Emu vs ostrich, it’s a showdown of two avian heavyweights. The Common ostrich is the biggest, heaviest bird in the world by a wide margin, the Emu takes fifth place, after the Somali ostrich and Northern and Southern cassowary. These are two gargantuan birds that are readily comparable. So what are the differences between emus and ostriches?
Let’s start with an obvious similarity: both the emu and ostrich are flightless.
Whilst both birds are huge, the ostrich is much taller at a maximum of 9.2ft (2.8 m) vs 6.2 ft (1.9m) and also heavier at 145kg (320 lb) maximum vs 65kg (143lb) maximum for an emu. Both birds have long necks, lay huge eggs, and can attain high running speeds over long distances.
There are many other differences between emus and ostriches - read on to find out!
Common Ostrich (Struthio camelus)
Emu (Dromaius novaehollandiae)
Ostriches are truly colossal, not just amongst birds but amongst all animals.
As we can see, ostriches are around three times heavier than emus and a quarter taller at least. Ostriches are much stronger and more powerful, but emus are still very large amongst birds. Their huge bodies and wings supply their extra weight. Emus have comparatively smaller wings.
Another key difference here is that female emus are taller and heavier than male emus - this is not common amongst birds. Contrastingly, male ostriches are much larger and heavier than female ostriches - males ostriches can weigh double that of female ostriches.
Male Ostrich walking on the grass
Ostriches are capable of reaching faster speeds than emus. The ostrich is the fastest animal on two legs and can comfortably achieve a top speed of 45mph (70kph). The Emu is also an excellent runner and can attain speeds of 30mph (50 km/h).
Both birds have tremendous stamina and can sustain high speeds for long durations. The ostrich is the best marathon runner on the planet and can run at speeds of around 35mph for some 30 minutes to 1 hour, enabling it to run a 26-mile human marathon in about 45 minutes.
The Emu also packs plenty of stamina and can run nonstop for half an hour or longer, cruising at a generous 25 to 30mph.
Both birds have exceptionally long, strong and specialised legs with large feet. Their legs work somewhat like elastic, enabling them to cover many metres in one stride. For example, ostriches can cover 5 metres in one just one stride!
Emus aren't as fast as Ostriches, but they can still reach impressive speeds of 45mph (70kph)
As mentioned, female emus are larger and heavier than males, which is quite unusual. Why? Because female emus are dominant and polyandrous, meaning they mate with multiple males.
Female emus usually mate with two or three males a year - the male incubates the eggs as the female wanders off to find another mate to breed with. Male emus may incubate and brood chicks from multiple fathers. Female emus compete with each other over unpaired males, rather than the other way around and can lay as many as three clutches per year. Some emu mates stick together for longer than a breeding season.
Researchers believe that reproductive dominance is why female emus are larger and heavier than males.
Male ostriches, on the other hand, are dominant and polygamous. Each male ostrich mates with a ‘harem’ of females, numbering between 3 and 8 individuals. The males fight vigorously to maintain their harem. Male ostriches also incubate the eggs and parent the chicks. Broods of ostrich chicks can merge into one large brood, so ostriches often end up rearing other ostrich’s chicks. Emus are the same - broods of multiple parents can merge into one large flock.
One male and three common ostriches
Female emus are larger than males. Male and female emus also look very similar to males, though their plumage is slightly darker.
Contrastingly, male ostriches are vastly larger than females. A male ostrich can be 3 feet taller and 50kg heavier than a female. Male ostriches also have dark black upper feathers and wings, while the female is predominantly brown.
Ostriches are considerably more sexually dimorphic than emus, meaning the males and females look different to each other.
Both birds are relatively long-lived. Emus average around 20 years in the wild but ostriches can live for 50 years, with some reaching the age of 60.
Both birds lay exceptionally large eggs, though ostrich eggs are larger. Ostrich eggs are around 6 inches long, weighing around 3lb, whereas emu eggs are around 5 inches long, weighing around 2lb - so not a huge difference.
Emu eggs are distinctive dark green with blue specks, whereas ostriches lay off-white eggs. Both birds lay many eggs, with ostriches laying between 12 and 18 and emus laying between 5 and 25, which is highly variable compared to other birds.
Both the emu and ostrich live in predominantly flat and arid climates. Their ways of handling this environment are similar, as while neither bird can fly, they travel long distances in search of food and water. Both emus and ostriches can cover many hundreds of miles in a week.
Emus are generally docile birds, except for the females during the breeding season. There have been two documented cases of emus attacking humans. On the other hand, ostriches tend to be much more aggressive and have been recorded viciously attacking and even killing humans. An ostrich’s kick is so powerful that it can kill a lion. Both emus and ostriches have large, sharp talons.
Ostrich eating grass
Both ostriches and emus are omnivores consuming a wide range of plants, animals and insects. Ostriches and emus are particularly fond of giant insects like large beetles, centipedes and spiders, but both will also eat small animals and reptiles.
Emus and ostriches both consume large volumes of stones and grit, which helps them grind and digest food in their gizzards, which are specialised stomachs. Birds don’t have teeth - their gizzards help them chew food. Since both emus and ostriches consume large volumes of dry grasses, they have very large gizzards.
Emu foraging for food on the grass
Emus and ostriches both have large feet with sharp talons. However, ostriches have just two toes, whereas emus have three. Ostrich feet are pretty bizarre and are surprising given their weight - that’s a lot of weight and force going through just two toes!
The foot of an Emu
It’s firstly worth pointing out that there are just one species of emu, whereas there are two species of ostrich; the Common ostrich and Somali ostrich.
There is little data on how many wild ostriches there are in the wild, but one study suggests that there are 150,000 ostriches.
On the other hand, Emus number around 625,000 to 725,000, considerably more than the ostrich. Ostriches are not a common sight in Africa, mainly because their habitats are so expensive. However, emus are pretty common in some parts of Australia. Overall, emus are more common than ostriches.
A small flock of Emus in the wild in Australia
Emus and ostriches do not seem to be obviously genetically related, but they are from the same family of flightless birds called the Ratites. The Ratites include Kiwis, cassowaries, ostriches, rheas and emus.
Studies have found that the Ratites don’t have much in common apart from the fact they are flightless, though emus are loosely related to rheas and cassowaries. Scientists have puzzled over why these flightless birds ended up in Australia, New Zealand, Africa and South America and whether they even share a common ancestor.
The formerly accepted theory was that the common ancestor of the Ratites walked the Gondwana supercontinent some 167 million years ago. Once the continent broke up, these flightless birds became distanced from each other and evolved independently.
A new theory suggests that the Ratites are linked to Tinamous, a group of terrestrial birds that can fly, unlike the Ratites. Interestingly, they believe that Tinamous learnt how to fly at some point, whereas the Ratites evolved to be flightless. Therefore, each Ratite bird, including emus and ostriches, might have evolved from different Tianomous.
There is still much debate about the origin and evolution of flightless birds, particularly the ostrich, which doesn’t seem related to other flightless birds.
A large flock of Ostriches, South Africa
Australia is home only to emus. There are no ostriches in Australia, and no emus in Africa. However, Australia is also home to the Southern cassowary, another large flightless bird.
Africa is home only to ostriches, and there are two species; the Common ostrich and the Somali ostrich. You cannot find ostriches anywhere else in the world other than Africa.
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