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 now 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 down stroke and 25 percent on the up stroke--in contrast to insects, which produce equal amounts of lift during their down and up strokes.

Researchers from Oregon State University, University of Portland and George Fox University published the new findings in the June 23 issue of the journal Nature.

Co-author Bret Tobalske said, "We were surprised to find that the up stroke in the hovering hummingbird was much less active than the down stroke. This finding provides new insight into evolutionary trends that led to sustained hovering in birds."

This allocation of wing workload differs from that of other birds, which use the down stroke to support 100 percent of their weight during slow flight and short-term hovering.

Insects support 50 percent of their weight with each stroke. Tobalske pointed out that despite different ancestries hummingbirds seem to have adapted insect flight performance using a bird-like wing that flexes, twists and arches in ways that the rigid insect wing cannot.

Previous research to determine how hummingbirds stayed aloft employed high-speed video, but motion analysis alone was not sufficient to fully reveal the underlying aerodynamics.

In this 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. By taking pictures with a special computer-coupled camera lighted with a laser, the d
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Contact: Richard Vines
rvines@nsf.gov
703-292-7963
National Science Foundation
22-Jun-2005

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