Analysis of coordinated circling and linear flights of a lycaenid butterfly species.

Circling and linear flights of a hairstreak Chrysozephyrus smaragdinus were recorded in natural habitat with a high-speed video camera. Circling flight paths were resolved into rotation and shift components; values on X- and Y-coordinates of the butterfly position were separately extracted against time and fitted with a regression line composed of a sinusoidal curve and a linear line. From the obtained parameters, diameter, rotation number, and flight velocity were calculated. Flapping movements were also analyzed. Two types of circling flights, horizontal and vertical, were discriminated. In both flights, the rotation diameter was about 10 cm, rotation number of 3/s, flight velocity of 0.9 m/s, and wing-beat frequency of 20/s. The coordination of paired butterflies in circling flight showed a higher correlation in the horizontal circling flight. In the vertical circling flight, butterflies accelerated the downstroke speed of the wing in the ascending phase. They flew about four times faster in linear flights than in circling flights due to the higher frequency of wing beats.