The Birds and the Bats

Two groups of modern vertebrates, the birds and the bats, have mastered flight. They do it very differently, though. Geoffrey Spedding, a University of Southern California professor of aerospace and mechanical engineering (in other words, a professor at my alma mater), reported on wind tunnel studies by writing, "Bats seem to be mostly specialized for agile and maneuverable flight in complex environments." Bats have a complex twisting motion that provides some lift on the upstroke, while birds rely almost entirely on the downstroke.