We have a small lot in Los Angles County.  There is enough room on it for our house, an avocado tree and the a sand box for out children to dig in. As soon as the sand went in we discovered that a the neighborhood was full of cats.  We asked all over the neighborhood and no one would admit to owning them and we could not see a collar or other identifying mark on them.  We called the Los Angeles Animal Control and they came out and after doing their own investigation set out traps for the cats.   The neighborhood is cleaner and birds are starting to come back.