Interesting. I must have misremembered what the AI told me back in March, when I asked about a similar gap in a Turkey Vulture. Here's what it (Gemini) actually said:

That "gap" is a fantastic detail to spot—it’s actually one of the most interesting parts of raptor aerodynamics. Depending on exactly where you're looking, it's either a Molt Gap or a functional feature called Wing Slotting.
Based on your photos (especially image_f8cb1d.png and image_f8cb00.png), you are likely seeing a combination of both.

1. The "Molt Gap" (The Missing Feather)

If you notice a clear "hole" or a missing section in the trailing edge of the wing where a feather should be, that is a molt gap.

• The Process: Large birds like Black Vultures can't afford to lose all their flight feathers at once (they'd be grounded). Instead, they drop and regrow feathers symmetrically one or two at a time.
• The Timing: In Pennsylvania, vultures typically molt their primary feathers during the spring and summer. A gap in the wing is a sign of a healthy bird refreshing its "flight gear" for the season.

2. Wing Slotting (The "Fingers")

The smaller, consistent gaps at the very tip of the wing are called slots. This isn't a defect; it's a high-performance aerodynamic design.

• Aerodynamics: These "slots" are created by emarginated feathers—feathers that are physically narrower at the tips. When the bird spreads its wing, these tips separate to act like "mini-wings" or winglets.
• Reducing Drag: Just like the winglets on a modern Boeing or Airbus, these gaps break up the large, energy-wasting air vortices that form at the wingtips.
• Tight Turns: This allows the vulture to soar at very low speeds and make tight turns in small thermals without "stalling" (losing lift and falling). Without those gaps, the vulture would have to fly much faster to stay in the air.

How to tell the difference in your shots:

• If it looks like a "comb" or fingers: That's natural slotting (the emarginated primaries).
• If there is a distinct "window" or a missing "tooth" in that comb: That is a molt gap.

The hawk in Image 2 definitely has the missing comb-tooth look.

So, I guess I was thinking of wing slotting, but this one has a molt gap.

Glad you caught that. Thanks!

Also, I just went back to the original photo. There are 11 others of the same bird at the same time. That's at least 2 separate bursts, and the gap wasn't being adjusted. They all show an identical looking gap. So I definitely agree that it's missing a feather or two there. Useful info for comparimg to other hawks around the same time, and it makes it more likely that these two birds are different, though the feather could have been lost between photos.