BOER P (1971) Counts of birds on North Sea in August 1970. LIMOSA 44 (1): 23-28.

During the period of August 18th-27th, 1970, bird counts were made from a trawler crossing the North Sea (Fig. 1). Counts made over sections of the route were compared with counts made when the ship was drifting with the engine stopped. It appeared that in the latter case Gulls, Skuas and Shearwaters came flying towards the trawler and swam around the ship. By comparing the numbers of Kittiwakes and Fulmars along sections of the courses with the numbers counted around the ship it could be concluded that the birds swimming around the ship came from an area of about 3272 km2. Counts from a (fishing-)ship that is not steaming are to be preferred over counts during part of the course, since the latter method is restricted to periods with a very calm sea, and the former gives more reliable results. The maximum distance at which a mediumsized bird can be identified is thought to be about 1 km. By taking the average number of birds observed at every point of observation (Fig. 1), that is over an area of 3272 km2 , the number of birds per unit of area could be calculated (Table 1 and 2). It appeared that at the time of the counts a number of species were still tied to the breeding sites. Species that had left their breeding grounds were seen to be scattered all over the North Sea (Arctic Skua, Kittiwake, A1cidae). Species of which most birds had left the breeding grounds (Great Skua, Fulmar) had spread out over a moderate distance from the coast. Of course those species which still had pulli to look after in the breeding colonies (Gannet, Great Black-backed Gull) were observed closest to the shore ##### Sooty Shearwater Puffinus griseus Northern Fulmar Fulmarus glacialis Northern Gannet Morus bassanus = Sula bassana Great Skua Stercorarius skua Black-legged Kittiwake Rissa tridactyla Leach's Storm Petrel Oceanodroma leucorhoa Pomarine Jaeger Stercorarius pomarinus Great Black-backed Gull Larus marinus Common Gull Larus canus canus European Herring Gull Larus argentatus Black Scoter Melanitta nigra Black-headed Gull Chroicocephalus ridibundus = Larus ridibundus Arctic Tern Sterna paradisaea Atlantic Murre Uria aalge Atlantic Puffin Fratercula arctica Razorbill Alca torda

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