Talk Effectiveness of bat mitigation on roads

Roads may have detrimental impact on bat populations by increasing mortality rates, fragmentation and habitat degradation. To comply with the legislative obligation to maintain favourable conservation status of bats it is essential for road and nature authorities to include effective mitigation strategies for bats when expanding or upgrading road infrastructures.

A range of mitigation measures has been installed on roads across Europe to function as road safe crossing structures for bats (e.g. culverts, bat gantries, hop-overs and green bridges) or to compensate for habitat destruction (e.g. artificial roost sites). These measures have been developed on the basis of general knowledge on bat ecology and landscape use, and observations of bats’ flight behaviour near roads. Intuitively the implemented measures will help bats to cross roads safely, and several studies have described bats using the structures to cross the roads. However, observations of bats flying along a structure do not imply that the structure effectively contributes to maintaining landscape permeability for bats or that the impact of the road has been mitigated and off-set on population levels. The proportion of bats that cross a road safely using the mitigation measures, i.e. documenting their effectiveness, has rarely been evaluated in quantitative terms, and the studies show inconsistent results, e.g. recent studies in UK and Poland have documented that gantries are inefficient to guide bats safely across roads. Only a couple of high profile studies in Wales and Germany have monitored and assessed the impact of road schemes and mitigation strategies on population levels.

The 53 European bat species have different flight patterns and show a high plasticity in their spatial and temporal behaviour, i.e. the effectiveness of a mitigation strategy may depend on species composition and landscapes structure. Furthermore, documentation of the effectiveness of bat mitigation structures and the overall mitigation strategy for a road scheme is often hampered because survey methodology in pre-construction assessments and post-construction monitoring projects differs (e.g. timing of year, equipment and location). As a consequence of the limitation and inconsistency in the knowledge of the effectiveness of bat mitigation measures, road agencies may currently implement measures which are inefficient.

To improve the understanding of the effectiveness of bat mitigation strategies on roads and advance on the developing cost-effective methods to mitigate road impact on bat conservation, we compiled up-to-date information on constructed bat mitigation measures and published studies on the efficiency of bat mitigation strategies on roads in Europe.

The presentation will present:

  • An overview of bat mitigation on roads in European countries.
  • An evaluation of the effectiveness of different types of mitigation measures, and
  • Recommendations for research needed to develop effective mitigation strategies for bats on roads.
bats; road mitigation; defragmentation; wildlife