Abstract
In 2023 and 2024, ornithological studies were conducted to provide baseline data for EIA of future offshore wind farms in the NSI area, located in the eastern part of the Danish North Sea. These surveys aimed to gather background data for future environmental impact assessments related to upcoming offshore wind farm projects. The ornithological studies consisted of two main components. The first component aimed to provide data on bird species abundances and distributions across the pre-investigation area and a 20 km buffer zone around it, referred to as the survey area, over the course of a year. To achieve this, eight aerial surveys were conducted between April 2023 and March 2024. During these surveys a total of 7 species groups and 28 species of birds were observed from the eight aerial surveys in the SNI area between April 2023 and March 2024. Each survey was performed using two aircraft and employed the distance sampling survey method. This approach allowed for the modelling of total abundances and distributions of selected bird species. Based on these modelled estimates, a persistency map for the survey area was created, highlighting areas of high or low importance for specific species or species groups across all surveys. Data from each of the eight surveys were used to derive information about the abundances and distributions of the following species/species groups: red-throated/black-throated diver, northern gannet, black-legged kittiwake, and razorbill/common guillemot. The maximum bird numbers per survey were 7,548 divers, 2,642 northern gannets, 3,669 black-legged kittiwakes, and 35,069 razorbills/common guillemots.
The other part aimed to describe the movements of flying birds in the pre-investigation area. Data from observations of flying birds from ship-based surveys gave information on the composition and flight altitude distribution of selected species or species groups. While almost 100% of some species flew very low over the sea surface (0-25 m), other species or species groups were recorded to fly higher. For example, common scoter and razorbill/common guillemot flew very low, whereas species of waders and gulls flew higher. Data from the ship-based surveys also gave information about the composition of species that are difficult to identify from aerial surveys, such as red-throated/black-throated divers and razorbill/common guillemots. While red-throated divers dominated the diver group, razorbills and common guillemots comprised 43% and 56% of the auk group. The species composition of the latter group varied considerably across the annual cycle.
Data from a vertical radar provided information on flight magnitude and altitude both day and night. The radar records objects that can be a single bird or a group of birds. Neither species nor group size can be inferred from data from the radar. There was both annual and diurnal variation in the bird flight activity. The movement of flying birds showed much higher flight activity in October 2023 than in any other month relating to bird autumn migration. The diurnal variation showed that the flight activity was highest at night in October 2023. Elevated activity was less pronounced during cruises in other months.
This report also presents a description of existing data. An overview of existing ornithological data from the Danish North Sea is presented. Data from an aerial survey in April/May 2019 was used to estimate abundances and distributions for selected species and species groups across the entire Danish part of the North Sea. On the basis of that dataset, total abundances and distribution of the following species could be generated: red-throated/black-throated diver, northern fulmar, northern gannet, black-legged kittiwake and razorbill/common guillemot. The total estimated abundances for these species were 22,648 divers, 46,437 northern fulmars, 31,723 northern gannets, 4,472 black-legged kittiwakes and 89,681 razorbills/common guillemots (Petersen, et al., 2024). These data can perspectivate bird abundances within the NSI area with densities and distributions in other parts of the Danish North Sea. Common scoters and red-throated divers are mainly found in the eastern parts of the bird survey area, and thus almost absent from the North Sea Energy Island study area. Bird species with a more pelagic distribution, such as northern fulmar, was found in smaller numbers in the NSI area than in the North Sea Energy Island area. Northern gannet and razorbill/common guillemot were found in comparable numbers between the two survey sites.