The first national breeding bird survey was organised by the British Trust for Ornithology and the Irish Wildbird Counsevancy. The Atlas presented the results of five summers of fieldwork (1968-72) carried out by volunteers and covering the whole of Britain and Ireland.
The maps reproduced here for species occurring in Pembrokeshire use the same categories of possible, probable and confirmed breeding as the original maps, but are shown as yellow, orange and red instead of different sized dots. All maps presented for this survey are at 10-km square (Hectad resolution). A maximum of 32 10-km squares cover the Vice County. This includes partial ones along boundaries with neighbouring counties Carmarthenshire and Ceredigion and along the coast.
Detail of the methodology, and the results for the whole country, are to be found in: Sharrock J.T.R. (1976) The atlas of breeding birds in Britain and Ireland. BTO/IWC and national maps for individual species can also be accessed from the BTO mapstore.