Screamers



Class Aves
Order Anseriformes
Suborder Anhimae
Family Anhimidae

Description
Large, heavy-bodied, fowl-like, semi-aquatic birds
with two distinctive bone spurs at the bend of
each wing

Size
Body length is 28–36 in (71–92 cm); 5–7 lb
(2–3 kg)

Number of genera, species
2 genera, 3 species

Habitat
Occur in the vicinity of tropical lowland lakes, ponds, marshes, and rivers.





Conservation status
The northern screamer (Chauna chavaria) is Near Threatened

Distribution
Tropical regions of South America, from Venezuela and Colombia south to Uruguay and northern Argentina





Evolution and systematics
Although screamers (family Anhimidae) are rather fowl-like in appearance, they are placed in the same order (Anseriformes) as the geese, swans, and ducks (family Anatidae). Prior to clarification of the evolutionary proximity of the screamers with the waterfowl, which was largely based on aspects of their internal anatomy, they had been considered more closely related to the rails (family Rallidae) or the storks and their allies (order Ciconiiformes).



 Because some of the characters of screamers are primitive, in particular their wing-spurs, they had even been thought to be the closest living relatives of the ancient bird progenitor, Archaeopteryx. The common ancestry of the screamers and the anatids is reinforced by aspects of the biology of the Australian magpie goose (Anseranas semipalmata), which shows similarities to the screamers in its manner of molting, the absence of webbing on the feet, plates on the tarsus, the formation of the sternum, and the tendency to perch in trees. 



Fossil remains of screamers are known from deposits of the Quaternary Period in Argentina. There are three living species: the horned screamer (Anhima cornuta), northern horned screamer (Chauna chavaria), and southern horned screamer (Chauna torquata).


Physical characteristics
Screamers are large, semi-aquatic, goose-like birds that swim well and occur near and in fresh water. They have a stout body, a crest or horn-like projection on the top of the head, a short, downcurved, fowl-like bill, rather thick, long legs, and stout feet lacking webbing between the strong toes. Their body length is 28–36 in (71–92 cm) and they weigh 5–7 lb (2–3 kg). Screamers have two sharp, spur-like outgrowths of fused carpal bones on each of their wings. The spurs are covered externally by keratin, a tough polysaccharide similar to the material in fingernails.




The presence of these two spurs is unique in screamers. Like most birds, the interior of most skeletal bones is permeated by abundant air sacs, which continue into a well-developed air-containing tissue in the dermis. Male screamers do not have a copulatory organ. The general body coloration is black or gray on top, and somewhat lighter below. The two genera of screamers have marked differences in their internal anatomy, and in addition the horned screamers (genus Anhima) have 14 tail feathers, while the crested screamers (Chauna) have 12.


Distribution
Screamers occur in tropical regions of South America, from Venezuela and Colombia south to Uruguay and northern Argentina.

Habitat
Screamers occur in the vicinity of tropical lowland lakes, ponds, marshes, and rivers.


Behavior
Screamers are non-migratory birds, remaining all year within their breeding area. They are somewhat gregarious. Outside the breeding season, horned screamers live in groups of five to 10 birds, while crested screamers are found in larger flocks that circle above water bodies in the evenings, calling vociferously. 




Screamers can fly well but slowly, and they may soar for extended periods of time. They swim well and may walk on dense mats of floating vegetation. They roost in trees. They sometimes use the sharp spurs on their wings as weapons in fights connected with pair formation. The spurs are also used as a defense against predators. Crested screamers have  goose-like call, and also a gargled throaty sound that resembles drumming. The horned screamer is less vocal, uttering a loud, shrill hoot. 

The cries of screamers are among the loudest of any birds.




Feeding ecology and diet
Screamers are vegetarians that feed on aquatic plants and

seeds.

Reproductive biology
The nests of screamers are rather large and are located near or in marshy vegetation in shallow water. Nests are constructed of plant materials. Screamers lay two to seven smooth, yellowish-white eggs, which are incubated by both parents. 



The down-covered young are nidifugous, meaning they leave the nest almost immediately after hatching. Both parents care for the young.





Conservation status
The World Conservation Union (IUCN) lists the northern screamer as Near Threatened. This species has declined greatly in range and abundance, and further deterioration of its circumstances would render it threatened.




Significance to humans
Screamers are sometimes hunted as food. Young screamers are sometimes caught and tamed by local people. They readily take to captivity and can be kept with chickens in farmyards, where they defend their companions against birds of prey and other enemies. Sometimes they are allowed to walk about at liberty in South American parks and zoos.