Resurrection of the New Papers

[Tim Williams <twilliams_alpha@hotmail.com>]

Really more to do with extant theropods, but WAIR does have relevance to the 
origin of avian flight...


Tobalske, B.W. and Dial. K.P. (2007).  Aerodynamics of wing-assisted incline 
running in birds.

Summary: "Wing-assisted incline running (WAIR) is a form of locomotion in 
which a bird flaps its wings to aid its hindlimbs in climbing a slope.  WAIR 
is used for escape in ground birds, and the ontogeny of this behavior in 
precocial birds has been suggested to represent a model analogous to 
transitional adaptive states during the evolution of powered avian flight.  
To begin to reveal the aerodynamics of flap-running, we used digital 
particle image velocimetry (DPIV) and measured air velocity, vorticity, 
circulation and added mass in the wake of chukar partridge _Alectoris 
chukar_ as they engaged in WAIR (incline 65?85°; N=7 birds) and ascending 
flight (85°, N=2).  To estimate lift and impulse, we coupled our DPIV data 
with three-dimensional wing kinematics from a companion study.  The ontogeny 
of lift production was evaluated using three age classes: baby birds 
incapable of flight [6?8 days post hatching (d.p.h.)] and volant juveniles 
(25?28 days) and adults (45+ days).  All three age classes of birds, 
including baby birds with partially emerged, symmetrical wing feathers, 
generated circulation with their wings and exhibited a wake structure that 
consisted of discrete vortex rings shed once per downstroke.  Impulse of the 
vortex rings during WAIR was directed 45±5° relative to horizontal and 21±4° 
relative to the substrate.  Absolute values of circulation in vortex cores 
and induced velocity increased with increasing age.  Normalized circulation 
was similar among all ages in WAIR but 67% greater in adults during flight 
compared with flap-running.  Estimated lift during WAIR was 6.6% of body 
weight in babies and between 63 and 86% of body weight in juveniles and 
adults. During flight, average lift was 110% of body weight.  Our results 
reveal for the first time that lift from the wings, rather than wing inertia 
or profile drag, is primarily responsible for accelerating the body toward 
the substrate during WAIR, and that partially developed wings, not yet 
capable of flight, can produce useful lift during WAIR.  We predict that 
neuromuscular control or power output, rather than external wing morphology, 
constrain the onset of flight ability during development in birds."


Rubenson, J., Lloyd,  D.G., Besier, T.F., Heliams, D.B., and Fournier, P.A. 
(2007). Running in ostriches (_Struthio camelus_): three-dimensional joint 
axes alignment and joint kinematics.  Journal of Experimental Biology 210: 
2548-2562.

Summary: "Although locomotor kinematics in walking and running birds have 
been examined in studies exploring many biological aspects of bipedalism, 
these studies have been largely limited to two-dimensional analyses.  
Incorporating a five-segment, 17 degree-of-freedom (d.f.) kinematic model of 
the ostrich hind limb developed from anatomical specimens, we quantified the 
three-dimensional (3-D) joint axis alignment and joint kinematics during 
running (at ~3.3 m s?1) in the largest avian biped, the ostrich.  Our 
analysis revealed that the majority of the segment motion during running in 
the ostrich occurs in flexion/extension.  Importantly, however, the 
alignment of the average flexion/extension helical axes of the knee and 
ankle are rotated externally to the direction of travel (37° and 21°, 
respectively) so that pure flexion and extension at the knee will act to 
adduct and adbuct the tibiotarsus relative to the plane of movement, and 
pure flexion and extension at the ankle will act to abduct and adduct the 
tarsometatarsus relative to the plane of movement.  This feature of the limb 
anatomy appears to provide the major lateral (non-sagittal) displacement of 
the lower limb necessary for steering the swinging limb clear of the stance 
limb and replaces what would otherwise require greater adduction/abduction 
and/or internal/external rotation, allowing for less complex joints, 
musculoskeletal geometry and neuromuscular control.  Significant rotation 
about the joints' non-flexion/extension axes nevertheless occurs over the 
running stride.  In particular, hip abduction and knee internal/external and 
varus/valgus motion may further facilitate limb clearance during the swing 
phase, and substantial non-flexion/extension movement at the knee is also 
observed during stance.  Measurement of 3-D segment and joint motion in 
birds will be aided by the use of functionally determined axes of rotation 
rather than assumed axes, proving important when interpreting the 
biomechanics and motor control of avian bipedalism."

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