The descriptive text, below the map, is from the Cornish Red Data Book (2009). The map on this web page depicts the organisms distribution and shows the records made pre-2000 and those made since.
Range & Status
Palearctic; in Britain and Ireland 138,000 breeding pairs (chiefly in the north) and 1,700,000 in winter.
Cornwall: abundant non-breeder, with tens of thousands in winter. Single pairs had nested at Dozmary Pool (1959), on The Lizard (1963) and at Stithians (1967-69), prior to the colonies which formed at Crowdy in 1976 and since 1990 at nearby Colliford (up to 100 pairs at each site). These are the only colonies west of Poole Harbour (Dorset). Isles of Scilly: common non-breeder, with three records of occasional breeding (the last in 1925). Winters in numbers of 100+.
Habitat & Ecology
Breeds by freshwater and brackish marshes. Colonies at Crowdy and Colliford fluctuate and interchange from year to year, depending on water levels. Other breeding waterbirds tend to benefit from the predator-mobbing behaviour of these gulls.
A sudden rise in water levels can destroy colonies at peak of breeding season.
The colony at Colliford is within the Cornwall Bird Watching and Preservation Society reserve.
I.J. Bennallick, S. Board, C.N. French, P.A. Gainey, C. Neil, R. Parslow, A. Spalding and P.E. Tompsett. eds. 2009. Red Data Book for Cornwall and the Isles of Scilly. 2nd Edition.Croceago Press.
The Cornish Red Data Book Project was led by the Cornwall and Isles of Scilly Federation for Biological Recorders (CISFBR). The full text and species accounts (minus the maps) are available on the CISFBR website.