There are people whose main job it is to shoot feral cats on San Clemente island in the USA, too, to protect the native shrikes and other birds.
There used to be a lot of goats there, too, and many were airlifted off rather than killed on the island, due to public outcry (how many of those complaining were willing to adopt feral goats, I wonder?).
Cats are wonderfully interesting creatures, and also dreadfully ferocious slaughter-bots of the local songbirds around my house. I would rather have the birds and a few more rodents. Please keep your cat(s) inside, take them outside on a leash, or don't adopt them in the first place.