Differences Between a Rhea vs. Ostrich

It is easy to confuse a rhea and an ostrich, especially if we only look at them in photos. They are both large flightless birds with very long necks and similar plumages. Despite their similarities, there are important differences. Such differences have resulted in their taxonomic classification being different. They are both from the same infraclass Palaeognathae, but their classification diverges from there.

We start by looking at the taxonomic classification of the rhea:

• Class: Aves
• Infraclass: Palaeognathae
• Order: Rheiformes
• Family: Rheidae
• Genus: Rhea
• Species: greater rhea (Rhea americana) Darwin's rhea (R. pennata) and puna rhea (R. tarapacensis)
  

The taxonomic classification of the ostrich is as follows:

• Class: Aves
• Infraclass: Palaeognathae
• Order: Struthioniformes
• Family: Struthionidae
• Genus: Struthio
• Species: common ostrich (Struthio camelus) and Somali ostrich (S . molybdophanes)

Learn more about the latter of these two birds with our article on keeping ostriches as pets.

Both the rhea and ostrich are types of flightless birds, but they are very different to birds like the penguin. It is true that they have very similar features, but there are significant physical differences between the rhea and the ostrich.

Physical characteristics of the rhea

Rheas are ovular in shape, but the different species have different sizes and weights:

• Greater rhea: length varies between 4.3' (1.34 m) and 5.5' (1.70 m) and weight ranges from 57.3 lb (26 kg) to 79 lb (36 kg).
  
  
• Lesser and puna rhea: length varies between 3' (0.92 m) and 3.2' (1 m) and weight ranges from 33 lb (15 kg) to 55 lb (25 kg).

All three rhea species have a smooth plumage with fine feathers on their face, neck and thighs, but each species has slight variances in color:

• Greater rhea: gray-brown on the head and neck, but the dorsal and anterior regions have black feathers, while the ventral one is lighter.
  
  
• Lesser rhea: brown upperparts with white markings.
  
  
• Puna rhea: grayer than the previous species, mainly on the head and neck, and has white spots on the upper region.

Common features of the three aforementioned species include long neck and legs, as well as large wings, despite their inability to fly. The wings of rheas are interesting in that with a claw on each of them, which they use for defense. A curious fact is that these animals only have three toes, something uncommon among all birds. Although they have feathers on their face, neck and thighs, they lack tail plumage.

Physical characteristics of the ostrich

Ostriches are the largest birds on the planet, so one of the main differences between these animals is their size. There are two species of ostrich, but with few obvious differences in terms of their physical dimensions. The common ostrich is generally about 6.5' (2 m) tall, but males can occasionally grow larger. Their weight ranges from 66 lb (30 kg) 286 lb (130 kg) or more. The Somali ostrich has similar size and weight ranges, with males being larger than females.

Coloration is also similar in both species. Males belonging to the common ostrich species are black in color with white wingtips and tail, while females are greyish brown. As for the Somali ostrich, males are also black with intense white on the tail and wings, while females are dark brown. The featherless areas of the body on this species are more bluish-gray than in the former.

Common characteristics in ostriches that differentiate them from rheas are their long necks and legs devoid of feathers. Like the rhea, they have a small head small in relation to the body. Unlike the rhea, they only have two toes. They have two strong claws on each leg, which they use for defense. Another difference from the genus Rhea is the presence of tail feathers.

In terms of habits and behaviors, we also find a series of differences that can help us identify rheas and ostriches.

Rhea behavior

Rheas are birds that tend to have gregarious habits and rarely remain alone. In the non-breeding season, they form groups of 5 to 30 individuals. This changes when they are about to reproduce, since the grouping decreases because the males claim territories for themselves.

These birds manage to run at high speed, so it is difficult for many predators to catch up with them. They are always alert to danger, especially if they are in small groups. One peculiarity in terms of behavior is that they run in a zigzag pattern, another ability which helps them evade predation.

Rheas have diurnal habits, meaning they are most active during daylight hours and sleep at night. When sleeping, their neck maintains a kind of S-shape position, resting their beak on their throat. Another custom of the rhea is taking dust baths to clean themselves.

Ostrich behavior

Ostriches are also gregarious land birds, maintaining groups of between 5 to 50 individuals. They generally mix with non-predatory mammals such as antelopes and zebras. In the non-breeding season they are distributed in areas of up to 15 km ². Unlike the rhea, the ostrich likes water quite to the point of taking baths in it if they have the opportunity to do so.

These birds reach high speeds. Despite the inability to fly, they use their wings to gain momentum and maintain balance while running. They can also be aggressive when defending themselves, for which they use their powerful clawed legs. A peculiarity of the ostrich is that they can lower their neck to the ground to try not to be seen, a trait which has led to the misconception that they bury their head in the ground.

Both ostriches and rheas have more in common with dinosaurs than you may think. Learn about these similarities with our guide to the different prehistoric birds.

One of the fundamental differences between these two birds is the type of food they eat.

Rhea diet

The rhea is an omnivorous bird. Although it feeds mainly on plants such as legumes when they are abundant, they include grasses and cereals in their diet when the former are scarce. Both plants and their seeds are their primary source of food. However, they are also known to consume certain animals, such as smaller birds, fish, insects and snakes. They also consume fresh fecal matter from other members of the group, as well as small rocks to aid digestion.

Ostrich diet

As for the ostrich, they mainly consume plants such as grasses, flowers, fruits and certain seeds. Their diet is a fairly selective, unlike the rhea which is generally more varied. Ostriches can also include lobsters and carrion in their diet, which has been left by a predator in the area. They can tolerate prolonged periods without water intake.

Learn more about different animal diets by looking at our article on seed predation in birds.

Another significant difference between the rhea and ostrich is the places which they inhabit. The rhea is a bird native to South America, while the ostrich is from Africa. We look at particular habitats for each bird.

Rhea habitat

The greater rhea inhabits Argentina, Bolivia, Brazil, Paraguay and Uruguay. They live in savannahs, scrublands, meadows and fields with crops. The lesser rhea is native to Argentina and Chile, being present in steppes, scrublands and wetlands. The pruna rhea is located in Argentina, Bolivia, Chile and Peru, developing in ecosystems such as those in which the lesser rhea is located.

Ostrich habitat

As we have stated above, the ostrich is a bird native to Africa. The common ostrich is typical of countries such as Algeria, Angola, Cameroon, Ethiopia, Kenya, Tanzania and Uganda, among others. It develops in savannahs or grasslands and scrub forests, being tolerant of dry and sandy areas. The Somali ostrich is native to Djibouti, Ethiopia, Kenya and, unsurprisingly, Somalia. Regarding the specific type of habitats, it is located in forests, savannahs, scrublands and meadows, both natural and mixed. Ostriches have also been introduced to a large number of countries as livestock.

In terms of reproductive process, we also find certain differences between the rhea and ostrich that are quite curious.

Rhea reproduction

When the reproductive season arrives, the rhea reduces the number of members of their group. This is because males become territorial and only allow the presence of a certain number of females to reproduce with them. During this time, groups of a single male with a few females are formed. A joint clutch of eggs will be formed in which all the females will lay between 13 and 30 eggs in total, although cases of up to 80 have been reported.

The male will be the one who will incubate the eggs and guard them with ferocity. Both males and females mate with several individuals.

Ostrich reproduction

The ostrich has a complex reproductive system, since the male carries out a precise courtship before mating. This bird also forms small groups led by a male and made up of three or five females, which will all mate with that male. The communal nest is built by the male and can house between 15 and 60 eggs. Unlike the rhea, incubation alternates so that the male does it at night and the females take turns during the day.

Learn more about the survival of various species by looking at our article on types of animal reproduction.

Ostriches are both wild and domesticated, so this is reflected in their conservation status. We look at the conservation status of each species individually:

• Greater rhea: near threatened
• Lesser rhea: least concern.
• Pruna rhea: near threatened.
• Common ostrich: least concern.
• Somali ostrich: vulnerable.

As you can see the ostrich and rhea are similar animals in that they are large flightless birds with similar morphologies. Although they have differences in terms of behavior and physical traits, we can most easily tell them apart by looking at their necks and tails. Rheas have feathers on their necks and thighs, while ostriches do not. If the bird has black feathers it will be an ostrich and ostriches have tail feathers, but rheas do not.

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