I should have known he wasn't working alone. There's a second squirrel who was zipping around the walls of the coop when I went in this evening. His girlfriend? His brother? His godfather? (have I just miffed the squirrel Mafia?)
Archie the Wonder Dog was on full alert but unable to catch Ninja Squirrel 2. But I could see him shaking his paw in frustration and saying, "Just you wait, I'll get you next time, Ninja Squirrel 2 ... I'll get you". Or maybe I just imagined that part. Still, it does seem that it would be a good melodramatic ending to the day.