Emu

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call of a female emu at the ZOOM Erlebniswelt Gelsenkirchen in Germany

The emu (Dromaius novaehollandiae) is the second-largest living bird by height, after its ratite relative, the ostrich. It is endemic to Australia where it is the largest native bird and the only extant member of the genus Dromaius. The emu's range covers most of mainland Australia, but the Tasmanian, Kangaroo Island and King Island subspecies became extinct after the European settlement of Australia in 1788. The bird is sufficiently common for it to be rated as a least-concern species by the International Union for Conservation of Nature.

Emus are soft-feathered, brown, flightless birds with long necks and legs, and can reach up to 1.9 metres (6.2 ft) in height. Emus can travel great distances, and when necessary can sprint at 50 km/h (31 mph); they forage for a variety of plants and insects, but have been known to go for weeks without eating. They drink infrequently, but take in copious amounts of water when the opportunity arises.

Breeding takes place in May and June, and fighting among females for a mate is common. Females can mate several times and lay several clutches of eggs in one season. The male does the incubation; during this process he hardly eats or drinks and loses a significant amount of weight. The eggs hatch after around eight weeks, and the young are nurtured by their fathers. They reach full size after around six months, but can remain as a family unit until the next breeding season. The emu is an important cultural icon of Australia, appearing on the coat of arms and various coins. The bird features prominently in Indigenous Australian mythology.

Contents

 * 1Taxonomy
 * 1.1History
 * 1.2Systematics
 * 2Common name
 * 3Description
 * 4Distribution and habitat
 * 5Behaviour and ecology
 * 5.1Diet
 * 5.2Breeding
 * 5.3Predation
 * 5.4Parasites
 * 6Relationship with humans
 * 6.1Economic value
 * 6.2Cultural references
 * 7Status and conservation
 * 8See also
 * 9Notes
 * 10References
 * 11External links

History
Emus were first reported as having been seen by Europeans when explorers visited the western coast of Australia in 1696. This was during an expedition led by Dutch captain Willem de Vlamingh who was searching for survivors of a ship that had gone missing two years earlier.[6] The birds were known on the eastern coast before 1788, when the first Europeans settled there.[7] The birds were first mentioned under the name of the "New Holland cassowary" in Arthur Phillip's Voyage to Botany Bay, published in 1789 with the following description:[8][9]

The species was named by ornithologist John Latham in 1790 based on a specimen from the Sydney area of Australia, a country which was known as New Holland at the time.[3][10] He collaborated on Phillip's book and provided the first descriptions of, and names for, many Australian bird species; Dromaius comes from a Greek word meaning "racer" and novaehollandiae is the Latin term for New Holland, so the name can be rendered as "fast-footed New Hollander".[11] In his original 1816 description of the emu, the French ornithologist Louis Jean Pierre Vieillot used two generic names, first Dromiceius and later Dromaius.[12] It has been a point of contention ever since as to which name should be used; the latter is more correctly formed, but the convention in taxonomy is that the first name given to an organism stands, unless it is clearly a typographical error.[13] Most modern publications, including those of the Australian government,[5] use Dromaius, with Dromiceius mentioned as an alternative spelling.[5]

Systematics
Mounted emu skeleton

Size comparison between a human, the mainland emu (centre), and the extinct King Island sub-species (right)

The emu was long classified, with its closest relatives the cassowaries, in the family Casuariidae, part of the ratite order Struthioniformes.[14] However, an alternate classification was proposed in 2014 by Mitchell et al., based on analysis of mitochondrial DNA. This splits off the Casuariidae into their own order, the Casuariformes,[15] and includes only the cassowaries in the family Casuariidae, placing the emus in their own family, Dromaiidae. The cladogram shown below is from their study.[16] Two different Dromaius species were present in Australia at the time of European settlement, and one additional species is known from fossil remains. The insular dwarf emus, D. n. baudinianus and D. n. minor, originally present on Kangaroo Island and King Island respectively, both became extinct shortly after the arrival of Europeans.[17][18] D. n. diemenensis, another insular dwarf emu from Tasmania, became extinct around 1865. However, the mainland subspecies, D. n. novaehollandiae, remains common. The population of these birds varies from decade to decade, largely being dependent on rainfall; in 2009, it was estimated that there were between 630,000 and 725,000 birds.[19] Emus were introduced to Maria Island[20] off Tasmania, and Kangaroo Island off the coast of South Australia, during the 20th century. The Maria Island population died out in the mid-1990s. The Kangaroo Island birds have successfully established a breeding population.[21]

In 1912, the Australian ornithologist Gregory M. Mathews recognised three living subspecies of emu,[22] D. n. novaehollandiae (Latham, 1790),[23] D. n. woodwardi Mathews, 1912[24] and D. n. rothschildi Mathews, 1912.[25] However, the Handbook of the Birds of the World argues that the last two of these subspecies are invalid; natural variations in plumage colour and the nomadic nature of the species make it likely that there is a single race in mainland Australia.[26][27] Examination of the DNA of the King Island emu shows this bird to be closely related to the mainland emu and hence best treated as a subspecies.[18]

Common name
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 Australia and New Guinea.[17] Another theory is that it comes from the word "ema", which is used in Portuguese to denote a large bird akin to an ostrich or crane.[7][28] In Victoria, some terms for the emu were Barrimal in the Dja Dja Wurrung language, myoure in Gunai, and courn in Jardwadjali.[29] The birds were known as murawung or birabayin to the local Eora and Darug inhabitants of the Sydney basin.[30]

Description
The emu is the second tallest bird in the world, only being exceeded in height by the ostrich;[31] the largest individuals can reach up to 150 to 190 cm (59 to 75 in) in height. Measured from the bill to the tail, emus range in length from 139 to 164 cm (55 to 65 in), with males averaging 148.5 cm (58.5 in) and females averaging 156.8 cm (61.7 in).[32] Emus are the fourth or fifth heaviest living bird after the two species of ostrich and two larger species of cassowary, weighing slightly more on average than an emperor penguin. Adult emus weigh between 18 and 60 kg (40 and 132 lb), with an average of 31.5 and 37 kg (69 and 82 lb) in males and females, respectively.[32] Females are usually slightly larger than males and are substantially wider across the rump.[33]

Emus have three toes on each foot in a tridactyl arrangement, which is an adaptation for running and is seen in other birds, such as bustards and quails. The ostrich has two toes on each foot.

Adult in South Eastern Australia

Although flightless, emus have vestigial wings, the wing chord measuring around 20 cm (8 in), and each wing having a small claw at the tip.[32] Emus flap their wings when running, perhaps as a means of stabilising themselves when moving fast.[7] They have long necks and legs,[33] and can run at speeds of 48 km/h (30 mph) due to their highly specialised pelvic limb musculature.[32] Their feet have only three toes and a similarly reduced number of bones and associated foot muscles; emus are unique among birds in that their gastrocnemius muscles in the back of the lower legs have four bellies instead of the usual three. The pelvic limb muscles of emus contribute a similar proportion of the total body mass as do the flight muscles of flying birds.[34] When walking, the emu takes strides of about 100 cm (3.3 ft), but at full gallop, a stride can be as long as 275 cm (9 ft).[35] Its legs are devoid of feathers and underneath its feet are thick, cushioned pads.[35] Like the cassowary, the emu has sharp claws on its toes which are its major defensive attribute, and are used in combat to inflict wounds on opponents by kicking.[36] The toe and claw total 15 cm (6 in) in length.[35] The bill is quite small, measuring 5.6 to 6.7 cm (2.2 to 2.6 in), and is soft, being adapted for grazing.[32] Emus have good eyesight and hearing, which allows them to detect threats at some distance.[37]

Emu head and upper neck

The neck of the emu is pale blue and shows through its sparse feathers.[32] They have grey-brown plumage of shaggy appearance;[17] the shafts and the tips of the feathers are black. Solar radiation is absorbed by the tips, and the inner plumage insulates the skin.[38] This prevents the birds from overheating, allowing them to be active during the heat of the day.[39] A unique feature of the emu feather is the double rachis emerging from a single shaft. Both of the rachis have the same length, and the texture is variable; the area near the skin is rather furry, but the more distant ends resemble grass.[7] The sexes are similar in appearance,[40] although the male's penis can become visible when he urinates and defecates.[41] The plumage varies in colour due to environmental factors, giving the bird a natural camouflage. Feathers of emus in more arid areas with red soils have a rufous tint while birds residing in damp conditions are generally darker in hue.[33] The juvenile plumage develops at about three months and is blackish finely barred with brown, with the head and neck being especially dark. The facial feathers gradually thin to expose the bluish skin. The adult plumage has developed by about fifteen months.[26]

The eyes of an emu are protected by nictitating membranes. These are translucent, secondary eyelids that move horizontally from the inside edge of the eye to the outside edge. They function as visors to protect the eyes from the dust that is prevalent in windy arid regions.[33] Emus have a tracheal pouch, which becomes more prominent during the mating season. At more than 30 cm (12 in) in length, it is quite spacious; it has a thin wall, and an opening 8 centimetres (3 in) long.[33]