Ratite: flightless birds of the southern continents

Defining characteristics

Ratites are best recognized by their flattened breastbone: they lack the pronounced central ridge or keel on the sternum that anchors large flight muscles in flying birds. Other shared features include a relatively large body size, long legs adapted for running in many species, and a generally reduced wing structure. They are often compared with other flightless birds, but ratites form a distinct assemblage based on skeletal traits.

Distribution and evolutionary background

Most ratite lineages occur primarily on landmasses that were once part of the southern super-continent Gondwana. This geographic pattern helps explain why related forms appear in Africa, Australia, New Zealand and South America. Modern genetic studies suggest a complex history involving ancient divergence, dispersal and repeated loss of flight in separate lineages rather than a single simple split.

Living and extinct examples

• Living: ostrich (Africa), emu and cassowary (Australia and New Guinea), rhea (South America), kiwi (New Zealand).
• Extinct: moas of New Zealand (moas), elephant birds of Madagascar (elephant birds), several island forms known only from fossils.

Relationships and classification

Historically, ratites were grouped together in the order Struthioniformes, separate from the small, ground-dwelling tinamous of South America. More recent analyses of DNA and morphology have shown closer connections: tinamous appear to be the closest living relatives of ratites and may be nested within the broader ratite radiation. Because of these findings, taxonomic arrangements are under revision and different authorities treat the group in different ways.

Importance and conservation

Ratites are important for studies of evolution, biogeography and the consequences of flight loss. Several species are threatened by habitat loss, hunting and introduced predators, and some large forms went extinct after human colonization of their islands. Conservation efforts focus on habitat protection, predator control and, for some species, captive breeding.

Further reading: textbooks on avian evolution and specialist reviews discuss ratite origins, the role of Gondwanan breakup, and the unique biology of both living and extinct species. See resources linked above for introductory entries.