Flap-bounding redpolls

The Sun came out; the birds came out; I came out — and took a distinctly odd picture. We are used to seeing folded wings on perched birds, and extended wings on flying birds. But, this shot shows folded wings on flying birds.

I was watching a flock of redpolls. They would alight on a bush, feed on seeds, and then abruptly take off all at once only to fly to an adjacent bush.

As do many small birds, redpolls use flap-bounding flight. Flight follows an undulatory path where birds flap through the troughs, and fold their wings to bound across the ridges where they follow a nearly ballistic trajectory. It is called bounding flight because it resembles the bounding gait of leaping earth-bound animals. Apparently such a flight pattern saves energy and allows birds to fly slower than their normal cruising speed. 

This view shows redpolls feeding on seeds before taking to the air once again.

As redpolls spend half their flight time flapping and half bounding (with folded wings), a typical view of them flying shows about half in each mode.

At one point, a distinctly odd image was captured where almost all were bounding. I suspect that there is a simple explanation. Birds take off together, and all start by flapping. Before they get out of synchronization, most will then begin bounding at the same time. A picture taken at that moment makes them look like a shoal of fish.