Anhima cornutahorned screamer

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.