Hoatzin

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iHoatzin

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Cuculiformes
Family:	Opisthocomidae Swainson, 1837
Genus:	Opisthocomus Illiger, 1811
Species:	O. hoazin

Binomial name

Ophisthocomus hoazin
(Muller, 1776)

The Hoatzin (Opisthocomus hoazin), also known as the Hoactzin, Stinkbird, or Canje Pheasant, is an odd species of tropical bird found in the swamps of the Amazon and Orinoco rivers in South America.

It is pheasant-sized — but much slimmer — long-tailed, long-necked and has a small head. It has an unfeathered blue face with red eyes, and its head is topped by spiky crest. It is a weak flier.

There has been much debate about its relationships with other bird species. It has been given its own family, the Opisthocomidae, and has most frequently been suggested to possibly be related to gamebirds, turacos, or ground-dwelling New World cuckoos. Cladistic analysis of skeletal characters supports a relationship of the Hoatzin to the seriema family, and more distantly to the turaco and cuckoo families. However, both turacos and cuckoos have zygodactyl feet (two toes forward, two backward), whereas the Hoatzin has the more typical anisodactyl foot with three toes forward, one backwards. Sibley considered it likely to be a basal cuckoo based on DNA hybridization (Sibley and Ahlquist 1990). Avise et al (1994) echoed Sibley and Ahlquist's previous treatment, this time based on DNA sequence analysis. Subsequently, Hughes and Baker (1999) proclaimed the relationships of the Hoatzin "resolved" to be with turacos on the basis of their own larger DNA sequence analysis. However, in a much more comprehensive DNA sequence analysis Sorenson et al (2003) noted that all three previous DNA studies were flawed with erroneous data. They found clear evidence against the aforementioned putative relationships, and proposed instead a possible relationship between Hoatzin and doves. This seems to be closest to fact. The most comprehensive study of avian families to date holds that the Hoatzin and doves are among a newly discovered group, Metaves, that also purports to include many others of the most historically problematic families, e.g., flamingos, grebes, tropicbirds, sandgrouse, mesites, etc. (Fain and Houde 2004). While the hypothesis of their relationship is based on DNA, it is notable that these birds share some obscure anatomical features, e.g., the notarium - a fused series of thoracic vertebrae. Some, like Hoatzin, doves, and flamingos, also are unique in feeding their young esophageal secretions.

The Hoatzin eats the leaves and fruits of the plants which grow in the marshes where it lives. One of this species' many peculiarities is that it has a digestive system unique amongst birds. Hoatzins use bacterial fermentation in the front part of the gut to break down the vegetable material they consume, like cattle and other ruminants. Unlike ruminants which possess a specialized stomach for bacterial fermentation, in the Hoatzin this is the function of the crop, an enlargement of the esophagus. The crop of the Hoatzin is so hypertrophied as to displace the flight muscles and keel of the sternum, much to the detriment of their flight. Because of aromatic compounds in the leaves they consume and the bacterial fermentation, the bird has a disagreeable, manure-like odor and is only hunted for food in times of dire need.

Hoatzins are gregarious and nest in small colonies, laying 2-3 eggs in a stick nest in a tree overhanging water in seasonally flooded forests. The chick, which is fed on regurgitated cud, has another odd feature; it has two claws on each wing. When disturbed, the chicks drop into the water to escape predation, then they use their clawed wings to climb back to the safety of the nest. This has inevitably led to comparisons to the fossil Archaeopteryx.

This is a noisy species, with a variety of hoarse calls, one of which has been described as like a heavy smoker's wheezing.

[edit] References

Avise, J.C., W.S. Nelson, and C.G. Sibley (1994). "Why one kilobase sequences from mitochondrial DNA fail to solve the hoatzin phylogenetic enigma." Molecular Phylogenetics and Evolution 3: 175-184.
Fain, M.G., and P. Houde. (2004). "Parallel radiations in the primary clades of birds." Evolution 58: 2558-2573.
Hughes, J.M., and A.J. Baker. (1999). "Phylogenetic relationships of the enigmatic hoatzin (Opisthocomus haozin) resolved using mitochondrial and nuclear gene sequences." Molecular Biology and Evolution 16: 1300-1307.
Sibely, C.G., and J.E. Ahlquist. (1990). Phylogeny and Classification of Birds. Yale University Press.
Sorenson, Michael D., E. Oneal, J. Garcia-Moreno, and D. P. Mindell. (2003). "More Taxa, More Characters: The Hoatzin Problem is Still Unresolved." Molecular Biology and Evolution: 20: 1484-1499.