I live on the Big Island in the winter. The feral cat population is unreal. People have an organization and they spay them and give them medical care and send them back in the wild.  They are all over my community. If they gave something to de-flea them it doesn't work because they are covered with fleas and they take them to every tall grasses and shrubs they hide in. Of course they eat the native birds but then again they eat the rats too. Since they eat the extensive rat population that hide in the cane fields maybe, just maybe I am a fan. One good thing a lot of the forest birds live in the higher elevations where the cats don't go.