Action: Provide bat boxes for roosting bats
Key messagesRead our guidance on Key messages before continuing
- Forty-two studies evaluated the effects of providing bat boxes for roosting bats on bat populations. Twenty-six studies were in Europe, nine studies were in North America, four studies were in Australia, two studies were in South America, and one study was a worldwide review.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (0 STUDIES)
BEHAVIOUR (42 STUDIES)
- Uptake (9 studies): Nine replicated studies in Europe and the USA found that the number of bats using bat boxes increased by 2–10 times up to 10 years after installation.
- Use (42 studies): Thirty-six of 41 studies (including 33 replicated studies and two reviews) in Europe, the USA, South America, and Australia found that bats used bat boxes installed under bridges and in forest or woodland, forestry plantations, farmland, pasture, wetlands, urban areas or unknown habitats. The other two studies in the USA and UK found that bats displaced from buildings did not use any of 43 bat houses of four different designs or 12 heated bat boxes of one design. One review of 109 studies across Europe, North America and Asia found that 72 bat species used bat boxes, although only 18 species commonly used them, and 31 species used them as maternity roosts. Twenty-one studies (including sixteen replicated studies, one before-and-after study and two reviews) found bats occupying less than half of bat boxes provided (0–49%). Nine replicated studies found bats occupying more than half of bat boxes provided (54–100%).
OTHER (21 STUDIES)
- Bat box design (15 studies): Two studies in Germany and Portugal found that bats used black bat boxes more than grey or white boxes. One of two studies in Spain and the USA found higher occupancy rates in larger bat boxes. One study in the USA found that bats used both resin and wood cylindrical bat boxes, but another study in the USA found that resin bat boxes became occupied more quickly than wood boxes. One study in the UK found higher occupancy rates in concrete than wooden bat boxes. One study in the USA found that Indiana bats used rocket boxes more than wooden bat boxes or bark-mimic roosts. One study in Spain found that more bats occupied bat boxes that had two compartments than one compartment in the breeding season. One study in Lithuania found that bat breeding colonies occupied standard and four/five chamber bat boxes and individuals occupied flat bat boxes. Three studies in the USA, UK and Spain found bats selecting four of nine, three of five and three of four bat box designs. One study in the UK found that different bat box designs were used by different species. One study in Costa Rica found that bat boxes simulating tree trunks were used by 100% of bats and in group sizes similar to natural roosts.
- Bat box position (11 studies): Three studies in Germany, Spain and the USA found that bat box orientation and/or the amount of exposure to sunlight affected bat occupancy, and one study in Spain found that orientation did not have a significant effect on occupancy. Two studies in the UK and Italy found that bat box height affected occupancy, and two studies in Spain and the USA found no effect of height. Two studies in the USA and Spain found higher occupancy of bat boxes on buildings than on trees. One study in Australia found that bat boxes were occupied more often in farm forestry sites than in native forest, one study in Poland found higher occupancy in pine relative to mixed deciduous stands, and one study in Costa Rica found higher occupancy in forest fragments than in pasture. One study in the USA found higher occupancy rates in areas where bats were known to roost prior to installing bat boxes.
Bats roost in caves, built structures, natural crevices (e.g. in rocks) and in trees. The provision of bat boxes is a widely used intervention, as a conservation measure and for research, and there is a lot of literature on the use of these structures by bats. However, the many different designs of bat box available makes it difficult to draw consistent conclusions as evidence in support of each individual design is lacking. Studies are also needed that evaluate the long-term effects of providing artificial roosts on bat populations, by observing changes in bat numbers over time, ideally in areas with and without bat boxes.
For evidence relating to other types of artificial roosts used during building developments, see ‘Threat: Residential and commercial development – Create alternative bat roosts within developments’.
Supporting evidence from individual studies
A replicated study in 1975–1987 in a mature coniferous forest in Suffolk, UK (Boyd & Stebbings 1989) found that the total population of brown long-eared bats Plecotus auritus (males, females and juveniles) occupying bat boxes doubled over the study period. The number of bats occupying the boxes increased from 73 to 140 bats. A total of 480 bat boxes were installed, but the proportion of boxes occupied is not reported. Bats roosted in the boxes both individually and in clusters of up to 20 bats. Bat boxes (10 cm x 15 cm x 15 cm internal dimensions) were constructed from untreated wood and installed in 1975. Two groups of four boxes (each facing north, south, east and west) were installed on each of 60 trees at a height of 3 or 5 m. In 1984 and 1985, the boxes were redistributed across 10 new sites within the forest. Boxes were checked and bats removed for identification and ringing 2–4 times/year in 1976–1987.
A replicated study in 1988–1990 at an urban institute in New York, USA (Neilson & Fenton 1994) found that displaced little brown bats Myotis lucifugus did not use any of 43 bat houses of four different designs and sizes. The four designs tested were 20 very small bat houses (longest dimension < 0.4 m, volume 0.002 m2, installed 3–4 m high on trees), eight small bat houses (20 x 15 x 15 cm with partitioned spaces, installed 2–7 m high on building walls), 11 Bat Conservation International (BCI) style bat houses (50 x 20 x 15 cm, installed 2–7 m high on building walls) and four large “Missouri” style bat houses (2.3 x 1 x 1 m with partitioned spaces below and an attic-like space above, installed on building roofs). Bats were excluded from five buildings in 1988–1990 due to renovations. Bats were captured and confined to bat houses overnight on 1–4 occasions/year between May and August in 1988–1990 with the aim of increasing uptake. Thirty-nine of 43 bat houses were regularly checked for bats between May and August 1988–1990.
A replicated study in 1976–1993 in a 360 km2 area of mixed woodland near Wareham, UK (Park et al. 1998) found a total of 1,662 bats of three species occupying up to 500 bat boxes at 20 sites. The bat species occupying bat boxes included: brown long-eared bats Plecotus auritus (976 bats), common pipistrelles Pipistrellus pipistrellus (355 bats), and Natterer’s bats Myotis nattereri (286 bats). Since 1976, approximately 500 timber bat boxes (10 x 15 x 15 cm internal dimensions) were installed across the study area. At each of 20 sites, three boxes were installed (facing north, southeast and southwest) on each of six trees 2.5–3 m above the ground. Boxes were checked and bats ringed approximately four times/year in March–October from 1977 to 1993.
A replicated study in 1996–1998 of 15 river bridges in coniferous forest in Oregon, USA (Arnett & Hayes 2000) found that bats used 13 of 15 (87%) bat boxes installed under 15 flat bottom bridges along five large streams. Within a year of installation, 10 boxes were used by bats. Bats were observed day roosting in five different boxes on 14 occasions (all solitary bats except for one group of eight individuals). Guano was collected from traps beneath 12 different boxes on 1–16 occasions. Wooden boxes (60 cm long x 60 cm wide x 30 cm deep) with eight boards placed inside (12 mm or 19 mm apart) to form crevices were fixed to the underside of the bridges between September 1996 and May 1997. Bridges varied in size (230–475 m width, 11–27 m length, and 3–6 m above the water). Day roosting bats were counted with a spotlight and guano traps were checked during 15 weekly surveys in June–September 1997 and 1998.
A replicated study in 1991–1993 in an urban area of Pennsylvania, USA (Brittingham & Williams 2000) found that maternity colonies of big brown bats Eptesicus fuscus and little brown bats Myotis lucifugus used pairs of bat boxes at five of nine sites after they had been excluded from buildings. At four of five sites where boxes were not used, bats either re-entered the building, found new roosts nearby or were not seen again. All occupied bat boxes faced a southeastern or southwestern aspect and received at least seven hours of direct sunlight. Unoccupied bat boxes received less than five hours of direct sunlight. Each of nine sites had a maternity colony of >30 bats that were excluded from buildings in 1991–1992. Homeowners installed pairs of wooden bat boxes (76 x 30 x 18 cm), one horizontally (30 cm tall) and one vertically (76 cm tall) side by side on the building close to the original roost. Emerging bats were counted on two nights in May–June and June–August in 1992 or 1993.
A replicated study in 1996–1998 in a pine grove Pinus sylvestris in Guadalajara, Central Spain (Paz et al. 2000) found bats occupying 8% of boxes and bat droppings in 2% of boxes checked. Bat species occupying the boxes were brown long-eared bats Plecotus auritus (176 bats) and common pipistrelles Pipistrellus pipistrellus (2 bats). Larger bat boxes were occupied more (9%) than smaller boxes (7%). The height and orientation of boxes did not have a significant effect on bat occupation. The larger boxes were based on the “Richter II” model (external dimensions: 40 cm height x 25 cm length x 22 cm width, internal capacity: 3,600 cm3). The smaller boxes were based on the “Stratmann FS 1” model (external dimensions: 40 cm height x 30 cm length x 11 cm width, internal capacity: 2,000 cm3). During April 1996, 203 bat boxes were installed on trees (108 large, 95 small) at heights of 2.9–5.5 m in rows spaced 50 m apart with an average density of 4 boxes/ha. Sixteen surveys with 2,134 total box visits were carried out in August–October 1996 and March–October 1997 and 1998.
A study in 1994–1997 in one forest site in Victoria, Australia (Ward 2000) found that lesser long-eared bats Nyctophilus geoffroyi, large forest bats Vespadelus darlingtoni, southern forest bats Vespadelus regulus and eastern false pipistrelles Falsistrellus tasmaniensis used nest boxes. A total of 73 bats of the four species were captured in nest boxes installed for feathertail gliders Acrobates pygmaeus. In July 1994, forty nest boxes were installed in a 7 ha area of forest dominated by Eucalyptus spp. Boxes were 50 m apart, had a 15 mm-wide entrance hole and were attached to tree trunks at 4.5 m above the ground. Nest boxes were checked approximately every two months between July 1995 and May 1997.
A replicated study in 1987–1996 in a deciduous forest in Bavaria, Germany (Kerth et al. 2001) found that female Bechstein’s bats Myotis bechsteinii roosted in 43 of 75 (57%) bat boxes, and black boxes in sunny locations were preferred by female bats during and after lactation. Female bats roosted more often during and after lactation in black bat boxes (186 bats during, 90 bats after) than white boxes (134 bats during, 22 bats after), and more in sun exposed boxes (276 bats during, 112 bats after) than shaded boxes (44 bats during, no bats after). Before giving birth, females roosted more in shaded locations (111 bats) than sunny locations (43 bats) but did not show a significant preference for black (76 bats) or white boxes (78 bats). Boxes of both colours were warmer in sunny locations (black: average 22°C; white: 20°C) than in the shade (black: 18°C; white: 17°C), and black bat boxes were warmer than white boxes. Seventy-five bat boxes (Schwegler design 2FN) were installed in 1987–1993. In 1996, 52 of the 75 boxes were rehung in pairs (one painted white, the other black) on 26 trees (half at shaded sites, half on trees exposed to the sun). Bat boxes were checked daily and box temperatures recorded in April–November 1996.
A replicated, controlled study in 1999–2000 in Fort Valley Experimental Forest, Arizona, USA (Chambers et al. 2002) found that bats used 17 of 20 artificial roosts (eight resin and nine wood) placed on snags in thinned (10 roosts) and unthinned (eight roosts) pine stands. Bats did not roost more often in natural control snags (five roosts). There was no difference in the use of two artificial bat roost designs (resin and wood, both 60 x 60 cm cylindrical designs). Resin roosts were made from polyester moulds shaped and painted to resemble exfoliating bark. Wood roosts were made from treated hardboard. Five resin and five wood artificial roosts were placed 2–4 m above the ground on snags in three unharvested stands and three thinned stands with a natural control roost on a snag at least 75 m away from each artificial roost. Nets below roosts were checked for guano 3–4 times in July–August in 1999 and 2000.
A replicated study in 1996–2000 in three farm forest plantations and one native forest in Queensland, Australia (Smith & Agnew 2002) found that 19 of 96 bat boxes (20%) were used by Gould’s long-eared bats Nyctophilus gouldi as maternity and other roosts. More bat boxes were occupied at two farm forestry sites in fragmented landscapes than in native forest (no boxes used) and one of the farm forestry sites bordering it (one box used). Approximately 20 other bat species were known to occur in the study area but did not use the bat boxes. Bat boxes were made from laminated plywood built to the British Tanglewood Wedge design (40 cm long x 20 cm wide x maximum of 18.5 cm deep). Twenty-four boxes were attached to trees at each of three sites 3 m or 6 m above the ground, evenly spaced and in different aspects. Boxes were checked 5–9 times between April 1996 and November 2000.
A replicated study in 2001 of three urban sites in Alentejo and Algarve, Portugal (Lourenço & Palmeirim 2004) found that soprano pipistrelles Pipistrellus pygmaeus used six of nine bat boxes. More bats were seen emerging from black bat boxes (maximum of 38) than grey boxes (maximum of six), although this difference was not statistically tested. No bats were seen to emerge from white bat boxes. The internal temperatures of different coloured bat boxes varied significantly (average maximum temperatures: black 37°C, grey 34°C and white 28°C). Maximum daily temperatures inside black bat boxes did not differ to those in roosts in the attics of nearby buildings. Three bat boxes (painted black, grey or white, all Bat Conservation International models) were placed facing south side by side at each of three sites 20 m from maternity roosts. Bat box temperatures were monitored using sensors and data loggers. Bat boxes were checked and emerging bats counted weekly in May–June 2001.
A replicated study in 1997 of 95 bat boxes in farmland, campgrounds and preserved areas in Colorado, USA (White 2004) found bats occupying 11 of 95 bat boxes (12% occupancy rate) at multiple sites, and occupancy was higher in areas where bats roosted prior to installing bat boxes. Big brown bats Eptesicus fuscus occupied 6 boxes, Myotis spp. two boxes and little brown bats Myotis lucifugus one box. Droppings of unknown bat species were found below two boxes. All bat boxes were occupied by one or two individuals, except one colony of 20 big brown bats. In areas where bats roosted prior to bat box installation, the occupancy rate increased to 64%. Bat box occupancy also increased when bat boxes had large landing areas, were mounted on buildings, and in areas of low canopy cover and human disturbance. No bat boxes mounted on trees were occupied. Ninety-five bat boxes were installed in preserved areas (47), remote campgrounds (8), rural farmland (39) and irrigated farmland (1), and placed on trees (40), buildings (42) and poles (13). Details of the locations of occupied bat boxes are not reported. Bat boxes were checked for occupancy and guano on the ground below at 15 or 30 day intervals in May–September 1997.
A replicated study in 1998–2001 of three forest stands in a mixed forest in Poland (Ciechanowski 2005) found that an average of four of 102 bat boxes (4%) were occupied by bats, and boxes became occupied more quickly in pine tree stands than deciduous stands. Bat species roosting in bat boxes were Nathusius’ pipistrelles Pipistrellus nathusii, or brown long-eared bats Plecotus auritus roosting individually or in groups. Bat boxes were occupied within two months in the pine stand, but within 13 months or more in beech and oak-beech stands. In 1998, 34 wooden bat boxes (Stratmann design, 40 x 13 x 4 cm) were installed in each of three stands (pine Pinus sylvestris, beech Fagus sylvatica and oak-beech Fagus sylvatica-Quercus robur). At all three stands, bat boxes were checked every 10 days in July–September 1998–1999, every two weeks in April–June 1999 and for two days in August 2001. The pine forest stand was also checked twice in July–August 2000.
A replicated study in 1999–2004 of a wetland on an island in Catalonia, Spain (Flaquer et al. 2006) found that soprano pipistrelles Pipistrellus pygmaeus used 69 bat boxes of two different designs with an average occupancy rate of 71%, and occupancy increased with time since installation. Occupation rates by females with pups increased from 15% in 2000 to 53% in 2003. Bat box preferences were detected in the breeding season only, with more bats in east-facing bat boxes (average 22 bats/box vs 12 bats/box west-facing), boxes with double compartments (average 25 bats/box vs 12 bats/box single compartment) and boxes placed on posts (average 18 bats/box) and houses (average 12 bats/box). Few bats used bat boxes on trees (average 2 bats/box). A total of 69 wooden bat boxes (10 cm deep x 19 cm wide x 20 cm high) of two types (44 single and 25 double compartment) were placed on three supports (10 trees, 29 buildings and 30 electricity posts) facing east and west. From July 2000 to February 2004, bat boxes were checked on 16 occasions. Bats were counted in boxes or upon emergence when numbers were too high to count within the box.
A replicated study in 1997–2004 in 66 agricultural areas in California, USA (Long et al. 2006) found that bats of five species used 141 of 186 bat boxes (76% occupancy rate), and the size, height and colour of bat boxes did not affect occupancy. Bat boxes were used by groups (48%) and individual bats (28%). Five bat species were recorded within bat boxes, with the Brazilian free-tailed bat Tadarida brasiliensis and Myotis spp. accounting for the majority of bat box occupancy (67% and 26% respectively). Size, colour and height of the bat boxes did not affect bat occupancy. Bat colonies (average of 64 bats) were more likely to use bat boxes that were shaded or exposed to the morning sun, mounted on buildings and close to a water source. Individual bats were more likely to use bat boxes that were mounted on poles and exposed to the full or afternoon sun. All bat boxes were plywood with one or more chambers and were small (<90 cm roosting space) or large (>90 cm roosting space). Bat boxes were mounted 2–9.5 m high singly, side by side or back to back on barns, sheds, poles, bridges or silos. Boxes were placed in different orientations and painted light, medium and dark colours. Bat boxes were checked annually in 1997–2004.
A replicated, site comparison study in 1985–2005 at 52 woodland sites in the UK (Poulton 2006) found an overall bat box occupation rate of 9%, although occupancy varied with box design and height, and increased with time since installation. A total of 5,986 boxes were occupied of 68,715 box inspections. Concrete bat boxes had higher occupancy rates than wooden boxes, with Schwegler design 1FF and 2FN boxes occupied the most (90% of records). Occupancy rates, bat counts and species counts were higher in bat boxes established for more than four years (18% occupancy, 60 bats and 15 species/100 box inspections) than boxes established for less than one year (8% occupancy, 22 bats and six species/100 box inspections). Occupancy rates were higher for Natterer’s bats Myotis nattereri in lower bat boxes (3% at £4 m, 2% at ³7 m), and higher for common noctule bats Nyctalus noctula in higher bat boxes (5% at £4 m, 7% at ³7 m). Bat boxes were installed on 1,410 trees across 52 sites (10–208 trees/site). Ten different bat box designs were included in the study (Schwegler designs 1FF, 1FS, 1FW, 2F, 2FN, SW, Wedge, Martin, CJM and Messenger). Boxes were inspected at monthly intervals in 1985–2005, but not all boxes were inspected monthly or yearly.
A replicated study in 1992–1999 in several small woodlots in a suburban area in Indiana, USA (Whitaker et al. 2006) found that four of nine artificial roost designs were used by a total of 709 bats over seven years. The designs used were single box (428 bats), triple box (210 bats), shake garland (96 bats) and Missouri-style bat boxes (65 bats). Five bat species used the artificial roosts both individually and in groups, with northern myotis bats Myotis septentrionalis using them most frequently (690 of the total 709 bats). From 1992 to 1994, 3,204 artificial roosts of nine designs were installed. Single boxes (715) were “bird house” style attached to deciduous trees. Triple boxes (259) were three single boxes surrounding deciduous trees. Single shakes (697) consisted of a pair of overlapping cedar shingles nailed to a tree. Shake garlands (842) had 10–20 shakes encircling deciduous tree trunks. Missouri style boxes (56) were 0.9 x 1.8 m. Tarpaper boxes (30) were wooden (0.9 x 0.9 m) and lined with tarpaper. Plastic/tarpaper skirts (176) had a length of tarpaper/plastic folded over and wrapped around a tree. Exfoliations (338) were loosened bark with the lower end wedged. Moved trees (91) were trees greater than 25 cm (diameter) at breast height which were topped and moved to loosen bark. Missouri style and tarpaper boxes were placed on posts 2.4 m high. The remaining structures were placed 3–11 m high on trees (same study areas as Hoeh et al. 2018). All structures were checked at least once/year in 1992–1999.
A study in 2004–2008 of five road developments and three residential and commercial developments in Ireland (Aughney 2008) found bats of four species occupying 33 of 150 bat boxes (22%) and bat droppings in 77 of 150 bat boxes (77%) across all eight sites. Overall, 91 individual bats were recorded occupying bat boxes, including soprano pipistrelles Pipistrellus pygmaeus (68), common pipistrelles Pipistrellus pipistrellus (17), Leisler’s bats Nyctalus leisleri (5) and Daubenton’s bat Myotis daubentonii (1). Bat droppings of Pipistrellus spp. were recorded in 62 bat boxes, Leisler’s bat droppings were recorded in 12 bat boxes and Myotis spp. droppings were recorded in three bat boxes. Bat boxes were either woodcrete (137 bat boxes; either Schwegler designs 1FD, 1FF, 1FN, 1FS, 2F, 2FN or 2F-DPF), wedge-shaped wooden bat boxes (5 boxes) or standard wooden bat boxes (8 boxes). At each of eight sites, 3–33 bat boxes were installed in 2002–2008 as mitigation for habitat loss. Each of the 150 bat boxes was checked once in June, October or November 2008.
A replicated, controlled study in 2000–2006 in tropical forest and pasture in the Caribbean lowlands, Costa Rica (Kelm et al. 2008) found that bats colonized all 45 artificial roosts in simulated tree trunks installed in forest and forest remnants within an average of three weeks. Five nectar or fruit-eating bat species colonized the artificial roosts permanently in group sizes (2–5 bats) similar to those in natural roosts (3–16 bats): Pallas’ long-tongued bat Glossophaga soricina, Commissaris’s long-tongued bat Glossophaga commissarisi, Seba’s short-tailed bat Carollia perspicillata, Sowell’s short-tailed bat Carollia sowelli and chestnut short-tailed bat Carollia castanea. Artificial roosts were simulated hollow tree trunks made from sawdust concrete slabs forming a square box (54 x 54 x 194 cm or 74 x 74 x 154 cm) and installed in the shade within forest (22 roosts) and forest remnants within pasture (23 roosts). Natural roosts were found and checked along a systematic line transect search. Artificial roosts were checked every 42 days on average with a total of 1,009 checks in 2000–2006.
A replicated study in 2003–2008 in a mixed forest in Poland (Lesiński et al. 2009) found that the occupancy of 70 bat boxes by four bat species increased by more than three times over two years. Bat box occupancy increased from 13% (9 of 70 boxes) in 2005 to 49% (34 of 70 boxes) in 2006 and 2007. Four bat species occupied bat boxes: greater mouse-eared bat Myotis myotis, common noctule Nyctalus noctula, Nathusius’ pipistrelle Pipistrellus nathusii and brown long-eared bat Plecotus auritus. In 2007, bat boxes were colonized first by brown long-eared bats in March and last occupied in October by common noctules. Nathusius’ pipistrelles were the most abundant species that used bat boxes (74% of records from May to September) and were found in the largest clusters in July (14 individuals). In 2003, 70 wooden bat boxes (Stratmann, internal dimensions 25 x 25 x 7 cm) were installed on trees 2.5–3 m above the ground with a southeastern orientation. In 2005 and 2006, bat boxes were checked once in August and from March 2007 to February 2008 boxes were checked monthly.
A replicated study in 2009 in 13 mixed or pine forests in East Lithuania (Baranauskas 2010) found that six bat species used bat boxes of four designs, but occupancy rates are not reported. Two bat species occupied the majority of bat boxes: Nathusius’ pipistrelles Pipistrellus nathusii (79% of all bats recorded and occupied boxes at all 13 sites) and soprano pipistrelles Pipistrellus pygmaeus (18% of all bats and occupied boxes at seven of 13 sites). The remaining bat species (pond bat Myotis dasycneme, brown long-eared bat Plecotus auritus, common noctule Nyctalus noctula and northern bat Eptesicus nilssonii) accounted for 2% of bats using bat boxes. Breeding colonies of Nathusius’ pipistrelles and soprano pipistrelles were found in standard and four and five chamber bat boxes. Flat bat boxes were not used by breeding colonies but were the only type of box in which all six bat species were found. In total, 504 bat boxes were installed (30–60 in each of 13 sites): 250 standard boxes (25 x 15 x 10 cm), 168 flat boxes (35 x 4 x 15 cm), 27 four chamber (30 x 15 x 15 cm) and 59 five chamber boxes (55 x 35 x 19.5 cm). Standard and flat wooden bat boxes were installed in 2004–2008, and four and five chamber bat boxes were installed in 2007–2008. All boxes were attached to trees facing southeast or southwest, 4–6 m above the ground and 20–200 m apart. Bat box checks and emergence surveys were carried out six times in May–October 2009.
A replicated study in 2007–2009 across Italy (Agnelli et al. 2011) found that up to a fifth of bat boxes were used by bats during the first year after installation, and use increased with box height and time since installation. The proportion of bat boxes used by bats increased in each of three years after installation (year one: range 12–21%; year two: 26–35%; year 3: 40%). Bat box use was also found to increase with the height of the boxes above the ground (data reported as correlation coefficients). Bat boxes were wooden with a single internal chamber and one entrance at the base. Boxes were installed by volunteers (total number of boxes not reported) following a public information project and advertising campaign. Monthly checks for signs of use (presence of bats or bat droppings) were carried out for approximately 300 bat boxes. Bats were not identified to species and details of bat box locations or habitat types are not reported.
A replicated study in 2005–2009 in seven sites of mixed woodland in northeast England, UK (Meddings et al. 2011) found that the overall bat occupancy of 90 bat boxes varied from 9% in 2006 to 18% in 2007. Occupancy rates in subsequent years were similar (12% in 2008 and 17% in 2009). The highest occupancy rate at one site was 27% (seven of 26 boxes). Four bat species occupied bat boxes: Pipistrellus spp., brown long-eared bat Plecotus auritus, Natterer’s bat Myotis nattereri and whiskered/Brandt’s bat Myotis mystacinus/Myotis brandtii. In 2006, birds (Parus spp.) occupied 37% of bat boxes. The installation of bird boxes (2–15 boxes/site) in February 2008 reduced bird occupancy of bat boxes to 17%. Woodland sites were small (<3 ha) linear blocks with trees <40 years old. In 2005–2006, bat boxes (Schwegler design 2FN, 16 cm diameter x 36 cm high) were installed in sets of three on trees, covering different aspects at least 4 m above the ground. Boxes were checked for bats in November 2006 and 2007, September 2008 and October 2009.
A randomized, replicated study in 2009–2010 in 26 managed pine forest sites in northern Arizona, USA (Mering & Chambers 2012) found that almost half the 104 artificial roosts installed across 26 sites were occupied by bats by the second year after installation. Bat occupancy was higher in the second year (49 of 104 roosts at 22 of 26 sites) than the first year (19 of 104 roosts at 13 of 26 sites). Resin roosts were occupied more quickly than wood roosts (resin: within 406 days; wood: 439 days). A total of 47 bats of five species were captured emerging from all artificial roosts. Four artificial roosts were installed/site 5 m above the ground on live ponderosa pine Pinus ponderosa trees. Half were constructed from wood (40 cm wide x 45 cm tall) and half from resin (60 x 60 cm). Roosts were checked every two weeks during May and September in 2009 and 2010. Mist nets or funnel bags were used to capture bats on emergence at dusk.
A replicated study in 2012 in urban parks and forested areas of 11 regions in Navarra, Spain (Alcalde et al. 2013) found that 60% of installed bat boxes had signs of occupation by 10 bat species. Out of 405 bat boxes installed, 241 had signs of bat occupation (60%) and bats were found roosting in 107 (26%). In total, 345 individuals of 10 species were recorded: 247 soprano pipistrelles Pipistrellus pygmaeus, 28 common pipistrelles Pipistrellus pipistrellus, 36 Leisler’s bats Nyctalus leisleri, 16 common noctules Nyctalus noctula, seven brown long-eared bats Plecotus auritus, six greater noctules Nyctalus lasiopterus, two Kuhl's pipistrelles Pipistrellus kuhlii, one Daubenton's bat Myotis daubentonii, one whiskered bat Myotis mystacinus and one barbastelle bat Barbastella barbastellus. Approximately 500 bat boxes of seven different models were placed 4–7 m high in forest areas, urban parks and close to rivers. Between September and November 2012, 405 bat boxes were inspected. Bat use of unoccupied boxes was assessed by the presence of guano.
A replicated, controlled study in 2011–2012 in ancient, mixed deciduous woodland in Buckinghamshire, UK (Dodds & Bilston 2013) found that brown long-eared bats Plecotus auritus and Natterer’s bats Myotis nattereri preferred three of five bat box designs. Three Schwegler designs were occupied most by brown long-eared and Natterer’s bats: 1FS (33% of total occupations), 2FN (29%), and 2F (27%). Schwegler 1FF boxes were rarely used (11%), and wooden Apex boxes were not used at all. Groups of five Schwegler woodcrete boxes (2F: 33 x 16 cm; 2FN: 36 x 16 cm; 1FS: 44 x 28 cm; 1FF: 43 x 27 cm) and one wooden Apex box (40 x 12 cm) were erected around 13 trees in March 2011. Groups of bat boxes were evenly spaced along a transect line of 300 m through the woodland. Bat boxes were checked monthly in May–October 2011 and 2012.
A replicated, site comparison study in 2009–2010 in five pasture and tropical forest fragments in Costa Rica (Reid et al. 2013) found that 26 of 48 bat boxes were used by at least five bat species, although only three boxes were colonised as permanent day roosts. Overall, 54% of bat boxes were occupied by bats. More bat boxes were occupied in forest fragments (17 of 18, 94%) than in pasture (12 of 30, 40%). At each of five sites, six bat boxes were installed in pasture on wooden or steel posts or on 4 m long tree limbs (replanted and allowed to grow for three months), and three to six bat boxes were installed on trees in adjacent forest fragments. Bat boxes were constructed from wood and concrete (interior dimensions: 40 x 40 x 60 cm) and mounted 2–3 m above the ground. Visual checks were carried out twice/month in 2009 and 2010, and motion-activated infrared video cameras were installed.
A review of 389 bat mitigation licences issued from 2003 to 2005 in England, UK (Stone et al. 2013) found that only three of 24 (13%) bat boxes were used by bats after development. The roost status, bat species and number of bats using the roosts before and after development are not reported. Most licensees (67%) failed to submit post-development reports, and post-development monitoring was conducted at only 24 of 1,690 (1%) bat boxes. The licences analysed were submitted to Natural England between 2003 and 2005, and were issued for three types of development (renovation, conversion and demolition).
A replicated study in 2005–2014 in a fiord landscape in Norway (Michaelsen et al. 2014) found that the number of soprano pipistrelle bats Pipistrellus pygmaeus using bat boxes increased more than tenfold over three years, with three larger bat boxes being used as maternity roosts. Soprano pipistrelles were first recorded using the boxes in 2010, five years after installation, with less than 100 individual bats counted. This number increased to an estimated 1,000–1,600 individuals in 2012 and 2013. Fewer bats were reported roosting in hollow trees after bat boxes were installed (data not reported and no statistical tests were carried out). All bat boxes had a black coating and were either Schwegler designs (2F, 2FN, 1FS, 1FW or 1FQ), a Bat Conservation International design, or from Hasselfeldt Naturschutz (Fledermausgroßraumhöhle FGRH with partitions). Bat boxes were installed in 2005–2014 in groups at three sites (total number of boxes not reported). Bat boxes and hollow trees previously used as roosts were inspected eight times between June and August 2012, and seven times between May and August 2013. Counts of emerging bats were also carried out in June 2014.
A replicated study in 1999–2015 of three broadleaved/mixed woodlands in County Galway, Ireland (McAney & Hanniffy 2015) found that bat boxes were used by seven bat species/species groups with an overall occupancy rate of 20% over 17 years. Pipistrellus spp. had the highest occupancy rate of boxes (14%) followed by Leisler’s bats Nyctalus leisleri (3%), brown long-eared bats Plecotus auritus (2%) and Daubenton’s bats Myotis daubentonii (0.4%). Pipistrellus spp. were found more often in Schwegler design 1FF boxes, and brown long-eared bats in Schwegler design 2FN boxes (data reported as statistical model results). Occupancy rates were also found to increase over time for Pipistrellus spp., brown long-eared bats and Leisler’s bats (data reported as statistical model results). In 1999, 162 Schwegler woodcrete bat boxes (designs 2FN, 1FF, 1FW or 2FN) were installed across three sites. They were hung on trees 4 m above the ground in pairs. The number of boxes varied at each site (10, 50, 62) and some boxes were relocated during the project. A total of 7,370 bat box inspections were carried out. Boxes were checked monthly between April and September in 1999–2015, although checks were not carried out in June or July from 2002 onwards.
A study in 2010–2015 in one wetland reserve in Basque Country, Spain (Alcalde & Martínez 2016) found that four bat species used bat boxes of three of four designs. Thirty-five of 93 bat boxes (38%) were occupied by bats seven years after installation. Overall, 240 individual bats were counted in bat boxes, including soprano pipistrelles Pipistrellus pygmaeus (207), Leisler’s bats Nyctalus leisleri (19), Kuhl's pipistrelles Pipistrellus kuhlii (13) and a Daubenton's bat Myotis daubentonii (1). Three of four box designs were occupied by 0.5–1.6 bats/visit. No bats were detected in boxes of one design (Schwegler 1FW). In late 2008, 95 bat boxes were installed in one 206 ha wetland reserve. Boxes of four different designs (Schwegler 1FF, 1FW, 2F double wall, 2FN) were attached to trees and buildings at a height of 3–6 m. Bat boxes were checked nine times between 2010 and 2015.
A replicated, before-and-after study in 2011–2015 of 17 building developments with replacement bat maternity roosts across Scotland, UK (Mackintosh 2016) found that three bat boxes provided at one site were used by a maternity colony, but bat boxes at 16 other sites were not used by maternity colonies. At one site, a group of three unheated bat boxes (Schwegler design 1FFH) was used by a maternity colony of soprano pipistrelles Pipistrellus pygmaeus after development, but fewer bats used them than the original roost (average count in original roost: 62 bats; average count in bat boxes after development: 20 bats). Alternative roosts at 16 other sites with heated (seven sites) or unheated bat boxes (9 sites) were not used by maternity colonies, but bat boxes at two sites (one heated, one unheated) were used by 2–5 individual bats. Bat boxes were mounted internally or externally on developed buildings, or on nearby trees, either singly or in groups (2–15 bat boxes). Bat box design varied at each site. 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.
A review in 2016 of 109 studies of bat box use from 17 countries across Europe, North America, Australia and Asia (Rueegger 2016) found that 71 bat species were reported to use bat boxes, although only 18 species commonly used boxes and 31 species used boxes as maternity roosts. Bat box design and dimensions varied between studies. Most bat boxes were made of timber, although woodcement was also frequently used in Europe. Sixty-seven of the reviewed studies used bat boxes for research purposes, 42 for bat conservation and one for community education. Twenty-two studies in this review (Boyd & Stebbings 1989, Neilson & Fenton 1994, Park et al. 1998, Arnett & Hayes 2000, Brittingham & Williams 2000, Ward 2000, Kerth et al. 2001, Chambers et al. 2002, Smith & Agnew 2002, Lourenço & Palmeirim 2004, White 2004, Ciechanowski 2005, Flaquer et al. 2006, Long et al. 2006, Whitaker et al. 2006, Kelm et al. 2008, Lesiński et al. 2009, Baranauskas 2010, Meddings et al. 2011, Mering & Chambers 2012, Dodds & Bilston 2013, Reid et al. 2013) have been summarized individually.
A replicated study in 2012–2013 at six churches in Norfolk, UK (Zeale et al. 2016) found that Natterer’s bats Myotis nattereri did not use any of the 12 heated bat boxes provided after being displaced from roosts inside the churches. Two bat boxes (Bat Conservation International design) containing heat mats and thermostats were installed at each of six churches, one inside the church and one outside at roof height. Acoustic deterrents and artificial lighting were used to deter bats from their existing roost locations inside the churches where droppings and urine were causing problems. Emergence surveys and radio-tracking were carried out at each site between July and September in 2012 or 2013.
A before-and-after study in 2014–2016 in one agricultural site in Navarra, Spain (Alcalde et al. 2017) found that common pipistrelles Pipistrellus pipistrellus colonized one bat box installed on a building constructed as an artificial roost. Six common pipistrelles roosted in the bat box in 2014 in the same summer that it was installed. Numbers increased to 15 in 2015 and to 36 in 2016. In July 2014, one bat box was attached to the outside wall of a building (2.6 x 2.6 x 3.2 m) constructed as an artificial roost. The artificial roost was built to replace a bat roost destroyed in a nearby building in 2013. Bats were counted weekly from mid-April to mid-July in 2015 and 2016 using an infrared light.
A before-and-after study in 2010–2017 of a residential building development in the Cotswold Hills, UK (Garland et al. 2017) found that five wall-integrated bat boxes were not used by a common pipistrelle Pipistrellus pipistrellus maternity colony six years after the original roost in a stone cottage wall was demolished. In 2010 (the year before demolition), the original roost was used by >76 bats. During the six years after construction, the bat boxes were used by low numbers of individual bats (0–3 bats/year) and were not used as a maternity roost. The five bat boxes (Schwegler design 1FR) were integrated within a purpose-built bat wall constructed on the east-facing gable end of an existing hay barn 30 m from the original roost. The bat wall also had multiple stone crevices leading to internal cavities. The original roost was demolished in late winter 2010 and the bat wall was completed in early spring 2011. Surveys were carried out every year in 2010–2017 including daytime inspections and evening emergence counts on 1–3 separate occasions/year.
A replicated study in 1994–2016 at four sites of regenerating forest in Melbourne, Australia (Griffiths et al. 2017) found that bat boxes were used more than expected by one bat species, whereas 12 bat species made little or no use of them. Gould’s wattled bat Chalinolobus gouldii used bat boxes 72% more than expected based on its documented occurrence in the area. The species formed maternity groups in bat boxes at all four sites. Seven bat species used bat boxes infrequently and less than expected. Five bat species did not use bat boxes at all. A total of 126 bat boxes of nine designs were installed on trees 4–6 m above the ground at four sites (20–40 boxes/site). Bat box checks were carried out monthly or bi-monthly over 5–22 years/site. A total of 444 surveys were carried out across all four sites.
A randomized, replicated, site comparison study in 2004–2012 in five pine forests in Spain (López-Baucells et al. 2017) found that bat boxes were used by three bat species with an overall occupancy rate of 15% over nine years. During 1,659 bat box inspections, 255 bat boxes were found to be occupied. Leisler’s bat Nyctalus leisleri was found in 29 of 200 bat boxes (15%) in groups of 1–11 individuals. Pipistrellus spp. (soprano pipistrelle Pipistrellus pygmaeus and Kuhl’s pipistrelle Pipistrellus kuhlii) were found in 39 of 200 bat boxes (20%), either breeding or alone (1–5 bats). Bat box occupancy rates increased with forest cover and distance from human settlements (data reported as statistical model results). Two hundred open-sided wooden bat boxes (10 cm deep x 19 cm wide x 200 cm high) were randomly installed on trees between 2003 and 2005 in clusters of 3–5 boxes in five pine forests. Boxes were placed 4 m above the ground with randomly chosen orientations. Annual box checks were carried out in each of nine years between 2004 and 2012 in summer and/or autumn.
A replicated study prior to 2016 in 146 forests and parks in Bavaria, Germany and Austria (Zahn & Hammer 2017) found that 25 of 146 (17%) groups of bat boxes were used as maternity roosts, 61 of 146 (42%) were used regularly by individual bats, and 60 of 146 (41%) were used only occasionally by individual bats or were not used at all. Thirteen bat species were recorded using the bat boxes. Bat box use increased with time since installation (<5 years: 26–54% of box groups regularly used; >10 years: 83–98%) and the size of bat box groups (<10 boxes/group: 58% of box groups regularly used; >30 boxes/group: 100%). However, these results were not tested for statistical significance. A total of 6,500 bat boxes were installed in groups on trees in 146 forests and parks. Boxes were installed in three group sizes (with approximately a third of the 146 boxes in each): small (3–10 boxes), medium (11–30 boxes) or large (>30 boxes). Boxes were also installed at three different time periods (with approximately a third of the 146 boxes in each): <5 years, 5–10 years and >10 years before the survey. Details and dates of installation and bat box surveys are not reported.
A replicated, before-and-after study in 1988–2018 in restored woodland near Melbourne, Australia (Griffiths et al. 2018) found that Gould’s wattled bats Chalinolobus gouldii used bat boxes more frequently than seven other bat species and were captured in higher numbers in the study area after bat boxes were installed. Ninety percent of bats (21,424 of 23,778) recorded using 37 bat boxes in 1994–2018 were Gould’s wattled bats. Gould’s wattled bats were recorded using bat boxes in each of 25 years of the study and used them as maternity roosts. Seven other bat species did not use bat boxes as maternity roosts and were recorded in them only occasionally and/or in low numbers (<1–6% of bats recorded; see original paper for data for individual species). More Gould’s wattled bats were captured in the study area after bat boxes were installed (average 49 bats/survey) than before (2 bats/survey) but the difference was not tested for statistical significance. Thirty-seven bat boxes of four designs (details not reported) were attached to Eucalyptus spp. trees (4–6 m above the ground). Boxes were checked monthly in 1994–2007 and every two months in 2008–2018. Bats were captured using four harp traps for two consecutive nights in autumn in each of two years before bat boxes were installed (1988, 1992) and in each of 18 years after (1996–2004, 2006–2013, 2018).
A replicated study in 2015–2016 of suburban woodlots in Indiana, USA (Hoeh et al. 2018) found that rocket boxes were used by more Indiana bats Myotis sodalis than bat boxes or bark-mimic roosts, and four of five rocket boxes installed were used as maternity roosts. Artificial roost type had a significant effect on maximum weekly counts of bats emerging (data reported as statistical model results). Maximum nightly counts and the total number of bat days (days in which at least one bat was observed using the roost) were higher in rocket boxes (205–210 bats/night; 4,340–7,770 bat days) than in bat boxes (7–22 bats/night; 24–172 bat days) or bark-mimic roosts (1–2 bats/night; 7–15 bat days), although no statistical tests were carried out. Six clusters of three bat boxes were installed (three in 2015, three in 2016) with each cluster containing one of each roost type: rocket box (2-chambered wooden box, 26 cm wide x 107 cm high), bat box (3-chambered traditional wooden birdhouse style box, 18 cm wide x 40 cm high), bark-mimic roost (modified BrandenBark polyurethane roost, 16 cm wide x 130 cm wide). Roosts were installed on posts (6 m high) along the southern edge of wooded areas (same study area as Whitaker et al. 2006). Bats were excluded from one of the six clusters to allow roost temperatures to be monitored. Daytime checks and emergence counts were carried out at least twice/week in March–October 2015 and 2016.
A review in 2018 of 119 studies of building developments in the UK (Lintott et al. 2018) found that a third of bat boxes installed to replace destroyed roosts were used by bats, mainly Pipistrellus spp., and bats were more likely to use bat boxes when a greater number were installed across a site. Bats were present in 31% of bat boxes after development with the majority used by Pipistrellus spp. (27%). A small number of bat boxes were used by brown long-eared bats (2%) and Myotis spp. (2%). The roost status and number of bats using the roosts before and after development are not reported. The probability of at least one bat box being occupied by bats increased when a greater number of bat boxes were installed across a site (data reported as statistical model results). The 119 studies (dates not reported) were collected from multiple sources, including practitioner reports and licence applications from across the UK, and reviewed in 2018.
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