Bells and bibs such as the Birdsbesafe(TM) have proven effective in reducing the number of birds cats hunt, but they don’t eliminate hunting entirely. A study in the UK compared the hunting of cats with no bells, cats with bells, and cats with an electronic sonic device. It found that cats equipped with a bell or bells captured 41% fewer birds, and the cats equipped with a sonic device caught 51% fewer birds. The results for the Birdsbesafe(TM) collar were similar in an Australian study; it reduced bird predation by 51%. Another study showed the Birdbesafe(TM) collar reduced hunting success by between 70 and 94%.
So bells and collars do reduce hunting success. They don’t work as well to protect young birds who haven’t yet learned to be cautious about cats, or to fly well enough to get awway. And adult birds who are protecting a nest are likely to take on a cat even if it is wearing a bell or collar. It must also be noted that while they do keep birds somewhat safer, they do absolutely nothing to protect the cat from other cats, stray dogs, wildlife, cars, diseases, toxins, or any of the other risks of free roam.