Sideways maneuvers enable narrow aperture negotiation by free-flying hummingbirds

Many birds routinely fly fast through dense vegetation characterized by variably sized structures and voids. Successfully negotiating these cluttered environments requires maneuvering through narrow constrictions between obstacles. We show that Anna's Hummingbirds (Calypte anna) can negotiate apertures less than one wingspan in diameter using a novel sideways maneuver that incorporates continuous, bilaterally asymmetric wing motions. Crucially, this maneuver allows hummingbirds to continue flapping as they negotiate the constriction. Even smaller openings are negotiated via a faster ballistic trajectory characterized by tucked and thus non-flapping wings, which reduces force production and increases descent rate relative to the asymmetric technique. Hummingbirds progressively shift to the swept method as they perform hundreds of consecutive transits, suggesting increased locomotor performance with task familiarity. Initial use of the slower asymmetric transit technique may allow birds t...

诸多鸟类日常会快速穿梭于结构与空隙大小不一的茂密植被中。要成功穿行于这类杂乱环境，需在障碍物间的狭窄通道内完成精准机动动作。
本研究发现，安娜蜂鸟（Calypte anna）可借助一种全新的侧向机动动作——该动作融合了连续且双侧不对称的翼部运动——穿过直径小于自身翼展的孔径。尤为关键的是，这类机动动作可让蜂鸟在通过窄通道时仍能持续振翅。
当需要穿行尺寸更小的开口时，蜂鸟则会采用速度更快的弹道轨迹：此时翅膀收拢、不再振翅；相较于前述不对称机动技术，该方式会降低升力产生并提升下降速率。
蜂鸟在连续完成数百次穿梭后，会逐渐转向该掠行通行方式，这表明随着任务熟练度的提升，蜂鸟的运动表现会得到增强。
最初采用速度较慢的不对称通行方式，或可让鸟类 t...