Identification of the Key Determinants of Bats’ Altitude Increase over the S3 Expressway in Poland with Mesh Screens Applied

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.