New findings debunk the myth: Seabirds avoid turbine blades

The effect of wind turbines on birds has been discussed for decades. Figures have been thrown around about how many birds die a year from rotating wind turbine blades or because the wind turbines are located exactly where the birds would otherwise live and find food.

For many years, the numbers have only focused on collisions with onshore wind turbines. For example, in an American study from 2010, it was estimated that a 165-square-meter Californian wind farm with a total capacity of 580 MW was responsible for the deaths of 67 golden eagles and 1,127 other birds of prey every year.

Other American studies from the 2010s have estimated numbers of between 250,000 and 500,000 dead birds a year throughout the USA. New studies from the USA indicate that around 700,000 birds are killed every year due to American wind turbines.

Danish wind turbine company Ørsted has collected figures from the U.S. Fish and Wildlife Service, which concludes that less than 300,000 birds die a year due to wind turbines in the USA.

Studies have also been carried out in Europe, and in 2012 the Spanish Ornithological Society estimated that 6 to 18 million birds and bats die a year due to wind turbines in Spain.

And in 2020, former American president Donald Trump proclaimed that wind turbines kill “all the birds”.

It is clear that there is a great deal of uncertainty surrounding the figures, and most studies also emphasize that the number of dead birds is relatively low compared to other causes of death. For example, in the USA, 6.6 million birds die a year from cell phone towers and 599 million die a year because they fly into tall glass buildings.

But as mentioned, most studies have focused on onshore wind turbines. Studies of how offshore wind turbines affect birds, including their migratory paths, have been sparse.

On the Ørsted’s website, a single British study of offshore wind turbines and birds is mentioned. The study observed six dead birds in two years.

Now, however, Swedish energy company Vattenfall has completed a two-year study of the behaviour of seabirds in connection with an offshore wind farm off Aberdeen in Scotland, which consists of 11 wind turbines.

The overall conclusion is that birds are really good at avoiding wind turbine blades, says Henrik Skov from DHI A/S, who has been the project manager of the study:

“However, in contrast to previous studies, where the behaviour of the birds has been investigated in relation to the entire wind farm, here we have been able to look at what happens to the individual bird when it flies into the park,” he says.

All birds avoided wind turbine blades

Specifically, Henrik Skov and his team have followed over 10,000 seabirds with advanced radar and over 3,000 seabirds with a combination of radars and high-resolution PTZ (pan, tilt, zoom) cameras at the moment they fly in the direction of the wind turbines. By triangulating video footage with radar, the researchers have been able to follow the flight of the individual bird in 3D.

The conclusion of the study is clear: When the birds come close to the wind turbines, they deflect in good time and fly parallel to the wind turbine blades. During the study, none of the registered birds were struck by blades.

Focus was on four species of seabirds: herring gull, tern, black-backed gull, and gannet. It turned out that black-backed gulls and gannets avoided the wind turbine blades when they were 40–50 meters from them, while herring gulls and terns detected the blades at a distance of 90–110 meters and 140–160 meters respectively.

The birds have different flight patterns around wind turbines. For example, gannets tend to reduce their flight height when they get close to the turbines, while herring gulls and terns increase their flight height slightly.

But the study also points out that it is not possible to generalise how seabirds avoid wind turbine blades and that the seabirds’ flight patterns change under certain weather conditions:

“When it’s very windy and there are high waves, and in turbulent wake fields behind the turbines, the birds show a slightly different flight pattern,” he says.

Different birds, different problems

Knud Flensted, biologist at DOF BirdLife (Danish Ornithological Society), finds the study “interesting, but not surprising”.

The four bird species that Vattenfall’s study has looked at are not known to be particularly sensitive to wind turbines—neither on land nor at sea. But there are many other species that can risk coming close to the turbines, Knud Flensted says and points out that it is known that especially eagles, vultures, and other large birds of prey are often not aware of the wind turbine blades, which out at the blade tip can spin at hundreds of kilometres per hour.

Other bird species, for example sea ducks, loons and auks, often stay far away from areas with offshore wind turbines, even if those are areas where they used to live in large numbers:

“So DOF BirdLife’s main concern is not so much collision with wind turbines. It’s more the cases where the wind turbines displace birds from their natural habitats,” Knud Flensted says.

In addition, Knud Flensted is also concerned about large offshore wind farms being placed directly on known migration routes and resting places, for example for birds of prey, between Scandinavia and Southern Europe:

“If one doesn’t pay attention to the birds’ most important habitats, turbines can end up being placed in an extremely inappropriate location—for example in the Wadden Sea, where we know that many young white-tailed eagles roost,” Knud Flensted says.

However, Dr. Rainer Raab from Technisches Büro für Biologie in Austria is not quite so worried. At a recent conference organized by the industry organization Green Power Denmark, he explained that very few of the 2,250 red kites that the researchers have followed over a ten-year period had died due to wind turbines. By far the biggest threat to the lives of the red kites, apart from natural causes, was when humans had been involved, for example in poisoning, shootings, and road kills.

Researchers from the Department of Ecoscience at Aarhus University have also looked at birds and wind turbines at Østerild Wind Turbine Test Field, where they have investigated how larger birds are able to avoid the rotating wind turbine blades.

Birds are generally good at avoiding the turbines, and compared to the past, researchers are now less cautious when assessing the extent of collisions between birds and wind turbines, says Ole Roland Therkildsen, senior advisor at the department:

“We can now assess with greater certainty the impact on a population from a single wind farm, but with the future development of wind energy both at sea and on land, it is evident that we have a huge knowledge gap in relation to how it affects bird populations overall ,” he says and recommends that more research be done on the coexistence between birds and wind turbines, as Denmark aims to quadruple onshore and quintuple offshore wind turbine electricity production.

And the project manager of the current study, Henrik Skov, sees many possibilities with the new results from Scotland. For example, the method can be developed to investigate the flight patterns of other bird species inside the offshore wind farms.