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Anhinga anhingaanhinga

By Laura Kearns

Geographic Range

The northernmost distribution of Anhinga anhinga leucogaster is in the United States from North Carolina to Texas. It has however been spotted as far north as Wisconsin. Its range also includes Mexico, Central America, Panama, and Cuba. The individuals found in the more northern areas of the U.S. migrate there in March and April and stay until October, then return to Mexico and more southern parts of the U.S. Anhinga anhinga anhinga is found in South America from Colombia to Ecuador, east of the Andes to Argentina, and in Trinidad and Tobago. The range is limited by cool temperatures and low amounts of sunshine. (del Hoyo, et al., 1992; Hennemann, 1985; Isenring, 1997)

Habitat

Anhinga anhinga prefers freshwater and coastal aquatic habitats that include shrub or tree-covered islands or shores; these habitats include lakes, marshes, swamps, mangrove swamps, shallow coastal bays, and lagoons. Within such habitats, anhingas are able to stalk slow-moving prey and seek refuge from danger in the water, and perch and sun itself in the treetops. (del Hoyo, et al., 1992; Owre, 1967)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • coastal

Physical Description

Anhingas have an average body length of 85 cm, weight of 1350 g, wingspan of 117 cm, and bill length of 81 mm. The head is small and appears to be merely an extension of its long snake-like neck. In the neck, the 8th and 9th cervical vertebrae create a hinge-like apparatus that allows the quick catching of prey. The long, sharp, serrated bill also aids it in hunting. The wings are broad, allowing it to soar, and the feet are webbed to facilitate swimming. The physical structure of the legs is, however, more suited to crawling out of water onto land and for climbing bushes and trees. The tail is long and is used for providing lift, steering, braking, and balancing. When spread in flight, the tail resembles that of a turkey. The overall body shape of anhingas resembles that of a cormorant; the hunting action of the head and neck is more similar to a heron.

Anhingas are sexually dimorphic; males have brighter colors than females. Males have greenish-black plumage overall, accentuated by silver-gray feathers on the upper back and wings that are edged with long white plumes. They also have black crests. Females are brown with a lighter brown head and neck; juveniles are a uniform brown color. Molting of all flight feathers at the same time render them flightless for a while. Unlike some aquatic birds, all of the body feathers become completely wet upon contact with the water, allowing them to dive through the water more easily. This feature, however, causes them to have little buoyancy, to lose heat quickly, and hinders flight. (del Hoyo, et al., 1992; Hennemann, 1982; Owre, 1967; Scott, 1983)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • Average mass
    1350 g
    47.58 oz
  • Average mass
    1080 g
    38.06 oz
    AnAge
  • Average basal metabolic rate
    3.2258 W
    AnAge

Reproduction

Anhingas are monogamous and pairs may reuse nests from year to year. The male begins courtship by soaring and gliding, followed by marking a possible nest location with leafy twigs. Then he performs behavioral displays to attract the female. Once the pair is formed, the male gathers nesting material, while the female builds a platform nest, which is usually on a branch overhanging water or in open areas in the tops of trees. The female constructs the nest by weaving sticks together and padding it with live twigs and green leaves. Usually, the highly territorial males defend any threats to nesting territories with extensive displays and even fighting. If another male approaches the territory, the resident male spreads its wings and snaps its beak. If no retreat occurs, fighting will commence by pecking at each other's heads and necks. Females are less aggressive, but will defend the nest if necessary. (Burger, et al., 1978; del Hoyo, et al., 1992)

Anhingas are believed to reach sexual maturity around two years of age. Breeding occurs seasonally in North America. In sub-tropical or tropical latitudes, breeding can occur throughout the year, or be triggered by wet or dry seasons. The female lays one egg every one to three days, until she has a clutch anywhere from two to six eggs. Average clutch size is four eggs. The oval-shaped eggs are bluish-white or pale green, sometimes occurring with brown speckles. (Burger, et al., 1978; del Hoyo, et al., 1992)

  • Breeding season
    Anhingas may breed seasonally or throughout the year, depending on latitude.
  • Average eggs per season
    4
  • Range time to hatching
    25 to 30 days
  • Average fledging age
    6 weeks

The parents share in incubating the eggs for 25 to 30 days. In Mexico, anhingas were documented as performing particular displays when males and females switch incubating duties at the nest. These displays included two parents vocalizing to one another, and the incubating bird neck-stretching toward the mate. After the birds intertwined necks and the returning bird passed nesting material to the incubating bird, the two switched places. Upon hatching, anhinga chicks are naked and helpless. They eventually grow a white down on their belly side and a dark down on their back side. At first the parents feed the chicks by dripping fluid and regurgitated material from partially digested fish down their throats. As the chicks grow older, they shove their heads down the parents' beaks to get this food material. The chicks are in the nest approximately three weeks, but if threatened, are able to drop into the water and swim away, later climbing out of the water and back into the nest. At the end of three weeks, they are able to climb out of the nest to a branch, and fledge at approximately six weeks. They stay with their parents for several more weeks before becoming independent. (Burger, et al., 1978; del Hoyo, et al., 1992)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • protecting
      • male
      • female

Lifespan/Longevity

Behavior

Anhingas start flight by either running on the surface of the water or diving from a tree. They usually return to the water by gliding into it from a perch or crawling into it from land. Only the head and neck are visible when in the water due to their low buoyancy. Most of the time spent in the water is devoted to fishing; otherwise they are found perched in trees. Often they crawl from the water and then up to a high perch in order to sun themselves. Similar to cormorants and turkey vultures, anhingas sun themselves by spreading out the wings, which dries out the plumage and absorbs heat from the sun. Anhingas lose heat quickly in the water due to their lack of an insulating layer of body feathers; thus, the sun's radiation helps them maintain body temperature. Anhingas are solitary but are sometimes found among groups of herons, cormorants, ibises, or storks. Although they nest in small loose groups, it is unusual to find them with other anhingas at other times of the year. (Burger, et al., 1978; del Hoyo, et al., 1992; Hennemann, 1982)

Communication and Perception

Normally quiet birds, vocalizations include clicks, rattles, croaks, and grunts. Anhingas typically call while on or near the nest, and occasionally while flying or perching. They are particularly silent and elusive when flightless due to molting. (Burger, et al., 1978; del Hoyo, et al., 1992; Hennemann, 1982)

Food Habits

Anhingas prey primarily on fish (Percidae, Centrarchidae, Peociliidae, Cyprinodontidae), but their diet can also include aquatic invertebrates and insects. Although not particularly fast swimmers, they are effective aquatic hunters, relying on their quick necks and sharp bills to catch prey. They target slower-moving species of fish and stalk them underwater, finally striking out with their long neck and spearing the prey with the beak. They then bring the prey above water and manipulate it in order to swallow the fish head first. (Owre, 1967)

  • Animal Foods
  • fish
  • insects
  • aquatic crustaceans

Economic Importance for Humans: Positive

Anhingas and their eggs are eaten by humans in parts of Asia. (del Hoyo, et al., 1992)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

In North America, anhingas have no particular economic impact, particularly since they do not eat the fish that humans might. (del Hoyo, et al., 1992)

Conservation Status

In the Americas, anhingas are abundant, although their aquatic habitats are threatened. DDT was found to have an effect on the reproductive success of these birds and banning of this pesticide in North America has benefited those birds that breed in the southern United States. (del Hoyo, et al., 1992)

Other Comments

Although anhingas resemble cormorants (Phalacrocorax species), the two have several differences. Cormorants are more powerful swimmers and thus able to hunt faster-swimming fish, whereas anhingas are much slower in the water and hunt slower-swimming fish. Anhingas are able to soar, but require gliding flights from trees in order to start flight, unlike cormorants, which are not able to soar and can easily take off from the water. Anhinga distributions are more limited by temperature due to their low metabolic rate. Cormorants are able to maintain higher body temperatures and are found in colder regions of North America. Also, anhingas use a flap and glide form of flight, whereas cormorants continually flap. (Owre, 1967)

Contributors

Laura Kearns (author), University of Michigan-Ann Arbor, Terry Root (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

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.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

diurnal
  1. active during the day, 2. lasting for one day.
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.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

food

A substance that provides both nutrients and energy to a living thing.

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).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

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

piscivore

an animal that mainly eats fish

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

solitary

lives alone

tactile

uses touch to communicate

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

References

Burger, J., L. Miller, D. Hahn. 1978. Behavior and Sex Roles of Nesting Anhingas at San Blas, Mexico. Wilson Bull., 90(3): 359-375.

Hennemann, W. 1982. Energetics and spread-winged behavior of anhingas in Florida. Condor, 84(1): 91-96.

Hennemann, W. 1985. Energetics behavior and the zoogeography of *Anhinga anhinga* and double-crested cormorants *Phalacrocorax auritus*. Ornis Scand., 16(4): 319-323.

Isenring, R. 1997. By the Wayside. Passenger Pigeon, 59(4): 347-358.

Owre, O. 1967. Adaptations for locomotion and feeding in the Anhinga and the Double-crested Cormorant. Ornithological Monographs, 6: 138-276.

Scott, S. 1983. Field Guide to the Birds of North America. Washington D.C.: National Geographic Society.

del Hoyo, J., A. Elliot, J. Sargatal. 1992. Handbook of the Birds of the World. Vol. 1, Ostrich to Ducks.. Barcelona: Lynx Edicions.

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