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Fri, 19 Apr, 2024
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? Emu
Conservation status: See text
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| Scientific classification |
| Kingdom: |
Animalia
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| Phylum: |
Chordata
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| Class: |
Aves
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| Order: |
Struthioniformes
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| Family: |
Casuariidae
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| Genus: |
Dromaius
Vieillot, 1816 |
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Species
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Dromaius novaehollandiae
Dromaius baudinianus(extinct)
Dromaius ater(extinct)
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The Emu ( pronounced [ˈiːmjuː], or (primarily American) [ˈiːmuː]) (Dromaius novaehollandiae/Dromiceius novaehollandiae, Latin for "fast-footed New Hollander.") 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.Three different emu species were common prior to European settlement in 1788:
- 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.
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Contents
Breeding
Adaptation
Dromaius or Dromiceius?
Breeding - Contents
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.
 Emu in Victoria ,Australia
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.)
 Baby Emu lying on the ground
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.
Adaptation - Contents
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. Emus have evolved a number of adaptions as the continent gradually became less fertile, hotter and dryer.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 tips, while the loose-packed inner plumage insulates the skin. A unique feature of the emu feather is its double rachis emerging from a single shaft. 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. 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 rivers— 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.
Dromaius or Dromiceius? - Contents
In his original 1816 description of the emu, Vieillot used two generic names; first Dromiceius, then Dromaius a few pages later. It has been a point of contention ever since which is correct; the latter is more correctly formed, but the convention in taxonomy is that the first name given stands, unless it is clearly a typographical error [1]. Most modern publications, including those of the Australian government [2], use Dromaius, with Dromiceius mentioned as an alternative spelling. However, the Dromiceius spelling was used by Russell in his 1972 naming of the dinosaur Dromiceiomimus. |
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