Ontogeny of aerial righting and wing flapping in juvenile birds

Abstract

Mechanisms of aerial righting in juvenile chukar partridge (Alectoris chukar) were studied from hatching to 14 days-post-hatching (dph). Asymmetric movements of the wings were used from 1 to 8 dph to effect progressively more successful righting behaviour via body roll. Following 8 dph, wing motions transitioned to bilaterally symmetric flapping that yielded aerial righting via nose-down pitch, along with substantial increases in vertical force production during descent. Ontogenetically, the use of such wing motions to effect aerial righting precedes both symmetric flapping and a previously documented behaviour in chukar (i.e. wing-assisted incline running) hypothesized to be relevant to incipient flight evolution in birds. These findings highlight the importance of asymmetric wing activation and controlled aerial manoeuvres during bird development and are potentially relevant to understanding the origins of avian flight.

Shifts in stability and control effectiveness during evolution of Paraves support aerial maneuvering hypotheses for flight origin

“…Wing movements with high control effectiveness change during evolution in a manner consistent with predicted shoulder joint mobility (criterion 1 of Gatesy and Baier, 2005). The high control effectiveness of asymmetric wing motions in roll and large inertia of ancestrally long tails echo ontogenetic changes in righting ability observed in young birds (Evangelista et al, 2014a). In maneuvering baby birds, asymmetric wing use occurs before symmetric wing use and precedes wing-assisted incline running (WAIR); the shift echoes the later evolution of symmetric wing protraction control effectiveness, although extant avian ontogenies are not necessarily linked to phylogenetic patterns in maneuvering and control.…”

“…Although early paravians may have been limited to tight coupling of vertebral and retricial movement (Gatesy and Dial, 1996), overall gross movement of the large tail of early paravians yielded high aerodynamic control effectiveness and the body possessed some degree of stability. Combined with likely dynamic forces and torques generated by either tail whipping at the root (Jusufi et al, 2008, Jusufi et al, 2011; Pittman et al, 2013) or mild asymmetric (Evangelista et al, 2014a) or symmetric forewing flapping (flapping limited by less robust skeletal and feather morphology or porosity), this suggests that early avialans and their ancestors were still capable of controlled aerial behaviors at high angles of attack (Figure 6–8). Gradual evolution of improved maneuvering ability (increased control effectiveness, reduced stability) via consistent aerodynamic mechanisms is consistent with a continuum of aerial behaviors ranging to full aerial (Dudley and Yanoviak, 2011; criteria 3 and 4 of Gatesy and Baier, 2005).…”

“…In planform, Onychonycteris appears superficially similar to extant bats but with a slightly longer tail, and may not be a sufficiently transitional form to observe the same changes seen here. We would predict that an as-yet-undiscovered bat ancestor should possess means of effecting maneuvers such as limb inertias, enlarged tails, patagia with measurable control effectiveness, and some degree of stability at higher angles of attack; we would also predict that baby bats perform aerial maneuvers such as righting via asymmetric wing uses (which were generally effective in roll at high angle of attack), possibly in a manner similar to baby birds Evangelista et al (2014a). Beyond birds, bats, and pterosaurs (vertebrate fliers in a very narrow sense), the presence of highly capable aerial control systems in all the other vertebrates that “just glide”, as well as in volant invertebrates such as ants, bristletails, and stick insects, provides further support (Dudley and Yanoviak, 2011; Munk, 2011; Zeng, 2013).…”

Flapping wing aerodynamics: from insects to vertebrates

“…For example, the observation of aerodynamically active wing strokes in the under-developed wings of juvenile birds suggests that distant ancestors of birds may also have benefitted from non-flying wings (Dial et al, 2008). Asymmetric wing motions used by juvenile chukar for aerial righting also suggest another key function of incipient wings -they facilitate controlled aerial maneuvering (Evangelista et al, 2014;Dudley and Yanoviak, 2011). Further studies are needed to determine whether the same aerodynamic mechanisms that are employed by adult birds and bats are also present in the wing strokes of juvenile vertebrates.…”

Biomechanics of aerial righting in wingless nymphal stick insects

“…Aerodynamic and inertial effects may both be present in specific cases. For example, juvenile birds with underdeveloped wings right themselves using active wing movements which may involve both aerodynamic and inertial components [10].…”