Cats. They are everywhere. Prowling down dark alleyways. Stretched out, sunbathing, atop garden walls. Leaping from the highest branches, using up every one of their nine livesThe idea that cats have multiple lives is a common myth in many countries. In Arabic traditions, they have six lives and in Germany, Greece and Brazil they have seven. .

Some slink back to their homes at night, the bells on their collars ringing gently as they fold through the catflap. Others, wild bands of feralWild or untamed. cats, stay out permanently - approximately 125,000 strays call the streets of Istanbul their home. 

Some people find it charming. An army of furry friends across the city, a mascot for every street and every neighbourhood. There is no doubt: humans adore cats. We have kept them as pets for millenniaThousands of years., and today we own hundreds of millions of them. They make for some of our most beloved characters, from Puss in Boots An Italian fairy tale about a cat who uses trickery to gain power. to DoraemonA fictional character in a Japanese anime and manga series. Doraemon is a robotic earless cat who travels back in time from the 22nd Century. . We upload hours of videos of them to YouTube and visit them in dedicated cat cafes. 

But wildlife lovers argue that the cats roaming freely through the world's towns and cities are an environmental catastrophe in the making. People forget, they say, that the furry felines of today are descendants of the Near Eastern wildcat, a fierce and solitary hunter. 

Many domesticated cats have retained this killer instinct: in the UK alone, cats kill up to 27 million birds every year. In the USA, the figure is four billion, with a staggering 22 billion small mammals also in the firing line.

The problem is not a new one. As long ago as 1894, a cat named Tibbles was blamed for single-handedly wiping out a small, flightless bird on Stephens Island, New Zealand. Half a century later, in 1949, lawmakers in the US state of Illinois passed a bill curbing cats' freedoms. The bill was later vetoed by the state's governor, who said officials had more important problems to focus on than "feline delinquencyWrongdoing and lawlessness.". 

But today, attitudes are changing. More and more nations are becoming strict on cats. As of last Octobre, felines in Melbourne, Australia, face a curfew that prevents them from leaving home. In the German town of Walldorf, cats are placed under strict controls during the breeding season of the rare crested larkThe crested lark makes its nest on the ground, making them vulnerable to predators. ends. Last year, Poland classified domestic cats as an "invasive alien species". 

Some are arguing for a more drastic solution. In 2016, the authors of Cat Wars declared that the "cuddly killers" should be reined in "by any means necessary". Neutering programmes, argue Chris Santella and Peter Marra, are not enough. Instead, euthanasiaThe deliberate and painless ending of a life. is essential to bringing the feline population down.

Their arguments ruffled many feathers. One reviewer called the book "sensationalist, one-sided [and] utterly anti-cat". 

And some say the danger posed by cats is overstated. Even Britain's Royal Society for the Protection of Birds agrees that the birds killed by cats are likely to be weak or sickly. "If you were to draw up a list of challenges facing our native wildlife," declared one RSPB official, "cats would not be near the top." 

Yes: Cats are a conservation nightmare. They kill small birds and mammals at an astonishing rate in both cities and the countryside. The world is finally waking up to this problem. 

No: Cats bring great joy and companionship to millions of people across the planet. And anyway, birds face bigger problems - like climate change, habitat loss and illegal hunting. 

Or... There is no need to reduce the number of cats in the world. But to protect wildlife, they should be kept indoors. Anyone who wants to take their cat outside should build a catio or buy a lead.