TY - JOUR

T1 - Airspeed of the Song Thrush in relation to the wind during autumnal nocturnal migration

AU - Sinelschikova, Alexandra

AU - Griffiths, Martin

AU - Vorotkov, Michael

AU - Bulyuk, Victor

AU - Bolshakov, Casimir

PY - 2019

Y1 - 2019

N2 - Nocturnally migrating birds were recorded by the optical-electronic matrix system, which permitted receiving their images and flight parameters in the dark. Among medium size birds the Song Thrushes (Turdus philomelos) were identified by their silhouette, linear size, wing-beat pattern, and phenology. The equivalent airspeed at 0m a.s.l (VEq) of the observed thrushes without wind assistance (mean value 14.3 m/s) was close to maximum range speed (Vmr) predicted from flight mechanical theory. This indicated the energy-selected migration strategy of the thrushes in autumn. The characteristic speed Vmr is wind-dependent:- it increases with increasing velocity of head- and sidewinds. A similar pattern of wind-dependence of airspeed has shown the Song Thrushes. They significantly increased their airspeed with increasing headwind component relative to its value in still air and decreased it with increasing tailwind component. We also found the effect of cross winds on airspeed:-those birds that compensated for wind drift completely along the leading line of the Courish Spit, which coincided with general migratory direction, increased their airspeed with increasing sidewind component. The flying birds tended to maintain their airspeed close to the speed of minimal cost of transport under various winds. Nevertheless, this trend was more in qualitative but not quantitative agreement with Pennycuick’s flight model:- migrating thrushes varied their airspeed in a smaller range than expected and their airspeed was significantly slower under calm and headwinds than the model predicted.

AB - Nocturnally migrating birds were recorded by the optical-electronic matrix system, which permitted receiving their images and flight parameters in the dark. Among medium size birds the Song Thrushes (Turdus philomelos) were identified by their silhouette, linear size, wing-beat pattern, and phenology. The equivalent airspeed at 0m a.s.l (VEq) of the observed thrushes without wind assistance (mean value 14.3 m/s) was close to maximum range speed (Vmr) predicted from flight mechanical theory. This indicated the energy-selected migration strategy of the thrushes in autumn. The characteristic speed Vmr is wind-dependent:- it increases with increasing velocity of head- and sidewinds. A similar pattern of wind-dependence of airspeed has shown the Song Thrushes. They significantly increased their airspeed with increasing headwind component relative to its value in still air and decreased it with increasing tailwind component. We also found the effect of cross winds on airspeed:-those birds that compensated for wind drift completely along the leading line of the Courish Spit, which coincided with general migratory direction, increased their airspeed with increasing sidewind component. The flying birds tended to maintain their airspeed close to the speed of minimal cost of transport under various winds. Nevertheless, this trend was more in qualitative but not quantitative agreement with Pennycuick’s flight model:- migrating thrushes varied their airspeed in a smaller range than expected and their airspeed was significantly slower under calm and headwinds than the model predicted.

UR - https://www.ornisfennica.org/latest.htm

M3 - Article

VL - 96

SP - 64

EP - 76

JO - Ornis Fennica

JF - Ornis Fennica

SN - 0030-5685

IS - 2

ER -