Bats, Birds and Purple Turbines

Earlier this year I came across a short report in the January issue of Oryx-The international Journal of Conservation, which suggested that wind turbines should be painted purple (see also BBC report). Beside making the landscape funky, there is scientific evidence that such a measure would have desirable impact on wildlife. But how and why?


According to RenewableUK, currently there are nearly 3500 wind turbines installed in the UK, and many more are planned both on land and offshore. This is of course a wonderful thing, however there is increasing concern over collision mortality of bats and birds around wind farms. It has been estimated that on average each wind turbine cause up to 23 collisions annually. Some areas are however more affected than others. The massive wind farm in Altamont Pass, California is known of its sever impact on birds of prey, including Golden Eagles and vultures. Despite individual collision rates per turbine per year are not high, due to the size of the wind-farm and the massive number of turbines many birds die here each year.

Turbines at Altamont Pass, California, USA.

It is not entirely clear why wind turbines attract bats and birds, but there is growing evidence that foraging plays a major role. It has been suggested that wind turbines attract insects, which in turn attract insectivorous bats and birds. This hypothesis is supported by a study, where turbines have been painted with UV reflective paint to make them more detectable for birds. Interestingly, bird mortality increased, which may be explained by the fact that UV paints tend to attract insects. Long and colleagues investigated the matter further by looking at how ten different colours attracted insects. Despite thy found large temporal variation, with insect counts being highest in July and at midday, overall a clear pattern emerged. Yellow colour attracted the most insects, followed by white and grey. This is worrying, since most wind turbines - as I'm sure most of us observed - are painted white or grey to make them visually less obstrusive for human eye. Purple colour on the other hand was found to attract the least number of insects, which suggest that collision mortality could be significantly reduced if turbines would be painted purple instead of the usual white or grey.

This measure alone however is unlikely to solve the problem entirely. It has been suggested that insects are also attracted to heat generated by the rotors, and that bats may investigate wind turbines as roost sites. Don't get me wrong, I'm not opposing or criticising wind energy on this ground, I'm just pointing out that they have some undesirable effect on wildlife which we could mitigate relatively easily.