Satellite Tracking of White-Tailed Sea Eagles in Mecklenburg-Western Pomerania and Brandenburg

The increase of wind power plants as a German strategy to develop green, renewable energy in order to overcome energy produced by nuclear power and fossil energy sources leads to a substantial collision risk for the white-tailed sea eagle. The aim of our study was to understand how frequently and under which circumstances eagles approach wind turbines in order to assess and minimize the collision risk in the future by means of satellite telemetry and behavioural observations. One territorial adult, two sub-adults and one immature bird have been fitted with satellite transmitters between 2007 and 2010. Additionally telemetry data of three adult birds and another 13 young eagles, which have been tagged for other projects between 2003 and 2010, has been evaluated for the first time in the present research project. In the evaluation no avoidance behaviour of the adult bird towards wind turbines could be identified for the different calculated home ranges by comparing average distances to random distances. The number of locations per km2 is significantly higher within the wind farm area than in the reference area (cropland without wind turbine). Thus on average, the adult bird returned more locations within the risk area than statistically expected. One of the three tagged eaglets has been recorded within a wind farm during the period of transmission. GPS data as well as visual observations have shown that the young bird repeatedly traversed the wind farm in the vicinity of its nest and showed no fear of the turbines. Although all three tagged young eagles (immature and sub-adult) had very large home ranges and might have crossed a number of wind farms, only one individual approached the risk area of a wind turbine. Among the attractive structures were: kettle holes, ponds, large bodies of water, perching trees on forest edges and local elevations. To estimate a possible collision risk with a wind turbine in the vicinity of the nest, the proportion of locations at a distance of 3000 m was looked at, a distance which is discussed in the recommendations for distances of wind turbines to important areas for birds by the Working Group of German State Bird Conservancies. The adult white-tailed sea eagle equipped with a satellite transmitter in this study showed only 17.3% of the locations in an area of 3000 m around the nest. Half (50%) of the localizations occur within a distance of 7486 m. The analysis of locations of another three territorial white-tailed sea eagles, which was satellite tagged for other studies, resulted in 80% locations in an area of 3000 m around the nest, 87% locations up to 3000 m and in one case even 98% of the recorded locations at distances up to 3000 m around the nest. The mean of all locations at distances from 50 m and up to 3000 m around the nest is 71% for all four white-tailed sea eagles. As a large proportion of the recorded locations of tagged adult birds can be found at a distance of 3000 m around the nest, the probability that the eagles enter the area of a wind turbine decreases significantly with increasing distance. If however, a preferred flight path towards a foraging habitat will be obstructed by a wind turbine, the probability of contact with wind turbines is increasing.