Double white lines on the bill of the Razorbill Alca torda: remnants of an association with the extinct Great Auk Penguinus impennis?

One of the diagnostic features of the Razorbill Alca torda is the distinct white line running vertically across the bill. Here we report the presence of two white bill lines in 10 wintering Razorbills from Newfoundland, Canada in addition to a small number of unreported birds from museum collections and personal records. Populations of Razorbills across their range have been divided into two major subspecies based on morphological variation, although molecular studies do not support such a subdivision. Molecular phylogeny of the auks place Razorbills as the closest relatives of the extinct Great Auk Penguinus impennis. Multiple white bill lines were a characteristic of the Great Auk and we speculate that this variation in the bill marking in the Razorbill is an atavism, reflecting their common ancestry.