Casuariidaecassowaries

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The family Casuariidae includes three living cassowary species, all of the genus Casuarius. They are found in the Australo-Papuan subregion of the world: on New Guinea, nearby islands, and the northeastern part of Australia. However, their previous distribution may have been wider, and the current distribution may not reflect natural ranges, as cassowaries have been heavily traded for at least 500 years.

Cassowaries are large ratites, and are among the largest birds in the world. Their drooping plumage is black and coarse, and they have brightly colored skin on their necks. All three species possess a casque, or helmet, on the top of the head, which grows slowly throughout the bird's first few years. The function of the casque is poorly understood; it was originally thought that the birds use it to push aside underbrush as they travel through the dense forests. However, more recently they have been observed using it to push aside forest litter in search of food on the ground. The casque may also be important in social dynamics, as it signals age of the individual. Two species of cassowary (the northern and southern cassowaries) have distinctive wattles, which are long folds of unfeathered skin that hang from the neck. The wattles are brightly colored; colors vary by subspecies and may change with mood of the bird. In general, the sexes are fairly similar, though females are slightly larger and more brightly colored, and have larger casques. Cassowaries can run at speeds up to 50 km/hr, and can jump 1.5m from a standing position. Another of their well-known features is the dagger-like claw on their innermost toe; this claw can be a deadly weapon and cassowaries may use it in defense by jumping and kicking with both feet. Humans have been killed by such attacks, as males can be extremely aggressive when protecting nests or young. Other distinctive features include an extremely long aftershaft, nearly as long as the main feathers (similar to Emus), and remiges that are reduced to bare quills and curve under the body. Their wings are stunted, with a smaller body-to-wing proportion than in some other ratites, and, like most other ratites, cassowaries have no tail feathers. They have small, rudimentary clavicles, a small procoracoid process, no syrinx, and reduced caeca. They have three toes like most ratites, and short middle phalanges.

All three cassowary species prefer rainforest habitat, as the birds require a large volume and diversity of fruit for their diet year-round. However, the three species are generally segregated by altitude, ranging from lowland swamp forests to higher altitude montane forests. They are generally shy birds, difficult to spot in the wild, though they travel regular paths in the forest and establish regular crossing points at rivers. They tend to remain solitary for much of the year, though pairs do form during the breeding season. Males will claim territories and pair with a female for a period of several weeks, during which time she will lay 3-5 eggs. Females may then mate with another male. Males will tend the eggs and young, remaining with the chicks for 9 months. Young cassowaries are striped brown, and do not fully gain adult plumage for 3 years.

Cassowaries have been commercially important to people for hundreds of years. They have been traded intensively for approximately 500 years, and are prized for their meat and feathers. Complete clutches of eggs are also valuable, and bring high prices because it is difficult to find nests. People still use these birds for food today; in New Guinea they may be raised in captivity and fed until they are large enough to sell for food or trade. They have also figured prominently in the mystic beliefs and rituals of many peoples, often viewed as a mother figure in legends. The biggest threat to cassowaries today is loss of habitat, especially with the destruction of rainforests, because they require large, continuous expanses of forest to adequately survive. They are also at risk from hunting and feather trades.

Cassowaries are closely related to emus; some classification schemes group them within the same family. It appears they evolved from a common ancestor in Australia, but the time of their divergence is still unclear. A fossil thought to be an intermediate form between cassowaries and emus dates back to the late Oligocene/ early Miocene

The three species of cassowary are found abundantly in the fossil record dating back to the Upper Pleistocene (c. 125,000-10,000 years ago), and earlier fossils have been found from the late Miocene/ early Pliocene.

Campbell, B. & E. Lack, eds. 1985. A dictionary of birds. Buteo Books, Vermillion, South Dakota.

del Hoyo, J., Elliott, A., & J. Sargatal. 1992. Handbook of the birds of the world, volume 1. Lynx Edicions, Barcelona.

Feduccia, A. 1999. The origin and evolution of birds. Yale University Press, New Haven.

Sibley, C. & Ahlquist, J. 1990. Phylogeny & classification of birds: a study in molecular evolution. Yale Univ. Press, New Haven.

Thomson, A. 1964. A new dictionary of birds. British Ornithologists' Union. McGraw-Hill Book Co., NY.

Contributors

Danielle Cholewiak (author).

Glossary

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

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.

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).

motile

having the capacity to move from one place to another.

oviparous

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

sexual

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

tactile

uses touch to communicate

visual

uses sight to communicate