I thought that was what the IR in the RGB+IR metering sensor was about. It will track warm bodies, so if it is temporarily obscured, or against a cluttered background, it will still stand out and be trackable.
Then again, I could just be making things up, as I don't think Canon has ever said how they use the IR data. I seem to recall someone shooting baseball, and being impressed with the tracking still working when the players moved behind some netting, which just reenforced my idea on how the IR is being used.
Assuming my IR idea is right, your owl might be too well insulated and not show up strong enough for older bodies. (I'm definitely into the realm of just making stuff up now!)
edit: http://infrared-birding.blogspot.com...d-birding.html