Proposals that New Zealand follow Australia's example in an effort to curtail a growing population of stray cats are "absurd", a scientist says.
Unitec research, which studied unmanaged cat colonies in Auckland over a 20-year period, found a growing cat population.
There were 1.4 million cats nationally, with potentially another 350,000 in the wild, researcher Mark Farnworth estimated.
Wild cats would be disease-ridden, with some having FIV - HIV for cats - and feline leukaemia virus, Farnworth said.
"This creates a problem because it's a reservoir of disease for our pet cats," he said.
New Zealand should look to Australia, which has stringent controls to manage the cat population, such as "curfews and containment of companion cats", the study said.
Other areas raised were compulsory registration and identification of cats, and exclusion zones around ecologically sensitive areas.
"Do I think these are things New Zealand will need to implement? I suspect so. New Zealand may at some stage need to consider other options," Farnworth said.
"I think cat registration is an important aspect of managing cat population."
While it was normal to go out and buy a dog, Kiwis often "acquire" cats.
"So a cat turns up in the backyard, and then they feed it, and then it's theirs. There's this idea that cats choose people," he said.
"Dogs are required to be registered, so we know roughly how many people have dogs. But cats aren't."
The SPCA last year rejected the idea of cat curfews and limiting cat numbers.
John Innes, from Landcare Research, said it was "absurd" to look to Australia as a model for restricting cats, because the two countries were so different ecologically.
In Australia, cats were controlled to protect other animals.
"They have rodents that are very vulnerable to cats, whereas in New Zealand we don't," he said.
"In Australia, the problem is with feral cats, and endemic valued, endangered rodents.
''So they have native rats like we have native birds. Having a rodent over there is not a bad thing, necessarily."
In New Zealand there were endangered native birds at risk, but they did not live in the urban centres, and cats were not the culprit killers, he said.
"Everybody automatically thinks cats are bad for wildlife, and the reason why in New Zealand it's not quite true is that the main prey of cats is small mammals," he said.
"If you look at cat diets, they live off rodents, rats, mice, small rabbits, things like that."
This leads to New Zealand cats eating ship rats, which prey on native birds.
"In New Zealand, cats are most helpful at night," said Innes.
"Cats eat a lot of ship rats. Ship rats probably eat more forest birds than cats put together. People just don't know them because they do it all at night up trees."
There was no wildlife case for restricting cats, he said.
"I've worked with tui restoration in Hamilton for a decade, and I've never had an account of a tui, one of our radio-banded birds, being killed by a cat," he said.