Moving creatures tuned for efficient cruising, according to Nature vol. 425, p707, and Nature Science Update 16 October 2003. Flying and swimming creatures move through air and water with up/down strokes that create vortices (patches of turbulence). The vortices are left behind as the creature moves forward, but they can hinder movement of wings or tails if the upstroke occurs too soon after the down stroke, i.e. if wing or tail beats are too rapid. For most efficient flight or swimming the creature must generate enough forward thrust to leave vortices behind, but not move its wings or flippers so rapidly that they encounter the last vortice on the upstroke. The efficiency of flight or swimming is described by a quantity called the Strouhal number, calculated as stroke speed multiplied by size, divided by forward speed. Tests show the most efficient flying and swimming occurs at Strouhal numbers 0.2 to 0.4. A group of scientists at the University of Oxford (UK) have made a survey of Strouhal numbers for numerous flying and swimming creatures at their cruising speeds (including insects, birds, bats, fish, dolphins and whales) and found they all have Strouhal numbers in the most efficient range.
Editorial Comment: Now for the million dollar question. Since it took intelligent scientists to work out the mathematical relationship between wing /flipper size, stroke rate and speed and derive the ideal Strouhal numbers, calculate how much more intelligence it will take to design and build creatures that work at the maximum Strouhal numbers?
Give up? Well-tuned machines that work efficiently are an indication they were designed and built by an intelligent engineer. The fact that swimming and flying creatures all work within the rage of efficient Strouhal numbers is tribute to the intelligence of the Creator God who made them. (Ref. Strouhal, flying, swimming)