Restrict artificial lighting in caves and around cave entrances
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Artificial lighting may disturb bats within caves, causing arousal during hibernation or roost abandonment. Lighting restrictions are often used alongside other interventions to reduce disturbance. See also ‘Impose restrictions on cave visits’.
Supporting evidence from individual studies
A controlled study in 1997–1998 in one cave in Arizona, USA (Mann et al 2002) found that using low intensity white lights or red lights within the cave resulted in fewer flights by roosting cave myotis bats Myotis velifer than when full white lighting was used, but the number of bat movements was similar between all three light treatments. When compared with full intensity white lighting, low intensity white lights or red lights resulted in fewer take-offs (full white: 23; low white: 12; red: 14) and landings (full white: 20; low white: 11; red: 12). However, the overall activity of the colony (all bat movements) did not differ between the three light treatments (full white: 64% of the colony active; low white: 62%; red: 63%). All three measures of bat activity were lowest when no lighting was used (take-offs: 9; landings: 9; proportion active: 54%). A colony of 1,000 cave myotis bats roosted in a large cluster within one room of the cave. Experimental tours were carried out through the room with five replicates of each of 24 treatment combinations. Treatments included light intensity and colour (no light, low intensity white light, full red light, full white light), size of tour group (0, 1–3 or 6–8 people), and voice intensity (no people talking, all members of group talking). A total of 120 experimental cave tours were carried out between April and September in 1997 and 1998. Bat behaviour was observed with a night-vision video camera and infra-red lights.Study and other actions tested