Age of enlightenment: long-term effects of outdoor aesthetic lights on bats in churches

Published source details Rydell J., Eklöf J. & Sánchez-Navarro S. (2017) Age of enlightenment: long-term effects of outdoor aesthetic lights on bats in churches. Royal Society Open Science, 4, 161077.
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This study is summarised as evidence for the following.

	Action	Category
	Leave bat roosts and roost entrances unlit Action Link

Leave bat roosts and roost entrances unlit

A replicated, before-and-after study in 1980–2016 of 36 rural churches in southwestern Sweden (Rydell et al 2017) found that all of 13 unlit churches continued to be used by brown long-eared bat Plecotus auritus colonies over 25 years, but bat colonies abandoned their roosts at 14 of 23 churches that were either partly or fully lit with floodlights. Unlit churches continued to be used by more bat colonies (13 of 13, 100%) than partly lit churches (7 of 13 bat colonies, 54%) or fully lit churches (2 of 10 bat colonies, 20%). Fewer bat colonies abandoned their roosts at partly lit churches (6 of 13, 46%) than at fully lit churches (8 of 10, 80%). All 36 churches were surveyed during one daytime visit in summer between 1980 and 1990 before lights were installed. Floodlights (1–4 lights) were installed on 23 churches (date of installation not reported). Lights were directed upwards illuminating the walls and tower of each church either on one side (partly lit, 13 churches) or from all directions (fully lit, 10 churches). Thirteen churches were left unlit. Surveys were repeated at each of 36 churches in May–October 2016 after lighting had been installed. Other confounding effects, such as changes in habitat and food availability in the wider landscape, were not accounted for.

(Summarised by: Anna Berthinussen)