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How Kiwi Came to New Zealand Research into the kiwi’s DNA suggests the species are more closely related to the Australian emu rather than the now extinct moa. KIWI FOREVER RESOURCE 4 GONDWANA > 80 MILLION YEARS AGO This suggests that kiwi developed outside New Zealand, after it separated from Gondwana, and migrated here later. It is thought their ancestors arrived about 60 million years ago. Just how that journey was made remains a mystery. Fossil records are a useful tool to help decipher what happened, but the oldest kiwi fossil (a leg bone found on the coast near Bulls) is only one million years old. That is a mere blip in time compared with the 50- to 80-million year-old fossils needed to tell the story. NEW ZEALAND Two possible explanations for kiwi’s arrival are... Walking to New Zealand As tectonic plates in the earth’s crust move, islands are pushed up above the sea and submerged. Over the eons, a string of islands have come and gone between New Caledonia and Northland, and this may have provided a route from Australia to New Zealand Flying here Of all today’s ratites, none can fly. Those who support the view that ratites share a common flightless ancestor, argue that means kiwi could not have flown here. Another argument against kiwi flying here is the theory that its ancestor was much bigger than today’s bird. It is based on the size of the kiwi egg, which should theoretically be laid by a bird two or three times larger – closer to a cassowary in size. A bird that size would have been much too big to fly across the Tasman Sea, even millions of years ago when it was much narrower. The Earth once looked very different. Bit by bit its lands have separated and joined, erupted and subsided, tilted and turned on its molten core. Oceans have come and gone. About 250 million years ago there was just one supercontinent – Pangea – surrounded by ocean. Its separation lead to the creation of the continents and landmasses we know today. One of Pangea’s major rifts formed Laurasia (today’s North America and Eurasia) and Gondwana. Gondwana went on to separate into Africa, South America, India and Antarctica/Australia. Continental drift broke New Zealand away from New Caledonia, New Guinea and Australia about 80 million years ago, sending this country into the longest period of isolation of any nonpolar landmass. New Zealand today Today New Zealand is a small archipelago in the South Pacific, about the same size as the British Isles or Japan. Species remain as reminders of New Zealand’s unique evolutionary past – wren, wattlebirds, weta, the giant podocarp forests – and the kiwi. How this unusual species evolved has a lot to do with how New Zealand’s land mass changed over time. KIWI FOREVER RESOURCE 4 Image: Rogan Colbourne, Department of Conservation How Kiwi Came to New Zealand When the kiwi first arrived in New Zealand about 60 million years ago, it is thought there was only one species. How the splits happened Isolation over generations. About 8 million years ago the next split occurred somewhere south of Okarito, when populations of the ancestral tokoeka were perhaps separated from one another by glaciers that created an inpenetrable barrier. New Zealand’s changing landscape influenced the way kiwi evolved. At various times the three main islands of New Zealand (North Island, South Island and Stewart Island) were joined together, split in quite different shapes, or under water. As the landscape changed, groups of kiwi became cut off from each other. Without flight there were many barriers keeping them isolated – mountains, wide rivers and seas, and harsh terrain including glaciers. Separated groups could only breed among themselves, sharing a gene pool. As generations passed, kiwi in each group became increasingly different from kiwi in other groups. Nature selected traits most useful to their local environments and the groups became so different they no longer naturally interbred. Eventually they became separate species altogether. Researchers think the first species separation occurred about 16 million years ago, when the brown kiwi group separated from the spotted kiwi. South of the glacial barriers, the tokoeka gradually evolved into its various forms during periods of isolation in ice ages, with Stewart Island birds separating from the rest about 4 million years ago. It is thought that the northern group, now known as rowi, extended as far north as Hawke’s Bay at a time when ‘Cook Strait’ ran through the Manawatu Gorge. Rowi reached the Taranaki area during a time when sea levels were low and the two main islands were joined by land. Some birds became isolated on the North Island about 6 million years ago and evolved into today’s brown kiwi. At about the same time, the spotted kiwi split into the two species now recognised. Compared with other bird groups that have been separated for such long periods of time, the design of kiwi has been remarkably conservative, with only slight physical and behavioural differences between species hiding the major differences in their genetic make-up. For example, for a long time taxonomists didn’t recognise rowi as a separate species because tokoeka and rowi look remarkably similar, with soft brown plumage, similar calls and shared incubation.