Abstract

A Black Guillemot Cepphus grylle at Cut End on the River Witham in Lincolnshire on 7th–10th December 2017 attracted considerable local attention. The bird’s largely white appearance resembled that of the distinctive, high-Arctic ‘Mandt’s Black Guillemot’ C. g. mandtii, and it attracted wider interest as potentially the first British record of this subspecies. During the BOURC review, it was found that the characters that define mandtii and exclude other subspecies