Why cats present dead mice to their owners
Paul Leyhausen proposed that cats adopt humans into their social group, and share excess kill with others in the group according to the local pecking order, in which humans are placed at or near the top. Another possibility is that presenting the kill might be a relic of a kitten's behavior of demonstrating for its mother's approval that it has developed the necessary skill for hunting.
I’vedeveloped the idea further. Humans frequently keep cats to kill vermin, notably mice. Presenting dead mice shows the owner that the cat is a good mouser. The owner is therefore more likely to keep the cat and other people will want kittens from it. This behaviour may therefore help the cat to survive and reproduce. Over a sufficiently long time cats may evolve a tendency to present dead mice and rats but avoid presenting birds.