawn from the research was the need for interdisciplinary studies to be carried out already during preliminary design work, to ensure a sustainable approach on the part of the road engineers, structural engineers, chiropterologists, and landscape architects involved in the road project. A detailed analysis of numerous factors relevant to the analysed dual carriageway demonstrated the importance of following the principles of sustainable design and collaboration within interdisciplinary design teams to select the best mitigation measures already at the pre-construction stage of the project.
... Overpasses are specifically built to facilitate bat movements, while underpasses are generally set for drainage or human activities (minor roads, agricultural tracks or hiking paths for instance) but are favorable to many taxa including bats. Underpasses have been shown to allow maintaining bat commuting routes and road permeability Møller et al., 2016) and seem more effective than overpasses (Abbott et al., 2012a(Abbott et al., , 2012bBach et al., 2004;Claireau et al., 2018). ...
... Finally, the relationships between bats and landscape contexts are species/guild-dependent (Ducci et al., 2015;Mendes et al., 2016) which is also the case for bat response to roads and underpasses (Abbott et al., 2012a(Abbott et al., , 2012bBhardwaj et al., 2017;Kerth and Melber, 2009;Medinas et al., 2019Medinas et al., , 2013. Thus, it is expected that landscape context will influence differently the use and attractiveness of underpasses depending on the species or guilds. ...
... (Fig. 1). In comparison with previous studies on underpass use by bats in Northern Europe (Abbott et al., 2012a(Abbott et al., , 2012bBach et al., 2004;Boonman, 2011), our study area has a less dense road network with more preserved landscapes and hosts a higher bat diversity with 27 bat species recorded at the regional scale (Bodin et al., 2011). ...
The worldwide expansion of road networks is a major concern in biological conservation because of its predominantly negative effects on terrestrial fauna. Roads also affect bats, acting as barriers to movements and causing direct mortality by collisions with vehicles. Among wildlife crossing structures existing to maintain landscape connectivity, road underpasses are considered as one of the most effective conservation measure for bats. While a few studies assessed the effects of underpass attributes on bat use, none to date has assessed the impact of landscape context on underpass use and attractiveness. To address this knowledge gap, we monitored bat activity during three consecutive nights around 24 underpasses selected along a gradient of forest cover. We compared
bat activity below and above underpasses (i.e., underpass use), at road sections with and without underpasses and at habitats adjacent to roads (i.e., underpass attractiveness). We found a significant positive effect of forest cover on both underpass use and attractiveness for Myotis spp. and Barbastella barbastellus, and significant negative effects of distance to the nearest forest patch for Rhinolophus spp. and hedgerow length for Myotis spp. Our
study highlights the key influence of landscape context on road underpass efficiency to maintain landscape connectivity for bats. We advocate for incorporating a landscape-scale approach in the decision-making process of underpass location during road project planning to enhance efficiency of such costly crossing structures.
... Ascensão and Mira, 2007;Chambers and Bencini, 2015;Waltho, 2000, 2005), however, species traits and ecologies may also influence structure use (e.g. Abbott et al., 2012a;Abbott et al., 2012b). In addition to environmental factors, it may be informative to evaluate species' ecologies and behaviour in order to predict their response to roads (Rytwinski and Fahrig, 2012) and crossing structures (Abbott et al., 2012a;Abbott et al., 2012b). ...
... Abbott et al., 2012a;Abbott et al., 2012b). In addition to environmental factors, it may be informative to evaluate species' ecologies and behaviour in order to predict their response to roads (Rytwinski and Fahrig, 2012) and crossing structures (Abbott et al., 2012a;Abbott et al., 2012b). ...
... This approach moves away from actions that are focused on a single species to those encompassing multiple species. In a similar way to anticipating or predicting the response to impacts, guilds can be used to predict the outcome of management or conservation strategies, such as the traits that influence the use of crossing structures along highways (Abbott et al., 2012a;Abbott et al., 2012b;Boonman, 2011;Kerth and Melber, 2009). Roads can have a negative impact on the activity and movement of insectivorous bats (hereafter referred to as "bats"; e.g. ...
Roads can form barriers to movement for many species, and may reduce the ability of individuals to access foraging and breeding habitat. The impacts of roads on terrestrial fauna has been well studied, however little is known of the impact of roads on insectivorous bats. Wildlife crossing structures (e.g. fauna underpasses) may reduce the barrier impacts of roads and improve connectivity across roads. Use of underpasses by wildlife likely varies among species depending on their movement behaviour. In this study, we investigated whether the flight patterns of insectivorous bats influenced their use of underpasses. We monitored bat activity under and above 6 open-span bridges, 6 box culverts and 6 unmitigated sites along a major highway in Australia. We used Poisson regression models within a Bayesian framework of inference to compare the activity of 12 bat species (grouped into three guilds based on their flight patterns: clutter-adapted, edge-adapted, and open-adapted species) under the structures, over the road above the structures, above unmitigated segments of the highway, and in the vegetation adjacent to the roads. Bats were less active above the road than they were in the surrounding vegetation or under bridges. Two of the three guilds (i.e. seven species) crossed the highway more under bridges than they did under culverts or by going over the road, which suggests that bridges may reduce barrier effects of the road better than culverts. Installing bridges instead of culverts may better reduce the impacts of roads on multiple insectivorous bats species with a single structure type.
... Bats have been observed using most of the measures as intended, but bats' use of the measures have rarely been studied in depth. A few recent, robust studies have shown that some mitigation structures can be effective while others are only used by a minor proportion of the bats to cross the roads safely (SWILD & NACHTaktiv 2007, Abbott et al. 2012a, 2012b, Berthinussen & Altringham 2012. ...
... Group A species such as Rhinolophus hipposideros, Myotis nattereri, Myotis bechsteinii, and Plecotus auritus, are sometimes registered in tunnels or culverts with extremely small cross sectional areas (< 2m high) (Abbott et al. 2012b, Bach et al. 2004). However, results are ambiguous and local conditions such as the presence of guiding structures and flight paths are important factors determining the use of underpasses (e.g. ...
... hedges) was not significant in explaining the use of culverts carrying waterways (Boonman 2011). However, it is likely that hedges and tree rows play a significant role in enhancing the use of tunnels, where there is no waterways guiding the bats (Abbott et al. 2012a, 2012b, Berthinussen & Altringham 2012). ...
... Most knowledge on bats and road mitigation measures are based on anecdotic observations and descriptive studies that only address bats' use of the measures. Only a few recent studies have adequately tested the effectiveness of mitigation measures (Abbott et al. 2012a, 2012b, Berthinussen et al. 2012, SWILD & NACHTaktiv 2007. These studies have shown that often only a minor proportion of the bats and bat species used the mitigation structures to cross the roads safely. ...
... In a controlled, site comparison study, Abbott et al. (2012b) examined whether inter-species differences in flight capability and sensory perception would influence bat use of potential underpasses. Bat activity in two narrow drainage culverts (<1.5 m in diameter, and L 43 m and 91 m, respectively) under a motorway were compared to bat activity in a nearby road underpass tunnel (H 6 m, W 16.6 m, L 26 m) under the motorway. ...
... Extremely manoeuvrable species in particular, including Rhinolophus hipposideros, Myotis emarginatus, Myotis bechsteinii, Myotis nattereri, Plecotus auritus and Plecotus austriacus, were registered in tunnels or culverts with small cross-sectional areas. Two narrow drainage pipes (< 2 m high) were used by Rhinolophus hipposideros and Myotis nattereri and to some extent by Plecotus auritus (Abbott 2012b). A narrow culvert (H 2 m, W 1.5 m) even proved quite effective for a nearby Myotis nattereri maternity roost and was used by about 88% of the individuals (Bach et al. 2004). ...
... Most knowledge on bats and road mitigation measures are based on anecdotic observations and descriptive studies that only address bats' use of the measures. Only a few recent studies have adequately tested the effectiveness of mitigation measures (Abbott et al. 2012a, 2012b, Berthinussen et al. 2012, SWILD & NACHTaktiv 2007. These studies have shown that often only a minor proportion of the bats and bat species used the mitigation structures to cross the roads safely. ...
... In a controlled, site comparison study, Abbott et al. (2012b) examined whether inter-species differences in flight capability and sensory perception would influence bat use of potential underpasses. Bat activity in two narrow drainage culverts (<1.5 m in diameter, and L 43 m and 91 m, respectively) under a motorway were compared to bat activity in a nearby road underpass tunnel (H 6 m, W 16.6 m, L 26 m) under the motorway. ...
... Extremely manoeuvrable species in particular, including Rhinolophus hipposideros, Myotis emarginatus, Myotis bechsteinii, Myotis nattereri, Plecotus auritus and Plecotus austriacus, were registered in tunnels or culverts with small cross-sectional areas. Two narrow drainage pipes (< 2 m high) were used by Rhinolophus hipposideros and Myotis nattereri and to some extent by Plecotus auritus (Abbott 2012b). A narrow culvert (H 2 m, W 1.5 m) even proved quite effective for a nearby Myotis nattereri maternity roost and was used by about 88% of the individuals (Bach et al. 2004). ...
... Las carreteras son infraestructuras cada vez más presentes en los paisajes actuales (Giulio et al. 2009), mejoran la comunicación humana y desempeñan un papel social importante en la sociedad de hoy en día (Trombulak & Frissell, 2000;Hawbaker et al 2004). Sin embargo, tienen una amplia gama de impactos ecológicos negativos en la vida silvestre (Abbott et al, 2012), además de destruir y degradar el hábitat natural (Forman et al., 2003), son un factor importante, causante de la pérdida de biodiversidad en todo el mundo (Giulio et al.2009). ...
... No obstante, la poca antigüedad de esta carretera (8 años), las 12 especies que utilizan estos pasos representan cerca del 50% de las especies presentes en Portugal Continental, lo que representan una elevada diversidad, cuando comparado con estudios similares (Kerth & Melber, 2009;Abbott et al., 2012). El alto índice de actividad (número de cruces) y la alta diversidad de especies registradas parecen indicar un elevado grado de adaptación de los murciélagos a estas estructuras. ...
... No obstante de estos resultados, habría que discernir si los datos sugieren un elevado grado de adaptación o simplemente un uso en la misma intensidad que el resto del entorno, lo que necesitaría la realización de estudios más amplios y detallados de la actividad e riqueza de murciélagos en los entornos de los pasos. De hecho, en Alemania se verifico que las captura en los pasos inferiores eran significativamente más elevadas en algunas especies que en los entornos, lo que sugiere que la eficacia de cruce en los pasos inferiores, puede ser mayor para algunas especies (Kerth & Melber, 2009) y en Irlanda, se observó la tendencia a volar a través de los pasos inferiores en lugar de sobre la carretera, lo que sugiere un grado de adaptación de las especies (Abbott et al., 2012). ...
The main goal of this study was to contribute for the knowledge of the use of under-roads passageways by bats in northern of Portugal. We selected five underpasses in a road stretch of 8.250 m located in a rural agricultural and grazing area. The average dimensions of underpasses were, 9 m wide, 4.25 m high and 34 m deep. The data was obtained through acoustic detection, mist net capture and roost inspection. Acoustic and mist netting results confirm the use of the underpasses by at least 12 species (Pipistrellus pipistrellus, P. kuhlii, P. pygmaeus, Myotis daubentonii, M. escalerai, M. myotis, Nyctalus leisleri, Plecotus austriacus, Rhinolophus ferrumequinum, R. hipposideros, R. mehelyi/R. euryale andEptesicus serotinus/E. isabellinus). Data from roost inspection in all the underpasses showed the presence of at least six species (M. daubentonii, M. myotis, N. leisleri, P. austriacus, Eptesicus serotinus/E. isabellinus yPipistrellus sp.), they used fissure within the tunnels of between 1.2 and 1.9 cm. For the same height (4.2-4.3 m) and width (9m), the underpasses most used were the longest. These results stress the importance of underpasses in improving the connectivity and permeability between areas, along with its potential to offer new roosts for bats. We encourage further monitoring and detailed ecological studies to better understand the physical and environmental characteristics that underpin the usage of such structures by bats.
... The higher probability of bats being road-killed in the proximity of streams and water reservoirs also may be related to the availability of water, a scarce and unevenly distributed resource in the region (Russo and Jones 2003;Rainho 2007;Rainho and Palmeirim 2011). Moreover, riparian corridors may also be used as bat flyways to cross roads (Abbott et al. 2012), increasing their risk of being hit by a car. ...
... Bats are referred to regularly use viaducts and underpasses for crossing roads (Kerth and Melber 2009;Abbott et al. 2012); consequently, the likelihood of roadkills close to viaducts should be lower, which also does not conform to our results. This contrasting result may be due to the association of these structures with streams and ponds in our study area, where bat foraging activity is usually enhanced. ...
Recent studies suggest that roads can significantly impact bat populations. Though bats are one of the most threatened groups of European vertebrates, studies aiming to quantify bat mortality and determine the main factors driving it remain scarce. Between March 16 and October 31 of 2009, we surveyed road-killed bats daily along a 51-km-long transect that incorporates different types of roads in southern Portugal. We found 154 road-killed bats of 11 species. The two most common species in the study area, Pipistrellus kuhlii and P. pygmaeus, were also the most commonly identified road-kill, representing 72 % of the total specimens collected. About two-thirds of the total mortality occurred between mid July and late September, peaking in the second half of August. We also recorded casualties of threatened and rare species, including Miniopterus schreibersii, Rhinolophus ferrumequinum, R. hipposideros, Barbastella barbastellus, and Nyctalus leisleri. These species were found mostly in early autumn, corresponding to the mating and swarming periods. Landscape features were the most important variable subset for explaining bat casualties. Road stretches crossing or in the vicinity of high-quality habitats for bats—including dense Mediterranean woodland (“montado”) areas, water courses with riparian gallery, and water reservoirs—yielded a significantly higher number of casualties. Additionally, more road-killed bats were recorded on high-traffic road stretches with viaducts, in areas of higher bat activity and near known roosts.
... Species adapted to open spaces are typically capable of longdistance travel at reduced energetic costs given that "a long, narrow wing works better than a short, wide one with the same area and profile, because it develops more lift, and less induced drag at the same angle of attack" (Pennycuick 2008:68). Hence, these species are more likely to occupy larger home ranges (O'Donnell 2001;Noer et al. 2012), while the opposite appears to be the case for clutter specialists (Monadjem et al. 2009;Abbott et al. 2012). Kelt and Van Vuren (2001) demonstrated that carnivorous terrestrial mammals have larger home ranges than omnivorous or herbivorous species of comparable body mass (Carbone and Gittleman 2002;Tucker et al. 2014), but this trend remains untested for bats. ...
Home range is an ecological concept that affects many aspects of the life of vertebrates and hence understanding how it varies between species is crucial. Mammalian home range size has been linked to body size and diet, but these studies were based predominantly on terrestrial species and most specifically excluded bats. As the only group of flying mammals, bats experience distinctly different constraints on movement, and hence home range. However, despite their diversity, relatively little is known about the home ranges of bats, and this is the first global review assessing correlates of their home range size. Our hypothesis is that home range will be impacted by different ecological conditions experienced by the bats and by the biological traits of the bats themselves. We performed a meta-analysis based on published data for 81 bat species to identify variables that contribute most to home range size. Sex, wing loading, functional group, colony size, dietary class, distance from the equator (latitudinal region), habitat type, and the interaction between habitat type and latitudinal region were all important explanatory variables. Wing loading was positively correlated with home range size—while females, open-air foragers, large colony sizes, and bats in temperate regions consistently had large home ranges. Understanding the correlates of home range has important implications, for example, for bat conservation and for assessing the risk of spillover of zoonotic pathogens from bats to humans and livestock.
... Steep frequency-modulated echolocation calls with very large bandwidths enable M. nattereri to detect and localize prey a few centimeters (up to 5 cm) away from the vegetation clutter (Siemers and Schnitzler 2000), at much closer distances than other Myotis bat species with lower call bandwidths (Siemers and Schnitzler 2004). Their broadband echolocation calls and high maneuverability enable M. nattereri bats to fly in cluttered spaces, including narrow drainage pipes used as under-road passageways (Abbott et al. 2012). Prey detection and capture are also supported by the characteristic fringe of hairs at the edge of the tail membrane (Czech et al. 2008). ...
... Similarly to other studies (Medinas et al. 2013), our results show that there is a higher number of bat roadkill accidents on road segments closer to bat roosts than on the remaining segments. Bridges could provide roosting places for some bat species (Keeley & Tuttle 1999, Frick et al. 2019; these are also places where riparian corridors, used as bat flyways (Abbott et al. 2012), cross the road. These facts could explain the high incidence of roadkills reported here in road segments with bridges. ...
A study on bat casualties was carried out between 2013 and 2016 on the 16-km road stretch passing through the Kresna Gorge-a European biodiversity hotspot with high conservation value. We found 78 road-killed bats belonging to ten species, adding new data on the bat species composition in the gorge. We identified one road section as a roadkill hotspot (a place where bats experienced collisions more frequently). Our analyses showed that more numerous bat casualties occurred on road segments close to bat roosts and on segments with bridges. The construction of a motorway through the Kresna Gorge has been planned for the near future. The consequent loss of large portions of high-quality habitats and the increase of bat road casualties due to the higher velocity and traffic intensity would negatively influence the bat populations in the region. The identified hotspots could be useful for the planning of appropriate mitigation measures against the bat roadkill in this and other regions.
... In Ireland, low-flying species adapted to foraging in cluttered habitats, such as Myotis spp. and Plecotus auritus, are more likely to use river bridges as under-road passageways than to cross directly over the road (Abbott et al., 2012a). Ac cording to Laforge et al. (2019), the use of those structures as crossing points by bats is dependent on the landscape features and are more attractive in areas with higher forest cover. ...
The increase in human population has resulted in environmental alterations and habitat fragmentation, such as those caused by road construction. Since the late 1990s, there has been an increase in studies evaluating the effects of roads on vertebrate populations; however, few studies have considered bats in road ecology studies. In this review on road ecology studies focusing on bats, we evaluated the impacts of roads on bat mortality, commuting, and foraging. We also evaluated the use of road structures as roosts and provide suggestions for future research and mitigation methods based on available results. Road impacts on bat activity and roadkill are strongly influenced by landscape features, and areas with short trees have more impact on roadkill. Also, in open areas, bats prefer to forage near roads whereas in woodland areas activity increases with distance from the road. Most studies evaluating the effects of roads on bats have been conducted in Europe, therefore it is essential that these studies are conducted in other areas, especially in developing countries. To ensure the conservation of bat species, it is imperative that studies consider all impacts that roads have on bat populations and that mitigation measures are applied, especially when road construction meets bat commuting or foraging paths.
... This is probably because higher values of accumulated aboveground net primary productivity (as measured by NDVI) tend to be associated with high insect availability areas that are temporally stable (Bailey et al., 2004), consistently improving the quality of foraging areas for many close-space aerial insectivorous bats, such as Rhinolophus spp.. High vegetation productivity is also often related to higher tree cover, which provides shelter resources for common bat species as P. kuhlii or P. pipistrellus (Kunz and Lumsden, 2003;Rodríguez-Aguilar et al., 2017). Moreover, in a landscape context with few hedgerows, roadside verges often represent the last remains of dense vegetation strips providing corridors and enhanced foraging opportunities in the immediate roadside vicinity (Abbott et al., 2012;Hale et al., 2015;Laforge et al., 2019), which increases the roadkill risk. Indeed, we also confirmed a strong positive relationship between areas of high bat activity and roadkill risk. ...
Highlights
• Bat roadkill hotspot locations may shift along time.
• Stable hotspots accounted only for 3% of road length, but for 27% of roadkilled bats.
• Spatiotemporal congruence of hotspots declined with decreasing vegetation productivity.
• Water stress on roadsides decrease the persistence of bat roadkill hotspots.
• Remote sensing information may be a tool for planners to minimize the impact of roads.
Abstract
Wildlife roadkill hotspots are frequently used to identify priority locations for implementing mitigation measures. However, understanding the landscape-context and the spatial and temporal dynamics of these hotspots is challenging. Here, we investigate the factors that drive the spatiotemporal variation of bat mortality hotspots on roads along three years. We hypothesize that hotspot locations occur where bat activity is higher and that this activity is related to vegetation density and productivity, probably because this is associated with food availability. Statistically significant clusters of bat-vehicle collisions for each year were identified using the Kernel Density Estimation (KDE) approach. Additionally, we used a spatiotemporal analysis and generalized linear mixed models to evaluate the effect of local spatiotemporal variation of environmental indices and bat activity to predict the variation on roadkill hotspot locations and to asses hotspot strength over time. Between 2009 and 2011 we conducted daily surveys of bat casualties along a 51-km-long transect that incorporates different types of roads in southern Portugal. We found 509 casualties and we identified 86 statistically significant roadkill hotspots, which comprised 12% of the road network length and contained 61% of the casualties. Hotspots tended to be located in areas with higher accumulation of vegetation productivity along the three-year period, high bat activity and low temperature. Furthermore, we found that only 17% of the road network length was consistently classified as hotspots across all years; while 43% of hotspots vanished in consecutive years and 40% of new road segments were classified as hotspots. Thus, non-persistent hotspots were the most frequent category. Spatiotemporal changes in hotspot location are associated with decreasing vegetation production and increasing water stress on road surroundings. This supports our hypothesis that a decline on overall vegetation productivity and increase of roadside water deficit, and the presumed lower abundance of prey, have a significant effect on the decrease of bat roadkills. To our knowledge, this is the first study demonstrating that freely available remote sensing data can be a powerful tool to quantify bat roadkill risk and assess its spatiotemporal dynamics.
... Some bat species are susceptible to high rates of road mortality (Lesi� nski et al., 2011;Medinas et al., 2013), while others avoid approaching and crossing roads (Medinas et al., 2019) due to the gap created in the canopy (Bennett and Zurcher, 2013;Hale et al., 2015), the presence of vehicles (Zurcher et al., 2010), and/or traffic noise (Schaub et al., 2008;Siemers and Schaub, 2011). Crossing structures, such as purpose-built wildlife underpasses, may reduce these impacts and maintain the connectivity of bats in the landscape, as bats can roost under and commute through culvert and bridge underpasses (Abbott et al., 2012;Bhardwaj et al., 2017). ...
In an attempt to improve cost-effectiveness, it has become increasingly popular to adapt wildlife crossing structures to enable people to also use them for safe passage across roads. However, the required needs of humans and wildlife may conflict, resulting in a structure that does not actually provide the perceived improvement in cost-effectiveness, but instead a reduction in conservation benefits. For example, lighting within crossing structures for human safety at night may reduce use of the structure by nocturnal wildlife, thus contributing to barrier and mortality effects of roads rather than mitigating them.
In this study, we experimentally evaluated the impact of artificial light at night on the rate of use of wildlife crossing structures, specifically underpasses, by ten insectivorous bat species groups in south-eastern Australia. We monitored bat activity before, during and after artificially lighting the underpasses. We found that bats tended to avoided lit underpasses, and only one species consistently showed attraction to the light. Artificial light at night in underpasses hypothetically increases the vulnerability of bats to road-mortality or to the barrier effect of roads. The most likely outcomes of lighting underpasses were 1. an increase in crossing rate above the freeway and a decrease under the underpasses, or 2. a reduction in crossing rate both above freeways and under the underpasses, when structures were lit. Our results corroborate those of studies on terrestrial mammals, and thus we recommend that underpasses intended to facilitate the movement of wildlife across roads should not be lit.
... Among mammals, medium and large-sized species have received greater attention from ecologists studying roads (Barthelmess & Brooks 2010;Cáceres 2011). Although smaller species are suggested to be less impacted by roadkills, collisions with vehicles are known to be an important cause of death of bats (Lesiński 2007(Lesiński , 2008Gaisler et al. 2009;Russell et al. 2009;Lesiński et al. 2010;Berthinussen & Altringham 2012;Abbott et al. 2012;Medinas et al. 2013;Fensome & Mathews 2016). Nevertheless, few studies have investigated the biological traits that influence bat-vehicle collisions, and none of them have focused in tropical areas. ...
Para a maior parte das pessoas, os morcegos passam despercebidos no dia a dia. A não ser que eles entrem em casa. Aí, a confusão está armada! Esses mamíferos voadores dão rasantes que assustam os desavisados. Nas ruas da cidade, é preciso ter olhos muito atentos para avistá-los em meio à folhagem das árvores.
Embora não vejamos os morcegos com frequência, não podemos esquecer o quanto eles são importantes na natureza. Esses animais são essenciais para a regeneração das florestas e outros serviços ecológicos. Quer exemplos? Muitas espécies de morcegos se alimentam de frutas e, quando fazem cocô, eliminam as sementes, que caem no solo e fazem brotar novas plantas. Já as que se alimentam do néctar das flores, podem carregar o pólen grudado em seu corpo e, ao pousarem, em outra flor, possibilitam a reprodução das plantas.
Mas, acredite: voando daqui para lá, os morcegos são rotineiramente atropelados em muitas estradas brasileiras. Pesquisas recentes demonstram que centenas deles (podendo chegar a milhares em algumas rodovias) morrem todos os anos em diferentes regiões do país, especialmente em trechos que cortam ou são vizinhos de grandes áreas verdes, como é o caso das unidades de conservação.
http://chc.org.br/artigo/atropelamento-de-morcegos/
... Na região Mediterrânica pensa-se que esta espécie esteja a ser atingida pelas mudanças na paisagem, perda de habitat, fragmentação do habitat [63], e pelos efeitos negativos da aplicação de pesticidas na agricultura e na floresta [52]. Por ser uma espécie de voo baixo o número de atropelamentos é também significativo [56,64] no entanto a perturbação dos abrigos é um dos principais fatores de ameaça [52]. Para a conservação desta espécie deverão ser adotadas medidas de conservação tais como a proteção legal dos principais abrigos de maternidade e de hibernação e a elaboração e implementação de planos de gestão nos habitats que envolvem os principais abrigos de modo a preservar a vegetação autóctone e a incentivar as práticas agropastoris extensivas com racionalização do uso de pesticidas [51]. ...
... Among mammals, medium and large-sized species have received greater attention from ecologists studying roads (Barthelmess & Brooks 2010;Cáceres 2011). Although smaller species are suggested to be less impacted by roadkills, collisions with vehicles are known to be an important cause of death of bats (Lesiński 2007(Lesiński , 2008Gaisler et al. 2009;Russell et al. 2009;Lesiński et al. 2010;Berthinussen & Altringham 2012;Abbott et al. 2012;Medinas et al. 2013;Fensome & Mathews 2016). Nevertheless, few studies have investigated the biological traits that influence bat-vehicle collisions, and none of them have focused in tropical areas. ...
In Brazil, studies on roadkills are recent and usually restricted to lists of species found at some road stretch. Among mammals, medium- and large-sized species have received greater attention. The present study aimed at presenting the first list of bat roadkills in Brazil, including comments on the traits that may cause roadkills. We recorded 415 deaths from 44 species of seven families in all Brazilian biomes. We did not observe
a relationship between body size or type of flight with the number of bat-vehicle collisions. Frugivore was the
trophic guild most victimized, possibly due to greater natural abundance, foraging in low height airspace, and
capacity to make long-distance movements. The elevated number of species recorded indicates that these roads
may exert a negative effect on bat fauna. We encourage road ecologists and environmental agencies to include
bats in their fauna monitoring of road infrastructure and request to make more accurate estimates of this impact
... As bats are highly mobile and can travel large distances between roosts and foraging grounds, they can be considerably affected by road systems. Road effects on bats include vehicle mortality (Kiefer et al., 1995;Lesiński et al., 2011), light pollution (Rydell, 1992;Stone et al., 2009;Stone et al., 2012), and the barrier and edge effects (Kerth and Melber, 2009;Abbott et al., 2012;Berthinussen and Altringham, 2012). Moreover, two recent studies found that bats may avoid foraging areas with loud traffic noise that can reduce their foraging efficiency (Schaub et al., 2008;Siemers and Schaub, 2011). ...
... Despite the existence of three underpasses within a 5 km stretch of motorway bisecting a forest, resident Bechstein's bats rarely used them and lost access to important roosting and feeding habitat (Kerth and Melber 2009). Lesser horseshoe bats made frequent use of three underpasses along a 1 km stretch of motorway, but 30 % still crossed directly over the road at traffic height (Abbott et al. 2012b). Some bats have been recorded making extensive detours to avoid crossing roads (e.g. ...
The effects of roads on bats have been largely neglected until recently, despite growing evidence for profound effects on other wildlife. Roads destroy, fragment and degrade habitat, are sources of light, noise and chemical pollution and can kill directly through collision with traffic. The negative effects of roads on wildlife cannot be refuted but at the same time road building and upgrading are seen as important economic drivers. As a consequence, infrastructure projects and protection of bats are often in conflict with each other. There is now growing evidence that fragmentation caused by roads reduces access to important habitat, leading to lower reproductive output in bats. This barrier effect is associated with reduced foraging activity and species diversity in proximity to motorways and other major roads. The effects of light and noise pollution may add to this effect in the immediate vicinity of roads and also make bats even more reluctant to approach and cross roads. Several studies show that vehicles kill a wide range of bat species and in some situations roadkill may be high enough to lead directly to population decline. Current mitigation efforts against these effects are often ineffective, or remain largely untested. The limited information available suggests that underpasses to take bats under roads may be the most effective means of increasing the safety and permeability of roads. However, underpass design needs further study and alternative methods need to be developed and assessed.
... Pipistrellus spp.) or high-flying species (e.g. Nyctalus leisleri; Abbott et al. 2012b), and preferred to use less exposed river bridges and underpasses to cross rather than flying directly over the road (Abbott et al. 2012a). Where individuals of Myotis spp. ...
Roads are a potential threat to bat conservation. In addition to the direct risk of collision of bats with vehicles, roads could pose a threat to bat populations as a result of habitat loss, degradation and fragmentation, and could act as barriers to movements of bats between habitats.
We performed a systematic review of the literature and conducted meta‐analyses to assess the threat posed by roads to bats as a result of 1) collisions between bats and vehicles and 2) roads acting as barriers to movements of bats.
Based on collated records of 1207 bat road casualties in Europe, we found that low‐flying species are more prone to collisions than high‐flying species, and that juveniles are more vulnerable to collisions than adults. In addition, meta‐analysis identified a significant bias towards male casualties. Casualties included rare species such as Barbastella barbastellus and geographically restricted species such as Rhinolophus species.
The bias towards male casualties could be indicative of greater natal philopatry or lower dispersal among females, or of sexual segregation in habitats of varying quality, i.e. females may occupy better quality habitats than males, and road density may be lower in better quality habitats.
Whether or not roads act as barriers to the movement of bats depends on a complex interplay of habitat and species‐specific behaviour. For example, the presence of favourable habitat for bats – notably woodland – was found in this review to be linked with significantly reduced barrier effects but a heightened risk of collision.
Our data suggest that roads do pose a threat to bats. Future research should assess the contribution of traffic noise and street lighting to the barrier effect of roads. Where new road schemes are monitored by ecological practitioners, it is vital that consistent protocols are employed to ensure that bat activity can be compared before and after the road is built. Evidence from such research should be used to minimize the risks for bats of any roads built in the future, and to design safe crossing points for bats.
... Erstellt für Tobias Budenz -3.1.2017 Altringham (2012);Abbott et al. (2012)). Um die erhaltenen Daten sinnvoll zu werten müssen wenigstens zwei Szenarien unterschieden werden. ...
Keine andere Methode der Fledermauserfassung erfreut sich heute einer so großen Beliebtheit und Verbreitung im Rahmen von Umweltgutachten wie die akustische Erfassung. Der große Bedarf an Daten für die Bewertung des Ausbaus erneuerbarer Energien - und hier vor allem der Windenergie - sowie die Vielzahl an hochentwickelten Geräten auf dem Markt sind sicherlich ein Grund hierfür. Ein anderer ist, dass sich diese Methode langsam aber sicher etabliert und eine Vielzahl von Untersuchungen ermöglicht. Und nicht zu Letzt haben eine Vielzahl an modernen Geräten diese Methode dorthin gebracht, wo sie sich heute befindet.
Wer sich mit der akustischen Erfassung beschäftigt wird schnell erkennen, dass es bei aller Euphorie doch auch recht viele offene Fragen zu den Möglichkeiten und Grenzen solcher Systeme gibt. Klare Definitionen zum Umgang mit den Daten fehlen meist. So gibt es zum Beispiel keine eindeutig beschriebenen Aktivitätsindizes.
Dieses Buch hat als Ziel einen Überblick der möglichen Anwendungen der akustischen Fledermauserfassung zu liefern. Ausführliche technische Vergleiche werden jedoch, abgesehen von wenigen Ausnahmen, nicht vorgenommen. Vielmehr werden die zahlreichen typischen Fragen zur Anwendung aufgegriffen. Wichtige technische Begriffe und physikalische Grundlagen zur Arbeit mit Ultraschall werden im letzten Kapitel kurz erläutert.
... This makes such areas particularly unsuitable for gleaning and hawking species (Adams, Law & French, 2009;Rainho, Augusto & Palmeirim, 2010;Webala et al., 2011). Pipistrellus spp., which accounted for over 80% of recorded bat activity in our study, are hawking bats and usually avoid cluttered habitats (Norberg & Rayner, 1987;Abbott, Harrison & Butler, 2012) but are also able to forage in the canopy (Plank, Fiedler & Reiter, 2011;Staton & Poulton, 2012). Kalko & Schnitzler (1993) showed that pipistrelle species can adjust their echolocation according to the cluttered environment, making them a more adaptable group in a complex habitat, with the same described for P. kuhlii (Berger-Tal et al., 2008). ...
The transformation of native habitats into forest plantations for industrial purposes frequently has negative consequences for biodiversity. We evaluated the impact of eucalypt plantations on native bats in a Mediterranean area, taking Portugal as a case study. We compared the overall bat activity, species richness and Kuhl's bat Pipistrellus kuhlii (the most abundant bat species in the area) activity between eucalypt plantations and native montado habitat, and examined the influence of stand, landscape and survey variables within plantations on the response variables. A set of 11 plantation stands, three landscape and two survey variables were employed as predictor variables using a zero-inflated Poisson generalized linear mixed model. Hawking and generalist bats of the genus Pipistrellus were the most frequently detected species. Bat activity, species richness and P. kuhlii activity were higher in native montado than in any of the eucalypt stands. Mature eucalypt plantations showed the highest bat activity, while clear-cut areas showed the lowest. Generally, within eucalypt stands, complex high-level vegetation structure, from the ground level up to 3 m high, and proximity to water points were associated with higher levels of bat and P. kuhlii activity and species richness. The results suggest that in order to promote bat diversity and activity in exotic eucalypt plantations in the Mediterranean region, it is important to provide a high density of water points, maintain plots of mature plantations and promote understorey clutter.
... Na região Mediterrânica pensa-se que esta espécie esteja a ser atingida pelas mudanças na paisagem, perda de habitat, fragmentação do habitat [63], e pelos efeitos negativos da aplicação de pesticidas na agricultura e na floresta [52]. Por ser uma espécie de voo baixo o número de atropelamentos é também significativo [56,64] no entanto a perturbação dos abrigos é um dos principais fatores de ameaça [52]. Para a conservação desta espécie deverão ser adotadas medidas de conservação tais como a proteção legal dos principais abrigos de maternidade e de hibernação e a elaboração e implementação de planos de gestão nos habitats que envolvem os principais abrigos de modo a preservar a vegetação autóctone e a incentivar as práticas agropastoris extensivas com racionalização do uso de pesticidas [51]. ...
... As bats are highly mobile and can travel large distances between roosts and foraging grounds, they can be considerably affected by road systems. Road effects on bats include vehicle mortality (Kiefer et al., 1995;Lesiński et al., 2011), light pollution (Rydell, 1992;Stone et al., 2009;Stone et al., 2012), and the barrier and edge effects (Kerth and Melber, 2009;Abbott et al., 2012;Berthinussen and Altringham, 2012). Moreover, two recent studies found that bats may avoid foraging areas with loud traffic noise that can reduce their foraging efficiency (Schaub et al., 2008;Siemers and Schaub, 2011). ...
Anthropogenic noise has a negative impact on a variety of animals. However, many bat species roost in places with high levels of anthropogenic noise. Here we test the hypothesis that torpid bats are insensitive to anthropogenic noise. In a laboratory experiment, we recorded skin temperature (Tsk) of bats roosting individually that were subjected to playbacks of different types of noise. We found that torpid bats with Tsk ~10°C lower than their active Tsk, responded to all types of noise by elevating Tsk. Bats responded most strongly to colony and vegetation noise, and most weakly to traffic noise. The time of day when torpid bats were exposed to noise had a pronounced effect on responses. Torpid bats showed increasing responses from morning towards evening, i.e. towards the onset of the active phase. Skin temperature at the onset of noise exposure (Tsk-start, 17 ~ 29°C) was not related to the response. Moreover, we found evidence that torpid bats rapidly habituated to repeated and prolonged noise exposure.
... Seven bat species were caught flying through motorway underpasses in Germany, but when activity levels were compared with sites in the surrounding forest, only Barbastella barbastellus and M. nattereri were caught significantly more often in the underpasses, suggesting their effectiveness as crossing structures may be species-specific [2]. The use of underpasses by at least six bat species was also reported in Ireland, with the tendency to fly through the underpasses rather than over the road being related to the degree of clutteradaptation of a species [27]. Our aim was to examine whether road crossing structures built for bats (or considered suitable for bats) are not only used but, moreover, are effective in guiding a significant proportion of bats safely over or under roads. ...
Major roads can reduce bat abundance and diversity over considerable distances. To mitigate against these effects and comply with environmental law, many European countries install bridges, gantries or underpasses to make roads permeable and safer to cross. However, through lack of appropriate monitoring, there is little evidence to support their effectiveness. Three underpasses and four bat gantries were investigated in northern England. Echolocation call recordings and observations were used to determine the number of bats using underpasses in preference to crossing the road above, and the height at which bats crossed. At gantries, proximity to the gantry and height of crossing bats were measured. Data were compared to those from adjacent, severed commuting routes that had no crossing structure. At one underpass 96% of bats flew through it in preference to crossing the road. This underpass was located on a pre-construction commuting route that allowed bats to pass without changing flight height or direction. At two underpasses attempts to divert bats from their original commuting routes were unsuccessful and bats crossed the road at the height of passing vehicles. Underpasses have the potential to allow bats to cross roads safely if built on pre-construction commuting routes. Bat gantries were ineffective and used by a very small proportion of bats, even up to nine years after construction. Most bats near gantries crossed roads along severed, pre-construction commuting routes at heights that put them in the path of vehicles. Crossing height was strongly correlated with verge height, suggesting that elevated verges may have some value in mitigation, but increased flight height may be at the cost of reduced permeability. Green bridges should be explored as an alternative form of mitigation. Robust monitoring is essential to assess objectively the case for mitigation and to ensure effective mitigation.
Guidance to quantify and manage traffic-related effects on bat populations, commissioned by the BMVBS (German ministry of traffic)
Human alterations of landscapes, such as habitat conversion and infrastructure buildouts have caused population declines and extinctions of numerous species. Anthropogenic change negatively impacts surrounding landscapes, but in some cases, lead to an increase in synathropy. Bats are one such group that often take advantage of human altered landscapes, roosting in anthropogenic structures such as buildings and transportation infrastructure. However, less is known about how non-traditional or artificial roost sites may affect persistence of synathropic bat species. We conducted a literature review to evaluate the ecological relationship between bats and artificial roosts, specifically transportation structures, as they are often the only roost structures available in some landscapes. Our evaluation revealed that numerous studies on artificial roost selection have been conducted in the eastern region of North America, as well as abroad. Use of transportation structures by bats varies across landscapes, specifically due to variation in annual climate, availability of natural roosts, and bridge structure design. This review enhances our understanding of bat roost ecology, possible pitfalls of synanthropic behaviour, and identify trends related to bat-bridge associations that may improve conservation outcomes for synanthropic species.
Although roads are important cultural objects in our society, they can have negative impacts on the environment. Bat populations are affected by roads in several ways, including habitat loss, death due to collision with vehicles, and reduced habitat connectivity. In recent years, different mitigation practices have been introduced to help animals safely cross roads, reduce road kills, and minimize habitat fragmentation. This study aims to investigate to what extent two types of existing wildlife crossings (a green bridge and an underpass) on the A21 highway (in Northern Germany) are used by bats. All-night acoustic recordings of bat activity at the wildlife crossings, on the highway, and in the surroundings show that bats use both mitigation structures. Our results indicate that bats use mitigation structures depending on their degree of clutter-adaptation: Species from the genus Myotis, which are highly clutter-adapted, were the most recorded in the underpass, while Pipistrellus spp., which are less clutter-adapted, were the most recorded on the Green Bridge. Contrary to expectations, many bat passes were registered on the highway as well. Long-term monitoring studies are needed (including counting of bat fatalities) to clarify if further mitigation measures are needed. In conclusion, the use of wildlife crossings as mitigation structures can be effective, mostly for clutter-adapted species (Myotis spp. and Plecotus auritus).
PDF available here: https://newzealandecology.org/nzje/3376
Roads and associated land transport activities can affect a wide range of indigenous terrestrial vertebrate species. National legislation, particularly the Resource Management Act 1991, requires that developers ‘avoid, remedy or mitigate’ the adverse environmental effects of their activities. How these effects are identified and
managed in New Zealand varies because regulators and land transport contractors deal with these issues on a case-by-case basis. In recent years, the effects of new road projects on long-tailed bats (Chalinolobus tuberculatus) have been receiving attention. In this review, we summarise evidence on likely road infrastructure impacts on bat populations and the efficacy of mitigation approaches, used both internationally and in New Zealand. Our findings indicate that most mitigation methods have little, if any, scientific evidence of their effectiveness. We recommend that such evidence is essential to guide investment in mitigating road effects on bats in New Zealand.
Given that such evidence is rare, future investment should be guided by an adaptive management framework that is justified by strong, inferential, evidence-based logic, and accompanied by robust, appropriately designed monitoring planned, in advance, to allow an objective assessment of a method’s effectiveness in mitigating an
impact. Because such monitoring may be beyond what a single development project can realistically achieve, we suggest the development of a collaborative funding model for supporting the testing and development of mitigation methods. This work is likely to have a significant influence on the future planning and design of road
infrastructure projects to minimise the impacts on bats and, more generally, on any native wildlife populations under threat from infrastructure development.
PDF available here: https://newzealandecology.org/nzje/3376
Thesis in French (English below):
Les infrastructures linéaires de transports (ILT), dont les routes, sont une des principales causes du déclin de la biodiversité. Bien que les évaluations environnementales permettent de limiter ce déclin, la séquence "Eviter, Réduire et Compenser" les impacts peine à s'appliquer pleinement. En effet, la séquence ERC fait bien souvent appel à des données qualitatives en oubliant les processus biologiques et/ou écologiques et leur échelle spatio-temporelle. L'impact des routes est globalement bien documenté pour plusieurs groupes biologiques, hormis pour les chauves-souris, pourtant susceptibles d'être très fortement affectées. Par ailleurs, leur protection stricte nécessite leur prise en compte dans la séquence ERC. Pour étudier l’impact des routes, et notamment des autoroutes, je me suis concentré sur l’étude des chauves-souris afin de mesurer et quantifier leur magnitude. Pour cela, différentes méthodes développées et réutilisables par les différents acteurs de terrain seront présentées. Ainsi, dans un premier temps, je me suis intéressé à une méthode de traitement des données issues d'écoutes acoustiques et à une méthode de valorisation. Dans un second temps, nous avons appliqué ces méthodes afin (i) de connaitre quels étaient les impacts des routes sur les populations de chauves-souris et (ii) afin d'évaluer l'efficience des mesures de réductions engagées pour réduire ces impacts. Nos principaux résultats montrent que les autoroutes ont un impact négatif significatif sur l'activité de chasse et de transit pour plusieurs espèces de chauves-souris jusqu'à au moins cinq kilomètres de distance à une autoroute. De plus, l'effet des autoroutes semblerait également avoir des conséquences sur la génétique des populations. Enfin, nous avons étudié les chiroptéroducs, ouvrages dédiés aux chauves-souris visant à réduire ces impacts par l'amélioration des connectivités écologiques. Ce type d'ouvrage dédié semble être approprié lorsqu'il est situé dans des corridors écologiques fins tels que les haies.
English:
Biodiversity is being lost at an increased rate as a result of human activities. One of the major threats to biodiversity is infrastructural development. Although the measures taken in environmental impact assessments can limit this loss, the mitigation hierarchy to "Avoid, Reduce and Offset" impacts on biodiversity is not fully functional. Indeed, the mitigation hierarchy often uses qualitative data and does not account for the biological and/or ecological processes and their different spatial and temporal scales. The impact of roads is well documented for several biological groups but not for bats whereas they are likely to be very strongly affected. Moreover, as they are strictly protected, they should be considered in the mitigation hierarchy. Therefore, through the study of bats, I investigated the effects of roads, especially major roads, and intended to measure and quantify the magnitude of their impacts. This thesis presents different methods developed to reach this objective and which may be used by stakeholders in the field. First, I intended to determine how to process data collected through passive acoustic monitoring and how to exploit these data. Then I determined what the impacts of roads on bat populations are and I proposed a method in order to assess the mitigation measures which presume to restore bat habitat connectivity. Our main results show a significant negative effect of roads on bats foraging and commuting behaviour for several species and up to at least five kilometres away from a major road. In addition, the effect of major roads also seems to have consequences on populations’ genetics. Finally, we studied bat overpasses which are structures specifically dedicated to bats and aiming at reducing the impacts of roads by improving bats’ habitat connectivity. These structures seem to be appropriate when located in narrow ecological corridors such as hedgerows.
Roading projects may have adverse effects on indigenous wildlife. In New Zealand the effects of roading on long-tailed bats (Chalinolobus tuberculatus) is an issue and projects have attempted to monitor and mitigate effects on bats populations. However, how to undertake monitoring and mitigation is unclear.
The New Zealand Transport Agency commissioned Wildland Consultants, Landcare Research and AECOM to:
review the literature on effects and mitigation of roads on bats, and relevant statutory processes
research road effects on long tailed bats
develop a framework for managing these effects.
Roads affect bats by severing their flight paths and depleting roosting habitat by removing trees. Most bat road research has quantified effects on behaviour rather than population survival, making prediction of effects difficult. No studies have demonstrated any mitigation options to be effective for bats. Demographic modelling indicated adult female survival is vital for the survival of long-tailed bat populations, and therefore must be preserved by roading mitigation.
Research showed that nightly bat emergence is related to temperature, indicating that bat monitoring should be undertaken when temperatures 1–4 hours after sunset are above 5ºC, and preferably in the 10–17ºC range. Field research also showed a negative relationship between bat activity and night-time traffic volume.
A framework guiding roading projects through the process of consents, ecological monitoring, and mitigation was developed and addresses ecological uncertainty around mitigation options, and describes improved bat monitoring.
Bats are long-lived mammals with low reproductive rates, making them susceptible to developments that reduce reproductive output or increase mortality. Roads destroy, degrade and fragment habitats, reducing the ability of bats to roost, feed and reproduce. Current mitigation techniques have not been proven to be effective at conserving bats at the population level. 1 Road effects vary among species depending on flight style and habitat use, but many species are affected. 2 Roads can act as barriers to the movement of bats, and many species suffer traffic mortality attempting to cross roads. 3 Artificial light deters some bat species while attracting others, and a policy of 'no lighting' is recommended for bats. 4 Traffic noise may reduce the flight activity and foraging efficiency of bats. 5 Protection of roosts and foraging sites during and after roadworks is critical to bat survival. 6 Underpasses can effectively reduce the barrier effect and reduce the number of roadkills for some bat species. 7 Other attempts to reduce the barrier and mortality effects for bats are unproven, and further research is required before widespread implementation. It is important to conduct thorough pre-construction bat surveys and bring objectivity and rigour into the design and testing of mitigation features.
The progressing fragmentation of the landscape by roads affects population dynamics and habitat use of many animals. Increasing traffic densities are a serious cause of mortality. Bats (Chiroptera) that are strictly protected by German and European law, are affected as well. In order to mitigate such impairments, arrangements for safe crossing possibilities have to be established. To do this, the effectiveness of existing crossing structures must be assessed. In this study, the activity of bats at three common bridges, two small underpasses and a Green Bridge along the Bundesautobahn 7 in Neuwirtshauser Forst (Bavaria, Germany) have been acoustically monitored. It is important to note, that the activity level does not represent the absolute number of crossings that took place. Instead, it provides indications as to which extend crossing structures are used by bats. I found differences in presence and activity of the various species and groups between the crossing structures. Bats of the genera Nyctalus, Eptesicus and Pipistrellus preferred overpasses, while the genus Myotis was detected almost exclusively in underpasses. My results support the hypothesis that the activity level at the different crossing structures correlates with the species-specific structural bonding. There was no evidence for a significant difference between the Green Bridge and the common bridges in this area.
Global increases in road networks have been matched by traffic flows and are implicated in declines of many sensitive species. Impacts on wildlife by linear development features such as roads include mortality due to vehicle collisions and secondary effects such as preventing traditional movements or severing links between populations. European legislation requires development activities to have ‘no detriment’ to the favourable conservation status of European protected species (EPS), including great crested newts (Triturus cristatus), hazel dormouse (Muscardinus avellanarius) and bats (Chiroptera). To protect these and other species, various mitigation measures are available. Within this review, we sought to identify best practice guidance for preventing and mitigating these impacts for EPS in Great Britain, evaluate the evidence underpinning these best practices and identity knowledge gaps that may impede progress in improving practices. Many current practices appear to be implemented at considerable cost despite limited evidence of their effectiveness. This is probably partly due to inadequate definition of effectiveness, which has most frequently been assessed as a reduction in absolute road mortality or increased frequency of safe road crossings. However, challenges in measuring benefits more appropriately, at spatial and temporal scales that are appropriate for population maintenance, may also have contributed. Evidence of the cost-effectiveness of mitigation works could underpin justification for the substantial investment required to implement many of the mitigation methods reviewed, could avoid the potentially wasteful use of ineffective methods and could better safeguard the conservation status of impacted EPS at local and national scales.
Bat populations are potentially vulnerable to the barrier effects of roads. However, empirical data on how road features facilitate or impede bat movements are scarce and essential for planning mitigation measures. We investigated bat movements across a motorway where it intersects with potential bat commuting routes along prominent linear landscape elements (treelines along hedgerows, minor roads, and rivers). Bat activity was recorded acoustically at four types of potential crossing routes; two under-motorway routes (river bridges and underpasses) and two over-motorway routes (overbridges and severed treelines), while simultaneously recording activity in the adjacent habitat. Bat activity above and below motorway structures and the timing of crossing flights with respect to motorway vehicles were also recorded. All bat species recorded in the adjacent landscape crossed the motorway. Bats used under-motorway routes, particularly river bridges, more than over-motorway routes. Contrary to expectations, many species flew across motorway gaps in treelines despite the lack of a guiding structure, including clutter-adapted species (Myotis spp., Plecotus auritus). Furthermore, bat passes were also recorded for the more collision-prone flight route at crossing structures (2% and 6.4% recorded above motorway level at river bridges and underpasses respectively, and 50% recorded on the underside of overbridges). In a subset of 10 nights of motorway-edge recordings, 18.3% of bat passes coincided with, and 17.1% were within 1–5 s of, passing vehicles. Our results highlight the prevalence of bat flyways along motorway-disrupted landscape features, and also the challenge in locating and designing crossing structures to minimize the risk of collision mortality.
Spectral and temporal features of echolocation calls emitted by 22 bat species from Italy (three rhinolophids, 18 vespertilionids and the molossid Tadarida
teniotis) are described. Time-expanded recordings of calls from 950 bats of known identity were examined. Rhinolophus
ferrumequinum, R.
hipposideros, R.
euryale and T.
teniotis could be identified by measuring the call frequency of highest energy (FMAXE). Quadratic discriminant function analysis with cross-validation was applied to calls from the remaining 18 species. A function based on start frequency (SF), end frequency (EF), FMAXE and duration (D) provided a correct overall classification of approximately 82%. A classification model at genus level that also comprised middle frequency (MF) and inter-pulse interval (IPI) reached 94% correct classification. Two separate discriminant functions were devised for species emitting FM (frequency modulated) and FM/QCF calls (i.e. calls consisting of a frequency-modulated component followed by a terminal part whose frequency is almost constant) respectively. The former function included SF, EF, FMAXE and D and provided an overall classification rate of 71%; the latter comprised EF, MF, D and IPI, and reached 96%. The functions may be applied to bat habitat surveys in southern Italy since they cover most of the species occurring in the area.
Bat wing morphology is considered in relation to flight performance and flight behaviour to clarify the functional basis for eco-morphological correlations in flying animals. Bivariate correlations are presented between wing dimensions and body mass for a range of bat families and feeding classes, and principal-components analysis is used to measure overall size, wing size and wing shape. The principal components representing wing size and wing shape (as opposed to overall size) are interpreted as being equivalent to wing loading and to aspect ratio. Relative length and area of the hand-wing or wingtip are determined independently of wing size, and are used to derive a wingtip shape index, which measures the degree of roundedness or pointedness of the wingtip. The optimal wing form for bats adapted for different modes of flight is predicted by means of mechanical and aerodynamic models. We identify and model aspects of performance likely to influence flight adaptation significantly; these include selective pressures for economic forward flight (low energy per unit time or per unit distance (equal to cost of transport)), for flight at high or low speeds, for hovering, and for turning. Turning performance is measured by two quantities: manoeuvrability, referring to the minimum space required for a turn at a given speed; and agility, relating to the rate at which a turn can be initiated. High flight speed correlates with high wing loading, good manoeuvrability is favoured by low wing loading, and turning agility should be associated with fast flight and with high wing loading. Other factors influencing wing adaptations, such as migration, flying with a foetus or young or carrying loads in flight (all of which favour large wing area), flight in cluttered environments (short wings) and modes of landing, are identified. The mechanical predictions are cast into a size-independent principal-components form, and are related to the morphology and the observed flight behaviour of different species and families of bats. In this way we provide a broadly based functional interpretation of the selective forces that influence wing morphology in bats. Measured flight speeds in bats permit testing of these predictions. Comparison of open-field free-flight speeds with morphology confirms that speed correlates with mass, wing loading and wingtip proportions as expected; there is no direct relation between speed and aspect ratio. Some adaptive trends in bat wing morphology are clear from this analysis. Insectivores hunt in a range of different ways, which are reflected in their morphology. Bats hawking high-flying insects have small, pointed wings which give good agility, high flight speeds and low cost of transport. Bats hunting for insects among vegetation, and perhaps gleaning, have very short and rounded wingtips, and often relatively short, broad wings, giving good manoeuvrability at low flight speeds. Many insectivorous species forage by `flycatching' (perching while seeking prey) and have somewhat similar morphology to gleaners. Insectivorous species foraging in more open habitats usually have slightly longer wings, and hence lower cost of transport. Piscivores forage over open stretches of water, and have very long wings giving low flight power and cost of transport, and unusually long, rounded tips for control and stability in flight. Carnivores must carry heavy loads, and thus have relatively large wing areas; their foraging strategies consist of perching, hunting and gleaning, and wing structure is similar to that of insectivorous species with similar behaviour. Perching and hovering nectarivores both have a relatively small wing area: this surprising result may result from environmental pressure for a short wingspan or from the advantage of high speed during commuting flights; the large wingtips of these bats are valuable for lift generation in slow flight. The relation between flight morphology (as an indicator of flight behaviour) and echolocation is considered. It is demonstrated that adaptive trends in wing adaptations are predictably and closely paralleled by echolocation call structure, owing to the joint constraints of flying and locating food in different ways. Pressures on flight morphology depend also on size, with most aspects of performance favouring smaller animals. Power rises rapidly as mass increases; in smaller bats the available energy margin is greater than in larger species, and they may have a more generalized repertoire of flight behaviour. Trophic pressures related to feeding strategy and behaviour are also important, and may restrict the size ranges of different feeding classes: insectivores and primary nectarivores must be relatively small, carnivores and frugivores somewhat larger. The relation of these results to bat community ecology is considered, as our predictions may be tested through comparisons between comparable, sympatric species. Our mechanical predictions apply to all bats and to all kinds of bat communities, but other factors (for example echolocation) may also contribute to specialization in feeding or behaviour, and species separation may not be determined solely by wing morphology or flight behaviour. None the less, we believe that our approach, of identifying functional correlates of bat flight behaviour and identifying these with morphological adaptations, clarifies the eco-morphological relationships of bats.
Bat researchers currently use a variety of techniques that transform echolocation calls into audible frequencies and allow the spectral content of a signal to be viewed and analyzed. All techniques have limitations and an understanding of how each works and the effect on the signal being analyzed are vital for correct interpretation. The 3 most commonly used techniques for transforming frequencies of a call are heterodyne, frequency division, and time expansion. Three techniques for viewing spectral content of a signal are zero-crossing, Fourier analysis, and instantaneous frequency analysis. It is important for bat researchers to be familiar with the advantages and disadvantages of each technique.
The changes in echolocation behaviour and the structure of calls ofPipistrellus pygmaeus (Leach, 1825) were studied in different habitats of a floodplain forest in south-eastern Moravia (Czech Republic) in 2001–2002.
Calls (403 observations) were recorded in different sites between April and mid June (before weaning) using a time expansion
bat-detector. Three signals per individual were analysed and descriptive statistics of variables of calls were presented.
Association of signal types with habitat structure (cluttered, side-cluttered, semi-cluttered and uncluttered space) was found
in echolocation sequences of the search phase of flight.P. pygmaeus used mainly narrowband signals (bandwidths less than 15 kHz) in uncluttered space and wideband signals (more than 15 kHz)
in cluttered space. Almost 6% of the inter pulse intervals of signals were twice (or more) longer than usual inter pulse intervals
(mainly in uncluttered space). In general, temporal variables of signals reached higher values in uncluttered spaces (except
for inter pulse interval) than in cluttered ones. On the contrary, spectral variables of signals reached lower values in uncluttered
habitats in comparison with cluttered ones. In addition, the signals were less variable in open spaces while in cluttered
and partly-cluttered habitats different and higher variability was found. We also studied the accuracy of identification of
pipistrelles by call parameters and possible misidentifications in relation to habitat structure. Multivariate discriminant
analyses were carried out on the time and frequency parameters of calls produced by pipistrelles.
This paper examines 167 records of 14 bat species killed on roads in Poland. Regional differences in the species composition of road traffic accident records resulted from differences in the structure of local bat faunas. Young-of-the-year individuals (ind.) were killed significantly more often than adults. The highest mortality occurred in August and in the first half of September during intense dispersal of young bats. The highest incidence of road casualties was noted in places where roads crossed bat flyways, especially at junctions with forest edges and tree alleys. The rate of mortality depended on the habitat. It was highest where roads approached tree stands (up to 6.8 ind./km/year) or crossed a forest (2.7 ind./km/year) and lowest within densely built-up areas of Warsaw (0.3 ind./km/year). The mean was 1.5 ind./km/Year in an 8-km section of a road near Warsaw. Road mortality depended on the hunting strategy of bats, in particular on the height of their flight. Road casualties were frequent for the low-flying gleaner, Myotis daubentonii (39.5% of the records), but rare for the high-flying aerial hawker, Nyctalus noctula (1.9%).
Fragmentation of the landscape is one of the greatest problems for animals which use large home ranges and/or different habitats within a landscape. Even in the case of undisturbed hunting habitats and roosts, disconnection of flight paths could lead to a decline in the populations of bats. Tunnels connecting both sides of a barrier, allowing exchange, can be used to minimise the impact of e.g. motorways. Results of studies in different parts of Germany and anecdotal observations in other parts of Germany demonstrate the use of tunnels for nine species of bats. Data are analysed with respect to different types of tunnels. Although our data do not allow quantitative analy- sis, observations suggest smaller bats like Myotis nattereri, and M. daubentonii can use relatively low and narrow tunnels, whereas the larger M. myotis, was only observed using larger tunnels. The results support the role of tunnels as effective for the conservation of the connectivity of landscapes.
Bats of the genus Myotis cannot be identified reliably using conventional acoustic analyses. Here we use morphology of echolocation calls to discriminate between Myotis spp. This method may be used to identify unknown roosts to species level. Echolocation calls of M. daubentonii, M. mystacinus and M. nattereri, were recorded in emergence flights from roosts. Images of echolocation calls were extracted for morphological analysis performed in SHAPE, a program that transforms two-dimensional outline data into Elliptic Fourier Descriptors. Species typical call shapes were described with Mahalanobis models. Discriminant Function Analyses (DFA) were applied with Mahalanobis scores of typical shape alone and with a spectral call parameter, maximum frequency. DFA achieved an overall correct classification rate of 88.9% using typical outline shapes alone. Correct classification of 100% of both M. daubentonii and M. mystacinus was achieved by both typical call outlines. For M. nattereri, 79.6% of calls were correctly classified by call morphology, but the addition of maximum frequency improved this to 96.3%. Shape analyses provide a quick and easy method of distinguishing Myotis species under field conditions and could be extended to include other species of bats that share conventional acoustic parameters.
Wildlife crossing structures are intended to increase permeability and habitat connectivity across roads. Few studies, however, have assessed the effectiveness of these mitigation measures in a multispecies or community level context. We used a null model to test whether wildlife crossing structures serve large mam-mal species equally or whether such structures limit habitat connectivity across roads in species-specific ways. We also modeled species responses to 14 variables related to underpass structure, landscape features, and hu-man activity. Species performance ratios (observed crossing frequency to expected crossing frequency) were evaluated for four large carnivore and three ungulate species in 11 underpass structures in Banff National Park, Alberta, Canada. Observed crossing frequencies were collected in 35 months of underpass monitoring. Expected frequencies were developed from three independent models: radio telemetry, pellet counts, and hab-itat-suitability indices. The null model showed that species responded to underpasses differently. In the pres-ence of human activity carnivores were less likely to use underpasses than were ungulates. Apart from hu-man activity, carnivore performance ratios were better correlated to landscape variables, and ungulate performance ratios were better correlated to structural variables. We suggest that future underpasses de-signed around topography, habitat quality, and location will be minimally successful if human activity is not managed.
Modern silvicultural methods employ various styles of selective harvesting in addition to traditional clear‐cutting. This can create a mosaic of patches with different tree densities that may influence habitat use by foraging bats. Use of forest patches may also vary among bat species due to variation in their manoeuvrability. Apart from studies investigating use of clear‐cuts, few have tested for differences in use of forest patches by bats, or for differences among bat species.
We investigated the influence of various harvesting regimes, which created forest patches of different tree densities, on habitat selection by foraging bats in the boreal mixed‐wood forest of Alberta, Canada. We also tested for variation in habitat selection among species related to differences in body size and wing morphology.
Over two summers we assessed habitat use by bats using ultrasonic detectors to count the echolocation passes of foraging bats. We measured activity in three forest types and four tree densities, ranging from intact (unharvested) forests to clear‐cuts.
Smaller, more manoeuvrable, species ( Myotis spp.) were less affected by tree density than the larger, less manoeuvrable, Lasionycteris noctivagans . Two Myotis spp. differed in their habitat use. Myotis lucifugus , an aerial insectivore, preferred to forage along the edge of clear‐cuts, while M. septentrionalis , a species that gleans prey from surfaces, did not forage in clear‐cuts but preferred intact forest.
The largest species in our study, L. noctivagans , preferred clear‐cuts and avoided intact patches. There were therefore differences in habitat selection by foraging bats among the species in our study area, and these were correlated with size and wing morphology.
Synthesis and applications . Our results suggest that, in the short term, thinning has minimal effect on habitat use by bats. They also indicate that silvicultural methods have different immediate effects on different species of bats that may be obscured if the community is studied as a single entity. Management for forest‐dwelling bats must take such species‐specific effects into consideration. Harvesting that creates a mosaic of patches with different tree densities is likely to satisfy the requirements of more species than a system with less diverse harvesting styles.
Recognizing the factor(s) that caused a demographic crash is a prerequisite to the development of a tailored population restoration plan. While habitat destruction leaves little scope for population persistence, cryptic habitat deterioration (for example through reduction of food resources) may similarly render an area totally inhospitable, while it still appears to have a suitable habitat configuration.
Most European bat species have undergone dramatic declines over the past decades. Once among the most widespread and abundant bat species of Central Europe, the lesser horseshoe bat, Rhinolophus hipposideros (Bechstein 1800), is today extinct in many regions. Although changes in the agricultural landscape have been suggested as the major cause of decline, recent studies have shown that this bat forages almost exclusively in woodland, a habitat that has increased in area across continental Europe over the past decades. This suggests that habitat eradication per se is unlikely to be the main cause of decline. But could cryptic habitat deterioration play a harmful role?
We looked at the abundance of insect prey in woodland in the vicinity of colonial roosts with diverging demographic status (extinct, declining or recovering populations), both in the Swiss lowlands (Swiss Plateau) and in the Alps. We predicted that population size correlates positively with prey abundance.
Diet composition mirrored local insect prey abundance, confirming an opportunistic foraging strategy. Prey abundance showed marked seasonal variation, but did not differ between sites harbouring extinct, declining or recovering populations. There was also no difference in food abundance between extinct populations in the lowlands and recovering populations in the Alps.
Synthesis and applications. Cryptic habitat deterioration through a reduction in prey abundance is unlikely to preclude recolonization of abandoned areas by presently recovering populations. However, sufficient areas of natural forest should be preserved or created around potential nursery roosts. Moreover, connectivity between forest patches must be ensured (by creation of hedges and tree lines) to prevent any spatial gap in recolonization within semi‐open agricultural landscapes. Other threatened European forest bats may also benefit from these measures.
Roads are a widespread and increasing feature of most landscapes. We reviewed the scientific literature on the ecological effects of roads and found support for the general conclusion that they are associated with negative effects on biotic integrity in both terrestrial and aquatic ecosystems. Roads of all kinds have seven general effects: mortality from road construction, mortality from collision with vehicles, modification of animal behavior, alteration of the physical environment, alteration of the chemical environment, spread of exotics, and increased use of areas by humans. Road construction kills sessile and slow-moving organisms, injures organisms adjacent to a road, and alters physical conditions beneath a road. Vehicle collisions affect the demography of many species, both vertebrates and invertebrates; mitigation measures to reduce roadkill have been only partly successful. Roads alter animal behavior by causing changes in home ranges, movement, reproductive success, escape response, and physiological state. Roads change soil density, temperature, soil water content, light levels, dust, surface waters, patterns of runoff, and sedimentation, as well as adding heavy metals (especially lead), salts, organic molecules, ozone, and nutrients to roadside environments. Roads promote the dispersal of exotic species by altering habitats, stressing native species, and providing movement corridors. Roads also promote increased hunting, fishing, passive harassment of animals, and landscape modifications. Not all species and ecosystems are equally affected by roads, but overall the presence of roads is highly correlated with changes in species composition, population sizes, and hydrologic and geomorphic processes that shape aquatic and riparian systems. More experimental research is needed to complement post-hoc correlative studies. Our review underscores the importance to conservation of avoiding construction of new roads in roadless or sparsely roaded areas and of removal or restoration of existing roads to benefit both terrestrial and aquatic biota.
Resumen: Las carreteras son una característica predominante y en incremento de la mayoría de los paisajes. Revisamos la literatura científica sobre los efectos ecológicos de las carreteras y encontramos sustento para la conclusión general de que las carreteras están asociadas con efectos negativos en la integridad biótica tanto de ecosistemas terrestres como acuáticos. Las carreteras de cualquier tipo ocasionan siete efectos generales: mortalidad ocasionada por la construcción de la carretera; mortalidad debida a la colisión con vehículos; modificaciones en la conducta animal; alteración del ambiente físico; alteración del ambiente químico; dispersión de especies exóticas e incremento en el uso de áreas por humanos. La construcción de carreteras elimina a organismos sésiles y a organismos de lento movimiento, lesiona a organismos adyacentes a la carretera y altera las condiciones físicas debajo ella misma. Las colisiones con vehículos afectan la demografía de muchas especies tanto de vertebrados como invertebrados; las medidas de mitigación para reducir la pérdida de animales por colisiones con vehículos han sido exitosas solo de manera parcial. Las carreteras alteran la conducta animal al ocasionar cambios en el rango de hogar, movimientos, éxito reproductivo, respuesta de escape y estado fisiológico. Las carreteras cambian la densidad del suelo, temperatura, contenido de agua en el suelo, niveles de luz, polvo, aguas superficiales, patrones de escurrimiento y sedimentación, además de agregar metales pesados (especialmente plomo), sales, moléculas orgánicas, ozono y mutrientes a los ambientes que atraviesan. Las carreteras promueven la dispersión de especies exóticas al alterar los hábitats, al estresar a las especies nativas y proveer corredores para movimiento. Las carreteras también promueven el incremento de la caza y la pesca, el hostigamiento pasivo de animales y modificaciones del paisaje. No todas las especies ni todos los ecosistemas son afectados por las carreteras de igual forma, pero en general la presencia de carreteras está altamente correlacionada con cambios en la composición de especies, los tamaños poblacionales y los procesos hidrológicos y geomorfológicos que afectan a la estructura de sistemas acuáticos y reparios. Se necesita más investigación experimental para complementar estudios correlativos post-hoc. Nuestra revisión hace énfasis en que en trabajos de conservación es importante evitar la construcción de nuevas carreteras en áreas carentes de ellas o en áreas con pocas carreteras, además de remover o restaurar carreteras existentes con la finalidad de beneficiar tanto a la biota acuática como la terrestre.
We studied the impact of road E461, Brno-Vienna, on bat mortality, with the goal to predict this impact after the road has
been reconstructed and turned into highway, R52. In the Czech territory, two proposed road sections of E461 were selected,
3.5 and 4.5 km long, and divided into segments 100 m in length. Bat carcasses were picked up from emergency stopping lanes,
and bat activity was recorded by ultrasound detectors along the road and 100 m away on both sides from the central strip.
From May to October 2007, 25 checks of bat mortality performed at weekly intervals revealed 119 bat carcasses representing
11 or 12 species.Pipistrellus nathusii, P. pygmaeus andMyotis daubentonii were the most frequent traffic casualties. The greatest mortality was documented from early July to mid-October, with a peak
in September. Monitoring bat activity by ultrasound detectors (one night per month in May, June and September) yielded 12
bat species and 3 species couples (Myotis mystacinus/brandtii, M. emarginatus/alcathoe, Plecotus auritus/austriacus), mostly the same taxa as found dead on the road. Significantly greater bat numbers were revealed in the section where the
road was situated between two artificial lakes, as compared to a road section without any lakes directly adjacent to the road.
In the former section, significant correlation was found between the number of carcasses found and the activity detected,
according to road segments.
Key wordsroad traffic-bat mortality-ultrasound detection
We present a hitherto unknown prey perception strategy in bats: Myotis nattereri (Vespertilionidae, Chiroptera) is able to perceive prey by echolocation within a few centimeters of echo-cluttering vegetation,
by using frequency-modulated search signals of very large bandwidth (up to 135 kHz). We describe the species’ search behavior
and echolocation repertoire from the field and from experiments in a flight tent. In the field, bats varied signal parameters
in relation to their distance from vegetation and usually flew close to vegetation. In the flight tent, M. nattereri detected and localized prey by echolocation alone as close as 5 cm from vegetation. Apparently, the bats were able to tolerate
some overlap between prey and clutter echoes. Passive prey cues (vision, olfaction, prey-generated sounds) were not used in
prey perception. The bats selected prey by size. The animals performed aerial catches and produced approach sequences typical
for aerial hawking bats, but were able to do so within a few centimeters of the substrate. M. nattereri thus has access to silent, suspended prey very close to vegetation (e.g., spiders, and caterpillars on threads).
Population declines for many bat species are associated with rapid, human-induced ecosystem changes. In this context, the
available species pool is determined in part by historical adaptation to the native ecosystem, but the resulting community
structure may be determined principally by the ability of evolved traits to function in the novel context of a human-dominated
ecosystem. To investigate the role of human disturbance as a determinant of bat communities, we surveyed assemblages and species
occurrence rates in 27 agriculturally dominated landscapes exhibiting a gradient of human-induced forest fragmentation in
Indiana, USA. We used multiple linear regression to explore the relationship of landscape environmental variables to species
diversity. We then examined the relationship between community structure, evolved species traits and fragmentation conditions
across a landscape using RLQ analysis. Overall, species diversity was positively related to the amount of forest and negatively correlated with amount
of urban development in a landscape. We also observed a significant relationship between evolved species traits and landscape-level
variables that is consistent with globally anticipated trends for bat species extinction risk. Our findings suggest that responses
of bat species to human modification of ecosystems on the scale of a few kilometers could drive distributional dynamics at
larger spatial and longer temporal scales.
A major target for environmental managers when trying to minimise the road-barrier effect on wildlife is to improve permeability
to animal movements. Previous studies have demonstrated that drainage culverts are used by vertebrates, although knowledge
of the main influencing factors remains limited. The use of 34 culverts from two roads in southern Portugal, differing in
traffic volume, vehicle speeds and configuration, was evaluated by the analysis of terrestrial vertebrate footprint data (408
passage-operative days). Culvert crossings were related to various explanatory variables by means of canonical ordination
techniques. We recorded 901 complete crossings, corresponding to an average of 2.2 crossings/culvert/operative day. Thirteen
taxa were detected, all in more than one passage. Animal species included reptiles, small mammals, lagomorphs, carnivores
and domestic dogs and cats. Our results suggest that fencing might have a funnelling effect, directing larger animals toward
culverts. Also, vegetation covering culvert entrances seems to have a positive effect, particularly on genets; longer passages
with entrances far from the pavement were, apparently, avoided by smaller animals; a lower number of crossings was detected
on passages with detritus pits; the closest passages to urban areas are more often used by domestic species; forest-living
species favour passages with low, open land cover nearby; and smaller species, like lagomorphs and small mammals, appear to
use more culverts near the pavement, which probably reflects the importance of road verges as refuges for these species. Although
not used by all species present in the study area, constructing numerous passages of different sizes without detritus pits
and which are distributed along roads might be an important step in mitigating road fragmentation effects on animal populations.
A year-round study was conducted on a 16.6-km road section crossing Kampinos National Park near Warsaw (central Poland). We
found 61 road-killed bats belonging to seven species. The most abundant were: Nyctalus noctula, Plecotus auritus, and Barbastella barbastellus. Bats were found between the middle of April and the end of October with peaks in July/August and October. The density of
bat casualties differed slightly in various habitats surrounding the road—lower values than expected were found only for windbreaks
and bushes. The prediction that low-flying species are killed more frequently was not confirmed—the most abundant N. noctula usually flies at heights over 10m above the ground. N. noctula, Myotis nattereri, and Pipistrellus nathusii were killed more frequently while Eptesicus serotinus less frequently than could be expected from the frequency with which they were captured in mist-nets on forest lanes.
KeywordsChiroptera–Mortality–Road traffic–Phenology–Landscape structure–Central Europe
Roads with high traffic volumes are a source of animal mortality, can disrupt normal animal movements and dispersal, and may
represent a potentially serious threat to wildlife population stability and viability. Retrofitting existing structures built
for other purposes (e.g., drainage culverts or small below-grade access roads) to facilitate wildlife crossing by animals
and to reduce mortality may be expensive if modifications to the existing structures themselves were involved. However, the
environmental context surrounding these structures may influence the willingness of animals to cross, and management of some
of these attributes may enhance the attractiveness of these structures. Culverts and underpasses are two common structures
along roads in Portugal. We quantified the response of small and medium-sized carnivores to the presence of both types of
existing passages by determining: (1) frequency of use; (2) whether use differed by type of passage, and if so; (3) by examining
if associated environmental attributes might explain the differences observed. We surveyed 57 different passages along 252km
of highway with a total sampling effort of 2,330 passage trap-days. The mean passage rate for carnivores combined was 0.7
complete passages per crossing structure per day. Crossings by weasel, polecat, otter, and wildcat were infrequent or absent.
Red fox, badger, genet and Egyptian mongoose used the crossing structures regularly and without obvious preference; stone
marten preferred underpasses. Regression analyses showed the frequency of use by carnivores varied with structural, landscape,
road-related features, and human disturbance with 17 of 26 (65%) attributes being significant. Larger passages with vegetation
close to the passage entrances, favorable habitat in the surrounding area, and low disturbance by humans were important key
features to regular use by the guild of species studied. Mitigation planning in areas with ecological significance for carnivores
will be beneficial. Structural attributes and human disturbances are more difficult or expensive to change, even though related
significantly to crossing use. Management of vegetation at passage entrances and restricting human use near passages in carnivore
suitable areas may substantially improve crossing attractiveness for the guild of carnivore species.
Animals using sound for communication emit directional signals, focusing most acoustic energy in one direction. Echolocating bats are listening for soft echoes from insects. Therefore, a directional biosonar sound beam greatly increases detection probability in the forward direction and decreases off-axis echoes. However, high directionality has context-specific disadvantages: at close range the detection space will be vastly reduced, making a broad beam favorable. Hence, a flexible system would be very advantageous. We investigated whether bats can dynamically change directionality of their biosonar during aerial pursuit of insects. We trained five Myotis daubentonii and one Eptesicus serotinus to capture tethered mealworms and recorded their echolocation signals with a multimicrophone array. The results show that the bats broaden the echolocation beam drastically in the terminal phase of prey pursuit. M. daubentonii increased the half-amplitude angle from approximately 40 degrees to approximately 90 degrees horizontally and from approximately 45 degrees to more than 90 degrees vertically. The increase in beam width is achieved by lowering the frequency by roughly one octave from approximately 55 kHz to approximately 27.5 kHz. The E. serotinus showed beam broadening remarkably similar to that of M. daubentonii. Our results demonstrate dynamic control of beam width in both species. Hence, we propose directionality as an explanation for the frequency decrease observed in the buzz of aerial hawking vespertilionid bats. We predict that future studies will reveal dynamic control of beam width in a broad range of acoustically communicating animals.
Many species of bat use ultrasonic frequency modulated (FM) pulses to measure the distance to objects by timing the emission and reception of each pulse. Echolocation is mainly used in flight. Since the flight speed of bats often exceeds 1% of the speed of sound, Doppler effects will lead to compression of the time between emission and reception as well as an elevation of the echo frequencies, resulting in a distortion of the perceived range. This paper describes the consequences of these Doppler effects on the ranging performance of bats using different pulse designs. The consequences of Doppler effects on ranging performance described in this paper assume bats to have a very accurate ranging resolution, which is feasible with a filterbank receiver. By modeling two receiver types, it was first established that the effects of Doppler compression are virtually independent of the receiver type. Then, used a cross-correlation model was used to investigate the effect of flight speed on Doppler tolerance and range-Doppler coupling separately. This paper further shows how pulse duration, bandwidth, function type, and harmonics influence Doppler tolerance and range-Doppler coupling. The influence of each signal parameter is illustrated using calls of several bat species. It is argued that range-Doppler coupling is a significant source of error in bat echolocation, and various strategies bats could employ to deal with this problem, including the use of range rate information are discussed.
We investigated patterns and processes of extinction and threat in bats using a multivariate phylogenetic comparative approach. Of nearly 1,000 species worldwide, 239 are considered threatened by the International Union for Conservation of Nature and Natural Resources (IUCN) and 12 are extinct. Small geographic ranges and low wing aspect ratios are independently found to predict extinction risk in bats, which explains 48% of the total variance in IUCN assessments of threat. The pattern and correlates of extinction risk in the two bat suborders are significantly different. A higher proportion (4%) of megachiropteran species have gone extinct in the last 500 years than microchiropteran bats (0.3%), and a higher proportion is currently at risk of extinction (Megachiroptera: 34%; Microchiroptera: 22%). While correlates of microchiropteran extinction risk are the same as in the order as a whole, megachiropteran extinction is correlated more with reproductive rate and less with wing morphology. Bat extinction risk is not randomly distributed phylogenetically: closely related species have more similar levels of threat than would be expected if extinction risk were random. Given the unbalanced nature of the evolutionary diversification of bats, it is probable that the amount of phylogenetic diversity lost if currently threatened taxa disappear may be greater than in other clades with numerically more threatened species.
Human transport by land, sea and air has increased exponentially through time in intensity, paralleling rises in population, prosperity and rates of technological change. Transport has considerable ecological effects, many of them detrimental to environmental sustainability. This volume brings together international experts from a variety of disciplines to review the ecological effects and their causes in terms of road, rail, ship and aircraft transport. The contributors have different attitudes and agendas. Some are ecologists, some planners, others social scientists. Focus ranges from identification of threats and amelioration of damaging effects through to future design of transport systems to minimize environmental degradation. Some chapters consider restricted areas of the globe; others the globe itself. Views encompass deep pessimism and cautious optimism.
Uniquely, the volume considers transport effects in all environments. This is the first book that attempts to discuss the relationship between human transport and all ecosystems. It appeals not only to the specialist environmentalist by picking out novel topics, but also to anyone involved in transport issues as it tackles the issues from an historical perspective, encompassing the past, present and future of the effects of human transport.
The pipistrelle (Pipistrellus pipistrelus) occurs as two phonic types in Britain, its echolocation calls failing into two distinct frequency bands, with mean frequencies of maximum energy at 55 kHz and 46 kHz. These are termed the 55 kHz and 45 kHz phonic types here for simplicity. Songflight calls produced by males in the mating season, probably to attract females, differed between the two phonic types in the number of components in the calls and the call parameters measured. Songflight calls on the 55 kHz phonic type, which generally consisted of three components, were of higher frequencies than those of the 45 kHz phonic type, usually of four components. There were also significant differences in call parameters among individuals. A discriminant analysis of songflight calls classified 100% of individuals to the correct phonic type. The relationships between echolocation call frequency and songflight call frequency differed significantly between phonic types. Social calls produced during flight also differed between phonic types, in the number of components and call parameters measured. Social calls were compared to songflight calls of each phonic type. Social calls of the 55 kHz phonic type did not differ significantly from songflight calls; there were small but significant differences between the two types of calls of the 45 kHz phonic type. The study provides support for the hypothesis that the phonic types should be treated as sibling species. If songflight calls are used for mate choice, the differences may allow reproductive isolation between the two phonic types. The functions of songflight calls and social calls need to be investigated through experimental studies to explain the implications of the differences between phonic types.
Abstract A huge road network with vehicles ramifies across the land, representing a surprising frontier of ecology. Species-rich roadsides are conduits for few species. Roadkills are a premier mortality source, yet except for local spots, rates rarely limit population size. Road avoidance, especially due to traffic noise, has a greater ecological impact. The still-more-important barrier effect subdivides populations, with demographic and probably genetic consequences. Road networks crossing landscapes cause local hydrologic and erosion effects, whereas stream networks and distant valleys receive major peak-flow and sediment impacts. Chemical effects mainly occur near roads. Road networks interrupt horizontal ecological flows, alter landscape spatial pattern, and therefore inhibit important interior species. Thus, road density and network structure are informative landscape ecology assays. Australia has huge road-reserve networks of native vegetation, whereas the Dutch have tunnels and overpasses perforating road barriers to enhance ecological flows. Based on road-effect zones, an estimated 15–20% of the United States is ecologically impacted by roads.
(1) Two hypotheses are tested in this paper: (i) wing morphology and echolocation-call `design' can determine foraging site selection and foraging behaviour in bats, (ii) echolocation-call `design' should be compatible with wing morphology (because some combinations of morphology and echolocation call would be maladaptive). (2) In support of our first hypothesis, significant correlations were established between wing morphology, echolocation call design, manoeuvrability and habitat use. (3) In support of our second hypothesis, significant correlations were established between those morphological parameters that improve manoeuvrability (low wingloading, low aspect ratio and high wingtip shape index) and echolocation calls that are resistant to acoustic clutter in support of our second hypothesis. (4) There was an association between foraging habitat and diet: bats that fed in the same habitats tended to take the same types of prey, while species foraging in different habitats had significantly different diets. (5) There was also a significant correlation between prey and predator size; large bats took insects over a range of sizes while small bats fed only on small prey.
The pipistrelle (Pipistrellus pipistrellus) occurs as two phonic types in Britain, its echolocation calls falling into two distinct frequency bands, with mean frequencies of maximum energy at 55 kHz and 46 kHz. These are termed the 55 kHz and 45 kHz phonic types here for simplicity. Songflight calls produced by males in the mating season, probably to attract females, differed between the two phonic types in the number of components in the calls and the call parameters measured. Songflight calls of the 55 kHz phonic type, which generally consisted of three components, were of higher frequencies than those of the 45 kHz phonic type, usually of four components. There were also significant differences in call parameters among individuals. A discriminant analysis of songflight calls classified 100% of individuals to the correct phonic type. The relationships between echolocation call frequency and songflight call frequency differed significantly between phonic types. Social calls produced during flight also differed between phonic types, in the number of components and call parameters measured. Social calls were compared to songflight calls of each phonic type. Social calls of the 55 kHz phonic type did not differ significantly from songflight calls; there were small but significant differences between the two types of calls of the 45 kHz phonic type. The study provides support for the hypothesis that the phonic types should be treated as sibling species. If songflight calls are used for mate choice, the differences may allow reproductive isolation between the two phonic types. The functions of songflight calls and social calls need to be investigated through experimental studies to explain the implications of the differences between phonic types.
Leisler's bats Nyctalus leisleri, from two nursery colonies were radio-tracked from April to August in 2 years. They commuted directly to foraging sites up to 13.4 km away at speeds often exceeding 40 km h-1. Except during lactation, individuals occasionally day-roosted away from the nursery in buildings or hollow trees. These were also sometimes used as night roosts, especially during rain, which also stimulated return to the nursery. On most nights the first flight lasted the longest. During preparturition, when distances from roost to foraging site were greatest, and time spent flying per night (tF) was least, there was often only one flight, with a second towards dawn on warmer nights, and occasionally a third. After parturition, in June, tF and the number of flights (NF) increased up to weaning, corresponding to rising energy demands. But distances to foraging sites fell, rising only slightly in postlactation, presumably because insects, and thus feeding patches, were more abundant than in preparturition. NF fell to preparturition levels after lactation. Exploratory behaviour by juveniles intensified with time – distances to feeding sites, tF and the total distance flown each night all increased; the distance flown each night was eventually greater than any recorded for adults. Roosting away from the nursery was also more common. Before dispersal, there were extended migrations by juveniles outside the summer range of the adults. Distances moved by two dispersed juveniles exceeded 34 km. Two-thirds of the recorded foraging time was over pasture or drainage canals. Foraging over other habitats, particularly lake and conifer forest, was greatest in preparturition. Other habitats foraged included lights, estuary, stream, beach and dunes.
Urbanisation affects indigenous fauna in many ways; some species persist and even increase in urban areas, whereas others are lost. The causative mechanisms determining changes in distributions and community structure remain elusive. We investigated three hypothesized mechanisms, which influence success or failure of the insectivorous bat assemblage across the urban landscape of Sydney, Australia; landscape heterogeneity (diversity of land uses), productivity (as indexed by landscape geology) and trait diversity. We present data on species richness and activity (bat passes per night) collected systematically using ultrasonic bat detectors from randomly selected landscapes (each 25 km2). Landscapes were categorized into classes including ‘urban’, ‘suburban’ and ‘vegetated’, where suburban sites were additionally stratified based on geology, as a proxy for productivity. Four landscape elements were sampled within each landscape, including remnant bushland (>2 ha), riparian areas, open space/parkland and residential/built space. We found that there was significantly greater bat activity and more species of bat in areas on fertile shale geologies (p<0.05), supporting the productivity, rather than the heterogeneity hypothesis. Within landscapes, there was no significant effect of the landscape element sampled, although bushland and riparian sites recorded greater bat activity than open space or backyard sites. Using general linear mixed models we found bat activity and species richness were sensitive to landscape geology and increasing housing density at a landscape scale. Using an RLQ analysis a significant relationship was found between these variables and species traits in structuring the community present (p<0.01). Specifically, open-adapted bats were associated with areas of greater housing density, while clutter-adapted bats were uncommon in urban areas and more associated with greater amounts of bushland in the landscape. Overall we found greater support for the productivity and traits hypotheses, rather than the heterogeneity hypothesis. The degree of urbanisation and amount of bushland remaining, in combination with landscape geology, influenced bat activity and mediated the trait response. Our findings reflect global trends of species diversity and abundance in urban landscapes, suggesting that processes affecting bat species distribution in urban ecosystems may be predictable at a landscape scale.
Large-scale anthropogenic habitat degradation is taking place in the Negev Desert and such degradation is considered to be the primary cause of population decline in many bat species. A study of bat community structure in the central Negev Desert Highlands was undertaken to examine habitat associations, activity patterns and the distribution of bats in relation to landscape structure. During 1999 and 2000, mist-nets and bat detectors were used to capture bats and to monitor their presence in natural and artificial sites. In total, 12 species of insectivorous bats were found. Communities of insectivorous bats were divided into three guilds based on foraging space: open space foragers, background-cluttered space foragers, and highly cluttered space foragers. Bats of the background-cluttered space guild foraged over a variety of habitats while bats from the other guilds were more restricted with regard to their foraging spaces. In both years, season had a significant effect on bat activity. Despite there being significantly more bat activity in artificial sites than in natural sites, bat species richness was least in the artificial sites. For most species of desert-dwelling bats, areas that are typified by dense vegetation cover and have a perennial water source are of primary importance.
Identifying the factors that influence the extinction risk of animals is essential in conservation biology because they help identify endangered species and provide the basis for their preservation.We present a
comparative study that uses data from the literature on the diet and morphological specialization of European and North American bat species to investigate the effect of specialization on extinction risk. We focused on bats because many species are endangered and their high ecological diversity makes them a good model system for our purpose. After correcting for phylogenetic inertia, we compared the influence of dietary niche breadth as a measure of food specialization and of wing morphology as a measure of foraging strategy, habitat adaptation, and migratory ability on the vulnerability of 35 insectivorous bat species. Our results do not support the hypothesis that a narrow dietary niche breadth is related to high extinction risk. Instead they suggest that habitat specialization, which is reflected in wing morphology, influences the extinction risk of bats. Our study shows that an initial risk assessment in temperate-zone bats could be based on data of wing morphology but not on dietary data obtained from fecal analyses.
Caves offer bats refuges for hibernation, breeding and other social events. Their quality is important for species distribution. The role of cave microclimate as well as other environmental factors influencing the distribution of cave-dwelling species, is poorly known. We tested the significance of cave variables (length, temperature, elevation, occurrence of water) and geographical location for the presence of bats during hibernation and the breeding season in five regions in Romania. To detect species' environmental relationships, we used canonical correspondence analyses for winter bat aggregations and principal components analysis for maternity colonies. We analysed the factors influencing the distribution of bats by using two sets of explanatory variables reflecting cave characteristics and geographical locations. Winter aggregation was divided into three groups: (1) bat species that prefer high temperatures (Rhinolophus euryale, Myotis cappacinii) and hibernate at a low altitude; (2) species ranging from mid- to high elevation and low temperature (Myotis myotis/oxygnathus group); (3) species that hibernate in large, cold cave systems with a constant flow of the water (Pipistrellus pipistrellus, Nyctalus noctula, Barbastella barbastellus). Maternity colonies were divided into those that select either high (rhinolophids) or low temperatures (My. myotis/oxygnathus and Miniopterus schreibersii). The most important factors influencing the distribution of bats are the temperature in caves and their geographical location. This information was combined with IUCN's Red List data as well as with the number of individuals occurring in caves with the aim of identifying the key sites for conservation. The majority of these sites, which also constitute the refuges for vulnerable species, are located in west and south-western Romania. Seven caves provide shelter throughout the year for 122 000 individuals of 14 species.
1. Echolocation and foraging behavior of the horseshoe bats Rhinolophus ferrumequinum and R. hipposideros feeding under natural conditions are described. 2. The calls of both species consisted predominantly of a long CF segment, often initiated and terminated by brief FM sweeps of substantial bandwidth. 3. R. hipposideros typically flew close to vegetation, and fed by aerial hawking, gleaning and by pouncing on prey close to the ground. R. hipposideros called with a CF segment close to 112 kHz which is the second harmonic of the vocalization; its calls included low intensity primary harmonics, and had prominent initial and terminal FM sweeps of considerable bandwidth. When searching for prey on the wing it had longer interpulse intervals than R. ferrumequinum, but emitted shorter pulses at a higher repetition rate; overall it had a similar duty cycle to R. ferrumequinum. 4. R. ferrumequinum, calling with a CF segment close to 83 kHz, also used harmonics other than the dominant secondary in its calls, and modified its echolocation according to ecological conditions. This species showed certain parallels with R. rouxi of Asia. It was observed feeding by aerial hawking and by flycatching. When scanning for prey from a perch (perch hunting), calls were of shorter duration, and interpulse intervals were on average longer, than when bats were flying. Mean duty cycle was longer in flight, and the bandwidths and frequency sweep rates of the FM segments in the calls increased in comparison with perched bats. 5. FM information may facilitate determination of target range and the location and nature of obstacles; it may also be involved in the interpretation of echoes and the detection of moving targets among clutter. The rising FM sweep initiating the call in both species when flying (and to a lesser extent perch hunting) in the wild must have a significant adaptive role, and should be considered an essential component of the call; rhinolophids should be termed FM/CF/FM bats.
The echolocation and hunting behavior of Daubenton's bat (Myotis daubentoni) were studied in the field under completely natural conditions using a multiflash photographic system synchronized with high-speed tape recordings. The hunting behavior of M. daubentoni is separated into four stages. In the search flight stage Daubenton's bat flies with an average speed of 3.40.6 m/s SD usually within 30 cm over water surfaces searching for insects. After the detection of potential prey, the approach flight stage occurs, during which the bat approaches the target in a goal-directed flight. The stage tail down indicates that M. daubentoni is close to the potential prey (approximately 10–22 cm) and is preparing for the catch. The insects are caught with the interfemoral membrane, the feet, and sometimes with the additional aid of a wing. In the stage head down, the bat seizes the prey during flight. Immediately afterwards, Daubenton's bat returns to search flight. M. daubentoni shows the typical echolocation behavior of a vespertilionid bat, emitting frequency-modulated (FM) echolocation signals. The three behavioral stages search, approach, and terminal phase (Griffin et al. 1960) are used to describe the pulse pattern of foraging M. daubentoni in the field. The terminal phase (or buzz) of Daubenton's bat is separated into two parts: buzz I and buzz II. Buzz II is distinguished from buzz I by the following characteristics: a sharp drop in terminal frequency, a distinct reduction in the bandwidth of the first harmonic, a continuous high repetition rate throughout the phase in the range 155–210 Hz, very short pulses (0,25–0.3 ms) and interpulse intervals (4.5–5.0 ms) at the end of the phase, and a distinct decrease in duty cycle. A pause in echolocation separates the end of the terminal phase from the ongoing search phase. The reduction in sound duration after the detection of a target and during pursuits with successfull or attempted catches is discussed in relation to the actual distance of the bat to the target at each stage. It is likely that Daubenton's bat reduces sound duration during approach and terminal phase in order to prevent an overlap of an outgoing pulse with the returning echo from the target. It is argued that the minimum detection distance can be estimated from the sound duration during search flight. Estimates of detection and reaction distances of M. daubentoni based upon synchronized photos and echolocation sequences are given to corroborate this hypothesis. An average detection distance of 128 cm and an average reaction distance of 112 cm were determined. Each behavioral stage of foraging M. daubentoni is characterized by a distinct pattern of echolocation signals and a distinct stage in hunting behavior. The approach flight in hunting behavior coincides with the approach phase and with buzz I in echolocation behavior. The stage tail down corresponds to buzz II. The stage head down is correlated with a pause in echolocation. Immediately afterwards, the bat returns into search flight and into the search phase, emitting search signals.
Echolocating bats adjust the time–frequency structure such as sweep rate and pulse interval of their sonar calls when they
move from open space to vegetation-dense environments. Emitted call intensity is equally important for echolocation, but adjustment
of signal intensity to different habitats has never been systematically studied in any bat species. To address this question,
we recorded sonar calls of the Neotropical trawling insectivorous bat Macrophyllum macrophyllum (Phyllostomidae) at three sites with different obstacle densities (clutter). We found a clear correlation between emitted
intensity and degree of clutter, with intensity proportional to decreasing clutter. In highly cluttered, semicluttered, and
open spaces, M. macrophyllum emitted calls with mean source levels (sound pressure level (SPL) 10cm from the bat’s mouth) of 100, 105, and 111dB SPL
root mean square (rms), respectively. To our knowledge, this is the first documentation of dynamic intensity adjustments in
bats. Phyllostomid bats were previously considered silent, but the 111-dB SPL rms emitted by free-ranging M. macrophyllum in open space is comparable to output in aerial insectivorous bats from other families. Our results suggest that the acoustic
constraints of habitats are better predictors of call intensity than phylogeny and therefore likely to be major drivers shaping
the sonar system of bats in the course of evolution.
KeywordsSource level-Biosonar intensity-Phyllostomidae-Bat-Echolocation
We studied the echolocation and hunting behavior of three aerial insectivorous species of bats (Vespertilionidae: Pipistrellus) in the field in order to characterize the signals used by the bats and to determine how call structure varies in relation to habitat structure (uncluttered versus cluttered space). We documented free-flying, naturally foraging wild pipistrelles in various habitats using multiflash stereophotography combined with simultaneous sound recordings. Then we reconstructed the bat's flight position in three-dimensional space and correlated it with the corresponding echolocation sequences. In all three species of pipistrelles, signal structure varied substantially. In echolocation sequences of the search phase we found a consistent association of signal types with habitat types. In uncluttered habitats (obstacles more than 5 m from the bat) pipistrelles emitted almost exclusively narrowband signals with bandwidths less than 15 kHz. In cluttered habitats (obstacles less than 5 m from the bat) they switched to signals with bandwidths of more than 15 kHz. Wideband signals were also used when the bats were turning in cluttered and uncluttered spaces and for an instant after turning away from obstacles. Prey detection occured only when the outgoing signal did not overlap with the returning echo from potential prey. The bats also avoided overlap of echoes from potential prey and obstacles. Based on the results of this study, we propose an overlap-free window within which pipistrelles may detect potential prey and which allows predictions of minimum distances to prey and clutter-producing objects.
A huge road network with vehicles ramifies across the land, representing a surprising frontier of ecology. Species-rich roadsides are conduits for few species. Roadkills are a premier mortality source, yet except for local spots, rates rarely limit population size. Road avoidance, especially due to traffic noise, has a greater ecological impact. The still-more-important barrier effect subdivides populations, with demographic and probably genetic consequences. Road networks crossing landscapes cause local hydrologic and erosion effects, whereas stream networks and distant valleys receive major peak-flow and sediment impacts. Chemical effects mainly occur near roads. Road networks interrupt horizontal ecological flows, alter landscape spatial pattern, and therefore inhibit important interior species. Thus, road density and network structure are informative landscape ecology assays. Australia has huge road-reserve networks of native vegetation, whereas the Dutch have tunnels and overpasses perforating road barriers to enhance ecological flows. Based on road-effect zones, an estimated 15-20% of the United States is ecologically impacted by roads.
Caves are an important resource to a large proportion of temperate bat species, primarily as mating and hibernation sites. However, information on bat use exists for only a small fraction of caves in many parts of the temperate world, in part because current survey methods are inappropriate for many species. We surveyed the UK’s largest karst landscape, the Yorkshire Dales, by monitoring autumn swarming (mating) activity at 53 caves using automated echolocation call loggers, followed by trapping. Over 60% of caves surveyed were used by bats, but there was considerable variation in activity. Swarming activity was positively correlated with chamber development and negatively correlated with the amount of water the cave carried: together these two predictors explained 45% of the variance. Entrance orientation and shelter explained a further 10%. Activity was not correlated with entrance size, altitude or connectivity to the nearest summer habitat. All five resident swarming species were caught at most sites: Myotis brandtii, Myotis daubentonii, Myotis mystacinus, Myotis nattereri and Plecotus auritus. Behaviour, species composition and sex and age ratios were typical of swarming reported in other studies. Bat populations and catchment sizes were large and despite the proximity of other suitable caves, bats showed high fidelity to single sites. Our results show that the national importance of these caves has been overlooked. We suggest that survey for swarming activity is a quick and effective method of identifying underground bat sites and is likely to uncover many previously unknown and important sites throughout the temperate world.
It is generally recognized that roads can adversely affect local animal populations but little is known how roads affect bats. In particular, no study compared the response of bats that differ in foraging ecology to motorways that cut through the breeding habitat. As bats are key species in conservation, such data are urgently needed for designing management plans. Using radio-telemetry, mist netting, and mark-recapture data we investigated the effects of a motorway with heavy traffic on the habitat use of two threatened forest-living bats. We compared barbastelle bats (Barbastella barbastellus), which forage in open space, to Bechstein’s bats (Myotis bechsteinii), which glean prey from the vegetation. Five of six radio-tracked barbastelle bats crossed the motorway during foraging and roost switching, flying through underpasses and directly over the motorway. In contrast, only three of 34 radio-tracked Bechstein’s bats crossed the motorway during foraging, all three using an underpass. Bechstein’s bats, unlike barbastelle bats, never crossed the motorway during roost switching. Moreover, only in Bechstein’s bats individuals foraging close to the motorway had smaller foraging areas than individuals foraging further away, whereas other forest edges had no such effect. Our data show that motorways can restrict habitat accessibility for bats but the effect seems to depend on the species’ foraging ecology and wing morphology. We suggest that motorways have stronger barrier effects on bats that forage close to surfaces than on bats that forage in open space, and discuss the implications of our findings for bat conservation during road construction.
We investigated the ability of brown long-eared bats to make use of visual cues when searching for food. By using petri dishes containing mealworms that were subjected to different levels of illumination, we presented four bats with different sensory cues: visual, sonar and a combination of these. The bats preferred situations where both sonar cues and visual cues were available, and the visual information was more important than the sonar cues. The bats did, however, emit echolocation calls throughout the experiments. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Field research on echolocation behavior in bats has emphasized studies of food acquisition, and the adaptive value of sonar signal design as been considered largely in the context of foraging. However, echolocation tasks related to spatial orientation also differ among bats and are relevant to understanding signal structure. Here, we argue that the evolution of echolocation in bats is characterized by two key innovations: first, the evolution of echolocation for spatial orientation and, second, a later transition for prey acquisition. This conceptual framework calls for a new view on field data from bats orienting and foraging in different types of habitats. According to the ecological constraints in which foraging bats operate, four distinct functional groups or guilds can be defined. Within each group, signal design and echolocation behavior are rather similar.
Echolocation operates through adaptive sensorimotor systems that collectively enable the bat to localize and track sonar objects as it flies. The features of sonar signals used by a bat to probe its surroundings determine the information available to its acoustic imaging system. In turn, the bat's perception of a complex scene guides its active adjustments in the features of subsequent sonar vocalizations. Here, we propose that the bat's active vocal-motor behaviors play directly into its representation of a dynamic auditory scene.
Anthropogenic disturbance is a major cause of worldwide declines in biodiversity. Understanding the implications of this disturbance for species and populations is crucial for conservation biologists wishing to mitigate negative effects. Anthropogenic light pollution is an increasing global problem, affecting ecological interactions across a range of taxa and impacting negatively upon critical animal behaviors including foraging, reproduction, and communication (for review see). Almost all bats are nocturnal, making them ideal subjects for testing the effects of light pollution. Previous studies have shown that bat species adapted to foraging in open environments feed on insects attracted to mercury vapor lamps. Here, we use an experimental approach to provide the first evidence of a negative effect of artificial light pollution on the commuting behavior of a threatened bat species. We installed high-pressure sodium lights that mimic the intensity and light spectra of streetlights along commuting routes of lesser horseshoe bats (Rhinolophus hipposideros). Bat activity was reduced dramatically and the onset of commuting behavior was delayed in the presence of lighting, with no evidence of habituation. These results demonstrate that light pollution may have significant negative impacts upon the selection of flight routes by bats.
The pipistrelle bat Pipistrellus pipistrellus is the most widespread in Europe, and is often the most abundant bat species in northern and central Europe. P. pipistrellus has traditionally been considered as one species throughout Europe. Here we show that: (i) the echolocation calls of pipistrelles fall into two distinct frequency bands in Britain, with frequencies containing most energy averaging 46 kHz and 55 kHz; (ii) roosts consist of bats which use only one form of echolocation; (iii) small but significant differences in average gross morphology exist between the phonic types; and (iv) the two phonic types occur in sympatry over much of Britain. Recordings made from European populations show that bimodal echolocation is also typical of continental pipistrelles, with only one phonic type found in some areas, two types in sympatry in others. The sympatric occurrence of two phonic types, the lack of mixing of types between colonies, and the morphological divergence between phonic types suggests that P. pipistrellus may actually consist of at least two cryptic sibling species. The evolution of bimodal echolocation in bats is discussed, and a model involving disruptive selection is presented to show how sympatric speciation may occur.
Aerial-hawking bats searching the sky for prey face the problem that flight and echolocation exert independent and possibly conflicting influences on call intervals. These bats can only exploit their full echolocation range unambiguously if they emit their next call when all echoes from the preceding call would have arrived. However, not every call interval is equally available. The need to reduce the high energetic costs of echolocation forces aerial-hawking bats to couple call emission to their wingbeat. We compared the wingbeat periods of 11 aerial-hawking bat species with the delays of the last-expected echoes. Acoustic flight-path tracking was employed to measure the source levels (SLs) of echolocation calls in the field. SLs were very high, extending the known range to 133 dB peak equivalent sound pressure level. We calculated the maximum detection distances for insects, larger flying objects and background targets. Wingbeat periods were derived from call intervals. Small and medium-sized bats in fact matched their maximum detection range for insects and larger flying targets to their wingbeat period. The tendency to skip calls correlated with the species' detection range for background targets. We argue that a species' call frequency is at such a pitch that the resulting detection range matches their wingbeat period.