The Coal Tit, Periparus ater, is a passerine bird in the tit family Paridae. It is a widespread and common resident breeder throughout temperate to subtropical Eurasia and northern Africa. The Spot-winged Tit (P. melanolophus) is sometimes included in this species; this may be correct, but more research is required to determine that species' status.
The Coal Tit is 10-11.5 cm in length, and has a distinctive large white nape spot on its black head. The head, throat and neck of the adult are glossy blue-black, setting off the off-white sides of the face (tinged grey to yellow depending on subspecies) and the brilliant white nape; the white tips of the wing coverts appear as two wingbars. The underparts are whitish shading through buff to rufous on the flanks. The bill is black, the legs lead-coloured, and irides dark brown.
The young birds are duller than the adults, lacking gloss on the black head, and with the white of nape and cheeks tinged with yellow.
While searching for food, Coal Tit flocks keep contact with incessant short dee or see-see calls. The species' song - if "song" it can be called - is a strident if-he, if-he, if-he, heard most frequently from January to June, but also in autumn. One variant of this song ends with a sharp ichi. North African birds also have a currr call similar to that of the European Crested Tit (Lophophanes cristatus) which is not found in Africa.
A number of Coal Tit subspecies are distinguished. The differences in coloration are quite pronounced in some of them, while their differences in size are more subtle. Coal Tits from Asia follow Bergmann's Rule, being larger in colder regions; those from further west, however, do not, as the birds from the uplands around the Mediterranean are larger than those from northern Europe. Across its range, tail length in relation to body length increases along a cline running from southwest to northeast.
The British race P. a. britannicus has an olive hue to its brownish-grey back plumage, distinguishing it from the continental European nominate subspecies P. a. ater and P. a. abietum in which the back is bluish grey without a hint of green or brown. The Irish race P. a. hibernicus is distinguished from britannicus by the pale sulphur-yellow cheeks, breast and belly. It also has a paler rump (due to light fringes of the uppertail coverts) and a larger bill than its relatives from Britain and the Continent.
The North African race P. a. ledouci has yellow underparts and cheeks, and the Cypriot P. a. cypriotes has a buff tinge to its upperparts, and deep buff underparts. Asian subspecies are generally rather dusky brownish except for the black-and-white head; they include among others P. a. michalowskii of the Caucasus, P. a. phaeonotus of Iran, or the Himalayan Coal Tit P. a. aemodius of southwestern China.