From Scientific American:
Previous investigations into the flight of the hummingbird had suggested that it could be employing the same mechanisms as insects, which often hover and dart in a manner similar to the bird. “But a hummingbird is a bird, with the physical structure of a bird and all of the related capabilities and limitations,” explains Douglas Warrick of Oregon State University. “It is not an insect and it does not fly exactly like an insect.” To unravel the hummingbird’s aerial secrets, Warrick and his colleagues used a technique called digital particle imaging velocimitry (DPIV). Usually employed by engineers, DPIV uses microscopic particles of olive oil that are light enough to be moved to and fro by the slightest changes in air currents. As a pulsing laser illuminates the droplets for short periods of time, a camera captures them on film. From the resulting images, the scientists determined exactly how the bird’s wings move the air around them.