Flight speeds of the barn swallow, Hirundo rustica

Abstract

A Doppler radar hand gun was used to measure flight speeds of barn swallows (Hirundo rustica) to determine whether mean flight speed coincides with either the minimum power, V_mp, or maximum range, V_mr, speeds predicted by aerodynamic theory. In addition, flight speeds are also compared with the maximum range speed, V′_mr, when the mechanical equivalent of the standard metabolic rate is included in the power curve. A total of 821 speed recordings were divided into two groups based on observed flight behaviour. Group A had characteristically low (0.5 m) and erratically. Mean flight speeds of 8.6 and 6.8 m∙s⁻¹ were determined for groups A and B, respectively. When compared separately, both means are significantly different from predicted values of V_mp (= 4.2 m∙s⁻¹, p < 0.001), V_mr (= 5.6 m∙s⁻¹, p < 0.001), and V′_mr (= 6.2 m∙s⁻¹, p < 0.001). It is likely that the birds fly at significantly higher speeds than the predicted optima for most routine flight activities. The penalties involved in departing from V_mp, V_mr, and V′_mr (assessed as percent increase in total aerodynamic power relative to V_mp, V_mr, or V′_mr) are substantial.