After we'd been feeding Notch for a few weeks, another squirrel showed up. It was early December, and according to other squirrel sites on the web, that was mating season. Since we'd been calling Notch "he", we decided the newcomer was "she", and since she had no ear notch, Dave dubbed her "Nonotchka". (We later found out that Notch was also female; when you see a male squirrel, their gender is quite obvious.)
Notch usually chased Nonotchka away from nuts, but at other times we saw them playing together in the red oak or sharing space on the fence.
Nonotchka is smaller than Notch, with longer ears and a somewhat thinner tail. At first she was nervous about taking our nuts, but she became much more trusting than Notch, and would climb up on our legs or scratch at the office door when she was hungry. She was the most friendly and trusting squirrel we've had visit.
Alas, after we'd known her about a year, she became pregnant and had a litter, and while she was caring for them (still visiting us regularly), she was injured (a long scratch on one leg, perhaps from a close encounter with a cat). It became infected and she had trouble getting around. We tried to make things as easy for her as we could, chasing away Notch and the other squirrels to make sure Nonotchka got enough to eat, and the scratch seemed like it was getting better ... and then she disappeared. We never saw her again. RIP, Nonotchka. We miss you.