Read the entire thread. When I started, the infestation of Tree Rats was so bad that the numbers were probably between 375-400 per year, but I wasn't keeping accurate records then. Once I started keeping accurate records, I *think* the most TRs was 322, but I can't say for sure. As for the chippers, my best year was about 75.
Now, they are relatively under control, as long as I keep eliminating them when I can.
Keep in mind that my entire lot is only about 1/5 of and acre and I only shoot in the backyard which is less than 1/10 of an acre. So that should let you know how bad things were before I started.
The chippers are harder to take not only because they are small, but I simply don't get as many chances... and they cause more problems than the TRs because they will burrow under and into my crawlspace and rats will use these same burrows to enter.
So far this year...
TR = 53
CH = 35
I have definitely been successful at lowering the populations in my VERY small yard. However, the ONLY way to keep it that way is to stay vigilant every year. Otherwise, at least where I live, they WILL regain their population in one season or less.