Action: Create or restore bat foraging habitat in urban areas
Key messagesRead our guidance on Key messages before continuing
- Three studies evaluated the effects of creating or restoring bat foraging habitat in urban areas on bat populations. One study in the USA evaluated restored forest fragments, and two studies in the UK and USA evaluated green roofs.
COMMUNITY RESPONSE (1 STUDY)
- Richness/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.
POPULATION RESPONSE (3 STUDIES)
- Abundance (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 significantly 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.
BEHAVIOUR (0 STUDIES)
Providing foraging habitat for bats in urban areas may reduce the impact of residential and commercial development. Existing foraging sites may be protected, or be replaced with suitable alternatives such as parks, woodland and wetlands. Bat activity was found to be higher in large parks in Mexico City than in natural forest or other urban habitats, although the number of species was higher in natural forest (Avila-Flores & Fenton 2005). Habitats should also be appropriately managed for bats, for example a study in Australia found more bat species in urban green spaces with a higher density of large trees and native plants (Threlfall et al. 2016). See also ‘Protect greenfield sites or undeveloped land in urban areas’.
Avila-Flores R. & Fenton M.B. (2005) Use of spatial features by foraging insectivorous bats in a large urban landscape. Journal of Mammalogy, 86, 1193–1204.
Threlfall C.G., Williams N.S.G., Hahs A.K. & Livesley S.J. (2016) Approaches to urban vegetation management and the impacts on urban bird and bat assemblages. Landscape and Urban Planning, 153, 28–39.
Supporting evidence from individual studies
A site comparison study in 2004–2005 in nine forest fragments within the Chicago metropolitan area, USA (Smith & Gehrt 2010) found that two of seven restored forest fragments had higher bat activity than two unrestored forest fragments. Bat activity was higher in two forest fragments that had been restored with multiple prescribed burns, invasive plant species removal and snag recruitment (average 7–19 bat passes/survey) than in two control sites with no restoration (average 1–4 bat passes/survey). Bat activity was similar between control sites and five other forest fragments that had been restored with multiple prescribed burns and various combinations of invasive species removal, snag recruitment and deer population control (1–6 bat passes/survey). Six bat species were recorded in total (see original paper for data for individual species). Fire suppression over the last 100 years had altered the structure of the nine forest fragments (10–260 ha in size). Seven of the nine forest fragments were being restored to open up the canopy, reduce tree density and remove invasive plant species. At each of nine sites, four bat detectors recorded bat activity for 4 h from sunset for five nights/year in June–September 2004 and May–August 2005.
A replicated, controlled, site comparison study in 2010 of 39 green roofs in Greater London, UK (Pearce & Walters 2012) found that ‘biodiverse’ green roofs had higher bat activity than conventional roofs, but ‘sedum’ green roofs had similar or lower bat activity than conventional roofs. When a small amount (<33%) of natural foraging habitat was located within 100 m of roofs, bat activity was higher over ‘biodiverse’ green roofs (average 7 bat passes/night) than conventional roofs (average 1.3 bat passes/night), and similar over ‘sedum’ green roofs (average 1 bat pass/night) and conventional roofs. However, when higher amounts of natural habitat cover were located within 100 m of roofs (33–66%), bat activity was similar between ‘biodiverse’ green roofs (average 10 bat passes/night) and conventional roofs (average 12 bat passes/night), and lower over ‘sedum’ green roofs (average 4 bat passes/night). Four bat species or species groups were recorded in total (see original paper for data for individual species). All green roofs had shallow substrate (20–200 mm). ‘Biodiverse’ roofs were planted with a variety of wild flowers, herbs, sedums, mosses and grasses. ‘Sedum’ roofs were planted with low-growing succulent plants. Conventional roofs were flat or shallow pitched with bitumen felt or paving slabs. Bat activity was recorded over each of 13 biodiverse, nine sedum and 17 conventional roofs for seven full nights in May–September 2010.
A replicated, controlled, paired sites study in 2013 of four paired roofs in New York City, USA (Parkins & Clark 2015) found higher activity over green roofs than conventional roofs for three of five bat species, but no difference in species richness. Five bat species were recorded over both green and conventional roofs. The average number of bat passes/night was higher over green roofs than conventional roofs for the eastern red bat Lasiurus borealis (green: 253; conventional: 128), big brown bat Eptesicus fuscus (green: 11; conventional: 0.6), and tricoloured bat Perimyotis subflavus (green: 12; conventional: 2). The average number of bat passes/night was similar over green and conventional roofs for the hoary bat Lasiurus cinereus (green: 56; conventional: 57) and silver-haired bat Lasionycteris noctivagans (green: 33; conventional: 24). Paired roofs were six or eight stories high and were located within one block of each other. One of each pair was a green roof with a waterproof membrane with growing substrate covered in vegetation. The other of each pair was a conventional roof with a ‘blacktop’ or concrete roofing material with no vegetation. Bat activity was recorded between May and September in 2013 with a bat detector deployed in the centre of each roof.
- Smith D.A. & Gehrt S.D. (2010) Bat response to woodland restoration within urban forest fragments. Restoration Ecology, 18, 914-923
- Pearce H. & Walters C.L. (2012) Do green roofs provide habitat for bats in urban areas? Acta Chiropterologica, 14, 469-478
- Parkins K.L & Clark J.A (2015) Green roofs provide habitat for urban bats. Global Ecology and Conservation, 4, 349-357