In the early morning of January 31, 2022, the White-tailed Eagle flew from the sleeping tree on the edge of the Oostvaardersplassen into the nature reserve, probably to forage. After a short period of rest in the swamp, the bird left the area around 10:50 am in an easterly direction, crossed the A6 highway and navigated into the polder of Southern Flevoland. Immediately after crossing the A6, the bird ended up in a wind farm, along the Roerdomptocht between the Ibisweg and the Vogelweg. Just before 11 am, the animal was hit by the rotors of one of the turbines and landed in the field next to it.
The transmitter’s accelerometer showed that the bird was not immediately dead after the impact. The bird was still moving between 11 a.m. and 12 noon. After that, the sensor of the transmitter stopped detecting movement and the temperature dropped rapidly. During the discovery of the cadaver, on February 1, 2022, it was confirmed that the bird was still alive immediately after the collision. Both claws were filled with heavy clay, which indicates that the animal tried to keep itself upright for another hour.
First results mortality
In 2019, 2020 and 2021, fifteen young White-tailed Eagles in the Netherlands were equipped with GPS transmitters with the aim of obtaining knowledge about the dispersion and survival of birds from the Dutch breeding population. Three birds have since died; two as a result of collisions with wind turbines and one as a result of a collision with a train. That means that within a few years of birth, twenty percent died, in all cases attributable to unnatural causes. The White-tailed Eagle is a long-lived species that can easily live to be fifteen to twenty years old.
The research with transmitters shows that young White-tailed Eagles in the Netherlands regularly commute back and forth between important hotspots in the regions of the Northern and Central Netherlands, and the Sweet Delta. For the Central Netherlands there is an important connection on a landscape scale between the core areas in Flevoland and the Veluwe. Birds that reside in the Oostvaardersplassen regularly fly to the Veluwerandmeren and to areas on the Veluwe and back. The birds have to pass through the large-scale wind farms in Flevoland. Because the number of breeding pairs of White-tailed Eagles in the Netherlands is still increasing, the number of shuttle flights between nature reserves will also take place more frequently. With the development of the Nieuw Land National Park, the important nature reserves of Lepelaarplassen, Oostvaardersplassen, Marker Wadden and Trintelzand will be scaled up and connected. White-tailed eagles already appear to exploit those areas in coherent food flights, in relation to the increasing populations of waterfowl they prey on. This also creates extra space for new breeding grounds for White-tailed Eagles and other birds of prey. Because the number of bird movements is expected to increase, both existing and planned wind farms will become a growing problem as a result of the additional expected deaths due to collisions with turbines. Other developments, such as the opening of Lelystad airport for large aircraft, will also pose an increasing risk in this regard.
Collision risks in Flevoland
To investigate collision risks, ‘high-resolution data’ is used to accurately map three-dimensional flight behaviour. In addition to geolocation, flight altitude is also registered. Recent research into the risks in Flevoland, commissioned by the province, shows that for a large part of the flight time, white-tailed eagles flying through Flevoland fly at ‘dangerous heights’, ie within reach of the increasingly higher wind turbines. In the environmental impact assessment of Windpark Zeewolde it was still assumed that effects on White-tailed Eagles could be excluded in advance by a predicted “very limited number of flight movements”, but the transmitter data show a different picture. Although the movements of the Sea Eagles are concentrated in the Oostvaardersplassen and on and around the Randmeren, risky flights also regularly take place in the Flevoland polders.This has now been confirmed by the victims found – in the past four years two White-tailed Eagles were found as victims of a collision with a turbine in Windpark Zeewolde. minimum number, because in the absence of victim monitoring most birds will not be found.
Measures to minimize collisions of vulnerable birds such as birds of prey with turbines are currently very limited in the Netherlands. To limit casualties from wind turbines, a detection system has been developed that registers approaching birds, including White-tailed Eagles, and uses repelling noise or a wind turbine standstill device. This system is currently only used in the Krammer wind farm and in a wind farm on Oost-Flakkee in the Krammer-Volkerak. Another possible measure is the periodic shutdown of turbines in the period when the risk of collisions is greatest and at locations where that risk is greatest. Research is currently being carried out in the province of Groningen into painting one of the blades of a turbine black. Abroad, this has resulted in a 70 percent reduction in bird casualties. It is better to take the flight movements of White-tailed Eagles and other birds into account already during the planning phase by not constructing wind farms at risky locations.
The research is being carried out by the Werkgroep Zeearend Nederland and Wageningen Environmental Research and financed by the province of South Holland, the province of Zeeland, the province of Flevoland, Staatsbosbeheer, the Prins Bernhard Cultuurfonds and the Bettie Wiegman fund.
Text: Stef van Rijn, Dirk van Straalen and Ralph Buij
Photos: Mennobart van Eerden; Working Group Sea Eagle Netherlands
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