The BTO winter atlas showed that Guillemots were present in some coastal 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 21 birds.
Small numbers were found feeding in coastal waters but many more during their occasional winter time visits to breeding locations.
Graham Rees