Regarding Kris Hansen’s idea of opossums to deter rats: that’s an excellent suggestion.
The estimate of bird loss stated in her letter is truly disturbing. I wonder, though, if pesticides and herbicides that humans seem to feel they need to use have affected bird population. Birds need potable water, insects, berries, and seeds to eat, and safe places for their nests. All these things are affected by poisons that humans use.
Personally, I’ve had feral cats living happily by my house. I also had a very popular bird feeder. Never did I see a dead bird. The cats were way more interested in chipmunks, and never did I have a single mouse in my house.