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.
The results indicate that hummingbirds get 25 percent of their lift capacity from the upstroke beating of their wings; the other 75 percent of the lift comes from each downstroke. Insects, in contrast, divide the work equally, getting 50 percent of the lift from each, and other types of birds rely solely on the downstrokes. "What the hummingbird has done is take the body and most of the limitations of the bird," Warrick says, "but tweaked it a little and used some of the aerodynamic tricks of an insect to gain hovering ability."