In our part of the country, the squirrels are special.
There are few trees big enough for them to nest in. The ones who do nest there don't last for long. They live in burrows. I have a small canyon next to my house. Other than that, there is very little habitat for them, and a lot of coyotes, their main predator. If we hit the populations in the canyon early and often, we can limit the number greatly because they will not pass over great distances of bare ground to expose themselves. We do have new ones from year to year, but no great population explosions.