Two of the tormenting treerats.
A family of probably 6-8 of them lives next door, and every morning they come over to torment Gus. I do believe they know he gets in trouble for barking at them, and intentionally taunt him. This seems to be one of their favorite things to do. The older treerats are not as spry as they once were. The younger ones will distract Gus by running down the pole and perching on the top of the fence, then the older one sprints across the power line. They are both getting in position here, and what you cannot see is Gus barking his head off from the ground directly below.