An animal charity says cat owners need to “take responsibility” for the suffering their pets cause to wildlife.
South Essex Wildlife Hospital said it is treating up to 60 animals a day, mostly birds, which have been attacked by cats, of which about half die.
On Facebook, it urged people to keep their cats indoors to stop the “daily slaughter” and “ecological disaster”.
The post has attracted hundreds of comments with many cat owners saying it is cruel to stop them going outdoors.
The hospital described the deaths of 37 birds in a single day as a “hoard of sacrifices to the cat gods” and said the charity’s volunteers were upset and stressed.
The charity’s founder, Sue Schwar, said: “Cats are lovely animals. They’re very graceful, intelligent and comforting to us but, out in the wild, they think they’re tigers.
“Our native wildlife hasn’t evolved with them so they do a lot of damage by climbing trees and raiding nests.
“I’m not saying they necessarily have to be shut indoors. A lot of people are turning to building enclosures for their cats or training them on harnesses.”
Responding on Facebook, Chrystal Weatherley said: “Find it very strange that an organisation who loves animals is advising cat owners to go against nature and keep our cats in. How cruel would that be?”
Another user, Jan Payne, commented: “How would you like to be kept in all day? It’s nature pure and simple”.
There are about 8 million cats in the UK and animal psychologist Dr Roger Mugford thinks owners should restrict the time they are allowed outside.
He said: “They’re committed predators. They’re hunters but they don’t have to be – they can play and be entertained by their owners instead.
“And it’s quite unnecessary to let cats out to do this hunting during this first three months of the spring.”
The advice from the RSPCA is for cat owners to “restrict outdoor access at dusk and dawn when wildlife is most active – and to attach a bell to a quick-release safety collar.”