Science Fair Project Encyclopedia
Dromaius baudinianus (extinct)
Dromaius ater (extinct)
- Note that the acronym EMU has several meanings.
The Emu (Dromaius novaehollandiae which, in Latin, means "fast-footed New Hollander", referring to Australia, whose old name was New Holland) is the largest bird native to Australia and, after the Ostrich, the second-largest bird that survives today.
It inhabits most of the less-populated areas of the continent, avoiding only dense forest and severe desert. Like all birds in the Ratite group, it is flightless, although unlike some it does have tiny wings hidden under the feathers.
The soft-feathered, brown birds reach 1.5 to 2 metres in height and weigh up to 60 kilograms, with the male marginally smaller.
Emus are opportunistically nomadic and follow rain, feeding on grains, flowers, fruit, soft shoots, insects, grubs, and whatever else is available. They are able to travel great distances at a fast, economical trot and, if need be, can sprint at 50 km/h.
- The Emu, Dromaius novaehollandiae, remains common in most of the more lightly settled parts of mainland Australia. Overall population varies from decade to decade according to rainfall; as low as 200,000 and as high as a million, but a typical figure is about half a million individuals. Although no longer found in the densely settled southern and south-western agricultural areas, the provision of permanent stock water in arid regions has allowed the mainland species to extend its range. There are three current sub-species or races of the emu across Australia:
- D. novaehollandiae novaehollandiae - South-east Australia - whitish ruff when breeding.
- D. novaehollandiae woodwardi - North Australia - slender, paler.
- D. novaehollandiae rothschildi - South-west Australia - darker, no ruff during breeding.
- D. novaehollandiae diemenensis - Tasmania - The Tasmanian Emu, became extinct around 1850.
- The Kangaroo Island Emu, D. baudinianus became extinct around 1827 as a result of hunting and frequent fires. The larger mainland species was introduced to Kangaroo Island in the 1920s.
- The small King Island Emu D. ater was about half the size of the mainland species. By 1805 it had been hunted to extinction by sealers and visiting sailors.
They pair in high summer and defend a territory of around 30 square km. Breeding takes place in the cooler months. As the days shorten, males undergo hormonal changes, lose appetite and construct a rough nest in a semi-sheltered hollow on the ground from bark, grass, sticks and leaves.
The pair mate every day or two and, every second or third day, the female lays a very large, thick-shelled dark green egg weighing about half a kilogram. The male becomes broody after about the seventh egg and begins sitting. From this time on, he does not eat, drink or defecate, and only stands to turn the eggs, which he does about 10 times a day.
For the next eight weeks, he will survive on accumulated body fat and any morning dew he can reach from the nest, losing up to one third of his body weight and become ever-weaker and more dazed.
The female usually continues laying but does not mate with the male again after he goes broody. About 8 or 10 eggs is typical but clutches of almost double this size are not uncommon. As with a great many other Australian birds (see Blue Wren), despite the nominal pair-bond, infidelity is the norm: once the male starts brooding, the female mates with other males instead. As many as half the chicks in the brood may be fathered by others.
Some females stay and defend the nest until the chicks start hatching but most leave the nesting area completely after a time and often nest again—in a good season a female emu may nest three times. (In the tropical north, where the seasons are reversed and it rains in summer, mating starts just before "the wet", and emus are reliably reported to delay mating if the season is late. The mechanism for this remains unknown.)
Despite the determined attention of the male, emu eggs are heavily predated, particularly by goannas, but it is estimated that four out of five chicks that hatch successfully survive to adulthood.
Newly hatched chicks are active and can leave the nest within a few days. They stand about 25 cm 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 at least six months, defending them and teaching them how to find food.
A male emu will often adopt any strange chick found wandering, so long as it is no bigger than his own brood. Chicks grow very quickly (up to a kilogram a week) and are full-grown in 12 to 14 months, but many 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 for about 10 years; captive birds can more than double that.
The Ratite group to which emus belong is very old. Emus have been walking the plains of Australia in something reasonably close to their present form for about 80 million years—Old Man Emu was around when the dinosaurs still walked. Their adaptation to a continent that has gradually become less fertile, hotter and dryer as it drifted north is extraordinary.
On very hot days, emus pant: they breathe rapidly, using their lungs as evaporative coolers. They can keep it up indefinitely and seem immune to the ill-effects of low blood CO2 levels, but must recharge their fluids by drinking every day. Nevertheless, emus do not waste water: for normal breathing in cooler weather, they have large, multi-folded nasal passages. Cool air warms as it passes through into the lungs, in turn 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.
Emu feathers are light in colour except for the dark tips: solar radiation is absorbed by the feather tips, while the loose-packed inner plumage insulates the skin: in combination, the dark and light areas of the plumage deflect or absorb all but 2% of the sun's radiant heat. The emu's steady walking pace of 4 to 7 km/h creates just enough breeze for optimum convective cooling of the hot black outer tips, and emus are thus able to forage right through the heat of the day when nearly all other animals must take shelter.
Emus are largely solitary creatures; unlike many other birds they seem to have no need for company and mutual grooming. They roam the continent searching for the best feeding areas, and although they can form enormous flocks, this is not a truly social behaviour, simply a matter of going where the food is.
According to folklore, emus have a mysterious mechanism to tell them where the rain is, and will travel for hundreds of miles to take advantage of a deluge. There is no evidence for this; in fact, they are very keenly attuned to subtle weather cues: particularly the sight of distant cloud formations but probably also the sound of thunder from afar.
In Western Australia, emu movements follow a distinct seasonal pattern—north in summer and south in winter—but further east their wanderings are more random. It's nothing unusual for a bird to walk 1000 km in a season, with 10 to 25 km a day being normal. (Male birds with chicks in tow must move more slowly, of course.)
Emus are also powerful swimmers capable of crossing any river—something they need to do from time to time as part of their wandering. Generally though, emus prefer to play in water rather than cross it: if a stream or dam is available, they take full advantage of it on hot days, sometimes rolling on their backs and kicking their legs in the air.
Emus and humans
In the wild, brooding males on the nest or with young chicks to protect are dangerous to approach too closely: they have powerful leg muscles, ferocious talons and are perfectly capable of disembowelling a predator of human size. However, in general emus are not likely to viciously attack, preferring to use their legs to move somewhere else if confronted. Like many other animals, an injured or cornered emu can be a very dangerous, and would only be approached by the most well trained (or idiotic) individuals. They also have a great sense of curiosity. Someone with bush skills can easily persuade a wild emu to come close and investigate by, for example, hiding in long grass and waving a coloured handkerchief on the end of a stick. This curiosity also results in emus exhibiting behaviour exhibited by other birds like magpies and bower birds, the habit of stealing shiny and brightly coloured objects. Emus, particularly those in semi-open captivity, who have little fear of humans, are also prone to pecking at hairy human heads and wooly clothing, which can be distressing for small children and tourists.
In 1975 a bizzarely shocking isolated incident occurred at Tindbilla nature reserve in Canberra. An unattended 21 month old toddler, Scott Woods, was pinned on his back by the claws of one of the free-ranging birds in the park. Upon hearing the child's screams, Scott's father scared the bird off with a tree branch. Scott required hospital attention, suffering a 7cm gash on his scalp along with other scratches and bruises, but otherwise survived the attack. There has been no explanation uncovered for the attack, only speculation that it may have had to do with the ball which Scott was playing with. The male bird may have mistaken the ball for an egg, and acted in a protective fashion (from Reference: Underhill, 1993)
The emu has long been a central part of Aboriginal cultural and economic systems. Europeans quickly learned to value emu meat and oil, and how to cook with their eggs. But until recent times, the emu was primarily thought of as a pest to be destroyed rather than as a resource to be harvested.
Europeans wiped out two species and a sub-species of emu on the smaller islands early in the 19th Century, and considerable effort was put into exterminating the last remaining species as well, but the creature's ability to disappear into the vast semi-arid mainland plains meant that it was never seriously threatened. Graziers regarded the emu as a competitor for food and water—a charge with some foundation, but which ignored the beneficial effect emu grazing has for soil, and their capacity to eat enormous quantities of plague insects like locusts or caterpillars.
Wheatgrowers had much more serious concerns: emus like to eat both soft young wheat shoots and ripe seed. Worse, they are difficult to fence out and the passage of a large number of birds through a paddock of ripe, stiff-stalked wheat tramples it flat, even if they do not stop to eat it. In 1901, Western Australian farmers built a tall, emu-proof fence 1,100 kilometres long. This protects the crops, but disrupts migration patterns. In the worst years, over 50,000 emus died, often by being crushed up against fences and starving.
In 1932, the anti-emu campaign briefly took on a bizarre flavour worthy of the Keystone Cops—particularly when one bears in mind that, along with the kangaroo, the emu is one of the two native animals making up the Australian coat of arms.
At the end of a dry summer at the height of the Great Depression, Western Australian farmers called in the army to fight an "Emu War" - with machine guns mounted on trucks. For several days, Lewis gunners tried to engage the enemy: farcical scenes resulted, with the birds taking few casualties and teaching the soldiers a thing or two about rapid battlefield manoeuvres. The artillery commander, a Major Meredith, later said, "If we had a military division with the bullet-carrying capacity of these birds it would face any army in the world." The experiment was quickly abandoned, amid debate as to who should pay for the wasted ammunition.
In 1988, long after emus had been protected by law, Western Australia took the lead again, but in a different direction and with a great deal more success. The WA Government issued a permit to the Aboriginal people of Willuna Station, allowing them to sell emu chicks to the public.
Aboriginal and European landowners in all states rapidly began learning how to farm emus, and the market for emu products grew explosively. The initial boom quickly faded, but there are about 250 emu farms in Australia today, and many more overseas.
Emus have a high bodyfat content, and emu oil is used for many purposes, particularly treatment of muscle aches and sprains. Emu skin makes excellent leather, and emu meat has very low fat and is rich in protein. The flavour is similar to beef and said to be delicious, if rather gamey. Emu eggs, because they have such thick shells, are popular for carving, and emu feathers are readily marketable.
Emus are particularly suitable for degraded, overgrazed properties: unlike cattle and (especially) sheep, they do not cause soil compaction or destroy grass roots, and emu dung gradually helps native vegetation recover.
- Underhill D (1993) Australia's Dangerous Creatures, Reader's Digest, Sydney, New South Wales, ISBN 0-86438-018-6
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