Abstract
In 2024, Ottvall Consulting AB, in collaboration with DCE - Danish Centre for Environment and Energy, Aarhus University, was commissioned by Zephyr/Vattenfall and Eolus Vind to undertake investigations of bird spring migration at Skagen, Denmark and at the Swedish west coast. The project continued similar investigations carried out in 2022 and 2023. The aim of the investigations was to assess the potential risk of collisions between birds and wind turbines in the planned offshore wind farms Poseidon Nord, Poseidon Syd (both managed by Zephyr/Vattenfall) and the windfarm Västvind (managed by Eolus) in the Swedish part of Kattegat and Skagerrak. Unlike the previous years, the offshore developer KonTiki commissioned and funded most of the migration study in 2024, and likewise commissioned, in collaboration with Eolus, the specific part of GPS-tagged raptors.
This report presents the results of the investigations carried out in 2024 in relation to the Poseidon project. It also includes the results from 2022 and 2023, highlighting similarities and differences in the bird migratory pattern between the three years. The data collected in 2024 will also support the assessment of the potential impact on birds from the Västvind project, but this is reported elsewhere on request from Eolus. The results from spring 2022 and 2023 have previously been reported by Christensen et al. (2023a, b, c).
As in 2022 and 2023, the 2024 study was conducted during the main spring migration period of birds, from March to June. In all years, the study design was set up to obtain data to support the assessment of the potential impact of the wind farm on migratory birds. The positions of the Poseidon wind farm areas are shown in Figure 1.
The study focused on estimating species-specific migration volume, flight altitude and direction of the substantial spring migration of birds occurring at the northernmost tip of Denmark, Skagen (Figure 1). For geographical reasons terrestrial bird species migrating over land, are concentrated at the Skagen peninsula on their way to breeding areas in northern Scandinavia, and substantial numbers of migrants cross the sea towards Sweden and Norway from this point. Observations were also made at the Swedish coast to record arriving migrating birds.
In all study years, special attention was given bird species of high conservation interest, specifically those listed in Annex 1 of the EU Birds Directive, as well as other regularly occurring migratory species.
The design of the study was created in a collaboration between Aarhus University and Ottvall Consulting. The aim was to provide data on species specific migration volumes, flight altitudes and flight direction of individuals and flocks of birds leaving the coast. This data would allow us to estimate the magnitude of bird numbers that will pass the planned wind farm areas and to provide estimates of the potential risk of collision with wind turbines for relevant bird species.
The present report presents data of the third year of the pre-construction investigations, which took place from mid-March to mid-June during spring 2024. Data from 2022 and 2023 (see Christensen et al. 2023a b, c) is included for comparison in the present report when appropriate. Estimates of the collision risk between birds and wind turbines based on our observations from all study years are also presented. The role of Ottvall Consulting was to organize and conduct observations of migratory birds along the Swedish west coast. Data from these surveys was delivered to Aarhus University, who conducted the collision risk analyses.
In the 2022 report, the estimation of collision risk was based on a preliminary designation of the wind farm areas, including both the Poseidon and Västvind projects. A later reduction in the size of the designated areas means that collision rates presented for the 2022 data (Christensen 2023a, b) have been lowered accordingly. The collisions rates for the updated wind farm areas are now based on new calculations presented in the present report, covering 2022, 2023 and 2024.