Flight speed of the song thrush (Turdus philomelos) during autumn nocturnal migration

Abstract

Nocturnally migrating birds were observed with Electronic-optical system for registration. The Song Thrushes have been distinguished among the nocturnal migrants by the linear size, wing-beat pattern and phonological data. The airspeed of the thrushes varies depending on wind direction and velocity. It increases with increasing headwind component relative to its value in calm air and decreases with increasing tail-wind component. The air speed of the migratory flight in thrushes is proportional to an effective wing-beat frequency calculated for the flapping phases and pauses between them. Under different wind conditions the birds maintain optimal physiological wing beat frequency within rather narrow range but vary their airspeed by duration of inertial phases of flight. The observed airspeeds of the Song Thrushes were close to the theoretically predicted maximum range speed indicating energy-selected migration strategy in autumn.