Action: Provide artificial roost structures for bats
- We found 22 replicated studies of artificial roost structures in Europe, North and South America, and Australia. In 21 of these studies artificial roosts were used by bats. In one study in the USA bats displaced from a building did not use any of 43 bat houses of four different designs.
- Fifteen studies provide occupancy rates of artificial roosts by bats with varied results. Seven studies found bats occupying less than half of bat boxes provided (4–49%). One study in Spain showed low occupancy of bird boxes by bats (3%). Six studies showed bats occupying more than half of bat boxes or artificial roosts provided (57–87%). One study in Costa Rica found bats occupying 100% of simulated hollow tree trunks in group sizes similar to those in natural roosts.
- One study in the UK found that a bat population using bat boxes in a woodland doubled over 10 years. One study in Poland found that the number of bats using bat boxes in a forest increased more than eight fold over three years.
- Eight studies looked at the position of bat boxes. Three of four studies in Europe and the USA found that orientation and/or the amount of exposure to sunlight were important for bat occupancy. One study found an effect of bat box height that varied between species, and one found no effect of height. Two studies found higher occupancy of bat boxes on buildings than on trees. One Australian study found that bat boxes were occupied more often in farm forestry sites than in native forest, and a study in Poland found higher occupancy in pine relative to mixed deciduous stands.
- Eleven studies in Europe and the USA looked at bat box design. 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 artificial roosts. One study in the UK found higher occupancy rates in concrete than wooden bat boxes. In a study in Spain more bats occupied bat boxes that had two compartments than one compartment. One study in the USA found that four of nine bat box designs were occupied by bats. One study in the UK found bats selecting three of five bat box types. One study in East Lithuania found that bat breeding colonies occupied standard and four/five chamber bat boxes and individuals occupied flat bat boxes. Three studies found that warmer bat boxes had higher occupancy rates or were used by more bats than cooler boxes.
- Four studies found that up to 37% of bat boxes were used by birds, marsupials or invertebrates.
Bats roost in caves, built structures, natural crevices (e.g. in rocks) and in trees. The provision of artificial roost structures for bats 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 artificial roost structures available makes it difficult to draw consistent conclusions as evidence in support of each individual design is lacking. We particularly highlight the small number of studies that have looked at the effects of providing artificial roosts on bat populations, by observing changes in bat numbers over time, preferably in areas with and without bat boxes.
We would recommend a systematic review of this subject.
Supporting evidence from individual studies
A replicated study in 1975–1985 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 from 73 to 140 bats. A total of 480 bat boxes were installed, but the proportion of boxes occupied by bats is not given. 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 on 60 evenly spaced trees and arranged into two groups of four boxes (each facing north, south, east and west) on each tree at 3 or 5 m high. In 1984 and 1985, boxes were redistributed across ten new sites within the forest. Boxes were checked and bats removed for identification and ringing two to four times every year from 1976 to 1987. The authors note that the number of bats present will be underestimated by the methods used in the study.
A replicated site comparison study from 1985 to 2005 at 52 woodland sites in the UK (Poulton 2006) found an overall bat box occupation rate of 8.7% (5,986 boxes occupied of 68,715 box inspections). Occupancy rates were higher in bat boxes in the west of the UK (15% in Devon and Wales) than in the east (4% in the Midlands and eastern England). Occupancy rates were higher in summer (10% in August and September) than winter (2% in February). Concrete bat boxes had higher occupancy rates than wooden boxes, with types 1ff and 2fn being 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/100 box inspections, 15 species/100 box inspections) than boxes established for less than one year (8% occupancy, 22 bats/100 box inspections, six species/100 box inspections). Occupancy rates were higher for Natterer’s bats Myotis nattereri in lower bat boxes (3% at <= 4 m, 1.6% at >= 7 m), and higher for noctule bats Nyctalus noctula in higher bat boxes (5% at <= 4 m, 7.2% at >= 7 m). Bat boxes were installed on a total of 1,410 trees across 52 sites (with 10–208 trees/site). Ten different types of bat box were included in the study but were not installed systematically (1ff, 1fs, 1fw, 2f, 2fn, SW, Wedge, Martin, CJM and Messenger). Most trees had two bat boxes installed (120 trees had one bat box, and 23 had at least five). A total of 3,024 boxes were inspected and 68,715 inspections were made. Inspections were made in one month intervals but not all boxes were inspected monthly or yearly. Due to an unbalanced design subsets of the data were used for analysis.
A replicated study between May and November 1989 in a 130 ha coniferous forest plantation in Spain (Benzal 1990) found brown long-eared bats Plectous auritus using bird boxes as day roosts. A total of 197 bats (49 males, 75 females and 73 juveniles) were found in 3% of bird box checks and bat droppings in 8% of checks. One hundred and twenty one bats were found roosting individually in the boxes (53% were males) and 31 groups of bats of 2–13 individuals were found (94% were females or juveniles). Bird boxes (dimensions not given) were installed in rows 50–70 m apart with an average density of four boxes/hectare in 1988 (total number of boxes not given). Between March and November 1989, 5,274 box checks were made with 2–12 days/visit. Bats were removed from boxes for identification, collection of biometric data and to be ringed.
A replicated study in May to August 1988–1990 at a large urban institute in New York, USA (Neilson & Fenton 1994) found that displaced little brown myotis 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), eight small bat houses (20 cm x 15 cm x 15 cm with partitioned spaces), 11 Bat Conservation International (BCI) style bat houses (50 cm x 20 cm x 15 cm) and four large “Missouri” style bat houses (2.3 m x 1 m x 1 m with partitioned spaces below and an attic-like space above). All bat houses were placed facing different directions. The very small bat houses were placed 3–4 m above the ground on trees, the small and BCI style bat houses were placed 2–7 m above the ground on the walls of buildings and the “Missouri” style bat houses were placed on building roofs.
A replicated study from 1977 to 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 (occupancy rates not given) at 20 sites (976 brown long-eared bats Plecotus auritus, 355 common pipistrelles Pipistrellus pipistrellus, and 286 Natterer’s bats Myotis nattereri). Since 1976, approximately 500 timber bat boxes (10 cm x 15 cm x 15 cm internal dimensions) were installed across the area. Each site comprised of six trees with three boxes per tree, facing north, south-east and south-west, 2.5–3 m above the ground. Adjacent sites were 0.5–2.75 km apart. Boxes were checked and bats ringed approximately four times a year in March–October from 1977 to 1993.
A replicated study in June–September 1997 and 1998 in coniferous forests in Oregon, USA (Arnett & Hayes 2000) found that bats used 13 out 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. Day roosting bats were counted with a spotlight and guano traps were checked weekly. Bridges varied in size from 230–475 m width, 11–27 m length, and 3–6 m above the water.
A replicated study in 1991–1993 in an urban area of Pennsylvania, USA (Brittingham & Williams 2000) found that big brown bats Eptesicus fuscus and little brown bats Myotis lucifugus used pairs of bat boxes at five out of nine sites when they had been excluded from buildings. At the four sites where boxes were not used, bats either re-entered the building, found new roosts in nearby buildings or disappeared. All bat boxes that were occupied were positioned in a south-eastern or south-western aspect and received at least seven hours of direct sunlight. Unoccupied bat boxes received less than five hours of direct sunlight. More big brown bats (at one site) were found in horizontal bat boxes (minimum of 47 bats emerging/night early summer, minimum of 67 emerging/night late summer) than vertical boxes across the summer (no bats emerging early summer, minimum of 11 bats emerging/night late summer). Little brown bats (at five sites) were found more in horizontal boxes in early summer (average 186 minimum bats emerging/night/site from horizontal boxes, average 79 minimum bats emerging/night/site from vertical boxes) and more in vertical boxes in late summer (average 58 minimum bats emerging/night/site from horizontal boxes, average 132 minimum bats emerging/night/site from vertical boxes). Differences were not tested for statistical significance. Horizontal bat boxes had significantly higher maximum temperatures than vertical boxes in the afternoon (average 2°C warmer) and early evening (average 1°C warmer). Each site had a maternity colony of at least 30 bats that were excluded from the buildings by homeowners from 1991 to 1992. Homeowners at each site were provided with a pair of wooden bat boxes (76 cm x 30 cm x 18 cm) and instructed to install one horizontally (30 cm tall) and one vertically (76 cm tall) side by side on the building within 5 m of the primary bat entrance.
A replicated study in April–November 1996 in deciduous forest in Bavaria, Germany (Kerth et al 2001) found that 21 marked female Bechstein’s bats Myotis bechsteinii within a colony roosted in 43 of 75 bat boxes (57% occupancy). Out of 23 pairs of black and white boxes, females roosted significantly more often during and after lactation in black bat boxes (186 ‘bat days’ [the sum of the number of individuals found over all survey days] during lactation, 90 ‘bat days’ after lactation) than white bat boxes (134 ‘bat days’ during lactation, 22 ‘bat days’ after lactation), and more in sun exposed boxes (276 ‘bat days’ during lactation, 112 ‘bat days’ after lactation) than shaded boxes (44 ‘bat days’ during lactation, no ‘bat days’ after lactation). Before giving birth, females roosted more in shaded locations (111 ‘bat days’) than sunny locations (43 ‘bat days’) but did not show a significant preference for black or white boxes (76 and 78 ‘bat days’ respectively). Boxes of each colour were significantly warmer in sunny locations (black average 22°C, white average 20°C) than boxes in the shade (black average 18°C, white average 17°C), and black bat boxes were significantly warmer than white boxes. Seventy five bat boxes (type Schwegler 2FN) were originally installed between 1987 and 1993 over a 0.4 km2 area. In 1996, 52 boxes were hung in pairs (one painted white, the other remained black) side by side on 26 trees (half at shaded sites, half on trees exposed to the sun). All bat boxes were checked daily and roost temperatures taken.
A replicated study in March to October 1996–1998 in a 60 ha 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. Larger bat boxes were occupied significantly more (9%) than smaller bat boxes (7%). The height and orientation of boxes did not significantly affect bat occupation. A quarter of bat boxes were parasitized with invertebrates (arachnids and hymenoptera), had nesting birds in them, or were damaged by arboreal birds, with a higher proportion of large bat boxes affected (28%, small boxes 16%). 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 2134 total box visits were carried out from August to October in 1996 and March to October 1997 and 1998. Bats captured in the boxes were brown long-eared Plecotus auritus (176 out of 178) and two common pipistrelles Pipistrellus pipistrellus. Recordings made with bat detectors in the study area showed the presence of Leisler’s bats Nyctalus leisleri, Daubenton’s bats Myotis daubentonii, Natterers’ bats Myotis nattereri and serotine bats Eptesicus serotinus.
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 from July to August in 1999 and 2000. Bats were observed on two occasions: two big brown bats Eptesicus fuscus in a wood roost, and a maternity colony of at least seven long-eared myotis Myotis evotis in a resin roost.
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 more 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. Four marsupials occupied 30% of bat boxes: feathertail gliders Acrobates pygmaeus (16 boxes), sugar gliders Petaurus breviceps (10 boxes), squirrel gliders Petaurus norfolcensis (four boxes) and the yellow-footed marsupial mouse Antechinus flavipes (one box). 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 site 3 m or 6 m above the ground, evenly spaced and in different aspects. Boxes at each site were checked five to nine times between April 1996 and November 2000.
A small replicated study in May–June 2001 in Alentejo and Algarve, Portugal (Lourenço & Palmeirim 2004) found that soprano pipistrelles Pipistrellus pygmaeus used six of nine bat boxes present at three urban sites. 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 significantly to those in roosts in the attics of nearby buildings. Three bat boxes (painted black, grey or white, all three compartment Bat Conservation International models) were placed facing south side by side at each site 20 m from maternity roosts. Bat box temperatures were monitored using sensors and data loggers. Bat boxes were checked and emerging bats counted weekly.
A replicated study in May–September 1997 in Colorado, USA (White 2004) found bats occupying 11 out of 95 bat houses (12% occupancy rate) at multiple sites. Big brown bats, Eptesicus fuscus occupied 6 boxes, Myotis spp. two boxes and little brown bats, Myotis lucifugus one box. All bat houses were occupied by one or two individuals, except one colony of 20 big brown bats. In areas where bats roosted prior to bat house installation, occupancy rate increased to 64%. The likelihood of bat house occupation increased when bat houses had large landing areas, were mounted on buildings rather than trees, and in areas of low canopy cover and human disturbance. No bat houses mounted on trees were occupied. Bat houses were installed in preserved areas (47), remote campgrounds (8), rural farmland (39) and irrigated farmland (1) placed on trees (40), buildings (42) and poles (13). Details of the locations of occupied bat houses are not given. Bat houses used were different sizes, colours and designs. Bat houses were checked for occupancy and guano on the ground below at 15 or 30 day intervals.
A replicated study in 1998–2001 in three different forest stands (pine, beech and oak-beech) in a mixed forest in Poland (Ciechanowski 2005) found that an average of four of 102 bat boxes (4%) were occupied by bats during each box check (Nathusius’ pipistrelles Pipistrellus nathusii, or brown long-eared bats Plecotus auritus roosting individually or in groups). The number of boxes occupied and the number of Nathusius’ pipistrelles occupying bat boxes was significantly higher in the pine stand (maximum nine boxes occupied, 36 bats/100 boxes) than the two deciduous stands (maximum two boxes and 1 bat/100 boxes in beech, one box and 0.2 bats/100 boxes in oak-beech). Bat boxes were occupied within two months in the pine stand, but more slowly in the beech and oak-beech stands (13 months or more). In 1998, 34 wooden bat boxes (Stratmann design, 40 cm x 13 cm x 4 cm) were installed per stand. 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 plot was checked additionally twice in July–August 2000. Birds nested in one bat box, woodpeckers destroyed three boxes, and wasp nests were found in 12 boxes.
A replicated study in 1999–2004 in 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%. During at least one of the four breeding seasons recorded, 96% of boxes were occupied and 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 higher abundance 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). Abundance was low in 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, the boxes were checked on 16 occasions. Bats were counted in boxes or upon emergence when numbers were too numerous to count within the box.
A replicated study in 1997–2004 in 66 rural agricultural areas in California, USA (Long et al 2006) found that bats used 141 out of 186 available bat houses, with an overall occupancy rate of 76% (48% by groups and 28% by individuals). Five bat species were recorded, with the Brazilian free-tailed bat, Tadarida brasiliensis and Myotis spp. accounting for the majority of bat house occupancy (67% and 26% respectively). Size, colour and height of the bat houses did not affect bat occupancy. Bat colonies (average of 64 bats) were more likely to use bat houses that were shaded or exposed to the morning sun, mounted on structures such as houses and that were within a quarter of a mile of a water source. Individual bats were more likely to use bat houses that were mounted on poles and exposed to the full or afternoon sun. Bat houses were not likely to become occupied if colonies had not moved in within the first two years. All bat houses were plywood with one or more chambers and categorized as small (< 90 cm roosting space) or large (> 90 cm roosting space). Bat houses were mounted singly, side by side or back to back on barns, sheds, poles, bridges or silos. All bat houses were placed within 4 km of a water source and 2–9.5 m high. Houses were placed in different orientations and painted light, medium and dark colours. Bat houses were inspected yearly, with occurrence, number and bat species recorded.
A replicated study in 1992–1999 in several small woodlots surrounded by agricultural, industrial and residential areas in Indiana, USA (Whitaker et al 2006) found that four out of nine artificial roost designs were used by a total of 709 bats over the seven year study. The designs 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 Myotis septentrionalis using them most frequently (690 out 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 m x 1.8 m. Tarpaper boxes (30) were wooden (0.9 m 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 up in trees. The majority of the artificial roosts were in shaded areas. All structures were checked at least once a year and bats were captured and identified to species when bats were present.
A replicated, controlled study in 2000–2006 in an area of tropical wet forest and pasture in the Caribbean lowlands, Costa Rica (Kelm et al 2008) found that bats colonized all 45 artificial roosts installed in two different habitats (22 in a continuous forest habitat and 23 in small fragments or tree stands in agricultural habitat). Average colonization time was three weeks in both continuous forest and disturbed habitat. Ten bat species occupied the artificial roosts. Five nectar or fruit-eating bat species colonized the artificial roosts permanently in group sizes similar to those in natural roosts (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, chestnut short-tailed bat Carollia castanea). Artificial roosts were simulated hollow tree trunks made from sawdust concrete slabs forming a square box and installed in the shade. Twenty-four roosts were 54 cm x 54 cm x 194 cm and 21 roosts were 74 cm x 74 cm x 154 cm. Natural roosts were found by a systematic line transect search. Roosts were frequently inspected (every 42 days on average) and bats were captured on 105 occasions using mist nets near roosts for identification.
A replicated study in 2005–2008 in a mixed forest in Poland (Lesiński et al 2009) found an increase in the occupancy rate of 70 bat boxes and the number of individuals using the bat boxes (from 17 bats, 13% occupancy in 2005 to 42 bats, 49% occupancy in 2006). Four bat species were found in the boxes: greater mouse-eared bat Myotis myotis, common noctule Nyctalus noctula, Nathusius’ pipistrelle Pipistrellus nathusii and brown long-eared bat Plecotus auritus. In 2007–2008, 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). The highest occupancy rate of all bat species (33 of 69 boxes) and number of individuals (128) was during August. In 2003, 70 wooden Stratmann bat boxes (internal dimensions 25 cm x 25 cm x 7 cm) were installed on trees up to 30 m from a forest road 2.5–3 m above the ground with a south-easterly orientation. In 2005 and 2006, boxes were checked once in August and from March 2007 to February 2008 boxes were checked monthly.
A replicated study in May–October 2009 in 13 different mixed or pine forests in East Lithuania (Baranauskas 2010) found that six bat species used bat boxes of four designs (occupancy rates are not given). The most abundant bat species that used the bat boxes were Nathusius’ pipistrelle Pipistrellus nathusii (79% of all bats recorded and occupying boxes at all 13 sites) and soprano pipistrelle Pipistrellus pygmaeus (18% of all bats and occupying boxes at seven of the 13 sites). The remaining bat species, the 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 the bat boxes. Breeding colonies of Nathusius’ pipistrelles and soprano pipistrelles were found in standard and four/five chamber bat boxes. Flat bat boxes were not used by breeding colonies, but were the only type of bat box in which all six species were found. In total, 504 bat boxes (30–60 installed in each area) were tested: 250 standard boxes (25 cm x 15 cm x 10 cm), 168 flat boxes (35 cm x 4 cm x 15 cm), 27 four chamber (30 cm x 15 cm x 15 cm), and 59 five chamber boxes (55 cm x 35 cm x 19.5 cm). Standard and flat wooden bat boxes were installed in 2004–2008 and four/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 away from each other. Bat boxes were checked six times between May and October 2009. The number of bats present was recorded upon emergence and using bat detectors.
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 bat boxes (90 in total) varied between 9% in 2006 to 18% in 2007 (12% in 2008 and 17% in 2009). The highest proportion of bat boxes occupied at one site was 27% (seven of 26 boxes). Four bat species occupied the bat boxes: Pipistrellus spp., brown long-eared bat Plecotus auritus, Natterer’s bat Myotis nattereri and whiskered bat Myotis mystacinus/Brandt’s bat Myotis brandti. In 2006, birds occupied 37% of bat boxes across the sites (most frequently blue tit Cyanistes (Parus) caeruleus and great tit Parus major). The installation of bird boxes (2–15 boxes/site) in February 2008 reduced bird occupancy of bat boxes to 17% across the sites. Woodland sites were small (< 3 ha) linear blocks with trees less than 40 years old. In 2005–2006, bat boxes (Schwegler 2FN, 16 cm diameter x 36 cm high) were installed in sets of three per tree, 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 replicated, controlled study in May–October 2011 and 2012 in ancient, lowland mixed deciduous woodland in Buckinghamshire, UK (Dodds & Bilston 2013) found that brown long-eared bats Plecotus auritus and Natterer’s bats Myotis nattereri favoured three of five bat box types: 1FS (33% of total occupations), 2FN (29%), and 2F (27%). The 1FF boxes were rarely used (11%), and the Apex box was not used at all. There was seasonal variation in bat occupancy rates, with a suggestion that nesting birds outcompeted bats for the 1FS boxes between May and June. Groups of Schwegler 2F, 2FN, 1FS, 1FF woodcrete boxes and 1 wooden Apex box were erected in 13 locations (five around each tree). The box clusters were located on trees with a proven history of good box occupancy levels - part of a 10 year woodland bat box scheme. The group positions were evenly spaced along a transect line of 300 m in homogenous habitat of predominantly semi mature pendunculate oak Quercus robur and ash Fraxinus excelsior closed canopy with lapsed hazel Corylus avellana coppice understorey. Box temperatures were compared and found to be similar, and consistent with the ambient temperature due to the shaded nature of the sites. Aspect was experimentally controlled by progressively rotating the box positions around the tree. Over the two years, 156 box checks were made for each box type, with a total of 149 bat box occupations. Differences between species were discussed in the study, but were not supported by statistical analysis and sample sizes were small.
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