How the Kiwi Species Evolved

It is difficult to be certain about the kiwi's evolutionary history as there are few fossil records - the oldest known fossil is a femur, about 1 million years old and found in coastal deposits near Marton, in the North Island.

Isolated by the changing landscape

New Zealand’s changing landscape and land formation is thought to have influenced the way kiwi evolved. At various times the three main islands of New Zealand (North Island, South Island and Stewart Island) were either joined together, split in different places and into different shapes, or were under water.

As the landscape changed, groups of kiwi became cut off from each other. Because they couldn't fly, they were kept isolated by physical barriers such as mountains and glaciers, wide rivers and seas, and by harsh terrain, including infertile volcanic soils.

Separated groups could only breed among themselves, sharing a gene pool.

As generations passed, kiwi in each group became increasingly different from kiwi in other groups.  Nature selected traits most useful to their local environments and the groups became so different they no longer naturally interbred. Eventually they became separate species altogether.

Changes took millions of years

Researchers think the first species separation happened when the brown kiwi group separated from the spotted kiwi. The next split happened somewhere south of Okarito on the West Coast of the South Island.  It is thought that impassable glaciers separated populations of the ancestral tokoeka. During periods of isolation in ice ages, the birds south of the glaciers gradually evolved into the various forms of tokoeka we know today, with Stewart Island birds separating from the rest about 4 million years ago.

It is thought that the group of birds north of Okarito, now known as rowi, extended as far north as southern Hawke’s Bay. At one stage of New Zealand's hisotry the seas strait that divides the North and South Islands ran through the Manawatu Gorge and provided a natural barrier.  Rowi remains have been found in pre-European Maori middens in the southern Hawke's Bay.

Brown kiwi ancestors reached the Taranaki area when sea levels lowered and the two main islands were joined by land. When the islands split again, some birds became isolated on the North Island about 6 million years ago and evolved into today’s brown kiwi species.

At about the same time, the spotted kiwi split into the two species recognised today - great spotted kiwi and little spotted kiwi.

Compared with other bird groups separated for such long periods, the design of kiwi has been remarkably conservative - despite major differences in their genetic make-up, there are only slight physical and behavioural differences between species. For example, for a long time taxonomists didn’t recognise rowi as a separate species because they look remarkably similar to tokoeka, with soft brown plumage, similar calls and shared incubation. It was only when the rowi's DNA was studied that it became obvious it is a different species.