Are Feral Cats an Invasive Species?

Are Feral Cats an Invasive Species? I'll put it this way, the ones who wiped out the birds in my neighborhood certainly are. My mockingbird and bluebird nesting pairs were reduced to a few feathers. My rock doves who regularly visited my back yard for years haven't been seen in about ten years. Invasive Species? I won't take this without fighting them, will you?