I've been feeling guilty about our 4 barn cats, all of whom live outside. The cats are thriving, but I understand that they might not be helping the local bird population. I just can't bring myself to not let them stay outside. The good news is that our barn has 4 or 5 barn swallow nests that turn out several batches of chicks each year. The adult swallows get aggressive when any of the cats walk below a nest.