A study in the Proceedings of the Royal Society B finds that pigeon wing-flapping produces distinct whistles, which can warn flock-mates, when merely taking off or when actively escaping predators.

But the ability that a lot of engineers would really like to put into robots is the flapping-wing flight of insects, with its attendant ability to hover.

The flapping wing represents a small change in the initial condition of the system, which causes a chain of events leading to large-scale alterations of events.