Bat overpasses: An insufficient solution to restore habitat connectivity across roads

Abstract

1. Roads have many negative effects on wildlife, including their role in habitat fragmentation. Habitat fragmentation affects bats during their daily movements between roosts and foraging areas. As bats are protected in Europe, developers must implement specific mitigation measures that are hierarchically structured to achieve a null net impact. However, very few specific mitigation measures have been undertaken specifically for bats. Bat overpasses (e.g. gantries) are among proposed improvements intended to reduce the impact of roads, but they have rarely been tested. The effectiveness of overpasses in facilitating safe road crossing of bats is critical for justifying the implementation of this mitigation measure.We therefore assessed whether bat overpasses are effectively used by bats.2. We studied three bat overpasses with different designs in France. We developed an innovative method to characterize bat crossings using acoustic flight path reconstruction (AFPR). We used six pairs of stereo acoustic recorders in different habitat types that were located on both sides of the road, and operated simultaneously throughout the night.3. Recording data contained 57,941 bat passes and 284 bat crossings from six species of bats at the three study sites. Our results suggest that crossings are more numerous if an overpass is located where bat commuting routes have been identified by environmental impact assessment. However, we found that the proportion of bat crossings along the commuting route was the same with or without an overpass; thus highlighting that bat overpasses do not fully restore habitat connectivity. Synthesis and applications.Our study demonstrates that acoustic flight path reconstruction (AFPR) is a useful approach to obtain information on bat flight behaviour. We also emphasize the importance of field testing the effectiveness of mitigation measures, such as those intended to offset the impact of roads on 574 |

Spatiotemporal persistence of bat roadkill hotspots in response to dynamics of habitat suitability and activity patterns

“…Thus, from the practical perspective, these results has important consequences, because in absence of significant landscape changes, it allows concentrating conservation efforts in spatially restricted areas, greatly improving the efficiency and cost-effectiveness of mitigation actions (Rytwinski et al, 2015). However, measures to reduce bat roadkills, such as overpasses, underpasses, barriers or strips to guide road crossings, are still a matter of debate, and further data are needed to assess their efficiency (Solowczuk, 2019;Claireau et al, 2018Claireau et al, , 2019Berthinussen and Altringham, 2012). Claireau et al (2019) highlighted that bat overpasses should be located on intersections between roads and bat commuting routes.…”

Comparing acoustic and radar deterrence methods as mitigation measures to reduce human-bat impacts and conservation conflicts

“…Current bat mitigation strategies for roads are at present regarded as largely insufficient [28]. Methods such as overpasses that are currently ineffective [70], could therefore be used in combination with acoustic deterrence, allowing bats to utilise safer flight lines over roads.…”

Accounting for automated identification errors in acoustic surveys

“…Echolocation calls were recorded using one automatic acoustic recorder per site survey (Song Meter SM2Bat+, Wildlife Acoustics Inc., Concord, MA, USA). The detectors automatically recorded all ultrasounds using predefined settings as recommended by the French bat monitoring program ‘Vigie‐Chiro’ (trigger level set to 6 dB Signal Noise Ratio and set to continue recording until 2.0 s after last trigger event, 384 kHz sampling rate; for further details see Azam et al., ; Barré et al., ; Claireau et al., ; Pauwels et al., ). Whilst continuous recording is typically used for monitoring birds and several other species groups, for bats which echolocate at high frequency, and so produce heavy sound files, it is necessary to use triggered recording, to be able to manage and store the data and process the recordings.…”

“…The latter four variables presented important environmental variability, and a similar gradient between sites located close to hedgerows and those in open areas ( Figure S1). for further details see Azam et al, 2018;Barré et al, 2018;Claireau et al, 2019;Pauwels et al, 2019). Whilst continuous recording is typically used for monitoring birds and several other species groups, for bats which echolocate at high frequency, and so produce heavy sound files, it is necessary to use triggered recording, to be able to manage and store the data and process the recordings.…”

“…This method can be applied to any acoustic taxa for which automated identification software and acoustic signature knowledge are already developed, and where confidence scores are provided. Taking the case of bats, we first manually checked a representative sample of a large number of bat recordings identified using an automated identification software (Tadarida; Bas et al, 2017) commonly used in bat studies (Barré, Le Viol, Bas, Julliard, & Kerbiriou, 2018;Barré, Le Viol, Julliard, Chiron, & Kerbiriou, 2017;Claireau et al, 2019;Pauwels et al, 2019;Pinaud, Claireau, Leuchtmann, & Kerbiriou, 2018). Using this sample, we then modelled the identification success for 10 species and two species groups of bats in relation to the confidence score provided by the software.…”