Question and Answers: Operation Ark

What is the problem?

Predator plagues. These are sudden eruptions in the populations of either rats, stoats or both in New Zealand's forests.

Stoats and rats eat native birds, and an explosion in their numbers can have a impact on endangered species that is easily equivalent to an outbreak of a lethal virus in the human population.

Predator plagues frequently occur as a result of heavy fruiting of beech, rimu and kahikatea trees, and sometimes because of warm winters. They may occur in one area and not another and vary in severity.

In 2000 and 2001, New Zealand's beech forests were heavily hit by predator plagues.

Why hasn't DOC done anything about predator plagues until now?

Because no one realised that they could have such a severe impact until recently. It has only been in the past few years that it was discovered that rats are a significant predator of kakariki and mohua, and that simultaneous rat and stoat control and monitoring is needed to protect these birds.

Thanks to the bad experience of the last two years, we now have a much clearer idea of the triggers of stoat plagues, although we still have a lot to learn about rat plagues. Operation Ark draws on this increased knowledge and will incorporate new knowledge as it is acquired.

When is the next stoat or rat plague going to happen in beech forests?

We know there won't be heavy beech fruiting this year in the Hawdon or Hurunui area, which suggests there won't be a stoat plague. Intensive rat trapping in the area hasn't turned up any rats either, which suggests there won't be a rat plague.

Predictions beyond a year in advance are impossible.

However, as a general rule of thumb plagues of differing degrees of severity seem to be a one-in-several-year event. They are often associated with mild winters so DoC will be looking out for that kind of risk factor under Operation Ark.

Will Operation Ark result in more 1080 use?

Yes, but it is difficult to say how much because it depends very much on where plagues occur, how often and what their severity is.

Aerial 1080, for instance, is not the silver bullet that some groups like to claim it is.

Stoats eat rats. Remove too many stoats in a plague year and the rats multiply and eat birds. Remove rats and hungry stoats eat birds. That's why rats and stoats must be controlled at the same time. To do that a number of methods must be used, not just 1080.

However, Operation Ark does anticipate more use of 1080 in controlled circumstances where there is a clear imperative, namely the loss of an entire species.

How much is all this going to cost?

Again that will depend on what plagues occur, how often , where, and what methods of predator control DoC selects from its arsenal.

Applying intensive stoat and rat trapping and monitoring, and targeted poisoning programmes to an area the size of Hurunui (6000 ha) could cost $270,000. If pest control at emergency levels is needed at several sites in one year, the cost would rise correspondingly.

What will this mean for DoC's existing pest control in non-ark areas?

Operation Ark may see some reprioritising of resources when there are widespread plagues in ark areas. But when this is not required DoC's other pest control work will continue as normal.

Work in kiwi sanctuaries will not be reduced as a result of Operation Ark.

What about predator plagues in other types of forests?

Predator plagues also occur in rimu and kahikatea forests. If Operation Ark proves to be successful it may be expanded to include these types of forest.

What will Operation Ark mean in the Orange-fronted kakariki's habitat?

In non-plague year's DoC will use an extraordinarily intensive trapping regime to protect the birds. This includes 1000 stoat/rat traps in the Hurunui on lines spanning 14km, and 1350 traps spanning 22km in the Hawdon area. These will be monitored every fortnight.

In plague years, DoC is likely to introduce specially designed poisoned bait stations in areas where there are high densities of stoats and rats, and it may also drop aerial 1080 around the area where the orange-fronted kakariki live to prevent continued reinvasion of their habitat by stoats and rats.

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