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Opisthocomus hoazinhoatzin

By Kellie Williams

Geographic Range

Opisthocomus hoazin are found throughout the Amazon in northern and central South America (Stotz et. al., 1996).

Habitat

The habitat of O. hoazin includes swamps, fresh water marshes, gallery forests, and the banks of rivers, lakes and streams (Stotz et. al., 1996, Strahl and Grajal, 1991).

Physical Description

Adult Hoatzins are approximately 24 to 26 inches in length. They have blue skin covering their faces and their eyes are red. The outer feathers are primarily chestnut-brown and the long tail is bronze-green and ends in a white band. The heads of Hoatzins are topped with a crest of reddish-brown feathers. The young are born without feathers but develop a layer of black down shortly after birth. A distinguishing feature of young Hoatzins are the pair of functional wing claws which are found on the ends of their wings on the first and second fingers. This feature is lost when the bird matures into an adult (De Schauensee, 1964, Grahm, 1990, Strahl and Grajal, 1991, Zahler, 1997).

Reproduction

Opisthocomus hoazin do not begin breeding until after their first year of life. The breeding season of O. hoazin occurs during the same time as the rainy season of their territory. Hoatzins build their nests on branches over the water about 6 to 15 feet above the surface. They normally lay two to three eggs and the incubation period lasts thirty-two days. Both male and female brood the young, which typically remain in the nest for two to three weeks after they hatch (Grahm, 1990, Strahl, 1988, Strahl and Grajal, 1991, Zahler, 1997).

Behavior

Hoatzins are very territorial, especially during the breeding season. Hoatzins seek a territory near water over which they can build their nests. Ideal locations can be scarce, so when a breeding pair establishes their territory, both the male and female actively defend it. A breeding pair will inform others of their territorial boundaries by displays of ritual copulations, loud noises and aggressive postures. Because water side territory can be scarce, young Hoatzins often live in their parents territory for a couple of years after they hatch. During this time they act as helpers to their parents by assisting with the care of new brood and by helping to defend the territory. Because O. hoazin have enlarged crops, they are clumsy flyers and it may take young Hoatzins up to seventy days before they can fly at all. Because of this, young Hoatzins have developed an unusual way of fleeing predators which include monkeys, hawks and snakes. When predators approach, young Hoatzins can use their wing claws to climb on the limbs of trees and out of the predator's reach. If escape is not possible in the trees, the young birds will drop into the water below the nest and swim beneath the surface until they reach safety (Grahm, 1990, Strahl and Grajal, 1991, Zahler, 1997).

Communication and Perception

Food Habits

Hoatzins are primarily folivores. Although they typically feed on less than twelve species of plants, they are capable of eating the leaves of more than fifty different species. The leaves of tropical legume plants are an example of a leaf that Hoatzins commonly feed on. Other foods that are sometimes included in the diet of Hoatzins include some flowers and fruits. Opisthocomus hoazin have developed a special system that allows them to feed on leaves. They have an enlarged crop in which symbiotic bacteria are stored and used to break down the cell walls of the leaves, allowing for them to be digested. This process is called foregut fermentation and O. hoazin are the only birds with this type of digestive system. The bacteria within the crop also act as a source of nutrients for Hoatzins by occasionally getting moved into their stomachs. The bacteria are introduced to young Hoatzins when an adult regurgitates a sticky substance containing large amounts of the bacteria and feeds it to the young. (Strahl and Grajal, 1991; Zahler, 1997)

  • Plant Foods
  • leaves
  • fruit
  • flowers

Economic Importance for Humans: Positive

Hoatzins are frequently hunted throughout South America (Strahl and Grajal, 1991).

Conservation Status

Although Opisthocomus hoazin is not considered an endangered species, human actions such as hunting and the destruction of their habitat are a growing threat to Hoatzin populations throughout South America (Strahl and Grajal, 1991). Currently the IUCN rates this species as being of "Least Concern" with respect to conservation.

Other Comments

Since Opisthocomus hoazin were first described in 1776, there has been a great deal of debate over their proper classification. For many years it was undecided whether Hoatzins were more closely related to galliforms or coockoos. Studies of DNA variation in O. hoazin have shown the coockoo to be their closest relative. Although this has been widely accepted in the scientific community, the question of who Hoatzins are most closely related to is still being debated. There have been recent studies that dispute the claim that Hoatzins are most closely related to the coockoo. One such study suggests that turacos are the closest relative of Hoatzins. (Adler, 1995; Hughes and Baker, 1999)

Contributors

Kellie Williams (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Neotropical

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

World Map

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.

folivore

an animal that mainly eats leaves.

herbivore

An animal that eats mainly plants or parts of plants.

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.

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.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

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

References

Adler, T. 1995. DNA Tests Identify Hoatzin's Cousins. Science News, 148: 388.

De Schauensee, R. 1964. The Birds of Colombia. Narberth, PA: Livingston Publishing Company.

Grahm, F. 1990. Avian Cattle. Audubon, 92: 12-14.

Hughes, J., A. Baker. 1999. Phylogenetic relationships of the enigmatic hoatzin (Opisthocomus hoazin) resolved using mitochondrial and nuclear gene sequences. Molecular Biology & Evolution, 16: 1300-1307.

Stotz, D., J. Fitzpatrick, T. Parker, D. Moskovits. 1996. Neotropical Birds. Chicago: The University of Chicago Press.

Strahl, S. 1988. The Social Organization and Behavior of the hoatzin Opisthocomus-hoazin in Central Venezuela. Ibis, 130: 483-502.

Strahl, S., A. Grajal. 1991. A bird with the guts to eat leaves. Natural History, Aug. '91: 48-55.

Zahler, P. 1997. Crazy Like a Hoatzin. International Wildlife, 27: 35-39.

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