Preventing birds from colliding with turbine blades is a constant challenge for wind farms.

It’s the biggest cause of direct bird mortality at wind farm sites. And it doesn’t just impact local wildlife populations and sometimes critical migrations – it also affects the deployment of on- and offshore wind farms. To plan, construct, and operate wind farms efficiently, methods need to be put in place to assess and minimise the risk of bird deaths.

There are many tools for detecting and deterring birds already available, ranging from wind farm bird radar and cameras to acoustics and lasers, and more are still being developed. In 2014, researchers at the Norwegian Institute for Nature Research (NINA) tested another possible approach – the use of ultraviolet light.

Many of the bird species that collide with offshore wind turbines are sensitive to the violet or ultraviolet light spectrum. Could ultraviolet light help birds avoid turbines and reduce mortality rates?

UV Light for Birds: How NINA Helped Birds to See Ultraviolet Light

Vision is the main sensory system that birds rely on. Ultraviolet lights around turbines was supposed to be a potentially effective way to warn and/or deter birds that fly at lower ambient light levels from colliding with them.

However, no proof-of-concept had shown whether UV-sensitive birds in flight respond to UV lights. Roel May and his team of researchers at NINA tested two types of lights to see if they would deter birds from a lit area:

• Light in the violet spectrum (400 nm), were used on Thursdays and Sundays
• Light in the ultraviolet spectrum (365 nm), were used on Tuesdays and Saturdays

On the intervening ‘control’ days (Mondays, Wednesdays, and Fridays), no lighting was used.

These lights were placed vertically on a mast outside Smøla wind farm, one of Norway’s largest onshore wind farms, during Spring 2014. Bird flight movements were monitored continuously for two months between dusk and dawn, using Robin Radar’s advanced bird detection radar. The radar system automatically tracked and stored all data on bird movement in a database for statistical analysis.

Do Birds in Flight Respond to Ultraviolet Light?

The results from the pilot study were promising. Compared to the ‘control’ days with no lighting, bird flight activity was:

• 27% lower when the ultraviolet light was on
• 12% lower when violet light was on

There was also a vertical displacement, which increased the average flight altitude of birds by 7m. While there were temporal changes, this effect persisted over the season at 40m above sea level and below.

However, according to Roel and the team at NINA, we’re still a long way off from a working design that could effectively mitigate collisions.

“Ultraviolet light was most effective, but the flight altitude was only seven metres higher than usual,” explained Roel. “This is not much given the size of a rotor blade, which is 40 to 50 metres.”

There are other challenges to consider, including UV light pollution. Because the effect of the ultraviolet light is limited, you’d need much stronger lights or a more directional design to create a functional solution. If humans or birds look at this light at close range, it may harm their eyesight, potentially causing blindness.

The stronger light also risks attracting insects, in turn attracting more birds or bats. This could end up increasing bird collisions, defeating the purpose of implementing the lights in the first place.

Further study into vision damage distance thresholds and how birds respond to other lighting arrangements (such as narrower, moving, or flickering beams) could reveal a solution for these challenges. But for now, unfortunately, ultraviolet light isn’t a viable method for mitigating bird deaths.

Using UV Light for Birds Helps Prevent Unnecessary Mortality 

This isn’t the only study that NINA has carried out to help find new ways of reducing the adverse impact of wind farms on bird collisions. They’ve tested painting turbine blades black to make them more visible, developed a GIS-micro-siting tool to identify updraft areas that attract soaring raptors, and more.

Each of these new methods will help to discover what could reduce bird mortality as larger wind farms are built in greater numbers. But none of them alone act as a silver bullet. Truly effective mitigation requires the right integration of tools, including radars, cameras, and analytics, all working together to reduce bird mortality.

To learn more about NINA’s study into ultraviolet lighting, read the full research report.