FLIGHT SPEED, FORAGING EFFICIENCY, AND DAILY ENERGY BUDGET OF THE BARN-SWALLOW, HIRUNDO-RUSTICA

Aerodynamic power equations predict optimal speeds at which birds ough t to fly if they are to maximize time spent in the air on a given ener gy store (minimum power speed, V-mp), distance covered using a given a mount of fuel (maximum range speed, V-mr), and rate of delivering food to the chicks in the nest (V-nest), or maximize the daily energy bala nce (V-DBAL). With the aerodynamic model employed, these speeds are 5. 3, 7.0, 7.9, and 8.9 m.s(-1), respectively, for the Barn Swallow, Hiru ndo rustica. A comparison of the predicted flight speed with both the mean and median flight speeds (8 m.s(-1) in both cases; n = 821) recor ded with Doppler radar indicates that Barn Swallows fly at speeds not significantly different from V-nest. The true sample size was unknown, and realistic sample sizes are drawn with bootstrap procedures and co mpared with those given by the number of measurements (821); no signif icant differences were found. To test the model, energy requirements f or growth, prey density, and time spent foraging were varied independe ntly in a sensitivity analysis. Large but realistic changes in these t hree variables do not contradict the model and predict speeds within t he range measured in the field.