Zoology: Universal laws rule animal fin and wing propulsion

All animals that have the ability to swim or fly, regardless of their species or the mode of movement that they use, bend their fins and wings following a universal common pattern, reports research published in Nature Communications. This work suggests that it is not a coincidence that, during steady motion, the wings of an airborne monarch butterfly bend in a proportionately similar location and to a similar maximum angle as, for example, the tail of a swimming bottlenose dolphin.

The way in which animals bend their fins and wings is believed to contribute to the efficiency of movements. It has been suggested that recreating this artificially could, in theory, improve proficiency of swimming and flight outside of the animal kingdom. However, whether recreating animal motion patterns in manmade devices would in reality increase motion efficiency remains inconclusive, mostly due to the lack of consensus regarding bending patterns.

By analysing video sequences of animals flying or swimming, Kelsey Lucas, Jack Costello and colleagues investigated whether a common pattern can be seen in relation to the way that wings and fins bend during motion. They find that, universally, fins and wings bend within very constrained ranges of flexion ratio and angle and the size of the animal, fluid medium (air or water) and type of animal does not significantly influence this bending pattern. They suggest that flexion ratio and angle are variables that were most likely selected independently in each species through evolution, despite a similar final outcome across the animal kingdom.

These results provide a new framework from which to understand and design flexible mechanical devices.