Department of Integrative Biology, University of California, , Berkeley, CA 94720, USA, Department of Civil and Environmental Engineering, University of California, , Berkeley, CA 94720, USA, Smithsonian Tropical Research Institute, Balboa, Republic of Panama.
Proc Biol Sci. 2014 Mar 26;281(1783):20140180. doi: 10.1098/rspb.2014.0180. Print 2014 May 22.
Animal fliers frequently move through a variety of perturbed flows during their daily aerial routines. However, the extent to which these perturbations influence flight control and energetic expenditure is essentially unknown. Here, we evaluate the kinematic and metabolic consequences of flight within variably sized vortex shedding flows using five Anna's hummingbirds feeding from an artificial flower in steady control flow and within vortex wakes produced behind vertical cylinders. Tests were conducted at three horizontal airspeeds (3, 6 and 9 m s(-1)) and using three different wake-generating cylinders (with diameters equal to 38, 77 and 173% of birds' wing length). Only minimal effects on wing and body kinematics were demonstrated for flight behind the smallest cylinder, whereas flight behind the medium-sized cylinder resulted in significant increases in the variances of wingbeat frequency, and variances of body orientation, especially at higher airspeeds. Metabolic rate was, however, unchanged relative to that of unperturbed flight. Hummingbirds flying within the vortex street behind the largest cylinder exhibited highest increases in variances of wingbeat frequency, and of body roll, pitch and yaw amplitudes at all measured airspeeds. Impressively, metabolic rate under this last condition increased by up to 25% compared with control flights. Cylinder wakes sufficiently large to interact with both wings can thus strongly affect stability in flight, eliciting compensatory kinematic changes with a consequent increase in flight metabolic costs. Our findings suggest that vortical flows frequently encountered by aerial taxa in diverse environments may impose substantial energetic costs.
动物在日常飞行中经常会穿过各种扰流区。然而，这些扰流区对飞行控制和能量消耗的影响程度基本上是未知的。在这里，我们使用五只安娜蜂鸟在稳定控制流中从人工花中进食，并在垂直圆柱体后面产生的涡旋尾流中，评估了在不同大小的涡旋脱落流中飞行的运动学和代谢后果。测试在三个水平空速（3、6 和 9 m s(-1)) 下进行，并使用三个不同的产生尾流的圆柱体（直径等于鸟类翼展的 38%、77%和 173%）。对于最小的圆柱体后面的飞行，仅显示出对翅膀和身体运动学的最小影响，而对于中等大小的圆柱体后面的飞行，则导致翅膀拍打频率的方差和身体方向的方差显著增加，尤其是在较高的空速下。然而，代谢率与未受扰飞行时相比保持不变。在最大圆柱体后面的涡街中飞行的蜂鸟在所有测量的空速下，翅膀拍打频率的方差以及身体滚动、俯仰和偏航幅度的方差都表现出最大的增加。令人印象深刻的是，与对照飞行相比，这种最后情况下的代谢率增加了高达 25%。因此，足以与两个翅膀相互作用的圆柱体尾流可以强烈影响飞行稳定性，引起代偿性运动学变化，从而导致飞行代谢成本增加。我们的发现表明，在不同环境中经常遇到的涡旋流可能会产生大量的能量成本。
