By Martin Scott, Andy Webb, Catherine Irwin and Richard Caldow
Abstract The Outer Thames Estuary Special Protection Area (SPA) was classified in 2010 in recognition of its importance for wintering Red-throated Diver Gavia stellata, a species listed in Annex I of the EU Birds Directive. At classification in 2010 the SPA was estimated to hold 6,466 individuals on the basis of visual aerial surveys between 1989 and 2006/07. Aerial surveys using digital photography in January and February 2013 produced a revised peak population estimate of 14,161 individuals. A new survey, carried out in early 2018 and reported here, used high-resolution digital video imagery and generated a peak population estimate of 22,280 birds (95% CI 15,611–29,784). This confirms that the Outer Thames Estuary SPA supports by far the largest aggregation of non-breeding Red-throated Divers in UK waters.
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