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 °C. The thermoneutral zone of emus lies between 10–15 and 30 °C.

Behaviour and ecology
Emus live in most habitats across Australia, although they are most common in areas of sclerophyll forest and savanna woodland, and least common in populated and very arid areas, except during wet periods. Emus predominately travel in pairs, and while they can form enormous flocks, this is an atypical social behaviour that arises from the common need to move towards food sources. Emus have been shown to travel long distances to reach abundant feeding areas. In Western Australia, emu movements follow a distinct seasonal pattern – north in summer and south in winter. On the east coast their wanderings do not appear to follow a pattern. Emus are also able to swim when necessary, although they rarely do so unless the area is flooded or they need to cross a river.

Diet
Emus forage in a diurnal pattern. They eat a variety of native and introduced plant species; the type of plants eaten depends on seasonal availability. They also eat insects, including grasshoppers and crickets, lady birds, soldier and saltbush caterpillars, Bogong and cotton-boll moth larvae and ants. This forms a large part of its protein requirements and intake. In Western Australia, food preferences have been observed in travelling emus: they eat seeds from Acacia aneura until it rains, after which they eat fresh grass shoots and caterpillars; in winter they feed on the leaves and pods of Cassia; in spring, they feed on grasshoppers and the fruit of Santalum acuminatum: a sort of quandong. They are also known to eat wheat crops, and any fruit or other crops that it can access, easily climbing over high fences if required. Emus serve as an important agent for the dispersal of large viable seeds, which contributes to floral biodiversity. One undesirable effect of this occurred in Queensland in the 1930s and 1940s when emus ate cactus in the outback there. They defecated the seeds in various places as they moved around, spreading the unwanted plant. This led to constant hunting campaigns to stop the cactus from being spread.

Emus also require pebbles and stones to assist in the digestion of the plant material. Individual stones may weigh 45 g (1.6 oz) and they may have as much as 745 g (1.642 lb) in their gizzard at one time. They also eat charcoal, however scientists still have not ascertained why. Captive emus are also known to eat shards of glass, marbles, car keys, jewellery and nuts and bolts.
Emus drink at infrequent intervals, but ingest large amounts when they do so. They typically inspect the water body in groups for a period before kneeling down at the edge of the water and drinking. They are observed to prefer kneeling on solid earth while drinking, rather than in rocks or mud, presumably due to a fear of sinking. They often drink continuously for 10 minutes, unless disturbed by danger, in which case they interrupt themselves to deal with the threat before resuming. Due to the arid environment, they often go one or two days without finding a source of water and drinking. They typically drink once per day or night, but can do so several times daily if supply is abundant. In the wild, they often share water sources with kangaroos, other birds and wild camels and donkeys that were let loose by European settlers. Emus are suspicious of these other species and tend to wait in bushes and wait for other types of animals to leave; they choose to drink separately to the other animals. If an emu senses abnormal circumstances or a threat, it drinks while standing.

Breeding
Emus form breeding pairs during the summer months of December and January, and may remain together for about five months. During this time they wander around in an area a few miles in diameter. It is believed they guard or find territory during this time. Both males and females increase in weight during this time and the female is slightly heavier at between 45 and 58 kg (99 and 128 lb). This weight is lost during the incubation period, the males losing around 9 kg (20 lb). Mating occurs in the cooler months of May and June, and the exact timing is determined by the climate, as the birds nest during the coldest part of the year. During the breeding season, males experience hormonal changes, including an increase in luteinizing hormone and testosterone levels, and their testicles double in size.

It is the females that court the males, and during the mating season, they become physically more attractive. The female's plumage darkens slightly and the small patches of bare, hairless skin just below the eyes and near the beaks turn turquoise-blue, although this is a subtle change. The female strides around confidently, often circling the male, and pulls its neck back while puffing out her feathers and crying out a low, monosyllabic sound that has been compared to human drums. This calling can occur when the males are not in view and more than 50 metres (160 ft) away and when the male's attention has been gained, the female can circle in a radius of 10–40 m. As the female circles its prospective mate, it continues to look towards him by turning its neck, while keeping its rump facing him. During this time, the female's cervical air sac may remain inflated as it calls out. The passive male retains the same colour hair, although the bare patches of skin also turn a light blue. The female has more black hairs on its head but gender differentiation can be difficult for humans. If the male shows interest in the parading female, he will move closer; the female continues to tantalise its target by shuffling further away and continuing to circle him as before.

Females are more aggressive than males during the courting period, often fighting one another for access to mates. Fights among females accounted for more than half of the violent incidents in one mating season study. If a female tried to woo a male that already had a partner, the incumbent female will try and repel the competitor by walking towards her challenger and staring in a stern way. If the male showed interest in the second female by erecting his feathers and swaying from side to side, the incumbent female will attack the challenger, usually resulting in a backdown by the new female. Some female-female competitions can last up to five hours, especially when the target male is single and neither female has the advantage of incumbency. In these cases, the animals typically intensify their mating calls and displays, which increase in extravagance. This is often accompanied by chasing and kicking by the competing females.