The BTO winter atlas showed that Coal Tit were present in most 10km squares during the winters of 1981-82, 1982-82 and 1983-84.
The darker the colour, the higher the relative total count for each 10km square. The darkest blue represents over 18 birds in a day. Probably numerically under recorded in dense conifer plantations during winter when they do not normally reveal themselves by singing.
Graham Rees