A new sausage bait targeting stoats is shaping up to be a valuable tool to protect kiwi and other native wildlife after impressive results in field trials.
The Department of Conservation has been working with pest control developer, Connovation, to develop and register a ready-made bait containing the toxin PAPP (para-aminopropiophenone), to which stoats are especially susceptible.
Stoats are relentless killers of native birds, bats and other wildlife, and the key cause of kiwi population decline on the mainland. They are on the target list for removal in New Zealand's Predator Free 2050 programme.
DOC Principal Science Advisor Elaine Murphy, who has led the PAPP sausage bait development over nine years, says the recent field trials were very successful.
"Over the past three years we've carried out two hand-laid trials and two aerial trials using PAPP sausage baits in the Borland valley in Fiordland National Park, which regularly has high stoat numbers but few rats.
"All the trials were very successful. Stoat detection was reduced by more than 95 per cent in the treatment areas following the hand-laid bait application and no stoats were detected in the treatment areas after the two aerial trials.
"This is an amazing result considering we only used one bait per 4-8 ha in the hand-laid trials and one bait per hectare in the aerial trials."
The first two trials involved hand-laying baits over about 1000 ha in the forest. A prefeed of non-toxic baits to prime the stoats was followed by two rounds of PAPP bait, a week apart.
The later aerial trials covered 2,000-4,800 ha with one non-toxic prefeed and a single application of PAPP bait. Stoats were monitored before and after the operations and in non-treatment areas using trail cameras and tracking tunnels.
Current stoat control methods are limited to labour-intensive trapping and aerial 1080 predator control operations that rely on stoats eating poisoned rodents.
New tools are needed to target stoats in environments where there are few rodents and when they invade pest-free islands, says Elaine Murphy.
"It's taken many years to develop and test this sausage bait but it's now showing great promise. New tools like this are key to achieving Predator Free 2050 and supporting native wildlife to thrive."
DOC will apply to register the PAPP sausage bait for stoats with the EPA (Environmental Protection Authority) and MPI (Ministry for Primary Industries) once research is complete later this year.
An application will also be made for another sausage bait containing small amounts of the toxin 1080 (sodium fluoroacetate), which has been extensively trialled over the past few years, targeting feral cats, mustelids and hedgehogs.
DOC is also planning field trials with a higher dose PAPP sausage bait for feral cats and ferrets after earlier trials showed promise.
PAPP was registered for use in New Zealand for stoats and feral cats in a paste form in 2011, but its use has been limited because it needs to be inserted in hand-made minced meat baits, which is impractical.
Carnivores such as stoats are particularly sensitive to PAPP but most birds and other mammals are less so. The potential risk to native birds from PAPP baits is considered very limited due to very low application rates in the environment and general low susceptibility.
Background information
PAPP is considered more humane than most other toxins used to control vertebrates. It causes low blood oxygen levels, rapid unconsciousness and death, typically within two hours. There is low risk of other animals being poisoned from eating dead stoats and there is an antidote.
Non-lethal testing of PAPP to assess risk for native birds has shown a range of responses. Kea and black-backed gulls are highly tolerant, while pūkeko and takahē are more susceptible, although they wouldn't be affected if they ate a single bait. Kiwi and weka are potentially more sensitive but kiwi have shown no interest in the meat baits in trials to date. A further trial with weka is planned to gauge their susceptibility to PAPP sausage baits.
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