Screamers are a small family of Neotropical waterfowl, placed in the Anseriformes
(with ducks, geese, and swans) but long separated from typical waterfowl.
The three species of Screamers have long been considered to form a separate
family. Only recently has genetic work also elevated the Magpie-Goose of
Australia to family status (e.g., Sibley & Ahlquist 1990, Sibley &
Monroe 1990, Dickinson 2003).
Perhaps the most impressive of the screamers is Horned Screamer (left) of the Amazon basin and related lowlands. It is a big, stocky bird with vestigial webbing between the front toes; it has a pronounced 'horn' in both sexes (an unmodified, unbranched feather shaft); and it has a hooked bill on a disproportionately small head. For the latter reasons screamers were once thought related to Galliformes [quail, pheasants, etc] but the biochemical evidence places them in the Anseriformes. Yet, although they are goose-like, numerous anatomical differences make them distinctive: the lack feather tracks so their feathers grow evenly all over the body; their bones are far more pneumatic than other birds, making the bone structure very lightweight; and they have a complicated system of air-sacs beneath the skin which, when contracted, can collapse rapidly with a distinctive cracking sound (Carboneres 1992).
All the screamers are birds of extensive swampy wetlands. We found the Horned Screamer that I photographed in small groups on a black-water oxbow lake left behind with changes in the main river channel in southeastern Peru. These are big, impressive goose-like birds. Screamers can be very vocal. The vernacular name comes from these vocalizations which are extremely loud and obnoxious. They are not melodic and yet the calls are extremely loud and can be given for hours on end. It is said that when a group is rising from a swamp and calling, the noise can be deafening.
Horned Screamer is in a monotypic genus. The two other screamers (Northern and Southern) are similar to each other and are assigned to the genus Chauna. They can give trumpeting notes; the local name for Southern Screamer (below) is "Tacha" or "Chajá" from its double-noted trumpeting call (Carboneres 1992). This shot does suggest the wildness of the swamps in which they live.
Screamers tend to mate for life — or at least for several years in a row — and they may breed at any time of the year. They are generally resident and hold territories as pairs (except Horned Screamer). However, when they are not breeding, they can form huge flocks and move locally and erratically in response to water conditions. Some flocks can have thousands of birds.
Screamers are entirely herbivorous; they eat a variety of aquatic plants,
including flowers, seeds, and roots. The tongue is horny (not fleshy) to
deal with tough plants. They can fly well — with necks outstretched like
storks — but are ponderous in taking off. They often roost in trees, and
some proclaim their territory in strident voices from treetop. Odd birds
— very much appropriately relegated to hot, muggy, swampland.
|Photos: The Horned Screamer
Anhima cornuta was photographed at Cocachoca, Tambopata Nature Reserve,
Madre de Dios, Peru, in July 1987. The Southern Screamer
Chauna torquata was in the Brazilian pantanal, 5 Aug 1999.
Photos © 2005 Don Roberson, all rights reserved.
There is no family book but this group is covered in standard waterfowl texts, and Carboneres (1992) provides a nice introduction with some fine photos.
Carboneres, C. 1992. "Screamers," pp. 528-535 in Handbook of the Birds of the World (del Hoyo, J., A. Elliott, & J. Sargatal, eds). Vol. 1. Lynx Edicions, Barcelona.
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