You probably know this anyway Specki but put the baby bird outside so the mother can see it's dead. When I had cats I had a distraught mother bird ouside until I put the dead baby where she could see it; she then went away. I have a cat pen and when I used to have cats I used to keep the cats in when I knew the birds had fledged. One day I went into the garden to see how the young birds were getting on; I scared one of them and it flew though the mesh of the pen, straight into the waiting mouth of one of my cats [I still feel bad about it years later]. I had a cat that was a silver tabby at the time, and I'd read that they were the worst of their breed for killing birds [she was a British Shorthair] and she certainly lived up to her reputation.