Seabirds Count is the fourth census of Britain and Ireland’s internationally important populations of breeding seabirds. Over 10,000 sites and 25 species were surveyed between 2015 and 2021, providing a comprehensive update on the state of these populations. These vital data will help aid our understanding of the relationships between seabirds and the pressures they face. Treated species: Northern Fulmar - Fulmarus glacialis, Manx Shearwater - Puffinus puffinus, European Storm-petrel - Hydrobates pelagicus, Leach's Storm-petrel - Hydrobates leucorhous, Northern Gannet - Morus bassanus, Great Cormorant - Phalacrocorax carbo, European Shag - Gulosus aristotelis, Arctic Skua - Stercorarius parasiticus, Great Skua - Catharacta skua, Mediterranean Gull - Ichthyaetus melanocephalus, Black-headed Gull - Chroicocephalus ridibundus, Common Gull - Larus canus, Lesser Black-backed Gull - Larus fuscus, Herring Gull - Larus argentatus, Great Black-backed Gull - Larus marinus, Black-legged Kittiwake - Rissa tridactyla, Sandwich Tern, Thalasseus sandvicensis, Roseate Tern - Sterna dougallii, Common Tern - Sterna hirundo, Arctic Tern - Sterna paradisea, Common Guillemot - Uria aalge, Razorbill - Alca torda, Black Guillemot - Cepphus grylle, Atlantic Puffin - Fratercula arctica