--- - |2 Law frequently demands the production, sometimes effortful, of adequate knowledge for decision making. This article explores the challenging epistemic demands made by nature conservation law during planning law approval processes for major offshore wind farms. It explores this area through the prism of co‐production: not only are ‘science’ and ‘facts’ socially and legally constructed, but in addition, scientific and factual findings shape society, and law and governance. Models are used in planning law to assess whether bird deaths associated with a proposed wind farm will have an adverse effect on the integrity of a protected site. As much as providing an accurate factual representation of the impact of a wind farm on biodiversity, the models contribute to the very possibility of governing the impact of these novel infrastructure developments on biodiversity. - Journal of Law and Society, Volume 45, Issue 3, Page 427-456, September 2018.