Emu
2007 Schools Wikipedia Selection. Related subjects: Birds
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| Dromaius novaehollandiae ( Latham, 1790) |
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Dromiceius novaehollandiae |
The Emu ( IPA pronunciation: [ˈiːmjuː]), Dromaius novaehollandiae, is the largest bird native to Australia and the only extant member of the genus Dromaius. It is also the second-largest bird in the world by height, after its ratite relative, the ostrich. The soft-feathered, brown, flightless birds reach up to 2 m (6 ft 7 in) in height. The Emu is common over most of mainland Australia, although it avoids heavily populated areas, dense forest and arid areas. Emus can travel great distances at a fast, economical trot and, if necessary, can sprint at 50 km/h (31 mph) for some distance at a time. They are opportunistically nomadic and may travel long distances to find food; they feed on a variety of plants and insects.
The Emu subspecies that previously inhabited Tasmania became extinct following the European settlement of Australia in 1788; the distribution of the mainland subspecies has also been affected by human activities. The Emu was once common on the east coast, but is now uncommon there; by contrast, the development of agriculture and the provision of water for stock in the interior of the continent have increased the range of the Emu in arid regions. Emus are farmed for their meat, oil and leather.
Taxonomy and distribution
Three different Dromaius species were common in Australia before European settlement, and one species is known from fossils. The small emus — Dromaius baudinianus and D. ater — both became extinct shortly after; however, the Emu, D. novaehollandiae, remains common. The population varies from decade to decade, largely dependent on rainfall; it is estimated that the Emu population is 625,000–725,000, with 100,000–200,000 in Western Australia and the remainder mostly in New South Wales and Queensland. D. novaehollandiae diemenensis, a subspecies known as the Tasmanian Emu, became extinct around 1865. Emus were introduced in Maria Island near Tasmania, and Kangaroo Island near South Australia, in the 20th century and have established breeding populations there.
There are three extant subspecies in Australia:
- In the southeast, D. novaehollandiae novaehollandiae, with its whitish ruff when breeding;
- In the north, D. novaehollandiae woodwardi, slender and paler; and
- In the southwest, D. novaehollandiae rothschildi, darker, with no ruff during breeding.
The species was first described under the name of the New Holland Cassowary in Arthur Phillip's Voyage to Botany Bay, published in 1789. The species was named by ornithologist John Latham, who collaborated on Phillip's book and provided the first descriptions of and names for many Australian bird species; its name is Latin for "fast-footed New Hollander". The etymology of the common name Emu is uncertain, but is thought to have come from an Arabic word for large bird that was later used by Portuguese explorers to describe the related Cassowary in New Guinea.
Physical description
Emus are large birds. The largest individuals can reach up to two metres (6 ft 7 in) in height (1–1.3 metres (3.2–4.3 ft) at the shoulder) and weigh between 30 and 45 kilograms (66–100 pounds). They have small vestigial wings and a long neck and legs. Their ability to run at high speeds is due to their highly specialised pelvic limb musculature. Their feet have only three toes and a similarly reduced number of bones and associated foot muscles; they are the only birds with gastrocnemius muscles in the back of the lower legs. The pelvic limb muscles of Emus have a similar contribution to total body mass as the flight muscles of flying birds.
Emus have brown to grey-brown plumage of shaggy appearance; the shafts and the tips of the feathers are black. Solar radiation is absorbed by the tips, and the loose-packed inner plumage insulates the skin. The resultant heat is prevented from flowing to the skin by the insulation provided by the coat, allowing the bird to be active during the heat of the day. A unique feature of the Emu feather is its double rachis emerging from a single shaft. The sexes are similar in appearance.
On very hot days, Emus pant to maintain their body temperature, their lungs work as evaporative coolers and, unlike some other species, the resulting low levels of carbon dioxide in the blood do not appear to cause alkalosis. For normal breathing in cooler weather, they have large, multifolded nasal passages. Cool air warms as it passes through into the lungs, extracting heat from the nasal region. On exhalation, the Emu's cold nasal turbinates condense moisture back out of the air and absorb it for reuse.
Reproduction
Emus form breeding pairs during the summer months of December and January, and may remain together for about five months. Mating occurs in the cooler months of May and June. During the breeding season, males experience hormonal changes, including an increase in luteinizing hormone and testosterone levels, and their testicles double in size. Males lose their appetite and construct a rough nest in a semi-sheltered hollow on the ground from bark, grass, sticks and leaves. The pair mates every day or two, and every second or third day the female lays an average of 11 (and as many as 20) very large, thick-shelled, dark-green eggs. The eggs are on average 134 x 89 millimeters (5.3 x 3.5 inches) and weigh between 700 and 900 grams (1.5–2 pounds), which is roughly equivalent to 10–12 chicken eggs in volume and weight. The first occurrence of genetically identical avian twins was demonstrated in the Emu.
The male becomes broody after his mate starts laying, and begins to incubate the eggs before the laying period is complete. From this time on, he does not eat, drink or defecate, and stands only to turn the eggs, which he does about 10 times a day. Over eight weeks of incubation, he will lose a third of his weight and will survive only on stored body-fat and on any morning dew that he can reach from the nest. As with many other Australian birds, such as the Superb Fairy-wren, infidelity is the norm for Emus, despite the initial pair-bond: once the male starts brooding, the female mates with other males and may lay in multiple clutches; thus, as many as half the chicks in a brood may be fathered by others, or by neither parent as Emus also exhibit brood parasitism. Some females stay and defend the nest until the chicks start hatching, but most leave the nesting area completely to nest again; in a good season, a female Emu may nest three times.
Incubation takes 56 days, and the male stops incubating the eggs shortly before they hatch. Newly hatched chicks are active and can leave the nest within a few days. They stand about 25 centimetres tall and have distinctive brown and cream stripes for camouflage, which fade after three months or so. The male stays with the growing chicks for up to 18 months, defending them and teaching them how to find food. Chicks grow very quickly and are full-grown in 12–14 months; they may remain with their family group for another six months or so before they split up to breed in their second season. In the wild, Emus live between 10 to 20 years; captive birds can live longer than those in the wild.
Ecology and behaviour
Emus live in most habitats across Australia, although they are most common in areas of sclerophyll forest and savanna woodland, and least common in populated and very arid areas. Emus are largely solitary, and while they can form enormous flocks, this is an atypical social behaviour that arises from the common need to move towards food sources. Emus have been shown to travel long distances to reach abundant feeding areas. In Western Australia, Emu movements follow a distinct seasonal pattern — north in summer and south in winter. On the east coast their wanderings do not appear to follow a pattern. Emus are also able to swim when necessary.
Their calls consist of loud booming, drumming and grunting sounds that can be heard up to two kilometres away. The booming sound is created in an inflatable neck sac.
Emus forage in a diurnal pattern. They eat a variety of native and introduced plant species; the type of plants eaten depends on seasonal availability. They also eat insects, including grasshoppers and crickets, ladybirds, soldier and saltbush caterpillars, Bogong and cotton-boll moth larvae and ants. In Western Australia, food preferences have been observed in travelling Emus: they eat seeds from Acacia aneura until it rains, after which they eat fresh grass shoots and caterpillars; in winter they feed on the leaves and pods of Cassia; in spring, they feed on grasshoppers and quandong fruit. Emus may serve as an important agent for the dispersal of large viable seeds, which could contribute to the maintenance of floral biodiversity.
Conservation status
Emus were used as a source of food by indigenous Australians and early European settlers. Aborigines used a variety of techniques to catch the bird, including spearing them while they drank at waterholes, poisoning waterholes, catching Emus in nets, and attracting Emus by imitating their calls or with a ball of feathers and rags dangled from a tree. Europeans killed Emus to provide food and to remove them if they interfered with farming or invaded settlements in search of water during drought. An extreme example of this was the Emu War in Western Australia in 1932, when Emus that flocked to Campion during a hot summer scared the town’s inhabitants and an unsuccessful attempt to drive them off was mounted. In John Gould's Handbook to the Birds of Australia, first published in 1865, he laments the loss of the Emu from Tasmania, where it had become rare and has since become extinct; he notes that Emus were no longer common in the vicinity of Sydney and proposes that the species be given protected status. Wild Emus are formally protected in Australia under the Environment Protection and Biodiversity Conservation Act 1999.
Although the population of Emus on mainland Australia is thought to be higher now than before European settlement, some wild populations are at risk of local extinction due to small population size. Threats to small populations include the clearance and fragmentation of areas of habitat; deliberate slaughter; collisions with vehicles; and predation of the young and eggs by foxes, feral and domestic dogs, and feral pigs. The isolated Emu population of the New South Wales North Coast Bioregion and Port Stephens is listed as endangered by the New South Wales Government.
Uses of Emu
The Emu was an important source of meat to the Aborigines in the areas to which it was endemic. The Emu fat was used as bush medicine, and was rubbed on the skin. It also served as a valuable lubricant. It was mixed with ochre to make the traditional paint for ceremonial body adornment, as well as to oil wooden tools and utensils such as the coolamon.
An example of how the Emu was cooked come from the Arrernte of Central Australia who call it Kere ankerre:
Emus are around all the time, in green times and dry times. You pluck the feathers out first, then pull out the crop from the stomach, and put in the feathers you've pulled out, and then singe it on the fire. You wrap the milk guts that you've pulled out into something [such as] gum leaves and cook them. When you've got the fat off, you cut the meat up and cook it on fire made from river red gum wood.
Commercial Emu farming started in Western Australia in 1987 and the first slaughtering occurred in 1990. In Australia, the commercial industry is based on stock bred in captivity and all states except Tasmania have licensing requirements to protect wild Emus. Outside Australia, Emus are farmed on a large scale in North America, with about 1 million birds in the US, Peru and China, and to a lesser extent in some other countries. Emus breed well in captivity, and are kept in large open pens to avoid leg and digestive problems that arise with inactivity. They are typically fed on grain supplemented by grazing, and are slaughtered at 50–70 weeks of age. They eat two times a day, they prefer 5 pounds of leaves each meal.
Emus are farmed primarily for their meat, leather and oil. Emu meat is a low-fat, low-cholesterol meat (85 mg/100 g); despite being avian, it is considered a red meat because of its red colour and pH value. The best cuts come from the thigh and the larger muscles of the drum or lower leg. Emu fat is rendered to produce oil for cosmetics, dietary supplements and therapeutic products. There is some evidence that the oil has anti-inflammatory properties; however, the US Food and Drug Administration regards pure emu oil product as an unapproved drug. Emu leather has a distinctive patterned surface, due to a raised area around the hair follicles in the skin; the leather is used in such small items as wallets and shoes, often in combination with other leathers. The feathers and eggs are used in decorative arts and crafts.