Phalacrocoracidaecormorants

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Phalacrocoracidae comprises a single genus (Phalacrocorax) (see van Tets (1976) support for two genera (Phalacrocorax (cormorants) and Leucocarbo (shags), and Siegel-Causey (1988) support for nine genera). There remains disagreement concerning the number of species within Phalacrocoracidea, but generally 38 species are recognized including the extinct spectacled cormorant (Phalacrocorax perspicillatus).

Cormorants and shags are distributed worldwide, with the largest diversity in tropical and temperate zones.

Cormorants and shags inhabit marine and inland waters. They are found along marine coastlines of continents and islands. Inland populations inhabit lakes, open swamps and marshes, and rivers.

Eggs are incubated for 24-31 days and hatch asynchronously. Chicks are altricial and acquire a dark or white down within a week. Chicks are brooded and fed by parents. Fledging age is variable and ranges between 35-80 days. Post-fledging care sometimes occurs at a crèche where parents continue to feed fledglings for two to four months. Adult plumage acquisition varies by species, ranging from one to four years. On average individuals begin breeding at two to four years.

Phalacrocoracids are medium to large birds (50-100 cm; 360-3875 g; 80-160 cm wingspan). Plumage in most species is iridescent black; some species have white on the head and underparts. During breeding the bare facial skin and gular pouch, eye-ring, bill and mouth lining become red, yellow, green or blue in color. Crests and plumes on the head and neck are present during breeding. Generally, the sexes are monomorphic in plumage, but dimorphic in size with males heavier and larger. Iris is yellow, blue, green, or brown. Juveniles are light brown and lighter on underparts. The slender, cylindrical bill is hooked, palate is desmognathous, nostrils obsolete (no exposed external nares). Legs are set far back on body and feet are totipalmate. Neck is long and laterally compressed.

Some marine phalacrocoracid species share breeding areas, or may breed alongside gulls, terns, penguins, sulids, or fur seals. Inland species may associate with herons, egrets, storks, ibises, and spoonbills.

Cormorants and shags feed primarily on fish (capelin, anchovy, herring, pilchard) although may take mollusks, crustaceans, cephalopods and polycheates. Inland diets include fish, frogs, aquatic insects, water snakes, and turtles.

Avian predators of cormorants and shags include: gulls (Larus dominicanus, L. occidentalis, L. argentatus, L. marinus, L. schistisagus, L. belcheri, L. glaucescens); sheathbills (Chionis); skuas (Catharacta skua lonnbergi); Marabou stork (Leptoptilus crumeniferus); kites (Haliastur sphenurus, Milvus migrans); Galapagos hawk (Buteo galapagoensis); eagles (Haliaeetus leucocephalus, H. leucogaster, H. vocifer, H. albicilla); turkey vulture (Cathartes aura); Andean condor (Vulture gryphus); crows (Corvus splendens, C. brachyrhynchos, C. ossifragus, C.caurinus, C. coraxC. rhipidurus, C. corone, C. macrorhynchos); boat-tailed grackles (Quiscalus major). Other predators include: river otter (Lutra canadensis); raccoon (Procyon lotor); Black-backed jackal (Canis mesomelas); fox (Vulpes fulva, V. vulpes, Alopex lagopus); hyena, cheetah, domestic and feral dog, and Nile crocodile.

Cormorants and shags are considered seasonally monogamous. Nest-sites and mates may change from year to year. Males display from a chosen nest-site by waving wings and pointing the bill skyward, exposing the skin of the throat. Males of some species swing their heads backwards until the nape touches the rump. These displays end when a female alights beside the male and greeting displays ensue. The female defends the nest-site and constructs the nest, while the male collects nest material. Nest construction may take from one to five weeks. Copulation occurs at the nest-site.

Cormorants and shags breed in colonies ranging in size from a few to hundreds of thousands of pairs. Breeding is considered seasonal, although tropical species may breed year round. Nest-sites are variable, located on cliff ledges, ground, or trees. Some nests consist of sticks, seaweed, feathers, and grass cemented together with excreta. Ground nests are often depressions in soft substrates like sand or guano. Clutch size varies with species, ranging from two to six eggs. The egg-laying interval is two to three days. Eggs are pale blue or green.

Parents take turns incubating eggs on foot webbing for about 24-31 days. Incubation stints are nearly equal in duration. Both parents take turns brooding and feeding chicks. Partially digested fish is taken from the parents' mouth. Fledging and independence generally occurs at 35-70 days.

Some phalacrocoracids are migratory, whereas others are sedentary. Cormorants and shags regurgitate pellets of fish bones and scales daily. Pursuit-diving is the technique used to capture prey items. The bird dives from the surface and propels itself through the water using its feet. Prey are captured in the bill, and upon return to the surface, prey items are manipulated with the bill until the prey can be swallowed head first. Neotropical cormorants plunge-dive (from the air) alone or in groups. Phalacrocoracids may forage singly or in groups (sometimes numbering in the thousands). Some species are cooperative foragers: groups swim together on the surface, moving in a coordinated fashion (influencing movements of shoals of fish), then dive in unison to capture fish. Some species also join mixed-species foraging flocks. Phalacrocoracids are also noted for standing with wings extended (perhaps to dry wings or for thermoregulation) and gular-fluttering.

Phalacrocoracids may flock together to roost, form large colonies for breeding, or use cooperative foraging strategies.

Phalacrocoracids vocalize markedly during the breeding season or when roosting. Males are characterized by louder grunts, croaks or barks. Females may elicit softer, hoarse hisses. Chicks solicit feeding with plaintive insistent calls. Specific vocalizations accompany breeding and threat displays.

Humans exploit phalacrocoracids extensively. Cormorants have been used in conjunction with fishing. One practice entails tethering cormorants by the neck, pulling them back to the boat after they successfully procure fish, then extracting the fish from the bird. A collar on the neck prevents the birds from swallowing the fish. In South America and South Africa, huge deposits of guano have accumulated in regions with large phalacrocoracid breeding colonies. Guano is collected then sold as fertilizer, and has been a tremendous source of revenue for countries such as Peru. Between 1848-1875 20 million tons of guano was exported from Peru to North America and Europe. In many parts of the world, phalacrocoracid eggs, young, and adults are collected for human consumption. In China and Argentina cormorants are collected for their perceived medicinal value. Some cultures use cormorant skins for clothing.

Phalacrocoracids may pose an economic threat to fish farms or hatcheries.

Fifteen phalacrocoracid species are included in the IUCN Red List of Threatened Species. One species, Spectacled Cormorant (Phalacrocorax perspicillatus), is 'Extinct'; two species, the Flightless Galapagos Cormorant (P. harrisi) and Chaatham Island Shag (P. onslowi), are 'Endangered' and eight are 'Vulnerable'. Major threats include human collection of eggs, birds, and guano; habitat destruction; pesticide poisoning; oil spills; over fishing.

The evolutionary relationships of cormorants and shags remain uncertain. Cormorants and shags have been considered closely related to other totipalmate birds (tropicbirds, frigatebirds, anhingas, gannets and boobies, pelicans), which when taken together, form Pelecaniformes. However, a hierarchy based on DNA hybridization includes cormorants and shags within a diverse group, Ciconiiformes. The composition of Phalacrocoracidae has been contested: some research suggests the group comprises only cormorants and shags, whereas other research supports the inclusion of anhingas. Morphological, ethological and molecular analyses suggest several hypotheses of sister group relationships: cormorants and shags as sister to anhingids forming a group sister to sulids; cormorants and shags as sister to a group comprising sulids and anhingids; cormorants and shags as sister to sulids forming a group sister to anhingids.

Old and New World phalacrocoracid fossils are well represented throughout the Tertiary, and extend back to the Eocene-Oligocene boundary.

Campbell, B., and E. Lack, editors. 1985. A Dictionary of Birds. Buteo Books, Vermillion, SD.

del Hoyo, J., Elliott, A. & Sargatal, J. (eds.) 1992. Handbood of the Birds of the World. Vol. 1. Lynx Edicions, Barcelona.

Feduccia, A. 1999. The Origin and Evolution of Birds, 2nd edition. Yale University Press New Haven.

Johnsgard, P. A. 1993. Cormorants, Darters, and Pelicans of the World. Smithsonian Institution Press Washington.

Sibley, C. G. & J. E. Ahlquist. 1990. Phylogeny and Classification of Birds, A Study in Molecular Evolution. Yale Univ. Press.

Siegel-Causey, D. 1988. Phylogeny of the Phalacrocoracidae. Condor 90:885-905.

Van Tets, G. F. 1976. Australasia and the origin of shags and cormorants, Phalacrocoracidae. Pp. 121-24 in: Proc. 16th Inter. Ornith. Congr. Canberra, Australia, 1974.

Contributors

Laura Howard (author), Animal Diversity Web.

Glossary

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

visual

uses sight to communicate