The accuracy of urban nesting gull censuses

Capsule The vantage point survey methods used in the 1999–2002 surveys of urban nesting large gulls in Britain and Ireland appreciably underestimated numbers, resulting in lower national totals and exaggerated national population changes, because they did not account for a substantial proportion of undetected nests.Aims To evaluate the efficiency of various survey methods for urban nesting large gulls.Methods Vantage point and street surveys of Herring and Lesser Black-backed Gulls Larus argentatus and Larus fuscus nests were made in six urban conurbations and used to compare detection efficiencies. Some nests missed by both methods were later identified by the presence of unfledged chicks. In later years, the numbers of nests which were actually missed was determined by using a ‘cherry-picker’ which allowed all nests to be located in Dumfries. The proportion of nests on industrial and commercial buildings was recorded.Results Vantage point and street surveys missed an appreciable number of nests and had ...