Cormorants and anhingas

(Phalacrocoracidae)

Class: Aves

Order: Pelecaniformes

Suborder: Pelecani

Family: Phalacrocoracidae

Thumbnail description
Sleek, dark-colored, large to medium-sized, long-necked waterbirds with all toes joined by webs (totipalmate); they pursue their prey (usually fish) underwater and often stand with wings spread to dry their poorly oiled, wettable plumage

Size
Variation among species ranges from 19 to 40 in (48–102 cm) and weight 1.5–7.7 lb (0.7–3.5 kg)

Number of genera, species
3 genera; 40 species

Habitat
Occur in freshwater ponds, lakes, rivers, and estuaries and in coastal marine waters

Conservation status
Endangered: 2 species; Vulnerable: 8 species; Near Threatened: 5 species

Distribution
Worldwide distribution in suitable habitat in the boreal, temperate, and tropical zones

Evolution and systematics

The 36 species of cormorants (also known as shags) and four of anhingas (also known as darters or snakebirds) make up the family Phalacrocoracidae. They are related to pelicans, frigatebirds, gannets, and tropicbirds, which are also waterbirds in the order Pelecaniformes. The Pelecaniformes lineage is ancient, with a fossil record extending to the Lower Eocene (>54 million years ago). Although cormorants and anhingas are considered here within one family, some taxonomists place anhingas in a separate family, the Anhingidae. Most taxonomists assign all of the cormorants to one genus, Phalacrocorax. Others, however, assign the flightless cormorant (Nannopterum species) and the pygmy cormorants (Halietor species) to separate genera.

Physical characteristics

Cormorants are sleek, large to medium-sized, long-necked waterbirds. The typical body length is 19–40 in (48–102 cm) and they weigh 1.5–7.7 lb (0.7–3.5 kg). The wings are relatively short and angular, and the spread tail is long and wedge-shaped. Cormorants are well adapted to flying and swimming, but because their legs are placed well-back on the body, they are rather clumsy when walking. When in the water, cormorants sit rather low because their bones are quite dense, with few air spaces, and their feathers are not well-oiled and so get wet when immersed. The bill of cormorants is rather thin and tubular, hooked at the tip, and is lacking in external nares (or nostrils); the edges of the bill have tooth-like serrations. The head and upper neck have powerful muscles for closing the bill; these originate in part from special long, sesamoid bones behind the back of the head and are used to maintain a tight grip on slippery fish that have been caught (the beak serrations are also useful in this regard). For many species, the head has a plumage crest during the breeding season. Cormorant species of the Northern Hemisphere are colored glossy blackish, while those of the Southern Hemisphere tend to have a grayish body with white underparts and some black markings. Males are usually somewhat larger than females; otherwise, the sexes look alike, although they may differ in behavior, at least during the breeding season.

Anhingas are even sleeker, longer-necked waterbirds than cormorants. The typical body length is 34–36 in (86–92 cm). The bill is long, sharply pointed, and bright yellow. The wings are relatively short and rounded, and the long tail is wedge-shaped when spread. The legs are placed well-back on the body. The sexes differ in both plumage and aspects of behavior. Male anhingas have an overall black body coloration, with white markings on the wings and neck. Females also have a black body, but a light-brown neck and head. Anhingas are skilled at flying and swimming, but are clumsy on land. Like cormorants, anhingas sit low in the water because of their dense bones and feathers that get wet when immersed.

Distribution

Cormorants are widely distributed over most of the world, with species ranging from the boreal zones to the tropics (except for some Pacific islands). Anhingas occur widely in tropical and subtropical regions.

Habitat

Cormorants inhabit freshwater wetlands, swamps, lakes, rivers, estuaries, and coastal waters. Anhingas occur in freshwater wetlands, swamps, lakes, rivers, and estuaries.

Behavior

Northern species of cormorants are migratory, breeding in northern parts of their range and wintering to the south. Northern populations of anhingas are also migratory. Both cormorants and anhingas are rather gregarious, often occurring in flocks and breeding in colonies. Cormorants fly somewhat directly, often close to the water surface, using strong, steady wingbeats. They also commonly fly in groups that arrange themselves in lines or V-shaped flocks for better aerodynamic efficiency. Anhingas are also strong fliers, and they soar well, sometimes at great altitude. After swimming, both cormorants and anhingas sit on exposed perches with wings spread to the sun to dry their plumage, which lacks oily repellants and thus gets soaking wet when immersed. Cormorants and anhingas are strong swimmers and pursue prey underwater using their feet for propulsion.

Feeding ecology and diet

Cormorants and anhingas feed mostly on fish, but may also eat frogs, large crustaceans, and squid. They catch prey by an agile, underwater pursuit. Cormorants catch their prey in the bill, while anhingas often spear their quarry.

Reproductive biology

Cormorants and anhingas often breed in colonies. They build awkward stick-nests in trees or sometimes on cliffledges. Nests of cormorants can be rather messy, being littered with seaweed, fish remains, and other debris. Cormorants and anhingas lay two to four, elongated, chalky-surfaced eggs which are pale green or blue. Both sexes incubate the eggs (23–25 days) and rear the young. Sexual maturity is generally reached in the third or fourth year.

Conservation status

The IUCN lists 15 species of cormorants as being at risk. Of these, two are Endangered: the flightless or Galapagos cormorant (Nannopterum harrisi) and the Chatham Island shag (P. onslowi). Another eight species are Vulnerable: the Campbell Island shag (P. campbelli), the New Zealand king shag (P. carunculatus), the Stewart Island shag (P. chalconotus), the Aukland Island shag (P. colensoi), the Pitt Island shag (P. featherstoni), the bank cormorant (P. neglectus), the Socotra cormorant (P. nigrogularis), and the Bounty Island shag (P. ranfurlyi). Four species are considered at Lower Risk, Near

Threatened: the pygmy cormorant (P. pygmeus), the redlegged cormorant (P. gaimardi), the crowned cormorant (P. coronatus), and the Cape cormorant (P. capensis). One species, the Pallas's cormorant (Phalacrocorax perspicillatus), is recently extinct. Almost all of these rare cormorants are endemic species, meaning they only occur in relatively small populations on one or a few isolated, oceanic islands. Endemic species are often at an inherently high risk of extinction. The oriental anhinga (or oriental darter; Anhinga melanogaster) is also listed by the IUCN as being at Lower Risk.

Significance to humans

In some regions where cormorants are abundant, they may be viewed as "pests" by human fishers because they are perceived to be catching "too many fish." In almost all of these cases, however, the cormorants are feeding on smaller species or size-classes of fish than the human fishers are seeking, and so are not in much direct competition. Sometimes, cormorants nesting in colonies kill their nesting trees with their caustic excrement, which may also be perceived to be a local management problem. Several species of cormorants are extremely abundant off parts of Peru and Chile, such that their excrement and that of other abundant seabirds is collected from desert islands as a phosphorus- and nitrogen-rich fertilizer known as guano. Several local Japanese cultures have learned to use tame cormorants to catch fish for the market. In these cases, the cormorants are tethered by a leg and are prevented from swallowing fish they catch by a soft noose or collar tied loosely around their throat. Cormorants and anhingas are also sought for observation by birders and other naturalists, and so contribute to local economic benefits through ecotourism. This is especially true of the rarer species.

Species accounts

Resources

Cramp, S., and K.E.L. Simmons, eds. The Birds of the Western Palearctic. Vol. 1, Ostrich to Ducks. Oxford: Oxford University Press, 1977.

Orta, J. "Family Phalacrocoracidae (Cormorants)." In Handbook of the Birds of the World. Vol. 1, Ostrich to Ducks, edited by Josep del Hoyo, Andrew Elliott, and Jordi Sargatal. Barcelona: Lynx Edicions, 1992.

Orta, J. " Family Anhingidae (Darters)." In Handbook of the Birds of the World. Vol. 1, Ostrich to Ducks, edited by Josep del Hoyo, Andrew Elliott, and Jordi Sargatal. Barcelona: Lynx Edicions, 1992.

Hennemann, W.W. "Spread-winged Behavior of Double-crested and Flightless Cormorants, Phalacrocorax auritus and P. harrisi: Wing Drying or Thermoregulation?" Ibis 126(1984): 230–239.

Jackson, J.A., and B.J.S. Jackson. "The Double-crested Cormorant in the South-central United States: Habitat and Population Changes of a Feathered Pariah. " Colonial Waterbirds 18 (special publ. no. 1) (1995): 118–130.

Mahoney, S.A. "Plumage Wettability of Aquatic Birds." Auk 101 (1984): 181–185.

BirdLife International. Wellbrook Court, Girton Road, Cambridge, Cambridgeshire CB3 0NA United Kingdom. Phone: +44 1 223 277 318. Fax: +44-1-223-277-200. E-mail: birdlife@birdlife.org.uk Web site:

IUCN–The World Conservation Union. Rue Mauverney 28, Gland, 1196 Switzerland. Phone: +41-22-999-0001. Fax: +41-22-999-0025. E-mail: mail@hq.iucn.org Web site:

[Article by: Bill Freedman, PhD]