A couple of years ago, I had a chance to borrow a very expensive infrared camera for a couple of hours. Here are a couple of shots taken late at night. This was just before the young fledged in 2008. In the first, Momma is looking out of her box on the tree:
In the second, Papa has just buzzed my head and landed on a branch. Notice that the brightest yellow is the warmest area of his body:
I could track them in flight on the camera screen but could not record fast enough unless they were stationary. It did allow me to figure out where they were hunting and when they were returning to the box to feed the owlets. I wish I could afford the really fast model!!