Environmental organisations are concerned about the impact of turbines on bird populations, particularly migrating birds. A Danish scientific study published in 2019 found evidence that larger birds were tending to avoid turbine blades, but said it didn't have sufficient evidence for smaller birds – and cautioned that the cumulative effect of farms could still have an impact on bird movements.
A full environmental impact assessment has to be carried out before a developer can apply for planning permission to develop an offshore wind farm. This would include desk-based studies as well as extensive surveys of the population and movements of birds and marine mammals, as well as fish and seabed habitats.
If a potential environmental impact is identified the developer must, as part of the planning application, show how the project will be designed in such a way as to avoid the impact or to mitigate against it.