Estimates of circulation and gait change based on a three-dimensional kinematic analysis of flight in cockatiels (Nymphicus hollandicus) and ringed turtle-doves (Streptopelia risoria)
Tyson L. Hedrick1,*,
Bret W. Tobalske2 and
Andrew A. Biewener1
1 Concord Field Station, Museum of Comparative Zoology, Harvard University,
Old Causeway Road, Bedford, MA 01730, USA
2 Department of Biology, University of Portland, 5000 N. Willamette
Boulevard, Portland, OR 97203, USA
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Fig. 2. The Harvard-Concord Field Station (CFS) wind tunnel, designed for use in
studies of animal flight.
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Fig. 3. Velocity profile in the mid-plane of the flight chamber in the Harvard-CFS
wind tunnel operating at an equivalent airspeed of 20 m s-1.
Airspeed was measured using a pitot-static probe placed at 121 locations in a
10 cm spaced grid pattern (see text for details). Each square represents the
center of a 10 cm square in the grid. (A) Variation in airspeed as a
paercentage of the mean. (B) Positive and negative deviations from the
mean.
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Fig. 4. A velocity traverse performed at mid-height and mid-plane, using a
pitot-static probe, with the equivalent wind speed at 10 m s-1.
Boundary-layer effects on flow velocity were not apparent until within 1 cm of
the left and right walls of the working section. Filled circles, traverse of
left side; open circles, traverse of right side. Note that the width of the
flight chamber at mid-plane is 121 cm, 1 cm greater than at the inlet, to
accommodate thickening of the boundary layer along the length of the flight
chamber. Left side and right side are referenced looking forward from inside
the flight chamber.
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Fig. 5. Average turbulence levels expressed as percentage turbulence at each of
nine locations in two planes (A, at 25 % depth from the front of the working
section; B, at 50 %) in the flight chamber. These values were obtained using a
30 cm diameter turbulence sphere. Left side and right side are referenced
looking forward from inside the flight chamber.
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Fig. 6. Digital particle image velocimetry (DPIV) was used to measure variations in
velocity and turbulence levels with the wind tunnel set at an equivalent
airspeed of 5 m s-1 along the x dimension (axis of
airflow). The DPIV system uses a YAG laser and synchronized stereo video
cameras to measure velocities U, V and W, corresponding to
the x, y and z axes, respectively, of particles suspended in
the moving air column. Variation in true airspeed (U) was relative to
a mean of 5.54 m s-1. Total turbulence (T) varied about a
mean of 0.23 %.
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Fig. 7. (A) Arrangement of the four high-speed video cameras around the flight
chamber of the wind tunnel and typical images from each camera. Cameras 1 and
2 (C1, C2) captured dorsal views of the bird, while cameras 3 and 4 (C3, C4)
captured either latero-dorsal or -ventral views of the bird and wings. (B)
Points marked on each bird that were digitized for three-dimensional
reconstruction. 1, back; 2, shoulder; 3, wrist; 4, tip of the ninth (longest)
primary; 5, tip of the fourth primary; 6, tip of the first primary. T1
designates the triangle used to represent the proximal wing section; T2
designates the triangle forming the distal wing section.
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Fig. 9. (A) Dorsal view of a dove in a medium-speed upstroke (7 m s-1)
posture showing the three markers on the wing (shoulder, wrist and ninth
primary tip) used to establish the position of the wing leading edge and the
incident airflow and effective wing length. As shown in the figure, an
extended proximal wing and slightly flexed distal wing (with effective length
less than geometric length) are typical of a medium-speed upstroke. (B) Dorsal
view of a cockatiel in mid-upstroke configuration in fast flight (11 m
s-1). Note that, although overall wingspan is similar in both
species, mean dove body mass is 83 % greater than that of the cockatiels,
leading to a much higher wing loading in doves.
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Fig. 11. Representative results obtained for kinematic and aerodynamic variables
similar to Fig. 10 but shown
for two wingbeats of a cockatiel flying at four different flight speeds. A, B
and C are taken from cockatiel 2, whereas D is taken from cockatiel 1, which
achieved a greater speed during experimental recordings. The y-axis
scales are identical to those used in Fig.
10; the x-axis scale is the same in all plots but
extended relative to those for the dove to account for the slightly lower
wingbeat frequency employed by the cockatiels.
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Fig. 12. A comparison of the mean proximal wing circulation during the upstroke and
the mean distal wing circulation during the downstroke for the doves (A) and
cockatiels (B) over the full range of flight speeds examined. Values are means
± S.D. (N=2). for each species at each speed. The shaded
region indicates the range of speeds in which downstroke and upstroke
circulation are approximately equivalent, resulting in a continuous-vortex
wake.
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Fig. 13. A comparison of estimated circulation resulting from translational and
rotational sources for two wingbeats of a dove at flight speeds of 1, 3 and 9
m s-1. Shaded regions indicate downstrokes.
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Fig. 14. The reduced frequency for all birds over the range of experimental speeds
studied. Values greater than 0.3 indicate that unsteady aerodynamic effects
may have a significant influence on airflow and lift generation
(Spedding, 1993 ). Results are
presented as inter-individual means ± S.D. (N=4).
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Fig. 15. A comparison of mass-specific whole wingbeat impulses obtained from
calculations of distal and proximal wing circulation with those determined
from measurements of the bird's vertical acceleration of its center of mass.
Inter-individual means and standard deviations are presented separately for
doves (A) (N=2) and cockatiels (B) (N=2).
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Fig. 16. Gait transition results obtained for dove 1 flying at 7 m s-1
over several wingbeat cycles lasting 2 s. (A) The vertical (z
direction) motions of the distal and proximal wing sections; (B) the mean
vertical acceleration achieved during each complete wingbeat (not including
acceleration to counteract gravity); (C) the mean distal wing circulation
produced during the downstroke (squares and solid line) in relation to the
mean proximal wing circulation produced during the subsequent upstroke
(circles and dashed line). The lines plotted in B and C represent cubic spline
fits to the data points. The shaded regions indicate wingbeats in which the
bird employs a vortex-ring gait.
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© The Company of Biologists Ltd 2002
/2-
). Note that
the vectors shown are not precisely to scale and that Wk
acts opposite to the direction of wing motion. Wk, airflow
generated by wing motion; Ve, effective wind-tunnel
airflow; Wiv, vertical induced airflow (equation 3);
Wit, total induced airflow perpendicular to
Wk+Ve; Wih,
horizontal induced airflow; 
) and (v) distal and proximal circulation
(
). The y-axis and x-axis scales are the same for all
speeds. Shading indicates downstroke periods, which were determined from the
z-axis (vertical) wrist motion.