The adult male has grey-brown upperparts and is dull reddish-brown below except for the centre of the belly which has a dirty white patch.

The Dartford warbler is usually resident all year in its breeding range, but there is some limited migration.

He introduced the English name and based his description on two specimens that had been obtained by the ornithologist John Latham from Bexley Heath, near Dartford in Kent.

[2] In 1783 Latham included the warbler in his A General Synopsis of Birds but did not coin the binomial name, Sylvia dartfordiensis, until the supplement to his work was published in 1787.

[3][4] However, in 1783, before the publication of Latham's supplement, the Dutch naturalist Pieter Boddaert introduced the name, Motacilla undata, based on a coloured plate of "Le Pitte-chou, de Provence" in Edmé-Louis Daubenton's Planches enluminées d'histoire naturelle.

[9][10] Altogether, this group of typical warblers bears a resemblance to the wrentit, the only species of Sylviidae from the Americas.

The largest European populations of Curruca undata are in the Iberian peninsula, others in much of France, in Italy and southern England and south Wales.

[16] It is formed mainly of grasses and is lined with a layer of finer material that can include thin roots and feathers.

[17] The clutch is typically 3–5 eggs which are smooth and glossy, with a white or occasionally pale green ground and marked with brown speckles which are sometimes concentrated at the larger end.

Dartford warblers almost died out in the United Kingdom in the severe winter of 1962/1963 when the national population dropped to just ten pairs.

Sylvia undata is also sensitive to drought affecting breeding success or producing heath fires, as occurred during 1975 and 1976 in England when virtually all juveniles failed to survive their first year.

[21] However, this species can recover well in good quality habitat with favourable temperatures and rainfall, thanks to repeated nesting and a high survival rate for the young.

[1] If the declines in southern Europe continue, the UK will become increasingly important for global conservation of this species".