Ah; interesting point! I know that hawks sometimes lose a feather that gets tangled in a barb during landing or takeoff, and they molt a feather or two at a time so they don't interrupt their flight control too much. I didn't think they could spread their non-wing-tip feathers quite so much. (And I now know that's not accurate; they actually can't spread those feathers - see below, where I've detailed some of my research.)

Just to be sure, I looked it up and found out that movement in the secondary flight feathers is not an action like us spreading our fingers—not for those feathers, anyway!

According to a Gemini search summary, those feathers are controlled individually and involuntarily by a group of muscles connected to one follicle per feather. These muscles help adjust the "camber" of the feather. This adjustment intentionally does not allow for feather separation the way we see in that photo because those feathers serve as an airtight sail by interlocking, and moving together as the camber is adjusted; fascinating!

Tiny specialized sensory feathers called filoplumes help sense and react to various changes in wind to make these tilting adjustments across the secondary feathers automatically. Interestingly, red-tailed hawks evidently have "many spectacularly long filoplumes associated with a single flight feather".

So it seems that is almost certainly a missing or broken feather!

And Oh My Goodness! there is a lot of information about feathers. Maybe we should do a series just on feathers—it would last a long time!