Conservation Evidence strives to be as useful to conservationists as possible. Please take our survey to help the team improve our resource.

Providing evidence to improve practice

Individual study: The effects of illuminating the roost entrance on the emergence behaviour of Pipistrellus pygmaeus

Published source details

Downs N.C., Beaton V., Guest J., Polanski J., Robinson S.L. & Racey P.A. (2003) The effects of illuminating the roost entrance on the emergence behaviour of Pipistrellus pygmaeus. Biological Conservation, 111, 247-252


This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Leave bat roosts and roost entrances unlit Bat Conservation

 replicated, controlled study in 2000 at two bat roosts within buildings in Aberdeenshire, UK (Downs et al. 2003) found that when roosts were left unlit more soprano pipistrelles Pipistrellus pygmaeus emerged than when roosts were illuminated with white or blue lights at both roosts, or red lights at one of two roosts. More soprano pipistrelles emerged when both roosts were left unlit (average 40 and 90 bats) than when roosts were illuminated with white light (2 and 24 bats) or blue light (6 and 62 bats). Red light only had an effect at one of two roosts. More bats emerged at one roost when it was unlit (40 bats) than when it was illuminated with red light (13 bats), but at the second roost similar numbers emerged with (72 bats) and without red light (90 bats). A hand-held halogen light with coloured filters was placed within 3–5 m of each of the two roosts. Over 20 nights in July–August 2000, nights with roosts unlit and nights with lighting were alternated. On nights with lighting, white, blue and red lights were rotated in a random order and changed every 30 seconds. On each of 20 nights, the number of bats emerging per 30 second interval was counted at dusk.

(Summarised by Anna Berthinussen)

Use low intensity lighting Bat Conservation

A replicated, controlled study in 2000 at two bat roosts within buildings in Aberdeenshire, UK (Downs et al. 2003) found that reducing the intensity of red light by adding 2–3 filters resulted in more soprano pipistrelles Pipistrellus pygmaeus emerging from the roosts than when only one filter was used. More soprano pipistrelles emerged from both roosts when red lights had two (73 and 72 bats) or three filters (76 and 127 bats) placed over them than when only one filter was used (35 and 26 bats). Over four nights in July–August 2000, each of two roosts were surveyed for one night with no lighting and for one night with red light of different intensities. A hand-held halogen light with 1–3 red filters was placed within 3–5 m of each of the two roosts. The number of filters (1–3) used on the red lights were rotated in a random order and changed every 30 seconds. On each of four nights, the number of bats emerging per 30 second interval was counted at dusk.

(Summarised by Anna Berthinussen)

Use red lighting rather than other lighting colours Bat Conservation

A replicated, controlled study in 2000 at two bat roosts within buildings in Aberdeenshire, UK (Downs et al. 2003) found that when roosts were illuminated with red light more soprano pipistrelles Pipistrellus pygmaeus emerged than when roosts were illuminated with white light, but no difference was found between red and blue lights. At both roosts, more bats emerged when the roost entrance was illuminated with red light (13 and 72 bats) than when it was illuminated with white light (2 and 24 bats). No difference was found between red and blue light (6 and 62 bats emerging) at either roost. A hand-held halogen light with coloured filters was placed within 3–5 m of each of the two roosts. Over 20 nights in July–August 2000, nights with roosts unlit and nights with lighting were alternated. On nights with lighting, white, blue and red lights were rotated in a random order and changed every 30 seconds. On each of 20 nights, the number of bats emerging per 30 second interval was counted at dusk.

(Summarised by Anna Berthinussen)