A curiosity is that the probable birds in PR101 appear to be flying in a direction perpendicular to the length of their linear formation. I spent some time trying to find an example of that online, with no luck. Then I noticed...
In my video above, the linear formation of geese
also appears to be flying in a direction perpendicular to the length of their linear formation, relative to closer stationary objects (a powerline and branches) in the frame and to the camera frame, wherein they are moving left to right, or eastward, despite the fact that their bodies point (tail to head) almost perfectly northward.
So these geese seem to be flying sideways. Maybe that's an optical illusion or maybe strong winds can push birds perpendicular to the direction they're trying to travel. And perhaps geese fly in a line, not V shape, depending on such wind conditions.
So the birds in PR101 might be oriented just like these birds, possibly by winds blowing them sideways (perpendicular to their linear formation) or it might be an illusory parallax artifact of the aircraft's motion. A number of potential variables are in play.
Sorry for how shaky the video is, it's hand held at high magnification (the camera's zoom goes to 83x optical).