The selection of appropriate avoidance rates for use in collision risk models at offshore windfarms is often a key part of the Environmental Impact Assessment process. Ideally, these avoidance rates should reflect the behavioural responses of birds to turbines. However, they are often used as a ‘fudge-factor’ to incorporate aspects of model error. The situation is further complicated by a lack of data for marine birds and offshore windfarms. As a consequence, present guidance is based on values that have been derived for terrestrial species at onshore windfarms. This study reviewed data that have been collected from offshore windfarms and consider how they can be used to derive appropriate avoidance rates for use in the offshore environment. Aims of the study were five-fold: To produce definitions for the types and scales of avoidance; To review current use of avoidance rates; To review and critique existing avoidance behaviour studies and any derived rates; To provide summary avoidance rates and a total avoidance rate for each priority species/species group based on the evidence available at present; To undertake an assessment of the sensitivity of the conclusions reached to inputs and conditions under which they were collected.
The study focussed on five priority species – northern gannet, black-legged kittiwake, lesser black-backed gull, herring gull and great black-backed gull – whose behaviour and distribution make them particularly prone to collision with offshore turbines.