June 26, 2013

Wildlife Wednesday: The Hoatzin, Opisthocomus hoazin

Picture Credit: Bing Images

Picture Credit: Bing Images

Picture Credit: Bing Images
The Hoatzin is such a bizarre bird that it almost has to be seen to be believed. A prehistoric looking bird with a punk haircut, there is considerable debate about which birds are most closely related to the Hoatzin. Traditionally it has been placed in the Galliformes along with pheasants, turkeys, curassows, etc.. More recently it has been placed with the cuckoos and some gene sequencing carried out by JM Hughes and AJ Baker at the Royal Ontario Museum suggests that its closest relatives are the turacos of sub-Saharan Africa.  Whatever its parentage, it is a pretty unique beast. It only eats leaves and is the only bird to have a gut like a cow where the cellulose from the leaves is broken down into sugars. This in turn requires a specially adapted skeleton and the weight of leaves it eats makes it fairly ungainly as it flies or clambers about the dense vegetation of its habitat. Adding to the interest is the fact that the nestlings have claws on their wings. When threatened, they fall out of the nest, which is usually over water, and when the danger is passed they use their wing-hooks to help them climb back into the nest. The Hoatzin is found in both the Amazon and the Orinoco basins of South America and is usually in fairly large groups.
The habitat of Hoatzins includes swamps, fresh water marshes, gallery forests, and the banks of rivers, lakes and streams.
Hoatzins do not begin breeding until after their first year of life. The breeding season of Hoatzin occurs during the same time as the rainy season of their territory. Hoatzins build their nests on branches over the water about 2 to 6 meter above the surface. They normally lay two to three eggs and the incubation period lasts 32 days. Both male and female brood the young, which typically remain in the nest for 2 to 3 weeks after they hatch.
Although they typically feed on less than twelve species of plants, they are capable of eating the leafs of more than fifty different species. The leafs 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 leafs. They have an enlarged crop in which symbiotic bacteria are stored and used to break down the cell walls of the leafs, 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.
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size has not been quantified, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Hoatzins are found throughout the Amazon in northern and central South America . In Suriname confined to the banks of the Corantijn River.
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