When I was in high school I did a science fair project that involved mice. Honestly it was mostly because my school tried to discourage us from using live subjects and I felt the need to push the boundaries. One of the hoops I had to jump through was to present the proposal to the IRB at a local community college. One of the IRB's requirements was to define the disposition of the mice after the project was complete. I decided to keep them as pets. Those mice lived an additional three years if memory serves, and they were every bit as suitable as pets as hamsters, reptiles, or similar small animals.
The squirrels in my yard are basically outdoor pets - we regularly have a suet cake hung in their trees, and I made a permanent feeder for them that's kept full year-round. Our squirrels are... rotund. The ones I'm watching now are very young, and are the third generation that have lived on our property since we moved in.
In the fall, I hunt squirrels with my daughters. They're small enough that they're consumed in one or two meals so nothing goes to waste, and they're intelligent enough that they're very difficult to hunt effectively. We don't shoot the ones in our yard, though. Those are pets.
