Andthing to deter my cat from murdering?

Ok, so my one true love (Pumpkin), has been hopeless at catching any kind of animal, including mice, for the last 3 years. I was happy with that. I thought it was because she was too loved to resort to violence and had plenty of food anyway. (she is just a tad chubby) but she's caught a couple of birds recently, also some mice and a poor bat. =( I know she's a cat, but is there Anything out there to stop her catching the birds? We live in the country in a safe place where she can go outside, and she never strays from the house/garden/shed area anyway so I don't want to keep her inside all the time.