Download How Kiwi Came to New Zealand

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
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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.
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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.