This video is described online as a “sandpiper murmuration”. Murmuration is a colloquial term that is normally applied to flocks of starlings, not sandpipers. Regardless of the semantics, this is certainly a beautiful video of a flock of birds. Hidden in their movements the observer can clearly see the confusion effect. The confusion effect is the phenomenon whereby a predator becomes confused by a group of rapidly moving prey, making it harder for the predator to pick out an individual to attack.
Many species possess a countershaded color pattern characterized by dark color on the dorsal surface and light color (or a lack of pigment) on the ventral surface. In organisms that form defensive groups, this color pattern is often an adaptive trait because it accentuates the confusion effect. You can clearly see the birds using their light colored feathers to ‘belly-flash’ would-be predators. Try it for yourself. How long can you watch a single bird before becoming confused?