Toxic meatballs target feral cats

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A little-known poison in the New Zealand's predator-free toolbox could humanely control the feral cats and stoats preying on native species.

The poison paste marketed as PredaStop, hidden within meatballs placed in bait stations, is described as humane, biodegradable, unlikely to kill native birds, and comes with an added bonus of an antidote. Its effect is described as similar to carbon monoxide poisoning. Death comes quickly, after a period of unconsciousness.

Until recently its use has flown under the radar, partly because of the low-uptake of the poison. Its manufacturer Connovation says the requirement to notify home-owners within a three-kilometre radius of poisoning programmes has “severely constrained its use” as the cost to notify thousands of home-owners can be “significant”.

Connovation has recently made an application to the Environmental Protection Agency seeking to reduce the notification requirement to homeowners that bait has been laid from three-kilometre radius of pest control operations to a 500-metres.

The manufacturer argues as most domesticated cats only stray 200 metres from their home, even with the reduced radius of notification, the risk of curious domestic cats inadvertently eating poison is negligible.

It’s hard to know whether the low uptake of the poison is down to the cost of notifying households, an aversion to raise the emotional issue with ratepayers, or the labour-intensive process of making the poison-laced meatballs which spoil quickly in warm weather.

Currently methods of controlling feral cats involve shooting, trapping and euthanising, or poisoning with a version of 1080. Sometimes they can be affected by eating carcasses of other animals which have been poisoned with brodifacoum or 1080, but hoping this will happen is not an effective way to control feral cat numbers. 

PredaStop offers what could be considered a more targeted and humane way of reducing their numbers.

The feral cat problem

Herding New Zealand’s feral cats together to get an estimate of their number is obviously tricky. Department of Conservation (DOC) scientists are unwilling to put a definitive number on them and say issues with counting methods mean it’s unclear how many there are, or if the number is growing.

Some surveys have been done on small areas. One 1991 study of rural land showed there could be up to a million across the country and the figure of 2.5 million feral cats has been mentioned in media before.

With no nightly food bowl, their dinner often comes at the expense of native birds, bats, insects, frogs and lizards.

Feral cats are known to be responsible for the extinction of the Stephens Island wren and for removing entire species from islands. Close to Mount Ruapehu a single feral cat was responsible for the death of 102 endangered short-tailed bats in 2010. It's thought the cat waited outside a tree the bats roosted in and hooked them out of the air as remains of bats were found under a small entrance to the tree over a number of days until the cat was caught.

“There are Tuatara in and around the huts. There are giant wētā. There are kōkako the rangers have to chase off the pumpkin patch in the garden.”

Often understanding feral cats’ impact is easiest to see once they have been removed from an environment.

The Department of Conservation’s threatened species ambassador Nicola Toki said Little Barrier Island is “absolutely bursting with life” because predators, including feral cats, have been removed.

“There are Tuatara in and around the huts. There are giant wētā. There are kōkako the rangers have to chase off the pumpkin patch in the garden,” said Toki.

Other islands where feral cats have been removed show similar results. Native species thrive once cats have been removed.

On Raoul Island, five locally extinct seabird species started breeding on the island within six years of feral cats and rats being removed. On Mangere Island in the Chatham Islands, Forbes parakeets and white-faced storm petrels recolonised the island.

“We’ve now got 4000 species on our threatened species list, that’s one of the highest proportions of threatened species in the world. Most of that is due to habitat loss and introduced predators and one of the best predators in the world is the cat.”

Birds are particularly susceptible to feral cats said Toki as they evolved over millions of years in a landscape without predators with “four legs, fur and teeth”. Ground-nesting birds are particularly at-risk.

“Our birds were literally sitting ducks because their response to a predator threat is to stop what they are doing and try and blend into the landscape.”

Standing still might work as a defence against threats from above but is useless when the predator is on the ground.

Skinks and lizards also fall prey to cats. In Otago, Toki said cats which had been eating endangered skinks were removed in an intensive trapping operation.

“We were checking the cat traps daily and getting these enormous feral cats. These aren’t the kind of cats that you are used to seeing slobbing around your house. These are big, muscly, well-built machines and they have been in that landscape for over 100 years.”

While feral cats are classified as pest species in many regional pest plans, they are covered by same declaration of sentience under the Animal Welfare Act as companion cats so it’s important they are treated humanely.

How it works

Originally tested as an antidote for human cyanide and radiation poisoning in the 1940s to the 1980s, para-aminopropiophenone (PAPP) was found to be far more toxic to carnivores than to the human volunteers who tried the poison in 1946. The 51 volunteers were dosed repeatedly and were observed exercising as well as reading magazines and reported no discomfort despite their blood oxygen levels lowering as a result of taking PAPP.

In New Zealand it’s particularly toxic to feral cats and stoats. The bait, concealed in a ball of minced meat dyed green, works by starving red blood cells of oxygen. This affects muscles and the brain. On average, within 45 minutes of eating the bait cats are unconscious and they die approximately two hours later, without spasms or periods of heavy breathing.

Birds are less susceptible to the poison, however, weka have been seen to become lethargic after eating it. Currently the poison can only be used in bait stations designed to exclude non-target species such as birds and stations must be cleared of baits after the operation has ended.

Bait stations are designed to reduce the chance of non-target species eating the bait. Photo: Rod Dickson

The poison is water soluble and breaks down in soil after a month, unlike some pesticides it does not accumulate in soil. Current rules recommend bait stations are placed away from waterways.

Secondary poisoning occurring from dogs or birds scavenging poisoned carcasses is a possibility, although the risk of death from this is lower from PredaStop than 1080. Small dogs in particular could be affected by eating a carcass or a dislodged bait, and areas where baits have been laid must be sign-posted. An antidote is available but due to the speed the poison works at, it needs to be administered promptly.

Trials of PredaStop

The Hawke's Bay Regional Council has recently completed a large pest control project over 8000 hectares of farmland. Feral cats are an issue in the area, with cats preying on native birds, lizards and insects. A previous trapping project caught six to eight times more feral cats than stoats.

The trial aimed to understand whether PredaStop is viable for large-scale projects, if it is more cost effective than trapping and to understand what measures could be taken to make sure domestic cats didn’t eat the bait. The council’s land services manager Campbell Leckie said the data from the project, which includes counting cat sightings on camera footage before and after the project is still being analysed.

"If we hadn’t moved the kākāpō when we did, there wouldn’t be any left. They would be inside a cat and gone forever.”

Two previous trials have been completed in Hawke's Bay where there are concerns around feral cats spreading toxoplasmosis to livestock, a disease which causes abortions in sheep and their impact on native wildlife. The first trial showed a reduction in feral cats of 50 percent after one bait. A second trial on a different farm where feral cats were threatening brown kiwi resulted in a 74 percent reduction after baits were laid twice in a row.

Leckie said no other trials are planned at present but “if this trial proves to be successful we will then consider PAPP as another tool in the tool bag for feral cat control on farmland”.

The future of feral cat control

The decision from the Environmental Protection Agency on the notification radius for PredaStop is still some time away. Public submissions have closed, but a public hearing is still to the held before the decision will be released.

In the meantime, research is being conducted into less labour-intensive options for spreading the poison, especially in large areas with difficult foot-access.

The option of aerial drops is being explored but this faces two challenges. The bait needs to land intact and still be attractive to feral cats and stoats. Meatballs won’t withstand a drop so DOC scientists are investigating other formulations which will cope with being dropped and will keep fresh longer than meatballs.

The second challenge is ensuring animals other than feral cats and stoats won’t be harmed if the poison is used without a bait station.

DOC’s biodiversity group principal scientist Dr Elaine Murphy said work is underway by Landcare Research on a non-lethal way to test the poison on other animals such as birds and lizards. The hope is that very small drops of blood could be used.

Murphy has also been looking at another control method which involves spraying poison on stoats stomachs with a device called a Spitfire. When the stoats groom themselves they ingest the poison. She said the technique also works with feral cats.

The Spitfire is placed in a tunnel. Sensors in the device calculate the size of the animal, so poison isn’t sprayed onto non-target species such as lizards. The current design of the Spitfire can deliver 100 doses before needing to be reloaded with poison.

Murphy said the current design of the Spitfire needs to be revised and improved before it could be considered for use. She estimates it will be five years before these new ways of using the poison will be viable.

Until then, protecting native species from feral cats would need to rely on the labour intensive, current methods of shooting, trapping and laying baits.

For New Zealand’s threatened species, the stakes in the race to find ways to reduce the number of introduced predators is high.

“We had to do an emergency evacuation and move kākāpō off Stewart Island after they had been rediscovered there because we realised cats were eating them to extinction. If we hadn’t moved the kākāpō when we did, there wouldn’t be any left.


Article by Farah Hancock. A Newsroom reporter based in Auckland who writes on education, conservation and technology.

Originally published OCTOBER 1, 2018 Updated October 1, 2018

This article has been reproduced with the kind permission of Newsroom

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