The researchers and Forest and Bird hope Dr Morgan's Cats to Go website will start people thinking about what their cat is doing to wildlife.
The website claims that ''cats are wiping out our native birds''.
Forest and Bird's Kevin Hackwell said research by University of Otago was the most in-depth done in New Zealand on domestic cats and showed cats did kill native wildlife but also that putting bells on cats halved the number of birds they killed.
''Gareth has done us a favour by raising the issue.''
If the figures from the Otago University study were extrapolated out for the whole of New Zealand, ''conservatively'' cats were killing ''about a million native birds'' a year, Mr Hackwell said.
He hoped people would become more responsible pet owners by putting bells on their cats and getting them neutered.
Research on domestic cats by Otago's zoology department and headed by Dr Yolanda van Heezik found 37 Dunedin cats known to be prolific hunters killed half the number of birds when the birds could hear them coming as they did when hunting silently.
Without collars, the cats caught 378 animals, including 82 birds, but only 41 birds were caught when the cats wore bells.
The research was based on what they returned home with.
''The bottom line is cats catch an awful lot of prey, including native and exotic birds, rats and mice, but it's in proportion to what is out there.''
Recent United States research had shown that cats caught more than they brought back to the house, often leaving their prey behind or eating it on site.
Ensuring cats were kept inside was more common in other countries, including Australia, she said.
While it was important cats' welfare was looked after, their impact on the country's biodiversity also needed to be thought about.
''There is potential in the future for a more effective device to reduce prey caught.''
The department had also done research which observed the impact of cats on lizards.
''Any cats have a significant impact on lizards. They really suffer.''