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