Experienced birders can often identify a bird after seeing only a flash of movement. The way a bird moves from perch to perch, how it uses its tail and wings when landing, the spring in its step — all can trigger recognition.
Any birder should be able to appreciate this point. You only need to think of a woodpecker or hummingbird to realize that you already know two types of birds with distinctive and instantly recognizable movements. Chickadees, jays, wrens, doves, sparrows, thrushes — each group has its unique gait and style.