Phalacrocoracidae is a family of approximately 40 species of aquatic birds found worldwide and commonly known as cormorants and shags. Several different classifications of the family have been proposed, but in 2021 the International Ornithologists' Union (IOU) adopted a consensus taxonomy of seven genera. The common names "cormorant" and "shag" have been assigned to different species in the family somewhat haphazardly.
Cormorants and shags are medium-to-large birds, with body weight in the range of and wing span of . The majority of species have dark feathers. The bill is long, thin and hooked. Their feet have webbing between all four toes. All species are fish-eaters, catching the prey by diving from the surface. They are excellent divers, and under water they propel themselves with their feet with help from their wings; some cormorant species have been found to dive as deep as . Cormorants and shags have relatively short wings due to their need for economical movement underwater, and consequently have among the highest flight costs of any flying bird.
Cormorant colonies nest around seacoasts, in trees, islets or cliffs. They are coastal rather than oceanic birds. Some species have colonised inland waters. Species may be found in all areas of the world except for the central Pacific islands.
Cormorants may descend from a freshwater ancestor in south Asia whose offspring adapted in time to new environments and spread across the Eurasian landmass and the world.
Names "Cormorant" is a contraction probably derived from Latin corvus marinus, "sea raven"; in the early 19th century, the similarly derived spelling "corvorant" was sometimes used. Indeed, "sea raven" or analogous terms were the usual terms for cormorants in Germanic languages until after the Middle Ages. The French explorer André Thévet commented in 1558: "the beak [is] similar to that of a cormorant or other corvid", which demonstrates that the mistaken belief that the birds were related to ravens lasted at least to the 16th century.
No consistent distinction exists 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 and Ireland Phalacrocorax carbo (now referred to by ornithologists as the great cormorant) and Gulosus aristotelis (the European shag). "Shag" refers to the bird's crest, which is conspicuous in the European shag, but less so in the great cormorant. As other species were encountered by English-speaking sailors and explorers elsewhere in the world, some were called cormorants and some shags, sometimes 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; for example, all species in the family which occur in New Zealand are known locally as shags, including four non-endemic species known as cormorant elsewhere in their range. In 1976, Gerard Frederick van Tets proposed to divide the family into two genera and attach the name "cormorant" to one and "shag" to the other, but this nomenclature has not been widely adopted.
Description
Cormorants and shags are medium-to-large seabirds. They range in size from the pygmy cormorant (Microcarbo pygmaeus), at as little as and , to the flightless cormorant (Nannopterum harrisi), at a maximum size and . The recently extinct spectacled cormorant (Urile perspicillatus) was rather larger, at an average size of . Nearly all the Northern Hemisphere species have mainly dark plumage, but many Southern Hemisphere species are black and white, and a few (e.g. the spotted shag of New Zealand) are quite colourful. Many species have areas of coloured skin on the face (the lores and the gular skin) which can be bright blue, orange, red or yellow, typically becoming more brightly coloured in the breeding season. The bill is long, thin, and sharply hooked. Their feet have webbing between all four toes, as in their relatives.
Habitat
Habitat varies from species to species: some are restricted to seacoasts, while others occur in both coastal and inland waters to varying degrees. They range around the world, except for the central Pacific islands.
Behaviour All cormorants and shags are fish-eaters, dining on small eels, fish, and even water snakes. They dive from the surface, though many species make a characteristic half-jump as they dive, presumably to give themselves a more streamlined entry into the water. Under water they propel themselves with their feet, though some also propel themselves with their wings (see the picture, commentary, and existing reference video). Imperial shags fitted with miniaturized video recorders have been filmed diving to depths of as much as to forage on the sea floor.
After fishing, cormorants go ashore, and are frequently seen holding their wings out in the sun. All cormorants have preen gland secretions that are used ostensibly to keep the feathers waterproof. Some sourcesCramp S, Simmons KEL (1977) Handbook of the Birds of the Western Palearctic Volume 1, Oxford University Press state that cormorants have waterproof feathers while others say that they have water-permeable feathers. Still others suggest that the outer plumage absorbs water but does not permit it to penetrate the layer of air next to the skin. The wing drying action is seen even in the flightless cormorant but not in the Antarctic shags or red-legged cormorants. Alternate functions suggested for the spread-wing posture include that it aids thermoregulation or digestion, balances the bird, or indicates presence of fish. A detailed study of the great cormorant concluded there is little doubt that it serves to dry the plumage.
Cormorants are colonial nesters, using trees, rocky islets, or cliffs. The eggs are a chalky-blue colour. There is usually one brood a year. Parents regurgitate food to feed their young.
Taxonomy
The genus Phalacrocorax, from which the family name Phalacrocoracidae is derived, is Latinised from Ancient Greek phalakros "bald" and korax "raven". This is thought to refer to the ornamental white head plumes prominent in Mediterranean birds of this species, or the creamy white patch on the cheeks of adult great cormorants, but is certainly not a unifying characteristic of cormorants.
The cormorant family was traditionally placed within the Pelecaniformes or, in the Sibley–Ahlquist taxonomy of the 1990s, the expanded Ciconiiformes. Pelecaniformes in the traditional sense—all waterbird groups with totipalmate foot webbing—are not a monophyletic group, even after the removal of the distantly-related tropicbirds. Their relationships and delimitation – apart from being part of a "higher waterfowl" clade which is similar but not identical to Sibley and Ahlquist's "pan-Ciconiiformes" – remain mostly unresolved. Notwithstanding, all evidence agrees that the cormorants and shags are closer to the darters and Sulidae (gannets and boobies), and perhaps the pelicans or even penguins, than to all other living birds.Kennedy et al. (2000), Mayr (2005)
In recent years, three preferred treatments of the cormorant family have emerged: either to leave all living cormorants in a single genus, Phalacrocorax, or to split off a few species such as the imperial shag complex (in Leucocarbo) and perhaps the flightless cormorant. Alternatively, the genus may be disassembled altogether and in the most extreme case be reduced to the great, white-breasted and Japanese cormorants.See , Orta (1992) and Kennedy et al. (2000) for a review of classification schemes. In 2014, a landmark study proposed a 7 genera treatment, which was adopted by the IUCN Red List and BirdLife International, and later by the IOC in 2021, standardizing it.
The cormorants and the darters have a unique bone on the back of the top of the skull known as the os nuchale or occipital style which was called a xiphoid process in early literature. This bony projection provides anchorage for the muscles that increase the force with which the lower mandible is closed. This bone and the highly developed muscles over it, the M. adductor mandibulae caput nuchale, are unique to the families Phalacrocoracidae and Anhingidae.
Several evolutionary groups are still recognizable. However, combining the available evidence suggests that there has also been a great deal of convergent evolution; for example, the cliff shags are a convergent paraphyletic group. The proposed division into Phalacrocorax sensu stricto (or subfamily "Phalacrocoracinae") cormorants and Leucocarbo sensu lato (or "Leucocarboninae") shags does have some degree of merit.Kennedy et al. (2000) The resolution provided by the mtDNA 12S rRNA and ATPase subunits six and eight sequence data is not sufficient to resolve several groups to satisfaction properly; in addition, many species remain unsampled, the fossil record has not been integrated in the data, and the effects of hybridisation – known in some Pacific species especially – on the DNA sequence data are unstudied.
A multigene molecular phylogenetic study published in 2014 provided a genus-level phylogeny of the family; this is now followed by most authorities, including the IOC World Bird List.
List of genera
As per the IOU, the IUCN Red List and BirdLife International, the family contains 7 genera:
Image Genus Species Microcarbo Crowned cormorant Microcarbo coronatus Little cormorant Microcarbo niger Little pied cormorant Microcarbo melanoleucos Pygmy cormorant Microcarbo pygmeus Reed cormorant or long-tailed cormorant Microcarbo africanus †Serventys' cormorant Microcarbo serventyorum Around Indian Ocean, one species extending from Central Asia into Europe. Mostly in freshwater habitat. Small (about 50–60 cm long), nondescript black to dark brown (except for one species with white underparts). Poikilocarbo Red-legged cormorant Poikilocarbo gaimardi Subtropical to subantarctic Pacific South America, ranging a bit into the southwestern Atlantic. Maritime. Mid-sized (around 75 cm), grey with scalloped wings and contrasting white/yellow/red neck mark and bare parts. Its high-pitched chirping calls are quite unlike those of other cormorants. Urile Brandt's cormorant Urile penicillatus Red-faced cormorant Urile urile Pelagic cormorant Urile pelagicus Spectacled cormorant †Urile perspicillatus Northern Pacific, one species extending into subtropical waters on the American West Coast. Maritime. Smallish to large (65–100 cm), generally black with metallic sheen (usually blue/green), in breeding plumage with bright bare facial skin in the eye region and two crests (crown and nape). Phalacrocorax Bank cormorant Phalacrocorax neglectus Socotra cormorant Phalacrocorax nigrogularis Pitt shag Phalacrocorax featherstoni Spotted shag Phalacrocorax punctatus Black-faced cormorant Phalacrocorax fuscescens Australian pied cormorant Phalacrocorax varius Little black cormorant Phalacrocorax sulcirostris Indian cormorant Phalacrocorax fuscicollis Cape cormorant Phalacrocorax capensis Japanese cormorant or Temminck's cormorant Phalacrocorax capillatus Great cormorant (including white-breasted cormorant and black shag) Phalacrocorax carbo Mostly around the Indian Ocean, one species group extending throughout Eurasia and to Atlantic North America. Maritime to freshwater. Size very variable (60–100 cm), blackish with metallic sheen (usually bronze to purple) and/or white cheek and thigh patches or underside at least in breeding plumage; usually a patch of bare yellow skin at the base of the bill. Gulosus European shag Gulosus aristotelis Breeds in the European Arctic, winters in Europe and North Africa. Maritime. Mid-sized (70–80 cm), glossy black, in breeding plumage with a forehead crest curled to the front. Nannopterum Flightless cormorant Nannopterum harrisi Neotropic cormorant Nannopterum brasilianum Double-crested cormorant Nannopterum auritum