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Hummingbirds are masters of the air — unique among birds for their ability to hover for long periods of time. Using a sophisticated digital imaging technique, scientists have determined the aerodynamics of hummingbird flight. These latest data disprove conclusions from numerous earlier studies that hummingbirds hovered like insects despite their profound muscle and skeletal differences.
The team found that hummingbirds support 75 percent of their weight during the wing's downstroke and 25 percent on the upstroke — in contrast to insects, which produce equal amounts of lift during their down- and up strokes.
In the study, the researchers applied digital particle imaging velocimetry (DPIV) to follow the flapping wings. DPIV is used in various applications to study flow characteristics of liquids and gases. Images taken with a computer-coupled camera lighted by a laser, the distance traveled by individual particles seeded in a liquid or gas can be tracked through successive images.
DPIV allows the researchers to follow the particles' movement image by image, like looking through the pages of a high-tech flipbook.
To observe the hummingbird in flight, the air in a wind tunnel was seeded with microscopic particles of olive oil, and digital images were captured every 300 microseconds as the bird hovered at a feeder. The wing beats caused the air to circulate, which in turn caused the floating oil particles to move. Computer-aided image analysis of each oil particle's position in consecutive frames allowed the scientists to reconstruct the lift and characteristics associated with each up and down wing movement.