Department of Integrative Biology, University of California, Berkeley, CA 94720, USA.
J Exp Biol. 2012 Oct 15;215(Pt 20):3603-11. doi: 10.1242/jeb.073114.
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 (V(O2)) 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 in sustained backward flight is similar to that in forward flight at equivalent airspeed, and is about 20% lower than hovering V(O2). 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.
后退飞行是种类繁多的蜂鸟科(Trochilidae)成员在从花朵后退时经常使用的瞬态飞行行为,也存在于各种其他鸟类和六足动物类群中,但这种有趣的运动模式的生物力学尚未被描述。我们在风洞中使用面罩呼吸计和高速录像术分别测量了安娜蜂鸟(Calypte anna)(Lesson)的耗氧量(V(O2))和飞行运动学,分别在后退、前进和悬停飞行时进行测量。我们出人意料地发现,在持续的后退飞行中,其与前进飞行在等效空速下相似,并且比悬停 V(O2)低约 20%。对于在高达 4.5 m s(-1)的后退空速范围内进行测量的鸟类,功率曲线类似于等效空速下的前进飞行。后退飞行通过陡峭的身体角度与大量的头部弯曲相结合而变得容易,并且还具有更高的翅膀拍打频率,相对于水平的较平的冲程平面角度,相对于纵轴的较高冲程平面角度,最大:最小翼位置角度的高比值,以及较高的上冲程:下冲程持续时间比。由于蜂鸟和某些六足动物飞行方式的趋同进化,飞行昆虫在后退飞行时可能会采用类似的运动学,例如在保持位置或举升负载时。我们提出,从花朵后退时的后退飞行行为以及其他解剖学,生理学,形态学和行为适应性,使蜂鸟能够严格保持空中花蜜摄取。