2013 Natural England (NE) Aerial Bird Surveys in the Outer Thames SPA dataset https://portal.medin.org.uk/portal/start.php?tpc=010_1029463f26a62ea9bf8ad0b5cae54aa6 The Outer Thames Estuary Special Protection Area (SPA) is designated for wintering red throated divers which are listed in Annex I of the European Union (EU) Birds Directive (79/409/EEC). The population of red-throated divers is currently designated as 6,466 individuals; 38% of the Great British population. This figure was taken from visual aerial surveys undertaken between 1989 and 2007. The aim of this project was to provide current information regarding the abundance and distribution of a variety of wintering bird species, predominantly red-throated divers, present within the Outer Thames Estuary SPA. Two high resolution digital aerial surveys of the Outer Thames SPA were conducted during January and February 2013. Each survey was flown on a series of transects separated by 1.8 km, collecting abutting 3 cm resolution imagery. Average coverage was 15%. Population estimates of red-throated divers were calculated using two methods 1) a design-based method and 2) a model-based estimate using a Generalised Additive Modelling (GAM) framework. Model-based estimates had tighter confidence limits around the population estimates and precision was improved from the design-based estimate. From the model-based calculations, red-throated divers peaked in February 2013 at an estimated 13,605 (12,712 â?? 14,489) individuals. This peak is more than double the designated SPA total and represents 79% of the wintering Great British population. Higher numbers of red-throated divers were recorded in the southern part of the Outer Thames SPA during February 2013. In January 2013, higher numbers of individuals were recorded in the northern part of the SPA. This suggests a movement further into the estuary between the two surveys. wide range of other bird species were recorded, including greylag geese, shelduck, wigeon, scaup, common scoters, red-breasted mergansers, black-throated divers, great northern divers, great crested grebes, fulmars, gannets, cormorants, shags, oystercatchers, lapwings, redshanks, great skuas, kittiwakes, black-headed gulls, common gulls, lesser black-backed gulls, herring gulls, great black-backed gulls, guillemots and / or razorbills, little auks and puffins. After red-throated divers, common gulls were the next most abundant species (12,403; 2,203-30,110). 9. A number of marine mammal species were also recorded during the aerial surveys including dolphins and / or porpoises not identified to species level, harbour porpoises and a phocid (seal) species. Marine mammals were most abundant in January 2013 (584; 356-880) and were distributed widely throughout the SPA. 10. Although it is necessary to treat modelling results based on two months of survey data with great caution, red-throated diver distributions on the SPA appeared to be related to various environmental valuables including: bathymetry, chlorophyll a, wave base, tidal base, aspect of the sea bed, slope of the sea bed, average sea surface temperature, distance from dredging operations and distance to coastline. The distributions of red-throated divers may also have been affected by shipping activity and the presence of operational and in-construction wind farms 20130805 20130805