Welcome to TCS!
Mu grandpa has been a farmer most of his life, stopping only because he couldn't physically do it anymore at 88. he has told me that the females are the ones who catch the rats. males normally don't bother trying to catch them because they are too viscous.
my old cat Muffin, she killed a number of mice in her life (she was on a leach too), while my cat Leo has caught 4 mice, and they are all still alive.
so I do think it is the need to provide for and protect the kittens
This thread is from 2006 originally; I'm not sure how many of the posters are still active now. Please come introduce yourself and your kitties over in our New Cats on the Block forum too: http://www.thecatsite.com/f/20/new-cats-on-the-block. We love pics of kitties too if you'd like to share any!