How Often Red Kites Actually Collide with Wind Turbines

With its long wings, the red kite uses thermal updrafts to quickly gain altitude. Where conditions are particularly good for this flying technique, there are often also ideal sites for wind power plants. It's no wonder, then, that collisions occasionally occur.

A study partially supported by the SNF, in which the Swiss Ornithological Institute participated, has now analyzed exactly when and where such fatal incidents occur. The findings could be incorporated into the planning of installations. For the project, several research teams from Austria, Germany, and other European countries tracked nearly 3000 Red Kites for up to eleven years using GPS trackers.

Over five hundred of the birds came from Switzerland. They were equipped with lightweight, solar-powered transmitters by the Swiss Ornithological Institute, usually as young birds, ten years ago. Since then, the researchers have been receiving approximately one position signal per hour from the birds, depending on battery charge.

Recovery and autopsy a huge effort

The ornithological team is using this large sample to study the migratory behavior of the Red Kite as well as its spread into alpine habitats. 'One unsolved question is why the population in Switzerland has increased significantly in recent decades. In the surrounding countries, the numbers have recently declined,' says Martin Grüebler, head of the Ecological Research department.

For the cross-border Life-Eurokite project, the Swiss datasets were combined with tracking data from other European countries. The aim of this collaboration is, among other things, to investigate the human-caused mortality of Red Kites. A newly published analysis of the datasets of all 3000 birds found that 41 individuals likely died from wind power plants over eleven years. To determine the cause of death, the various research teams follow a standardized protocol: The GPS data indicate whether the bird died at the site of an installation. If possible, the dead birds are then promptly recovered and an autopsy is conducted.

According to Grüebler, the recovery of the birds is a huge effort. This is because enough people must always be ready across Europe, and country-specific regulations must also be observed - for example, involving authorities. Together, researchers from all countries were able to confirm a collision with a wind power plant as the definite cause of death for 25 of the killed birds. The remaining 16 were classified as very likely or possible.

No deaths from wind power in Switzerland

Almost half of the collisions occurred in northern Germany - where the number of wind turbines is particularly high. Another twelve collisions took place in Spain and France - often during the annual migration south.

Of the Swiss cohort, four birds died from wind power installations in France, Spain, and Germany. No such fatalities were recorded in Switzerland itself. 'But there are also not yet as many installations here as in our neighboring countries,' Grüebler notes.

In addition to evaluating collisions, the team also assessed near-misses based on the GPS data. These are situations where Red Kites passed wind installations without harm. These observations provided information about which type and size of wind turbines are more or less dangerous.

The bottom line: The larger the rotors, the more likely a collision is. An increase in rotor diameter by 25.5 meters increased the likelihood of a collision fivefold. Conversely, it was beneficial if the rotor blades were installed as high as possible. Red Kites, with their low flight altitude, then tend to fly beneath them.

Different story for eagles and bats

'In the future, the number of wind power installations in Europe will increase manifold. Thus, this danger could carry more weight,' says Grüebler. A yet unpublished study of the Life-Eurokite project addresses the importance of other human-induced causes of death for the Red Kite, such as illegal shootings and poisonings. Based on the findings regarding wind power, the research team recommends building installations with as much ground clearance as possible to protect the Red Kite. But it's not that simple. As Grüebler explains, higher rotors could pose a danger to other birds of prey, like various eagles or vultures. Or to passerines during migration and to bats. Because flying height is very species-specific.

This is precisely why it's important to find out as much as possible about the lifestyle of different animal species. 'The more we know, the better we can plan wind energy installations and sites that have the least impact on wildlife.'

(*) J. Skrábal et al.: Red kite (Milvus milvus) collision risk is higher at wind turbines with larger rotors and lower clearance, evidenced by GPS tracking. Biological Conservation (2025)

The text of this news article, a downloadable image, and more information are available on the Swiss National Science Foundation's website.

Press contact:
Martin Grüebler
Head of Ecological Research
Swiss Ornithological Institute
Seerose1, 6204 Sempach
Tel.: +41 41 462 97 22
Email: martin.gruebler@vogelwarte.ch

Editor's note: Image rights belong to the respective publisher.