Managing Pests

These introduced predators hunt u sing their sense of smell and kiwi have a strong odour - their natural defences have evolved to deal with animals that don't have a sense of smell.

The result is that only about 5% of wild-born chicks make it to adulthood, and this makes predator control crucial.

BNZ Save the Kiwi has invested in several successful predator control experiments. Some techniques – such as trapping – have been proven to be very effective and successful in medium-sized areas which are accessible to people. However, they also have high labour costs and may not be suitable on difficult or remote country, or in very small areas - when a site is too small, predators find the kiwi chicks before they find the traps..

Controlling pests over large areas

To stop the decline of brown kiwi, great spotted kiwi and Fiordland tokoeka we need to control predators over large, often remote areas.

The challenge is finding ways to do this that won’t cost too much, or be too labour intensive, or too difficult in tough terrain.

If we can’t, kiwi will inevitably be limited to living in a few quite small safe intensively managed populations, while unmanaged populations in the wild will continue to decline or become extinct.

Tools are also needed to reduce the damage that dogs cause in some parts of New Zealand. In Northland, dogs have surpassed stoats, ferrets and cats as the most critical kiwi killer because they kill adult breeding birds, yet few tools or techniques are available to deal with them.

Saving Tongariro’s kiwi

Before mammalian predators arrived in New Zealand, about 1400 kiwi lived in the 20,000-hectare Tongariro Forest Conservation Area, in the central North Island. By 1998, its population of western brown kiwi had plummeted to just 100 adult birds.

Since 1995, Operation Nest Egg has been an important tool in helping protect the kiwi, but it is labour intensive and therefore expensive to use over such a large area. Ground trapping was not possible as much of the terrain was difficult and inaccessible.

That is why the results from a 2006 aerial 1080 (monosodium fluoroacetate) operation are so promising. While it was targeted to kill possums and rats, stoats were also killed – rats eat the baits, and stoats eat the rats. Another 1080 operation is scheduled for the 2011 calendar year.

Monitoring by the Department of Conservation revealed remarkable results for kiwi chicks and other native birds. In the breeding season before the operation, fewer than one third of chicks survived their first six months. Following the 1080 drop, the huge reduction in predators meant 57% of kiwi chicks survived, allowing another 32 juveniles to join the growing kiwi population. As well:

• Fantail/piwakawaka breeding success was 45%, the best recorded since 2002/03. Outside the operation area only 21% of chicks survived.
• The tomtit/miromiro population increased dramatically.
• 14 out of 16 blue duck/whio chicks fledged, while only 3 out of 10 survived outside the operation area.

Tongariro forest’s kiwi population has grew to about 180 birds.

A surprise for researchers was that the high breeding success for kiwi and fantails was maintained into the second season after the 1080 operation, before stoat populations had built up again.

Since then, a ferret problem has taken out many adult breeding birds. Ferrets have increased because rabbit populations have bounced back from low numbers caused by the rabbit calicivirus disease.

The focus is now going on how to deal with ferrets, which are trappable with DOC 250 traps, but these are more difficult to set. Community groups are being recommended to have DOC 250s in their predator-control arsenal.