The BTO winter atlas showed that Yellowhammers were present in the majority of 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 75 birds seen in a day.
Flocks found at a good seed source provided the largest numbers.
Graham Rees