Wildlife adaptation of existing bridges

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Background

Conventional (non-wildlife) bridges are used by wildlife to various extent, and these bridges could with relatively small efforts be adapted to further facilitate wildlife use. Examples of improvements are:

  • screening of traffic noise and visual impacts, 
  • vegetation or other natural structures that cover and guide animals to the passage, 
  • feeding stations that attract animals to the passage,
  • adapted fencing to funnel animals to the passage,
  • daytime illumination in underpasses,
  • limiting human disturbance (traffic, pedestrians etc) in and near the passage. 

Adaptation of non-wildlife bridges could potentially be a very cost-efficient way to minimize barrier effects compared to construction of new passages particularly for wildlife. However, the effect of these different improvement opportunities are not known, so currently it can only be considered a promising potential, that cannot yet substitute true wildlife passages. Also it is not known to what degree these types of improvements can increase the functionality of true wildlife passages lacking them.

Adaptation of a number of bridges is currently under planning (see below), and these mitigation measures provide an opportunity to learn more about how they can improve wildlife use of conventional bridges. Upcoming road upgrading or construction projects provides further opportunities for wildlife adaptation and, accordingly, for studying the expected increase in wildlife use. 

Activities

In this subproject we will monitor wildlife´s use of existing bridges before and after wildlife adaptation. Improvement types tested are dependent on what is most likely to be applied in full scale on bridges, but will as a minimum include screening and vegetation/natural structures. One special option is to use simple temporary screens (dense fabric) particularly for visual purposes, that could easily be mounted/demounted along fences and bridge railings.

As far as possible, each improvement type will be studied in separation, with control and test trials on selected pairs of passages (BACI approach). Field methods will include studies of animal movements and behaviour near and through the passages as indexed by a combination of photo traps, sand beds, track stations and snow tracking. Effect sizes are compared with the cost of each improvement type.

The results will be published scientifically.

Output

This subproject gives values of the increased efficacy for wildlife of different bridge improvement types. Efficacy is separated between species and categories of animals (age and gender) to put light on population level impacts. The most important outcome is that the results enables cost-efficiency comparisons between different improvement types and with true wildlife passages. In addition, the subproject contributes to the knowledge about wildlife passages on more general levels, e.g.:

  • better estimates of wildlife use of conventional bridges (by the studies of un-improved control sites), and
  • better knowledge of the relative contribution of different design components in true wildlife passages (such as screening, vegetation etc.). 

Study objects/sites

Trafikverkets bridge data base (BaTMan) contains hundreds of bridges with dimensions and siting allowing wildlife use, and that also are suitable for wildlife adaptation. Planning for study sites is currently underway and candidate bridges include:

  • Bridge over river Lagan at motorway E4 in Småland (vid rastplats Sjöboda; knr 7-564). Planned adaptation: screens along the motorway, adjusted fencing, widened land passage on one side of river, human recreation (fishing) directed to other side. 
  • Bridge over minor road at motorway E4 in Småland (knr 7-587). Planned adaptation: screens along the motorway, guiding structures. 
  • Bridges over minor road at E6 Hallandsås (knr 11-546). Planned adaptation: screening along the motorway, vegetation around entrance. 
  • Red deer underpass at national road 11 near Vomb. Proposed improvement: temporary visual screening along the road.
  • Reindeer bridge over E4 at Harrioja (Haparanda). Planned improvements: adapted fencing (closing of nearby fence openings), limitation traffic over the bridge.
  • Four moose underpasses at national road 31 near Tenhult. Proposed improvement: temporary visual screening along the road.
  • Bridge over minor road at road 23/34 at Brokind. Planned adaptation: adapted fencing and cattle grid to guide animals particularly fallow deer. 
  • Numerous bridges at motorway E4 between Järna and Linköping for which adaptation can be motivated by the adjacent new highspeed railway Ostlänken 

Other bridges/sites can be selected for research, depending on where new adaptations will be planned. The research budget assumes that the technical measures as such are financed from other sources (Trafikverkets investments). The number of adapted bridges available for research may therefore be a limiting factor for this subproject.

Photo © Enviroplanning AB.