 Additionally, birds on a high-protein diet grew yellower (higher hue) green tail feathers than birds on a low-protein diet.Hummingbird flight has been studied intensively from an aerodynamic perspective using wind tunnels and high-speed video cameras.Two studies of rufous or Anna's hummingbirds in a wind tunnel used particle image velocimetry techniques to investigate the lift generated on the bird's upstroke and downstroke.