The  following was adapted from original text by Mark L. Tasker in Seabird Populations of Britain and Ireland (with permission from A&C Black, London).

 

The Common (or Mew) Gull breeds across the Palaearctic and in North America. They breed on coasts and at inland sites, and spend the winter inland, on estuaries and at sea. Terrestrial foods include earthworms, beetles and other insects, while discarded fishery wastes supplements natural food at sea. In Britain and Ireland their breeding distribution is virtually confined to Scotland and north-west Ireland.

 

The Common Gull is a colonial breeder, but can also breed in solitary nests. During Seabird 2000 over half (57%) of the total population in Britain and Ireland were breeding inland. Despite the inland bias in the distribution, this was the first time that all inland-breeding [1] Common Gulls had been censused. There is no reason to suggest that coastal and inland nesting Common Gull populations are in anyway separate. Therefore, it is essential that inland colonies are surveyed as thoroughly as those on the coast if an accurate assessment of the current status of Common Gulls in Britain and Ireland is to be made.

 

 

Only coastal-nesting Common Gulls were counted fully during both Operation Seafarer (1969-70) and the SCR Census (1985-88) so comparison between Seabird 2000 population estimates and the previous censuses are based only on coastal colonies. During the SCR Census (1985-88) the total inland population was estimated to be 60,000 pairs. This was based largely on the fact that in 1988-89 some 40,000 pairs were nesting at just a few colonies in the Mortlach Hills (Moray) and Correen Hills (Gordon) in NE Scotland. During Seabird 2000, survey coverage was based on a list of colonies extracted from the SCR Database that were known to have existed at some time between 1969 and 1998. However, this list was neither comprehensive nor up to date and was amended by BTO County Bird Recorders with records of new colonies and of those that had ceased to exist. Common Gulls nest in many inland areas of Scotland and remoter areas of England and Ireland. Coverage of such areas during Seabird 2000, by the relatively small number of observers involved, is difficult to assess but it is likely that all areas were covered at least once during the period of the survey. If however the species is mobile between sites within this count period, some breeding sites could have been missed and other groups of birds double-counted. There has never been a census of this species over one year that would enable this possibility to be assessed.

 

 

During Seabird 2000, the recommended census unit for Common Gulls was the apparently occupied nest (AON). Counts of AONs were conducted either within the colony or from a suitable vantage point. Large colonies were surveyed using sample quadrat counts of AONs. At colonies that could not be accessed (e.g. on marshy ground or on islands) and where there was no suitable vantage point, flush counts of individuals attending the colony were made. Counts of individuals were divided by two to provide a rough approximation of the number of AONs present. This is the least accurate method for censusing breeding gulls, as such counts will include an unknown percentage of non-breeders and attendance at the colony by both breeders in a pair is highly variable throughout the day and throughout the breeding season. The accuracy of counts of individuals is difficult to assess. However during both the SCR Census (1985-88) and Seabird 2000, similar proportions of the total number of AONs counted were derived from counts of individuals, i.e. 30% and 38% respectively.

 

 

Counts of breeding gulls within each admin area during Seabird 2000 and during previous censuses from gull surveys are presented differently from other species to take into account the variation in coverage of inland and coastal colonies during Seabird 2000 and the previous two censuses. Since no inland colonies were surveyed during Operation Seafarer (1969-70), Table 1 compares counts from all three censuses from coastal colonies only, but also gives the total number present in both inland and coastal colonies during Seabird 2000.

 

Census Methods     Data Processing and Analysis     References     Seabird 2000

 

[1] Coastal colonies were regarded as those being within 5km of the high water mark; inland colonies were further from the sea than this. All colonies in Orkney, Shetland and the Western Isles were regarded as coastal.