What a startling photograph that is of the osprey, et'! So, mantling does look like a hover, as I'd imagined, only in the case of the photo link you gave, the osprey's position is a stationary hover. Since the photolink mentions "chicks," I take it that the osprey is mantling over at least one very large chick--its feathers appear to be the same as the adult with the piercing eyes.

I've seen ospreys on the Outer Banks (NC) carry sticks in their talons for nest building. They carry the sticks with aeronautical sense: fore to aft. Many thanks for the link to that unforgettable photograph!

Too bad the heraldry information didn't suggest that sometimes feathers were used for the mantling in a coat of arms, although greenery was mentioned as being usual. How delightful! I think I've just learned my first heraldry term!