Kiwi are Ratites

The group includes some of the world’s largest birds – ostriches, emu and the now extinct moa – as well as cassowaries and rheas. Kiwi are the smallest ratite.  

Nearly all the ratites live in the southern hemisphere. It is thought their original home was Gondwana, the ancient super-continent that once included South America, Africa and Madagascar, Antarctica, Australia, New Zealand and the Indian subcontinent.

Unlike other ratites, kiwi have four toes instead of only two or three, and their large, dinosauric feet mean they can walk almost silently, their tread muffled by fleshy footpads.

Flightless

Ratites are flightless because their breastbone (sternum) is flat – there is no keel to attach the strong muscles needed for flight. This flat chest gave ratites their name. Ratis means ‘raft’ in Latin - a boat without a keel.

How ratites evolved

Debate continues about whether ratites lost their ability to fly, or could never fly. For a long time it has been thought they shared a common flightless ancestor and today’s species are so different because they dispersed, then evolved in geographic isolation from each other.

However, in 2008 a researcher with the University of Florida challenged this, suggesting each species individually lost its flight after diverging from ancestors that could fly. That would mean modern ratites are the products of parallel evolution – different species in different areas all following the same evolutionary course.

How kiwi evolved

Scientists once believed that New Zealand’s moa and kiwi evolved from a common ancestor. However, after studying ratite DNA, and looking at the tiny details of modern ratite bodies, scientists now believe the kiwi is more like the Australian emu than the moa.

This may mean that only ancient moa were around when New Zealand broke away from Gondwana an estimated 80 million years ago. Kiwi, ostrich, emu and cassowary ancestors developed outside New Zealand, and the kiwi arrived here later.