screamer, common name for gregarious, aquatic birds comprising three species in the family Anhimidae. Although they are related to the ducks and geese, they do not resemble them in outward appearance. Screamers possess some unusual anatomical features, such as a layer of insulating air cells that separate the outer skin from the body. This feature is also seen in the pelicans. They share another peculiarity solely with colies, penguins, and ostriches—their feathers grow over the body without any bare spaces (called apteria) in between. Another peculiarity of the screamers is their hollow bones. Finally, they lack particular rib bones that are functional as strengthening elements in all other birds except the extinct Archaeopteryx. The turkey-sized horned screamer ( Anhima cornuta ) is the largest of the family. It is distinguished by a 3- to 4-in. (8- to 10-cm) hornlike projection on its forehead and by two sharp wing spurs. A creature of the wetlands and tropical rain forest, it is found throughout most of South America. The slightly smaller crested screamer ( Chauna torquata ) is native to swamps and plains from Brazil to N Argentina. It is distinguished by a short, feathered neck crest. The swan-sized black-necked screamer ( C. chavaria ) of N Colombia and Venezuela is the smallest and darkest of the family. Using their short, conical, fowllike bills, screamers feed primarily on a vegetable diet of succulent grasses and seeds, although the horned screamer occasionally eats insects as well. Screamers are strong fliers and generally roost in trees. However, their delicate, shallow nests of rushes are built on the water or in marshes. Their white or buffy eggs number from two to six per clutch. Both sexes share incubation duties. The chicks are downy and resemble baby swans. Screamers are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Anseriformes, family Anhimidae.