I think you're right about environments, Bee. When I lived in the Sacramento area, the climate was relatively mild - hot and dry in the summer and wet and mild in winter. The elevation was about 40 feet above sea level, and we rarely had frost or snow.
Now I'm in a forested area, 2,300 feet above sea level. We have coyotes and mountain lions to keep the feral cat population down, and we have snow two to five times a season. It's still a very moderate climate (and not as beastly hot during the summer), but I think the wilder environment keeps the cat population in balance. We have lots of songbirds. We also have lots of rodents, and I'm glad we have a four cats to keep the rodents in check (even though I am fond of only one of the four, and he's more-or-less useless in the rat control department). I suppose if we didn't have cats to keep the rodents in check, we'd have more rattlesnakes (the cats tend to keep them away, too).
Now I realize the rattlesnakes are an endangered species and all, but I'd rather not have them in the yard. I'm funny that way.

But in the city of Sacramento, feral cats could be a problem, and they really did have a bad effect on the songbird population. I'd rarely see birds smaller than magpies and jays, and the population of wonderful California quail* seemed to go down as the number of cats increased. It's all a matter of balance. If we humans are going to affect the balance by feeding feral cats, then I think we need to be responsible in sterilizing them and keeping them healthy. Seems to me you're doing the right thing, Bee.

-Joe-


*I was worried this year because I hadn't seen any quail - but last week, I saw several broods, a total of over 40 birds in the neighborhood. Made me feel a lot better.