Flight speed adjustment by three wader species in relation to winds and flock size

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Flight speed adjustment by three wader species in relation to winds and flock size. / Hedenström, Anders; Åkesson, Susanne.

In: Animal Behaviour, Vol. 134, 01.12.2017, p. 209-215.

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TY - JOUR

T1 - Flight speed adjustment by three wader species in relation to winds and flock size

AU - Hedenström, Anders

AU - Åkesson, Susanne

PY - 2017/12/1

Y1 - 2017/12/1

N2 - The selection of flight speed (airspeed) in migrating birds depends on multiple internal and external factors, such as wing morphology, weight and winds. Adjustment with respect to side winds to maintain an intended track direction may include a shift in heading direction and/or an increase in airspeed. Compensation for cross-winds cannot always be achieved if visual references are lacking or may not even be beneficial if adaptive wind drift is favourable. Flock size is an additional, although often neglected, factor that could influence the airspeed of birds. Here, we show that responses to cross-winds to achieve compensation differed on a small geographical scale (a few kilometres) in migrating shorebirds, where the availability of topographical features such as coastlines may play an important role for the birds' behaviour. We also show that airspeed was significantly influenced by flock size in three species of shorebirds, increasing with increasing flock size. This is contrary to the prediction based on the hypothesis of energy saving by flight in flock formation, but in agreement with empirical findings for migrating terns. The reason why flock size influences airspeed remains unclear, but we propose a mechanistic explanation based on the largest/heaviest individual(s) determining the speed of the flock.

AB - The selection of flight speed (airspeed) in migrating birds depends on multiple internal and external factors, such as wing morphology, weight and winds. Adjustment with respect to side winds to maintain an intended track direction may include a shift in heading direction and/or an increase in airspeed. Compensation for cross-winds cannot always be achieved if visual references are lacking or may not even be beneficial if adaptive wind drift is favourable. Flock size is an additional, although often neglected, factor that could influence the airspeed of birds. Here, we show that responses to cross-winds to achieve compensation differed on a small geographical scale (a few kilometres) in migrating shorebirds, where the availability of topographical features such as coastlines may play an important role for the birds' behaviour. We also show that airspeed was significantly influenced by flock size in three species of shorebirds, increasing with increasing flock size. This is contrary to the prediction based on the hypothesis of energy saving by flight in flock formation, but in agreement with empirical findings for migrating terns. The reason why flock size influences airspeed remains unclear, but we propose a mechanistic explanation based on the largest/heaviest individual(s) determining the speed of the flock.

KW - airspeed

KW - drift

KW - flock size

KW - migration

KW - optimal flight

KW - shorebird

KW - wind compensation

U2 - 10.1016/j.anbehav.2017.10.022

DO - 10.1016/j.anbehav.2017.10.022

M3 - Article

VL - 134

SP - 209

EP - 215

JO - The British Journal of Animal Behaviour

JF - The British Journal of Animal Behaviour

SN - 1095-8282

ER -