Study Reveals How Hummingbirds Hover
Hummingbirds can hover for prolonged periods unlike most other birds. It has been assumed that they fluttered their wings more like insects than birds to maintain hovering position long enough to eat. But a new study challenges previous assumptions about how hummingbirds hover.
Researchers from the University of Portland and Oregon State University analyzed the movements of air around the wings of a rufous hummingbird to understand their hovering capabilities. They used digital particle imaging velocimetry (DPIV) equipment to measure the movement of tiny drops of olive oil in their air when the hummingbird was hovering at a feeder in a wind tunnel. The DPIV is a laser device linked to a computer to calculate and record the measurements. A high-speed camera allowed researchers to capture hummingbird wing motion every 250 millionths of a second. The images show how much lift the hummers produce with each flap.
The results defied previous assumptions that hummingbird wing motion provided an equal amount of lift with upstroke and downstroke, similar to that of insects. Birds get all of their lift while flying from the downstroke of their wings, whereas bugs get equal lift from both upstroke and downstroke. Hummingbirds, however, get 75 percent of their lift from the downstroke and 25 percent from the upstroke.
"We were surprised to find that the upstroke in the hovering hummingbird was much less active than the downstroke," says biologist Bret Tobalske from the University of Portland. "This finding provides new insight into evolutionary trends that led to sustained hovering in birds."
--Jamie Tidd, Bird Watcher's Digest
