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reproduction trends in herring, lesser black backed & great black backed gulls in britain and ireland
Pages 16 (4016 words)
The breeding population of great black backed, lesser black backed and herring gulls at coastal sites was definitively surveyed three times during the 20th century, in Operation Seafarer (1969-1970), the Seabird Colony Register Census (1985-1987) and Seabird 2000 (1998-2002).
However the greatest change was observed in herring gull numbers, which decreased markedly from 343600, through 177000 to 147100 by the time of Seabird 2000. The reasons for the change in herring gull numbers were suggested to relate to a reduction in food availability due to changed fishing practices in the North Sea, as well as diseases such as avian botulism. In addition pollution, particularly by organochlorides, and mink predation were indicated to be important. Whilst the numbers changed minimally great black backed gulls were believed to be subject to similar pressures to herring gulls. Little evidence has been provided to explain alterations in lesser black backed gull numbers. In this research the author examined the gull populations regionally within each country by comparing population shifts by east/west coast and by longitude. An interesting finding when comparing the lesser black backed gull population regionally, although west Scotland's population was two times greater than east Scotland's at the Seafarer count, the east coast population had increased 155% by the Seabird count. As seen by the analysis of data the breeding pair population in East Scotland is catching up with the population in the western part of the country. ...
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