Hoatzin
Encyclopedia
The Hoatzin also known as the Hoactzin, Stinkbird, or Canje Pheasant, is a species of tropical
bird
found in swamp
s, riverine forest and mangrove
of the Amazon
and the Orinoco delta in South America
. It is notable for having chicks that possess claw
s on two of their wing digit
s.
It is the only member of the genus
Opisthocomus (Ancient Greek
: "wearing long hair behind", referring to its large crest), which in turn is the only extant genus in the family
Opisthocomidae. The taxonomic position of this family has been greatly debated, and is still far from clear.
-sized, with a total length of 65 centimetres (26 in), with a long neck and small head. It has an unfeathered blue face with maroon
eyes, and its head is topped by a spiky, rufous crest. The long, sooty-brown tail is broadly tipped buff
. The upperparts are dark, sooty-brown-edged buff on the wing coverts, and streaked buff on the mantle and nape. The underparts are buff, while the crissum, primaries
, underwing coverts and flanks are rich rufous-chestnut, but this is mainly visible when it opens its wings. The alternative name of "stinkbird" is derived from the bird's manure-like odour, caused by its digestive system.
The Hoatzin is herbivorous, eating leaves and fruit, and has an unusual digestive system with an enlarged crop used for fermentation of vegetable matter, in a manner broadly analogous to the digestive system of mammalian ruminants. The name Stinkbird is related to a strong smell produced by this bird, perhaps due to the fermentation of leaves.
This is a noisy species, with a variety of hoarse calls, including groans, croaks, hisses and grunts. These calls are often associated with body movements, such as wing spreading. Calls are used to maintain contact between individuals in groups, warn off threats and intruders and by chicks begging for food.
in 1776. It is arguably the most enigmatic living bird in regard to its phylogenetic relationships. No satisfying evolution
ary hypothesis has been proposed, and the situation has become worse with the availability of DNA sequence
data.
There has been much debate about the Hoatzin's relationships with other birds. Because of its distinctness it has been given its own family
, the Opisthocomidae, and its own suborder, the Opisthocomi. At various times, it has been allied with such taxa as the tinamou
s, the Galliformes
(gamebirds), the rails, the bustard
s, seriema
s, sandgrouse
, dove
s, turaco
s and other Cuculiformes
, and mousebird
s. Altogether, it has been most frequently suggested to be related to Galliformes, turacos, or the ani
s (New World cuckoos).
, which are considered unreliable and generally dismissed today; the gamebirds together with the waterfowl
belong to the Galloanserae whereas the Hoatzin does not. Cladistic
analysis of skeletal characters, on the other hand, supports a relationship of the Hoatzin to the seriema family Cariamidae, and more distantly to the turaco
and cuckoo
families. However, cuckoos have zygodactyl
feet (two toes forward, two backward) and turacos are semi-zygodactylous, whereas the Hoatzin has the more typical anisodactyl foot with three toes forward, one backwards. The evolution of avian dactyly, on the other hand, is not entirely resolved to satisfaction.
Sibley and Ahlquist
in 1990 considered it likely to be a basal
cuckoo
based on DNA-DNA hybridization. Avise et al. in 1994 found mtDNA cytochrome b
sequence data to agree with Sibley and Ahlquist's previous treatment. Subsequently, Hughes and Baker in 1999 proclaimed to have "resolved" the relationships of the Hoatzin to be with turacos, based on their own analysis of 6 sets of mtDNA and one of nDNA sequences.
However, using mt and nDNA sequences of increased length, Sorenson et al. in 2003 noted that all three previous DNA studies were apparently flawed due to errors in methodology, small sample size
, and sequencing
errors; their study strongly suggested against a close relationship between the Hoatzin and cuckoos or turacos. It was not possible, though, to reliably determine the Hoatzin's closest living relatives. Even though it tended to group with doves, this was not at all well-supported, with little more than 10% likelihood
at best that such an arrangement was accurate according to Sorenson et al.s analysis.
Fain and Houde in 2004 proposed a dichotomy
in the Neoaves (neognaths excluding fowl) based on β-fibrinogen
intron
7 (FGB-int7) sequences. In their suggested phylogeny, the Hoatzin was a basal member of the Metaves, a proposed clade that would include many other historically problematic bird families, such as flamingo
s, grebe
s, tropicbird
s, sandgrouse and mesite
s. While the doves did also group with the "Metaves", no close relationship between these and the Hoatzin within Metaves was recovered.
While the other major neoavian lineage, Coronaves, largely agreed in its internal phylogeny with what is currently emerging as consensus,e.g. that there is a major clade of "near passerine
s" and that the Charadriiformes
are quite distinct. the interrelationships of the "Metaves" were not resolvable. Nor do supposed metavian groupings like flamingos and nightjar
s or tropicbirds and hummingbird
s seem to have a factual basis rather than being artifactually grouped based on molecular homoplasies or lack of informative characters within the group, as Fain and Houde originally suggested; Metaves instead may be a "wastebasket taxon".
It seems probable that the taxa included in the Metaves by Fain and Houde contain some good clade
s, such as Caprimulgiformes
, the Mirandornithes
, or the Apodiformes
. Considering that some "odd Gruiformes
" which might be each other's closest living relatives make up most of the remaining Metaves, the doves, the Hoatzin, and sandgrouse would remain as "Metaves incerta sedis" (Metaves with uncertain placement). This would seem to suggest that the Hoatzin is at least more closely related to doves than to many of the other purported 'coronavian' families that previously have been suggested. Subsequent multigene studies of Ericson et al. 2006 and of Hackett et al. 2008 corroborated the Metaves clades, dependent on the inclusion of one and two genes respectively, but the latter did not recover Hoatzin with Metaves.
More recently, Houde embarked on sequencing the entire genome of the Hoatzin. As of 2011, it was reported that more than 1.4 billion pase pairs of Hoatzin DNA had been sequenced, roughly equal to its entire haploid genome, but that only about 2.4% of its genome had yet been assembled. Completion of this project would be welcomed for more reasons than resolution of Hoatzin relationships. Out of the diverse Class Aves, the genomes of no more than 4 species of birds including of the waterfowl/fowl and songbirds have been sequenced. Moreover, much might be learned by coordinating these efforts with that of the metagenomic analysis of the Hoatzin foregut ruminant bacterial microflora.
More data has probably been analysed for the Hoatzin than for any other non-ratite
bird. As can be seen, not even unequivocal distant relatives can be determined. Thus, those that place the Hoatzin into an order
of its own, Opisthocomiformes, might express the continuing uncertainty most adequately.
As regards other material evidence, the undisputed fossil
record of the hoatzins consists of a single backside of the cranium of a fossil hoatzin, specimen UCMP 42823. It is of Miocene
originOriginally believed to be of Late Miocene age – some 10–5 million years old –, the bone was found in association with fossils of the monkey Cebupitheca sarmientoi which today is usually considered of Early or Middle Miocene, possibly 18 but at least some 12 million years of age. and was recovered in the upper Magdalena River Valley
, Colombia
in the well know fauna of La Venta
. This has been placed into a distinct, less derived genus, Hoazinoides
, but clearly would be placed into the same family as the extant species. It markedly differs insofar as that the cranium of the living Hoatzin is characteristic, being much domed, rounded, and shortened, and that these autapomorphies were less pronounced in the Miocene bird. Miller discussed these findings in the light of the supposed affiliation of the hoatzins and the Galliformes, which was the favored hypothesis at that time, but had been controversial almost since its inception. He cautioned, however, "that Hoazinoides by no means establishes a phyletic junction point with other galliforms." for obvious reasons, as we know today. Anything other than the primary findings of Miller are not to be expected in any case, as by the time of Hoazinoides, essentially all modern bird families are either known or believed to have been present and distinct. Going further back in time, the Late Eocene
or Early Oligocene
(some 34 million years ago) Filholornis from France
has also been considered "proof" of a link between the Hoatzin and the gamebirds. The fragmentary fossil Onychopteryx from the Eocene
of Argentina
and the quite complete but no less enigmatic Early-Middle Eocene (Ypresian
-Lutetian
, some 48 million years ago) Foro panarium
are sometimes used to argue for a hoatzin-cuculiform (including turacos) link. But as demonstrated above, this must be considered highly speculative, if not as crassly off the mark as the relationship with Cracidae
discussed by Miller.
Hoazinavis
is an extinct genus of early hoatzin from Late Oligocene and Early Miocene (about 24–22 mya) deposits of Brazil. It was collected in 2008 from the Tremembé Formation of São Paulo, Brazil. It was first named by Gerald Mayr, Herculano Alvarenga and Cécile Mourer-Chauviré in 2011 and the type species is Hoazinavis lacustris.
Namibiavis
is an extinct genus of early hoatzin from early Middle Miocene (about 16 mya) deposits of Namibia. It was collected from Arrisdrift, southern Namibia. It was first named by Cécile Mourer-Chauviré in 2003 and the type species is Namibiavis senutae.
and to a lesser degree fruit
s and flower
s of the plants which grow in the marshy and riverine habitats where it lives. It clambers around clumsily among the branches, and being quite tame (though they become stressed by frequent visits), often allows close approach and is reluctant to flush. The Hoatzin uses a leathery bump on the bottom of its crop to help balance itself on the branches. It was once thought that the species could only eat the leaves of arums
and mangroves
, but the species is now known to consume the leaves of over fifty species. One study undertaken in Venezuela
found that the Hoatzins diet was 82% leaves, 10% flowers and 8% fruit.
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, much like cattle
and other ruminant
s. Unlike ruminants, however, which possess the rumen
(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 large as to displace the flight muscles and keel of the sternum, much to the detriment of their flight capacity. 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 by humans for food in times of dire need. Any feeding of insects or other animal matter is purely accidental.
Hoatzins are seasonal breeders, breeding during the rainy season
, the exact timing of which varies across its range. Hoatzins are gregarious and nest in small colonies
, laying two or three egg
s in a stick nest in a tree hanging over water in seasonally flooded forests. The chicks, which are fed on regurgitated fermented food, have another odd feature; they have two claws on each wing. Immediately upon hatching, they are able to use these claws, as well as their oversized feet, to scramble around the tree branches without falling into the water. When predators such as the Great Black Hawk
attack a hoatzin nesting colony, the adults fly noisily about, trying to divert the predator's attention, while the chicks move away from the nest and hide among the thickets. If discovered, however, they have another amazing trick: they drop into the water and swim under the surface to escape, then later use their clawed wings to climb back to the safety of the nest. This has inevitably led to comparisons to the fossil bird Archaeopteryx
, but the characteristic is rather an autapomorphy, possibly caused by an atavism
towards the dinosaur
ian finger claws, the developmental genetics ("blueprint") of which presumably is still present in the avian genome
.
. In fact, its survival seems to be more assured than that of many other endemics of its range. In Brazil, indigenous peoples sometimes collect the eggs for food, and the adults are occasionally hunted, but in general this is rare, as it is reputed to have a bad taste. While its preferred habitats, mangrove and riverine forest, are disappearing quickly in some regions, it is less threatened than terra firme forest, which is the primary target for deforestation
in the Amazon. The Hoatzin therefore remains fairly common in a large part of its range. The Hoatzin is the national bird of Guyana.
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
found in swamp
Swamp
A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...
s, riverine forest and mangrove
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
of the Amazon
Amazon Basin
The Amazon Basin is the part of South America drained by the Amazon River and its tributaries that drains an area of about , or roughly 40 percent of South America. The basin is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela...
and the Orinoco delta in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. It is notable for having chicks that possess claw
Claw
A claw is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. However, the word "claw" is also often used in reference to an invertebrate. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end...
s on two of their wing digit
Digit (anatomy)
A digit is one of several most distal parts of a limb, such as fingers or toes, present in many vertebrates.- Names:Some languages have different names for hand and foot digits ....
s.
It is the only member of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Opisthocomus (Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
: "wearing long hair behind", referring to its large crest), which in turn is the only extant genus in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Opisthocomidae. The taxonomic position of this family has been greatly debated, and is still far from clear.
Description
The Hoatzin is pheasantPheasant
Pheasants refer to some members of the Phasianinae subfamily of Phasianidae in the order Galliformes.Pheasants are characterised by strong sexual dimorphism, males being highly ornate with bright colours and adornments such as wattles and long tails. Males are usually larger than females and have...
-sized, with a total length of 65 centimetres (26 in), with a long neck and small head. It has an unfeathered blue face with maroon
Maroon (color)
Maroon is a dark red color.-Etymology:Maroon is derived from French marron .The first recorded use of maroon as a color name in English was in 1789.-Maroon :...
eyes, and its head is topped by a spiky, rufous crest. The long, sooty-brown tail is broadly tipped buff
Buff (colour)
Buff is a pale yellow-brown colour that got its name from the colour of buff leather.Displayed on the right is the colour buff.EtymologyAccording to the Oxford English Dictionary, buff as a descriptor of a colour was first used in the London Gazette of 1686, describing a uniform to be "A Red Coat...
. The upperparts are dark, sooty-brown-edged buff on the wing coverts, and streaked buff on the mantle and nape. The underparts are buff, while the crissum, primaries
Flight feather
Flight feathers are the long, stiff, asymmetrically shaped, but symmetrically paired feathers on the wings or tail of a bird; those on the wings are called remiges while those on the tail are called rectrices . Their primary function is to aid in the generation of both thrust and lift, thereby...
, underwing coverts and flanks are rich rufous-chestnut, but this is mainly visible when it opens its wings. The alternative name of "stinkbird" is derived from the bird's manure-like odour, caused by its digestive system.
The Hoatzin is herbivorous, eating leaves and fruit, and has an unusual digestive system with an enlarged crop used for fermentation of vegetable matter, in a manner broadly analogous to the digestive system of mammalian ruminants. The name Stinkbird is related to a strong smell produced by this bird, perhaps due to the fermentation of leaves.
This is a noisy species, with a variety of hoarse calls, including groans, croaks, hisses and grunts. These calls are often associated with body movements, such as wing spreading. Calls are used to maintain contact between individuals in groups, warn off threats and intruders and by chicks begging for food.
Taxonomy, systematics and evolution
The Hoatzin was originally described by German zoologist Statius MüllerPhilipp Ludwig Statius Müller
Philipp Ludwig Statius Muller was a German zoologist.Statius Muller was born in Esens, and was Professor of Natural Science at Erlangen. Between 1773 and 1776, he published a German translation of Linnaeus's Natursystem...
in 1776. It is arguably the most enigmatic living bird in regard to its phylogenetic relationships. No satisfying evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary hypothesis has been proposed, and the situation has become worse with the availability of DNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
data.
There has been much debate about the Hoatzin's relationships with other birds. Because of its distinctness it has been given its own family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
, the Opisthocomidae, and its own suborder, the Opisthocomi. At various times, it has been allied with such taxa as the tinamou
Tinamou
The tinamous are a family comprising 47 species of birds found in Central and South America. One of the most ancient living groups of bird, they are related to the ratites. Generally ground dwelling, they are found in a range of habitats....
s, the Galliformes
Galliformes
Galliformes are an order of heavy-bodied ground-feeding domestic or game bird, containing turkey, grouse, chicken, New and Old World Quail, ptarmigan, partridge, pheasant, and the Cracidae. Common names are gamefowl or gamebirds, landfowl, gallinaceous birds or galliforms...
(gamebirds), the rails, the bustard
Bustard
Bustards, including floricans and korhaans, are large terrestrial birds mainly associated with dry open country and steppes in the Old World...
s, seriema
Seriema
The seriemas are the sole extant members of the small and ancient family Cariamidae, which is also the sole surviving family of the Cariamae. Once believed to be related to cranes, they have been placed by one recent study near the falcons, parrots and passerines, as well as the extinct terror birds...
s, sandgrouse
Sandgrouse
The sandgrouse are a family, Pteroclididae, of 16 bird species, the only living members of the order Pteroclidiformes. They are restricted to treeless open country in the Old World, such as plains and semi-deserts. They are distributed across northern, southern and eastern Africa as well as...
, dove
Dove
Pigeons and doves constitute the bird family Columbidae within the order Columbiformes, which include some 300 species of near passerines. In general terms "dove" and "pigeon" are used somewhat interchangeably...
s, turaco
Turaco
The turacos make up the bird family Musophagidae , which includes plantain-eaters and go-away-birds. In southern Africa both turacos and go-away-birds are commonly known as louries. They are semi-zygodactylous - the fourth toe can be switched back and forth...
s and other Cuculiformes
Cuculiformes
The near passerine bird order Cuculiformes traditionally included three families as below:* Musophagidae - turacos and allies* Cuculidae - cuckoos, coucals, roadrunners and anis* Opisthocomidae - Hoatzin...
, and mousebird
Mousebird
The mousebirds are a small group of birds which have no known close affinities to other groups, though they and the parrots and cockatoos may be closer to each other than to other birds. The mousebirds are therefore given order status as Coliiformes...
s. Altogether, it has been most frequently suggested to be related to Galliformes, turacos, or the ani
Crotophagidae
The anis are a small family of gregarious birds occurring in the Americas. They are part of the cuckoo order Cuculiformes and are sometimes placed as a subfamily Crotophaginae within the cuckoo family Cuculidae....
s (New World cuckoos).
History of the debate
Placement with the gamebirds is historical, based mainly on phenetic considerations of external morphologyMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
, which are considered unreliable and generally dismissed today; the gamebirds together with the waterfowl
Waterfowl
Waterfowl are certain wildfowl of the order Anseriformes, especially members of the family Anatidae, which includes ducks, geese, and swans....
belong to the Galloanserae whereas the Hoatzin does not. Cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
analysis of skeletal characters, on the other hand, supports a relationship of the Hoatzin to the seriema family Cariamidae, and more distantly to the turaco
Turaco
The turacos make up the bird family Musophagidae , which includes plantain-eaters and go-away-birds. In southern Africa both turacos and go-away-birds are commonly known as louries. They are semi-zygodactylous - the fourth toe can be switched back and forth...
and cuckoo
Cuckoo
The cuckoos are a family, Cuculidae, of near passerine birds. The order Cuculiformes, in addition to the cuckoos, also includes the turacos . Some zoologists and taxonomists have also included the unique Hoatzin in the Cuculiformes, but its taxonomy remains in dispute...
families. However, cuckoos have zygodactyl
Dactyly
In biology, dactyly is the arrangement of digits on the hands, feet, or sometimes wings of a tetrapod animal. It comes from the Greek word δακτυλος = "finger".Sometimes the ending "-dactylia" is used...
feet (two toes forward, two backward) and turacos are semi-zygodactylous, whereas the Hoatzin has the more typical anisodactyl foot with three toes forward, one backwards. The evolution of avian dactyly, on the other hand, is not entirely resolved to satisfaction.
Sibley and Ahlquist
Sibley-Ahlquist taxonomy
The Sibley-Ahlquist taxonomy is a bird taxonomy proposed by Charles Sibley and Jon Edward Ahlquist. It is based on DNA-DNA hybridization studies conducted in the late 1970s and throughout the 1980s....
in 1990 considered it likely to be a basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
cuckoo
Cuckoo
The cuckoos are a family, Cuculidae, of near passerine birds. The order Cuculiformes, in addition to the cuckoos, also includes the turacos . Some zoologists and taxonomists have also included the unique Hoatzin in the Cuculiformes, but its taxonomy remains in dispute...
based on DNA-DNA hybridization. Avise et al. in 1994 found mtDNA cytochrome b
Cytochrome b
Cytochrome b/b6 is the main subunit of transmembrane cytochrome bc1 and b6f complexes. In addition, it commonly refers to a region of mtDNA used for population genetics and phylogenetics.- Function :...
sequence data to agree with Sibley and Ahlquist's previous treatment. Subsequently, Hughes and Baker in 1999 proclaimed to have "resolved" the relationships of the Hoatzin to be with turacos, based on their own analysis of 6 sets of mtDNA and one of nDNA sequences.
However, using mt and nDNA sequences of increased length, Sorenson et al. in 2003 noted that all three previous DNA studies were apparently flawed due to errors in methodology, small sample size
Sample size
Sample size determination is the act of choosing the number of observations to include in a statistical sample. The sample size is an important feature of any empirical study in which the goal is to make inferences about a population from a sample...
, and sequencing
DNA sequencing
DNA sequencing includes several methods and technologies that are used for determining the order of the nucleotide bases—adenine, guanine, cytosine, and thymine—in a molecule of DNA....
errors; their study strongly suggested against a close relationship between the Hoatzin and cuckoos or turacos. It was not possible, though, to reliably determine the Hoatzin's closest living relatives. Even though it tended to group with doves, this was not at all well-supported, with little more than 10% likelihood
Likelihood
Likelihood is a measure of how likely an event is, and can be expressed in terms of, for example, probability or odds in favor.-Likelihood function:...
at best that such an arrangement was accurate according to Sorenson et al.s analysis.
Fain and Houde in 2004 proposed a dichotomy
Dichotomy
A dichotomy is any splitting of a whole into exactly two non-overlapping parts, meaning it is a procedure in which a whole is divided into two parts...
in the Neoaves (neognaths excluding fowl) based on β-fibrinogen
Fibrinogen
Fibrinogen is a soluble plasma glycoprotein, synthesised by the liver, that is converted by thrombin into fibrin during blood coagulation. This is achieved through processes in the coagulation cascade that activate the zymogen prothrombin to the serine protease thrombin, which is responsible for...
intron
Intron
An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final...
7 (FGB-int7) sequences. In their suggested phylogeny, the Hoatzin was a basal member of the Metaves, a proposed clade that would include many other historically problematic bird families, such as flamingo
Flamingo
Flamingos or flamingoes are gregarious wading birds in the genus Phoenicopterus , the only genus in the family Phoenicopteridae...
s, grebe
Grebe
A grebe is a member of the Podicipediformes order, a widely distributed order of freshwater diving birds, some of which visit the sea when migrating and in winter...
s, tropicbird
Tropicbird
Tropicbirds are a family, Phaethontidae, of tropical pelagic seabirds now classified in their own order Phaethontiformes. Their relationship to other living birds is unclear, and they appear to have no close relatives. There are three species in one genus, Phaethon...
s, sandgrouse and mesite
Mesite
The mesites are a family of birds of uncertain affinities. They are smallish, near flightless birds endemic to Madagascar. Generally brownish with paler undersides, they are of somewhat pheasant-like appearance and were initially placed with the Galliformes...
s. While the doves did also group with the "Metaves", no close relationship between these and the Hoatzin within Metaves was recovered.
While the other major neoavian lineage, Coronaves, largely agreed in its internal phylogeny with what is currently emerging as consensus,e.g. that there is a major clade of "near passerine
Near passerine
Near passerine or higher land-bird assemblage are terms often given to arboreal birds or those most often believed to be related to the true passerines due to ecological similarities; the group corresponds to some extent with the Anomalogonatae of Garrod All near passerines are land birds...
s" and that the Charadriiformes
Charadriiformes
Charadriiformes is a diverse order of small to medium-large birds. It includes about 350 species and has members in all parts of the world. Most Charadriiformes live near water and eat invertebrates or other small animals; however, some are pelagic , some occupy deserts and a few are found in thick...
are quite distinct. the interrelationships of the "Metaves" were not resolvable. Nor do supposed metavian groupings like flamingos and nightjar
Nightjar
Nightjars are medium-sized nocturnal or crepuscular birds with long wings, short legs and very short bills. They are sometimes referred to as goatsuckers from the mistaken belief that they suck milk from goats . Some New World species are named as nighthawks...
s or tropicbirds and hummingbird
Hummingbird
Hummingbirds are birds that comprise the family Trochilidae. They are among the smallest of birds, most species measuring in the 7.5–13 cm range. Indeed, the smallest extant bird species is a hummingbird, the 5-cm Bee Hummingbird. They can hover in mid-air by rapidly flapping their wings...
s seem to have a factual basis rather than being artifactually grouped based on molecular homoplasies or lack of informative characters within the group, as Fain and Houde originally suggested; Metaves instead may be a "wastebasket taxon".
It seems probable that the taxa included in the Metaves by Fain and Houde contain some good clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
s, such as Caprimulgiformes
Caprimulgiformes
The Caprimulgiformes is an order of birds that includes a number of birds with global distribution . They are generally insectivorous and nocturnal...
, the Mirandornithes
Mirandornithes
Mirandornithes is a clade that consists of flamingos and grebes. The relationships of both groups have been problematic. Flamingos had been placed with numerous branches within Neognathae, such as ducks and storks. The grebes had been placed with the loons. However recent studies seem to confirm...
, or the Apodiformes
Apodiformes
Traditionally, the bird order Apodiformes contained three living families: the swifts , the tree swifts , and the hummingbirds . In the Sibley-Ahlquist taxonomy, this order is raised to a superorder Apodimorphae in which hummingbirds are separated as a new order, Trochiliformes...
. Considering that some "odd Gruiformes
Gruiformes
The Gruiformes are an order containing a considerable number of living and extinct bird families, with a widespread geographical diversity. Gruiform means "crane-like"....
" which might be each other's closest living relatives make up most of the remaining Metaves, the doves, the Hoatzin, and sandgrouse would remain as "Metaves incerta sedis" (Metaves with uncertain placement). This would seem to suggest that the Hoatzin is at least more closely related to doves than to many of the other purported 'coronavian' families that previously have been suggested. Subsequent multigene studies of Ericson et al. 2006 and of Hackett et al. 2008 corroborated the Metaves clades, dependent on the inclusion of one and two genes respectively, but the latter did not recover Hoatzin with Metaves.
More recently, Houde embarked on sequencing the entire genome of the Hoatzin. As of 2011, it was reported that more than 1.4 billion pase pairs of Hoatzin DNA had been sequenced, roughly equal to its entire haploid genome, but that only about 2.4% of its genome had yet been assembled. Completion of this project would be welcomed for more reasons than resolution of Hoatzin relationships. Out of the diverse Class Aves, the genomes of no more than 4 species of birds including of the waterfowl/fowl and songbirds have been sequenced. Moreover, much might be learned by coordinating these efforts with that of the metagenomic analysis of the Hoatzin foregut ruminant bacterial microflora.
More data has probably been analysed for the Hoatzin than for any other non-ratite
Ratite
A ratite is any of a diverse group of large, flightless birds of Gondwanan origin, most of them now extinct. Unlike other flightless birds, the ratites have no keel on their sternum—hence the name from the Latin ratis...
bird. As can be seen, not even unequivocal distant relatives can be determined. Thus, those that place the Hoatzin into an order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of its own, Opisthocomiformes, might express the continuing uncertainty most adequately.
Fossil record
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
record of the hoatzins consists of a single backside of the cranium of a fossil hoatzin, specimen UCMP 42823. It is of Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
originOriginally believed to be of Late Miocene age – some 10–5 million years old –, the bone was found in association with fossils of the monkey Cebupitheca sarmientoi which today is usually considered of Early or Middle Miocene, possibly 18 but at least some 12 million years of age. and was recovered in the upper Magdalena River Valley
Magdalena River Valley
The Magdalena River Valley is a valley in Colombia located within the Colombian Andes mountain ranges. The valley is specifically located between the Cordillera Central and Cordillera Oriental and crossed by the river of the same name, the Magdalena River....
, Colombia
Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...
in the well know fauna of La Venta
La Venta (Colombia)
La Venta is a settlement between the modern Tolima Department and Huila Department, Colombia. Nearby, one of the richest Neogene fossil assemblages in the whole of South America is known...
. This has been placed into a distinct, less derived genus, Hoazinoides
Hoazinoides
Hoazinoides is an extinct genus of bird from the middle Miocene from the"Monkey Beds" of the Villavieja Formation of La Venta, Colombia. It is a member of the family Opisthocomidae, which also includes the hoatzin and several other extinct genera. The only known species is Hoazinoides magdalenae...
, but clearly would be placed into the same family as the extant species. It markedly differs insofar as that the cranium of the living Hoatzin is characteristic, being much domed, rounded, and shortened, and that these autapomorphies were less pronounced in the Miocene bird. Miller discussed these findings in the light of the supposed affiliation of the hoatzins and the Galliformes, which was the favored hypothesis at that time, but had been controversial almost since its inception. He cautioned, however, "that Hoazinoides by no means establishes a phyletic junction point with other galliforms." for obvious reasons, as we know today. Anything other than the primary findings of Miller are not to be expected in any case, as by the time of Hoazinoides, essentially all modern bird families are either known or believed to have been present and distinct. Going further back in time, the Late Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
or Early Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
(some 34 million years ago) Filholornis from France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
has also been considered "proof" of a link between the Hoatzin and the gamebirds. The fragmentary fossil Onychopteryx from the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
and the quite complete but no less enigmatic Early-Middle Eocene (Ypresian
Ypresian
In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between and , is preceded by the Thanetian age and is followed by the Eocene Lutetian age....
-Lutetian
Lutetian
The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between and . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Middle Eocene subepoch...
, some 48 million years ago) Foro panarium
Foro (bird)
Foro is a mysterious genus of bird that lived during the early to mid-Eocene around the Ypresian-Lutetian boundary, some 48 million years ago. It is known from fossils found in the Green River Formation of Wyoming. Only a single species, Foro panarium, is known.Its relationships are unknown. It is...
are sometimes used to argue for a hoatzin-cuculiform (including turacos) link. But as demonstrated above, this must be considered highly speculative, if not as crassly off the mark as the relationship with Cracidae
Cracidae
The chachalacas, guans and curassows are birds in the family Cracidae.These are species of tropical and subtropical Central and South America. One species, the Plain Chachalaca, just reaches southernmost Texas in the USA...
discussed by Miller.
Hoazinavis
Hoazinavis
Hoazinavis is an extinct genus of early hoatzin from Late Oligocene and Early Miocene deposits of Brazil. It was collected in 2008 from the Tremembé Formation of São Paulo, Brazil. It was first named by Gerald Mayr, Herculano Alvarenga and Cécile Mourer-Chauviré in 2011 and the type species is...
is an extinct genus of early hoatzin from Late Oligocene and Early Miocene (about 24–22 mya) deposits of Brazil. It was collected in 2008 from the Tremembé Formation of São Paulo, Brazil. It was first named by Gerald Mayr, Herculano Alvarenga and Cécile Mourer-Chauviré in 2011 and the type species is Hoazinavis lacustris.
Namibiavis
Namibiavis
Namibiavis is an extinct genus of early hoatzin from early Middle Miocene deposits of Namibia. It was collected from Arrisdrift, southern Namibia. It was first named by Cécile Mourer-Chauviré in 2003 and the type species is Namibiavis senutae....
is an extinct genus of early hoatzin from early Middle Miocene (about 16 mya) deposits of Namibia. It was collected from Arrisdrift, southern Namibia. It was first named by Cécile Mourer-Chauviré in 2003 and the type species is Namibiavis senutae.
Feeding
The Hoatzin eats the leavesLeaves
-History:Vocalist Arnar Gudjonsson was formerly the guitarist with Mower, and he was joined by Hallur Hallsson , Arnar Ólafsson , Bjarni Grímsson , and Andri Ásgrímsson . Late in 2001 they played with Emiliana Torrini and drew early praise from the New York Times...
and to a lesser degree fruit
Fruit
In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...
s and flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s of the plants which grow in the marshy and riverine habitats where it lives. It clambers around clumsily among the branches, and being quite tame (though they become stressed by frequent visits), often allows close approach and is reluctant to flush. The Hoatzin uses a leathery bump on the bottom of its crop to help balance itself on the branches. It was once thought that the species could only eat the leaves of arums
Araceae
Araceae are a family of monocotyledonous flowering plants in which flowers are borne on a type of inflorescence called a spadix. The spadix is usually accompanied by, and sometimes partially enclosed in, a spathe or leaf-like bract. Also known as the Arum family, members are often colloquially...
and mangroves
Avicennia
Avicennia is a genus of flowering plants currently placed in the bear's breeches family, Acanthaceae. It contains mangrove trees, which occur in the intertidal zones of estuarine areas and are characterized by aerial roots. Species of Avicennia occur worldwide south of the Tropic of Cancer.The...
, but the species is now known to consume the leaves of over fifty species. One study undertaken in Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...
found that the Hoatzins diet was 82% leaves, 10% flowers and 8% fruit.
Fermentation (biochemistry)
Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...
in the front part of the gut to break down the vegetable material they consume, much like cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
and other ruminant
Ruminant
A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...
s. Unlike ruminants, however, which possess the rumen
Rumen
The rumen, also known as a paunch, forms the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. It serves as the primary site for microbial fermentation of ingested feed...
(a specialized stomach for bacterial fermentation) in the Hoatzin this is the function of the crop
Crop (anatomy)
A crop is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion that is found in many animals, including gastropods, earthworms, leeches, insects, birds, and even some dinosaurs.- Bees :Cropping is used by bees to temporarily store nectar of flowers...
(an enlargement of the esophagus). The crop
Crop (anatomy)
A crop is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion that is found in many animals, including gastropods, earthworms, leeches, insects, birds, and even some dinosaurs.- Bees :Cropping is used by bees to temporarily store nectar of flowers...
of the Hoatzin is so large as to displace the flight muscles and keel of the sternum, much to the detriment of their flight capacity. Because of aromatic compounds in the leaves they consume and the bacterial fermentation, the bird has a disagreeable, manure
Manure
Manure is organic matter used as organic fertilizer in agriculture. Manures contribute to the fertility of the soil by adding organic matter and nutrients, such as nitrogen, that are trapped by bacteria in the soil...
-like odor and is only hunted by humans for food in times of dire need. Any feeding of insects or other animal matter is purely accidental.
Breeding
Wet season
The the wet season, or rainy season, is the time of year, covering one or more months, when most of the average annual rainfall in a region occurs. The term green season is also sometimes used as a euphemism by tourist authorities. Areas with wet seasons are dispersed across portions of the...
, the exact timing of which varies across its range. Hoatzins are gregarious and nest in small colonies
Bird colony
A bird colony is a large congregation of individuals of one or more species of bird that nest or roost in close proximity at a particular location. Many kinds of birds are known to congregate in groups of varying size; a congregation of nesting birds is called a breeding colony...
, laying two or three egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
s in a stick nest in a tree hanging over water in seasonally flooded forests. The chicks, which are fed on regurgitated fermented food, have another odd feature; they have two claws on each wing. Immediately upon hatching, they are able to use these claws, as well as their oversized feet, to scramble around the tree branches without falling into the water. When predators such as the Great Black Hawk
Great Black Hawk
The Great Black Hawk, Buteogallus urubitinga, is a bird of prey in the family Accipitridae, which also includes the eagles, hawks and Old World vultures....
attack a hoatzin nesting colony, the adults fly noisily about, trying to divert the predator's attention, while the chicks move away from the nest and hide among the thickets. If discovered, however, they have another amazing trick: they drop into the water and swim under the surface to escape, then later use their clawed wings to climb back to the safety of the nest. This has inevitably led to comparisons to the fossil bird Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
, but the characteristic is rather an autapomorphy, possibly caused by an atavism
Atavism
Atavism is the tendency to revert to ancestral type. In biology, an atavism is an evolutionary throwback, such as traits reappearing which had disappeared generations before. Atavisms can occur in several ways...
towards the dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
ian finger claws, the developmental genetics ("blueprint") of which presumably is still present in the avian genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
.
Relationship with humans
Though conspicuous, even attractive, at close range due to its bizarre shape and striking colors, unwariness and a poor flier, it is not considered endangeredEndangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
. In fact, its survival seems to be more assured than that of many other endemics of its range. In Brazil, indigenous peoples sometimes collect the eggs for food, and the adults are occasionally hunted, but in general this is rare, as it is reputed to have a bad taste. While its preferred habitats, mangrove and riverine forest, are disappearing quickly in some regions, it is less threatened than terra firme forest, which is the primary target for deforestation
Deforestation
Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....
in the Amazon. The Hoatzin therefore remains fairly common in a large part of its range. The Hoatzin is the national bird of Guyana.
External links
- Cornell Lab of Ornithology: Mystery Birds: Hoatzin Adults and Young. Retrieved 2008-JUN-16.
- Hoatzin videos, photos & sounds on the Internet Bird Collection.
- saveamericasrainforests.org: Photo of adult bird in rear aspect, showing wing coloration. Retrieved 2007-FEB-28.
- treknature.com: Photo of adult bird showing head and neck to good effect. Retrieved 2007-FEB-28.
- Stamps (for BoliviaBoliviaBolivia officially known as Plurinational State of Bolivia , is a landlocked country in central South America. It is the poorest country in South America...
, GuyanaGuyanaGuyana , officially the Co-operative Republic of Guyana, previously the colony of British Guiana, is a sovereign state on the northern coast of South America that is culturally part of the Anglophone Caribbean. Guyana was a former colony of the Dutch and of the British...
, SurinameSurinameSuriname , officially the Republic of Suriname , is a country in northern South America. It borders French Guiana to the east, Guyana to the west, Brazil to the south, and on the north by the Atlantic Ocean. Suriname was a former colony of the British and of the Dutch, and was previously known as...
) - Hoatzin photo gallery VIREO