GPS devices on birds of prey reveal wind turbine collision dangers

Wageningen Environmental Research, in partnership with Werkgroep Zeearend Nederland and Grauwe Kiekendief – Kenniscentrum Akkervogels, conducted a study that summarised the knowledge on risks of birds of prey collisions with wind turbines for Flevoland province.

The analyses in the study, which was funded by the Province of Flevoland and the Ministry of Agriculture, Nature, and Food Quality as part of the WUR Knowledge Base Program KB36 Biodiversity in a Nature-Inclusive Society, are based on a sample of juvenile white-tailed eagles and harriers outfitted with GPS transmitters between 2019 and 2021.

The chance of collision is determined by flight movements and altitude

The flight period of birds of prey at the height of the turbine rotors determines the risk of collision with wind turbines. However, weather conditions, time of day, and season all have a role in this.

A significant portion of the flight duration was spent at rotor height. White-tailed eagles flew 34% of the time at turbine rotor height in the Flevoland province, while marsh harriers flew 14% of the time. The majority of both types of flights took place at low altitudes of less than 25 meters, the province’s lowest ‘tip low’ of turbine rotors.

The findings revealed that meteorological conditions had a significant impact on the flight altitude of both birds of prey. The most common flights occurred at rotor height between 12:00 and 15:00. Based on the observed flying motions and altitudes, possible collision risk regions for both birds of prey were identified.

Flevoland turbine replacement

Flevoland is replacing aging, tiny turbines with low tip depression with a smaller number of larger turbines with higher tip depression. With this improvement, both total power and total rotor surface increase dramatically.

How do you lessen the possibility of a collision?

There are several approaches for reducing the likelihood of birds of prey colliding with Flevoland turbines. According to the research, this can be accomplished by establishing a standstill period, such as turning down turbines between 10:00 and 18:00 in the months of April and May. According to statistics from GPS transmitters, this already reduces the danger of collision by 26% for the marsh harrier and 21% for the white-tailed eagle.

A pause based on video detection of an incoming bird of prey is another method that has already proven effective elsewhere. Painting a single turbine rotor black, which was previously successful for a variety of bird species in Norway, has yet to be shown useful for birds of prey in the Netherlands. Such precautions should concentrate on the most dangerous turbines, which have the greatest overpasses.

The most significant measure is the prohibition of installing turbines in regions where crash risks are considerable. The transmitter data of the young white-tailed eagles demonstrate that the Flevopolders are crossed significantly more frequently than was predicted during the wind farm planning phase. The turbines on the polders directly south of the Oostvaardersplassen are especially dangerous since white-tailed eagles travel through those polders on their way between the Oostvaardersplassen and moist areas in the province’s south and the Veluwe. In recent years, two white-tailed eagles were killed after they collided with wind turbines.

The Effects of Population Size

The critical demand for wind energy production is being addressed as the number of wind turbines increases, but the harmful consequences on birds are increasing. Even with a small number of casualties, this can have a significant impact on some species. This is especially troublesome for slow-reproducing species, species already under threat, or endangered species like marsh harriers and white-tailed eagles.

Before today, little was known about the hazards of birds of prey colliding with wind turbines in the Netherlands, as well as where and when such risks are greatest. This makes it difficult to implement effective mortality prevention methods. The precise flight data from GPS transmitters provides fresh insights that enable such measures.

Image source: WUR

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