A passerine spreads its tail to facilitate a rapid recovery of its body posture during hovering

作者：Su Jian Yuan; Ting Shang Chieh; Chang Yu Hung; Yang Jing Tang^*

来源：Journal of the Royal Society Interface, 2012, 9(72): 1674-1684.

DOI：10.1098/rsif.2011.0737

• bird tail
• tail spreading
• hovering
• pitch stabilization

We demonstrate experimentally that a passerine exploits tail spreading to intercept the downward flow induced by its wings to facilitate the recovery of its posture. The periodic spreading of its tail by the White-eye bird exhibits a phase correlation with both wingstroke motion and body oscillation during hovering flight. During a downstroke, a White-eye's body undergoes a remarkable pitch-down motion, with the tail undergoing an upward swing. This pitch-down motion becomes appropriately suppressed at the end of the downstroke; the bird's body posture then recovers gradually to its original status. Employing digital particle-image velocimetry, we show that the strong downward flow induced by downstroking the wings serves as an external jet flow impinging upon the tail, providing a depressing force on the tail to counteract the pitch-down motion of the bird's body. Spreading of the tail enhances a rapid recovery of the body posture because increased forces are experienced. The maximum force experienced by a spread tail is approximately 2.6 times that of a non-spread tail.

• 出版日期2012-7-7