Bats and urbanisation: on the road to coexistence

Urbanisation can be described as the most ecologically damaging change in land use, posing significant threats to global biodiversity. Most bat species are threatened by urbanisation, due to the lack of vegetation, scarcity of prey, artificial lighting, noise and generic disturbance in urban areas. However, buildings can also offer important roosting sites to bats, and some species have adapted to forage near street lamps. To date, our understanding of what influences bat species in urban habitats is still very limited, and further studies are needed focusing on the effects of urbanisation on bats, in order to apply the necessary preventive measures to make the coexistence between bats and humans possible. In this study, data from a citizen science project were used to quantify the importance of fine-scale habitat configuration and composition for bats, focusing on urban areas and their surroundings. Specifically, relationships between bat distribution and activity in built-up areas in Norfolk (UK) were analysed in relation to fine-scale remote sensing data representing the impervious surface (i.e. buildings and roads), waterbodies (drains, lakes and rivers) and tree-cover density. Furthermore, hypothetical future scenarios were considered, assuming an increase in impervious surface, woodland surface, or number of impervious patches, and the effects of these changes on bat species were quantified. Over a million bat recordings from four years of monitoring (2013-2016) were used in this study. The complex interspecific variability in habitat selection by different bat species was highlighted. Lakes and discontinuous woodland were the most preferred habitats. Urban areas were the least selected habitat, confirming urbanisation as the most ecologically damaging land use type. However, the way in which urbanisation affected bat populations greatly depended on the species considered. Species of the genus Myotis, barbastelle and brown long-eared bat were the most impacted, whereas species of the genera Nyctalus and Pipistrellus, as well as serotine, were less impacted. Potential evidence of Nathusius' pipistrelle migratory behaviour was detected. Bats were shown to be more capable of exploiting rural areas than large urban centres, probably due to lower disturbance, lower levels of artificial lighting, a greater amount of old buildings and greater proximity to foraging sites. Management plans aimed at improving the suitability of built up areas for bats would therefore have a much more positive effect if performed in small urban centres, suburbs and villages. The ecological land-use complementation approach, which involves the allocation of different types of urban green patches in close proximity to each other, seems the most sensible solution to encourage the exploitation of large urban areas by bats. Connections among these strategic green areas in cities, rural areas and natural habitats should be improved. New buildings should be located in already existing urban areas, with no creation of new urban patches, in order to avoid disturbance in potential commuting or foraging sites. Expansion of discontinuous woodland surface should be encouraged, while the preservation of unmanaged areas within large plantations, as well as the use of bat boxes, would support the exploitation of continuous woodland by bats.