Bat-friendly cities: urban planning recommendations from new citizen science study

The researchers, who collaborated with citizen scientists to monitor Berlin’s bats, recommend minimising artificial light at night and creating good access for bats to forest patches and water bodies.

Urbanisation is one of the biggest drivers of biodiversity loss. Global urban area has doubled in the past 30 years and, by 2050, 68% of the world’s population is expected to live in urban areas¹. Given the huge growth in urban areas, conservation measures are needed to make cities more suitable for wildlife.

To inform such measures, this study investigated the effects of urban landscape features on bats. Urbanisation has contributed to severe declines in many bat species around the world by removing mature forests, green spaces and water bodies – all vital habitats for bats’ insect prey. Impervious surfaces (such as buildings and roads) and plant-free areas in cities fragment existing habitats.  In addition, many bat species prefer to avoid light at night.

Together with over 200 citizen scientists, the researchers recorded bat vocalisations at 600 sites in urban and suburban districts of Berlin over the period 2019–2020. This generated a rich set of data that allowed the researchers to calculate how different landscape features and levels of artificial light influence the occurrence probability of bats at each site (i.e. the likelihood that a species will occur).

The results show how diverse ecological features – at the landscape, rather than local level – support diverse species. For instance, more Pipistrellus species were recorded at sites with higher levels of tree canopy and where large forest patches were within a 1500 metre radius. For soprano and Nathusius’ pipistrelles (Pipistrellus pygmaeus and P. nathusius), landscape-scale canopy cover within a 1000-metre and 500-metre radius, respectively was more important to their occurrence probability than local-scale cover (within 100 metres).

Occurrence probability of Pipistrellus species (although not common pipistrelles (P. pipistrellus)) increased with larger water surface area, at both the local and the landscape scale, and in areas close to water bodies. At the local scale, all species tended to avoid areas with high levels of impervious surfaces, such as streets and buildings, most likely because they offer little prey for the bats. As the effects of impervious surfaces were comparably small, however, the researchers say that as long as other habitat requirements are met, the level of sealed surfaces does not appear to matter to bat species.

Artificial light had negative effects on all bat species. Notably, occurrence probability of soprano pipistrelles dropped to near zero in areas where artificial light was just half the highest levels measured at the study sites. In fact, among all environmental factors considered in the study, increased light levels had the most negative effect on the occurrence of mouse-eared bats (Myotis spp.) and soprano pipistrelles.

The researchers say that their findings highlight the importance of reducing night lighting as far as possible. Dimming protocols and motion-activated lighting could play an important role here. To help bats fly around in unlit areas, the researchers recommend connecting fragments of forest and water bodies with uninterrupted vegetated corridors (such as residential gardens and tree lines) without lighting.

They point to separate research showing that even ‘fussy’ specialist species, which depend upon very specific conditions, can live in urban environments if patches of suitable habitat are large enough and well connected.

They further stress that deciduous woodlands, with many old trees and standing deadwood, are particularly important because they provide homes for bats and many of the insects they eat.

While the researchers accept that even improved urban ecosystems cannot meet the needs of all species, their recommended measures would still increase the value of urban spaces for many bats and other wildlife. This is particularly true for cities surrounded by intensively farmed land with few insects.

Footnote:

1. See: United Nations Department of Economic and Social Affairs. (Available from: 2018 Revision of World Urbanization Prospects | Multimedia Library - United Nations Department of Economic and Social Affairs [Accessed 31 October 2022].

Source:

Lewanzik, D., Straka, T.M., Lorenz, J., Marggraf, L.., Voigt-Heucke, S., Schumann, A., Brandt, M., Voigt, C.C. (2022) Evaluating the potential of urban areas for bat conservation with citizen science data. Environmental Pollution, 297: 118785.

To cite this article/service:

“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.

Notes on content:

The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.