Anhima cornuta

Geographic Range

Horned screamers are a native species of the Neotropical region. These non-migratory birds live in a range throughout northern South America that stretches from the Amazonian regions of Venezuela, to the eastern llanos of Columbia, to eastern Bolivia and south-central Brazil. They are now extinct in Trinidad.

• Biogeographic Regions
• neotropical neotropical
  • native native

Habitat

Horned screamers are found in the vicinity of tropical lowland fresh water, such as lakes, ponds, rivers, marshes, and swamps. They often roost in trees and shrubs of wooded river banks and wet savannas.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial
• freshwater freshwater

• Terrestrial Biomes
• savanna or grassland savanna or grassland

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• coastal coastal

• Wetlands
• marsh marsh
• swamp swamp

• Other Habitat Features
• riparian riparian

Physical Description

Horned screamers are large, heavy bodied, fowl-like birds that are most recognizable by their two bone spurs at the bend of each wing and the 15 cm, yellowish-white horn-like projection at the top of their heads. The 2 to 5 cm long bone spurs are a result of fused carpel bones and are covered with keratin. The horn-like projection, which gives these birds their name, is composed of cartilage. When young are born they lack the horn but it slowly grows as they age. Horns seem to be ornamental as they do not have a defensive purpose. They are not firmly attached to the skull, swing back and forth as the birds’ heads move, and are easily broken off. After breaking off they will grow back over time.

Typically, Anhima cornuta has a gray or black body that fades into a white abdomen. In addition to the abdomen, the wings and crown are also white. The head is small in proportion to the body and has a variety of patterns and colors of plumage. The bill is short with a downward curve and the irises of the eyes are bright orange or yellow. The feathers of the body grow evenly and cover the skin without any bare spaces. Horned screamers have long reddish legs with strong, stout, ash grey feet that lack webbing. The feet lack arches, thus the hind toe is at the same level as the front three on each foot. On the alular digit, screamers have a small, nonfunctional claw. Males and females are similar in appearance.

Horned screamers possess some additional unusual anatomical features. Most of their bones are permeated with abundant air sacs that also exist in the subcutaneous tissue in the dermis of the skin. This construction results in a rumbling or crackling noise when these birds take off as the air sacs rapidly collapse. The presence of subcutaneous air sac diverticula allows horned screamers to regularly use soaring flight instead of using muscle energy to remain airborne. These air filled spaces may also act to facilitate pneumatic movement. Horned screamers also lack uncinate processes on their ribs (which act as strengthening elements in all other birds except the extinct Archeopteryx ). They have an extraordinarily light-weight bone structure in comparison to birds of similar size.

Of the three species of screamers , A. cornuta is the largest in size. The other screamer species, crested or southern screamers ( Chauna torquata ) and northern screamers ( Chauna chavaria ), lack the horn-like projection and differ in color and patterning.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike
• ornamentation ornamentation

Reproduction

Horned screamers pair for life, or for at least several years. Pairs stay together throughout the year, seeking isolation in marshy areas in late winter and early spring to trumpet in duets. There are different mating behaviors in Anhima cornuta . “Head bobbing” occurs when one screamer approaches its partner and both birds stretch their necks out and bob their heads up and down one to three times. The main courtship behavior, done all year long, is known as “social preening.” This occurs when two birds preen the feathers on each other’s necks and heads. Often times there are fights connected with pair formation. Males will use the sharp spurs on their wings as weapons against one another.

Before copulation males walks around females with their bills pressed downward against their inflated crops, neck retracted, and dorsal feathers partially erected. After circling, males will bow their head 1 to 3 times in front of females. During copulation, which takes place on land, males will mount females for ten seconds while grabbing the female's neck with his bill and flapping both wings slowly.

• Mating System
• monogamous monogamous

Horned screamers are year-round breeders with no particular breeding season. When large flocks of non-breeding birds are sighted it suggests that maturation has been delayed for several years. Anhima cornuta individuals build large nests of plant materials, such as reeds and sticks, that are 8 to 10 centimeters deep. Nests are near or in marshy vegetation in shallow water, typically around eight centimeters deep. Two to eight smooth yellowish-white oval eggs are laid at intervals of 35 to 40 hours by the female. Both parents spend time incubating the eggs. The eggs average 84 mm in length and weigh an average of 150 grams.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• oviparous oviparous

Horned screamer females usually incubate the eggs during the day, taking short breaks when the male takes over. Males incubate the eggs at night. When the young screamers hatch their eyes are open and they are covered with down. They are nidifugous (young leave the nest immediately after birth) and can run as soon as they are hatched. The young are precocial and follow both parents who offer some food to the young for 60 to 75 days. The parents will also pick up and drop food items in front of the chicks, presumably to encourage feeding.

• Parental Investment
• precocial precocial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • protecting
    • male
    • female
• pre-independence
  • protecting
    • male
    • female

Lifespan/Longevity

There is no known information on the lifespan of Anhima cornuta .

Behavior

Screamers are non-migratory birds that remain within their breeding area all year. Anhima cornuta is a semi-social bird, forming small groups of 5 to 10 individuals, with no conspicuous flocking. They can be seen flying, soaring, swimming, grazing, and roosting in trees. They fly for an average of five seconds and walk for an average of twenty-two seconds at a time.

Screamers can be easily spotted during the morning hours after dawn perched in trees and bushes along water. They then return to the ground to search for food. Horned screamers exhibit two main behaviors on the ground: standing and preening. Standing involves wings folded, neck partially retracted, and occasionally, one foot raised. Preening involves preening the breast area and wings and is most commonly done in the morning. Three shaking behaviors associated with standing and preening are wing shake, tail shake, and tail wag. After long sessions of preening and standing, screamers will often stretch using the jaw stretch, the wing and tail stretch, or will stretch both wings at once.

• Key Behaviors
• scansorial
• terricolous
• flies
• glides
• diurnal diurnal
• motile motile
• sedentary sedentary
• territorial territorial
• social social

Home Range

Horned screamers often live in groups of 5 to 10 birds in territories where they actively defend their food sources and mates by protecting it against intruders. For example, when one bird sees an intruder, the birds of that territory will immediately gang up on the intruder. The initial signs that a fight is to begin include inflated, extended necks and erect dorsal plumage. As the fighters continuously flap their wings, their shoulders are pushed forward to show off their spurs. It is not uncommon to find broken spurs in the breasts of both intruding and resident birds after fights. Once the intruder leaves the territory, resident birds celebrate by calling for almost a minute after the victory. Screamers tend to stay within 100 m of their perch when searching for food.

Communication and Perception

Horned screamers are less vocal than their relatives, southern screamers , but their vocalizations are are very loud. There are three main vocalizations: “mo-coo-ca”, a honking “yoik-yok”, and the trumpet. When calling, the birds’ necks are fully inflated and often shaking. Calling can be done from the ground and from the air. Vocal communication is used for territorial defense, mating, and other purposes. More specifically, the “mo-coo-ca” is used to alarm others of a disturbance of potential predators or the relocation of other screamers. Honking is used for greeting and distance calling. Trumpeting is typically used for distance calling, the morning wake-up call, and as a high-intensity greeting. It was also noted that once or twice each day the screamers will perform loud calls. Often these are initiated by an adult bird, or group of birds, and the response is given by neighbors. Typically, male birds have lower frequency calls than females. Screamers are named for their loud vocalizations. Also, a local Indian name given to the birds is “mahooka” based on the sound of their calls.

• Communication Channels
• visual visual
• acoustic acoustic

• Other Communication Modes
• duets duets
• choruses choruses

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Horned screamers are mainly herbivorous, eating foliage, grains, and other plant parts. Insects are thought to be a main component of juvenile diet. Screamers graze during mid-morning to late afternoon along grasses and sedges near the water. They peck at leaves, stems, flowers, and vines and graze with lateral head movements. Food is swallowed almost immediately unless the food is longer than the bird’s beak. A less common technique for finding food is digging and filtering through wet mud. Horned screamers rarely drink from their local water source but when they do, they dip their heads in and take large gulps. Their horned tongues allow these birds to manipulate and eat tough plants.

• Primary Diet
• herbivore herbivore
  • folivore folivore

• Animal Foods
• insects

• Plant Foods
• leaves
• roots and tubers
• wood, bark, or stems
• seeds, grains, and nuts
• flowers

Predation

Humans, who hunt Anhima cornuta for food, are the only known predators of these birds.

Ecosystem Roles

Screamers are primary consumers, eating plants. Their grazing may influence the composition of plant communities where they live. Their nests of twigs and plant life creates habitat for small invertebrates.

• Ecosystem Impact
• creates habitat

Economic Importance for Humans: Positive

Horned screamers are hunted for food in South America. Additionally, 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 the chickens against birds of prey and other enemies. Also, it is not uncommon to see them walk about freely in South American zoos and parks.

• Positive Impacts
• pet trade pet trade
• food food

Economic Importance for Humans: Negative

Other than the deafening screech of the horned screams, no negative effects have been noted.

Conservation Status

Anhima cornuta is currently not considered threatened. Populations are sometimes controlled by hunters.

Other Comments

There are three living species in the screamer family: horned screamers ( Anhima cornuta ), northern horned screamers ( Chauna chavaria ), and southern or crested screamers ( Chauna torquata ). Horned screamers were first described by Linnaeus in eastern Brazil in 1766 as Palamedea cornut . Although screamers (family Anhimidae ) are more like game-birds in appearance, they closely related to geese, swans, and ducks (in the order Anseriformes ). Fossil remains of screamers are known from deposits of the Quaternary Period in Argentina.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Sarah Arnosky (author), Kalamazoo College, Ann Fraser (editor, instructor), Kalamazoo College.

References

Campbell, B. 1974. Anhima cornuta. Pp. 49, 229 in The Dictionary of Birds in Color . New York: The Viking Press.

Freedman, B. 2002. Screamers (Anhimidae). Pp. 393-396 in Grzimek's Animal Life Encyclopedia , Vol. 8/Birds 1, 2nd Edition. Farmington Hills, MI: Gale Group.

Gill, F., F. Stokes, C. Stokes. 1974. Observations on the horned screamer. The Wilson Bulletin , 86/1: 43-51.

Herklots, G. 1961. The Birds of Trinidad and Tobago . London: Collins Clear-Type Press.

Naranjo, L. 1986. Aspects of the Biology of the Horned Screamer in Southwestern Columbia. Wilson Bulletin , 98/2: 243-256.

O'Connor, P. 2004. Pulmonary pneumaticity in the post cranial skeleton of extant Aves: a case study examining Anseriformes. Journal of Morphology , 261/2: 141-161.

Ramel, G. 2005. "Earth-Life Web Productions" (On-line). Anseriformes. Accessed November 11, 2006 at http://www.earthlife.net/birds/anseriformes.html .

Roberson, D. 2005. "Creagrus at Monterey Bay" (On-line). Screamers (Anhimidae). Accessed October 13, 2006 at http://montereybay.com/creagrus/screamers.html .

Stettenheim, P. 2000. The integumentary morphology of modern birds- An overview. American Zoology , 40/1: 461-477.

1964. Screamer. Pp. 718-719 in A New Dictionary of Birds . New York: McGraw-Hill Book Company.

2001. Screamer. Pp. 102 in The Columbia Encyclopedia , Vol. 20/1, 6th Edition. New York: Columbia University Press. Accessed November 11, 2006 at http://www.bartleby.com/br/65.html .

The British Ornithologists' Union. 1985. Screamers. Pp. 525 in A Dictionary of Birds . Vermillion: Buteo Books.