Retain existing bat roosts and access points within developments
Overall effectiveness category Evidence not assessed
Number of studies: 3
Background information and definitions
Many bat species are known to roost in the crevices and roof voids of buildings. Existing roosts and their access points may be conserved during residential or commercial developments, for example by retaining a roof space used as a roost during renovations.
For interventions that involve creating new bat roosts or relocating access points within developments, see ‘Create alternative bat roosts within developments’ and ‘Relocate access points to bat roosts within developments’.
Supporting evidence from individual studies
A before-and-after study in 2004–2008 of one building renovation in Ireland (Aughney 2008) found that retaining four existing bat access points, along with restricting the timing of roofing work, resulted in similar numbers of brown long-eared bats Plecotus auritus using a roost within an attic before and after renovations. Fifteen brown long-eared bats were counted roosting in the attic space of the building before the renovation work. After the renovation work, sixteen brown long-eared bats were recorded exiting the roost through the retained access points. The building was an 18th century Georgian house that had the roofing felt and roof slates replaced. Original access points to the roost within the attic of the building were retained by installing four vents in the ridge tiles. The renovations were completed outside of the maternity season (date not reported). The attic was surveyed once in 2004 before the renovations, and once with an emergence survey in September 2008 after the renovations.Study and other actions tested
A replicated, before-and-after study in 2011–2015 of nine bat maternity roosts retained within building developments across Scotland, UK (Mackintosh 2016) found that four of nine retained roosts were used by maternity colonies after development, and two of the roosts were used by greater or similar numbers of bats. Average roost counts before and after development at the four roosts either remained stable (before: 2 brown long-eared bats Plecotus auritus; after: 2 brown long-eared bats), increased by 7% (before: 476 soprano pipistrelles Pipistrellus pygmaeus; after 507 soprano pipistrelles), decreased by 39% (before: 341 soprano pipistrelles; after: 208 soprano pipistrelles), or could not be counted (use inferred from brown long-eared bat droppings only). The other five roosts were not used at all (two brown long-eared bat roosts, two common pipistrelle Pipistrellus pipistrellus roosts) or had signs of use by bats at a later date (one whiskered bat Myotis mystacinus roost). Original roosts were either retained (seven sites) or partially retained (two sites), and original access points were reinstated. The numbers of bats counted before development at each roost were extracted from reports submitted with licence applications. Bats were counted at each roost after development during at least one dusk emergence or dawn re-entry survey between May and September 2015.Study and other actions tested
A review in 2018 of 283 studies of building developments in the UK (Lintott & Mathews 2018) found that two-thirds of retained and modified bat roosts were used by bats after development, and retained roosts were more likely to be used than new bat lofts or bat boxes installed to replace destroyed roosts. Bats used 67% of roosts that were retained and modified during reroofing work, whereas 52% of newly created bat lofts and 31% of bat boxes were used (the number of bats using roosts and bat lofts/bat boxes before and after development were not reported). Bats were four times more likely to be present in retained roosts than in new bat lofts and bat boxes installed to replace destroyed roosts (data reported as statistical model results). Retained roosts with enhancements, such as timber crevices and squeeze boxes, were six times more likely to be used by pipistrelles Pipistrellus spp. than those without enhancements. Retained roosts were also used by brown long-eared bats Plecotus auritus and Myotis spp. (see original report for data for individual species). The 283 studies (52 for retained and modified roosts, 112 for bat lofts, 119 for bat boxes; dates not reported) were collected from multiple sources, including practitioner reports and licence applications from across the UK, and reviewed in 2018.Study and other actions tested