Abstract
Currently, according to SNH (2010) guidance the recommended avoidance rate for swans under the Band Collision Risk Model (CRM) is 98 %. The objective of the present report is to evaluate available contemporary information on the most suitable value for an avoidance rate for swans that may encounter operational onshore wind farms.
We highlight that the avoidance rates recommended by SNH (2010) consist largely or entirely of a Micro component and do not, as claimed by SNH (2010), encapsulate both potential Micro and Macro (displacement) components. If there is evidence or arguments to support the need for such Macro avoidance measures to be considered as relevant in assessments of wind farm proposals, then the avoidance rates of SNH (2010) should be regarded as minima. We refer to reviews and other studies which document that large wildfowl (including swans) are susceptible to displacement (Macro avoidance).
Whitfield (2010) argued that swans should probably be considered to have similar avoidance rates to geese. At that time, the SNH guidance recommended a 95 % avoidance rate for swans. On the basis of Whitfield (2010) the avoidance rate for swans was increased to 98 % in SNH (2010), although the avoidance rate for geese was given as 99 % in SNH (2010). SNH (2013) later recommended increasing the 99 % avoidance rate of SNH (2010) for geese, to 99.8 %.
Subsequent to Whitfield (2010), based on a later published study by Fijn and colleagues (2012) in a Dutch polder for Bewick’s swan, the present report derives an estimated avoidance rate (Micro avoidance only) of 99.7 % or, including displacement of flying birds (Macro avoidance), at 99.8 %1. If reported displacement of feeding birds would have been included, the derived avoidance rate would have been still higher.
Despite some previous reviews (e.g. Rees 2012) and the findings of Fijn et al. (2012), it is apparent from recent information that feeding large wildfowl (including, likely, swans) are not always dissuaded from feeding within turbine arrays. Hence, we do not recommend that assessments of wind farm proposals that involve feeding swans within proposed arrays should de facto increase our derived 99.7 % and 99.8 % avoidance rates to yet higher rates.
In assessments of wind farm proposals where swans are flying across a proposed development area that intercepts a commuting route we would recommend that rates of 99.7 % and/or 99.8 % should be used (according to circumstance), and not 98 % (SNH 2010).
While we acknowledge that these rates are based empirically on only a single study, we present several corroborative lines of other evidence; and note that the study was fundamentally precautionary as regards swan mortality. Our recommended avoidance rates are applicable only to the original Band CRM and not to any subsequent model extensions.