Both through ongoing and previous studies of the conflict between birds and wind turbines carried out in the Smøla wind-power plant, the white-tailed eagle, Haliaeetus albicilla, has been identified as the most vulnerable species. The Smøla wind-power plant has an impact on the white-tailed eagle both through increased disturbance as well as increased mortality from collisions with turbines.
The assessments are based on a set of different data sources and different analyses. (i) Monitoring data on reproductive success and nest locations for the white-tailed eagle. (ii) Data on eagle night roosts. (iii) Analysis of flight activity levels and collision risk modelling. (iv) Sensitivity analysis for birds in general based on data from the Merlin avian radar and (v) analysis of turbine-related collision risk sensitivity from bird fatality data. Together these data sources form a solid basis for assessing the potential impacts of a repowered Smøla wind-power plant.
In general, we expect the layout with 30 5MW turbines to have lowest conflict level for the white-tailed eagle. The modeled collision risk of a repowered wind power plant with 30 turbines are expected to have approximately 32% of the collision risk compared to the existing wind-power station, i.e. significantly less than in the existing wind-power plant. A renewed wind-power plant with 50 3MW turbines is expected to have a collision risk that is approximately 71% of that of the existing wind-power plant. The reduced risk of a power plant with 30 turbines compared to the existing wind-power plant and the 50-turbine layout is due to both the reduction of the number of turbines, and better individual turbine siting.
Also, when assessing the impact on the breeding performance of the eagles, the 30-turbine layout is expected to have a lower conflict level compared to the 50-turbine layout. This is mainly due to fewer turbines and greater distances between turbines and nest sites in the southwestern part of the wind-power plant. For other parts of the area we expect minor differences for the two layouts compared to the existing wind-power plant.
Considering the distance to night roosts there are minor differences between the two proposed layouts. North of the wind-power plant, there are several important night roosts that are being used by a relative large number of eagles. However, both proposed layouts have increased distances between the turbine locations and these roosts compared to the existing wind-power plant. The proposed 50-turbine layout will have a higher density of turbines in in southwest and thus a higher risk for the eagles in this area.
A summed vulnerability map for white-tailed eagles was developed, based on data on reproductive success, nest location, flight activity levels and night roost locations. According to this summed vulnerability map, the eagles have the highest vulnerability is present in the outer edges of the proposed layouts, as well as in an area in the south west between the two westernmost turbine strings. Other parts of the wind-power plant will have less vulnerability compared to the existing wind-power plant. Overall, the 30-turbine layout is expected to have least impact to the summarized white-tailed eagle vulnerability.
Analysis of the radar data provides a picture of the bird activity in general and not only for the white-tailed eagle. The results show that the lowest vulnerability is expected for the 30-turbine layout. The radars reduced ability to track objects close to the existing turbines make it difficult to compare the two proposed layouts with the existing wind-power plant.
An analysis of the potential variables that can explain where the white-tailed eagle collisions take place in the existing wind-power plants, shows that collisions among adult white-tailed eagle are more likely to take place at turbines that are further from the nest sites than those that are close. However, there is greater likelihood of collision at turbines that have several nest sites within 1 km distance. A possible explanation for this could be that territorial adults inside the wind-power plant keep other eagles away from their own nest site.
Based on modeling of collision risk at the individual turbines for the 50-turbine layout, it is expected that the turbines 1, 13 and 19 in the northern part, turbine 22 and 23 in the southwest have the highest collision risks. For the 30-turbine layout it is predicted that turbines 1, 9, 10, and 13 will have the highest collision risks. All of these turbines are located in the northwestern corner of the wind-power plant. From the analyses of the summed vulnerability based on multiple data sources, the turbines located along the western turbine string and in the southwestern corner are expected to be the most sensitive turbines for both proposed layouts.
We recommend that an adaptive management plan is established as a follow-up program that regularly assesses the conflict level with the white-tailed eagle and whether mitigation measures should be initiated. This requires monitoring of the conflict level in the post construction period. The ongoing project INTACT working on identifying potential mitigation measures. Results from the INTACT project will be ready well in advance of the construction phase of a repowered Smøla wind-power plant, and should be taken into account in the follow-up program. In addition to mitigation measures, compensation measures could be used to compensate for e.g. bird mortality in the repowered wind-power plant.