Emu - Description

Description

Emus are large birds. The largest can reach up to 150–190 cm (59–75 in) in height, 1–1.3 m (3.3–4.3 ft) at the shoulder. In length measured from the bill to the tail, Emus range 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). Emus weigh between 18 and 60 kg (40 and 130 lb), with an average of 31.5 kg (69 lb) and 36.9 kg (81 lb) in males and females, respectively. Females are usually larger than males by a small amount, but are substantially wider across the rump.

They have small vestigial wings, the wing chord measuring around 20 cm (7.9 in) long, and have a small claw at the tip of the wing. The bill is quite small, measuring 5.6 to 6.7 cm (2.2 to 2.6 in). The Emu flaps its wings when it is running and it is believed that they stabilise the bird when it is moving. It has a long neck and legs. Their ability to run at high speeds, 48 km/h (30 mph), 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. When walking, the Emu takes strides at every 100 cm (3.3 ft), but at full gallop, a stride can be as long as 275 cm (9.02 ft). Its legs are devoid of feathers and underneath its feet are thick, cushioned pads. Like the Cassowary, the Emu has sharp claws on its toes which are its major defensive attribute. This is used in combat to inflict wounds on opponents by kicking. The toe and claw are a total of 15 centimetres (5.9 in). They have a soft bill, adapted for grazing.

The Emu has good eyesight and hearing, which allows it to detect nearby threats. Its legs are among the strongest of any animals, powerful enough to tear down metal wire fences.

The neck of the Emu is pale blue and shows through its sparse feathers. They 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. Both of the rachis have the same length, and the texture is variable; the near the quill it is rather furry, but the external ends resemble grass. The sexes are similar in appearance, although the male's penis can become visible when it defecates. The plumage varies in colour due to environmental factors, giving the bird a natural camouflage. Feathers of Emus in more arid area with red soil have a similarly tinted plumage but are darker in animals residing in damp conditions.

The eyes of an Emu are protected by nictitating membranes. These are translucent, secondary eyelids that move from the end of the eye closest to the beak to cover the other side. This is used by the Emu as a protective visor to protect its eyes from dust that is prevalent in windy and arid deserts. The Emu also has a tracheal pouch, which becomes more prominent during the mating season. It is often used during courting, and it has speculated that it is used for communication on a day-to-day basis. The pouch is more than 30 centimetres (12 in), is spacious and the wall in very thin. Its opening's width is only 8 centimetres (3.1 in). The quantity of air that goes through the pouch, as determined by the Emu deciding to open or close it, affects the pitch of an Emu's call. Females typically cry more loudly than males.

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. As with other ratites, the Emu has great homeothermic ability, and can maintain this status from -5 to 45 degrees. The thermoneutral zone of Emus lies between 10–15 degrees and 30 degrees.

As with other ratites, the Emu has a relatively low rate of metabolism compared to other types of birds, but the rate depends on activity, especially due to resulting changes to thermodynamics. At -5 degrees, the metabolism rate of an Emu while sitting down is around 60% of the value for one that is standing, as the lack of feathers under its stomach leads to a higher rate of heat loss when it is standing up and exposing the underbelly.

Their calls consist of loud booming, drumming, and grunting sounds that can be heard up to 2 kilometres (1.2 mi) away. The booming sound is created in an inflatable neck sac that is 30 cm (12 in) long and thin-walled. The different sounds produced can be used to distinguish males and females. The loud booming caused by inflation of the cervical sac corresponds to females, while loud grunts are limited to male Emus.