Fig. 4. Here, we superimpose some of the typical instantaneous acceleration vectors from mid-downstroke and mid-upstroke on the lateral-view high-speed video footage. The same cockatiel is used in all frames and the vector scale is the same in each case. Note that the inertial acceleration vectors are small in size here because the wing is typically at maximum velocity when near mid-stroke; inertial accelerations were much more pronounced at other points in time such as the ends of upstroke and downstroke. In upstroke at faster flight speeds, lift and drag forces tended to vary together and were either both small, as shown in the 7 m s^–1 upstroke, or both larger, as shown in the 13 m s^–1 upstroke. The scale bar indicates an acceleration of 10 m s^–2, equivalent to a force of 0.81 N applied to the cockatiel's whole body mass. Note that the aerodynamic acceleration vectors include drag from the data cable and accelerometers.