When a cat attacks a bird or mouse what is the kill ratio When a cat goes after a bird or mouse, the kill ratio—meaning how often the cat actually kills what it catches—can vary quite a bit depending on the cat and the situation. Studies suggest that cats don’t always kill their prey. In fact, many domestic cats engage in what’s called surplus killing or play hunting, where they catch prey but don’t kill or eat it. That said, when they do go in for the kill: Success rates for birds are generally lower than for rodents. Birds are quicker and more alert, so cats may only succeed in about 10–30% of their attempts. For mice and other small mammals, the success rate is higher—often 50–70%, especially if the cat is experienced or feral. Interestingly, cats don’t always hunt out of hunger. Even well-fed house cats may stalk and pounce just to satisfy their instincts. And while some cats are ruthless little ninjas, others are more like clumsy hobbyists.