Birds of Australia
The Southern Cassowary
The Southern Cassowary is one of five families of ratites. The word 'ratite' comes from the Latin ratis meaning raft and relates to the fact that ratites have no keel to the sternum. No keel means no anchorage for their wing muscles thus these birds are flightless. The other ratite families are the ostrich, emu, rhea and kiwi. Most of the ratites, including the moa and the elephant bird, are now extinct.
There are three species of cassowary – two in New Guinea and one in Australia. The southern cassowary is the largest and is Australia's largest land animal.
Cassowaries have the taxonomical name of Casuarius casuarius johnsonii. This is derived from the Malay word kesuari meaning cassowary. Other common names are the double- or two-wattled cassowary, and the Australian cassowary. It is found in northern Indonesia, New Guinea and north eastern Australia. Elevations below 1,100m in Australia and 500m in New Guinea are preferred.
Its principal habitat is tropical rainforests but it is also found in woodlands, melaleuca swamps and mangroves. It can even be seen on beaches. A mix of habitats provides a more easily procurable year-round source of fleshy fruits.
It is of similar size to the emu but is much heavier. Cassowaries range from 127 to 170 cm and weigh around 36 to 50 kg (males). Females are heavier and up to 68 kg. The maximum size recorded was 190 cm tall and 83 kg weight. It may live to around 50 years of age.
It would be difficult to mistake a cassowary for any other bird. Its most distinguishing feature is its casque or helmet, a large, grey-brown bony lump on the top of its head. The head is very colourful with two red wattles hanging from the neck in front of the throat. The head and neck have no feathers. The head is blue as is the front of the neck. The back of the neck is red. Despite such bright colouring around the head, the bird is surprisingly difficult to spot in the forest.
The casque is composed of a central core of cartilage and an outer covering of a horn-like material. It continues to grow as the bird ages so it certainly indicates age and thus may indicate dominance. It is also believed by some authorities to have a function in picking up low vibrating rumbles made by other cassowaries.
The feathers are unusual too with each quill splitting into two. The coarse, glossy black feathers are more hair-like than normal feathers. There are no barbules to the feathers and no tail feathers. The wings curve around the body but are only vestigial stubs with a few, long, modified quills.
The female is the larger of the sexes with a taller casque and brighter colouring. The legs are strong and powerful. Each foot has three very powerful, thick toes. There is a lethal dagger-shaped spur on the inner toe. This spur can be up to 12cm long. If provoked or cornered the cassowary is quite capable of killing a dog or a human. Heavily muscled legs and blade-like claws give it good protection against predators.
When moving through the forest, the cassowary keeps its head down and lifts the legs up under the chin. It can cover short distances at 40km per hour. It is also able to swim.
The female is the dominant sex. Individuals remain in an area throughout the year, living a solitary life and only coming together with another to mate in late winter or spring. The male builds up a mattress of herbaceous plant material up to 100cm wide and to a depth of 5 to 10 cm. This allows drainage away from the eggs.
During the breeding season, the cassowaries have a booming call (as does its relative the emu). Males hiss and rumble and chicks give high-pitched whistles to keep in touch with the male.
The chicks are very attractive with dark brown and creamy white stripes. After three to six months, the stripes fade away. Juveniles are not as bright as adults and have browner plumage.
Only the ostrich and emu have larger eggs. The egg of the cassowary weighs 584g. Three to four eggs are laid in a clutch. Each egg measures 138 x 95mm. The eggs are a bright pea-green. The surface is granulated. The male incubates the eggs and raises the chicks. Incubation takes around 50 days and the male chases them off when they are about twelve months old. By the time they are three, the cassowary is mature.
The hen may mate with several males, leave eggs with all of them and walk off, taking no further interest in the eggs or chicks.
The southern cassowary has a vital part to play in the ecology of the rainforest. The cassowary is the only bird large enough to swallow some of the large seeds of tropical plants. Fallen fruit forms the greater part of the cassowary diet but they also forage for fungi, small vertebrates and some insects. Seeds and vegetation from over 200 different plant species have been found in the stomachs of cassowaries. Such a diverse diet helps support the ecosystem of the area.
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Some fruits will only germinate if they have passed through the digestive system of the cassowary. The dispersion of over 100 tree and shrub species would be affected if the cassowary were to become extinct. Such an animal or bird is regarded as a 'keystone species'. This is defined as a species whose occurrence contributes significantly to an area's diversity and whose extinction would lead to the extinction of other forms of life.
The dung of the cassowary contains many hundreds of seeds and fruits, some of which are only partly digested when expelled. Such partially digested fruits are eaten by other animals such as musky rat-kangaroos, bush rats and white-tailed rats.
Due to a short digestive tract and a rapid rate of digestion, the cassowary is also able to eat the fruits of toxic plants. The residue is eliminated in the faeces before absorption of the toxins can take place.
Threats to this amazing creature include habitat loss and fragmentation. Fortunately the greater part of their remaining habitat lies in protected areas. Cassowaries are opportunists and have been quick to learn that humans and their surrounds (including cars) often mean an easy meal.
Feeding cassowaries from cars encourages the birds to approach cars and fatalities on the roads account for many deaths. Dogs kill chicks or packs of dogs pursue birds to the point of exhaustion. Wild pigs compete for food, destroy nests and eat the eggs of the cassowary.
Cassowaries should be left undisturbed. Once conditioned to humans, cassowaries can become less cautious, more aggressive and more vulnerable to accidents. They can be dangerous if cornered or threatened. If threatened by an aggressive cassowary, back off slowly and try to place some obstacle between yourself and the bird.
On the IUCN Red List of Threatened Species, the southern cassowary is listed as vulnerable. Like the Suffolk Punch horse, it is estimated that there are less southern cassowaries than there are pandas.
Nurseries of food plants are being established and these will be used to replace cleared land and to form corridors between the remaining patches of cassowary habitat. The extinction of the cassowary would be a major disaster for the areas in which it lives.