生物谷报道：美国研究人员在英国《自然》（Nature）杂志上撰文说，与许多生物学家的看法相反，鸟类翅膀扇动的幅度相对较小，只有19度。 利用4台同步高速数码摄像机，美国蒙大拿大学的科学家肯尼思·戴尔及同事记录了北美洲的一种鸟——石鸡的成长过程。他们每两天对这些鸟记录一次，从它们孵出来开始，直至成年。 他们利用计算机技术分析石鸡翅膀形状和扇动情况后惊讶地发现，石鸡翅膀扇动的角度相对于地面都在一个非常窄的幅度范围内。不管是跑动、拍打翅膀或学习从几乎垂直的斜面上起飞的雏鸟，还是能够自由滑行和俯冲的成年鸟，都通过改变身体的姿势完成飞行特技，而鸟翅相对于地面的倾角基本相同，翅膀扇动幅度保持在19度。（生物谷援引新华网）
生物谷推荐英文原文：
Nature advance online publication 23 January 2008 | doi:10.1038/nature06517; Received 20 August 2007; Accepted 27 November 2007; Published online 23 January 2008
A fundamental avian wing-stroke provides a new perspective on the evolution of flight
Kenneth P. Dial1, Brandon E. Jackson1 & Paolo Segre1
Flight Laboratory, Division of Biological Sciences, University of Montana, 32 Campus Drive, Missoula, Montana 59812, USA
Correspondence to: Kenneth P. Dial1 Correspondence and requests for materials should be addressed to K.P.D. (Email: kdial@mso.umt.edu).
Abstract
The evolution of avian flight remains one of biology's major controversies, with a long history of functional interpretations of fossil forms given as evidence for either an arboreal or cursorial origin of flight. Despite repeated emphasis on the 'wing-stroke' as a necessary avenue of investigation for addressing the evolution of flight1, 2, 3, 4, no empirical data exist on wing-stroke dynamics in an experimental evolutionary context. Here we present the first comparison of wing-stroke kinematics of the primary locomotor modes (descending flight and incline flap-running) that lead to level-flapping flight in juvenile ground birds throughout development (Fig. 1). We offer results that are contrary both to popular perception and inferences from other studies5, 6, 7. Starting shortly after hatching and continuing through adulthood, ground birds use a wing-stroke confined to a narrow range of less than 20°, when referenced to gravity, that directs aerodynamic forces about 40° above horizontal, permitting a 180° range in the direction of travel. Based on our results, we put forth an ontogenetic-transitional wing hypothesis that posits that the incremental adaptive stages leading to the evolution of avian flight correspond behaviourally and morphologically to transitional stages observed in ontogenetic forms.
FIGURE 1. Locomotor development during ontogeny in the chukar partridge from hatching to adulthood.
Our data suggest a default or basal wing-stroke is used by young and adults and may exist in all birds (Supplementary Videos). The fundamental wing-stroke described herein is used days after hatching and during all ages and over multiple behaviours (that is, flap-running, descending and level flight) and is the foundation of our new ontogenetic-transitional wing hypothesis. At hatching, chicks can ascend inclines as steep as 60° by crawling on all four limbs. From day 8 through adulthood, birds use a consistently orientated stroke-plane angle over all substrate inclines during wing-assisted incline running (red arcs) as well as during descending and level flight (blue arcs). Estimated force orientations from this conserved wing-stroke are limited to a narrow wedge (see Fig. 3b).
