This report presents data on monitoring investigations of birds carried out during 1999-2005 in relation to the construction of the world’s first two large offshore wind farms at Horns Rev and Nysted in Denmark. We consider the hazards turbines posed to birds and the physical and ecological effects that these cause. We propose a series of hypotheses relating to these effects on birds at the two sites, testing to see if birds do indeed show reactions to the turbines once erected, relative to their “unaffected” behaviour we monitored during pre-construction baseline studies. In this way, the effects of the construction of the wind farms at sea could be predicted from our hypotheses and validated by post construction monitoring and data collection which was a condition of planning permission for the Danish projects. Throughout, we have restricted our studies primarily to waterbirds, because these are the species that exploit the offshore environment in general and the two study areas in particular, because Denmark has a special responsibility for the maintenance of their populations and the habitat that they use and because long lived birds with relatively low annual breeding success (which include many waterbirds) are those most susceptible to additional mortality. This does not mean that other species (such as many bird of prey and short-lived land birds that pass through the areas on migration) are not important, but their study was generally beyond the scope of these investigations. In general terms, the potential effects of the construction of a wind farm on birds were considered to rise from three major processes:
1. A behavioural element caused by birds avoiding the vicinity of the turbines as a behavioural response to a visual (or other) stimulus. This can have two effects:
- a barrier effect affecting bird movement patterns, potentially increasing costs
- the displacement of birds from favoured distribution, equivalent to habitat loss
2. Physical changes due to construction (physical habitat loss, modification to bottom flora and fauna and creation of novel habitats, e.g. for resting on the static superstructure).
3. A direct demographic element resulting from physical collision with the superstructure (mortality).