I think this might be a good time to point out just how lousy Hill's sightings really were. These were brief, naked eye views of flying birds with very few details actually seen. No wing noise was noted.
The full field notes are here, but here are some excerpts (the bold font is mine):
Sighting: 5 January 2006 by Geoff Hill Transcribed from notes written immediately after sighting We left camp (Beavertown) at about 0610 and floated out to the [LOCATION WITHHELD] and then up and out to the Choct. We then floated down and up into [location withheld]. About 10 min into our paddle up [LOCATION WITHHELD] I saw a bird with a wingspan greater than a Wood Duck fly over my head and away from me. The time was 0638. The bird was not exactly like anything I’ve seen before. It reminded me of a small loon. It had a long neck and long tail. Wingbeats seemed rather stiff and shallow. Chet mentioned that it seemed too small for a cormorant. I agree that it definitely was not a cormorant but the stiff wingbeats were reminiscent of a cormorant. In the early morning light I could see no coloration. It was certainly not a duck of any species, not an anhinga, not a cormorant, not a heron. I am rather confident that it was an ivorybill. It flew at tree-top level over my head and dead straight away. It was in view for about 2 seconds.
Sighting: 21 January 2006 by Geoff Hill Time: 0955 Notes and drawing made immediately after sighting. Notes transcribed from handwritten originals. Naked-eye view. Bird flushed from about 30 feet (10 m) as I was moving noisily through a flooded tupelo/cypress stand. It came off a tree trunk about 3 to 5 feet from the water. I never saw it perched. Flight was strong and fast. It seemed not to need many wingbeats to cover the first 100 feet. It made no sound at all as it flew. With naked eye and the bird flying away I saw few details: jet black except wide striking white band on trailing edge of wings. It looked larger and longer-winged than a pileated. It flew about 300 feet and landed in a distant tree. I could see it going in to land but it disappeared completely from view as it did so. About 1 min later, just as I turned my video camera on, I heard a second bird from my right knock and then double knock. I may have captured this on tape. I did not detect either bird again.