Well, sharp and in focus are two completely different things.
Here is an article about heat haze. If you look about a third or so down the article under "What is Heat Haze?", you will see an image of a range rover in a field of grass, along with a cropped version. Look at that and look at your owl photo and see if it matches. Yours, obviously is more blurry, but see what you think. I'm not completely convinced that this is your issue here, but it seems the most likely to me.
Heat Haze in Photography