Threats
Historically, the range of the North Island kokako has shrunk as its forest home has shrunk.
According to Maori tradition the kokako was once common "on all the ranges of North Island forests"
and sub-fossil remains indicate a widespread distribution before the arrival of European settlers.
Three-quarters of native forests present in 1000 AD have now gone, and many native birds,
which evolved with kokako, have disappeared also. The small tattered forests that remained were then
overrun by introduced mammals, so that today key pest species, such as ship rats and possums, are firmly
established in the very centres of our largest forests. Kokako are best understood with this history in mind.
The mammalian predators which threaten kokako today are quite different to the avian predators that hunted
their ancestors a thousand years ago.
Video cameras
have shown that ship rats and possums are key predators at kokako nests.
Both are arboreal omnivores which mainly eat plant matter or insects, but bird's eggs and
chicks are taken when they can find them.
The key cause of population decline has been diagnosed to be predation at nests, especially by ship rats
and possums. Happily, we now know we can counter these threats. Research by the Department of Conservation and Landcare Research
has given us a clear understanding of how introduced rats and possums impact on kokako breeding, and how we can systematically
rebuild kokako populations. Intensive control of pests is known to reverse declines within a few years.
Management has assured that the low point for kokako (an estimated 350 pairs in the late 1980's) is
now behind us and the current estimate is 640 pairs. Kokako at Mapara have increased from 5 pairs to over 40 pairs and at Waimana
from 17 pairs to over 140 pairs, similar increases are occurring at all managed sites.
See our kokako range page for where they all are. Our
hope is to steadily bring more sites under management and restore kokako to areas from which they have vanished. The pest-management
we undertake is widely beneficial, improving the lot of many species of birds, reptiles, insects and plants as we increase kokako numbers.
At issue now is whether these efforts are sustainable - financially, ecologically, and politically.
56 Million Years of Isolation
To understand the threats to kokako it helps to briefly look at New Zealands geological history.
New Zealand was once part of the great, southern Gondwana continent. 56 million years ago it began
to split off; at a time when while mammals were still evolving and spreading.
New Zealand rifted off eastwards, forming the Tasman sea, before any mammals reached it
(2 bat species arrived here after we'd split off from Australia). For 56 million years our fauna evolved
in the absence of predatory mammals.
Birds took many of the ecological niches which mammals fill elsewhere. During the last millennium humans
have brought a suite of pest-mammals with them. Mammals hunt by stealth and smell; their quite different
hunting style has decimated the unique fauna of this land. Our small isolated country has found itself
caring for a disproportionate number of threatened species!
