Why can't Kiwis fly?

Here is an extract from a NZ Herald Article

Simple: they don't have to - or at least they didn't until humans brought dangerous predators such as dogs, stoats, ferrets, possums and cats to New Zealand. Before then native birds such as weka, the New Zealand falcon/k?rearea, the extinct laughing owl, giant eagle and adzebill killed kiwis, but the national bird had developed defences to deal with these hazards. Chiefly, it had become nocturnal, thus avoiding most enemies except perhaps the laughing owl, which was a skilled night-time hunter.

A further reason why kiwis haven't had to fly is that they are masters of disguise. Maori recognised this, naming the kiwi 'te manu huna a Tane' (the hidden bird of Tane). Its mottled plumage, blending perfectly with the forest understorey, provides an ideal
defence against predatory birds that hunt by sight. And it was (and still is) adept at camouflaging its nest before leaving on a nightly foraging expedition. Unfortunately the kiwi's characteristic scent is an easy giveaway to introduced mammals, which use their sense of smell to hunt.

Did kiwis ever fly? We don't know. Like most ratites (the bird group to which the kiwi belongs), the kiwi lacks the flat sternum to which flight muscles attach; all that remain are tiny vestigial wings.

Not for nothing was the kiwi dubbed Apteryx, meaning 'wingless'.

But not all modern ratites are flightless, so it is possible that the kiwi used to fly. Scientists envisage three possibilities: that the kiwi was already here when New Zealand broke away from Gondwanaland 83 million years ago and may or may not have been already flightless; that at some point during the last 50 million years a flightless kiwi walked to New Zealand, making its way across islands that rose and fell, from New Caledonia down through Norfolk Island and on to the Northland peninsula; or thirdly, that there was a flying kiwi ancestor which dropped in on New Zealand from Australia in relatively recent times.

Fossil evidence doesn't give any answers. The oldest known kiwi fossil is a femur bone found near Marton in what were once sand dunes, but this fossil is much too young to throw light on the kiwi's origins. DNA evidence is probably the best hope to answer the question of kiwi flight, but at present it is inconclusive.

Read more about some quirky Kiwi questions here ....