Hovering performance of Anna's hummingbirds (Calypte anna) in ground effect

Erica J. Kim, Marta Wolf, Victor Manuel Ortega-Jimenez, Stanley H. Cheng, Robert Dudley

Research output: Contribution to journalArticlepeer-review

21 Citations (SciVal)

Abstract

Aerodynamic performance and energetic savings for flight in ground effect are theoretically maximized during hovering, but have never been directly measured for flying animals. We evaluated flight kinematics, metabolic rates and induced flow velocities for Anna's hummingbirds hovering at heights (relative to wing length R 5.5 cm) of 0.7R, 0.9R, 1.1R, 1.7R, 2.2R and 8R above a solid surface. Flight at heights less than or equal to 1.1R resulted in significant reductions in the body angle, tail angle, anatomical stroke plane angle, wake-induced velocity, and mechanical and metabolic power expenditures when compared with flight at the control height of 8R. By contrast, stroke plane angle relative to horizontal, wingbeat amplitude and wingbeat frequency were unexpectedly independent of height from ground. Qualitative smoke visualizations suggest that each wing generates a vortex ring during both down-and upstroke. These rings expand upon reaching the ground and present a complex turbulent interaction below the bird's body. Nonetheless, hovering near surfaces results in substantial energetic benefits for hummingbirds, and by inference for all volant taxa that either feed at flowers or otherwise fly close to plant or other surfaces.
Original languageEnglish
Article number20140505
JournalJournal of the Royal Society Interface
Volume11
Issue number98
DOIs
Publication statusPublished - 2014

Subject classification (UKÄ)

  • Biological Sciences

Keywords

  • ground effect
  • hovering
  • induced velocity
  • metabolic power
  • vortex wake

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