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, Vmp, or maximum range, Vmr, 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 above the ground) and straight flight paths. Group B flew higher (>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 Vmp (= 4.2 m∙s−1, p < 0.001), Vmr (= 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 Vmp, Vmr, and V′mr (assessed as percent increase in total aerodynamic power relative to Vmp, Vmr, or V′mr) are substantial.