I think if any bird were to swear, it would definitely be the Townsend’s Solitaire. In winter, when they move to lower elevations to feed on juniper berries, they do not like to share—no matter if it’s a small patch or a much larger area covered in juniper. And it doesn't seem to matter if the other birds are members of its own species. In the mountains, if you want to locate this thrush, go to an area with juniper berries, or if you come across Bohemian Waxwings away from urban areas, there’s a good chance there are juniper berries nearby—and one very ticked-off Townsend’s Solitaire. It will be calling out, making aggressive gestures with its wings and tail feathers, and going after individual waxwings as they try to eat the berries. Just last week, I could see and hear several hundred waxwings, but I could also hear one very agitated solitaire.
In the picture with the solitaire, its territory includes two patches of juniper berries. One is above the road, out in the open, which it has to defend from the waxwings. But this evening, toward the end of the day, it was feeding on berries hidden by the woods. When it needed a break, it would perch on one of three spruce trees while light snow fell. With an overcast sky and lack of light, I was able to get this picture with a blue-grey cast.