Introduction
- Project description
- This case demonstrates the value of improving conditions for horseshoe bats within established roosts. Whilst considering the threat of disturbance from predators and climate change, we have improved the microclimatic conditions in the roost and incorporated exclusion devices for predators.
- Ecologist’s name and contact details
- Tom Kitching, Marina Bollo Palacios & Henry Schofield. Vincent Wildlife Trust - tomkitching@vwt.org.uk
- Client’s name
- VWT
- Planning authority
- South Hams District Council
- Brief site description
- High Marks Barn was constructed in the early 1800s for agricultural purposes, but today is a privately owned nature reserve situated within the South Hams SAC in South Devon. The barn itself is a large stone-built structure, open from floor to ceiling, with two lean-to sections facing South and West. The roof structure is timber-made, lined with bitumastic felt and plastic windbreak mesh (for bats to perch on) and this is covered with natural Brazilian slates.
The barn is situated within a small paddock, which forms the boundaries of the site owned by Vincent Wildlife Trust. The location is situated on the upper slopes of a wooded valley, with a desirable mosaic of ancient woodland, riparian habitat and permanent pasture which suits greater horseshoe bats. The bats are known to use a number of natural subterranean hibernacula within a few miles of the roost.
The site is a SSSI; designated for its breeding colony of greater horseshoe bats and smaller number of overwintering bats. The barn was purchased by Vincent Wildlife Trust in 1995 and was then renovated in 2003 to repair the roof and maintain the structural integrity of the barn. The colony has grown rapidly, and in 2017 was the second largest known maternity colony of greater horseshoe bats in the UK with a peak count of 864 adults and 360 juveniles. The barn is also used by small numbers of other bat species including lesser horseshoe, natterer’s, brown long-eared and Barbastelle.
In summer 2018, we were greatly concerned as no animals were recorded emerging from the building. The obvious reason for this was the occurrence of several barn owls, with lots of evidence of nesting and feeding remains within the building. Concerns were also raised over the impact of the exceptionally hot summer and whether this caused conditions in the roost to become too hot. Analysis of several hundred owl pellets revealed only one greater horseshoe bat skull, suggesting predation was taking place but this was perhaps not the primary cause of colony desertion.
A licence was granted to modify the two roost entrances to exclude owls, including the novel use of a ‘tip tray’ on the smallest entrance and a large timber baffle over the primary access point for the bats. These changes were easily navigable by bats and owls were successfully excluded from the building. The bats first returned in September 2020, having bred in another location that summer.
In 2021, funding was awarded by the Green Recovery Challenge fund to further enhance the building with an insulated ‘bat loft’ and hibernaculum, to provide more roosting opportunities in otherwise unused parts of the building and provide different microclimates available to the bats during periods of extreme temperatures.
This case study is a good example of work undertaken by Vincent Wildlife Trust as part of its Roost Resilience project to improve conditions for bats within some of the UK’s most important roosting sites for horseshoe bats.
Pre-works roost structure
- Type of structure
- Building
- Use
- Agricultural Building
- Condition
- Not In Use
- Approx. age
- 200 years
- Main construction material of walls
- Stone
- Roof design
- Hipped
- Roof material
- Slate
- Internal roof structure
- Timber Frame
- Lighting present on site and its proximity to the roost
- None
- Photos or annotated figures of roost structure
Pre-works roost description
- Species
- Greater horseshoe bat
- Number of bats max count
- 864
- Type of roost
- Maternity Roost
- Evidence of bats
- Bats Seen in Roost
- Roost location
- Roof Timbers
- Aspect of roost
- Various
- Height of roost entrance (m)
- 2
- Roost material(s)
-
- Bitumen Felt
- Slate Tiles
- Timber Roof Frame
- Timber
- Other
- Nearest commuting feature
- Woodland
- Distance to nearest commuting feature (m)
- 0
- Photos or annotated figures of roost
Proposed works
- Description of works
- Predator exclusions have been installed on both entrances to exclude barn owls and other potential predators (such as martens, which are soon to be reintroduced to the county). These include a tipping-plate design and vertical baffles to prevent climbing and obstruct flight paths into the building.
As the bats were previously only roosting in the much smaller, west-facing lean-to off the main barn building, enhancements were installed to improve the internal resources available to the bats within the main structure. A raised, heavily insulated loft was built into the internal void behind the south-facing aspect of the main barn, creating a warmer and more stable enclosed environment than the bats were currently using. This means that in critical months of the bats' reproductive cycle, they have access to a part of the building which will retain heat for longer during cold nights. The bat loft also provides warmer conditions in the early hours of the morning, as it is built around the part of the roof which is first exposed the the morning sun. The loft was being used by the entire maternity colony within 6 months of it being built and is now the primary location which the bat colony use as the creche for their young in July.
In periods of inclement cold weather, overwintering bats were often found using sub-optimal conditions within the building, areas which fluctuated readily with the external temperatures. By providing an insulated hibernaculum, designed to maintain stable cool temperatures and humidity on the lower parts of the building, we have provided the bats with a sheltered area within which to conserve energy during torpor. The hibernaculum was built in the northern section of the barn on the ground floor, using materials with good thermal properties and course surfaces for roosting bats to perch on. This has been shown to provide an area with greatly reduced daily fluctuations in temperature, providing increased protection for overwintering bats using the building in winter months. This was also adopted in the winter following construction.
- Type of impact upon the roost
- Disturbance
- Relevant annotated figures
Monitoring data
- Length of monitoring proposed
- Perpetual annual monitoring, following existing 25 years of existing data
- Frequency of monitoring
- Summer and winter NBMP monitoring
Final details
- Lessons learned
- Consider disturbance of in-situ bats, construction of the entrance modifications was fairly simple, as at the time no bats were present in the roost.
Building the loft and hibernaculum was more difficult due to some 200 bats returning before the construction. Thankfully, after the initial disturbance the bats appeared to become accustomed to our presence and settled in the adjacent lean-to of the building, we were able to close off this section of the building to reduce excessive disturbance from noise and lighting required to work. Construction of the loft took 4 weeks, but the bats remained in the building for the duration and were torpid for all but the first day of construction where they awakened to move position. This was surprising as the work involved heavy machinery, particularly to create the foundations for the steel support beams.
