Deriving Collision Avoidance Rates for Red Kites Milvus milvus


Title: Deriving Collision Avoidance Rates for Red Kites Milvus milvus
Publication Date:
August 01, 2006
Pages: 14

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Whitfield, D.; Madders, M. (2006). Deriving Collision Avoidance Rates for Red Kites Milvus milvus. Report by Natural Research Ltd. pp 14.

Several 'Band' Collision Risk Model (CRM) avoidance rate estimates have been derived for several birds of prey, but none are available for red kites due to a lack of appropriate available data. In the absence of any means to use an empirically derived avoidance rate, two options are available in practice: use a generic 95% 'precautionary' rate or use a rate based on empirically derived measures in other birds of prey. A generic 'precautionary' Band CRM avoidance rate of 95%, proposed before any empirical measures were derived, is increasingly being revealed to produce unrealistic predictions of collision fatality rates. Given a similarity between many recently derived estimates of CRM collision avoidance rates in birds of prey, a more reasonable approach to derive a likely avoidance rate in a bird of prey such as the red kite where there is no empirically based estimate is to assume that it too will be similar. This assumption should preferably be qualified if possible, however, by an assessment of whether kites are more or less likely to die through collision than other species.


Most estimates of avoidance rates for birds of prey lie between 98% and 100%. At least at some sites avoidance rates are not 100% in red kites and so an initial assumption was made that red kites would show an avoidance rate of above or equal to 98% but below 100%. This assumption was checked using data for several birds of prey collected at 13 wind farms in northern Spain by Lekuona & Ursúa (2006). These data indicated that red kites (and black kites) were not relatively vulnerable to collision strikes compared with other birds of prey. (Griffin vultures and common kestrels appeared to be relatively vulnerable to collision strikes.) Thus, the initial assumption was not contradicted, so it was concluded that an appropriate avoidance rate for red kites should probably be over 98%; likely around 99%. Clearly, however, empirically derived measures should be sought through work at operational wind farms.

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