The cats were removed from Stephens Island,
but it was too late for the wren.
Now only known from a few cat-chewed museum specimens,
evolving to be flightless had proven fatal.
So it seems there is a trade-off.
The freedom of island life allows a species to relax its guard,
but that can leave it defenceless.
on the main islands of New Zealand,
similar dramas have played out time and time again.
Forests dominated by giant kauri trees once covered the North Island.
The fragments that remain look much like they have for millennia,
but looks can be deceiving.
A few centuries ago,
this forest echoed with the calls of strange and wonderful birds.
Most famous was the giant moa,
which looked a bit like an ostrich,
but taller than an elephant.
And there are many more birds
whose haunting songs now exist here only in memory.