I was going to comment about this in another thread but then got distracted. The member in that thread lives in Hawaii and his almost always outside cats are always busy killing the rats. In Hawaii rats have been a huge problem. Some of the birds found no where else on earth went extinct because of the rats. They tried introducing mongoose to control the rats but it didn't work and the mongoose became a problem. The one thing that has worked is cats. So in Hawaii the cats are preventing the rats from overrunning everything. The rats came on the early sailing ships that first visited the islands and with no natural predators became a huge problem.One aspect of this debate is cats impact on the environment, and the belief that cats are not indigenous and do not belong in the natural ecosystem.
The problem with that is like most things it has some grey areas and is not black and white.
Cats have been a part of the European ecosystem as long as agricultural has been in practice, and for thousands of years they coexisted with wild life quite nicely. And anywhere there is rats, whether they are indigenous or not, cats may be an essential component to maintaining a balance. We have rats here, and the rats eat whole nests of baby birds and probably other things we would rather they didn’t and as 90 percent of what a cat catches is rodents, in this area I think the cats probably do more to save the lives of birds than they catch.
And there is things people can do to help protect birds from prowling cats, like ensuring areas likely to attract feeding, bathing, drinking birds are raised and open and have no cover for a cat to sneak up.
I think it is more a question of how many cats is a good number to maintain a healthy balance, but like it or not, if your ecosystem has rats, outdoor cats are probably an essential part of the equation.
For people who live in rural areas their cats are almost a necessity. We often refer to them as working cats. Most of the animals in a rural household are some type of working animal. The dog that greets you when you get out of your car is doing his job. He announces to the resident that someone is visiting. He probably also helps keep track of the kids, if there are any and may even herd chickens and sheep. The cats do their part by keeping vermin at bay. They work for a living and truly enjoy their jobs. The goats running around are probably there to help keep the weeds and undergrowth mowed down. So the majority of those living there are working to help in some capacity.
My cats are mostly working cats. Some of them don't want to go out much anymore, they don't like having to confront the feral cats and they don't like fighting. But most of them do go out for a while and some are outside all the time. They rarely get birds. I can tell because when they do get one they leave behind the feathers. I can usually tell what kind of bird they got. It's almost never the ones that like nesting here. Their main prey is small vermin. Mice are on the top of the list. They sometimes share those with me. Also ground squirrels and small rabbits. The Missouri river is just 1/4 of a mile from me with dense trees along the river bottom. But none of the little problem critters that live there are here, because my working cats keep them at bay. They do not destroy the environment, they help keep it in balance. I sometimes lament that they don't hunt deer. Maybe I need a bigger kitty. Much bigger.