How Kiwi Came to New Zealand RESOURCE 4

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KIWI FOREVER How Kiwi Came to New Zealand RESOURCE 4

Research into the kiwi’s DNA suggests the GONDWANA species are more closely related to the Australian > 80 MILLION emu rather than the now extinct moa. 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 The Earth once looked very different. up above the sea and submerged. Over the eons, a string of Bit by bit its lands have separated and joined, erupted and islands have come and gone between New Caledonia and subsided, tilted and turned on its molten core. Oceans have Northland, and this may have provided a route from Australia come and gone. to New Zealand About 250 million years ago there was just one supercontinent Flying here – Pangea – surrounded by ocean. Its separation lead to the Of all today’s ratites, none can fl y. Those who support the creation of the continents and landmasses we know today. view that ratites share a common fl ightless ancestor, argue that means kiwi could not have fl own here. One of Pangea’s major rifts formed Laurasia (today’s North America and Eurasia) and Gondwana. Another argument against kiwi fl ying here is the theory that its ancestor was much bigger than today’s bird. It is based on Gondwana went on to separate into Africa, South America, the size of the kiwi egg, which should theoretically be laid by a India and Antarctica/Australia. bird two or three times larger – closer to a cassowary in size. Continental drift broke New Zealand away from New Caledonia, A bird that size would have been much too big to fl y across New Guinea and Australia about 80 million years ago, sending the Tasman Sea, even millions of years ago when it was much this country into the longest period of isolation of any non- narrower. polar landmass. New Zealand today Today New Zealand is a small archipelago in the South Pacifi c, 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 How Kiwi Came to New Zealand RESOURCE 4 Image: Rogan Colbourne, Department of Conservation Image: Rogan

When the kiwi ﬁ rst arrived in New Zealand How the splits happened about 60 million years ago, it is thought there Researchers think the ﬁ rst species separation occurred about 16 million years ago, when the brown kiwi group separated was only one species. from the spotted kiwi.

Isolation over generations. About 8 million years ago the next split occurred somewhere New Zealand’s changing landscape inﬂ uenced the way kiwi south of Okarito, when populations of the ancestral tokoeka evolved. At various times the three main islands of New were perhaps separated from one another by glaciers that Zealand (North Island, South Island and Stewart Island) were created an inpenetrable barrier. joined together, split in quite different shapes, or under water. South of the glacial barriers, the tokoeka gradually evolved As the landscape changed, groups of kiwi became cut off from into its various forms during periods of isolation in ice ages, each other. Without ﬂ ight there were many barriers keeping with Stewart Island birds separating from the rest about 4 them isolated – mountains, wide rivers and seas, and harsh million years ago. terrain including glaciers. Separated groups could only breed It is thought that the northern group, now known as rowi, among themselves, sharing a gene pool. extended as far north as Hawke’s Bay at a time when ‘Cook As generations passed, kiwi in each group became increasingly Strait’ ran through the Manawatu Gorge. different from kiwi in other groups. Nature selected traits most Rowi reached the Taranaki area during a time when sea levels useful to their local environments and the groups became so were low and the two main islands were joined by land. different they no longer naturally interbred. Eventually they Some birds became isolated on the North Island about became separate species altogether. 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.