Knowledge of the long-term impacts of offshore wind energy on seabird populations is in its infancy. Ambitious European Union renewable energy targets mean that the North Sea contains more offshore wind farms than anywhere else globally, with many further sites proposed.
Most North Sea seabird species are undergoing long-term declines, yet wind turbines are known to present issues for birds, including direct collision mortality.
The Environmental Impact Assessment process for a large-scale wind energy development must include an analysis of the potential collision risk to birds. This analysis is undertaken via collision risk models, which require the input of an in-flight bird density figure.
It is the derivation of this density figure which has received little attention thus far from ornithologists and marine planners. Usually a mean figure derived following two years of baseline surveys is used. However, it is arguable that mean densities are not always either representative or sufficiently precautionary, and this serves to compromise any attempt at wider Cumulative Impact Assessment. Another area of concern is the length of time accorded to species’ breeding seasons, which may influence the impacts attributable to any particular Special Protection Area (SPA) designated for that species.
In this research, comparisons and analyses were made of the implications of differences in the expression of bird density and of the definition of breeding seasons relating to four exemplar taxa (northern gannet Morus bassanus, lesser black-backed gull Larus fuscus and black-legged kittiwake Rissa tridactyla) across a total of six large wind farms in the UK section of the southern North Sea.
This reinterpretive review suggests it is more precautionary to measure density via a peak, rather than a mean figure. However, wider questions are raised regarding the central role of density for collision risk modelling purposes. A further conclusion is that the definition of a species’ breeding season significantly influences the assessment of the impacts of offshore development on the integrity of any breeding sites designated for that species.