Yesterday was a special day for 20 rowi (a species of the flightless kiwi) who were flown from the South Island to their new home on Mana Island, near Wellington. It was reported that this was the first time that this species of kiwi had been in the North Island for over a century.
So how do we know that rowi used to be in the North Island?
Today kiwi are absent from large areas of New Zealand, including the southern North Island (North Island brown kiwi occur from the central North Island northwards). We know that kiwi used to occur in the southern North Island because their bones have been found in caves and other deposits. However, trying to identify kiwi species just by looking at the shape and size of their bones is tricky.
Little spotted kiwi is the only species that can be identified from its bones because they are much smaller than the other kiwi species. The bones of great spotted kiwi and the three species of brown kiwi (rowi, North Island brown kiwi and tokoeka) can’t be identified to species because they overlap in size and shape.
This is the kind of puzzle that DNA can solve. As part of my PhD I examined the past distribution of each kiwi species by sequencing DNA from kiwi bones that had been collected from throughout New Zealand. Some of these bones were up to several thousand years old, but they still contained small amounts of DNA!
Surprisingly I found that the bones in the southern North Island were most closely related to rowi, rather than the geographically closer North Island brown kiwi. Today rowi only naturally occur in one small population at Okarito on the West Coast of the South Island and they are the rarest species of kiwi. My DNA work showed that they used to occur as far north as the southern Hawke’s Bay. You can read the published results here.