 At maximum descent speed, about 10 g of gravitational force occurs in the courting hummingbird during a dive.By comparison to humans, this is a g-force acceleration causing near loss of consciousness in fighter pilots during flight of fixed-wing aircraft in a high-speed banked turn.The outer tail feathers of male Anna's ("Calypte anna") and "Selasphorus" hummingbirds (e.g., Allen's, calliope) vibrate during courtship display dives and produce an audible chirp caused by aeroelastic flutter.