Backward flight in hummingbirds employs unique kinematic adjustments and entails low metabolic cost

Nir Sapir, Robert Dudley

Research output: Contribution to journalArticlepeer-review


Backward flight is a frequently used transient flight behavior among members of the species-rich hummingbird family (Trochilidae) when retreating from flowers, and is known from a variety of other avian and hexapod taxa, but the biomechanics of this intriguing locomotor mode have not been described. We measured rates of oxygen uptake (VO2) and flight kinematics of Anna's hummingbirds, Calypte anna (Lesson), within a wind tunnel using mask respirometry and high-speed videography, respectively, during backward, forward and hovering flight. We unexpectedly found that VO2 in sustained backward flight is similar to that in forward flight at equivalent airspeed, and is about 20% lower than hovering VO2. For a bird that was measured throughout a range of backward airspeeds up to a speed of 4.5.m.s-1, the power curve resembled that of forward flight at equivalent airspeeds. Backward flight was facilitated by steep body angles coupled with substantial head flexion, and was also characterized by a higher wingbeat frequency, a flat stroke plane angle relative to horizontal, a high stroke plane angle relative to the longitudinal body axis, a high ratio of maximum:minimum wing positional angle, and a high upstroke:downstroke duration ratio. Because of the convergent evolution of hummingbird and some hexapod flight styles, flying insects may employ similar kinematics while engaged in backward flight, for example during station keeping or load lifting. We propose that backward flight behavior in retreat from flowers, together with other anatomical, physiological, morphological and behavioral adaptations, enables hummingbirds to maintain strictly aerial nectarivory.

Original languageEnglish
Pages (from-to)3603-3611
Number of pages9
JournalJournal of Experimental Biology
Issue number20
StatePublished - Oct 2012
Externally publishedYes


  • Avian locomotor mode
  • Calypte anna
  • Flight agility
  • Mask respirometry
  • Mass-specific metabolic rate
  • Nectarivory

ASJC Scopus subject areas

  • Insect Science
  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science
  • Animal Science and Zoology
  • Molecular Biology
  • Physiology


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