In reply to Tom Valentine:
A couple of things occur to me (and I've also spent the last week being mesmerised by lapwing displays). The first is that the actual changes in absolute velocity are probably less than they seem. We tend to visualise speed by scaling to the size of the animal and imagine what that would be if it were a sports car or a fighter plane, but that isn't how physics works. I often marvel at the manoeuvrability of dragonflies. How can they possibly stop from full speed and instantaneously reverse? It seems impossible, but, just in terms of the forces generated, are they actually changing velocity so much quicker than you can? Obviously, if an aircraft could do the same scaled up velocities in terms in body-lengths per second, the forces would be unsurvivable. Actually, doesn't f=ma tell us the same thing?
Second, even if some very large forces are generated by small animals, (like a flea, for example), as well as having small masses, they are disproportionately strong compared with human scale musculoskeletal structures (because cross-sectional area increases as the square of length, and mass as the cube).
So lapwings, dragonflies, peregrines, gannets and woodpeckers are amazing (and gannets and woodpeckers have specific adaptations to cope with their brains decelerating) but not physical laws are being violated! Being small has its advantages.