Changes in the gull populations of SW Wales

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Abstract
The breeding populations of the Larus gulls in SW Wales are reviewed, using all the available information hut specifically drawing on the data from the islands of Skomer, Skokholm, St Margarets and Caldey. After increasing steadily for many years, Herring Gull numbers have recently declined rapidly. Some populations of Great Black-backed Gulls have been greatly affected by deliberate control measures but the records show a similar pattern to that of Herring Gulls, with large decreases being recorded recently despite the lifting of these controls. The decreases in the populations of these species are coincident with botulism poisoning of adult birds during the breeding season, probably resulting from feeding on refuse tips. There may be a connection between the introduction of black plastic bags for refuse collection and the outbreak of botulism in SW Wales. Lesser Black-backed Gull populations continue to increase at a rate that has been roughly constant for at least 15 years. This species rarely feeds at refuse tips in the area, the large quantities of small fish brought to the breeding colonies are thought to originate from the Nephrops fisheries in the Celtic Sea. It appears likely that the populations of Herring and Great Black-backed Gulls will continue to decline, at least until breeding success improves. Numbers of Lesser Blackbacked Gulls may continue to increase, although control measures are being implemented at some colonies in an attempt to reduce them.