Dartford Warblers have a small world range encompassing southern England, the Channel Islands, western and southern France, Iberia, peninsular Italy, the larger west Mediterranean islands and coastal North Africa.
    In Britain they were once much more widespread but suffered a steep decline in the late 19th century, probably as a result of habitt loss. Severe winters in the 1960s  caused numbers to fall to no more than 11 pairs by the middle of the decade. This was followed  by a steady, though fluctuating, recovery. The 1968-72 Breeding Atlas estimated the 1974 population to be 560 pairs, a total which had almost tripled by 1994, then fell back after another harsh winter in 1995-96 before rallying to around 2000 by the turn of the century.
    In Wiltshire Dartford Warblers were probably common in the 19th century, when their preferred gorse habitat was being managed for fuel. Cold winters towards the end of the 19th century leading up to a particularly severe winter in 1916-17 reduced the national population to the lowest level since records began and marked the end of the species' regular appearance in Wiltshire in all but a few isolated pockets. The surrounding counties of Hampshire, Dorset and Somerset still retained resident populations and many of the records in Wiltshire since the mid 20th century have occurred near the Hampshire border in particular. There have also been occasional records of breeding on Salisbury Plain and scattered reports of individuals elsewhere in the county.

The following references are used throughout these species’ accounts, in the abbreviated form given in quotation marks:
1968-72 Breeding Atlas” – Sharrack, J.T.R. 1976:  The Atlas of Breeding Birds in Britain and Ireland. T. & A. Poyser
1981-84 Winter Atlas” – Lack, P.C. 1986:  The Atlas of Wintering Birds in Britain and Ireland. T. & A. Poyser
1988-91 Breeding Atlas” – Gibbons, D.W., Reid, J.B. & Chapman, R.A. 1993: The New Atlas of Breeding Birds in Britain and Ireland 1988-91. T. & A. Poyser
“Birds of Wiltshire” – Ferguson-Lees, I.J. et al. 2007: Birds of Wiltshire, published by the tetrad atlas group of the Wiltshire Ornithological Society after mapping fieldwork 1995-2000. Wiltshire Ornithological Society.
Bird Atlas 2007-2011”-– Balmer, D.E., Gillings, S., Caffrey, B.J., Swann, R.L., Downie, I.S. and Fuller, R.J. 2013: The Breeding and Wintering Birds of Britain and Ireland. BTO Books. 
WTA2” – ("Wiltshire Tetrad Atlas 2 ") the present electronic publication, bringing together the Wiltshire data from “Birds of Wiltshire” and “Bird Atlas 2007-11”, together with data from further fieldwork carried out in 2011 and 2012.
"Hobby" - the annual bird report of the Wiltshire Ornithological Society.