Northern gannet (Morus bassanus) are thought to be susceptible to impacts arising from both habitat loss, due to displacement from offshore wind farms (OWFs), and collision with wind turbine blades. Historically, impact estimates from both pathways have been calculated separately and then simply summed when used in Environmental Impact Assessment (EIA) and Habitats Regulations Assessment (HRA). However, this approach could overestimate impacts because some of the birds displaced from an array will not be at risk of collision.
With the aim of producing more realistic collision risk estimates, Natural England commissioned HiDef Aerial Surveying Ltd. to deliver an evidence-based approach to ensuring avoidance of OWF arrays (also termed macro-avoidance) by gannet is accounted for in collision risk assessments.
Nine studies, identified during a literature review, reported suitable gannet macro-avoidance rates (proportions of birds avoiding an OWF array) that ranged from 0.617 to 1.000. These rates were calculated at a range of sites using varying methods. A quality scoring system was applied to these studies which was used to produce a weighted mean overall macro-avoidance rate of 0.8330 (95% CI 0.4410 – 0.9959). However, given uncertainties associated with this method, a simple mean approach was deemed more robust, resulting in a macro-avoidance rate estimate of 0.8564 (95% CI 0.5349 – 0.9736).
To incorporate macro-avoidance into collision risk modelling, it was recommended that the input densities are corrected by agreed macro-avoidance rates, and a ‘within wind farm’ avoidance rate is applied when undertaking CRM.