Cormorants and Shags
The Cormorants and Shags (Phalacrocoracidae) form a large group within the Pelecaniiformes of about 40 species and a good number of subspecies. All of them are readily to be recognized as belonging to this group by their shape and posture. They vary in size from duck to big goose format and are all true waterbirds, found on both salt and/or fresh water. Since nearly all of them frequent at least coastal waters during a part of the year all members are considered seabirds. A few are truly pelagic.
Cormorants and Shags (Phalacoracidae) belong to the Pelicaniformes and are related to the Pelicans, Tropicbirds, Frigatebirds, Gannets and Darters. The origin of the Pelecaniformes dates back to late Cretaceous, but the first Cormorants presumably diverged late Paleocene, early Oligocene (about 30 My ago). In late Paleocene Cormorants were aready there, or at least the ancestors of both the Cormorants and the closely related Darters. The oldest fossil records date from early Oligocene-late Miocene. Many different species (ca 30) have been found in Miocene, Pliocene and Pleistocene deposits (Johnsgard 1993). Members of the family can be found almost globally. The Blue-eyed Shags and related almost certainly evolved in the Southern Hemisphere, but for the other members of the family their evolution is still not well understood.
The complexitiy of the relations within this group is subject of discussion for a long time and many proposals have been done. Van Tets (1976) provided the first meaningful classfication of this group and divided it into two genera: Leucocarbo for the Shags and Phalacrocorax for the Cormorants and subdivided both genera in several subgenera.
Siegel-Causey (1986) studied this theme extensively by using 137 qualitative osteological characteristics of almost all recent taxa to construct a hypothetical familiy tree. He concluded that the family comprises two subfamilies: the Phalacrocoracina (Cormorants) comprising four genera of all-dark, coastal species. Microcarbo (Microcormorants), Compsohalieu (Marine cormorants), Hypoleucos (Mesocormorants) and Phalacrocorax (Macrocormorants). The other group is formed by Leucocarboninae (Shags) comprising five genera of variably plumaged coastal and pelagic species: Leucocarbo (Guano shags), Notocarbo (Blue-eyed shags), Nesocarbo (Campbell Island Shag), Euleucocarbo (New Zealand blue-eyed shags) and Stictocarbo (Cliff shags).
Johnsgard (1993) reduced the number of genera to Phalacrocorax and Leucocarbo.
A more recent study by Kennedy et al. (2000) based on genetic analysis resulted in a revision of the taxonomy by Siegel-Causey. A few species appeared to belong to other groups and they rejected a few of the subgenera. Nelson (2005) sticks to the single genus Phalocrocorax for all Cormorants and Shags.
Presently most Cormorants and Shags are still, conservatively, assigned to Phalacrocorax, but two disitinct groups are separated from this genus: Microcarbo for a group of small Cormorants and Leucocarbo for the Blue-eyed Shags. Nonetheless still several different groupings can be distiguished.
The results of both studies are used to group the Cormorants and Shags in the respective pages here and follows the accepted nomenclature of the IOC. The final word on the taxonomy of this group has not yet been spoken.
The articles of Siegel-Causey and Kennedy et al. can be downloaded from the References page.
- Cliff Shags: Phalacrocorax
- Marine Cormorants: Phalacrocorax
- Spotted Shags: Phalacrocorax
- Blue-eyed Shags: Leucocarbo