Really, it's a bird.
Living in a rural area can be a hoot. We love watching the animals and their antics. This window splatter was caused by a bird flying into one of our picture window. The detail is amazing, you can see feathers, the long beak and the head tuft. I believe it is (was?) some kind of wood pecker.
On another window there is a chickadee that likes to fly into it repeatedly. It will fly into it, get up fly in a circle and slam into the window again. After two times, it rests for about five minutes then repeats the process. He will do this for hours. Well, you know what they say about "bird brains".