For the past week or so we have had an American robin (male) coming to our bird feeder. They don't usually come near our feeder because it has nothing they eat, but this one seems to like digging around in the soft soil around it. He has been aggressively defending the area, which is something I've never seen a robin do before. He dives at everything that comes close, from cardinals to mourning doves to sparrows. At one point a whole flock of blackbirds landed in the yard and he tried (unsuccessfully) to guard the small spot of soil from the whole flock. He has even gotten into physical altercations with mockingbirds. Is this normal? All the robins I have ever seen seem to tolerate other birds and don't monopolize one spot. It is also winter here, so I don't think it has anything to do with breeding ground territory. He struts around on the ground and puffs up his chest continually, even when there aren't any birds nearby. I also haven't seen any other robins in the area recently, so he seems to be alone. Does anyone know what is going on here? Is this typical behavior I just haven't noticed before, or is this something strange?