Letter

Nature 435, 1094-1097 (23 June 2005) | doi:10.1038/nature03647; Received 9 March 2005; Accepted 18 April 2005

Aerodynamics of the hovering hummingbird

Douglas R. Warrick1, Bret W. Tobalske2 & Donald R. Powers3

  1. Department of Zoology, Oregon State University, 3029 Cordley Hall, Corvallis, Oregon 97331, USA
  2. Department of Biology, University of Portland, 5000 North Willamette Boulevard, Portland, Oregon 97203, USA
  3. Biology Department, George Fox University, 414 North Meridian Street, Newberg, Oregon 97132, USA

Correspondence to: Douglas R. Warrick1 Correspondence and requests for materials should be addressed to D.R.W. (Email: warrickd@science.oregonstate.edu).

Despite profound musculoskeletal differences, hummingbirds (Trochilidae) are widely thought to employ aerodynamic mechanisms similar to those used by insects. The kinematic symmetry of the hummingbird upstroke and downstroke1, 2, 3 has led to the assumption that these halves of the wingbeat cycle contribute equally to weight support during hovering, as exhibited by insects of similar size4. This assumption has been applied, either explicitly or implicitly, in widely used aerodynamic models1, 5, 6, 7 and in a variety of empirical tests8, 9. Here we provide measurements of the wake of hovering rufous hummingbirds (Selasphorus rufus) obtained with digital particle image velocimetry that show force asymmetry: hummingbirds produce 75% of their weight support during the downstroke and only 25% during the upstroke. Some of this asymmetry is probably due to inversion of their cambered wings during upstroke. The wake of hummingbird wings also reveals evidence of leading-edge vortices created during the downstroke, indicating that they may operate at Reynolds numbers sufficiently low to exploit a key mechanism typical of insect hovering10, 11. Hummingbird hovering approaches that of insects, yet remains distinct because of effects resulting from an inherently dissimilar—avian—body plan.

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