THIS morning I left my two cats sleeping on the bed.

When I get home there will be two indentations in the duvet, each with a tell-tale trace of cat hairs. Not hygienic, I know, but what can you do? They're family.

If you're Gareth Morgan, the solution is simple. You gradually get rid of cats by not replacing them when they die.

A New Zealand environmentalist and economist, he advocates a land cleansed of cats. His website Cats To Go (I looked it up and read "Save up to £50 by recycling your old cat", which struck me as distinctly odd before I realised I'd been directed to a site dealing in the recycling of vehicle catalytic convertors) has a picture of a kitten with red eyes and devil's horns. Inter alia it also says: "The fact is that your furry friend is actually a friendly neighbourhood serial killer."

His argument is simple: New Zealanders own more cats per capita than any other country, and cats have wiped out many native birds. Keep your cats inside at all times, he urges their owners.

It's an old argument, with some validity. Over here, the RSPB website says the UK's cats catch up to 275 million prey items, including 55m birds, each year.

But then it says this: "Despite the large numbers of birds killed, there is no scientific evidence that predation by cats in gardens is having any impact on bird populations UK-wide. This may be surprising, but many millions of birds die naturally every year, mainly through starvation, disease, or other forms of predation. There is evidence that cats tend to take weak or sickly birds."

Online, the Morgan debate has, to no-one's surprise, pitted cat lovers against cat haters. Some cat lovers wonder whether Morgan was the sort of sociopath who hurt cats when he was growing up. But more reasoned opponents insist that while cats' killing is gratuitous, the same goes for humans, and that, in killing rodents, which often eat native birds' eggs, cats are doing birds a favour.

One of my cats has brought home mice and birds, but the fitting of a louder bell to his collar has lessened such activities. Keeping him indoors just wouldn't be natural. I sympathise with Morgan's argument, but his dream of a land purged entirely of felines? Not a cat in hell's chance, I should have thought.