From some quick browsing, it seems like most, if not all birds will rouse. It sounds much like it serves most of the same functions as a puppy dog shake - floofing up the feathers/fur, shaking off water/dust, or for some invigoration after a nap.

I also stumbled on this short article about it as part of a pre-flight behavior and how as a photographer to use this understanding as a tool to catch take off shots:

A raptor at rest will often perform one or more of the following behaviors just prior to taking off.

• poop (possibly a weight-saving device)
• wing-stretch (stretches flight muscles prior to use)
• turn into the breeze or wind (makes takeoff easier, so it requires less energy)
• rouse (shaking to reorganize out of place feathers, which makes flight more efficient)

All these things do line up with my own experiences watching birds.