US cats kill an estimated 1.3 to 4 billion birds each year, up to 22 billion mammals, and hundreds of millions of reptiles and amphibians

They are the killers in our midst: savage creatures who go for the neck and then tear their victims to shreds. You may know them as Mog, or Tibbles, or Mr Pickles, but left to their own devices cats are responsible for the deaths globally of tens of billions of songbirds, mammals and reptiles and lizards.

The carnage they wreak in the natural world is driving some species to the brink of extinction. They need to be kept under house arrest. Feral cats, indeed, ought to be poisoned.

That is the message of Cat Wars, a new book by the ornithologist Peter Marra and a journalist named Chris Santella, which categorises cats as an invasive species, akin to Asian tiger mosquitos carrying dengue and west nile viruses.

If you must let your cat out, put it on a lead, say the authors of Cat Wars

Dr Marra, director of the Smithsonian migratory bird centre in Washington, says he is not a cat-hater. “I have had them as pets in the past,” he said. Yet he cited stark studies which suggested the havoc they were wreaking on separate parts of the natural world.

“There had never been a book like this that really brought together this science in a way that’s accessible for most people,” he said. “Even as I was pulling the scientific studies together, it was just jaw-dropping to me, how clear this is and how long we have known this. Paper after paper, study after study, shows not only [cats’ effect on] biodiversity but also the effects on human health.”

The authors argue that toxoplasmosis, which is spread by a parasite in cat faeces and can cause fevers, headaches or even death for people with immune deficiencies, represents “a looming public health crisis”.

Conservative attempts to tally up the animal toll in the United States led Dr Marra to conclude that cats were killing 1.3 to 4 billion birds each year, up to 22 billion mammals, and hundreds of millions of reptiles and amphibians.

Britain, he says, has less of a problem with feral cat colonies which account for about 69 per cent of the bird killing in America. However, “in England you have a little over eight million cats, most of them owned cats”, he said. “Most of them are let outside. That’s really not a good thing. I have friends in the RSPB — they themselves have cats and joke about it. They get it but they just refuse to keep their cats inside.”

He thinks cat owners should ponder the treatment of dogs, once allowed to roam free, now on leads outside. “Dogs were biting people. Rabies was transmitted, dogs were hit by cars. We have finally figured out that keeping them on leads was the responsible thing,” he said. If you want to take your cat outside, he suggests doing the same.

Naturally this advice has not been universally welcomed. Initial online reviews of the book, apparently penned by staunch cat-lovers, warned that readers would be helping to “spread hatred and killing of innocent cats”.

Others claimed, less creditably, that the authors had no scientific evidence for their claims. Dr Marra says he is not surprised. “We called it Cat Wars for a reason,” he said.


  • Cats catch up to 55 million birds a year, according to recent estimates by the Mammal Society.
  • Experts suggest that the UK’s cats kill up to 275 million animals a year, although estimates vary widely due to the number of victims brought home and those that manage to escape before dying.
  • The bird species most frequently targeted are house sparrows, blue tits, blackbirds and starlings.
  • There are an estimated 7.4million domestic cats in Britain, according to the RSPCA.
  • Retailers have developed “cat bibs” that can be attached to collars to prevent cats from achieving the precise angle needed to catch birds.