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Description

Typically, all cassowaries are shy birds that are found in the deep forest. They are adept at disappearing long before a human knows they are there. The southern cassowary of the far north Queensland rain forests is not well studied, and the northern and dwarf cassowaries even less so. Females are larger and more brightly coloured than the males. Adult southern cassowaries are 1.5 to 1.8 m (4 ft 11 in to 5 ft 11 in) tall, although some females may reach 2 m (6 ft 6 + 1 ⁄ 2 in), and weigh 58.5 kg (130 lb). However, it is not uncommon to see exceptionally large females topping the scales beyond 70 kg (150 lb), with the largest maximum recorded being a southern cassowary at 85 kg (187 lb) and 190 cm (6 ft 3 in) tall.

Hence, by technicality, all three species of cassowaries are considered as Asia's largest bird since the extinction of the Arabian ostrich. Moreover, not only is the cassowary Asia's largest bird, within New Guinea, the cassowary is the island's second largest terrestrial animal after the introduction of Cervidaes such as the rusa deer, chital, and fallow deer.

All cassowaries' feathers consist of a shaft and loose barbules. They do not have rectrices (tail feathers) or a preen gland. Cassowaries have small wings with five or six large remiges. These are reduced to stiff, keratinous quills, resembling porcupine quills, with no barbs. The furcula and coracoid are degenerate, and their palatal bones and sphenoid bones touch each other. These, along with their wedge-shaped body, are thought to be adaptations to ward off vines, thorns, and saw-edged leaves, allowing them to run quickly through the rainforest.

Unlike the majority of birds, cassowaries lack a tongue. Their beaks are pointed, sharp and robust but not serrated, which allows them to pick up fruit or small animals much easier than the short bills of an emu or an ostrich.

Cassowaries have three- toed feet with sharp claws. The inner (first) toe has a dagger -like claw that may be 125 mm (5 in) long. This claw is particularly fearsome, since cassowaries sometimes kick humans and other animals with their powerful legs. Cassowaries can run at up to 50 km/h (30 mph) through the dense forest and can jump up to 1.5 m (4 ft 11 in). They are good swimmers, crossing wide rivers and swimming in the sea.

All three species have a keratinous, skin-covered casque on their heads that grows with age. The casque's shape and size, up to 18 cm (7 in), is species-dependent. C. casuarius has the largest and C. bennetti the smallest (tricorn shape), with C. unappendiculatus having variations in between. Contrary to earlier findings, the hollow inside of the casque is spanned with fine fibres.

Several functions for the casque have been proposed. One is that they are a secondary sexual characteristic. Other suggested functions include batting through the underbrush, as a weapon in dominance disputes, or pushing aside leaf litter during foraging. The latter three are disputed by biologist Andrew Mack, whose personal observation suggests that the casque amplifies deep sounds. This is related to a discovery that at least the dwarf cassowary and southern cassowary produce very low-frequency sounds, which may aid in communication in dense rainforests. The "boom" vocalization that cassowaries produce is the lowest-frequency bird call known and is at the lower limit of human hearing. Recent study suggests that casque acts as a thermal radiator, offloading heat at high temperatures and restricting heat loss at low temperatures.

The average lifespan of wild cassowaries is approximately 18–20 years, with those held in captivity living up to 40 years.