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Anhima cornutahorned screamer

By Sarah Arnosky

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. (Freedman, 2002; Naranjo, 1986)

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. ("Screamer", 1964; Freedman, 2002; Gill, et al., 1974)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • coastal
  • Average elevation
    1,000 m
    ft

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. ("Screamer", 1964; Campbell, 1974; Freedman, 2002; Herklots, 1961; Naranjo, 1986; O'Connor, 2004; Roberson, 2005; Stettenheim, 2000; "Screamers", 1985)

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. ("Screamer", 1964; Campbell, 1974; Freedman, 2002; Herklots, 1961; Naranjo, 1986; O'Connor, 2004; Roberson, 2005; Stettenheim, 2000; "Screamers", 1985)

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. ("Screamer", 1964; Campbell, 1974; Freedman, 2002; Herklots, 1961; Naranjo, 1986; O'Connor, 2004; Roberson, 2005; Stettenheim, 2000; "Screamers", 1985)

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. (Freedman, 2002)

  • Average mass
    3150 g
    111.01 oz
  • Range length
    71 to 92 cm
    27.95 to 36.22 in
  • Average wingspan
    1.7 m
    5.58 ft

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. (Freedman, 2002; Naranjo, 1986; "Screamers", 1985)

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. (Freedman, 2002; Naranjo, 1986; "Screamers", 1985)

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. (Campbell, 1974; Freedman, 2002; Gill, et al., 1974; Naranjo, 1986; "Screamers", 1985)

  • Breeding interval
    Horned screamers breed continuously throughout the year, the interval of egg laying is not known and may depend on available nutrition for females.
  • Breeding season
    Screamers breed during any season.
  • Range eggs per season
    2 to 8
  • Average eggs per season
    3
  • Range time to hatching
    40 to 47 days
  • Range fledging age
    60 to 75 days
  • Average time to independence
    1 years

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. (Naranjo, 1986; Roberson, 2005)

  • Parental Investment
  • 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. (Naranjo, 1986; "Screamers", 1985)

  • Average territory size
    100 m^2

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. (Naranjo, 1986; "Screamers", 1985)

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. (Campbell, 1974; Freedman, 2002; Gill, et al., 1974; Naranjo, 1986; "Screamers", 1985)

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. (Naranjo, 1986; Roberson, 2005; "Screamers", 1985)

  • 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. (Freedman, 2002)

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. ("Screamer", 2001)

  • 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. (Naranjo, 1986; Roberson, 2005)

Economic Importance for Humans: Negative

Other than the deafening screech of the horned screams, no negative effects have been noted. (Naranjo, 1986)

Conservation Status

Anhima cornuta is currently not considered threatened. Populations are sometimes controlled by hunters. (Roberson, 2005)

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. (Ramel, 2005; Stettenheim, 2000)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

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

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

choruses

to jointly display, usually with sounds, at the same time as two or more other individuals of the same or different species

coastal

the nearshore aquatic habitats near a coast, or shoreline.

diurnal
  1. active during the day, 2. lasting for one day.
duets

to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

food

A substance that provides both nutrients and energy to a living thing.

freshwater

mainly lives in water that is not salty.

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.

social

associates with others of its species; forms social groups.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born

References

1964. Screamer. Pp. 718-719 in S Thomson, ed. 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 B Campbell, E Lack, eds. A Dictionary of Birds. Vermillion: Buteo Books.

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

Freedman, B. 2002. Screamers (Anhimidae). Pp. 393-396 in M Hutchins, J Jackson, W Bock, eds. 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.

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