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What Works in Conservation 2021

 | 
William Junior Sutherland
, 
Lynn V. Dicks
, 
Silviu O. Petrovan
, 
et al.

2. Bat conservation

2.1 Threat: Residential and commercial development

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Likely to be beneficial

Retain existing bat roosts and access points within developments

1Three studies evaluated the effects of retaining existing bat roosts and access points within developments on bat populations. Two studies were in the UK and one was in Ireland.

2COMMUNITY RESPONSE (0 STUDIES)

3POPULATION RESPONSE (0 STUDIES)

4BEHAVIOUR (3 STUDIES)

5Use (3 studies): One before-and-after study in Ireland found similar numbers of brown long-eared bats roosting within an attic after existing access points were retained during renovations. One replicated, before-and-after study in the UK found that four of nine bat roosts retained within developments were used as maternity colonies, in two cases by similar or greater numbers of bats after development had taken place. One review in the UK found that bats used two-thirds of retained and modified bat roosts after development, and retained roosts were more likely to be used than newly created roosts. Assessment: likely to be beneficial (effectiveness 77 %; certainty 60 %; harms 0 %).

https://www.conservationevidence.com/​actions/​947

Unknown effectiveness

Change timing of building work

6One study evaluated the effects of changing the timing of building work on bat populations. The study was in Ireland.

7COMMUNITY RESPONSE (0 STUDIES)

8POPULATION RESPONSE (0 STUDIES)

9BEHAVIOUR (1 STUDY)

10Use (1 study): One before-and-after study in Ireland found that carrying out roofing work outside of the bat maternity season, along with retaining bat access points, resulted in a similar number of brown long-eared bats continuing to use a roost within an attic.

11Assessment: unknown effectiveness (effectiveness 50 %; certainty 12 %; harms 0 %).

https://www.conservationevidence.com/​actions/​950

Create alternative bat roosts within developments

12Eleven studies evaluated the effects of creating alternative bat roosts within developments on bat populations. Nine studies were in Europe and two were in the USA.

13COMMUNITY RESPONSE (0 STUDIES)

14POPULATION RESPONSE (0 STUDIES)

15BEHAVIOUR (11 STUDIES)

16Use: (11 studies): Two replicated studies in the USA and UK found that bats did not use any of the alternative roosts provided in bat houses or a purpose-built bat wall after exclusion from buildings. Three studies (two replicated) in the USA and UK and one review in the UK found that bat boxes or bat lofts/barns were used by bats at 13–74 % of development sites, and bat lofts/ barns were used by maternity colonies at one of 19 development sites. Three of five before-and-after studies in Portugal, Ireland, Spain and the UK found that bat colonies used purpose-built roosts in higher or similar numbers after the original roosts were destroyed. The other two studies found that bats used purpose-built roosts in lower numbers than the original roost. One review in the UK found that new bat boxes/lofts built to replace destroyed roosts were four times less likely to be used by returning bats than roosts retained during development.

17Assessment: unknown effectiveness (effectiveness 45 %; certainty 35 %; harms 0 %).

https://www.conservationevidence.com/​actions/​949

Create or restore bat foraging habitat in urban areas

18Three studies evaluated the effects of creating or restoring bat foraging habitat in urban areas on bat populations. One study in each of the UK and USA evaluated green roofs and one study in the USA evaluated restored forest fragments.

19COMMUNITY RESPONSE (1 STUDY)

20Richness/diversity (1 study): One replicated, controlled, site comparison study in the USA found no difference in species richness over green roofs and conventional unvegetated roofs.

21POPULATION RESPONSE (3 STUDIES)

22Abundance (3 studies): One site comparison study in the USA found higher bat activity (relative abundance) in two of seven restored forest fragments in urban areas than in two unrestored forest fragments. One replicated, controlled, site comparison study in the UK found greater bat activity over ‘biodiverse’ green roofs than conventional unvegetated roofs, but not over ‘sedum’ green roofs. One replicated, controlled, site comparison study in the USA found greater bat activity for three of five bat species over green roofs than over conventional unvegetated roofs.

23BEHAVIOUR (0 STUDIES)

24Assessment: unknown effectiveness (effectiveness 60 %; certainty 36 %; harms 0 %).

https://www.conservationevidence.com/​actions/​954

Exclude bats from roosts during building work

25One study evaluated the effects of excluding bats from roosts during building work on bat populations. The study was in the UK.

26COMMUNITY RESPONSE (0 STUDIES)

27POPULATION RESPONSE (0 STUDIES)

28BEHAVIOUR (1 STUDY)

29Behaviour change (1 study): One replicated, before-and-after study in the UK found that excluding bats from roosts within buildings did not change roost switching frequency, core foraging areas or foraging preferences of soprano pipistrelle colonies.

30Assessment: unknown effectiveness (effectiveness 45 %; certainty 23 %; harms 17 %).

https://www.conservationevidence.com/​actions/​1930

Legally protect bats during development

31Four studies evaluated the effects of legally protecting bats by issuing licences during development on bat populations. The four studies were in the UK. COMMUNITY RESPONSE (0 STUDIES)

32POPULATION RESPONSE (0 STUDIES)

33BEHAVIOUR (2 STUDIES)

34Change in human behaviour (2 studies): One review in the UK found that the number of development licences for bats more than doubled over three years in Scotland. One review in the UK found that 81 % of licensees did not carry out post-development monitoring to assess whether bats used the roost structures installed.

35OTHER (3 STUDIES)

36Impact on bat roost sites (3 studies): One review in the UK found that licenced activities during building developments had a negative impact on bat roosts, with 68 % of roosts being destroyed. One replicated, before-and-after study in the UK found that five of 28 compensation roosts provided under licence were used, and two by similar or greater numbers of bats after development. One review in the UK found that 31–67 % of compensation roosts provided under licence were used by bats.

37Assessment: unknown effectiveness (effectiveness 45 %; certainty 35 %; harms 10 %).

https://www.conservationevidence.com/​actions/​1935

Protect brownfield or ex-industrial sites

38One study evaluated the effects of protecting brownfield or ex-industrial sites on bat populations. The study as in the USA.

39COMMUNITY RESPONSE (1 STUDY)

40Richness/diversity (1 study): One study in the USA found that five bat species were recorded within a protected urban wildlife refuge on an abandoned manufacturing site.

41POPULATION RESPONSE (0 STUDIES)

42BEHAVIOUR (0 STUDIES)

43Assessment: unknown effectiveness (effectiveness 40 %; certainty 20 %; harms 0 %).

https://www.conservationevidence.com/​actions/​953

Relocate access points to bat roosts within developments

44Two studies evaluated the effects of relocating access points to bat roosts within building developments on bat populations. One study was in Ireland and one in the UK.

45COMMUNITY RESPONSE (0 STUDIES)

46POPULATION RESPONSE (0 STUDIES)

47BEHAVIOUR (2 STUDIES)

48Use (2 studies): One before-and-after study in Ireland found that fewer brown long-eared bats used a roost after the access points were relocated, and no bats were observed flying through them. One before-and-after study in the UK found that few lesser horseshoe bats used an alternative access point with a ‘bend’ design to re-enter a roost in a building development, but the number of bats using the roost increased after an access point with a ‘straight’ design was installed.

49Assessment: unknown effectiveness (effectiveness 45 %; certainty 32 %; harms 10 %).

https://www.conservationevidence.com/​actions/​946

No evidence found (no assessment)

50We have captured no evidence for the following interventions:

  • Educate homeowners about building and planning laws relating to bats to reduce disturbance to bat roosts
  • Increase semi-natural habitat within gardens
  • Install sound-proofing insulation between bat roosts and areas occupied by humans within developments
  • Plant gardens with night-scented flowers
  • Protect greenfield sites or undeveloped land in urban areas.

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