Welsh Journals

THE LARUS GULLS BREEDING ON SKOMER, SKOKHOLM AND GRASSHOLM ISLANDS M. P. HARRIS Department of Zoology, University College of Swansea INTRODUCTION Various studies which are being undertaken on Skomer Island on the Herring Gull (Larus argentatus), Lesser Black-backed Gull (L. fuscus) and Great Black-backed Gull (L. marinus) depend upon estimates of the numbers of breeding birds. This paper presents the results of a census of gulls made on Skomer in May 1962 and on Grassholm in June 1962, and also a summary of gull censuses on Skokholm. Mr. D. R. Saunders, Warden of Skomer, has kindly supplied his estimate of the number of breeding Great Black-backed Gulls on Skomer. This figure may be lower than it might have been in view of recent (1960-62) control measures. The Skomer totals are compared below with those given earlier by Buxton and Lockley (1950). Lesser Black- Great Black- Herring Gull backed Gull backed Gull 1945 c. 660 pairs c. 1,090 pairs c. 40 pairs 1946 c. 700 II c. 1,000 II c. 60 II 1962 c. 1,070 II c. 1,400 II c. 235 II The increase in the population shown above may be due in part to local protection (except perhaps for the Great Black-backed Gull) but also reflects the general increase in the population of these species in Wales. HERRING GULL ON SKOMER The census area was divided into three parts-the Neck, the main island, and the detached Mew and Garland Stones. These and other features referred to here are shown on the maps in Bux- ton and Lockley. All nests found on the Neck were marked as part of a separate study which enabled an accurate count (400) to be made. The main island coastline was visited between the 15th and the 24th May 1962 and thoroughly searched for nests. Only those with eggs or young were counted but very few breeding pairs would be without clutches at this time. The largest colonies were found on the coast between North Stream and North Castle (c. 100 pairs), Skomer Head and Pig Stone Bay (77 pairs), Skomer Head and Tom's House (105 pairs), and the Mew Stone and High Cliff (58 pairs). Nesting on the remaining coastline was sporadic for example, only 40 nests were found in a distance of a mile and a quarter between North Stream and the Table. Approximately 50 pairs nested in the Lesser Black-backed Gull colonies in the