Emus

(Dromaiidae)

Class Aves

Order Struthioniformes

Suborder Casuarii

Family Dromaiidae

Thumbnail description
Large, flightless birds with tiny wings, three toes, and brown-black plumage

Size
60–75 in (150–190 cm); 75–110 lb (35–50 kg)

Number of genera, species
1 genus; 3 species

Habitat
Forest, woodlands, savanna, heath, and grasslands

Conservation status
Extinct: 2 species; Not threatened: 1 species

Distribution
Continental Australia and, formerly, Tasmania, King, and Kangaroo Islands

Evolution and systematics

Emus belong to the group of large, flightless birds known as the ratites that have in common massive, muscular legs, small wings, and a distinctive palate. Their inability to fly is due to the lack of a keel to the sternum, which in flying birds serves as the attachment point of flight muscles. The term "ratites" is derived from the Latin "ratis" for "raft", a boat without a keel. The origin of these birds has recently been clarified by the discovery of numerous good fossils in North America and Europe. Whereas it used to be thought that the ratites had a southern origin, in the old continent of Gondwana, new fossil evidence has shown flying ratites inhabited the Northern Hemisphere in the Paleocene and Eocene, 40–70 million years ago. The present Southern Hemisphere distribution of the ratites probably results from the spread of flying ancestors of the group from the north. The first evidence of ratites in Australia comes from the Eocene and the first recognizable Dromaiidae from the Miocene, 20 million years ago. The emu, Dromaius novaehollandiae, appears in the Pleistocene, only 2 million years ago.

Physical characteristics

Emus are large, cursorial, flightless birds, with long, scaly legs, three toes, and no preen gland. Weighing 51–120 lb (23–55 kg) and standing 6.5 ft (2 m) tall, emus are second only to ostriches in bird size. Although emus usually walk, their long, muscular legs are adapted to running, and they can run up to 30 mph (48 km/h), reaching strides of 9 ft (2.7 m) long. Their plumage is dark brown just after the annual molt, but fades during the year to pale brown. The wings are small, only one tenth the length of the body, and are hidden by the plumage. The main shaft and aftershaft of the feathers are equal in length so that every feather appears double. Pale blue skin shows clearly through the sparse feathers of the long neck. Females are slightly larger than males, weighing 90 lb (41 kg) versus male weights of 80 lb (36 kg). The females have a stronger blue coloration on the bare skin of the neck and head.

The sexes can be further distinguished during the laying period. The hen molts before laying and is a dark bird at this time, whereas the male does not molt until he is incubating,

and is paler than the female. New chicks are striped longitudinally with black, brown, and cream. They weigh 1 lb (0.5 kg) and stand approximately 5 in (12 cm) tall. Birds in their first year have black feathers covering their heads and necks, and the bare skin of the adult appears during their second year of life.

In the 15 ft (4.5 m) gut the gizzard is very muscular, capable of grinding, with the help of ingested stones, hard seeds and nuts. The emu bill is broad and soft, adaptable for grazing. The emu has a tracheal pouch, part of its air sac system, which is used for communication. The pouch is over 12 in (30 cm) long, very thin-walled, and allows the emu to produce deep guttural grunts. The pouch develops fully during breeding season and is used for courtship.

Distribution

Emus lived on Australia, Tasmania, and on King and Kangaroo islands. The only surviving species is confined to the Australian mainland. Because emus are nomadic and all members of the populations respond to the same environmental cues, large movements can occur. In Western Australia a fence has been built to protect the agricultural areas from emus moving towards the southern winter rains. Movements are often seen in Western Australia, where they can be detected on this fence, and also occur in eastern Australia, when emus swim the Murray River in large numbers.

Habitat

Emus are omnivores, at home in eucalypt forest and woodland, acacia woodland, savanna and heath, pine woodland, coastal heath, open spinifex and other tussock grassland, and in remnant vegetation along salt watercourses and on high alpine plains. They swim well and have been found on islands up to 3 mi (5 km) off the coast. Emus drink frequently, probably every day, taking 0.2–0.4 gal (600–1,500 ml) of water at a time. The chicks also need water, but usually obtain it from the leaves of succulent plants that they eat.

Behavior

Behavior has been studied only in the surviving species Dromaius novaehollandiae. Many accounts describe emus as flock birds but this is an artifact of observations on captive and semi-captive birds. In open country emus live as pairs in home ranges of about 12 mi² (30 km²). They will defend significant parts of these areas, but usually try to avoid meeting other emus. In confrontations, they use kicking as a defense. The members of a brood may stay together for some months after they are deserted by their father, but will eventually break up and form pairs, rather than remain as a flock.

Emus have two basic calls, each of which can vary greatly in intensity. The grunt is given mainly by the male and has an aggressive message. The drum or boom is given mainly by females and has a territorial motivation. For the drum, the bird uses the tracheal pouch as a resonating chamber and the low frequency call carries 0.6 mi (1 km). Chicks have a piping call until their voice breaks, at about five months old, when a hole opens in their trachea, and communication with the air sac in the neck is established. Emus display by fluffing out their neck while they drum and, at other times, by stretching themselves up to their full height and grunting with vigor.

Feeding ecology and diet

Emus feed on nutritious parts of plants, fruits, seeds, flowers, and green shoots. They also take grasshoppers, beetles, and caterpillars, often in great quantities. In order to grind up hard material, emus eat pebbles and stones. Individual stones may weigh 0.1 lb (45 g) and individual gizzards may contain 1.6 lb (745 g) of mineral material. Experiments in a zoo, where emus were fed marbles, showed that such hard materials could be retained in the gizzard for over 100 days. It was thought that this might be a useful method of marking the birds, getting them to eat marbles of different colors at different sites, but the method failed because the bird's bill was too weak to pick up the marbles. Emus also eat quantities of charcoal, but the function of this material is unknown. Emus exhibit very strong specific search images, concentrating on one food even though alternative foods are readily available. They also move great distances searching for food.

Reproductive biology

Reproductive biology has been studied only in the surviving species D. novaehollandiae. In southern Australia emus usually lay in autumn, on a platform 3.3 ft (1 m) in length consisting of sticks, grass, and debris on the ground. The clutch varies with the rainfall, from eight to 20 eggs, which are dark green and have a pimply texture. Each egg weighs 1.5 lb (0.7 kg), is 5–6 in (13–15 cm) high, and the shells are 0.03 in (0.8 mm) thick. Incubation is by the male alone, although in captivity hens have been observed to sit for short periods. The male chases the female from the nest when the clutch is completed; she may mate with another male, move away on migration, or remain in the territory, defending it for some weeks. Wild males do not leave the vicinity of the nest, unless disturbed, and do not eat, drink or defecate during incubation. They lose 10–20 lb (5–9 kg) during this period. The chicks hatch after about 56 days, often over four days, and the male then leaves the nest area with them. They stay with their father for 5–7 months. Emus can lay at a year old, but most do not breed until they are two. Wild birds live only six or seven years, although captive ones may live much longer. Under captive conditions some males will have two mates, but this is rare in the wild.

Conservation status

The emu is secure on the Australian mainland and has been reintroduced to Tasmania. The Tasmanian emu, a subspecies of D. novaehollandiae, died out in 1865, and the dwarf species D. ater of King Island and D. baudinianus of Kangaroo Island were exterminated by human activity before 1810 and 1827 respectively. Fears have long been expressed for the survival of the emu on mainland Australia. In fact the bird is surviving well and will continue to do so while two thirds of Australia is unoccupied or used only as rangeland. It seems to be one of those species that can sustain very large population fluctuations.

On an area of 1,000 mi² (2,500 km²) in Western Australia, the number of birds fluctuated between five and 970 over ten years. Estimates of the total population of emus in Australia vary from half to one million. Emus are vulnerable as eggs and hatchlings. Buzzards eat the eggs, and young emus are hunted by dingoes, eagles, non-native foxes, dogs, and cats.

Significance to humans

The emu is the national bird of Australia and appears on that country's coat of arms. For the Australian Aborigines the emu was as central to their existence as was the American buffalo to Native Americans. The emu provided food, and their fat and organs were also used for medicine. The bird was incorporated into their rituals and mythology. Emus were killed for meat by early European settlers. Later emus damaged crops in some areas, leading to organized campaigns to eradicate the birds, including the brief 1932 "emu war" in which machine guns were used. Bounties were paid on their heads in some areas, but recently fences have been used to keep emus out of areas where they might cause damage. Europeans have attempted to farm emus, because they reproduce well in captivity and grow fast, but so far have been unable to establish stable markets for any commercially viable quantity of product. Emu farming began in Australia in the 1970s. The insular species were killed for food by settlers, sealers, and whalers until they became extinct.

Species accounts

List of Species

Emu

Dromaius novaehollandiae

taxonomy

Casuarius n. hollandiae Latham, 1790, New Holland (=Sydney, Australia).

other common names

French: Émeu d'Australie; German: Emu; Spanish: Emú.

physical characteristics

60–75 in (150–190 cm); female 57–106 lb (26–48 kg), male 39–103 lb (18–47 kg). The plumage is brown, sometimes ticked, the feathers long and shaggy.

distribution

Away from settled areas, the emu can be seen anywhere in Australia, but it visits the arid zone only when good rains have fallen there.

habitat

Emus are able to live in all types of native Australian vegetation.

behavior

Emus live as pairs in large territories; young birds remain with their male parent for about seven months, and may then form small flocks until maturity.

feeding ecology and diet

The emu feeds on nutritious parts of plants, fruits, seeds, flowers, and green shoots.

reproductive biology

Emus breed as pairs in natural conditions, the female laying up to 20 eggs that she leaves the male to incubate. The male also guards the chicks for about seven months.

conservation status

Not threatened. The emu is secure in mainland Australia.

significance to humans

The emu has been seen as a pest in some areas and elsewhere as a potential farm animal from which meat, leather and fat can be harvested.

King Island emu (extinct)

Dromaius ater

taxonomy

Dromaius ater Vieillot, 1817, King Island, Tasmania.

other common names

English: Black emu; French: Émeu noir; German: Emu King Island; Spanish: El Emú de King Island.

physical characteristics

Height 55 in (140 cm); 51 lb (c. 23 kg). A small, black emu, with grayish juveniles and striped chicks.

distribution

King Island, Tasmania.

habitat

Not known.

behavior

Not known.

feeding ecology and diet

Ate berries, grass, and seaweed.

reproductive biology

Not known.

conservation status

Extinct.

significance to humans

Source of food to sealers and settlers.

Kangaroo Island emu (extinct)

Dromaius baudinianus

taxonomy

Dromaius baudinianus Parker, 1984, Kangaroo Island, South Australia.

other common names

English: Dwarf emu; French: Ému de Baudin; German: Emu Kangaroo Island; Spanish: El Emú de Kangaroo Island.

physical characteristics

A small, black emu, slightly larger than the King Island emu.

distribution

Kangaroo Island, South Australia.

habitat

Not known.

behavior

Not known.

feeding ecology and diet

Not known.

reproductive biology

Not known.

conservation status

Extinct.

significance to humans

Source of food to sealers and settlers.

Resources

Books

Bird, David M. The Bird Almanac: The Ultimate Guide to Essential Facts and Figures of the World's Birds. Buffalo: Firefly Books, 1999.

Davies, S. J. J. F. Ratites and Tinamous. Oxford: Oxford University Press, 2002.

del Hoyo, J., A. Elliot, and J. Sargatal, eds. Ostrich to Ducks. Vol. 1, Handbook of the Birds of the World. Barcelona: Lynx Edicions, 1992.

Marchant, S., and P. J. Higgins. Ratites to Ducks. Vol 1, Handbook of Australian, New Zealand and Antarctic Birds. Oxford: Oxford University Press, 2001.

Whitfield, P., ed. The MacMillan Illustrated Encyclopedia of Birds. New York: Collier Books, 1988.

Periodicals

Davies, S. J. J. F. "The food of emus." Australian Journal of Ecology 3 (1978): 411–22.

Davies, S. J. J. F. "Nomadism in response to desert conditions in Australia." Journal of Arid Environments 7 (1984): 183–95.

Grice, D., G. Caughley, and J. Short. "Density and distribution of emus." Australian Wildlife Research 12 (1985): 69–73.

Organizations

Birds Australia. 415 Riversdale Road, Hawthorn East, Victoria 3123 Australia. Phone: +61 3 9882 2622. Fax: +61 3 98822677. E-mail: [email protected] Web site: <http://www.birdsaustralia.com.au>

Emu Farmers Federation of Australia. c/o Secretary, Arthur Pederick, P.O Box 57, Wagin, Western Australia 6315 Australia. Phone: +61 8 9861 1136.

S. J. J. F. Davies, ScD