A full county avifauna of this Welsh county, the first complete account of Caernarfonshire’s birds since publication of The Birds of Caernarfonshire by John Barnes in 1997. Information is now available from recent publicat ons including the new BTO Atlas covering the period from 2007 to 2011 and particularly The Breeding Birds of North Wales, covering this area at tetrad (four 1 km squares) level, rather than the 10 km square level used by the BTO. Every tetrad in Caernarfonshire, well as the other north Wales counties, was visited by fieldworkers between 2008 and 2011, with some additional visits in 2012. The results of this work give the most complete picture yet obtained of the county's bird population.