In recent years, cats have become the biggest threat to the country's wildlife, killing tens of billions of animals each year, including pet and stray cats, feral cats, farm cats and other ownerless cats  Animal charities have suggested that collars with bells could be fitted to cats
Cats don't pay attention to the sound of bells when they are catching.
 Collared cats are at least a third less successful than other cats, leading to a dramatic reduction in the number of animals killed