KEY POINTS:
It's a tragic fact that at least 90 per cent of juvenile kiwi on the mainland fail to reach adulthood mainly because of predators. Strong protection measures are needed or kiwis will become extinct: it's as simple as that.
One such measure is 1080 poison, and it is having marked success in controlling rats and stoats and helping kiwi populations grow.
I have listened to and read many debates around 1080 during the Environmental Risk Management Authority's recent hearings into the poison, and it is heartening that, despite the noise from its vocal detractors, 1080's many successes are being aired.
I have been studying kiwi in the field for more than 20 years and have watched as their population has been decimated by stoats, the main enemy of the juvenile kiwi, and ferrets and dogs.
Six years ago, there were about 78,000 kiwi in New Zealand. Today, there are around 70,000 and the number continues to fall. Compare that to the 12 million kiwi estimated to have been in New Zealand before humans arrived.
There is no time to sit back and watch kiwi numbers drop any lower.
Kiwi need to reach 20 weeks of age before they can protect themselves against stoats, but without our help most of them do not reach that age.
A recent large-scale kiwi conservation project that highlighted to me the benefits of 1080 was in the Tongariro Forest around its nationally designated kiwi sanctuary last September. It was one of the largest-ever kiwi protection trials.
Around 14,000ha of the forest was targeted in a two-day multi-agency aerial 1080 operation to control possums and prevent the spread of possum-borne bovine tuberculosis.
Pest numbers were measured before and after the operation across the sanctuary treatment site and, as a control, at the untreated but very similar Pukepoto Forest.
A month after the operation, there was no sign of any possums and stoats in the sanctuary, and rats were barely detectable. Tracking rates in the treatment area plummeted from 70 per cent before the operation to 0.9 per cent for rats, and from 19 per cent to 0 per cent for stoats.
Tracking rates are used to measure the abundance of small mammals. A high value indicates high abundance.
They are measured by putting tracking tunnels out in lines in a forest and then recording how many tunnels are visited by small mammals on any one night. Animals that pass through the tunnels leave distinctive tracks on pieces of paper inside each tunnel.
By reading the papers, it's possible to tell whether the tunnel was entered by mice, rats or stoats on the night it was set. A tracking rate of 50 per cent for rats would indicate, for example, that 50 per cent of the tunnels were visited by rats on the night the tunnel was set. Tunnels are usually set for at least two nights. They are baited with a small piece of meat on the first night, and peanut butter on the second night.
Stoat and rat tracking rates in the treated area had grown to 9 and 6 per cent respectively by May this year, but were still well down on those in the untreated area - 53 per cent and 51 per cent. These figures speak volumes about the need for rigorous and ongoing controls.
The pest kill gave the sanctuary's kiwi a protective window of opportunity during the critical five-month breeding season when they are most vulnerable to stoats.
At present, 13 of 21 radio-tagged chicks (62 per cent) have survived, compared with just one in 12 before the operation. Five are now big enough to be stoat proof and the others are quickly approaching the 1100g threshold weight.
No kiwi were monitored in the control zone, so from a scientific point of view the trial's results are strongly suggestive rather than categorical, but they show what we are seeing all round the country - that 1080 is doing a good job to help kiwi populations.
Other bird species also benefited from the 1080 drop. Thirteen of 32 fantail nests were successful in the treatment area compared with just four of 22 nests in the non-treatment site. Tomtits will be monitored this winter to see how they have fared in the experiment.
These findings have added to our growing understanding that a well-executed aerial 1080 operation for possums enables a "baby boom" of birds that can survive into adulthood. In fact, only one boom year in every four is required for kiwi populations to recover.
Several years ago I worked with the Royal Forest and Bird Protection Society to push for designated and protected kiwi zones. Our work attracted significant government funding for the project in 2000, and kiwi sanctuaries are now becoming a success story.
In general, kiwi populations are stable in such pest-free reserves and sanctuaries, but the sanctuaries by their nature are limited in size and kiwi numbers are still decreasing on the mainland.
New Zealanders have taken kiwi conservation to heart. I see this on my many trips around the country to help communities with initiatives.
It is pleasing to see the effort going into schemes to protect our national bird.
But despite their efforts and the population increases in kiwi sanctuaries, it is New Zealand's rugged back country where the challenges lie.
Aerial dropping of 1080 is the only effective method of controlling pests in such environments. Laying traps and bait-stations in millions of hectares of mountainous forest is simply not possible.
Its cost-effectiveness on a large scale is its great power. But it is not just a money issue: the trials show that 1080 kills the pests that kill kiwis, and it helps kiwi thrive.
Radio-tagged kiwi have been followed through a number of 1080 drops around the country in recent years and not one has died because of the poison. With strict controls on its use and ongoing research into making it more targeted towards pest species, 1080, from a scientific point of view, is the answer.
* John McLennan, an ecological adviser and research scientist, has specialised in kiwi conservation for more than 20 years.
