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Gefahren künstlicher Beleuchtung für ziehende Vögel und Fledermäuse. - Artificial light as a threat for birds and bats.
Abstract and Figures
This paper compiles the state of knowledge on the effects of artificial light on flying birds and bats, namely in order to deduce recommendations for bird- and bat-friendly navigation lights at wind energy turbines (WEA). More than 400 studies have been evaluated with regard to their relevance to the problem. Selected papers on orientation mechanisms which are closely related to ambient light and may therefore be of great importance for further insights into the subject area of light attraction were included. ”Mass collisions“ of birds as described for illuminated vertical structures (transmission towers/masts, lighthouses, high buildings etc.) could not be observed at illuminated WEA so far. Compared to unlighted facilities, the collision rates tend to be higher at illuminated facilities onshore. For offshore facilities, however, a high risk can be assumed due to the constant obstruction lights for shipping traffic. Constant light and intermittent light with longer light periods respectively likely increase the attraction of birds under fog, drizzle, rain, snowfall, low visibility, heavy clouds or comparable conditions of poor visibility. Findings on effects of specific light colours are contradictory. The knowledge about bat collisions at WEA and the corresponding related factors is low. A direct attraction of bats by WEA-lighting is not verified so far. Light sources, especially ultraviolet light-emitting lamps, do affect bats mainly indirectly by the attraction of insects. The red intermittent or constant light that is used for WEA marking in the USA does neither cause a significant aggregation of insects nor higher collision rates compared to unlighted facilities. There are hints on higher collision rates for facilities that are illuminated with strobe lights. The number of bat collisions at WEA tends to increase in warm, calm weather conditions when the animals’ activity is high. Low visibility, heavy clouds, drizzle and fog apparently also increase the collision risk. Concerning the lighting design necessary to ensure a safe air and ship traffic at a tall structure, intermittent light with a short “on” phase and a long “off” phase with the lowest possible intensity and a synchronization of the flash regime of all WEA in a wind park are recommended, while recommendations on light colour are currently not possible. In case of massive bird migration in collision-supporting weather/viewing conditions and in case of high bat activity at low wind forces which are, however, above threshold for the facility operation, a shutdown of the facility should be considered. There is still need for further research on the range of the light effects and on the significance of light intensity and light colour at identical flashing regimes.
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