Two-years to repair bat roost bridges
Forestry and Land Scotland work to repair two masonry bridges in Rosehall Forest (nr Lairg) to allow access for timber harvesting has taken around two years to complete as experts worked around a colony of bats.
Lying on a well-used recreational and Core Path route both bridges were regularly inspected and were suitable for pedestrian use.
However, when harvesting operations in adjacent woodlands became due, structural assessment determined that both needed work done to enable heavy machinery to cross them.
As well as finding serious structural issues that meant the bridges were unable to bear the weight of harvesting machinery, ecologists also discovered bats using the bridge as a roost.
FLS Civil Engineer, Anna Torode, said;
“The bridges were in a really poor condition with severe scaling, lots of missing mortar and a number of cavities.
“There was also evidence that attempted repairs in the past had used cement mortar, which over time has the effect of increasing the amount of erosion damage to the stone work.
“There was a huge amount of work to do – and then there were also the bats.”
After an initial survey by Skye based Arborteering found bats under the larger bridge, further surveys were required over the course of several months by a licensed bat surveyor. Techniques such as echo-location recording and analysis and infrared filming determined the numbers of bats roosting, access points, and the time of year roosts were found to be in use.
Pipistrelle bats and Myotis genus bats were found to be using nine exit/entrance points to bridge roosts and taking advantage of the foraging areas in the surrounding habitat.
FLS’ Environment Advisor, Colin Leslie, added;
“With all species of bats being protected in the UK, it is a criminal offence to disturb bats or damage or destroy a roost. Before any work could begin, a special licence is required from NatureScot that can only be obtained once a mitigation plan has been drawn up and measures agreed and put in place to protect the bats.
“The mitigation plan involved using ‘exclusion curtains’ to prevent the bats from returning to roost in the bridge after they had left, and erecting new bat boxes in adjacent trees to provide alternative roost sites.
“Protecting the bats was the longest part of the whole operation.”
During the process of replacing the concrete mortar with lime mortar, any cavities formed had to be covered up overnight to prevent bats using them as roosts. Once re-mortared they still had to be covered with damp hessian to prevent the mortar drying out too quickly.
With mortaring complete, holes will now be drilled in the carriageway, the structure flushed out and then a liquid grout pumped in that will permeate the structure and solidify over the course of two weeks to make the bridges far more stable.
The final stage of the bridges will involves re-tarring the carriageway surface.
Operations began at beginning of April and are expected to be completed by mid-August (for both bridges)
Ongoing monitoring throughout the restoration ensured that no bats were harmed or disturbed.
Anna, said;
“It has been a lengthy process – over 24 months – and very involved but it’s just part and parcel of the sorts of things we do to protect wildlife as we go about the business of harvesting timber.”
Notes to Editors
- Forestry and Land Scotland (FLS) manages forests and land owned by Scottish Ministers in a way that supports and enables economically sustainable forestry; conserves and enhances the environment; delivers benefits for people and nature; and supports Scottish Ministers in their stewardship of Scotland's national forests and land.
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