Kiwi birds don't have to fly. Photo / Thinkstock
Why can't kiwis fly?
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/karearea, 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.
Why are ultraviolet rays so strong over NZ?
UV rays are emitted by the sun but almost all are blocked by the Earth's ozone layer. While people often focus on the dangers of UV radiation because it can cause skin cancer, the sun's rays are also responsible for the formation of vitamin D, which is vital for human health. There are three reasons why ultraviolet rays are so intense in New Zealand:
1. The Earth's orbit isn't circular. During December and January the sun and Earth are 147 million km apart, but in June and July the distance is 152 million km. This means that the Southern Hemisphere summer receives 7 per cent more UV radiation than the Northern Hemisphere summer.
2. There is less protective ozone in the Southern Hemisphere than in the Northern Hemisphere.
3. The air is much cleaner in the Southern Hemisphere, and especially in New Zealand, than in the Northern Hemisphere, where most of the world's population lives.
Has NZ always been in the same place?
No, the land that we called New Zealand has been shunted around various parts of the globe before arriving where it is today.
About 500 million years ago it was part of the supercontinent Gondwanaland (which included today's Africa, India, South America, Australia, Antarctica and Papua New Guinea), and it was located in the Northern Hemisphere. By 300 million years ago, it had moved close to the South Pole, to latitude 60-70o South, then 200 million years ago it began to move into temperate latitudes. Gondwanaland began to break apart 160 million years ago. South America and Africa were the first to break away, about 160 million years ago, followed by India 100 million years ago. Then only Antarctica, Australia and New Zealand remained attached. This rump of Gondwanaland itself began to break apart 83 million years ago when New Zealand drifted towards its present position.
And what of the future? At present New Zealand is being stretched out, with the West Coast region moving north-east at 2-3 metres per century, relative to the Southern Alps on the eastern side. Some geologists predict that one day all landmasses will again coalesce into one giant supercontinent like Ur, of 3 billion years ago.
Why do pukeko risk their lives by venturing so close to the road?
We have all seen pukeko wandering along road verges, and have occasionally spotted a mass of feathers in the middle of the road, evidence that a luckless pukeko didn't time his or her run very well. But it seems that the swamp hens have logical reasons for frequenting roadsides. Lincoln University researchers studied a population of 20-30 pukeko living in a small wetland just north of Christchurch, which was completely surrounded by roads, including a motorway.
Spending time near the roads had its costs: during the two-year study there were 20 pukeko road deaths. But there were also benefits: these included the ability to find fresh grass shoots which p?keko relish, the abundance of spiders which they enjoy eating, and the availability of road grit that is an aid to digestion. The dead pukeko were found to have significant amounts of quartz grit in their gizzards.
Other than being a food source, a roadside is also an area for adult interaction among p?keko, a place where they can size each other up better than in a swamp where there is less visibility. It is no accident that the p?keko that haunt roadsides are adult pairs or trios (the dominant unit of breeding groups in p?keko); no juveniles were seen dicing with death near the tarmac during the study.
If you dug a hole through the earth from NZ where in the world would you end up?
Supposing you could travel through the centre of the Earth (and not be fried by the molten core on the way), most New Zealanders would end up in either Spain or Portugal, although some might find themselves in the ocean off the Spanish or Portuguese coast.
Confusion on this question is caused by the fact that people in the United Kingdom traditionally refer to New Zealand and Australia as 'the Antipodes' (from the Greek 'opposed foot'), and New Zealanders and Australians as 'Antipodeans'. In fact the United Kingdom's antipodes lie much further to the south: London's latitude is 51o North, placing its antipodes in the ocean south of New Zealand.
The antipodes of some of New Zealand's centres are:
Auckland - about 100 km from Malaga (Spain)
Hamilton - Cordoba (Spain)
Wellington - about 160 km from Madrid (Spain)
Christchurch - near Cervo (Spain)
Dunedin - in the Bay of Biscay north of Spain and east of Bordeaux.
* Why Can't Kiwis Fly? by Gerard Hutching, published by Penguin is available now. RRP $30.
- www.nzherald.co.nz
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