Quantifying the dynamic wing morphing of hovering hummingbird

Masateru Maeda,Ikuo Kitamura,Hiroto Tanaka,Toshiyuki Nakata,Hao Liu

doi:10.1098/rsos.170307

Masateru Maeda, Ikuo Kitamura + Show 3 more

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https://doi.org/10.1098/rsos.170307

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Abstract

Animal wings are lightweight and flexible; hence, during flapping flight their shapes change. It has been known that such dynamic wing morphing reduces aerodynamic cost in insects, but the consequences in vertebrate flyers, particularly birds, are not well understood. We have developed a method to reconstruct a three-dimensional wing model of a bird from the wing outline and the feather shafts (rachides). The morphological and kinematic parameters can be obtained using the wing model, and the numerical or mechanical simulations may also be carried out. To test the effectiveness of the method, we recorded the hovering flight of a hummingbird (Amazilia amazilia) using high-speed cameras and reconstructed the right wing. The wing shape varied substantially within a stroke cycle. Specifically, the maximum and minimum wing areas differed by 18%, presumably due to feather sliding; the wing was bent near the wrist joint, towards the upward direction and opposite to the stroke direction; positive upward camber and the ‘washout’ twist (monotonic decrease in the angle of incidence from the proximal to distal wing) were observed during both half-strokes; the spanwise distribution of the twist was uniform during downstroke, but an abrupt increase near the wrist joint was found during upstroke.

Highlights

Hummingbirds are the only bird group that is capable of sustained hovering and are reported to have the highest mass-specific metabolic rate among vertebrates [1]
This feature results in more than half the wing length of a hummingbird’s wing being composed solely of primary feathers, the mass is concentrated to the proximal portion and the inertial power would be reduced
For this study we neglected the potential wall effect and we assumed that the wing kinematics and morphing were bilaterally symmetric about the 4 sagittal plane during stable hovering flights; we focused on the right wing for data acquisition and subsequent analyses

Summary

Introduction

Hummingbirds (family Trochilidae) are the only bird group that is capable of sustained hovering and are reported to have the highest mass-specific metabolic rate among vertebrates [1]. Some species of hummingbirds migrate between North America and Central America. To help manage such high energy demands, 2017 The Authors. One of the unique features of the hummingbird wing is that the arm wing is very short and the hand wing is relatively long, and the joint between them (elbow joint) cannot be stretched because of the anatomical restriction [2,3] This feature results in more than half the wing length (distance between wing base and wing tip) of a hummingbird’s wing being composed solely of primary feathers, the mass is concentrated to the proximal portion and the inertial power would be reduced. The span ratio of rufous hummingbirds is nearly 100% at hovering and never less than 85% at higher flight speeds, whereas other birds have span ratios between 20 and 80% (see [4], fig. 10)

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