Shield lights to reduce mortality from artificial lights
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Lights that are not designed to be seen as warnings can be shielded, so that the light from them is directed down (or in the required direction). This can reduce the light projected into the sky and therefore the visibility and attractiveness of the lights to birds.
Supporting evidence from individual studies
A replicated, controlled study at a resort on Hawaii, USA, in 1980 and 1981 (Reed et al. 1985), found that significantly fewer Newell’s shearwaters Puffinus newelli were found grounded under security lights on nights when twelve of the brightest lights had ‘hoods’ placed on them, compared to alternate nights when lights were not shielded (272 birds on 32 ‘shielded’ nights vs. 444 birds on 32 control nights). The reduction was greater in 1981 (52%) than 1980 (29%), possibly because peak shearwater fledging coincided with a full moon (and so higher ambient light) in 1980, but with a new moon in 1981. The shields reduced upwards radiation of light and during the experiment most other lights on the resort were permanently shielded.Study and other actions tested