What kind of birds are called ratites?

Ratites are a group of large, flightless birds that include ostriches, emus, cassowaries, rheas, and kiwis. Some key features define ratites:

• They cannot fly, unlike most birds.
• They have a flat, raft-like sternum (breastbone) without a keel that other birds use to anchor flight muscles.
• They have lighter, less pneumatized (air-filled) bones compared to birds that fly.
• They have simplified wings with long arms and primary feathers that look more like fur or hair.
• They have no true tail but a pygostyle (fusion of caudal vertebrae) without rectrices (tail feathers).

Origins and Evolution

The origins and evolutionary history of ratites has long intrigued biologists. Here are some key points about their evolution:

• The ancestorial ratites separated from flying birds (Neognathae) over 80 million years ago during the Late Cretaceous.
• The earliest ratites evolved in the continental landmass Gondwana before it broke up into today’s southern continents.
• As Gondwana divided, different ratite lineages were isolated on different continents and evolved independently.
• Traditionally ratites were thought to have lost the ability to fly independently, but recent research suggests flying ancestors settled different continents and only later lost flight.
• Ostriches evolved in Africa, emus and cassowaries in Australia, rheas in South America, and kiwis in New Zealand.
• New Zealand split off from Gondwana earlier than the other continents, allowing kiwis to evolve into a more basal, distant ratite lineage.

This continental isolation and independent evolution led to the unique traits and behaviors of modern ratites that we recognize today.

Characteristics of Modern Ratites

Despite their inability to fly, ratites are highly successful, adaptable birds filling ecological niches as large terrestrial grazers and predators. Here are some key characteristics for each living lineage of ratites:

Ostriches

• Native to Africa.
• The largest and fastest ratites, reaching up to 9 feet tall and weights over 300 lbs.
• Long, bare legs and neck, with soft feathery wings and tail.
• Males are black with white wing and tail plumes.
• Females are gray-brown.
• Run up to 45 mph.
• Powerful kick for defense.
• Lay largest bird eggs, 4-5 lbs.
• Grazers feeding on grasses, shrubs, seeds.

Emus

• Native to Australia.
• Second tallest ratite after ostrich, 5-6 feet tall.
• Shaggy, double layer of feathers.
• Long neck and legs with small head.
• Males dark gray, females light brown.
• Can run 30 mph.
• Broad diet includes fruits, seeds, insects, greens.
• Males incubate eggs and raise chicks.

Cassowaries

• Native to New Guinea and northeastern Australia.
• Short and sturdy, 4-6 feet tall.
• Black plumage with distinct casque (helmet) on head.
• Bright blue and red skin on neck.
• Sharp claws used for defense.
• Mostly frugivorous, eating fallen fruits.
• Males incubate eggs and raise chicks.
• Can be aggressive and considered dangerous.

Rheas

• Native to South America.
• 4-5 feet tall with small heads and long legs.
• Gray-brown body feathers, lighter underparts.
• Males larger and more ornamented than females.
• Fast runners reaching 40 mph.
• Omnivorous, eating grasses, fruits, seeds, insects.
• Males build nests and incubate.

Kiwis

• Native and endemic to New Zealand.
• Smallest ratites, 15-20 inches tall.
• Stout, round body with thin legs.
• Brushtail of long whiskery feathers.
• Nocturnal, with reduced vision but excellent sense of smell.
• Omnivorous, probing soil for worms, insects.
• Unique among birds with nostrils at tip of bill.
• Males incubate eggs and raise chicks.
• Endangered with vulnerable populations.

Unique Adaptations

While sharing many features, ratites also evolved unique adaptations suited to their environments. These include:

Conclusion

Ratites encompass several lineages of large, flightless birds united by key anatomical traits adapted for a terrestrial lifestyle. While they share common origins and ratite characteristics, each living species has unique adaptations shaped by millions of years evolving on their respective continents. Ostriches, emus, cassowaries, rheas, and kiwis fill distinctive ecological roles in Africa, Australia, South America, and New Zealand where they continue to fascinate biologists and nature enthusiasts. Their shared history as descendants of extinct Gondwanan ancestors offers a living glimpse into the distant Mesozoic past.