There is no consistent distinction between cormorants and shags. The names "cormorant" and "shag" were originally the common names of the two species of the family found in Great Britain, Phalacrocorax carbo (now referred to by ornithologists as the Great Cormorant) and P. aristotelis (the European Shag). "Shag" refers to the bird's crest, which the British forms of the Great Cormorant lack. As other species were discovered by English-speaking sailors and explorers elsewhere in the world, some were called cormorants and some shags, depending on whether they had crests or not. Sometimes the same species is called a cormorant in one part of the world and a shag in another, e.g., the Great Cormorant is called the Black Shag in New Zealand (the birds found in Australasia have a crest that is absent in European members of the species). Van Tets (1976) proposed to divide the family into two genera and attach the name "Cormorant" to one and "Shag" to the other, but this flies in the face of common usage and has not been widely adopted.
This FanPost was written by a member of the Royals Review community. It does not necessarily reflect the views of the editors and writers of this site.