Use lights low in spectral red to reduce mortality from artificial lights
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
Background information and definitions
Birds are most sensitive to red light, meaning that if bulbs used at night emit less red light then they may prove less attractive to birds, whilst remaining equally visible to humans.
Supporting evidence from individual studies
A study on an oil rig in the southern North Sea on three nights in October 2007 (van de Laar 2007) found that the number of migrating birds circling the rig was 10-50% of the number expected when the majority of external lights were replaced with ‘low red’ bulbs (150-2,500 birds observed circling vs. 750-5,000 birds expected). Low red bulbs emit lower levels of red light than standard bulbs. Attracted birds were mainly songbirds, waders and wildfowl and expected numbers were estimated based on previous observations and calculated from the number of migrating birds recorded on nearby islands, the number observed from the rig and the weather conditions.Study and other actions tested
A replicated, controlled study from Friesland, the Netherlands (Poot et al. 2008), in September-November 2003, found that on clear nights, significantly fewer migrating birds were attracted to two 1,000 W lamps when they were covered with opaque white or red filters (61% of 38 birds and 54% of 13 birds reacting to each), compared with green (13% of eight) or blue (3% of 37) filters. The same pattern, but with higher overall levels of attraction were detected on overcast nights (white: 81% of 156 birds reacting; red: 54% of 24; green: 27% of 77; blue: 5% of 38).Study and other actions tested