Flight speeds and climb rates of Brent Geese: mass-dependent differences between spring and autumn migration

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Flight speeds and climb rates of Brent Geese: mass-dependent differences between spring and autumn migration. / Green, Martin; Alerstam, Thomas.

I: Journal of Avian Biology, Vol. 31, Nr. 2, 2000, s. 215-225.

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T1 - Flight speeds and climb rates of Brent Geese: mass-dependent differences between spring and autumn migration

AU - Green, Martin

AU - Alerstam, Thomas

PY - 2000

Y1 - 2000

N2 - Aerodynamic theories of bird flight predict that horizontal flight speed will increase with increasing load whereas vertical Eight speed will decrease. Horizontal flight speed for birds minimizing overall time on migration is predicted to be higher than flight speed for birds minimizing energy expenditure. In this study we compare flight speeds of Brent Geese Branta b. bernicla recorded by tracking radar and optical range finder during spring and autumn migration in southernmost Sweden, testing the above-mentioned predictions. Geese passing Sweden in spring are substantially heavier than in autumn and there might also be a stronger element of time-selection in spring than in autumn. Recorded airspeeds were significantly higher in spring (mean 19.0 m s(-1)) than in autumn (mean 17.3 m s(-1)), the average difference bring slightly larger than predicted due to the mass difference alone. The effects on airspeed of wind, vertical speed, flock size and altitude were also analysed, but none of these factors could explain the seasonal difference in airspeed. Hence, the results support the hypothesis of mass-dependent flight speed adjustment. The difference between the two seasons was not large enough to corroborate the hypothesis of a stronger element of time-selection in spring, but this hypothesis cannot be rejected. Vertical flight speeds were lower in spring than in autumn, supporting a negative effect of load on birds' Right power margin.

AB - Aerodynamic theories of bird flight predict that horizontal flight speed will increase with increasing load whereas vertical Eight speed will decrease. Horizontal flight speed for birds minimizing overall time on migration is predicted to be higher than flight speed for birds minimizing energy expenditure. In this study we compare flight speeds of Brent Geese Branta b. bernicla recorded by tracking radar and optical range finder during spring and autumn migration in southernmost Sweden, testing the above-mentioned predictions. Geese passing Sweden in spring are substantially heavier than in autumn and there might also be a stronger element of time-selection in spring than in autumn. Recorded airspeeds were significantly higher in spring (mean 19.0 m s(-1)) than in autumn (mean 17.3 m s(-1)), the average difference bring slightly larger than predicted due to the mass difference alone. The effects on airspeed of wind, vertical speed, flock size and altitude were also analysed, but none of these factors could explain the seasonal difference in airspeed. Hence, the results support the hypothesis of mass-dependent flight speed adjustment. The difference between the two seasons was not large enough to corroborate the hypothesis of a stronger element of time-selection in spring, but this hypothesis cannot be rejected. Vertical flight speeds were lower in spring than in autumn, supporting a negative effect of load on birds' Right power margin.

U2 - 10.1034/j.1600-048X.2000.310213.x

DO - 10.1034/j.1600-048X.2000.310213.x

M3 - Article

VL - 31

SP - 215

EP - 225

JO - Journal of Avian Biology

JF - Journal of Avian Biology

SN - 0908-8857

IS - 2

ER -