The deadly interaction of wind turbines and wildlife has long vexed both the wind industry and ecologists, but a UK research team may have an answer: Paint them purple.
It turns out that turbines are most often painted the very colors that attract the most insects—and, in turn, flocks of hungry birds and bats on the lookout for a ready-made insect buffet.
Painting the turbines purple—apparently, the ultimate insect turn-off—could end up saving the insects, their predators and the structures themselves.
So concludes the team from Loughborough University, which has found significant differences in insect attraction to various colors.
“The phenomenon of wildlife mortality at wind turbine installations has been generating increasing concern, both for the continued development of the wind industry and for local ecology,” the UK scientists write in “Insect attraction to wind turbines: does colour play a role?” recently published in the European Journal of Wildlife Research.
Although a 2000 study focused on the UV reflectance of turbine blades (finding that higher reflectance drew more birds and, thus, more bird deaths), the Loughborough University scientists in Leicestershire are apparently the first to consider the influence of turbine color.
Their conclusion: The same whites and light grays commonly used to make wind turbines less visually obtrusive are “among those found to attract significantly more insects than other colors.” And the single biggest insect come-on is yellow—the same color required on offshore turbines in the UK to ensure visibility to ships.
The findings suggest that color “may well have a role to play in potential mitigation” of wildlife mortality, the team said.
Studying the Spectrum
The scientists conducted their experiment over three years at a 13-meter (42.6 feet) light gray turbine located in a meadow at a local public park. The team prepared a series of cards, about 8 ½ by 12 inches, in a variety of colors: white, light gray, dark gray, blue, red, purple, yellow, brown, green and black.
White, light gray and, less often, dark gray are all common turbine colors. The other colors were chosen either to provide a spectrum of choices or because certain insects are known to express innate color preferences. A transparent card was added as a control.
In 59 10-minute sessions, the researchers observed a total of 2012 insects, noting which color card they landed on.
“Color was found to have an overall significant effect on insect count,” the team concluded. The most common turbine colors—white and light gray—“were significantly more attractive than all other colors” tested, except for yellow. Purple, on the other hand, “attracted significantly fewer insects than any of the other colors tested.”
The Reflectance Factor
The researchers also studied the changing influences of seasons, weather, wind speed, reflectance and times of day on the insects.
The reflectance association proved strongest. Consistent with the 2000 bird study, “both peak UV [ultraviolet] reflectance and peak IR [infrared] reflectance significantly influenced insect count,” the scientists noted.
They added: “It could be speculated that the UV paint would increase the attraction of insects to the turbine, and thus the attraction of insectivorous birds; this theory is supported by the fact that the vision of many insects is shifted towards the UV portion of the spectrum”—a trait in flies, for example, that canny spiders frequently exploit.
White and yellow gave the highest IR reflectance peak, while the transparent card gave the highest UV peak, the team found.
Decreasing Foraging Opportunities
“The finding that the common turbine colors white and light gray were amongst the most attractive colors to insects, independent of time of day, is of significant importance,” the team wrote.
“Insects attracted to a turbine mast and rotor present a foraging opportunity to local insectivores, and thus this is likely to greatly increase the time spent in the vicinity of the turbine, which in turn increases the risk of fatal interaction with operational rotors.”
It also increases the chances of insects becoming trapped in turbine rotors, the researchers added.
“It therefore appears important to consider alternative turbine colors for future installations, particularly in areas known to be high in insectivore activity,” they conclude.