Cassowaries

En règle générale, tous les casoars sont des oiseaux timides que l'on trouve dans la forêt profonde ....

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 were 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 (5–6 ft) tall, although some females may reach 2 m (6.6 ft),[18] and weigh 58.5 kg (130 lb).

All cassowaries have feathers that consist of a shaft and loose barbules. They do not have rectrices (tail feathers) or a preen gland. Cassowaries have small wings with 5–6 large remiges. These are reduced to stiff, keratinous quills, resembling porcupine quills, with no barbs. A claw exists on each second digit of the feet. 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.

Cassowaries use their feet as weapons

Cassowaries have three-toed feet with sharp claws. The second toe, the inner one in the medial position, sports a dagger-like claw that may be 125 mm (5 in) long. This claw is particularly fearsome since cassowaries sometimes kick humans and animals with their enormously 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 (5 ft). They are good swimmers, crossing wide rivers and swimming in the sea.

Close-up of the head of a southern cassowary

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. Casuarius casuarius has the largest and Casuarius bennetti the smallest (tricorn shape), with Casuarius unappendiculatus having variations in between. Contrary to earlier findings, the hollow inside of the casque is spanned with fine fibres that are believed to have an acoustic function. Several functions for the casque have been proposed. One is that they are a secondary sexual characteristic. Other suggested functions include being used to batter through underbrush, as a weapon in dominance disputes, or for 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.

Earlier research indicates the birds lower their heads when running "full tilt through the vegetation, brushing saplings aside and occasionally careening into small trees. The casque would help protect the skull from such collisions". Cassowaries eat fallen fruit and consequently spend much time under trees where seeds the size of golfballs or larger fall from heights of up to 30 m (100 ft); the wedge-shaped casque may protect the head by deflecting falling fruit.[citation needed]

It also has been speculated that the casques play a role in either sound reception or acoustic communication. 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 rainforest. The "boom" vocalisation that cassowaries produce is the lowest-frequency bird call known and is at the lower limit of human hearing. A cooling function for the very similar casques of guineafowl has been proposed.

The average lifespan of wild cassowaries is believed to be about 40 to 50 years.