The remarkable birdlife of New Zealand evolved in the absence of apex predators. Cats introduced into the area have decimated their population. Cat owners in New Zealand may have to change their habits.

For many generations, the Lyall’s wren was perfectly attuned to New Zealand’s remote mammal-free landscape at the bottom of the South Pacific Ocean.

When people, ancestors of the Mori, first arrived in New Zealand in the 13th century, the small, flightless bird found itself unprepared for predators such as the Polynesian rat.

The bird had been wiped out on the two main islands by the time European settlers arrived in the early nineteenth century. Only a small population remained on Stephens Island, an island separated from the northern tip of New Zealand’s South Island by the Cook Strait.

The Lyall’s wren is only known to European science because of specimens collected after a lighthouse was built on the island. Lighthouse keepers introduced cats, one of whom is thought to have been named “Tibbles,” which spawned a feral population. Within a year, cats had wiped out Lyall’s wren; the last example seen was one brought back to the lighthouse by the keeper’s cat in February 1895.

During the tens of millions of years since the landmass separated from the supercontinent Gondwana, New Zealand’s idiosyncratic native bird species filled every evolutionary niche. Many of them, including the kiwi, which has become the nation’s emblem, “forgot” how to fly along the way. When mammals arrived, New Zealand’s native bird species were confronted with threats that evolution had not foreseen.

New Zealand has recently attempted to correct this. Along with bird conservation programmes that have been in place for over a century, the Predator Free 2050 campaign aims to eradicate introduced pests like rats, stoats, ferrets, weasels, and possums. Feral cats, however, have been left off the list. Campaigners argue that this is an oversight and that they should be included.

Conservation groups are pushing for the first national cat management act, which would cover the entire country. However, there are broader issues for the hundreds of thousands of New Zealand households that have a cat; should New Zealand’s cats be kept isolated from the outside world?

—- Cat ownership in New Zealand is the highest in the world, with nearly half of all households owning at least one cat. My sister, for example, lives in a cul-de-sac a half-hour drive north of Wellington, New Zealand’s capital. It’s a great place for kids and cats to run around on quiet roads. Her family has a cat named Zoe, and almost all of her neighbours do as well. With large gardens to explore and acres of scrub and native bush to prowl on nearby hillsides, the cats are outside more than they are inside.

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With plenty of space and a love of the outdoors, New Zealanders frequently let their cats roam free, at least during the day. The cats on my sister’s street are all neutered or spayed, as are 88% of the country’s companion cats. While this is a high rate by international standards, it is far from complete. And, in some cases, cats may have had a litter of kittens before being neutered. Even if only 12% of its domestic cat population breeds, the stray or feral population will grow steadily.

Nobody knows how many feral cats exist in New Zealand, but the figure could be as high as 2.5 million – nearly one wild cat for every two people. According to Amelia Geary, regional conservation manager for the Royal Forest and Bird Protection Society, feral cats have colonised every environment, from the mountains to the coast.

If the estimates are correct, there are a lot of hungry mouths prowling the countryside. Cats are natural, patient hunters who have had a significant impact on the flightless bird population in New Zealand.

“They have directly contributed to the extinction of 11 bird species and may have contributed to the extinction of ten more,” says Geary. “And now, those more vulnerable species have gone they’ve moved on to eating everything else – lizards, and vertebrates, and endangered native bats.

“They have been observed eating penguins,” she adds. “They’re eating endangered lizards in the mountains. They are common. And, unlike the UK, when a species becomes extinct, such as the Eurasian crane, we don’t have the luxury of simply slipping over to Germany to get more birds to start a new population. In this country, extinction is permanent.”

The Royal Forest and Bird Protection Society has previously estimated that feral cats may kill up to 1.1 million native birds each year, in addition to tens of millions of introduced birds. They claim that cat predation is exacerbated by rats and mustelids such as the stoat. which was introduced by British settlers in the nineteenth century. Many of the more vulnerable birds, such as the nocturnal ground parrot, the kkpo, only survive because breeding populations were relocated to predator-free islands before it was too late.

It is no longer just small or slow-moving birds that are endangered. Cats are now being blamed for a significant decline in the population of kea, a powerful alpine parrot that occasionally preys on sheep lambs in New Zealand’s snowy high country. Warmer winters caused by climate change are thought to be allowing cat litters to survive over winter in these areas.

The effect cats have isn’t just limited to predation – the recent boom in feral cat populations is even being felt in New Zealand’s marine environment

According to Jessi Morgan, chief executive of the conservation group Predator Free New Zealand Trust, New Zealand’s birds are especially vulnerable to cat predation. Many are flightless, nest and fledge on the ground, and some emit a strong, mammalian-like odour that cats can detect. “Cats are the top predators around here,” she says.

Morgan recently hiked along the Milford Trek, one of New Zealand’s most popular – but remote – hiking trails, and was surprised to see cats roaming there as well. “We had to get there by boat, and the only way a cat could get there is through this massive pass,” she explains. “Seeing them in this environment is quite terrifying.”

Cats have an impact that extends beyond predation. The recent increase in feral cat populations is even affecting the marine environment in New Zealand. Toxiplasma, or toxo, is a parasite carried by feral cats that has been linked to the extinction of some of New Zealand’s indigenous dolphin species, according to Geary. “They have an indirect effect on our endangered dolphins, Maui and Hector’s dolphins, because they wash up on the beach infected with toxoplasmosis, and cats are the only hosts of toxoplasmosis. Toxoplasmosis oocysts can remain dormant in soil for years.” The cysts can be swept out to sea if a cat defecates near a stream that then floods.

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