Colours of Wildlife: Kiwi
Created | Updated Oct 23, 2016
Kiwi
Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
Here you see a Common Kiwi, Apteryx australis. This, too, is a mini-watercolour painting, to suit the subject, the smallest living kind of ratite bird. The ratites are the birds like ostriches, emus, cassowaries, and rheas – mainly large and flightless. But they're also distinguished from other birds by other features, like having a specific kind of lower jaw – they're also called Palaeognaths, or 'ancient jaws'. There is one palaeognath group that can still fly – the tinamous of South and Central America. These are the closest living relatives of the ratites.
Many-times Flightless
An amazing aspect of the living ratites, is that they are all likely to have evolved from flying ancestors – mostly, separately! Today they're found in South America – the rheas – in Africa – the ostriches – in Australia – the emu's and cassowaries – and in New Zealand. Fossil ratites are known from much of Asia as well as Europe. Today the places ratites live are all separated by great distances and also big stretches of ocean. So … seeing as they can't fly … how did they get to all those places? Some people supposed that their ancestors lived before the break-up of the continents. We know that they were connected, forming a single supercontinent, Pangaea. But that was VERY long ago. Pangaea existed mainly in the Permian and Triassic periods; by 200 million years ago it was already breaking up, and when the dinosaurs went extinct, 65 million years ago, the continents were already mostly separated like they are today. So do ratites go back to the Triassic? Actually, birds as a distinct group only evolved from around the late Jurassic, 150 million years or so ago, and even the very first palaeognath birds, the ones that all the living ratites are descended from, at earliest must have lived in the Late Cretaceous, 80-70 million years ago. Actual fossil paleognaths are only known from around 50 million years ago, well after the extinction of the dinosaurs. So … these birds could not have 'already been' in the places they are today. They needed to get there, somehow.
But … the thing is, the paleognath ancestors whose fossils we found, could fly!. Fifty or so million years ago, they were small, partridge-like birds that lived mostly in forests and swamps. They had small wings but could certainly fly well enough. So these small, flying ancestors of the living ratites could move around and populate the world. Which they did. Prehistoric, flying paleognaths are known from the Americas, Europe, and other places.
This solves a puzzle of the distribution of these birds, but then the question becomes … why did they lose the ability to fly? All living ratites are flightless, but seeing as they got where they are today by flying, they all must have lost the ability to fly afterwards! So … flightlessness evolved multiple, separate times, in the ratites, but not to a comparative degree in any other group of birds. The only modern flightless birds that come from flying ancestors, are birds living on predator-free islands, and the penguins, which have lost flight ability to gain swimming ability. But ratites like ostriches, rheas, emus and cassowaries live on continents where there are plenty of predators. They
're safe today because they are big, but their flying ancestors weren't. So it remains a puzzle why they became flightless – and big, which goes along with that.
Last of a Lineage
Getting to the old Kiwi … they live today on the islands of New Zealand and were likely never found anywhere else. New Zealand is separated from Australia by a big stretch of ocean; there were connections with Australia and Antarctica in very ancient times, and New Zealand hosts a kind of reptile called a Tuatara which is a throwback to a group that lived in the times of the dinosaurs and earlier, and became extinct everywhere else. But most of the present animal life on the island comes from more recent imports, mainly birds, which flew there when the islands were already isolated. The native birds of New Zealand are fascinating and almost all species are entirely restricted to the islands. Unfortunately many New Zealand bird species are already extinct, having suffered from hunting and habitat destruction starting upon the arrival of the native Maori people, and much of it also being due to the later arrival of the Europeans.
One such extinct group is the Moas. These were also ratites, and indeed the tallest birds ever to exist. The giant Moa of the South Island could reach a head height of 3.6 m/12! There were many other moa species, from these giants down to ones the size of a turkey. Indeed the islands of New Zealand had the richest fauna of ratite bird species to be found anywhere in the world. And today they are all gone.
Well, not all! The kiwis are still there. They escaped extinction because of being small, night-active, forest-living birds, not good targets for hunting, and at least some of the indigenous forests survived. Kiwis look very different from ostriches and the other large ratites, but studying them has indicated they clearly belong to the group.
What is highly funny, though, is that kiwis are apparently NOT very closely related to the moas with which they shared the islands of New Zealand! Their closest ratite relatives were, according to genetic studies, the Elephant Birds, which lived on the island of Madagascar – which today are also sadly extinct, thanks to humans. There's quite a vast distance between Madagascar and New Zealand … pretty much the whole Indian Ocean and the entire Australian Continent along with the a stretch of the Pacific Ocean. Kiwis are also closer to the living emus and cassowaries of Australasia, than they were to the moas. So: the ancestors of the moas and of the kiwis both separately must have landed on New Zealand as flying birds, and probably at different times (the kiwi perhaps later than the moas) and independently became flightless. Kiwis might never have been large, while moas became large after becoming flightless.
Kiwis are completely flightless. Their wings are almost entirely atrophied, and they have no keel on their breastbone, which in flying birds anchor the powerful chest muscles necessary for flight. Kiwis also don't have vaned feathers, instead being covered by long, hair-like plumes. They look shaggy and almost mammalian.
Kiwis have some unique features. Their nostrils are at the tips of their bills, unlike in all other birds where the nostrils lie at the base of the bill. They use their bills to probe into the mouldy forest soil in search of earthworms and other digging critters. (They also eat fallen fruits and seeds.) Kiwi territory can be recognized by the crater-like holes they leave by probing all over the place. They also have long hair-like feathers called vibrissae at the base of their bills. These function much like the whiskers of cats and other nocturnal mammals, being used to 'feel' their way in the dark. They use their strong legs and feet to scratch and dig in the soil. They move around the forest understory, snuffling much like dogs in search of titbits. The male gives the main call, a mournful two-part whistle. The female makes a lower, harsher cry.
One other very unusual feature of the kiwi is that it lays the largest egg, compared to body size, of any bird species! An adult kiwi is about the size of a chicken, but it lays an egg six times as large as a chicken egg. An x-ray of a female carrying an egg shows it to be taking up almost all of her body cavity! Laying such an egg must be an heroic endeavour. She may even lay a clutch of two or three of them! She makes her nest in a natural cavity between tree roots, or in a burrow. Like with other ratites, the male kiwi does the egg-incubating duty (except for one species, the Greater Spotted Kiwi, where the male helps). Kiwi chicks look very much like the adults, not having a downy stage but emerging with the shaggy hair-like feathers. Some scientists used to think the huge egg was a result of kiwis being descended from much larger birds like moas, the reduction in body size somehow not matched by a reduction in eggs size. At present though there's no sign of kiwis having been bigger in the past.
At present, five species of kiwi survive on New Zealand, as well as some subspecies. Their relationships are still being studied. They look much the same, except for their size and details of their shaggy plumage. Kiwis today are regarded favourably by humans. The Maoris hold them in high esteem and no longer hunt them for their plumage, as they did earlier, instead gathering it from birds dying of natural causes or from captive birds. The kiwi is the national symbol of New Zealand and their rugby team is called the kiwis. We also here in South Africa use Kiwi shoe polish! It's a brand well supported in the UK and US.
The greatest threat for kiwis at present is from mammalian predators introduced to New Zealand by humans: cats, dogs, ferrets and stoats. The little flightless birds can't defend themselves against these. There is at present a big project ongoing to eliminate these predators from the islands. This will benefit the kiwis and the numerous other unique birds and other critters of New Zealand. At present, kiwis can be considered reasonably secure, among the native fauna. They do well given some protection and are found in several reserves. They're even able to tolerate some man-changed habitats and sometimes feed on pastures. Kiwis are found in only a few zoos outside of New Zealand.
