Talk Roads and bats: use of existing gantries for the restoration of ecological connectivity

Linear transport infrastructures, including roads and highways, are known to have negative impacts on wildlife. In addition to direct impact (animal mortality) roads have an important impact on habitat loss and fragmentation. For bats, the construction of a highway can lead to destruction of bat roosts and loss of foraging areas. Such infrastructures also induce fragmentation and loss of connectivity between roosts or between roosts and foraging areas. In some cases, it may impact reproduction of bats and thus the viability of the populations. However, highways are strong economic drivers, new ones are created and others are modernized. Therefore, it is necessary for stakeholders to be able to reconcile economic development and biodiversity conservation. As part of mitigation measures such as the restoration of ecological connectivity, several studies suggest that underground passages are quite effective for the passage of bats, and their most convenient conformation is known. But in some situations, technical constraints only allow the installation of crossings over the highway. Depending on the characteristics of certain sites, it is possible to adapt the designs of these overpasses (e.g. material, shape) to increase their use by bats. Indeed, in Europe, they are multiple, complex and often represent a significant cost hardly acceptable by civil society. Among the experiments already carried out, gantries with fences, ropes installed on two floors with carved polystyrene balls, large metal walkways with shaped holes honeycombs, etc. have been tested. In France, the likely number of wildlife crossings is 2000 (12 000 km of highway with 1 wildlife crossing about every 6 kilometers), while among these overpasses only 4 are designed for bats including 1 temporary, since 2012. For bats, the monitoring is often concentrated at the overpasses and the methods used are trajectography with thermal camera and/or acoustic monitoring. In this talk, we will (i) propose an overview of experiments already carried out in Europe, (ii) based on experiment feedbacks, we will discuss why these experiments failed to evaluated the effectiveness of the overpasses (lack of methodology, lack of initial state or control, metrics used…etc), (iii) present an alternative innovative device: the installation of a standard gantry on a motorway in service. This will allow to define what are the factors that determine the success of overpasses for bats. This standard gantry (type "signaling gantry") will be installed at an interruption of ecological corridor for bats. The goal is to evaluate its effectiveness compared to other more complex and more expensive structures. If the result is positive, we would have found a simple, cheap, and discreet way, to restore flight routes for bats. This experience will be carried out and tested by a stakeholder: "Autoroutes du Sud de France" (Vinci) associated with a technical research department: "Naturalia environnement" in collaboration with two research laboratories: the National Museum of Natural History of Paris (France) and the Institute of Zoology and museum of Greifswald (Germany).

Landscape ecology; Habitat fragmentation; Ecological connectivity; Highways; Overpasses for bats; Gantries