This report seeks to review current knowledge of the effects that offshore wind farms have on birds and to identify sensitive offshore locations where bird conservation interests and wind energy development may conflict. It seeks to provide information for all stakeholders in the development of offshore wind farms. The specific objectives of the project were to; (i) produce a review of the available reports, data and information relating to the effects of offshore wind farms on birds, (ii) establish the locations of offshore sites and areas that hold important bird populations, (iii) identify the bird migratory routes that may encroach upon prime offshore wind energy development areas, (iv) identify gaps and uncertainties in the existing knowledge and recommend further studies that are needed to address these, and (v) provide an inventory of planned and ongoing studies.
There are currently only eight operation offshore wind farms, all within northern Europe. As a result, there are only a small number of studies of the effects of offshore wind farms on bird populations. At Lely, in the Netherlands, two diving duck species (pochard and tufted duck) have been studied to investigate their flight behavior in the vicinity of wind turbines, mainly at night using radar tracking techniques. The main finding of this study was that these ducks were able to adjust their flight behavior according to the ambient light levels, and as a result were able to fly around the turbines, even in conditions of darkness. The study also showed that most birds passed around the outer turbines rather than between turbines, and led the authors to suggest that lines of turbines may act as a barrier. Study of a single offshore turbine in Sweden showed a similar change in flight patterns to avoid flying in close proximity to the turbine, with lower numbers flying within 500m.
The most comprehensive studies have been carried out at Tunø Knob, where a small (10-turbine) offshore wind farm was developed in an area used by substantial wintering seaduck populations. The species studied were mainly eider (peak 5,800), with smaller number of common scoter (peak 700). The main focus of the work was the potential disturbance effect of the wind farm. No significant disturbance effect was attributable to the wind farm. Changes in bird numbers in the wind farm area were highest after the wind farm had been constructed. The only detectable effect was that the eiders avoided flying and landing within 100m of turbines, but this had no impact on their feeding distribution. No significant effect was apparent on common scoter either though the results were not so conclusive for this species as sample sizes were smaller. The close link between bird abundance/distribution and that of their food supply highlighted the importance of integrated ecological study if impacts are to be fully understood.
A further study at Tunø Knob using a radar tracking showed that both eider and common scoter were also flying through the area at night. These birds did, however, modify their behavior around the turbines, with less flights withing 1500m of turbines at night (consistent with the Lely studies - the birds appear to maintain a greater distance from the turbines in conditions of poor visibility). Eiders tended to avoid flying between closely spaced (<200m) turbines, suggesting, as in the Lely study, that rows of wind turbines could potentially act as flight barriers. This has implications for wind farm design; long lines of turbines should be avoided in order to reduce effects on flight lines. They also suggested keeping distance between turbines as small as possible to minimize the total area of the wind farm.
More studies have been undertaken on the effects of onshore wind farms on birds, and some of these can provide useful information in the assessment of the likely effects of onshore locations too. However, there are differences between the new proposed offshore wind farms in the UK and the wind farms at which such studies have been carried out, and the implication of these difference must be carefully considered. The new offshore sites are likely to use larger, quieter turbines, with slower rotational speeds, and they are likely to be larger scale developments.
Studies at the onshore wind farm at Blyth Harbour in north-east England have covered a range of seabird/coastal species and are particularly relevant to offshore developments. A collision study here found that wind farm mortality was much less than the existing background mortality, including overhead wires (which resulted in double the collision rate in the study area compared with the wind farm). No evidence was found of any significant disturbance effects, other than during construction (when some species were temporarily displaced.