Black Squirrels

It has been a long time since I have seen a black squirrel in Pennsylvania were I live or hunt. When my family took a trip to Niagara Falls they were all over the place. When I was 12 or 13 years old, hunting squirrels with my father, I saw one (my first sighting of one). That all changed two years ago. Everyday on my way to work, I would look in this yard were I first saw the squirrel. Sometimes I would see it and sometimes not. Well yesterday driving by the same yard, I saw it again. But know there are now 4 of them. I just thought is was pretty unusual to see them in the place I live and not in the real wild. I would like to know if anyone else has seen any black squirrels lately?