The Winter Atlas maps 200 species occurring in Britain and Ireland in winter. The maps are derived from surveys of birds present in Britain and Ireland during the three winters, 1981/82, 1982/83 and 1983/84. The surveys were organised by the British Trust for Ornithology and the Irish Wildbird Counsevancy, as were the earlier breeding birds surveys.
The maps reproduced here for species occurring in Pembrokeshire use the same "assessment of relative abundance" as the original maps, but are shown as light, mid and dark blue instead of different sized dots. For example, a map with light blue squares only indicates that the species is more abundant elsewhere in Britain.
Detail of the methodology, and the results for the whole country, are to be found in: Lack, P.C. (1986) The atlas of wintering birds in Britain and Ireland. T. & A.D. Poyser and national maps for individual species can also be accessed from the drop-down list at the bottom of the BTO Atlas page.
All the Pembrokeshire maps can be accessed by clicking here or on the "1980s BTO winter atlas" tag below.