We had a problem with one of our cats killing birds. (Watched out the window one time as he waited stealthily under the low branches of a tree waiting for the opportunity to jump up and grab a victim) We tried many different collars so we could put a bell on him to alert the birds, but without a lot of luck. He would always come home without collar and bell. We kept trying, though, until he finally got older and lost interest in or the ability to catch the birds. Good luck.