To many of us humans cats are icons of cuteness, but, increasingly, across the world nature defenders are calling for us to limit their liberty on account of the wildlife, chiefly birds, that they kill each year. But what is the truth? Should we be keeping our furry friends indoors, or saying, 'Hey bird lovers, leave those cats alone?'

Are you telling me cats are being imprisoned in homes?

In some places. For instance, in Walldorf, Germany, an area which is home to the rare ground-nesting crested lark, the local district has ordered residents to lock their cats indoors, or leash them when outdoors, over summer for the next three years. Failure to do so will result in significant fines: €500 (£420) if a cat is caught outside; €50,000 if it kills or harms an endangered lark. In Australia too, cat owners have been urged to keep their pets inside after research found every single feral cat slaughters more than 740 local wildlife creatures each year. It was estimated that there three million mammals, two million reptiles and a million marsupials were dying every day from feral or pet cat attacks.

Isn't this all a bit of an over-reaction? I mean in a ranking of a list of threats to birds, surely cats would not come that highly?

Indeed. The RSPB, notably, says "there is no clear scientific evidence that such [cat-caused] mortality is causing bird populations to decline" and focuses instead on the impact of global warming, intensive agriculture and expanding towns and cities. But nevertheless, thenumbers of birds killed in the UK are enormous. One study estimated 160 to 270 million animals annually, a quarter of them birds.

Don't a lot of owners keep their cats indoors anyway?

In the UK around 70 percent of owners let their cats roam outside. That percentage is almost reversed in the United States, where 70 percent keep them indoors, less because of threat to wildlife and more because of concerns about coyotes and traffic. Some may also have been influenced by the 2016 book by ecologist Peter P Marra, Cat Wars: The Devastating Consequences of a Cuddly Killer, which begins with the story of the Lyall’s wren, a small, flightless bird that once lived on Stephens Island, New Zealand, but was made extinct by the arrival of Europeans with their cats.

What wildlife is at risk in Scotland?

As well as birds, bats are also significantly preyed upon by cats, and across the UK around 250,000 are killed each year. The endangered wildcat has also long been impacted by the presence of domestic cats. Once widespread, they have been driven to the verge of extinction by interbreeding with domestic cats, as well as habitat loss and hunting.