Population Trends in Larids Dissertation Example | Topics and Well Written Essays - 11250 words

Population Trends in Larids - Dissertation Example ing gulls regionally, it was interesting to note that while the western colonies which were 10 times later than the eastern colonies in England during the seafarer census, the western colonies have declined by almost 27,000 pairs while the east coast colonies have steadily grown over the censuses. Although still much smaller than the west coast, it will be interesting to see if the decline in the west and increase in the east will continue. In striking contrast, at the seafarer census the east Scotland colonies were nearly three times those of the west coast. However, by the seabird census the populations on the east and west coast of Scotland were virtually identical. When examining the herring gull by latitude one of the greatest differences noted is the drastic decrease of the population in the 56-58N latitude in particular. The huge colonies present at Seafarer had been decimated by the seabird census. In fact, much of the herring gull population has seen a phenomenal decrease in the latter part of the 20th century. Table of Contents 1.0 Chapter 1 - Introduction 3 3.0 Chapter 3 - Methodology 17 4.0 Chapter 4.0 - Results/Analysis 22 Appendices 61 1.0 Chapter 1 - Introduction 1.1 Background Information There have been 3 major surveys conducted in Britain and Ireland that have measured the breeding populations of great black backed, lesser black backed and herring gulls. These are the Operation Seafarer surveys, conducted in 1969-70; the Seabird Colony Register census, conducted in 1985-87; and Seabird 2000, conducted in 1998-2002. By analysis of the differences in the numbers observed in these three surveys, it is possible to show variation in population trends over time of these three very closely related bird species. Species... This dissertation reveals that gulls are known to feed at areas of sewage outflow to the sea, such as in the Bristol Channel. It has been noted that they appear well adapted to feeding in polluted areas, as they have a well-developed detoxification system. There was a change in the numbers of lesser black backed gulls feeding at sewage outlets in South Wales, where a 289% increase in numbers between the 1970s and 1990s was observed in one study. However, it was also found that feeding from sewage outlets was overall much more common in black-headed gulls than lesser black backed or herring gulls, with 11% of the population of black headed gulls feeding at sewage outlets, compared to 3% for herring gulls and 7% for lesser black backed gulls. In conclusion, there was also a difference in feeding patterns throughout the year, with far more gulls feeding at sewage outlets during the summer, compared to winter. This has a particular significance in that the summer is when breeding pairs are incubating and caring for offspring, which could then be affected by the parental diet. Refuse, whether sewage or on land, supports 43-75% of the diet of lesser black backed and great black backed gulls. However, it is often juvenile, non-breeding gulls that are found at sewage outlets, which means that offspring are less likely to be affected. There has been a link between salmonellae occurrence in gulls and the number of human cases in local hospitals, with this being linked to a similar contaminated food source, as opposed to direct infection.