It was odd. Maybe the smaller bird was being chased by the larger and wasn't watching where he was going. I began to take a few shots of the grain elevator against the gray sky while my scalp recovered, and suddenly that bird flew straight toward me again. I snapped his picture as he approached, then ducked and he sailed right over my head.
Once again, as he turned away, I saw that he was chasing a smaller bird. I don't know if they were playing tag, and the tree was base, but the big, bad, bird was definitely "IT". Leaving the area, I snapped a few more pictures and hurried home, eager to see if I had managed to get a picture of the bird before I ducked. Sure enough. There he is. He's a little camouflaged by the tree behind him, but you can see the approach.
If he had looked over my shoulder, he would have seen this old railroad track---a much better landing strip than my head!
UPDATE: Since I wrote this, I talked with some friends and also did a little research. The bird is a "Mississippi Kite" a bird of prey like a falcon. It does chase smaller birds and it also attacks humans if it perceives them as a threat. I was probably within twenty feet of his nest, hence the attack. Here is a link that discusses the Kite as a bird that does, in fact, live in Oklahoma: http://oklahomabirdsandbutterflies.com/cat/3/20