Feral cats can even help to prevent an H5N1 outbreak. Compound 1080 will be useless.
WELLINGTON, New Zealand––What most threatens the unique New Zealand bird ecology, an estimated 2.5 million feral cats, or 124 million factory-farmed chickens?
Calling feral cats “stone cold killers,” New Zealand conservation minister Tama Potaka in late November 2025 formally added feral cats to the “Predator Free 2050” hit list.
Potaka outlined tactics to be used against cats similar to those used in Australia, and already used against brush possums, introduced from Australia in 1837.
Those tactics chiefly rely on broad distribution of poisons, notoriously sodium fluoroacetate, better known by the brand name Compound 1080.
Ethics & unintended consequences
“Critics worry about ethics and unintended consequences,” reported CNN. “But support is high: more than 90% of public submissions during a national consultation backed stronger management of feral cats.
“Officials were clear,” CNN said. “Pet cats are not part of this plan. The emphasis remains on responsible ownership, including microchipping, desexing, and keeping pets indoors or away from wildlife zones.”
While Potaka’s declaration of war on feral cats made global headlines, in reality it means nothing much new, since the New Zealand government has already been encouraging––and practicing––feral cat massacres as part of the national “Predator Free 2020” program for at least 20 years.
Has the sustained high-intensity killing, including cat-killing contests for school children, called off at one point but later resumed, actually accomplished anything to save New Zealand birds?
(See New Zealand exempts cats from killing contest, finds cure for FIP.)
(Facebook photo)
94 unique native bird species
Consider this: New Zealand has 94 native bird species not found anywhere else.
Feral cats were first documented in New Zealand in 1819, fifty years after the arrival of the first Europeans. Between then and 1950, New Zealand lost 56 bird species, many of the losses attributed––rightly or wrongly––to cat predation.
The extinct species, including all of the extinctions blamed on cats, were mostly already scarce, found almost exclusively in limited island habitats, like Lyall’s wren in 1899, extinct on the New Zealand mainland centuries before any cats arrived.
The last survivors inhabited Stephens Island, only six-tenths of a square mile in size, offering scant opportunity––if any––for the Lyall’s wren population to recover and return to the mainland.
Cattle, sheep, & goats
Also occurring between 1819 and the early 20th century, the introduction to New Zealand of cattle, sheep, and goat farming, the construction of cities and transportation infrastructure, and industrialization completely transformed the habitat.
New Zealand had previously been isolated from outside influence for circa 82 million years: since 20 million years before an asteroid killed the dinosaurs.
The first humans reached New Zealand, bringing Polynesian rats with them, only about 1,000 years before the first Europeans brought the first black rats and Norway rats.
Rats, in absence of cats, stoats, weasels, and any other predators adapted to hunt them, are believed to have caused more New Zealand bird extinctions than all other introduced species combined.
No more extinctions since 1950
Feral cats, mostly hunting rats and also introduced mice and rabbits, had already colonized practically all of New Zealand by 1950.
Since 1950, though, New Zealand has not had another documented bird extinction.
Neither has New Zealand experienced an outbreak of the H5N1 avian influenza. But 76 migratory bird species spend parts of each year in New Zealand, including 32 native New Zealand species who visit other places. Any one of those species could potentially bring back H5N1.
What if it did?
“Won’t be possible to eradicate H5N1 from wild birds”
Warns the New Zealand Ministry for Primary Industries website, “The H5N1 strain that is spreading around the globe could arrive here through wild birds.
“The H5N1 strain of bird flu has adapted to wildlife and has caused high numbers of deaths in wild birds overseas.
“If H5N1 arrives in New Zealand and spreads in the wild bird population, it won’t be possible to eradicate it from wild birds and management options will be limited.”
When H5N1 reaches New Zealand, as it surely will, having already been found in bird populations as remote as Antarctica, feral cats––along with other persecuted non-native bird predators such as stoats, weasels, ferrets, and brush possums––may be the most effective defense against H5N1 that native New Zealand birds have.
Naive about predators––& more so to disease
Why?
First of all, because while native New Zealand birds as of 1819 were naïve to the presence of mammalian predators, they have now had 200 years––more than 200 generations, for most species––to learn to avoid cats, stoats, weasels, ferrets and brush possums.
Conversely, native New Zealand birds have had no history of responding to H5N1, and very little history of exposure to any avian influenza. The likelihood of H5N1 rapidly cutting through any New Zealand bird species it afflicts could scarcely be higher.
Second, predators are creatures of opportunity, killing primarily the sick, the injured, the old, and unattended young. If H5N1 begins dropping native New Zealand birds, a healthy predator population can help to keep the infection from spreading by hunting the potential carriers.
Potential point sources
How many potential point sources are there in New Zealand from which an H5N1 outbreak might spread?
Apart from the risk of migratory wild birds infecting other wild birds, New Zealand hosts approximately 165 farms raising chickens for meat, plus another 170 farms raising chickens for eggs.
Beyond that, as many as 50,000 New Zealand households informally keep about half a million chickens, turkeys, ducks, and other poultry for personal use and as pets.
Most of those birds are outdoors much of the time, thereby easily exposed to infectious droppings from any migratory birds bringing H5N1.
Killing predators “became a national totem”
Oddly enough, considering the decades-long Australian obsession with killing “non-native” species other than cattle and sheep in the name of conserving native wildlife, the notion of doing the same––other than on remote islands––does not seem to have gripped the New Zealand public imagination until “celebrity physicist Paul Callaghan popularized the dream of a predator-free country” circa 2011, reported Henri Astier, New Zealand correspondent for BBC News.
The idea “bubbled up and became a national totem,” Auckland University biologist and “Predator Free 2050” project advocate James Russell told Astier.
“Politicians then got on board,” passing a law in 2016 targeting rats, mustelids, and brush possums for extermination, Astier continued.
Wellington tries to wipe out rats
“Predator Free 2050 Ltd., a public body, was set up to channel government and private money into local projects to test eradication strategies,” Astier recounted.
“The most ambitious of them is Predator Free Wellington. In a city of 200,000 people,” which happens to be the New Zealand capital city, “it aims to kill off a range of pests, notably rats,” who––once established––have never been eradicated from any urban habitat worldwide.
The province of Alberta, Canada, including the cities of Edmonton and Calgary, has largely managed to keep rats out, but rats had not yet become established in Alberta when the program started.
Cats were not officially on the New Zealand hit list legislated in 2016, but had already long been targeted by New Zealand economist Gareth Morgan, 72.
Three scientists favored cats
Dominion Post “World of Science” columnist Bob Brockie (1932-2025) refuted Morgan on February 4, 2013.
“Three acclaimed world experts on animal predator/prey relationships live, or lived in the Hutt Valley,” near Wellington, Brockie began, listing “Mike Fitzgerald, John Flux and the late John Gibb – all former population biologists in the now-defunct Department of Scientific Industrial Research.
“These scientists spent decades investigating feral cats, rats and rabbits in the Rimutaka bush, suburban Melling, and on Wairarapa farmland and none would agree with Morgan’s views,” Brockie wrote.
“Setting thousands of traps, Fitzgerald calculated the number of cats and rats in the Orongorongo Valley for 23 years. The cats held the rat numbers in check for years, but when cat numbers fell, the rat population shot up. The cats also held the riverbed rabbits in check and their population also shot up when the cats disappeared,” Brockie summarized.
Cats “actually benefitted native birds”
“Flux logged everything his cat Peng You brought to his Melling house for 17 years. The cat brought home 558 little victims,” about one per 11 days, “which included 53 native birds (mainly silvereyes) and 151 foreign birds (such as blackbirds and sparrows).
“Peng You never killed tui or New Zealand pigeons,” Brockie detailed. “Indeed, these species established themselves on the Melling property during his time there. More to the point, Peng You killed 63 rats, 221 mice, 35 rabbits, and two weasels,” all of them also bird predators or competitors.
“On balance,” Brockie reported, “Flux thinks his cat, and probably other suburban cats, actually benefited native bird populations by killing so many of their more numerous predators.
“In a two-year trial in the Wairarapa in the 1960s,” Brockie continued, “Gibb showed that cats were more effective than pest destruction boards in controlling rabbits. To prove his point, Gibb persuaded the board to stop shooting rabbits on 1,200 hectares of hill pasture and scrub for three years. At the end of that time there were fewer rabbits there than on the adjacent shot-over land.”
$300,000 to kill one stoat
Despite the efforts of Brockie, Fitzgerald, Flux, and Gibb––and even Brockie favored using Compound 1080 against brush possums––the Morgans, Callaghans, and Russells have prevailed to the extent that in 2022, reported CNN correspondent Dhruv Tikekar, the New Zealand Department of Conservation “launched a major biosecurity response involving trapping experts, dogs, trail cameras, helicopters and boats that took eight months to finally trap and kill” a single male stoat seen on one two-square-mile island off Fiordland, at cost of about $300,000.
“Predator-free 2050,” observed Tess McClure for the Guardian on September 10, 2023, “has so far only succeeded on offshore islands and fenced sanctuaries, but it spurred a vast expansion of expertise in catching and killing furry creatures.
“New Zealanders are the world experts” at poisoning wildlife
“New Zealanders are the world experts, leading the charge in developing new technology, new tools, new methods,” Elizabeth “Biz” Bell told McClure, who identified her as “one of the conservation world’s great mass killers.”
Explained McClure, “Visit any elimination project around the world, Bell says, and you’ll typically find a New Zealander involved somewhere: piloting a helicopter to drop poisoned bait or demonstrating new forms of rodent traps.”
(Daniel Leventhal photo)
Two years later, none of that has changed, including that “Predator Free 2050” has yet to clear predators from any mainland habitat.
And none of that New Zealand expertise in killing mammals will be of any use at all against H5N1.
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