18 Nov 2020 Black Wind Turbines: the way forward for reducing avian collision risk?
A recent paper entitled ‘Paint it black: Efficacy of increased wind turbine rotor blade visibility to reduce avian fatalities,’ was widely reported by the UK media. Reports stated that a reduction of over 70% in bird fatalities could be expected as a result of changing the colour of turbine blades, thereby making them more visible to birds.
In this article BSG Ecology Director Owain Gabb provides a short non-technical review of the paper, and comments on its potential relevance to UK schemes.
Laboratory studies have demonstrated that motion smear from turbine blades can be reduced through painting one of the blades on a standard three blade rotor black. Birds do not necessarily associate motion smear with a moving part, and improving their ability to see turbines in this way therefore potentially reduces fatality.
The researchers set out to test this theory at the 68 turbine Smøla wind farm in Norway, a site at which bird fatality levels had been studied since 2006, and at which a considerable number of white-tailed eagle deaths had been recorded. They were therefore able to place their results in the context of this data set. Their research commenced in 2013.
Four turbines within the wind farm were selected, and one of the rotor blades of each painted black. Four neighbouring turbines were identified as controls.
Search dogs were then used to locate bird carcasses at the eight turbines at regular intervals over a period of three and a half years (289 surveys were completed at the control and 290 surveys at the painted turbines). Results were compared to existing fatality data for the turbines (obtained from well over 300 searches at both the four trial turbines and the controls), collected over the seven and a half years prior to the study commencing.
The study found no incidence of collision fatality of white-tailed eagle at either the control or the painted turbines during the monitoring period. Kestrel (2), greylag goose, common snipe (4), an unidentified wader and a variety of common passerines were found dead beneath the control turbines, with a greylag goose the only non-passerine collision victim at the painted turbines. At least ten bird species were found dead beneath the control turbines and four beneath the painted turbines during the study.
Data collected prior to the painted turbine study indicated that the control turbine blades had previously killed at least seven birds of six species (including one white-tailed eagle), and the turbines that were subsequently painted eleven birds of six species (including six white-tailed eagles). Monitoring effort was not consistent across the period, however; rather it was varied in accordance with the requirements of previous studies.
Statistical analyses accounted for between year variability in detected fatality as well as in the lack of consistent search effort between years. No evidence was found that birds avoided visible (painted) turbines thereby colliding with control machines, or that local resident species had habituated to the wind farm, resulting in lower fatality rates.
The authors concluded that the results indicated a genuine decrease in raptor collision at Smøla, but noted the need to test this conclusion further at other sites if the effectiveness and wider applicability of the mitigation technique was to be fully understood.
If painting of rotor blades is found to be effective in reducing collision risk through studies at other wind farm sites, it could become a standard technique for reducing fatality. If blades are painted ahead of turbine construction, the associated cost will be limited and the measure will be attractive to developers.
Currently the study is limited in terms of scale, and studies at other wind farms for which high quality post construction fatality data exists will be needed to put the conclusions into context. Logically, regular dog searches are only likely to be completed at sites with clear ornithological issues, as they are very expensive to complete at high intensity over long periods. It is therefore unclear where these sites and studies are likely to come from – in UK terms at least. While searches for dead bats are now completed at many operational UK sites, these tend to cover short periods within the bat active season: dead birds recorded during bat searches may not be logged in the field, let alone consistently reported.
Without additional data the effectiveness of the measure cannot be assessed. This is because the number of raptors other than white-tailed eagle killed by the turbines concerned during both the monitoring prior to the study and during the study itself was very small (two kestrels over the whole period). It appears that in the seven and a half years prior to their painting the four painted turbines had not killed a kestrel or any other raptor than white-tailed eagle. This makes it very difficult to agree with the authors’ conclusion that ‘raptor’ (if they intend it as a catch-all term) collision had declined.
The case that white-tailed eagle collisions have been reduced as a result of the measure is more credible. In the absence of further studies to demonstrate this, a proportionate approach might be to consider incorporation of black-bladed machines at new wind farms within the current range and projected range of the species in the UK  over the operational life of any new wind farm schemes.
BSG Ecology provides all aspects of ecological support for wind farm applications UK wide. If you would like advice or support on a project please contact one of our offices.
Top image: Buzzard carcass beneath a wind turbine courtesy of Joanne Martin Conservation Dogs
 May R, Nygård T, Falkdalen U, Åström J, Hamre Ø, Stokke BG. Paint it black: Efficacy of increased wind-turbine rotor blade visibility to reduce avian fatalities. Ecol Evol. 2020;10:8927–8935. https://doi.org/10.1002/ ece3.6592
 Motion smear is the blurring effect we see when an object is moving too rapidly for our eyes to process (like the wings of a humming bird).
 Hodos, W. (2003). Minimization of motion smear: Reducing avian collisions with wind turbines. Period of performance: July 12, 1999-August 31, 2002. (NREL/SR-500-33249). Retrieved from Golden, Colorado, USA. https://www.nrel.gov/docs/fy03osti/33249.pdf
 Willow ptarmigan is excluded from the results considered above. Birds are regularly found dead at the wind farm, but collisions are understood to be with the turbine bases and would not be influenced by the painting.
 Albeit it should be noted there was a decline in fatality levels at the control turbines as well as the painted turbines during the work.
 White-tailed eagle currently has a small and range-restricted population in the UK (notwithstanding recent English reintroductions which are in their early stages).