Conserve roosting sites for bats in old structures or buildings
Overall effectiveness category Likely to be beneficial
Number of studies: 3
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Background information and definitions
Old structures or buildings and the roosting spaces within them may be conserved as roosting sites for bats. Conflict may arise when old buildings are also used by humans, and solutions may be sought to both conserve bat roosts and reduce any negative impacts on human inhabitants or visitors.
Supporting evidence from individual studies
A before-and-after study in 1993–1997 of a disused railway tunnel in Wiltshire, UK (Mitchell-Jones et al 2007) found that conserving a roosting site by constructing walls with access grilles at the ends of the tunnel, along with attaching wood to the tunnel walls, resulted in an increase in the number of hibernating bats. More bats were counted hibernating in the tunnel after the end walls were constructed and wood attached (before: 117 bats; two years after: 190 bats). During fourteen subsequent surveys (dates not reported), the number of hibernating bats increased to 678, with 30% of bats roosting behind the wood on the tunnel walls. The majority (94%) were Natterer’s bats Myotis nattereri. Brown long-eared bats Plecotus auritus, Daubenton’s bats Myotis daubentonii, whiskered/Brandt’s bats Myotis mystacinus/brandtii and barbastelle bats Barbastella barbastellus were also recorded. The end walls with access grilles were constructed in 1994, and wood was attached to the tunnel walls in 1994 and 1995. The temperature was reported to be more stable after the end walls were constructed (before: not reported; after: 8˚C) and humidity inside the tunnel increased (before: 80%; after: 95%). Hibernating bats were counted in the winters of 1993 and 1996/1997.Study and other actions tested
A before-and-after study in 2000–2011 in a cellar in Brandenburg, Germany (Haensel et al 2011) found that after the cellar was emptied of rubbish, an increasing number of bats used it as a winter roost over an 11-year period. Results were not statistically tested. Eleven years after an ice cellar was emptied of rubbish, 127 bats of four species were recorded hibernating, compared to eight bats of three species in the year the cellar was emptied. Natterer’s Myotis nattereri, Daubenton’s Myotis daubentonii, brown long-eared Plecotus auritus and barbastelle Barbastella barbastellus bats hibernated in the cellar in increasing numbers (winter 2000/01: Natterer’s = 4; Daubenton’s = 1, brown long-eared = 3, barbastelle = 0 individuals; winter 2010/11: Natterer’s = 59; Daubenton’s = 30, brown long-eared = 30, barbastelle = 8 individuals). Greater mouse-eared bats Myotis myotis were also recorded in low numbers throughout the study (0–4 individuals/year; see original paper for details). In 2000 and 2001, a disused stone cellar (4.5 m wide x 6 m long x 9 m high; previously used for ice storage) located in a biosphere reserve (1,291 km2) was emptied of rubble and rubbish to create space for roosting bats. Human access was prohibited. Bats were monitored once/year between December and mid-February in 2000/01–2010/11. In winters of 2000/01 and 2001/2, the authors report that the census may have been limited by the height of their ladder.Study and other actions tested
A before-and-after study in 2012–2013 at one church in Norfolk, UK (Zeale et al 2016) found that two sections of an existing roost within the church that were ‘boxed-in’ continued to be used by Natterer’s bats Myotis nattereri, but the number of bats using the roost after it had been ‘boxed-in’ was reduced by half. The ‘boxed-in’ areas continued to be used by up to 52% of bats (46 of 88) that originally roosted in the church. Up to 28 of the bats that originally roosted in the church used an external roost location in the church porch as a new roost site. The ‘boxed-in’ areas (5 m long) were accessible to bats via existing entry points and were sealed off from the internal spaces of the church. They included roof timbers and mortise joints that had previously been used by the bats. The roosts were ‘boxed-in’ after the build-up of droppings and urine within the church interior caused problems for human visitors. Emergence surveys and radio-tracking were carried out at each site between July and September in 2012 or 2013.Study and other actions tested
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This Action forms part of the Action Synopsis:Bat Conservation
Bat Conservation - Published 2021