ASK AN EXPERT: Were kiwi always flightless?

Hana (10 years old) asks:

I am researching Kiwi adaptations for homework. We have to come up with some questions about them and then find the answers. One of my questions was: were kiwis always flightless – if not, what was the benefit of losing the ability to fly? The internet didn’t have the answers to this specific question so I was wondering if you could help me understand this or help me research this further.

Dr. Mike Dickison, Natural History Curator at Whanganui Museum says:

Kiwi belong to a group of birds called ratites, which includes the moa, the ostrich, the emu, and some other giant birds.

Although they can’t fly, we know from the fossil record and DNA that they’re descended from flying birds. Not long ago we found fossils of the kiwi’s ancestor, from 20-million-year-old rocks in Central Otago. It was much smaller than modern kiwi, and probably could fly (although we haven’t found its wing bones yet).

Lots of birds become flightless, especially if there are no predators living on the ground: flying is hard work, and birds will stop doing it if they don’t need to. In New Zealand, eagles and hawks were flying around during the day, so there was space for a small nocturnal bird that lived on the ground.