I've been pondering this.. and I wonder if the answer lies in how we treat cats when they are young.. both of mine didn't really get access to the outside till they were relatively old compared to usual. My girl was from a rescue centre and was scared of everything so never wanted to jump the 2 foot out of the window of the flat I lived in till she was ~5yrs old as this would have been a leap into the unknown so even tho the windows were frequently open and there was a catflap in the window (from my previous cat a much more adventurous type) she never went out. My boy, who I got 6 months after i got her as a tiny kitten, could also never get the hang of the window catflap, and as a result didn't go out till he was fairly old either and then initially only for a few hours a day when i was in and could leave the window open. They are both, frankly, useless hunters, I get a bird or 2 in fledgling season and that's all and i really doubt they're on a killing spree the rest of the year and not bringing the kills in (for a start, the killing part seems to mostly elude them, I've released most of their catches), and I wonder if the reason for this is because they weren't out an about at a critical time for training for this?