Maintaining ecological connectivity during the construction phase of projects is increasingly requested by administrative bodies in areas where ecological connectivity is considered important. Guidance features already exist for bats (cables, nets…), especially in Great Britain where they are known as “Bat-bridges” but their effectiveness has been contested and is highly dependent upon the local topography and vegetation cover.
Within the context of an environmental constrained road bypass project (in the Oise department North of Paris), Egis Structures et Environnement installed a lightweight and low-cost temporary guidance device for bats during the construction phase. It was made up of ropes and “acoustic reflectors”. The reflectors had multiple facets like those of a golf ball. Made out of a light material, the reflectors were placed in staggered rows with a 1.5m interval along two ropes. The multiple reflective surfaces would result in the increase in number of bat echolocation calls being returned.
Located along an old flight corridor for bats, interrupted by road construction works, the device was confirmed an efficient success. To test the effectiveness of the device, we surveyed bats at nightfall using two technologies: 3D bat trajectory monitoring system (Bat3Data®)* and a thermal camera. The results showed after forest clearing and setting up the temporary guidance device that the connectivity of the flight paths was partially reestablished. The return flight path at the forest edge by the Common Pipistrelle (observed before installation of the device) was not observed after device installation. Specific bat behavior was shown both by the trajectory monitoring (Bat3Data®) and by the thermal camera:
- Pipistrelles bat crossing just above the guidance device;
- Greater mouse-eared bat and Long-eared bat flying just under the device;
- Common noctule bat flying very high over the device.
The installation of the lightweight device (ropes and acoustic reflectors) has therefore allowed the quick reestablishment of the transit flight line functionality for bats.
Egis Environnement is continuing with its R&D work to optimize further the acoustic performance of the device. Egis has already received 1st prize at the IDRRIM 2015 awards (a French-based best-practice championship for infrastructure and biodiversity) in the category of “ingenious solutions”.
*presented by poster at the IENE in 2015
Bat; 3D trajectory; ecological connectivity; acoustic reflectors; eco-design; Bat3Data®