Captive, non-native animals, such as housecats, have a huge detrimental impact on native wildlife.
We have a large garden. Four years ago we foolishly got a kitten for a child's birthday. Despite collar bells etc., the following spring it slaughtered every nestling in the garden, even climbing into bushes to rob nests.
Swallows and house martins nesting around the house were easily plucked from the air. Stoats, weasels and dragonflies were no match for this killing machine.
"Sadly", last autumn it met it's match with a passing car. This spring we have loads of baby birds once again.