The Dartford warbler (Sylvia undata) is a typical warbler from the warmer parts of western Europe and northwestern Africa. Its breeding range lies west of a line from southern England to the heel of Italy (southern Apulia). The Dartford warbler is usually resident all year in its breeding range, but there is some limited migration.
The species is naturally rare. The largest European populations of Sylvia undata are in the Iberian peninsula, others in much of France, in Italy and southern England and south Wales. In Africa it can be found only in small areas in the north, wintering in northern Morocco and northern Algeria. source