Changes in Stone CurlewBurhinus oedicnemusdistribution and abundance and vegetation height on chalk grassland at Porton Down, Wiltshire

Annual surveys of breeding Stone Curlews at the Chemical and Biological Defence Establishment at Porton Down between 1987 and 1994 indicate that it is an important site for the species, having held up to 12% of the national breeding population. However, the population and the proportion of pairs nesting on chalk grassland declined between 1992 and 1994 after an increase since 1988. A comparison of measurements of sward height in 1989 and 1994 indicates that sward height had increased at breeding sites on seminatural chalk grassland which were used when the number of pairs nesting on downland was increasing. The sites with the smallest increases in sward height were those at which Stone Curlews continued to nest. The changes in vegetation are believed to be attributable to increased rainfall and lower densities of Rabbits. The implications of the results for conservation and management are discussed.