Well, almost all. Very small insects fly in air that's like swimming through treacle to them, but for most everything else, from bees to baracuda, one number describes the beating of wings and tails.

A quantity called the Strouhal number measures how efficiently an animal cruises. The number describes how much up-and-down movement a wing or tail makes relative to a creature's forward speed. It is calculated as stroke speed multiplied by size, divided by forward speed.

Flying and swimming is most efficient at Strouhal numbers of 0.2-0.4. The cruising speeds of everything from bumble-bees to blue whales, via mackerel, locusts, pigeons and bats, fall in this range, Taylor's team finds. Bumble-bees go faster than whales, at about 30 kilometres per hour to whales' 20.