Effects of artificial lights and moonlight on petrels at St Kilda: Effects of lights on petrels

Capsule: When moonlight levels are low, shearwaters and storm-petrels are attracted to artificial lightingat night at St Kilda and may be killed, but impacts are lessened by deliberate light reduction measures. Aims: To determine the scale and impacts of attraction of petrels to artificial lights at St Kilda, investigateinfluences of the lunar cycle, and assess effects of reducing artificial light emissions. Methods: Nightly numbers of Manx Shearwaters Puffinus puffinus, Leach’s Storm-petrels Oceanodromaleucorhoa and European Storm-petrels Hydrobates pelagicus attracted by artificial lights were recordedin September and October from 2005 to 2008. Effects of experimental reductions to light emissions in2007 and 2008 were assessed, together with variation in annual moonlight, mortality rates, and age ofbirds found. Results: Reductions to light emissions caused a decrease in numbers of Leach’s Storm-petrels attracted,but had less effect on attraction of Manx Shearwaters. Only juveniles were found, the majority afternights with little or no moonlight, and mortality was extremely infrequent. Only one European Storm-petrelwas found, and Leach’s Storm-petrel and Manx Shearwater totals were small compared with estimatedbreeding totals at St Kilda. Conclusions: Numbers of petrels attracted to artificial lights on St Kilda were low. However, reductionsto light emissions were still beneficial in reducing numbers of young that became disorientated, grounded,or died during fledging periods. Therefore, reductions to light emissions should be encouraged. A reviewof this phenomenon across the UK found it to be rare in breeding areas away from St Kilda.