Animal Diversity Web

Ge­o­graphic Range

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

• Biogeographic Regions
• neotropical
  • native

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).

• Terrestrial Biomes
• rainforest

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).

• Other Physical Features
• endothermic
• bilateral symmetry

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).

• Key Reproductive Features
• iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• oviparous

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).

• Key Behaviors
• flies
• motile

Com­mu­ni­ca­tion and Per­cep­tion

• Perception Channels
• visual
• tactile
• acoustic
• chemical

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)

• Primary Diet
• herbivore
  • folivore

• 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.

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Migratory Bird Act

  No special status

• CITES

  No special status

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.

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.